UBC Theses and Dissertations

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UBC Theses and Dissertations

The role of starvation in the population dynamics of larval Pacific herring, Clupea harengus pallasi McGurk, Michael Douglas 1985

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c. T H E R O L E O F S T A R V A T I O N I N T H E P O P U L A T I O N D Y N A M I C S O F L A R V A L P A C I F I C H E R R I N G , CLUPEA HARENGUS PALLASI by Michael Douglas McGurk B.Sc, McGill University, 1975 M.Sc, Memorial University, 1978 T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F D O C T O R O F P H I L O S O P H Y in T H E F A C U L T Y O F G R A D U A T E S T U D I E S (Department of Zoology) We accept this thesis as conforming to the required standard T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A November 1985 ^c^vlichael Douglas McGurk, 1985 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e h e a d o f my d e p a r t m e n t o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f Zoology The U n i v e r s i t y o f B r i t i s h C o l u m b i a 1956 Main Mall V a n c o u v e r , Canada V6T 1Y3 D a t e F e b - 1 9 ' 1 9 8 6 )E-6 (3/81) Abstract S t a r v a t i o n has l o n g b e e n h y p o t h e s i z e d t o be a n i m p o r t a n t agent o f m o r t a l i t y i n first-feeding l a rva l fishes. I m e a s u r e d t h e degree o f s t a r v a t i o n i n f o u r n a t u r a l c o h o r t s o f la rva l Paci f ic h e r r i n g , Clupea harengus pallasi, f r o m B a m f i e l d I n l e t , B r i t i s h C o l u m b i a , i n o r d e r t o d e t e r m i n e i f s t a r v a t i o n o c c u r r e d , a n d , i f i t d i d , t o d e t e r m i n e i t s re la t i ve i m p o r t a n c e i n t h e d y n a m i c s o f t h e p o p u l a t i o n s . A m o r p h o m e t r i c c o n d i t i o n f a c t o r was used t o d iagnose t h e n u t r i t i o n a l s t a t u s o f t h e larvae r a t h e r t h a n a c h e m i c a l o r h i s t o l o g i c a l i n d e x i n o r d e r t h a t la rge n u m b e r s o f larvae c o u l d b e s c r e e n e d . T h e c o n d i t i o n f a c t o r was d e r i v e d f r o m five b o d y m e a s u r e m e n t s a n d d r y w e i g h t . I t was c a l i b r a t e d w i t h l e a r n i n g samp les o f f e d a n d s t a r v e d larvae r e a r e d f r o m t h e egg i n l a b o r a t o r y a q u a r i a a n d i n in situ c u l t u r e c h a m b e r s s u s p e n d e d i n B a m f i e l d I n l e t . T h i s c o n d i t i o n f a c t o r was shown t o be s u p e r i o r t o t h e o t h e r m a j o r m o r p h o m e t r i c c o n d i t i o n f a c t o r , F u l t o n ' s f a c t o r , because i t was i n d e p e n d e n t o f t h e size o f t h e fish, because i t s c o n s t i t u e n t va r iab les were r e n d e r e d o r t h o g o n a l t o ( i n d e p e n d e n t o f ) each o t h e r , a n d because i t s c o n s t i t u e n t va r iab les c o u l d be ass igned some b i o l o g i c a l m e a n i n g . T h e ef fects o f t h e s h o c k o f n e t c a p t u r e o n t h e p o s t p r e s e r v a t i o n m o r p h o m e t r y a n d d r y w e i g h t o f Pac i f i c h e r r i n g la rvae w e r e m e a s u r e d f r o m t o w i n g e x p e r i m e n t s . O n l y la rvae less t h a n 14 m m l o n g were a f fec ted b y n e t c a p t u r e . G o m p e r t z m o d e l s were d e v e l o p e d t o c o r r e c t t h e m o r p h o m e t r y a n d d r y w e i g h t o f field-caught la rvae so t h a t t h e y c o u l d be c o m p a r e d w i t h t h e l e a r n i n g samp les o f f e d a n d s t a r r e d l a b o r a t o r y - r e a r e d larvae. D e l a y e d f e e d i n g e x p e r i m e n t s s h o w e d t h a t s t a r v i n g Pac i f i c h e r r i n g la rvae have 6-8.5 days a t 6 -10° C a f t e r t h e e x h a u s t i o n o f t h e y o l k i n w h i c h t o feed b e f o r e t h e y enter a s t a t e o f i r revers ib le s t a r v a t i o n . T h i s is a r e l a t i v e l y l o n g p e r i o d o f t i m e c o m p a r e d t o o t h e r species t h a t have pe lag ic larvae. T h e l e n g t h o f t h i s t i m e p e r i o d was s h o w n t o b e d u e a l m o s t e n t i r e l y t o t h e r e a r i n g t e m p e r a t u r e . O t h e r r e a r i n g e x p e r i m e n t s s h o w e d t h a t de layed f e e d i n g a n d s t a r v a t i o n a f fec ted t h e o n s e t a n d r a t e o f r i n g d e p o s i t i o n i n t h e s a g i t t a l o t o l i t h s as we l l as m o r p h o m e t r y a n d d r y w e i g h t . O n l y p o p u l a t i o n s w i t h a n average l i n e a r r a t e o f g r o w t h o f 0.36 m m d - 1 o r h i g h e r d e p o s i t e d r i n g s a t a d a i l y r a t e . W i l d la rvae were s a m p l e d w i t h t o w e d p l a n k t o n n e t s a n d w i t h a s t a t i o n a r y n i g h t - l i g h t i n B a m f i e l d I n l e t a n d s u r r o u n d i n g areas. S t a r v a t i o n was d i a g n o s e d i n 4 . 9 - 9 0 . 0 % o f t h e 7 - 2 0 m m l o n g . M o s t o f i i these s t a r v i n g la rvae were 9 - 1 5 m m l o n g a n d t h e y were f o u n d w i t h i n 3 k m o f t h e h a t c h s i t e . T h e ra tes o f g r o w t h i n l e n g t h a n d w e i g h t , a n d t h e w e i g h t - l e n g t h e x p o n e n t s , decreased w i t h i n c r e a s i n g p o p u l a t i o n d e n s i t y a n d i n c r e a s i n g p e r c e n t o f t h e p o p u l a t i o n d iagnosed as s t a r v i n g . T h e d i f f u s i o n coe f f i c ien ts , m o r t a l i t y r a t e s , a n d d i s p e r s a l v e l o c i t i e s , i nc reased w i t h i n c r e a s i n g a b u n d a n c e a n d pe rcen t s t a r v i n g . T h e s e r e s u l t s s u p p o r t t h e h y p o t h e s i s t h a t s t a r v a t i o n p lays a ro le i n t h e e a r l y l i fe h i s t o r y o f Pac i f i c h e r r i n g b u t t h e d i r e c t ro le is m i n o r — s t a r v a t i o n was d i r e c t l y r e s p o n s i b l e f o r o n l y 3 - 2 3 % o f t h e t o t a l m o r t a l i t y r a t e . S t a r v a t i o n m a y have a n a d d i t i o n a l i n d i r e c t ef fect o n m o r t a l i t y by i n c r e a s i n g t h e v u l n e r a b i l i t y o f t h e fish t o p r e d a t o r s . T h i s h y p o t h e s i s c a n n o t be r e j e c t e d . N e i t h e r can t h e hyp o thes is o f d e n s i t y - d e p e n d e n t p r e d a t i o n . A m o d e l o f m o r t a l i t y r a t e i n m a r i n e pe lag i c fish eggs a n d la rvae was d e v e l o p e d i n o r d e r t o t e s t t h e h y p o t h e s i s o f a m o r t a l i t y - p a t c h i n e s s i n t e r a c t i o n . T h e m o d e l was based o n t h e o b s e r v a t i o n t h a t t h e d a i l y i n s t a n t a n e o u s m o r t a l i t y ra tes o f m a r i n e pe lag i c eggs a n d larvae are h i g h e r t h a n e x p e c t e d f r o m t h e t r e n d o f m o r t a l i t y r a t e w i t h d r y w e i g h t i n t h e sea. T h i s e x t r a m o r t a l i t y was p o s i t i v e l y c o r r e l a t e d w i t h t h e p a t c h i n e s s o f t h e s p a t i a l d i s t r i b u t i o n o f t h e eggs a n d la rvae, w h i c h suggests t h a t i t is caused b y t h e a g g r e g a t i o n o f p r e d a t o r s o n p a t c h e s o f t h e i r prey. T h e p r o d u c t o f w e i g h t - d e p e n d e n t m o r t a l i t y , 5 . 2 6 x l 0 - 3 W~02&, a n d 1 + L l o y d ' s p a t c h i n e s s i n d e x p r e d i c t s m o r t a l i t y ra tes close t o t h o s e t h a t have b e e n m e a s u r e d f r o m t h e field by o t h e r w o r k e r s . T h e r e s u l t s o f t h e field s t u d y a n d t h e m o d e l l i n g exerc ise of fer s t r o n g s u p p o r t t o t h e i d e a t h a t s t a r v a t i o n is a r e l a t i v e l y m i n o r p h e n o m e n o n i n w i l d h e r r i n g la rvae . M e c h a n i s m s t h a t c o n t r o l t h e s p a t i a l p a t c h i n e s s o f eggs a n d larvae a n d , t h e r e f o r e , t h e i r v u l n e r a b i l i t y t o p r e d a t o r s , a p p e a r t o be f a r m o r e i m p o r t a n t . T h e m o r t a l i t y - p a t c h i n e s s h y p o t h e s i s of fers a n e w r o u t e t o t h e s t u d y o f t h e effects o f p r e d a t i o n o n n a t u r a l p l a n k t o n i c c o m m u n i t i e s . i i i Table of Contents A b s t r a c t 1 1 L i s t o f Tab les v i i i L i s t o f F i g u r e s x A c k n o w l e d g e m e n t s x m C h a p t e r 1 : G r o w t h , C o n d i t i o n , M o r t a l i t y , a n d D i s p e r s a l o f L a r v a l Pac i f i c h e r r i n g , Clupea harengus pallasi, o f B a m f i e l d I n l e t , B r i t i s h C o l u m b i a C h a p t e r S u m m a r y 1 I n t r o d u c t i o n 1 M a t e r i a l s a n d M e t h o d s 3 S t u d y S i te 3 S a m p l i n g G e a r 6 L a b o r a t o r y A n a l y s i s 8 O t o l i t h R i n g s 9 Size a n d G r o w t h 9 H a t c h D a t e s 11 A g e i n g H C o n d i t i o n F a c t o r s 13 D i f f u s i o n a n d M o r t a l i t y 13 P a t c h i n e s s 16 R e s u l t s a n d D i s c u s s i o n 16 N u m b e r a n d o r i g i n o f c o h o r t s 16 H a t c h D a t e s 2 1 L e n g t h w i t h D a t e 2 1 O t o l i t h R i n g N u m b e r w i t h T i m e 26 L e n g t h w i t h O t o l i t h A g e 29 G r o w t h D i f f u s i o n 29 W e i g h t - A g e R e l a t i o n s h i p s 29 W e i g h t - L e n g t h R e l a t i o n s h i p s 36 C o n d i t i o n F a c t o r s 36 C a t c h C u r v e s a t D a t e 43 C a t c h C u r v e s w i t h S t a t i o n 43 D i f f u s i o n R a t e s 56 P a t c h i n e s s 61 M o r t a l i t y R a t e s 64 D i s p e r s a l R a t e s 69 D i s t r i b u t i o n o f R e l a t i v e H a t c h D a t e s 70 C o r r e l a t i o n s B e t w e e n P o p u l a t i o n P a r a m e t e r s 70 T h e R o l e o f S t a r v a t i o n 79 D e n s i t y - D e p e n d e n c e a n d S p a t i a l A g g r e g a t i o n 8 1 C h a p t e r 2 : N a t u r a l M o r t a l i t y R a t e s o f M a r i n e Pe lag ic F i s h Eggs a n d L a r v a e : t h e R o l e o f P a t c h i n e s s C h a p t e r S u m m a r y 83 I n t r o d u c t i o n 83 T h e M o d e l 84 Sources o f D a t a 85 R e s u l t s 86 D i s c u s s i o n 100 C o n c l u d i n g R e m a r k s 101 L i t e r a t u r e C i t e d 103 v A p p e n d i x A : E f f e c t s o f D e l a y e d F e e d i n g a n d T e m p e r a t u r e o n t h e A g e o f I r r e v e r s i b l e S t a r v a t i o n a n d o n t h e R a t e s o f G r o w t h a n d M o r t a l i t y A p p e n d i x S u m m a r y 131 I n t r o d u c t i o n 131 M a t e r i a l s a n d M e t h o d s 132 E g g I n c u b a t i o n 132 E x p e r i m e n t a l A p p a r a t u s 133 S a m p l i n g 134 R e s u l t s 134 B e h a v i o u r 134 A g e o f I r r e v e r s i b l e S t a r v a t i o n 135 G r o w t h R a t e s 135 M o r t a l i t y R a t e s 147 D i s c u s s i o n 150 A p p e n d i x B : R i n g D e p o s i t i o n i n t h e O t o l i t h s o f L a r v a l Pac i f i c H e r r i n g A p p e n d i x S u m m a r y 176 I n t r o d u c t i o n 176 M a t e r i a l s a n d M e t h o d s 177 E x p e r i m e n t a l G r o u p s 177 R e a r i n g C o n d i t i o n s 177 H a t c h i n g 183 F o o d , 183 S a m p l e s 184 R i n g C o u n t i n g 184 D a t a A n a l y s i s 185 R e s u l t s 185 D i s c u s s i o n 189 v i A p p e n d i x C : M u l t i v a r i a t e A n a l y s i s o f M o r p h o m e t r y a n d D r y W e i g h t o f L a r v a l Pac i f ic H e r r i n g A p p e n d i x S u m m a r y 193 I n t r o d u c t i o n 193 M a t e r i a l s a n d M e t h o d s 195 L a r v a e 195 S a m p l i n g 195 S t a t i s t i c a l A n a l y s i s 196 R e s u l t s 198 G r o w t h 198 C o n d i t i o n F a c t o r s 209 C l a s s i f i c a t i o n F u n c t i o n s 220 D i s c u s s i o n 225 A p p e n d i x D : E f fec ts o f N e t C a p t u r e o n t h e P o s t p r e s e r v a t i o n M o r p h o m e t r y , D r y W e i g h t , a n d C o n d i t i o n F a c t o r o f L a r v a l P a c i f i c H e r r i n g A p p e n d i x S u m m a r y 233 I n t r o d u c t i o n 233 M a t e r i a l s a n d M e t h o d s 234 R e s u l t s 238 D i s c u s s i o n . 248 A p p e n d i x E : H a t c h i n g E x p e r i m e n t s 250 A p p e n d i x F : N e t E v a s i o n 258 v i i List of Tables T a b l e 1 .1 . D i s t a n c e s f r o m t h e h e a d o f B a m f i e l d I n l e t t o t h e s a m p l i n g s t a t i o n s 7 T a b l e 1.2. P e r c e n t o f n o n - y o l k - s a c la rvae 7 - 2 0 m m l o n g i n n u t r i t i o n a l classes 44 T a b l e 1.3. P e r c e n t o f t o t a l s t a r v i n g la rvae c a p t u r e d w i t h a p l a n k t o n - n e t a t s t a t i o n 49 T a b l e 1.4. C o r r e l a t i o n m a t r i x o f p o p u l a t i o n p a r a m e t e r s 77 T a b l e 1.5. T h e m o r t a l i t y ra tes d i r e c t l y a t t r i b u t a b l e t o s t a r v a t i o n 80 T a b l e A . l . T h e ra tes o f g r o w t h a n d m o r t a l i t y f o r 26 p o p u l a t i o n s 141 T a b l e A . 2 . T i m e p e r i o d s o f d e v e l o p m e n t a l s tages o f l a r v a l m a r i n e fishes 153 T a b l e A . 3 . G r o w t h r a t e s , m o r t a l i t y r a t e s , a n d r e a r i n g c o n d i t i o n s o f e x p e r i m e n t a l fish . . . . 162 T a b l e A . 4 . G r o w t h r a t e s a n d m o r t a l i t y r a t e s f r o m p u b l i s h e d r e a r i n g e x p e r i m e n t s 165 T a b l e A . 5 . G r o w t h r a t e s a n d m o r t a l i t y r a t e s f o r field p o p u l a t i o n s 167 T a b l e B . l . T h e e x p e r i m e n t a l g r o u p s a n d t h e i r r e a r i n g c o n d i t i o n s 178 T a b l e B .2 . Regress ions o f m e a n s t a n d a r d l e n g t h o n age f o r 7 g r o u p s o f h e r r i n g larvae . . . . 186 T a b l e B .3 . Regress ions o f m e a n r i n g n u m b e r o n age f o r 7 g r o u p s o f h e r r i n g larvae 188 T a b l e C . l . T h e m e a n ( ± 1 S D ) b o d y d i m e n s i o n s f o r t h r e e p o p u l a t i o n s 199 T a b l e C .2 . P a r a m e t e r va lues o f t h e one -cyc le a n d t w o - c y c l e G o m p e r t z g r o w t h f u n c t i o n s . . . 204 T a b l e C .3 . P r i n c i p a l c o m p o n e n t ana lys is o f t h e m o r p h o m e t r y a n d d r y w e i g h t 212 T a b l e C . 4 . E x p a n d e d p r i n c i p a l c o m p o n e n t s 218 T a b l e C . 5 . P r i n c i p a l c o m p o n e n t ana lys i s o f t h e t w o - v a r i a b l e d a t a set 219 T a b l e C . 6 . T h e p e r c e n t c o r r e c t l y c lass i f ied 222 T a b l e C . 7 . Regress ions o f l o g e W o n l o g e L f o r field a n d l a b o r a t o r y fish 228 v i i i T a b l e D . l . M e a n ( ± 1 S D ) b o d y m e a s u r e m e n t s o f s t a r v e d a n d fed fish 239 T a b l e D . 2 . T h e F - r a t i o s o f t h r e e - w a y analyses o f va r iance o f s ix b o d y m e a s u r e m e n t s . . . . 243 T a b l e D . 3 . P C ana lys i s o f b o d y m e a s u r e m e n t s o f t o w e d a n d n o n - t o w e d larvae 247 i x List of Figures F i g . 1 .1 . M a p o f B a m f i e l d I n l e t - T r e v o r C h a n n e l a rea 4 F i g . 1.2. L e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f h e r r i n g larvae c a p t u r e d i n 1981 17 F i g . 1.3. L e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f h e r r i n g larvae c a p t u r e d i n 1982 19 F i g . 1.4. R e g r e s s i o n o f a r c s i n y/P o n t i m e 22 F i g . 1.5. M e a n ( ± 1 S D ) s t a n d a r d l e n g t h - a t - a g e 24 F i g . 1.6. T h e d i s t r i b u t i o n o f o t o l i t h r i n g n u m b e r s w i t h t h e d a t e o f c a p t u r e 27 F i g . 1.7. P l o t o f s t a n d a r d l e n g t h o n o t o l i t h - a g e 30 F i g . 1.8. P l o t o f t h e s t a n d a r d d e v i a t i o n s o f t h e m e a n l e n g t h s a g a i n s t t i m e 32 F i g . 1.9. M e a n ( ± 1 S D ) d r y w e i g h t - a t - a g e 34 F i g . 1.10. W e i g h t - l e n g t h curves 37 F i g . 1 .11 . M e a n ( ± 1 S D ) C F - a t - a g e 39 F i g . 1.12. M e a n ( ± 1 S D ) C V l - a t - a g e 4 1 F i g . 1.13. P e r c e n t o f t o t a l s t a r v i n g larvae c a p t u r e d w i t h p l a n k t o n - n e t s p l o t t e d a g a i n s t l e n g t h . 45 F i g . 1.14. P e r c e n t o f t o t a l s t a r v i n g larvae c a p t u r e d w i t h a n i g h t - l i g h t p l o t t e d a g a i n s t l e n g t h . . 47 F i g . 1.15. P l a n k t o n - n e t catches a t d a t e a n d s t a t i o n 50 F i g . 1.16. N i g h t - l i g h t catches a t d a t e 52 F i g . 1.17. A g e f requenc ies o f p l a n k t o n - n e t catches 54 F i g . 1.18. Regress ions o f l o g e ( d e n s i t y ) o n z2 / * f o r p l a n k t o n - n e t catches 57 F i g . 1.19. Regress ions o f l o g c ( n u m b e r s ) o n m x2 / * f o r n i g h t - l i g h t catches 59 F i g . 1.20. L l o y d ' s p a t c h i n e s s i n d e x o n d a t e 62 x F i g . 1 .21. Regress ions o f l o g e ( d e n s i t y ) on age f o r p l a n k t o n - n e t catches 65 F i g . 1.22. Regress ions o f l o g e ( n u m b e r ) o n age f o r n i g h t - l i g h t catches 67 F i g . 1.23. D i s p e r s a l ve loc i t i es 71 F i g . 1.24. H a t c h d a t e f requenc ies 73 F i g . 1.25. P l o t s o f p o p u l a t i o n p a r a m e t e r s o n a b u n d a n c e a n d t h e f r a c t i o n s o f s t a r v i n g la r rae . . 75 F i g . 2 . 1 . P l o t o f t h e m o r t a l i t y ra tes o f m a r i n e o r g a n i s m s on d r y w e i g h t 87 F i g . 2.2. R e g r e s s i o n o f p a t c h i n e s s o n d r y w e i g h t 94 F i g . 2.3. R e g r e s s i o n o f r e s i d u a l m o r t a l i t y r a t e s o n 1 + p f o r fish eggs a n d larvae 96 F i g . 2.4. P l o t o f p r e d i c t e d m o r t a l i t y ra tes a g a i n s t m e a s u r e d m o r t a l i t y ra tes 98 F i g . A . l . G r o w t h i n m e a n ( ± 1 S D ) s t a n d a r d l e n g t h a t 6 ° , 8 ° , a n d 10° C 136 F i g . A . 2 . G r o w t h i n m e a n ( ± 1 S D ) t i ssue d r y w e i g h t a t 6 ° , 8 ° , a n d 1 0 ° C 138 F i g . A . 3 . P l o t o f GL a g a i n s t t h e age o f first f e e d i n g 143 F i g . A . 4 . P l o t o f Gw a g a i n s t t h e age o f first f e e d i n g 145 F i g . A . 5 . S u r v i v a l o f l a r v a l Pac i f i c h e r r i n g a t 3 t e m p e r a t u r e s a n d 8 f e e d i n g t r e a t m e n t s . . . 148 F i g . A . 6 . P l o t o f Mt o n t e m p e r a t u r e a n d t h e age o f first f e e d i n g 151 F i g . A . 7 . P l o t o f t, o n ty f o r t h e larvae o f 25 species o f m a r i n e fishes 156 F i g . A . 8 . P l o t o f t, o n t e m p e r a t u r e fo r t h e larvae o f 25 species o f m a r i n e fishes 158 F i g . A . 9 . P l o t o f GL a g a i n s t t e m p e r a t u r e f o r field p o p u l a t i o n s o f h e r r i n g larvae 168 F i g . A . 1 0 . P l o t o f Mt a g a i n s t t e m p e r a t u r e f o r field p o p u l a t i o n s o f h e r r i n g larvae 170 F i g . A . l l . P l o t o f Mt o n GL f o r e x p e r i m e n t a l a n d field p o p u l a t i o n s o f h e r r i n g larvae . . . . 173 F i g . B . l . D i a g r a m o f t h e i n s i t u c u l t u r e c h a m b e r 179 x i F i g . B .2 . D e t a i l o f t h e i n s i t u c u l t u r e c h a m b e r 181 F i g . B .3 . R e l a t i o n s h i p b e t w e e n t h e average r a t e s o f r i n g d e p o s i t i o n a n d g r o w t h i n l e n g t h . . 190 F i g . C . l . M e a n ( ± 1 S D ) s t a n d a r d l e n g t h a t age o f 1 9 8 1 A , 1 9 8 1 B , a n d 1 9 8 1 C 205 F i g . C .2 . M e a n ( ± 1 S D ) d r y w e i g h t a t age o f 1981A , 1 9 8 1 B , a n d 1981C 207 F i g . C.3 . R e g r e s s i o n o f l o g e W o n l o g e L, a n d i t s res idua ls 210 F i g . C .4 . S c a t t e r p l o t o f P C 2 o n P C I fo r t h e p o o l e d d a t a o f 1 9 8 1 A , 1 9 8 1 B , a n d 1 9 8 1 C . . . . 214 F i g . C.5 . M e a n s ( ± 1 S D ) a t age o f t h e s i x P C s o f 1 9 8 1 A , 1 9 8 1 B , a n d 1981C 216 F i g . C.6 . S c a t t e r p l o t o f P C 3 o n P C 4 f o r t h e p o o l e d d a t a o f 1 9 8 1 B a n d 1 9 8 1 C 223 F i g . C .7 . P l o t o f W o n L f o r r e a r e d a n d w i l d Paci f ic a n d A t l a n t i c l a rva l h e r r i n g 229 F i g . D . l . R e l a t i o n s h i p s o f p o s t p r e s e r v a t i o n b o d y d i m e n s i o n s b e t w e e n t o w e d a n d c o n t r o l fish . 2 4 1 F i g . D .2 . P l o t o f P C 5 o n P C I f o r t h e p o o l e d c o n t r o l a n d t o w e d h e r r i n g larvae 244 F i g . E . l . D i s t r i b u t i o n o f h a t c h i n g w i t h t i m e 2 5 1 F i g . E .2 . W h i s k e r a n d b o x p l o t o f t h e s t a n d a r d l e n g t h a t h a t c h 254 F i g . E .3 . W h i s k e r a n d b o x p l o t o f t h e d r y w e i g h t a t h a t c h 256 F i g . F . l . C u m u l a t i v e dens i t ies o f p l a n k t o n - n e t a n d n i g h t - l i g h t catches p l o t t e d a g a i n s t l e n g t h . 259 x i i Acknowledgements I t h a n k m y research s u p e r v i s o r , D r . N o r m a n J . W i l i m o v s k y , f o r d i r e c t i n g m e t o w a r d s a field p r o j e c t b a s e d a t t h e B a m f i e l d M a r i n e S t a t i o n . D r . D o u g l a s E . H a ^ assis ted m e i n c o l l e c t i n g eggs f r o m c a p t i v e h e r r i n g a t t h e Pac i f i c B i o l o g i c a l S t a t i o n i n t h e s p r i n g s o f 1980 a n d 1983 a n d p r o v i d e d some adv i ce d u r i n g t h e course o f t h i s research p r o j e c t . M r . G a r y K i n g s t o n ass is ted i n r e a r i n g h e r r i n g larvae i n 1980. D r . Jef f rey M a r l i a v e o f t h e V a n c o u v e r P u b l i c A q u a r i u m a d v i s e d m e o n t h e p r o p e r techn iques f o r r e a r i n g h e a l t h y h e r r i n g la rvae . I g r a t e f u l l y a c k n o w l e d g e t h e s t a f f o f t h e B a m f i e l d M a r i n e S t a t i o n : D r . R o n a l d F o r e m a n , M s . S a b i n a L e a d e r , M s . A n n Bergey, M r . T o m B e d f o r d , a n d M r . S i g u r d T v e i t , f o r ass is t i ng i n t h e c o l l e c t i o n o f t h e field s a m p l e s . I a lso w i s h t o t h a n k t h e rev iewers o f t h e m a n u s c r i p t s g e n e r a t e d f r o m t h i s thes is : D r . N o r m a n J . W i l i m o v s k y , M r . S h a w n R o b i n s o n , M r . J o h n A n d e r s o n , a n d M r . M i c h a e l S t . J o h n ; t h e i r c r i t i c i s m s a n d c o m m e n t s g r e a t l y i m p r o v e d t h e final d r a f t o f t h e thes is . D r . A l l a n G . L e w i s d e t e c t e d a ser ious e r r o r i n t h e first d r a f t o f t h e thes i s a n d asked some p o i n t e d q u e s t i o n s . I t h a n k m y p a r e n t s , M r . S t a n l e y E . M c G u r k a n d M r s . P. R u t h M c G u r k , f o r t h e i r c o n s t a n t s u p p o r t over m y l o n g career as a s t u d e n t . I e x t e n d spec ia l t h a n k s t o M r . R o n a l d S. K o n g f o r t h e i n t a n g i b l e s . T h i s research was s u p p o r t e d by t w o U n i v e r s i t y o f B r i t i s h C o l u m b i a S u m m e r Research Scholar -s h i p s , a G r a d u a t e Research , E n g i n e e r i n g a n d T e c h n o l o g y A w a r d f r o m t h e B r i t i s h C o l u m b i a Science C o u n c i l , a n d by N a t i o n a l Sciences a n d E n g i n e e r i n g Research C o u n c i l o f C a n a d a g ran ts t o D r . N o r m a n J . W i l i m o v s k y . x i i i Chapter 1 Growth, Condition, Mortality, and Dispersal of Larval Pacific Herring, Clupea harengus pallasi, of Bamfield Inlet, British Columbia Chapter Summary F o u r c o h o r t s o f w i l d Pac i f i c h e r r i n g la rvae were s a m p l e d f r o m h a t c h t o age 4 0 - 6 0 d i n a s m a l l coas ta l i n l e t i n o r d e r t o d e t e r m i n e t h e ro le o f s t a r v a t i o n i n t h e i r p o p u l a t i o n d y n a m i c s . S t a r v a t i o n was d i a g n o s e d i n 4 . 9 - 9 0 . 0 % o f t h e 7 - 2 0 m m l o n g larvae u s i n g a m o r p h o m e t r i c c o n d i t i o n f a c t o r . M o s t o f these s t a r v i n g la rvae were 9 - 1 5 m m l o n g a n d t h e y were f o u n d w i t h i n 3 k m o f t h e h a t c h s i t e . T h e ra tes o f g r o w t h i n l e n g t h a n d w e i g h t , a n d t h e w e i g h t - l e n g t h e x p o n e n t s , decreased w i t h i n c r e a s i n g p o p u l a t i o n d e n s i t y a n d i n c r e a s i n g p e r c e n t o f t h e p o p u l a t i o n c lass i f ied as s t a r v i n g . T h e d i f f u s i o n coe f f i c ien ts , m o r t a l i t y r a t e s , a n d d i s p e r s a l v e l o c i t i e s , i nc reased w i t h i n c r e a s i n g a b u n d a n c e a n d p e r c e n t s t a r v i n g . T h e s e r e s u l t s s u p p o r t t h e h y p o t h e s i s t h a t t h e s t a r v a t i o n o f first-feeding la r rae plays a ro le i n t h e s u r v i v a l o f l a r v a l P a c i f i c h e r r i n g b u t t h e d i r e c t ro le is m i n o r — s t a r v a t i o n was d i r e c t l y r e s p o n s i b l e f o r o n l y 3 - 2 3 % o f t h e t o t a l m o r t a l i t y r a t e . S t a r v a t i o n m a y have a n a d d i t i o n a l i n d i r e c t ef fect o n m o r t a l i t y b y i n c r e a s i n g t h e v u l n e r a b i l i t y o f t h e fish t o p r e d a t o r s . T h i s h y p o t h e s i s c a n n o t be r e j e c t e d . N e i t h e r c a n t h e h y p o t h e s i s o f d e n s i t y - d e p e n d e n t p r e d a t i o n . Introduction Year -c lass s t r e n g t h o f fish p o p u l a t i o n s is b e l i e v e d by m a n y fisheries sc ien t is ts t o b e l i m i t e d by s u r v i v a l d u r i n g t h e e a r l y l i fe h i s t o r y s tages, p a r t i c u l a r l y t h e l a rva l s tage ( C u s h i n g 1975; L a s k e r 1985) . Severa l m e c h a n i s m s o f m o r t a l i t y have b e e n p r o p o s e d . H j o r t (1913 , 1926) sugges ted t h a t c a t a s t r o p h i c s t a r v a t i o n o f first-feeding l a r v a l A t l a n t i c h e r r i n g , Clupea harengus harengus, was t h e m a j o r cause o f t h e i r m o r t a l i t y . T h i s h y p o t h e s i s p r e d i c t s t h a t s t a r v i n g fish larvae s h o u l d b e f o u n d i n n a t u r e a n d t h a t t h e i r r e l a t i v e a b u n d a n c e s h o u l d b e d i r e c t l y c o r r e l a t e d w i t h t h e m o r t a l i t y r a t e . S t a r v i n g fish larvae have b e e n f o u n d i n t h e field ( S h e l b o u r n e 1957: p l a i c e , Pleuronectes platessa; O ' C o n n e l l 1980: n o r t h e r n a n c h o v y , Engraulis mordax; K a s h u b a a n d M a t t h e w s 1984: f r e s h w a t e r s h a d , Dorosoma s p p . ) b u t i t is s t i l l u n c l e a r h o w i m p o r t a n t s t a r v a t i o n is as a d i r e c t source o f m o r t a l i t y . I t s ro le as an i n d i r e c t source 1 o f m o r t a l i t y , as a f a c t o r t h a t r e n d e r s fish m o r e v u l n e r a b l e t o p r e d a t o r s , is even' less c lear as n o one has y e t r e p o r t e d a n y r e l a t i o n s h i p b e t w e e n t h e degree o f s t a r v a t i o n a n d m o r t a l i t y r a t e f o r l a r v a l fishes. T h e o f fshore t r a n s p o r t o f fish eggs a n d larvae has b e e n p r o p o s e d as a n o t h e r m e c h a n i s m o f e a r l y l i fe h i s t o r y m o r t a l i t y , espec ia l l y f o r t h o s e species w i t h i n s h o r e j u v e n i l e nu rse ry areas ( C o l t o n a n d T e m p l e 1 9 6 1 ; B a i l e y 1 9 8 1 ; P a r r i s h e t a l . 1981) . S tevenson (1962) r e p o r t e d t h a t t h e o f fshore t r a n s p o r t o f l a r v a l Pac i f i c h e r r i n g , Clupea harengus pallasi, f r o m t h e i r c o a s t a l a n d e s t u a r i n e h a t c h i n g s i tes was t h e d r i v i n g v a r i a b l e b e h i n d year-c lass v a r i a t i o n . H e based t h i s c o n c l u s i o n o n t h e o b s e r v a t i o n t h a t he never f o u n d any l a r v a l h e r r i n g o f fshore ( > 12 k m ) f r o m t h e i r h a t c h i n g s i te i n B a r k l e y S o u n d , B r i t i s h C o l u m b i a . T h e p r o x i m a t e cause o f d e a t h i n t h i s m o d e l is p r e s u m a b l y s t a r v a t i o n caused by i n a d e q u a t e dens i t i es o f f o o d i n o f fshore w a t e r s . S tevenson ' s s u g g e s t i o n t h a t o s m o r e g u l a t o r y p r o b l e m s m a y also b e i n v o l v e d does n o t a p p e a r l i k e l y as Pac i f i c h e r r i n g la rvae b e e n s h o w n t o b e ab le t o t o l e r a t e h i g h - s a l i n i t y ocean ic w a t e r s ( A l d e r d i c e a n d H o u r s t o n 1985) . T h e of fshore t r a n s p o r t hyp o thes is p r e d i c t s t h a t l a rva l h e r r i n g s h o u l d be f o u n d o f fshore , t h a t t h e y s h o u l d be m o r e e m a c i a t e d t h a n those larvae i n n e a r s h o r e w a t e r s , a n d t h a t t h e r a t e o f t r a n s p o r t s h o u l d be d i r e c t l y c o r r e l a t e d w i t h t h e r a t e o f m o r t a l i t y . Recen t w o r k o n t h e d i s t r i b u t i o n o f l a r v a l fishes has c h a l l e n g e d t h i s h y p o t h e s i s ; s t u d i e s on t h e d i s p e r s a l o f l a r v a l A t l a n t i c h e r r i n g i n es tua r ies ( G r a h a m 1972; A b l e 1978; F o r t i e r a n d L e g g e t t 1982, 1983; B o w l e s et a l . 1984; H e n r i e t a l . 1985) a n d o n c o n t i n e n t a l shelves ( l ies a n d S i n c l a i r 1982; S i n c l a i r a n d l ies 1985) , a n d s t u d i e s o n t h e d i s p e r s a l o f o t h e r species o f l a r va l fishes i n es tua r ies (Pearcy 1962; W e i n s t e i n e t a l . 1980; S e t z l e r e t a l . 1981) a n d o n c o n t i n e n t a l shelves (Bo lz a n d L o u g h 1984; O ' B o y l e e t a l . 1984; S m i t h a n d M o r s e 1985) have s h o w n t h a t l a r va l fishes are n o t pass ive ly d i s t r i b u t e d by w a t e r c u r r e n t s . I n s t e a d , t h e y t e n d t o m a i n t a i n t hemse lves i n so-ca l led " r e t e n t i o n z o n e s " . T h e m o s t l i k e l y m e c h a n i s m o f r e t e n t i o n i n es tuar ies is d a i l y v e r t i c a l m i g r a t i o n b e t w e e n t w o c o u n t e r - f l o w i n g w a t e r layers . O n c o n t i n e n t a l shelves t h e m o s t l i k e l y m e c h a n i s m s i n v o l v e p h y s i o g e o g r a p h i c f e a t u r e s s u c h as t h e a n t i - c y c l o n i c g y r e over Georges B a n k ( S m i t h a n d M o r s e 1985) . W a r e (1975) a n d o t h e r s have p r o p o s e d t h a t p r e d a t i o n , n o t s t a r v a t i o n , is t h e m a i n agent o f d e a t h i n t h e sea a n d t h a t t h e effects o f p r e d a t i o n are m o d u l a t e d by t h e r a t e a t w h i c h t h e fish g r e w o u t o f t h e size r a n g e o f p a r t i c u l a r v u l n e r a b i l i t y . S t a r v a t i o n m a y p lay a ro le i n t h i s process by r e d u c i n g g r o w t h ra tes a n d b y r e d u c i n g t h e a b i l i t y o f f i s h t o evade p r e d a t o r s . T h i s g r o w t h - m o d u l a t e d - p r e d a t i o n 2 h y p o t h e s i s p r e d i c t s t h a t l a r v a l g r o w t h a n d m o r t a l i t y ra tes s h o u l d be i nve rse l y c o r r e l a t e d w i t h i n a species o r s p a w n i n g s t o c k . I t is a r g u e d i n A p p e n d i x A ( F i g . A . l l ) t h a t t h e r e is l i t t l e o r n o c o r r e l a t i o n b e t w e e n t h e r a t e s o f m o r t a l i t y a n d t h e l i n e a r ra tes o f f g r o w t h i n l e n g t h fo r 11 r e c o r d s o f w i l d c o h o r t s o f A t l a n t i c a n d P a c i f i c h e r r i n g l a r vae . A l l t h r e e h y p o t h e s e s share t h e a s s u m p t i o n t h a t s t a r v a t i o n p lays a ro le e i t h e r as a d i r e c t o r an i n d i r e c t source o f m o r t a l i t y . T h i s field s t u d y was d e s i g n e d t o t e s t a l l t h r e e h y p o theses, w i t h a p a r t i c u l a r f ocus o n t h e ro le o f s t a r v a t i o n . T h e s t u d y p o p u l a t i o n s were c o h o r t s o f Pac i f ic h e r r i n g larvae t h a t h a t c h every M a r c h - A p r i l i n a s m a l l c o a s t a l i n l e t o n t h e wes t coast o f V a n c o u v e r I s l a n d , B r i t i s h C o l u m b i a . T h e ra tes o f g r o w t h i n l e n g t h a n d w e i g h t , t h e ra tes o f o t o l i t h r i n g d e p o s i t i o n , t h e n u t r i t i o n a l s t a t u s as i n f e r r e d f r o m m o r p h o m e t r y , t h e ra tes o f d i s p e r s a l f r o m t h e h a t c h i n g s i tes , a n d t h e ra tes o f m o r t a l i t y , we re m e a s u r e d i n o r d e r t o d e t e r m i n e i f s t a r v a t i o n o c c u r r e d , u n d e r w h a t c o n d i t i o n s i t was f o u n d , a n d w h a t was i t s i m p a c t o n t h e n u m e r i c a l d y n a m i c s o f t h e c o h o r t s . Materials and Methods S t u d y S i te B a m f i e l d I n l e t is a s m a l l i n l e t o n t h e s o u t h e r n coas t o f B a r k l e y S o u n d , B r i t i s h C o l u m b i a ( F i g . 1.1). B a r k l e y S o u n d is t h e m o s t s o u t h e r l y m a j o r i n d e n t a t i o n o n t h e s o u t h w e s t coas t o f V a n c o u v e r I s l a n d . B a m f i e l d I n l e t is 3.8 k m l o n g a n d has a n average w i d t h o f 200 m . T h e d e p t h increases f r o m 1 m a t t h e h e a d t o 60 m a t t h e m o u t h , w h e r e t h e I n l e t enters T r e v o r C h a n n e l . T h e r e is n o s i l l a t t h e m o u t h o f t h e I n l e t . T r e v o r C h a n n e l is a d r o w n e d r i v e r va l ley , i t s d e p t h increases f r o m a b o u t 30 m a t C a p e Bea le t o 140 m a t N a n a t I s l a n d . T h e c u r r e n t p a t t e r n i n B a r k l e y S o u n d is c y c l o n i c w i t h a l a n d w a r d t r a n s p o r t o f h i g h - s a l i n i t y ocean ic w a t e r a l o n g t h e s o u t h e a s t e r n shore ( T r e v o r C h a n n e l ) a n d a s e a w a r d t r a n s p o r t o f l o w - s a l i n i t y w a t e r a l o n g t h e n o r t h e a s t e r n shore ( H o u r s t o n 1959; Stevenson 1962) . 3 Figure 1.1. Map of the Bamfield Inlet-Trevor Channel area showing the sampling stations. 4 The temperature of the surface water in Bamfie ld Inlet ranges from 9-17° C . A thermocline occurs at 4-6 m , below which the water ranges from 8-10° C . The salinity of the surface waters ranges from 13-31%o. There is a shallow halocline in the top 4 m and below 10 m the water is a constant 3 1 -32%o salinity. Bamfield Inlet can be considered a partial ly-mixed estuary, the inflow of fresh water into the Inlet from surface runoff causes a net mot ion to seaward of the low-salinity surface water. To maintain continuity of volume there is a sub-surface inflow of saline water. T h e runoff into the Inlet is entirely from rainfal l and not from snowmelt and so the estuarine c irculat ion rate is highest in winter when the heaviest rains occur. The average annual ra infal l in the Bamfield area is 251 c m . T h e secchi disk depths range from 4-10 m in the spring and summer. The t ida l regime is the mixed semi-diurnal type. T w o stations were regularly sampled in the Inlet: U p p e r Bamfield (A) , and off the Bamfield M a r i n e Stat ion (B). Occasional samples were taken at one station in Grappler Inlet (C), and at six stations in Trevor Channe l : off Bamfie ld Inlet (D), K e l p Bay (E), Whit t les tone Po in t (G), Cape Beale (H), Ohia t Rock (I), and Nanat Island (J). The mean water depths at each stat ion and the distances from the hatching site i n Bamfield Inlet to each of these stations were taken from Canadian Hydrographic Service maps (Table 1.1). Sampl ing Gear The p lankton was sampled w i t h twin bongo plankton-nets and a night-l ight. The twin bongos had a m o u t h diameter of 40 c m , the net was 1.5 m long and the mesh diameter was 471 / i m . The two codends were made of hard plastic and each had two holes of 4 c m diameter cut into their sides covered w i t h 73 fim diameter mesh. A flowmeter was placed slightly off center i n the mouth of one of the nets. The bongos were towed at a speed of 1-2 m s - 1 at a depth of about 2 m in Bamfield Inlet and in some stations outside the Inlet. In 1982 most of the tows outside the Inlet were oblique tews to 20-50 m depth . Each tow took 5—15 m i n to complete after which the contents of the codends were immediately preserved in 2 % formaldehyde and seawater (about 30%? salinity) or in 37% isopropyl alcohol. T h e nets were washed down after each tow. The samples were drained after 24 hours and fresh preservative was added. 6 TABLE 1.1. Distances from the head of Bamfield Inlet (hatching sites) to the sampling stations, and the water depth at the stations. Station X Depth (km) (m) A 0.9 6.2 B 2.8 32.2 C 4.5 4.2 D 4.2 92.2 E 6.0 102.2 G 7.7 32.2 H 12.8 57.2 I 6.9 27.2 J 10.1 142.2 7 T h e n i g h t - l i g h t floated a t t h e sea su r face a t t h e d o c k o f t h e B a m f i e l d M a r i n e S t a t i o n , o p p o s i t e s t a t i o n B . T h e l i g h t was set o u t a f t e r c i v i l t w i l i g h t a n d p l a n k t e r s were a l l o w e d t o a c c u m u l a t e a b o u t i t f o r severa l h o u r s . A d i p n e t was used t o c a p t u r e any fish larvae w i t h i n a 0.5 m r a d i u s o f t h e l i gh t . T h e c a p t u r e success was e s t i m a t e d t o b e close t o 1 0 0 % . O n e h a l f o f each s a m p l e was i m m e d i a t e l y p r e s e r v e d i n 2 % f o r m a l d e h y d e a n d seawate r ( S = 3 0 % j ) a n d t h e o t h e r h a l f i n 3 7 % i s o p r o p y l a l c o h o l . L a b o r a t o r y A n a l y s i s E a c h h e r r i n g l a r v a w a s c o u n t e d i n t h o s e s a m p l e s w i t h less t h a n 10000 h e r r i n g la rvae. S a m p l e s w i t h m o r e t h a n 10000 h e r r i n g larvae were s u b - d i v i d e d w i t h a p l a n k t o n s p l i t t e r a n d a t least t h r e e s u b s a m p l e s were c o u n t e d . T h e m e a n n u m b e r o f l a rvae p e r s u b s a m p l e was m u l t i p l i e d b y t h e n u m b e r o f s u b s a m p l e s t o o b t a i n t h e e s t i m a t e d t o t a l n u m b e r . T h e t o t a l d e n s i t y o f la rvae i n a l e n g t h class i was (1-1) Si = w h e r e n r = t h e t o t a l n u m b e r o f la rvae o f a c o h o r t m e a s u r e d i n a s a m p l e , n , = t h e n u m b e r o f m e a s u r e d la rvae o f t h a t s a m p l e (per H ^ m 3 ) t h a t f e l l i n l e n g t h class i, N= t h e t o t a l n u m b e r o f larvae o f a c o h o r t i n a s a m p l e , a n d V = t h e v o l u m e o f w a t e r filtered b y t h e t w o p l a n k t o n - n e t s ( c a l c u l a t e d by m u l t i p l y i n g t h e n u m b e r o f r e v o l u t i o n s r e c o r d e d b y t h e flowmeter b y t w o t i m e s a c a l i b r a t i o n coe f f i c ien t s u p p l i e d b y t h e m a n u f a c t u r e r t i m e s t h e r a t i o o f t h e a r e a o f t h e m o u t h o f t h e n e t t o t h e a rea o f t h e f u n n e l o f t h e flowmeter). T h e la rvae w e r e s t o r e d a t 2 0 ° C f o r a t leas t 30 d b e f o r e m e a s u r i n g i n o r d e r t o a l low t h e d i m e n s i o n s t i m e t o s t a b i l i z e . A t leas t 100 larvae f r o m each s a m p l e were r a n d o m l y chosen a n d m e a s u r e d f o r s t a n d a r d l e n g t h (L) ( = n o t o c h o r d l e n g t h ) w i t h t h e v e r n i e r scale o f a c o m p o u n d m i c r o s c o p e . Fou r o t h e r m o r p h o m e t r i c c h a r a c t e r s were m e a s u r e d w i t h a n o c u l a r m i c r o m e t e r f o r s u b s a m p l e s o f 1 0 - 1 5 l a r vae : (1) a n a l b o d y d e p t h (ABD), t h e d o r s a l - v e n t r a l d e p t h o f t h e b o d y a t t h e anus, e x c l u d i n g t h e g u t ; (2) p e c t o r a l b o d y d e p t h (PBD), m e a s u r e d a t t h e p e c t o r a l g i r d l e , i n c l u d i n g t h e g u t ; (3) h e a d w i d t h (HW), m e a s u r e d across t h e d o r s a l su r face o f t h e h e a d , i n c l u d i n g t h e eyebal ls ; (4) eye d i a m e t e r IED), a l w a y s m e a s u r e d a l o n g t h e a n t e r o p o s t e r i o r ax is . D r y w e i g h t , W, was m e a s u r e d by r i n s i n g a l a r v a i n 8 -f resh w a t e r , d r y i n g i t a t 6 0 ° C f o r 24 h , a n d w e i g h i n g t h e res idue w i t h a n e l e c t r o b a l a n c e t o t h e neares t Mg-A l l s t a n d a r d l e n g t h s i n t h i s p a p e r are f o r m a l i n fixed l e n g t h s . S t a n d a r d l e n g t h s h r i n k s by 5% i n a 2-5% f o r m a l d e h y d e a n d seawa te r ( S = 3 0 % c ^ s o l u t i o n ( S c h n a c k a n d R o s e n t h a l 1978; H a y 1982) . P r e s e r v a t i o n i n a l c o h o l does n o t change t h e l ive s t a n d a r d l e n g t h o f Pac i f i c h e r r i n g larvae ( A p p e n d i x B , M a t e r i a l s a n d M e t h o d s ) so t h e m e a s u r e d l e n g t h s o f a l coho l -p rese rved larvae were first c o r r e c t e d fo r n e t - c a p t u r e , i f t h e y h a d b e e n c a p t u r e d w i t h a p l a n k t o n - n e t , a n d t h e n t h e y were r e d u c e d by 5% i n o r d e r t o c o m p a r e t h e m w i t h t h e l e n g t h s o f f o r m a l i n - p r e s e r v e d larvae. O t o l i t h R i n g s T h e n u m b e r o f r i n g s i n t h e s a g i t t a l o t o l i t h s o f some larvae were c o u n t e d i n o r d e r t o age t h e m a n d t h e r e b y c o n s t r u c t a g r o w t h c u r v e . T h e cu rve was t h e n used t o v e r i f y t h e g r o w t h curves d e r i v e d f r o m t h e l e n g t h - a t - d a t e d a t a . A l c o h o l - p r e s e r v e d larvae were m e a s u r e d f o r s t a n d a r d l e n g t h a n d t h e n t h e t w o s a g i t t a e o f each fish were r e m o v e d a n d t h e r i n g s were c o u n t e d a c c o r d i n g t o t h e p r o t o c o l d e s c r i b e d i n A p p e n d i x B ( M a t e r i a l s a n d M e t h o d s ) . T h e average ra tes o f o t o l i t h r i n g d e p o s i t i o n were c a l c u l a t e d as t h e s lope o f t h e l i n e a r p r e d i c t i v e regress ion o f m e a n r i n g n u m b e r o n t i m e . E a c h m e a n was we igh t e d ' w i t h i t s s a m p l e size d i v i d e d by i t s v a r i a n c e ( G i l b e r t 1973) . A g e w a s c a l c u l a t e d f r o m t h e r i n g c o u n t by a s s u m i n g t h a t r i n g d e p o s i t i o n b e g a n i m m e d i a t e l y a f t e r c o m p l e t e y o l k a b s o r p t i o n , 5 d a f t e r h a t c h at 8 - 1 0 ° C ( A p p e n d i x A ) , a n d t h a t one r i n g was l a i d d o w n each day . Size a n d G r o w t h T h e d i m e n s i o n s o f t h e larvae were c o r r e c t e d f o r p r e - f i x a t i o n s h r i n k a g e o r e x p a n s i o n c a u s e d by n e t - c a p t u r e w i t h t h e G o m p e r t z m o d e l s d e s c r i b e d i n A p p e n d i x D ( F i g . D . l ) . T h e c o h o r t s o f la rvae were s e p a r a t e d b y eye o r , w h e n t h e d i s t r i b u t i o n s o v e r l a p p e d each o t h e r , w i t h a l e n g t h - f r e q u e n c y ana lys i s p r o g r a m ( M a c D o n a l d a n d P i t c h e r 1979; M a c D o n a l d 1980) . T h e bas ic a s s u m p t i o n o f t h e p r o g r a m is t h a t t h e l e n g t h - f r e q u e n c i e s are m i x t u r e s o f n o r m a l d i s t r i b u t i o n s . 9 The mean lengths-at-date were fit with a linear growth model, (1.3) L = Lo + GL T, where Lo=length at hatch (mm), <3x=growth rate (mmd-1), and T— date (d from mean hatch date), and a one-cycle Gompertz function (Zweifel and Lasker 1976), (1.4) L = I o e x p [ ^ ( l - e x p [ - a r ] ) ] , where A0= the growth rate at hatch (d - 1), and a=the rate of exponential decay of Ao (d_ 1). The lengths-at-otolith-age were fit using equation (1.4) but t (=age=ring count plus 5 d) was substituted for T. The mean weights-at-age were fitted with an exponential growth model, (1.5) W= W0exp(Gwt), where W0=weight at hatch (fig) and Gw = growth rate (d - 1), and a two-cycle Gompertz function, (1.6) W= ^ o e x p ^ U - e x p t - a m i n ^ f ^ + yU -exp I - ^ m a x ^ - f ^ ) ] ) ] , where .Ao=the growth rate at hatch (d - 1), a=the rate of exponential decay of Ao (d_ 1), t* =the age at the end of the first cycle of growth and the beginning of the second cycle (d), Bo =the growth rate at the start of the second cycle (d—*), 8 = the rate at which 5b decays with time (d_ 1), and min and max are functions that choose the minimum and the maximum of their two arguments. The two-cycle growth function was fitted to the weight data because the growth curves have two distinct cycles: an initial period of no increase of weight or a decrease in weight during which the yolk is absorbed and the larvae learn how to feed, and a second period of steady increase as the larvae feed successfully. The one-cycle function was fitted to the length data even though a two-cycle function may have provided a marginally better fit because the one-cycle function was later rearranged in order to calculate age from length. This could not be done with a two-cycle function. These functions and all other non-linear functions in this thesis were fit with the BMDP:AR non-linear least-squares regression program (Dixon 1983). When the data consisted of mean lengths-at-date or weights-at-date with associated variances then each mean was weighted by its sample size divided 10 by its variance (Gilbert 1973). When the data consisted of individual lengths-at-otolith-age then each length was loge-transformed in order to stabilize the variance with age. Lo was set at 7.7 mm and Wo at 160 fig, based on laboratory hatching experiments (Appendix E). Hatch Dates The dates at the beginning, mid-point, and end of the hatching periods were estimated from the rates at which yolk-sac larvae disappeared from the catches. The ratios of yolk-sac to non-yolk-sac larvae, P, calculated from the pooled catches for each day, were normalized with the arcsin transformation and then regressed on date. Each transformed ratio was weighted with its sample size in order to account for the fact that the accuracy of a ratio varies inversely with its sample size (Gilbert 1973). The surface water temperature at Bamfield Inlet was 8-10° C so the duration of the yolk-sac stage was 4-6 d (Appendix A). Therefore, the mean hatch date was about 5 d before the date at which P = 0.5. Ageing There were two possible methods of ageing the larvae: (1) using the time elapsed between the mean date of hatch and the date of capture or, (2) using standard length as an index of age. The first method ignores the fact that hatching is not instantaneous and so some larvae in every catch would have their ages either underestimated or overestimated. Some plankton-net catches would have to be discarded if they were taken before the date of mean hatch. The second method avoids bias due to non-instantaneous hatch and so it provides population parameters with lower associated estimation errors. It allows the inclusion of all catches in the analysis regardless of whether they were captured before or after the mean hatch date. Its only serious drawback is that length is not a reliable index of age in starving larvae, but since the population data are accompanied by data on condition I was confident this bias could be avoided. Age was estimated from the length-at-date data using the rearranged equation (1.4) after t was substituted for T, (1-7) . . . i ^ - i ^ ) ] , 11 and after the length-frequencies had been corrected for the phenomenon of growth diffusion. Growth diffusion is the increase in the variance of the mean length of a cohort with increasing age, and it is caused by variations in the growth trajectories of individual fish that accumulate with time. It causes the number of day classes inferred from the length distribution to increase with increasing time. The simplest way of correcting for this is to compress the length distribution of a day's pooled catches by an amount proportional to the increase in the standard deviation of the mean length since the end of the hatching period. Thus, the compressed difference in length between a fish of length L and the estimated mean length at that date, L, (calculated from equation (1.4)), is equal to the observed length difference divided by the ratio of the standard deviation of L, s, to the estimated standard deviation of L at the age at the end of the hatching period, s*, — s* (1-8) LcompTesse<i = L H (X — i/)oi»er«ed-S s* and *-at-age were calculated for each cohort by fitting a Gompertz curve to the plot of s on T, (1.9) * = « o e x p [ | ( l - e x p [ - ? 7 ; ] ) ] , where S Q = the standard deviation at T = 0, and G and g are fitted constants. Weight-Length Relationships The linear allometric relationship, (1-10) loge W — loge oj + eg loge L, and a non-linear allometric relationship, (1.11) loge W=b1-b2(b3- log, Lf<, were fit to the weight-length data of each cohort. Equation (1.11) was derived by Theilacker (1980a) by eliminating time from two one-cycle Gompertz equations describing growth in length and weight, ax and a2 are constants, corresponds to the natural logarithm of the asymptotic dry weight, 63 corresponds to the natural logarithm of the asymptotic standard length, 64 is the ratio of the decay parameters in the one-cycle length and weight Gompertz curves, and b2 has no obvious biological interpretation. 12 C o n d i t i o n F a c t o r s T h e n u t r i t i o n a l s t a t u s o f t h e h e r r i n g la rvae was e s t i m a t e d f r o m t h e i r m o r p h o m e t r y a n d d r y w e i g h t w i t h t w o c o n d i t i o n f a c t o r s . T h e first was F u l t o n ' s f a c t o r , (1.12) C F = W/I?, w h e r e is i n m g a n d L is i n m m , w h i c h has b e e n w i d e l y used i n la rva l h e r r i n g research ( B l a x t e r 1 9 7 1 ; H e m p e l a n d B l a x t e r 1963; V i l e l a a n d Z i j l s t r a 1 9 7 1 ; E h r l i c h et a l . 1976; W e s t e r n h a g e n a n d R o s e n t h a l 1981) . R e a r i n g e x p e r i m e n t s w i t h fed a n d s t a r v e d 0 - 2 0 d o l d larvae ( A p p e n d i x A a n d C ) s h e w e d t h a t a va lue o r C F < 1.68 i n d i c a t e s i r reve rs ib le s t a r v a t i o n , a va lue o f C F b e t w e e n 1.68-2.42 i n d i c a t e s revers ib le s t a r v a t i o n a n d a va lue o f C F > 2.42 i n d i c a t e s success fu l f e e d i n g . C F was c a l c u l a t e d f o r b o t h yo l k -sac a n d n o n - y o l k - s a c la rvae . T h e s e c o n d c o n d i t i o n f a c t o r was a m u l t i v a r i a t e one w h o s e d e r i v a t i o n is d e s c r i b e d i n A p p e n d i x C : (1.13) C V l = 1 4 . 1 9 1 - 4 . 3 8 9 1 o g e L + 2 . 1 8 4 I o g e ABD+ 2 . 1 9 7 1 0 ^ P B D - 1 2 . 3 3 1 1 0 ^ HW + 3 . 7 7 0 1 o g e £ Z ? + 0 . 4 1 9 1 o g e W. A va lue o f C V 1 < 0 i den t i f i es a fed l a r v a a n d a va lue o f C V 1 > 0 iden t i f i es a s t a r v e d la rva . C V l was c a l c u l a t e d o n l y f o r n o n - y o l k - s a c larvae because i t was c a l i b r a t e d w i t h n o n - y o l k - s a c larvae. T h e t w o c o n d i t i o n f a c t o r s were w e i g h t e d b y t h e c a t c h - p e r - u n i t - e f f o r t o f each s a m p l e i n o r d e r t h a t t h e m e a n f a c t o r s - a t - a g e w o u l d m o r e a c c u r a t e l y r e p r e s e n t t h e t r u e p o p u l a t i o n m e a n s . D i f f u s i o n a n d M o r t a l i t y T h e r a t e s o f d i f f u s i o n a n d m o r t a l i t y were e s t i m a t e d f r o m t h e d e n s i t y d a t a w i t h t h e a i d o f a d i f f u s i o n - m o r t a l i t y p o p u l a t i o n m o d e l ( O k u b o 1980) , M m as i a , as. as dt xdx ox dx w h e r e £ = t h e m e a n d e n s i t y ( n u m b e r 1 0 - 3 m - 3 ) , z = t h e d i s t a n c e f r o m t h e h a t c h i n g s i te t o t h e s a m p l i n g s t a t i o n ( k m ) , Kh=the h o r i z o n t a l d i f f u s i v i t y , u = t h e r a t e o f h o r i z o n t a l a d v e c t i o n ( k m d - 1 ) , a n d M = t h e r a t e o f m o r t a l i t y c a u s e d b y s t a r v a t i o n a n d p r e d a t i o n ( d _ 1 ) . 13 A d v e c t i o n w a s i g n o r e d i n t h i s m o d e l f o r t h r e e reasons : f i r s t , i t s i n c l u s i o n makes an a n a l y t i c a l s o l u t i o n o f e q u a t i o n (1.14) e x c e e d i n g l y d i f f i c u l t ( R a m m i n g a n d K o w a l i k 1980) . S e c o n d , s ince t h e n e w l y - h a t c h e d la rvae have o n l y one d i r e c t i o n i n w h i c h t o s w i m , d o w n B a m f i e l d I n l e t , i t is n o t poss ib le t o s e p a r a t e t h e processes o f a d v e c t i o n a n d d i f f u s i o n . T h i r d , s t u d i e s o n t h e d i s t r i b u t i o n o f la rva l fishes i n t h e sea has i n d i c a t e d t h a t t h e y may be c a p a b l e o f e n o u g h d i r e c t e d m o v e m e n t t o m a i n t a i n themselves i n r e t e n t i o n zones. T h i s m e a n s t h a t d i f f u s i o n i n t h e s t r i c t d e f i n i t i o n o f t h e w o r d , as a process d r i ven b y B r o w n i a n m o t i o n , m a y n o t o p e r a t e . R a t h e r , t h e larvae d isperse f r o m a r e g i o n o f h i g h c r o w d i n g t o a r e g i o n o f lower c r o w d i n g a n d t h e d i s p e r s a l p rocess is o n l y a s s u m e d t o be m o d e l l e d by t h e a n a l y t i c a l exp ress ion f o r m o l e c u l a r d i f f u s i o n . T h i s a s s u m p t i o n has b e e n f o u n d t o w o r k r e m a r k a b l y we l l f o r a w i d e r a n g e o f o r g a n i s m s f r o m p o l l e n g r a i n s t o insec ts t o m u s k r a t s ( O k u b o 1980) . T h e r e are t h r e e m o d e l s o f Kh, t h e s i m p l e s t ( t he F i c k i a n m o d e l ) assumes t h a t i t is c o n s t a n t , i.e. Kh = K. T h e J o s e p h - S e n d n e r m o d e l assumes t h a t Kh — Px, w h e r e P is a d i f f u s i o n v e l o c i t y , a n d t h e O z m i d o v m o d e l assumes t h a t Kh — \ ^ x^/3 w h e r e 7 is t h e " e n e r g y d i s s i p a t i o n p a r a m e t e r " ( O k u b o 1980) . B e f o r e s o l v i n g e q u a t i o n (1.14) we assume t h a t u = 0, t h a t t h e larvae were d i s t r i b u t e d u n i f o r m l y w i t h i n a v e r t i c a l l aye r o f c o n s t a n t t h i c k n e s s h, a n d t h a t C n u m b e r o f larvae h a t c h i n s t a n t a n e o u s l y f r o m a p o i n t sou rce a t x = 0. T h e s o l u t i o n s a re : (1 .15a) S ( * , s ) = S o exp(--^-M0, * = (1-156) • S{t,x) = Soexp(~-Mt), S o = ^ ^ ; (1 .15c) S(t,x)=S0exp(-^--Mt), S o = - J ^ ; f o r t h e F i c k i a n , J o s e p h - S e n d n e r , a n d O z m i d o v m o d e l s , r e s p e c t i v e l y . T h e s e s o l u t i o n s are based o n t h e a s s u m p t i o n o f r a d i a l l y s y m m e t r i c s p r e a d i n g f r o m a p o i n t source b u t t h i s is n o t t h e s i t u a t i o n i n t h e l o n g , n a r r o w c h a n n e l o f B a m f i e l d I n l e t . Howeve r , O k u b o (1980) has s h o w n t h a t t h e e q u a t i o n o f m o t i o n f o r a p o p u l a t i o n d i s p e r s i n g f r o m a r e f l e c t i n g b o u n d a r y is i d e n t i c a l 14 t o e q u a t i o n s (1 .15a) - (1 .15c ) e x c e p t t h a t So is d o u b l e d . T h e r e f o r e , I a s s u m e d t h a t t h e c a n o n i c a l f o r m s of e q u a t i o n s (1 .15a) - (1 .15c ) were s t i l l v a l i d f o r t h i s case. T h e b e s t s ing le d i f f u s i o n m o d e l was se lec ted by regress ing log,, ( c u m u l a t i v e dens i t i es ) o r l o g e ( c u m u l a t i v e n u m b e r s ) o n x2/t, x/t, a n d x2/3/t; t h e m o d e l w i t h t h e h i g h e s t c o r r e l a t i o n coef f i -c ients was chosen . Cases i n w h i c h t was less t h a n 1.0 d were o m i t t e d f r o m t h e regress ions because t h e y p r o d u c e d e n o r m o u s a n d o b v i o u s l y e r r o n e o u s values o f x 2 /t, x/t, a n d x 2 / 3 ft. M was e s t i m a t e d by s t a n d a r d c a t c h c u r v e ana lys i s ( R i c k e r 1975) as t h e s lope o f t h e regress ion o f l o ^ ( c u m u l a t i v e dens i t i es ) or l o g , ( c u m u l a t i v e m f i n b e r s ) o n age. I t was also e s t i m a t e d by first c o r r e c t i n g t h e dens i t i es o r n u m b e r s fo r d i f f u s i o n a n d t h e n reg ress ing t h e l o g e - t r a n s f o r m e d c u m u l a t i v e dens i t i es o r n u m b e r s o n age, e .g. f o r e q u a t i o n (1 .15a) t h e regress ion e q u a t i o n was l o g e S(t, x)+—= l o g , S0 - Mt. T h e a s s u m p t i o n o f i n s t a n t a n e o u s h a t c h was r e l a x e d i n o r d e r t o fit t h e m o d e l t o t h e d e n s i t y - a t - d a t e d a t a . T h e d e n s i t y o f t h e n e w l y - h a t c h e d day-classes was a s s u m e d t o fo l l ow a G a u s s i a n d i s t r i b u t i o n w i t h d a t e , ( 1 . 1 6 , ^ ^ [ - f c ^ l ] , w h e r e < o = t h e m e a n h a t c h age (d ) (to = T — t), a n d < r = t h e s t a n d a r d d e v i a t i o n o f to • S u b s t i t u t i n g e q u a t i o n (1.16) i n t o e q u a t i o n s (1 .15a) - (1 .15c ) a n d r e a r r a n g i n g gives t h e c o m p l e t e p o p u l a t i o n m o d e l s , M 7 . ) • S(r, f c,,) = ^ , x p [ - ! ^ - J ^ r 5 j - M ( r - M ] , ( 1 . 1 7 . ) SIT.t,.,) = ,xp - - ^ L - -*(!•- *)]. G 2 J T 0 15 io a n d c we re e s t i m a t e d f r o m h i s t o g r a m s o f log,, ( c u m u l a t i v e d e n s i t y ) o r l o g , ( c u m u l a t i v e n u m b e r s ) o n T - t . P a t c h i n e s s L l o y d ' s p a t c h i n e s s i n d e x ( L l o y d 1967; P i e l o u 1977) was c a l c u l a t e d as (1 .18) p = 1 + {var'S"1 - 1 J 5 " " 1 , w h e r e S = t h e m e a n l a r v a l d e n s i t y ( n u m b e r s 1 0 - 3 m ~ 3 ) o f a day 's p o o l e d s a m p l e s , a n d var is t h e v a r i a n c e o f S. T h i s p a t c h i n e s s i n d e x is a m e a s u r e o f h o w m a n y t i m e s m o r e c r o w d e d a n average i n d i v i d u a l is r e l a t i v e t o a n i n d i v i d u a l i n a p o p u l a t i o n w i t h t h e same m e a n dens i ty b u t r a n d o m l y d i s t r i b u t e d . A c o m p l e t e l y r a n d o m d i s t r i b u t i o n m e a n s t h a t t h e m e a n a n d t h e var iance are e q u a l a n d p = 1.0. Results and Discussion N u m b e r a n d O r i g i n o f C o h o r t s T h r e e c o h o r t s were f o u n d i n t h e 1981 catches ( F i g . 1.2). T h e first c o n s i s t e d o f a f e w larvae l o n g e r t h a n 16 m m f o u n d f r o m 3 1 M a r c h t o 8 A p r i l i n t h e n i g h t - l i g h t catches. T h e s e c o n d c o h o r t d o m i n a t e d t h e 1 9 8 1 c a t c h e s , i t was f o u n d i n a l l s a m p l e s f r o m B a m f i e l d I n l e t , a n d i n a l l s a m p l e s f r o m o u t s i d e t h e I n l e t b e g i n n i n g o n 3 A p r i l a t s t a t i o n D . T h e eggs were p r o b a b l y l a i d be low t h e low t i d e l i ne a t t h e h e a d o f t h e I n l e t . T h e t h i r d c o h o r t c o n s i s t e d o f p o s t - y o l k - s a c larvae w h i c h first a p p e a r e d i n t h e p l a n k t o n - n e t ca tches o f s t a t i o n B o n 30 A p r i l . I t m a y have h a t c h e d f r o m eggs l a i d s o m e w h e r e i n T r e v o r C h a n n e l close t o t h e m o u t h o f B a m f i e l d I n l e t o r i n G r a p p l e r I n l e t , a n d t h e n d i s p e r s e d in to t h e I n l e t . C o h o r t s f o u r , five, s ix , a n d seven were f o u n d i n t h e 1982 catches ( F i g . 1.3). C o h o r t f o u r c o n s i s t e d o n l y o f e a r l y s tage la rvae, a n d c o h o r t f ive c o n s i s t e d o f b o t h yo lk-sac a n d n o n - y o l k - s a c la rvae. T h e s i x t h c o h o r t was b y f a r t h e m o s t a b u n d a n t o f t h e seven c o h o r t s . I t h a t c h e d f r o m m a n y h u n d r e d s o f square m e t e r s o f s p a w n l a i d o n eelgrass b e d s a l o n g t h e shores a n d t h e b o t t o m o f t h e h e a d o f B a m f i e l d I n l e t o n 2 - 3 A p r i l . T h e n e w l y - h a t c h e d yo lk -sac la rvae first a p p e a r e d i n p l a n k t o n - n e t s a m p l e s f r o m s t a t i o n A o n 12 A p r i l . T h e s e v e n t h c o h o r t was r e p r e s e n t e d by t w o 9.0 m m l o n g yo lk -sac larvae c a u g h t 16 F i g u r e 1.2. L e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f h e r r i n g larvae c a p t u r e d i n t h e B a m f i e l d I n l e t — T r e v o r C h a n n e l a r e a i n 1981 w i t h p l a n k t o n - n e t s a n d a n i g h t - l i g h t . T h e c i r c l e d n u m b e r s i n d i c a t e t h e c o h o r t s a n d t h e b r o k e n l ines c o n n e c t t h e m e a n s t a n d a r d l e n g t h s o f t h e c o h o r t s . 17 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 3 20 20 > ON 20 LU ID 20 O LU 20 CC U_ 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 0 © III © 27 May 24 May 21 May 20 May 18 May 15 May 14 May 12 May 11 May 9 May 8 May 8 May 5 May 3 May 2 May 30 April 29 Aprl 27 Aprt 28 Apr! 24 April 22 Aprl 21 Apr) 20 Aprl 19 Aprl 18 Aprl 17 Apr* 18 Apr! 15 Aprl 14 Aprl 13 Aprl 12 Aprl 11 Apr! 10 Apr! 9 Apr! 8 Aprl 7 Aprl 6 April 5 Aprl 4 Aprl 3 Aprl 2 Aprl 1 Aprl 31 March 30 March 20 25 30 . 35 STANDARD LENGTH (MM) 40 18 F i g u r e 1.3. L e n g t h - f r e q u e n c y d i s t r i b u t i o n s o f h e r r i n g larvae c a p t u r e d i n t h e B a m f i e l d I n l e t - T r e v o r C h a n n e l a rea i n 1982 w i t h p l a n k t o n - n e t s a n d a n i g h t - l i g h t . T h e c i r c l e d n u m b e r s i n d i c a t e t h e c o h o r t s a n d t h e b r o k e n l ines c o n n e c t t h e m e a n s t a n d a r d l e n g t h s o f t h e c o h o r t s . 19 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 0 II ® — "-*> 20 May 16 May 12 May 11 May 8 May 7 May 6 May 4 May 3 May 29 April 27 Apri l 26 April 23 Apri l 20 April 19 Apri l 17 Apri l 16 April 14 April 12 April 8 April 5 April 2 April 29 March 27 March 25 March 23 March 21 March 19 March 17 March 15 March 13 March 10 15 20 25 30 S T A N D A R D L E N G T H (MM) 35 2 0 a t s t a t i o n B o n 7 M a y . T h e f o l l o w i n g ana lys is is c o n c e r n e d a l m o s t e n t i r e l y w i t h c o h o r t s t w o , t h r e e , five, a n d s ix . T h e catches o f c o h o r t s one , f o u r , a n d seven were t o o low t o a l low any ana lyses . H a t c h D a t e s T h e h a t c h i n g p e r i o d s o f c o h o r t s t w o , f o u r , five, a n d s ix l a s t e d 13.8 , 27 .3 , 23.0 a n d 11.2 d , respec-t i v e l y ( F i g . 1.4). T h i s does n o t i m p l y t h a t h a t c h i n g was evenly d i s t r i b u t e d over these p e r i o d s , m o s t la rvae h a t c h e d w i t h i n 2 - 4 d a t t h e m i d p o i n t o f t h e h a t c h i n g p e r i o d (see D i s t r i b u t i o n o f H a t c h D a t e s a n d F i g . 1.24). T h e 27.3 a n d 23.0 d p e r i o d s o f c o h o r t s f o u r a n d five were a l m o s t c e r t a i n l y a r t i f a c t s o f t h e s t a t i s t i c a l p r o c e d u r e used t o c a l c u l a t e t h e m e a n ha tch d a t e . T h e t r u e l e n g t h o f t h e h a t c h i n g p e r i o d s was p r o b a b l y less t h a n 14 d f o r a l l c o h o r t s . T h e m e a n h a t c h da tes were 26 M a r c h 1 9 8 1 , 14 M a r c h 1982, 25 M a r c h 1982, a n d 13 A p r i l 1982 f o r c o h o r t s t w o , f o u r , five, a n d s ix , r espec t i ve l y . T h e m e a n d a t e o f h a t c h f o r c o h o r t t h r e e was e s t i m a t e d t o have b e e n 23 A p r i l 1 9 8 1 by a s s u m i n g t h a t t h e average r a t e o f g r o w t h i n l e n g t h over t h e first 10 d was t h e same as t h a t o f c o h o r t t w o . T h e t i m e s b e t w e e n t h e m e a n h a t c h da tes were 28, 1 1 , a n d 19 d f o r c o h o r t s 2 - 3 , 4 - 5 , a n d 5 -6, r e s p e c t i v e l y . T h e m e a n s e p a r a t i o n i n t i m e was 19.3 ( S D = 8 . 5 ) d , w h i c h was close t o t h e m e a n s e p a r a t i o n t i m e o f 17.50 ( S D = 6 . 5 3 ) d fo r c o h o r t s o f A t l a n t i c h e r r i n g larvae ( L a m b e r t 1984) . However , t h e s e p a r a t i o n t i m e s d i d n o t f a l l o n t h e curve r e l a t i n g c o h o r t s e p a r a t i o n t i m e a n d t h e l i n e a r r a t e o f g r o w t h i n l e n g t h c a l c u l a t e d by L a m b e r t a n d W a r e (1984) fo r l a r va l A t l a n t i c h e r r i n g , capelin,Mallotus villosus, A t l a n t i c m a c k e r e l , Scomber scombrus, a n d w h i t e h a k e , Urophysis tenuis; t h e s e p a r a t i o n t i m e s c a l c u l a t e d f r o m t h e i r e q u a t i o n r a n g e d f r o m 6 .8 -8 .7 d w h i c h is 2 . 2 - 2 . 8 t i m e s less t h a n t h e q u a n t i t y o b s e r v e d i n t h i s s t u d y . L e n g t h w i t h D a t e G o m p e r t z g r o w t h f u n c t i o n s p r o v i d e d m a r g i n a l l y b e t t e r fits t o t h e l e n g t h - a t - d a t e d a t a t h a n t h e l i n e a r g r o w t h m o d e l ( F i g . 1.5). GL r a n g e d f r o m 0 . 3 5 6 - 0 . 4 1 4 m m d - 1 . T h e ra tes o f c o h o r t s t w o , t h r e e , a n d five were a b o u t 1 4 % h i g h e r , o n t h e average, t h a n t h e r a t e o f c o h o r t s ix . A l l f o u r g r o w t h r a t e s are t h e h i g h e s t r e c o r d e d f o r w i l d p o p u l a t i o n s o f Pac i f i c h e r r i n g larvae a n d t h e y are a m o n g t h e h i g h e s t r e c o r d e d f o r A t l a n t i c h e r r i n g larvae ( A p p e n d i x A , T a b l e A . 5 ) . T h e y are h i g h e r t h a n a l m o s t a l l g r o w t h 2 1 F i g u r e 1.4. L i n e a r p r e d i c t i v e regress ion o f a rcs in y/P on t i m e f o r c o h o r t s t w o , f o u r , five, a n d s ix , w h e r e P is t h e r a t i o o f yo l k -sac t o n o n - y o l k - s a c la rvae . T h e n u m b e r s are t o t a l s a m p l e sizes. 22 zz ARCSIN(P) 1/2 (DEGREES) o o o CO o ID O M ° ,, II ro o 0 ro 0) 03 i O 05 X x = ro - i l l ,| CO (5' o cn o? — • ro 3 Ol n co ro i CO 09 CO CO X o O I O 3J O - i -< O 2.' i M o 12 O fl) j 5 C D ? o " cn ro 33 ro cn I ro X cn O n -< O 2. " "I O ID O J j 3 ( 0 ° 0 ii cn ?° 5 5 CD _| o I 00 0) =! x F i g u r e 1.5. M e a n ( ± 1 S D ) s t a n d a r d l e n g t h o f c o h o r t s t w o , t h r e e , five, a n d s ix a n d t h e fitted l i n e a r a n d one-cyc le G o m p e r t z g r o w t h cu rves . SA0 a n d sa are t h e a s y m p t o t i c s t a n d a r d d e v i a t i o n s o f t h e G o m p e r t z p a r a m e t e r s AQ a n d a ; SGL is t h e a s y m p t o t i c s t a n d a r d d e v i a t i o n o f GL • 24 30 25 — L= 7.7e s. = 0.001 S o t = 0.001 -0.027T 0.046(1-e ) 5~oT7 20 15 o z LU I Q DC < Q 25 < r-20 1 if ft --- L= 7.7 - 0.390T s„ = 0.004 -0.048T /, 0.062(1-e ) / 0.048 L = 7.7e , S. = 0.002 ' / "o s„ = 0.003 15 10 / L= 7.7 - 0.414T s„ = 0.010 j I i i_ 0.024T -0.028T 0.043(1-e ) 0~0TB L= 7.7e s- = 0.003 "o s„ =0.008 20 40 60 0 20 DAYS FROM HATCH DATE 40 2 5 r a t e s r e p o r t e d f o r l a b o r a t o r y - r e a r e d p o p u l a t i o n s o f l a r v a l Paci f ic a n d A t l a n t i c h e r r i n g ( A p p e n d i x A , T a b l e A . 3 ) . O t o l i t h R i n g N u m b e r w i t h T i m e N i n e t y - f o u r o f t h e 96 1981 fish t h a t we re e x a m i n e d f o r o t o l i t h r i n g s b e l o n g e d t o c o h o r t t w o , a n d t w o b e l o n g e d t o c o h o r t one ( F i g . 1.6). T h e m e a n r i n g n u m b e r o f t h e 7 A p r i l c o h o r t t w o s a m p l e was 8.4 ( S D = 3 . 0 ) , i n d i c a t i n g t h a t r i n g s were d e p o s i t e d a t a d a i l y r a t e f o r a t leas t t h e first week a f t e r t h e e s t i m a t e d d a t e o f a b s o r p t i o n o f t h e yo lk -sac (31 M a r c h ) . T h e s lope o f t h e reg ress ion o f r i n g n u m b e r o n t i m e f r o m t h e m e a n h a t c h d a t e was 0.90 ( S E = 0 . 0 4 ) d _ 1 , w h i c h was s i g n i f i c a n t l y (P < 0 .01) less t h a n I d - 1 . T h e first t w o s a m p l e s o f 1982 a l c o h o l - p r e s e r v e d fish (26 A p r i l , 6 M a y ) were m i x t u r e s o f c o h o r t s five a n d s ix a n d t h e t h i r d s a m p l e (16 M a y ) was c o m p o s e d o n l y o f fish f r o m c o h o r t five. T w o m e a n s were i d e n t i f i e d i n t h e 26 A p r i l s a m p l e w i t h M c D o n a l d a n d P i t c h e r ' s (1979) f r e q u e n c y ana lys is p r o g r a m : 8.5 (SD==2 .8 , n = 6 8 ) r i n g s , a n d 19.7 ( S D = 3 . 2 , n = 2 4 ) r i n g s , p r e s u m a b l y c o r r e s p o n d i n g t o c o h o r t s s ix a n d five, r espec t i ve l y . T h e m e a n r i n g n u m b e r f o r c o h o r t s ix i n d i c a t e d t h a t r i n g s were d e p o s i t e d a t an average r a t e o f 1 d - 1 d u r i n g t h e 8 - 9 d a f t e r a b s o r p t i o n o f t h e y o l k . T h e s a m p l e c a p t u r e d o n 6 M a y was c l e a r l y a m i x t u r e o f c o h o r t s five a n d s ix because i t s p a n n e d a r a n g e o f 27 r i n g s , t o o la rge fo r a s ing le c o h o r t . T h e f r e q u e n c y ana lys i s p r o g r a m was n o t ab le t o i d e n t i f y t w o u n i q u e g r o u p s i n t h e s a m p l e so t h e m e a n r i n g n u m b e r f o r c o h o r t five was fixed a t t h e m o d e o f 32 r i n g s a n d t h e m e a n r i n g n u m b e r f o r c o h o r t s ix was t h e n c a l c u l a t e d as 19.3 ( S D = 4 . 3 , n = 6 5 ) r i n g s . T h i s i n d i c a t e s a r i n g d e p o s i t i o n r a t e o f 1.09 d _ 1 a n d a m e a n h a t c h i n g d a t e o f 12 A p r i l , w h i c h agrees w i t h t h e d a t e c a l c u l a t e d f r o m y o l k - s a c a b u n d a n c e . T h e s lope o f t h e regress ion o f m e a n r i n g n u m b e r o n t i m e f o r c o h o r t f o u r was 1.26 ( S E = 0 . 0 1 ) d - 1 ' , w h i c h was s i g n i f i c a n t l y g r e a t e r (P < 0 .001) t h a n 1 d _ 1 . T h e f a c t s t h a t t w o o f t h e t h r e e e s t i m a t e d r a t e s o f r i n g d e p o s i t i o n were e q u a l t o o r g r e a t e r t h a n 1 d _ 1 , a n d t h a t t h e l i n e a r r a t e s o f g r o w t h i n l e n g t h were e q u a l t o o r g r e a t e r t h a n 0.36 m m d - 1 , t h e r a t e a t w h i c h r i n g d e p o s i t i o n was d e t e r m i n e d t o be d a i l y i n l a b o r a t o r y r e a r i n g e x p e r i m e n t s (Gef fen 1982; T h i s s t u d y : A p p e n d i x B ) , s u p p o r t t h e a s s u m p t i o n t h a t o t o l i t h r i n g d e p o s i t i o n i n w i l d l a n a e was d a i l y . 26 F i g u r e 1.6. T h e f r e q u e n c y d i s t r i b u t i o n s o f o t o l i t h r i n g n u m b e r s w i t h d a t e o f c a p t u r e fo r larvae o f c o h o r t s one (c i r c led n u m b e r s ) , t w o , five, a n d s ix . T h e h o r i z o n t a l b a r s m a r k t h e m e a n r i n g n u m b e r a n d t h e boxes m a r k t h e s t a n d a r d d e v i a t i o n o f t h e m e a n f o r each s a m p l e . T h e so l id l ines are t h e regress ions o f r i n g n u m b e r o n t i m e s ince t h e m e a n h a t c h da tes f o r c o h o r t s t w o a n d five. T h e b r o k e n l i ne is t h e average r a t e o f r i n g d e p o s i t i o n fo r c o h o r t s ix . 27 50 40 DC 30 LU c o ZD Z o z b: 20 10 0 1981: COHORT 2 Y=-2.79+0.90X s b=0.04 r = 0.92 n = 94 30 MARCH 10 20 APRIL 30 10 MAY 20 1982: COHORT 5 Y= -20.61 +1.26X s b=0.01 r = 0.99 n=63 COHORT 6 ring rate = 1.09 day 20 30 MARCH 10 20 APRIL 30 10 20 MAY 30 L e n g t h w i t h O t o l i t h A g e A l l o t o l i t h - a g e d la rvae were p o o l e d i n o r d e r t o c a l c u l a t e a s ing le G o m p e r t z l e n g t h - a t - o t o l i t h - a g e c u r v e because t h e r e a p p e a r e d b y o b s e r v a t i o n t o b e n o d i f fe rence b e t w e e n c o h o r t s i n t h e i r t r e n d s o f l e n g t h w i t h age a n d because o n l y by p o o l i n g c o u l d t h e l e n g t h range be e x t e n d e d t o a m a x i m u m o f 27.5 m m ( F i g . 1.7). T h e e s t i m a t e d va lue o f A0, 0.047 ( S D = 0 . 0 0 1 ) d _ 1 , f e l l w i t h i n one s t a n d a r d d e v i a t i o n o f J4Q e s t i m a t e d f r o m t h e l e n g t h - a t - d a t e curves o f c o h o r t s t w o , t h r e e , a n d s ix . T h e e s t i m a t e d value o f a , 0 .031 ( S D = 0 . 0 0 1 ) d - 1 , was s l i g h t l y h i g h e r t h a n those e s t i m a t e d f o r t h e l e n g t h - a t - d a t e curves o f c o h o r t s t w o , t h r e e , a n d s ix b u t lower t h a n t h a t o f c o h o r t five. T h e r e l a t i v e l y h i g h a va lue m e a n s t h a t t h i s p o o l e d l e n g t h - a g e curve c a n n o t b e used t o c a l c u l a t e a c c u r a t e ages f o r fish l a r g e r t h a n a b o u t 29 m m , t h e r e a r r a n g e d G o m p e r t z e q u a t i o n p r e d i c t s a n age o f 213 d fo r a fish 35 m m l o n g , wh ich is u n r e a s o n a b l e . T h e l e n g t h - o t o l i t h - a g e curve ver i f ies t h e l e n g t h - a t - d a t e curves. T h e i n c l u s i o n o f la rge n i g h t - l i g h t e d s p e c i m e n s m a k e s t h e l e n g t h - a t - d a t e curves m o r e re l i ab le as a g i n g t o o l s t h a n t h e p o o l e d l e n g t h - o t o l i t h - a g e c u r v e . T h e r e f o r e , age was ass igned w i t h t h e l e n g t h - a t - d a t e curves o f each c o h o r t . G r o w t h D i f f u s i o n T h e s t a n d a r d d e v i a t i o n s o f t h e m e a n l e n g t h s - a , t - d a t e o f c o h o r t s t w o / t h r e e , f o u r / f i v e , a n d s ix i n c r e a s e d r a p i d l y f r o m h a t c h t o a n a s y m p t o t e by t h e fifteenth day a f t e r t h e m e a n h a t c h da tes ( c o h o r t s t w o a n d t h r e e , a n d f o u r a n d five, were p o o l e d because c o h o r t s t h r e e a n d f o u r h a d i nsu f f i c i en t d a t a t o fit s e p a r a t e c u r v e s ) ( F i g . 1.8). T h e e s t i m a t e d h a t c h i n g p e r i o d s o f c o h o r t t w o , five, a n d s ix e n d e d 6.9 ( = 1 3 . 8 / 2 ) , 11.5 ( = 2 3 . 0 / 2 ) , a n d 5.6 ( = 1 1 . 2 / 2 ) d , r e s p e c t i v e l y , a f t e r t h e i r m e a n ha tch d a t e s . T h e d u r a t i o n o f t h e h a t c h i n g p e r i o d o f c o h o r t t h r e e was u n k n o w n b u t i t was a s s u m e d t o have b e e n s i m i l a r t o t h a t o f c o h o r t t w o , i.e. 14 d . For t h e sake o f s i m p l i c i t y I a s s u m e d t h a t t h e h a t c h i n g p e r i o d s o f c o h o r t s t w o / t h r e e , f o u r / f i v e , a n d s ix e n d e d 5.5 d a f t e r t h e i r m e a n h a t c h i n g d a t e s . T h e l e n g t h d i s t r i b u t i o n s o f t h e s a m p l e s c a p t u r e d a f t e r t h i s age were c o m p r e s s e d i n o r d e r t o c o r r e c t f o r g r o w t h d i f f u s i o n . W e i g h t - A g e R e l a t i o n s h i p s T h e t w o - c y c l e G o m p e r t z w e i g h t cu rves p r o v i d e d m a r g i n a l l y b e t t e r fits t o t h e w e i g h t - a t - a g e d a t a (age e s t i m a t e d f r o m l e n g t h ) t h a n t h e one-cyc le curves ( F i g . 1.9). B o t h one - a n d t w o - c y c l e curves gave 29 F i g u r e 1.7. P l o t o f s t a n d a r d l e n g t h on o t o l i t h - a g e f o r larvae o f c o h o r t s one , t w o , five a n d s ix . T h e so l i d l i ne is t h e fitted G o m p e r t z g r o w t h c u r v e . 30 30 COHORT • 1 i i i i i 1 1— 0 20 40 60 A G E ( D A Y S ) 31 F i g u r e 1.8. P l o t o f t h e s t a n d a r d d e v i a t i o n s o f t h e m e a n l e n g t h s a g a i n s t t i m e s ince t h e m e a n hatch d a t e f o r c o h o r t s t w o / t h r e e , f o u r / f i v e , a n d s ix. T h e curves are t h e fitted G o m p e r t z m o d e l s . 32 F i g u r e 1.9. M e a n ( ± 1 S D ) d r y w e i g h t - a t - a g e o f c o h o r t s t w o , t h r e e , five a n d s ix a n d t h e fitted l i n e a r m o d e l s a n d t w o - c y c l e G o m p e r t z m o d e l s . 34 50.0 [ 10.0 5.0 1.0 0.5 o °-1 • 50.0 > CC Q 10.0 5.0 , w „ -10.388MIN( t ,6.6K 1.141(1-e ) 10.388 — W=0.16e / » ' / - o . o o 7 M A X ( t -6.6 , o ) 0.114(1-6 ) 0.007 — W = 0.16e - W = 0.16e 0.083t 1.0 0.5 -0.002MIN(t,4.7) 0 .314(1-e ) 0.002 - W - 0 . 1 6 e -0 .016MAX0-4 .7 ) , 0 .127(1-e ) / + 0.016 . / 1 0.1 -19.711MIN(t,8.7> 3 .912(1-e ) rem -0.001MAX(t-8.7,0) 0.011(1-e ) "0 .001 0.074t — W = 0.16e -21.516MIN(t,5.3) 0 .002(1-e ) "21.516 . - 0 . 0 0 0 0 4 M A X ( t - 5 . 3 ) x . DJ2Q2QQ(1-e ) 0.00004 20 40 60 0 20 AGE (DAYS) 35 much better fits than the exponential model. The estimated times of the start of the second growth cycle ranged from 4.7-8.7 d, which compares well with the 4-6 d period of complete yolk absorption recorded for Pacific herring larvae reared at 6-10° C (Appendix A). Gw ranged from 0.063-0.084 d _ 1 with cohorts two, three, and five having rates 18-32% higher than the rate for cohort six. Weight-Length Relationships The log-log plots of dry weight on standard length were curvilinear for all cohorts (Fig. 1.10). This was not an artifact of correcting body dimensions for net capture because the uncorrected dimensions were also non-linear. The slopes of the linear allometric model ranged from 2.81 (SE=0.04) to 3.93 (SE=0.03), and the slope for the pooled data set was 3.59 (SE=0.02,r=0.97,n=1799). Condition Factors The plots of the mean (± 1 SD) catch-p er-unit- weigh ted CF-at-age and CVl-at-age indicate only one major difference between the cohorts in their time trajectory through the nutritional classes (Figs. 1.11 and 1.12): the ages of some larvae in cohorts two, five, and six were underestimated because they were starving and had low individual rates of growth in length. Some non-yolk-sac larvae were assigned ages as low as 0 d indicating that the degree of underestimation was as large as 4-5 d. The CF-at-age trajectory entered the reversibly starving class by day 5-6 and exited by day 28-32 after grazing the line of irreversible starvation. The CVl-at-age trajectory (non-yolk-sac larvae) entered the fed category about 8-12 d after hatch or 3-7 d after the estimated age of complete absorption of the yolk. Larvae longer than about 20 mm begin to undergo changes in body shape, such as a decrease in the ED/HD ratio, that are unrelated to physical condition but are related instead to metamorphosis to the juvenile body form (Appendix C). This meant that the CV1 value of larvae longer than 20 mm actually increased with time. Therefore, CV1 is only suitable for larvae less than 20 mm long or younger than 30 d. Plankton-net and night-light catches exhibited similar trajectories of mean CF- and CVl-at-age. The 0-28 d old night-light catches of cohort two had average mean CF values that were generally higher than those caught with the plankton-net but this may have been the result of the low sample sizes of these night-light catches. 36 F i g u r e 1.10. W e i g h t - l e n g t h curves f o r c o h o r t s t w o , t h r e e , five, a n d s ix . E v e r y f o u r t h case was p l o t t e d . 37 CO 50.0 h 10.0 5.0 1.0 0.5 g 0.1 r -X g LU & 1 0 0 Q 5.0 - 5 3.934 --- W= 2.07x10 L sa= 0.033 r = 0.98 n = 752 • 0.056 " — log eW = 65.71-65.88(3.76-log e L) —I 1 1 1 1 1 ' 1 • I I ' I 1 ' ' • ' — - W = 9 . 2 1 x 1 0 ~ 5 L 3 ' 2 9 4 s a j = 0.081 r = 0.97 n=90 0.066 log e W = 43.09-44.21 (3.50-log e L) i 1 i i i i i i — i i J 1.0 0.5 0.1 -- 5 3.382 — W = 8.76x10 L s a =0.036 r=0.97 n=441 0.029 log e W=93.09-94.04(3.54-log e L) - J 1 — i — i — i — i — i i i i i • • i • i i 11 • 10 20 30 log e W = 37.41 -39.12(3.25- log e L) I I I I 1—1 I 1—1—1 1 L 0.050 10 20 STANDARD LENGTH (MM) F i g u r e 1.11. P l o t s o f m e a n ( ± 1 S D ) C F - a t - a g e f o r c o h o r t s t w o , t h r e e , five, a n d s ix ( C F is F u l t o n ' s c o n d i t i o n f a c t o r ) . T h e b r o k e n l ines s e p a r a t e n u t r i t i o n a l classes. 39 PLANKTON-NET CATCHES • .1 f t NIGHT-LIGHT CATCHES V/ 1 4 •-.(••),•- •~..,tl , t '" ' -t 40 0 20 AGE (DAYS) 40 6 0 40 F i g u r e 1.12. P l o t s o f m e a n ( ± 1 S D ) C V l - a t - a g e fo r c o h o r t s t w o , t h r e e , five, a n d s ix ( C V l is a m u l t i v a r i a t e c o n d i t i o n f a c t o r ) . T h e b r o k e n l i ne separa tes s t a r v i n g f r o m fed larvae. 4 1 NIGHT-LIGHT CATCHES • 2 t S T A R V E D S T A R V E D > O 2 't'h - 2 _1 1 L -2 0 F E D S T A R V E D m t F E D _ I I 1 L -S T A R V E D •f F E D S T A R V E D In U ; Jr F E D _ i 1— S T A R V E D F E D _ i i 1 -4 0 6 0 0 2 0 AGE (DAYS) 4 0 6 0 42 According to the CF data the highest percents of starving (CF < 2.42) plankton-net caught larvae less than 20 mm long were found in cohorts-three and two (92.5 and 90.7%) followed by cohorts six and five (76.1 and 44.7%) (Table 1.2). This ranking was reversed according to the CV1 data: the highest percent starving (CV1 > 0) was found in cohort six (90.0%), followed by cohorts three, two, and five (48.6, 28.7, and 4.9%). The CF data of the night-light catches ranked cohorts six and five as containing the highest percent starving, 97.6 and 78.0%, respectively, compared to 44.6% for cohort two. The CV1 data of the night-light catches gave a similar ranking: 35.0% starving for cohort six followed by 3.6% for cohort two. It is apparent that CF and CV1 measure different aspects of condition. Few larvae longer than 14 mm were classified as starving according to their CV1 values but a significant proportion of the larvae classified as starving according to their CF values are 15-20 mm long (Figs. 1.13 and 1.14). Only when the majority of the starving larvae are grouped in the 9-11 mm length range, as they are in cohort six, are the two condition factors in agreement. The majority of the larvae classified as starving with CF or CV1 were captured in Bamfield Inlet, particularly at station A near the spawning beds (Table 1.3). Some starving cohort three and five larvae were captured at stations outside the Inlet. Catch Curves at Date Ninety-four of the 117 tows were done after civil twiilight and the other 23 tows were performed during daylight hours (Figs. 1.15 and 1.16). Two of the cohort six plankton-net catches were taken before the date of mean hatch. Catch Curves with Station The catch curves at station show that only cohorts two and six were sampled over the entire period of early development (Figs. 1.17 and 1.21). The larvae of cohort three were not sampled beyond about age 25 and the larvae of cohort five were not well sampled until about age 20. The pattern of recruitment to the stations supports the conclusion that cohorts two and six hatched in upper Bamfield Inlet and dispersed down the Inlet to Trevor Channel. The pattern for cohort three 43 T A B L E 1.2. P e r c e n t o f n o n - y o l k - s a c l a rvae 7-20 m m l o n g i n n u t r i t i o n a l classes d e n n e d b y C F a n d C V 1 . C o h o r t I r r e v e r s i b l y R e v e r s i b l y T o t a l S t a r v e d s t a r v e d s t a r v e d s t a r v e d C F : P l a n k t o n - n e t C V 1 : P l a n k t o n - n e t 2 28.6 62 .1 90.7 28.7 3 22.7 70.0 92.5 48.6 5 2.3 42.4 44.7 4.9 6 2.0 74 .1 76 .1 90.0 C F : N i g h t - l i g h t C V 1 : N i g h t - l i g h t 2 0.0 44.6 44.6 3.6 3 - - - -5 7.4 70.6 78.0 0.0 6 24.5 73.0 97.6 35.0 44 F i g u r e 1.13. P e r c e n t o f t o t a l s t a r v i n g larvae < 20 m m l o n g c a p t u r e d w i t h a p l a n k t o n - n e t p l o t t e d a g a i n s t l e n g t h f o r c o h o r t s t w o , t h r e e , five, a n d s ix . 45 P L A N K T O N - N E T C A T C H E S • C V 1 > 0 10 15 20 STANDARD LENGTH (MM) 4 6 F i g u r e 1.14. P e r c e n t o f t o t a l s t a r v i n g larvae c a p t u r e d w i t h a n i g h t - l i g h t < 20 m m l o n g p l o t t e d a g a i n s t l e n g t h fo r c o h o r t s t w o , t h r e e , five, a n d s ix . 47 NIGHT-LIGHT C A T C H E S 30 CD z O 20 ^ 10 o CM I (D Z 20 > DC < h-CO 1 0 < o 0 LL. O ^ 20 Z 111 o DC £ 10 i • C F < 1 . 6 8 • 1.68£CF<2.42 C V 1 > 0 uJ J U L dili lullkl J 10 15 20 10 15 STANDARD LENGTH (MM) 20 48 T A B L E 1.3. P e r c e n t o f t o t a l s t a r v i n g n o n - y o l k - s a c larvae 20 m m l o n g c a p t u r e d w i t h a p l a n k t o n - n e t a t s t a t i o n . X 2 C o h o r t 3 5 6 ( k m ) C F C V 1 C F C V 1 C F C V 1 C F C V 1 0.9 71 .1 91.0 18.1 18.6 36.5 3.7 96.8 98.6 2.8 2 0 . 1 8.0 64.2 79.8 51.2 84.5 2.3 1.1 4.2 5.8 0.8 - - - - - -4.5 0.1 0.2 - - 0.1 0.5 - -6.0 2.7 - - - 4 .1 5.7 0 .1 -6.9 0.3 - - - 1.7 - 0.5 0.2 7.7 - - 8.5 1.6 6.1 5.6 0.2 -10.1 - - - - - - - -12.8 - - 9.3 - - - - -49 F i g u r e 1.15. P l a n k t o n - n e t catches ( n u m b e r 10 3 m 3 ) a t d a t e (days f r o m m e a n h a t c h d a t e ) a n d s t a t i o n f o r c o h o r t s t w o , t h r e e , five, a n d s ix . T h e curves are t h e c o m p l e t e p o p u l a t i o n m o d e l s ( e q u a t i o n (1 .17a) ) . 50 F i g u r e 1.16. N i g h t - l i g h t catches ( n u m b e r s ) a t d a t e (days f r o m m e a n h a t c h d a t e ) f o r c o h o r t s t w o , five, a n d s ix. T h e curves are t h e c o m p l e t e p o p u l a t i o n m o d e l ( e q u a t i o n ( 1 . 1 7 a ) ) . 52 53 Figure 1.17. Age frequencies of plankton-net catches of cohorts two, three, five, and six, separated by station. The solid horizontal bars indicate the range of ages at which the larvae were completely recruited to each station. 54 55 suggests t h a t i t m a y have d r i f t e d i n t o t h e I n l e t f r o m a h a t c h i n g s i te i n T r e v o r C h a n n e l . T h e p a t t e r n f o r c o h o r t five is a m b i g u o u s ; i f i t h a t c h e d i n B a m f i e l d I n l e t t h e u n d e r r e p r e s e n t a t i o n o f t h e e a r l y s tages c a n b e e x p l a i n e d i f t h e larvae d i d n o t d isperse c o n t i n u o u s l y f r o m t h e I n l e t b u t t e n d e d t o r e m a i n s t a t i o n a r y a t o r close t o s t a t i o n s B a n d D . D i f f u s i o n R a t e s F i v e o f t h e seven regress ions o f l o g e ( c u m u l a t i v e d e n s i t y o r n u m b e r ) o n x2ft, x/t, a n d x 2 / 3 / * , w i t h t h e h i g h e s t c o r r e l a t i o n coef f i c ien ts , were regress ions o f d e n s i t y o n x 2 /t ( r = 0 . 5 6 - 0 . 9 7 ) . O n l y one d a t a set , c o h o r t t w o n i g h t - l i g h t , was bes t fit w i t h an O z m i d o v m o d e l . T h e reg ress ion f o r c o h o r t five n i g h t - l i g h t was n o t s i g n i f i c a n t . T h e r e f o r e , t h e F i c k i a n m o d e l was a d o p t e d f o r t h e p o p u l a t i o n ana lys i s . T h e K va lues o f t h e p l a n k t o n - n e t ca tches were s i m i l a r t o t hose o f t h e n i g h t - l i g h t catches f o r each c o h o r t (F igs . 1.18 a n d 1.19). C o h o r t s t w o a n d five h a d K values t h a t were w i t h i n one s t a n d a r d e r r o r o f each o t h e r w h i l e c o h o r t s ix h a d a K va lue a b o u t f o u r t i m e s h i g h e r , i n d i c a t i n g a m u c h m o r e r a p i d r a t e o f d i s p e r s a l . C o h o r t t h r e e h a d a n even h i g h e r K va lue t h a n t h a t o f c o h o r t s ix . However , t h e r e is s o m e q u e s t i o n as t o t h e v a l i d i t y o f t h i s e s t i m a t e because o f u n c e r t a i n t y a b o u t t h e l o c a t i o n o f t h e ha tch s i t e . T h e ages o f r e c r u i t m e n t t o s t a t i o n s A a n d B ( F i g . 1.17) i n d i c a t e d a poss ib le r a t e o f d i s p e r s a l o f c o h o r t t h r e e i n t o t h e I n l e t o f a b o u t 0.3 k m d - 1 . E x t r a p o l a t i n g t h i s r a t e back t o age, zero m e a n s t h a t t h e la rvae h a t c h e d a b o u t 4.9 k m f r o m s t a t i o n A . A d j u s t i n g t h e s a m p l i n g s t a t i o n s x values a n d r e c a l c u l a t i n g t h e d i s t r i b u t i o n o f d e n s i t y w i t h x 2 /t gives a K va lue o f 0.306 ( S E = 0 . 0 8 9 ; r = 0 . 7 2 ) , w h i c h is i n t e r m e d i a t e b e t w e e n those o f c o h o r t s t w o / f i v e a n d s ix a n d is , t h e r e f o r e , m o r e r e a s o n a b l e . T h e ages o f s t a r v i n g la rvae were u n d e r e s t i m a t e d because t h e i r g r o w t h r a t e s were low. To c o r r e c t f o r t h i s t h e regress ion ana lys i s was r e p e a t e d u s i n g o n l y f e d larvae, t h o s e w h o s e C V 1 values were less t h a n zero (F igs . 1.18 a n d 1.19). T h e e s t i m a t e d K values fo r t h e p l a n k t o n - n e t catches o f c o h o r t s t w o a n d five were u n c h a n g e d b u t t hose f o r c o h o r t s t h r e e a n d s ix changed g r e a t l y . T h e regress ion o f t h e d e n s i t y o f f e d la rvae o n x 2/t f o r c o h o r t t h r e e b e c a m e n o n - s i g n i f i c a n t . T h e s lope o f t h e regress ion f o r c o h o r t s ix n e a r l y d o u b l e d , t h e r e b y h a l v i n g t h e e s t i m a t e d K va lue . D e s p i t e t h i s decrease t h e K \ a l u e w a s s t i l l a t least t w i c e as la rge as those fo r c o h o r t s t w o a n d five. 56 F i g u r e 1.18. Regress ions o f l o g e ( c u m u l a t i v e d e n s i t y ) o n x2/t fo r p l a n k t o n - n e t catches o f c o h o r t s t w o , t h r e e , five, a n d s ix. x is t h e d i s t a n c e f r o m t h e h a t c h s i te t o t h e s a m p l i n g s i t e . 57 CV1<0 PLANKTON-NET log„S =5.863-1-688x2/t S E B = 0.207 r =0.88 K = 0.148 SEK=0.018 P< 0.001 10 15 0 x 2 / t ( K M ^ A Y - 1 ) 10 58 F i g u r e 1.19. Regress ions o f l o g e ( c u m u l a t i v e n u m b e r s ) o n x?/t f o r n i g h t - l i g h t catches o f c o h o r t s t w o , five, a n d s ix . x is t h e d i s t a n c e f r o m t h e h a t c h s i te t o t h e s a m p l i n g s i t e . 59 10" ALL NIGHT-LIGHT 10" • l o g e S = 6 . 4 8 5 - 2 . 2 9 8 x 2 / t S E b = 0.482 vn C V K O NIGHT-LIGHT 2 log e S = 9 . 9 0 5 - 6 . 2 7 1x 2 /t S E b =2 .346 r = 0 . 8 8 K = 0 . 0 4 0 P < 0 . 0 0 1 10' DC 111 £ i o 2 l o g e S = 6 . 8 2 3 - 1 . 0 6 3 x 2 / t S E b = 5.928 r =0.13 K =0.235 P >0.05 10' 6 l o g e S = 3 . 9 7 6 - 0 . 3 7 5 x 2 / t S E b =0.145 r =0.56 K =0.667 S E K =0.258 ,_, P < 0 . 0 0 1 l o g e S = 3 . 8 5 2 - 0 . 3 5 0 x 2 / t S E b = 0 . 1 3 8 8 0 x 2/t (KM 2DAY" 1) T h e c o r r e c t e d K va lue f o r t h e n i g h t - l i g h t ca tches o f c o h o r t t w o f e l l b y a s i g n i f i c a n t 5 0 % a n d t h e va lue f o r t h e n i g h t - l i g h t ca tches o f c o h o r t s ix i nc reased by a n o n - s i g n i f i c a n t 8 % . T h e n i g h t - l i g h t catches o f c o h o r t five were n o t a d j u s t e d because t h e y c o n t a i n e d n o s t a r v i n g la rvae. T h e s e K va lues are close t o t h e va lues o f a p p a r e n t d i f f u s i v i t y m e a s u r e d f r o m i n s t a n t a n e o u s dye-release e x p e r i m e n t s i n t h e u p p e r m i x e d layer o f t h e sea. T h e K values m e a s u r e d i n t h i s s tudy , w h e n c o r r e c t e d t o u n i t s o f c m 2 s _ 1 a n d p l o t t e d a g a i n s t t h e scale o f d i f f u s i o n ( 1 - 1 0 k m ) , f a l l en t i re l y w i t h i n t h e enve lope o f d a t a s u m m a r i z e d by O k u b o (1971) . P a t c h i n e s s L l o y d ' s p a t c h i n e s s i n d e x , p, decreased w i t h age i n c o h o r t t w o f r o m a va lue a t h a t c h o f 3.8 t o a va lue o f 1.0 a t a b o u t d a y 25 a n d b e g a n t o r ise aga in w i t h i n c r e a s i n g age ( F i g . 1.20). M a r l i a v e (1980) r e p o r t e d t h a t Pac i f i c h e r r i n g b e g i n t o s c h o o l a t t h e age o f 16 d a n d e x h i b i t c o m p l e t e l y d e w l o p ed s c h o o l i n g b e h a v i o u r b y d a y 25. P r e s u m a b l y , t h e r ise i n p a t c h i n e s s a f t e r day 25 was t h e r e s u l t o f t h e a g g r e g a t i o n o f t h e larvae i n t o schoo ls . A p a t t e r n o f d e c r e a s i n g pa tch iness w i t h age ( 0 - 2 7 d ) was also o b s e r v e d i n c o h o r t s t h r e e a n d s ix b u t n o obv ious p a t t e r n was seen f o r c o h o r t five. T h i s was p r o b a b l y d u e t o t h e l a c k o f y o u n g c o h o r t five la rvae c a p t u r e d i n t h e s a m p l e s . T h e regress ions o f p o n age ( < 27 d ) f o r c o h o r t s t w o a n d s ix were i n d i s t i n g u i s h a b l e f r o m each o t h e r , t h e i r s lopes were n o t s i g n i f i c a n t l y d i f f e r e n t ( t - t e s t , P < 0 .01) . H e n r i e t a l . (1985) r e p o r t e d a s i m i l a r r a n g e o f p f o r l a rva l A t l a n t i c h e r r i n g o f t h e S t . L a w r e n c e r i v e r e s t u a r y : 1 .63-3 .52 . T h e y also f o u n d t h a t p decreased w i t h i n c r e a s i n g size a n d age o f t h e la r \ae a n d t h a t i t i n c r e a s e d w i t h i n c r e a s i n g a m p l i t u d e o f t h e t i d e s . A s i m i l a r U - s h a p e d p a t t e r n o f p a t c h i n e s s w i t h age was r e p o r t e d b y H e w i t t (1981) f o r l a r v a l n o r t h e r n a n c h o v y a n d j a c k m a c k e r e l , Trachurus symmetricus, o f t h e s o u t h e r n C a l i f o r n i a B i g h t b u t t h e ages a t m a x i m u m d i s p e r s i o n ( = m i n i m u m pa tch iness ) were m u c h less: 17 a n d 9 d , r e s p e c t i v e l y . A l s o , t h e m i n i m u m p f o r n o r t h e r n a n c h o v y never f e l l b e l o w 6.0 a n d t h a t f o r j a c k m a c k e r e l never f e l l b e l o w 4 .0 . E v e n a t m a x i m u m d i s p e r s i o n these t w o species were never r a n d o m l y d i s t r i b u t e d . Pac i f i c h e r r i n g , i n c o n t r a s t , r eached c o m p l e t e r a n d o m d i s p e r s i o n b y age 2 5 - 3 0 d . 6 1 F i g u r e 1.20. P l o t s o f L l o y d ' s p a t c h i n e s s i n d e x , p, o n days f r o m h a t c h d a t e f o r c o h o r t s t w o , t h r e e , five, a n d s ix . T h e regress ions used o n l y d a t a f o r larvae less t h a n 28 days o l d . 62 cn CO P = 3.77-0.11T r = 0.65 S E b = 0.03 P<0.01 CO CO LU O CL P =2.30 SD =0.90 L3 P =2.09 SD =0.82 P =3.98-0.10T r = 0.81 S E b = 0.02 P<0.01 0 20 40 0 20 40 DAYS FROM HATCH DATE Mortality Rates The right-hand limbs of the catch curves decreased at a roughly constant rate for all cohorts and gears except for the plankton-net catches of cohort five (Figs. 1.21 and 1.22). The variation from the trend line in the right-hand limbs was mainly caused by the stacking up of larvae at the mean ages at dates of sampling. This is particularly obvious in the night-light catches of cohort two. Therefore, there is no evidence of a sharp change in the slope of the catch curve that would be expected if catastrophic starvation was a significant source of mortality. May (1974) reached the same conclusion after reviewing the catch curves of the larvae of several species of fish. The effects of correcting the densities and numbers for diffusion varied between cohorts and gears but, on the whole, it tended to elevate the M values (the K values used for correcting the densities were those estimated from the fed larvae). Diffusion-correction of the cohort two catches raised the plankton-net M value by about 24% and the night-light value by about 29%. Both were significantly higher than their uncorrected counterparts.- The corrected M values calculated from the two gears were not significantly different from each other. The cohort three plankton-net catches were not corrected for diffusion because there was no trustworthy estimate of K. The M value of the uncorrected catch curve is the most accurate value available. Correcting the plankton-net catches of cohort five for diffusion elevated the regression of density on age to significance and produced a much higher M value. It is the most accurate one for this cohort because M is usually equal to, if not greater than, the exponential rate of growth in weight in the first year of life (Ricker 1975). The night-light catches of cohort five were not corrected for diffusion because the regression of density on x2/t was not significant. Correcting the plankton-net and night-light catches of cohort six increased the M value of the former by an insignificant 2% and the M value of the latter by a significant 37%. The mortality rates calculated from the 1982 night-light catches were probably seriously biased by active avoidance of the gear. The evidence for this is: (1) there was a complete absence of large cohort six larvae that should have been attracted to the light. All of the night-lighted cohort six fish were 64 Figure 1.21. Regressions of loge (cumulative density) on age for plankton-net catches of cohorts two, three, five, and six. The broken lines indicate the data used in the regressions. 65 P L A N K T O N - N E T C A T C H E S UNCORRECTED 2 log e S= 6.094-0.074t r=0.89 SE M =0.006 P<0.001 DIFFUSION C O R R E C T E D , 2 l og e S= 7.233 -0.092t r=0.86 SE M =0.008 P<0.001 3 log e S=1.560-0.094t r=0.59 SE M =0.029 P<0.005 5 log e S= 1.986-0.020t r=0.13 SE M =0.023 P>0.05 log eS = 10.006-0.298t r=0.97 SE M =0.012 P<0.001 5 log e S=4.600-0.064t 20 r=0.40 SE M =0.022 P<0.005 6 log B S = 11.217-0.305t r=0.96 SE M =0.015 P<0.001 40 60 0 A G E ( D A Y S ) 20 40 60 F i g u r e 1.22. Regress ions o f l o g e ( c u m u l a t i v e n u m b e r ) o n age f o r n i g h t - l i g h t catches o f c o h o r t s t w o , five, a n d s ix . T h e b r o k e n l ines i n d i c a t e t h e d a t a used i n t h e regress ions. T h e s o l i d h o r i z o n t a l l ines i n d i c a t e t h e age r a n g e o f c o m p l e t e r e c r u i t m e n t t o t h e n i g h t - l i g h t . 67 co 10" •10" rr 10 4 in co I 10 2 1 NIGHT-LIGHT CATCHES UNCORRECTED log eN = 8.569-0.068t r=0.61 SEM=0.015 P<0.001 5 logeN=9.133-0.158t r=0.77 SEM=0.026 P<0.001 JL 1 0 | 6 !ogeN = 4.525-0.0115t r=0.89 i o r r - ; P<0.001 1 0 20 40 DIFFUSION CORRECTED 2 log eN = 10.578-0.088t r=0.70 SEM=0.015 P<0.001 • 6 log eN = 5.284-0.152t r=0.92 SEM=0.011 -* P<0.001 L _i i 1 1— 60 0 AGE (DAYS) 20 40 60 s m a l l e r t h a n t h e average l e n g t h a t r e c r u i t m e n t t o t h e n i g h t - l i g h t ( A p p e n d i x F ) . N o t u n e x p e c t e d l y , t h e u n c o r r e c t e d a n d d i f f u s i o n - c o r r e c t e d M values f o r t h i s c o h o r t were ve ry d i f fe ren t f r o m those e s t i m a t e d f r o m t h e p l a n k t o n - n e t ca tches, b e i n g o n l y h a l f o f t h e l a t t e r ' s va lue . (2) T h e M value o f t h e n i g h t -l i g h t ca tches o f c o h o r t f ive was m o r e t h a n t w i c e as h i g h as t h e d i f f u s i o n - c o r r e c t e d p l a n k t o n - n e t va lue , i n d i c a t i n g t h a t o t h e r m e c h a n i s m s were r e m o v i n g larvae f r o m t h e p o p u l a t i o n ava i lab le t o t h e n i g h t -l i g h t . O n e l i k e l y m e c h a n i s m was t h e a v o i d a n c e o f t h e gear by la rvae because t h e gear also a t t r a c t e d p r e d a t o r s . (3) I n 1982 I o b s e r v e d j u v e n i l e r o c k f i s h e s , Sebastes s p p . , h o v e r i n g a b o u t t h e l i gh t every n i g h t s t r i k i n g a t any l a r va l fish t h a t a p p r o a c h e d . N o such a c t i v i t y was seen i n t h e s p r i n g o f 1 9 8 1 . I s p e c u l a t e t h a t t h e i nc reased a b u n d a n c e o f these p r e d a t o r s i n 1982 over 1 9 8 1 was a f u n c t i o n a l r e s p o n s e t o t h e t r e m e n d o u s a b u n d a n c e o f c o h o r t s ix la rvae. T h e m o r t a l i t y ra tes r e p o r t e d here are w i t h i n t h e range o f t hose r e p o r t e d f o r w i l d p o p u l a t i o n s o f l a r v a l Pac i f i c a n d A t l a n t i c h e r r i n g ( A p p e n d i x A , T a b l e A . 5 ) . T h e r a n g e o f M f o r c o h o r t s t w o , t h r e e , a n d five, 0 .064—0.094 d _ 1 , c o r r e s p o n d s t o a i n f e r r e d p e r i o d o f de layed f e e d i n g o f 0 - 2 d a f t e r h a t c h a c c o r d i n g t o d e l a y e d f e e d i n g e x p e r i m e n t s o n l a b o r a t o r y - r e a r e d Pac i f i c h e r r i n g larvae ( A p p e n d i x A ) . T h e M va lue o f c o h o r t s ix , 0.305 d _ 1 , c o r r e s p o n d s t o a n i n f e r r e d p e r i o d o f de layed f e e d i n g o f a b o u t 16 d . T h i s suggests t h a t p r e d a t i o n as we l l as s t a r v a t i o n was i m p o r t a n t i n t h e m o r t a l i t y o f t h i s c o h o r t because Pac i f i c h e r r i n g la rvae d o n o t s u r v i v e s u c h a l e n g t h y p e r i o d o f s t a r v a t i o n . D i s p e r s a l R a t e s T h e v e l o c i t y o f d i s p e r s i o n o f t h e cen te r o f d i s t r i b u t i o n o f a c o h o r t t h a t is d i s p e r s i n g a c c o r d i n g t o F i c k ' s l a w is f o u n d b y s o l v i n g e q u a t i o n (1 .15a) w i t h respec t t o x/t ( K e n d a l l 1948; O k u b o 1980) . T h e r e s u l t is (1.19) v w h i c h r a p i d l y converges t o (1.20) v = ±2{KM)i as t goes t o i n f i n i t y . T h i s c a l c u l a t e d d i s p e r s a l r a t e p r o v i d e d r e a s o n a b l e fits t o t h e ranges o f age-a t - r e c r u i t m e n t f o r c o h o r t s t w o a n d five b u t less so f o r c o h o r t s i x ( F i g . 1.23). T h e f a c t t h a t t h e 69 a g e s - a t - r e c r u i t m e n t f o r s t a t i o n s H a n d G o f c o h o r t s ix were se r ious ly u n d e r e s t i m a t e d suggests t h a t t h e r e w a s f a s t e r d i s p e r s a l f r o m t h e m o u t h o f t h e I n l e t i n a n o r t h e a s t d i r e c t i o n t h a n a s o u t h w e s t d i r e c t i o n . T h e s e d i s p e r s a l speeds were l o w e r t h a n t h e e s t i m a t e d speed o f 1 .0 -1 .1 k m d - 1 r e p o r t e d f o r la rva l Pac i f i c h e r r i n g d i s p e r s i n g f r o m T o q u a r t B a y s o u t h w e s t a l o n g t h e n o r t h e r n coas t o f B a r k l e y S o u n d by S t e v e n s o n (1962) . S tevenson (1962) e s t i m a t e d M = 0 . 4 1 d _ 1 a n d so, f r o m e q u a t i o n (1 .20) , i f = 0 . 6 1 - 0 . 7 4 k m 2 d _ 1 , a va lue 1.6-1.9 t i m e s g r e a t e r t h a n t h a t e s t i m a t e d f r o m t h e p l a n k t o n - n e t catches o f c o h o r t s ix . H o w e v e r , t h e a b u n d a n c e o f la rvae i n t h e T o q u a r t B a y h a t c h i n g s is a lways m a n y t i m e s g r e a t e r t h a n a n y h a t c h i n g s t h a t o c c u r i n B a m f i e l d I n l e t a n d s ince a b u n d a n c e a n d K are p o s i t i v e l y c o r r e l a t e d (see s e c t i o n b e l o w o n C o r r e l a t i o n s o f P o p u l a t i o n P a r a m e t e r s ) t h i s m a y e x p l a i n t h e h i g h e r i f va lues f o r T o q u a r t B a y c o h o r t s . D i s t r i b u t i o n o f R e l a t i v e H a t c h D a t e s T h e d i s t r i b u t i o n s o f d e n s i t y a n d n u m b e r o n T - ( i n d i c a t e t h a t h a t c h i n g was n o r m a l l y d i s t r i b u t e d w i t h t i m e i n a l l f o u r c o h o r t s e x c e p t f o r t h e n i g h t - l i g h t catches o f c o h o r t s i x w h i c h were t o o f e w t o c o n s t r u c t a n o r m a l d i s t r i b u t i o n ( F i g . 1.24). T h e use o f o n l y f e d larvae ( C V 1 < 0) d i d n o t s i g n i f i c a n t l y a l t e r to o r cr. C o h o r t s ix was a p p r o x i m a t e l y 13 t i m e s m o r e a b u n d a n t t h a n c o h o r t t w o i n t h e p l a n k t o n -n e t ca tches , 48 t i m e s m o r e a b u n d a n t t h a n c o h o r t five, a n d 1800 t i m e s m o r e a b u n d a n t t h a n c o h o r t t h r e e . T h e to a n d a va lues were used i n t h e c o m p l e t e p o p u l a t i o n m o d e l , e q u a t i o n (1 .17a) , w h i c h , w h e n p l o t t e d a g a i n s t d a t e , a p p e a r s t o desc r i be t h e t r e n d s o f p o p u l a t i o n a b u n d a n c e r e a s o n a b l y wel l (F igs . 1.15 a n d 1.16). T h e o n l y e x c e p t i o n was t h e p r e d i c t e d n i g h t - l i g h t e d n u m b e r s a t d a t e o f c o h o r t s i x . A n exce l len t fit was o b t a i n e d b y a s s u m i n g t h a t a — 0 . 1 . T h e p o p u l a t i o n m o d e l o f t h e c o h o r t t h r e e p l a n k t o n - n e t ca tches a s s u m e d K = 0. C o r r e l a t i o n s B e t w e e n P o p u l a t i o n P a r a m e t e r s T h e g r o w t h r a t e s , w e i g h t - l e n g t h e x p o n e n t s , d i f f u s i o n coe f f i c ien ts , m o r t a l i t y r a t e s , a n d d i s p e r s a l speeds were c o r r e l a t e d w i t h p o p u l a t i o n a b u n d a n c e a n d w i t h t h e p e r c e n t o f t h e 7 - 2 0 m m l e n g t h class 70 F i g u r e 1.23. P l o t o f t h e d i s t a n c e f r o m t h e h a t c h s i te t o each s t a t i o n , x, a g a i n s t t h e age r a n g e o f c o m p l e t e r e c r u i t m e n t t o each s t a t i o n f o r c o h o r t s t w o , t h r e e , f i ve , a n d s ix . T h e so l id l ines were c a l c u l a t e d f r o m t h e d i s p e r s a l v e l o c i t i e s , v, f o r p l a n k t o n - n e t ( p - n ) a n d n i g h t - l i g h t (n-1) ca tches . 7 1 10 r 0 20 40 0 20 40 AGE (DAYS) 72 Figure 1.24. The hatch date frequencies for plankton-net and night-light samples of cohorts two, three, five, and six. 73 P L A N K T O N - N E T N I G H T - L I G H T co 10" 10' 1 h o I S = 4 8 3 8 . 9 - A L L : - t 0 = 0 . 3 - J i .71 o = 1 . 6 n 1 - C V K O : r ?" il t 0=°-1 : \ a = 1 . 4 i * 10 1 0 ' o O 1 o DC m 10 4 ID Z 10* 1 r o I S = 3 5 . 3 O - A L L : - t 0 = 0 . 0 - a = 1 . 3 - C V K O : I !| t 0 = - 0 . 5 • . nr. I a = 1 . 2 I S = 1 3 0 6 . 1 - A L L : t 0 = 0 . 2 o = 1 . 8 C V K O : t 0 = 0 . 3 a = 1 . 8 DC LU CD o Z N = 1 6 9 2 2 - ALL : n i n t 0 = 0 . 1 a = 1 . 8 -1 ' u - C V K O : - ! ! : t 0 = 0 . 0 1 a = 1.9 I N = 9 4 3 1 A L L : t 0 = - 2 . 4 o = 1 . 3 10^ 1 0 ' 1 h I S = 6 2 7 3 8 . 1 r-» - ALL : _j t. t 0 = 0 . 8 -rr^ri .J t a = 2 . 0 - ! *. i ; - C V K O : - i i t 0 = 0 . 0 - a = 2 . 1 • • 2 0 I N = 7 0 2 - 6 - ALL : - t 0 = - 0 . 1 rn a = 3 . 4 • „rJ! . i 1 - C V K O : • • ; t 0 = - 1 . 3 -J ! 1 a = 4 . 0 T-t (DAYS) 2 0 74 F i g u r e 1.25. P l o t s o f p o p u l a t i o n p a r a m e t e r s on t h e t o t a l p l a n k t o n - n e t a b u n d a n c e a n d t h e f r a c t i o n s o f s t a r v i n g la rvae ( C F < 2.42 a n d C V 1 > 0 ) . 75 r = - 0 . 7 8 r = - 0 . 2 4 r = - 0 . 8 8 1 0 2 1 0 4 0 4 5 9 0 4 5 90 NUMBER/1000M 3 ASIN(%CF<2.42) ASIN(%CV1>0) TABLE 1.4. Correlation matrix of population parameters calculated from plankton-net catches. The fractions of the formation. 7-20 mm length class classified as starving ware linearized with the arcsin \/X trans-GL Gw K M v ES %GF %CV1 GL 1.00 Gw 0.82 1.00 a2 0.52 0.85 1.00 K -0.85 -0.99 -0.93 1.00 M -0.95 -0.92 -0.75 0.97 1.00 V -0.91 -0.95 -0.83 0.99 0.99 1.00 ES -0.78 -0.37 -0.26 0.89 0.71 0.63 1.00 %CF -0.24 -0.22 0.26 0.01 0.05 0.04 -0.26 1.00 %CV1 -0.88 -0.96 -0.66 0.89 0.90 0.88 0.39 0.45 1.00 77 t h a t was c lass i f ied as s t a r v i n g by C V 1 , b u t n o t w i t h t h e p e r c e n t s t a r v i n g as c lass i f ied by C F ( F i g . 1.25 a n d T a b l e 1.4). S i m i l a r r e s u l t s have b e e n r e p o r t e d by o t h e r w o r k e r s : B l a x t e r (1971) r e p o r t e d t h e s u r p r i s i n g f a c t t h a t t h e r e was an inverse r e l a t i o n b e t w e e n t h e C F o f l a r v a l C l y d e Sea A t l a n t i c h e r r i n g a n d t h e b i o m a s s o f p l a n k t o n i c f o o d . V i l e l a a n d Z i j l s t r a (1971) f o u n d n o c o r r e l a t i o n b e t w e e n t h e average C F va lues o f A t l a n t i c h e r r i n g o f t h e c e n t r a l a n d s o u t h e r n N o r t h Sea a n d subsequen t year-c lass size. B o t h sets o f o b s e r v a t i o n s suggest t h a t C F was n o t m e a s u r i n g t h e t r u e c o n d i t i o n o f t h e larvae. T h e m o s t a b u n d a n t c o h o r t , n u m b e r s ix , h a d l o w e r ra tes o f g r o w t h i n l e n g t h a n d d r y w e i g h t , a l ower w e i g h t - l e n g t h e x p o n e n t , a n d a g r e a t e r p r o p o r t i o n o f 7 - 2 0 m m l o n g larvae c lass i f ied as s t a r v i n g , t h a n t h e o t h e r t h r e e c o h o r t s . A c c o m p a n y i n g these i n d i c a t i o n s o f low n u t r i t i o n a l s t a t u s was a h i g h e r r a t e o f d i f f u s i o n f r o m t h e I n l e t t h a n c o h o r t s t w o a n d five, a n d a h i g h e r r a t e o f m o r t a l i t y t h a n c o h o r t s t w o , t h r e e , a n d five. T h e s e r e s u l t s were s u p p o r t e d b y t h e ana lys i s o f t h e n i g h t - l i g h t ca tches . C o h o r t s ix h a d a l a r g e r d i f f u s i o n coe f f i c ien t a n d a h i g h e r m o r t a l i t y r a t e t h a n c o h o r t t w o . I t also h a d a h i g h e r percen t s t a r v i n g , as c lass i f ied b y C V 1 , t h a n c o h o r t s t w o o r five. I t was n o t u n e x p e c t e d t h a t t h e d i f f u s i o n ra tes were c o r r e l a t e d w i t h p o p u l a t i o n d e n s i t y . A d v e c t i o n was i g n o r e d i n t h e p o p u l a t i o n m o d e l p a r t l y because h e r r i n g larvae were a s s u m e d c a p a b l e o f m o v i n g f r o m a r e g i o n o f h i g h c r o w d i n g t o one o f l o w e r c r o w d i n g , w h i c h w o u l d r e s u l t i n h i g h e r r a t e s o f d i s p e r s a l i n p o p u l a t i o n s o f h i g h e r i n i t i a l d e n s i t y . T h e a l t e r n a t e h y p o t h e s i s is t h a t d i s p e r s a l r a t e was d r i ven by t h e t r a n s p o r t o f s t a r v i n g larvae b y w a t e r c u r r e n t s . I n t h i s m o d e l s t a r v i n g larvae lose t h e a b i l i t y t o c o n t r o l t h e i r v e r t i c a l p o s i t i o n , p e r h a p s because o f a low spec i f i c g r a v i t y ( H e n r i e t a l . 1985) , a n d are t r a n s p o r t e d away f r o m t h e h a t c h s i te a t a f a s t e r r a t e t h a n f e e d i n g la rvae. T h e ev idence does n o t s u p p o r t t h i s second h y p o t h e s i s , t h e g r e a t m a j o r i t y o f s t a r v i n g larvae were f o u n d w i t h i n 3 k m o f t h e h e a d o f B a m f i e l d I n l e t a n d m o s t la rvae c a p t u r e d a t d i s t a n t s t a t i o n s i n T r e v o r C h a n n e l were c lass i f ied as f e d . A l l t h e p o p u l a t i o n p a r a m e t e r s were m o r e h i g h l y c o r r e l a t e d w i t h t h e p e r c e n t o f t h e 7 - 2 0 m m l e n g t h g r o u p c lass i f ied as s t a r v i n g by C V l t h a n w i t h t o t a l p o p u l a t i o n a b u n d a n c e . T h e c o r r e l a t i o n b e t w e e n p e r c e n t s t a r v i n g , as c lass i f ied b y C V l , a n d p o p u l a t i o n a b u n d a n c e was r e l a t i v e l y low, o n l y 0 .39. T h i s suggests t h a t d e n s i t y - d e p e n d e n c e was n o t t h e sole f u n c t i o n o p e r a t i n g i n t h i s s y s t e m . H i d d e n va r iab les , 78 p e r h a p s ava i l ab le f o o d d e n s i t y , m a y also have b e e n i n f l u e n c i n g t h e degree o f s t a r v a t i o n e x p e r i e n c e d b y each c o h o r t . T h e R o l e o f S t a r v a t i o n T h e r e s u l t s o f t h i s s t u d y s u p p o r t a l l t h r e e h y p o t h e s e s o f l a rva l m o r t a l i t y . S t a r v i n g larvae were f o u n d i n n a t u r e a n d t h e i r r e l a t i v e a b u n d a n c e was p o s i t i v e l y c o r r e l a t e d w i t h t h e i r m o r t a l i t y r a t e . O f f s h o r e t r a n s p o r t o f t h e larvae was d o c u m e n t e d a n d t h e r a t e o f t r a n s p o r t was c o r r e l a t e d w i t h b o t h t h e r a t e o f m o r t a l i t y a n d w i t h t h e re la t i ve a b u n d a n c e o f s t a r v i n g la rvae . Inve rse c o r r e l a t i o n s were f o u n d b e t w e e n t h e ra tes o f g r o w t h a n d m o r t a l i t y , a n d b e t w e e n g r o w t h a n d p o p u l a t i o n a b u n d a n c e . T h e m o r t a l i t y r a t e d i r e c t l y a t t r i b u t a b l e t o s t a r v a t i o n , Ms, c a n b e c a l c u l a t e d i f i t is a s s u m e d t h a t a l l 7 - 2 0 m m l o n g larvae c lass i f ied as s t a r v i n g b y C V l were d e s t i n e d t o d ie w i t h i n several days o f e n t e r i n g t h e s t a r v i n g ca tegory . T h e n , (1 .21) M . = - - ^ l o g e ( l - X ) 120 w h e r e fao—age (d ) a t w h i c h t h e m e a n l e n g t h o f a c o h o r t is 20 m m , a n d X = t h e f r a c t i o n o f t h e 7-20 m m l e n g t h class c lass i f ied as s t a r v i n g . M, is o n l y 3 - 2 3 % o f t h e t o t a l m o r t a l i t y r a t e (Table 1.5), a s u r p r i s i n g l y l o w a m o u n t c o n s i d e r i n g t h e c o r r e l a t i o n b e t w e e n M a n d p e r c e n t C V l > 0. T h i s is s i m i l a r t o t h e r e s u l t s r e p o r t e d f o r n o r t h e r n a n c h o v y larvae i n t h e s o u t h e r n C a l f o r n i a B i g h t by O ' C o n n e l l (1980) . H e d i a g n o s e d a n average o f 8 % o f h is c a p t u r e d larvae as s t a r v i n g u s i n g a h i s t o l o g i c a l m e t h o d . I f a l l s t a r v i n g anchov ies d i e d w i t h i n 10 d ( t he l a r g e s t s t a r v i n g fish was 10 m m w h i c h c o r r e s p o n d s t o a n age o f 10 d u s i n g M e t h o t a n d K r a m e r ' s (1979) g r o w t h e q u a t i o n f o r w i l d fish a t 16.2° C ) t h e n f r o m e q u a t i o n (1.21) M, = 0 . 0 0 8 d _ 1 , w h i c h was 3 . 6 % o f t h e average t o t a l m o r t a l i t y r a t e o f 0.22 d - 1 ( Z w e i f e l a n d S m i t h (1981) : q u a r t e r l y e s t i m a t e s f o r t h e years 1951-75; H e w i t t a n d M e t h o t (1982) : a n n u a l e s t i m a t e s f o r 1978-79) . T h i s is s i m i l a r e n o u g h t o t h e r a n g e c a l c u l a t e d i n t h i s s t u d y t o s u p p o r t t h e i d e a t h a t t h e l a r g e s t p a r t o f t h e t o t a l m o r t a l i t y r a t e i n l a r v a l h e r r i n g a n d a n c h o v y is d i r e c t l y a t t r i b u t a b l e t o p r e d a t i o n , n o t s t a r v a t i o n . S t a r v a t i o n m a y p l a y a n a d d i t i o n a l i n d i r e c t ro le i n t h e s u r v i v a l o f l a r v a l h e r r i n g t h r o u g h i t s nega t i ve ef fects o n t h e r a t e a t w h i c h t h e la rvae g r o w t h r o u g h t h e size r a n g e o f v u l n e r a b i l i t y , a n d t h r o u g h i t s n e g a t i v e ef fects o n t h e larvae 's a b i l i t y t o evade p r e d a t o r s , a n d t o recover f r o m w o u n d i n g , i n f e c t i o n , 79 T A B L E 1.5. T h e m o r t a l i t y ra tes d i r e c t l y a t t r i b u t a b l e t o s t a r v a t i o n , Ms. C o h o r t ho M. Me as p e r c e n t (d) ( d - 1 ) o f M 2 31.5 0.011 12.0 3 30.5 0.022 23.4 5 29.7 0.002 3.1 6 34.6 0.067 21.8 80 or p a r a s i t i s m . T h e ev idence f o r t h i s h y p o t h e s i s is a s ign i f i can t c o r r e l a t i o n b e t w e e n log,, ( M — Me) a n d l o g e ( l - X ) , loge[M-M.) = - 2 . 8 3 - 0 . 5 9 l o g „ ( l - X ) , r = 0 .98 , P < 0 . 0 1 . H o w e v e r , t h i s c o r r e l a t i o n d e p e n d s s t r o n g l y o n t h e s ing le d a t a p o i n t f o r c o h o r t s ix , as d o a l l t h e c o r r e l a t i o n s s h o w n i n F i g . 1.25 a n d T a b l e 1.4. M o r e o v e r , t h e m o r t a l i t y r a t e s f o r m a r i n e fish larvae are n o h i g h e r , o n t h e average, t h a n those f o r p e l a g i c m a r i n e fish eggs w h o s e m o r t a l i t y is a l m o s t so le ly d u e t o p r e d a t i o n ( D a h l b e r g 1979; M a y 1974) . D e n s i t y - D e p e n d e n c e a n d S p a t i a l A g g r e g a t i o n T h e r e is a n o t h e r h y p o t h e s i s t h a t c o m p e t e s w i t h t h e s t a r v a t i o n a n d s t a r v a t i o n - p r e d a t i o n i n t e r a c -t i o n h y p o t h e s e s : t h e a g g r e g a t i o n m o d e l o f p r e d a t i o n . T h i s h y p o t h e s i s s ta tes t h a t m o r t a l i t y d u e t o p r e d a t i o n is h i g h e r f o r o r g a n i s m s t h a t are d i s t r i b u t e d i n h i g h - d e n s i t y pa tches t h a n i t is f o r o r g a n i s m s d i s t r i b u t e d i n l o w e r - d e n s i t y p a t c h e s . T h u s , a l t h o u g h t h e f o u r c o h o r t s o f Pac i f i c h e r r i n g larvae h a d t h e same t r a j e c t o r y o f p a t c h i n e s s w i t h age, t h e pa tches o f c o h o r t s i x larvae were m u c h denser t h a n t h o s e o f t h e o t h e r c o h o r t s . T h e h i g h dens i t i es o f t h e pa tch(es) m a y have s i g n a l l e d p r e d a t o r s t o s w i t c h t h e i r f e e d i n g t o l a r v a l h e r r i n g , a n d t h e y a g g r e g a t e d o n t h e pa tches , c a u s i n g t h e h i g h m o r t a l i t y r a t e o f c o h o r t s ix . T h e l o w e r d e n s i t y pa tches o f t h e o t h e r t h r e e c o h o r t s were p r e s u m a b l y less p o w e r f u l s igna ls t o p r e d a t o r s a n d so l o w e r ra tes o f p r e d a t i o n a n d m o r t a l i t y e n s u e d . T h e e v i d e n c e fo r t h i s h y p o t h e s i s is o n l y i n d i r e c t : first, t h e inc reased a b u n d a n c e o f j u v e n i l e Sebastes s p p . a t t h e n i g h t - l i g h t i n 1982 over t h e i r a b u n d a n c e i n 1 9 8 1 suggests t h a t these p r e d a t o r s h a d m o v e d i n t o t h e I n l e t i n response t o t h e t r e m e n d o u s a b u n d a n c e o f c o h o r t s ix larvae o r t h a t t h e y a l r e a d y r e s i d e d i n t h e I n l e t b u t h a d l e a r n e d t o c o n c e n t r a t e t h e i r f o r a g i n g o n la rva l fishes. T h e second a r g u m e n t is t h a t p r e y s w i t c h i n g is k n o w n t o o c c u r i n p r e d a t o r s i n response t o changes i n t h e t y p e s o f ava i lab le f o o d . T h e p e l a g i c n e a r s h o r e m a r i n e e n v i r o n m e n t d u r i n g t h e s p r i n g b l o o m is c h a r a c t e r i z e d by s u d d e n i n f l u x e s o f n e w l y - h a t c h e d o r g a n i s m s . T h e t h i r d a r g u m e n t is t h a t a l l o t h e r hyp otheses are less l i ke ly : d i r e c t s t a r v a t i o n does n o t a c c o u n t f o r m o r e t h a n 2 3 % o f t h e t o t a l m o r t a l i t y r a t e , a n d a s t a r v a t i o n - p r e d a t i o n i n t e r a c t i o n is u n l i k e l y f o r t h e reasons d iscussed a b o v e . 8 1 T h i s h y p o t h e s i s d i f fe rs f r o m o t h e r m o d e l s o f d e n s i t y - d e p e n d e n t m o r t a l i t y i n l a r v a l fishes, e.g. W a r e (1975) , i n t h a t i t has a n a d d e d d i m e n s i o n o f s p a t i a l o r g a n i z a t i o n . I t p r e d i c t s t h a t t w o c o h o r t s o f l a r v a l fishes m a y have t h e same i n i t i a l n u m b e r b u t d i f f e ren t m o r t a l i t y ra tes i f t h e i r degree o f pa tch iness d i f fe rs . P a t c h i n e s s is i n h e r i t e d f r o m t h e s p a w n i n g b e h a v i o u r o f t h e p a r e n t s a n d t h e n i t is i n f l u e n c e d b y t h e p h y s i o g e o g r a p h i c f e a t u r e s o f t h e e n v i r o n m e n t a n d b y m e t e o r o l o g i c a l even ts such as s t o r m s . T h i s h y p o t h e s i s suggests t h a t i n f o r m a t i o n o n t h e s p a t i a l d i s t r i b u t i o n o f l a rva l fishes is as i m p o r t a n t as i n f o r m a t i o n o n t h e i r a b u n d a n c e a n d p h y s i c a l c o n d i t i o n t o an u n d e r s t a n d i n g o f t h e i r p o p u l a t i o n d y n a m i c s . C h a p t e r 2 descr ibes i n d e t a i l a m o d e l o f m o r t a l i t y r a t e i n m a r i n e pe lag ic fish eggs a n d larvae t h a t i n c o r p o r a t e s t h e d i r e c t ef fects o f l a r va l s t a r v a t i o n a n d t h e effects o f s p a t i a l p a t c h i n e s s . 82 Chapter 2 Natural Mortality of Marine Pelagic Fish Eggs and Larvae: the Role of Spatial Distribution Chapter Summary T h e d a i l y i n s t a n t a n e o u s n a t u r a l m o r t a l i t y r a t e s o f m a r i n e pe lag ic f i sh eggs a n d larvae are h i g h e r t h a n e x p e c t e d f r o m t h e t r e n d o f m o r t a l i t y r a t e w i t h d r y w e i g h t i n t h e sea. T h i s e x t r a m o r t a l i t y is p o s i t i v e l y c o r r e l a t e d w i t h t h e pa tch iness o f t h e i r d i s t r i b u t i o n , w h i c h suggests t h a t i t is caused by t h e a g g r e g a t i o n o f p r e d a t o r s o n patches o f eggs a n d larvae. T h e p r o d u c t o f w e i g h t - d e p e n d e n t m o r t a l i t y , 5 . 2 6 x l 0 - 3 W~02h, a n d 1 -I- L l o y d ' s p a t c h i n e s s i n d e x p r e d i c t s m o r t a l i t y ra tes close t o those t h a t have b e e n m e a s u r e d f r o m t h e f i e l d by o t h e r w o r k e r s . M e c h a n i s m s w h i c h c o n t r o l t h e s p a t i a l pa tch iness o f eggs a n d larvae m a y c o n t r o l e a r l y l i fe h i s t o r y s u r v i v a l a n d t h e r e b y i n f l u e n c e re la t i ve year-c lass s t r e n g t h o f a d u l t fish s t o c k s . Intro duction M o d e l s o f m o r t a l i t y r a t e i n m a r i n e pe lag ic f i sh eggs a n d larvae have h i t h e r t o b e e n based o n size-d e p e n d e n t p r e d a t i o n ( U r s i n 1967; W a r e 1975; P e t e r s o n a n d W r o b l e w s k i 1984) . P r e d a t i o n i n c l u d e s search , w h i c h i m p l i e s t h a t t h e s p a t i a l d i s t r i b u t i o n o f t h e eggs a n d larvae m a y h e l p d e t e r m i n e t h e m a g -n i t u d e o f t h e i r p r e d a t i o n m o r t a l i t y . T h i s c h a p t e r descr ibes a m o d e l o f m o r t a l i t y r a t e t h a t i n c o r p o r a t e s t h e effects o f s p a t i a l p a t c h i n e s s . P e t e r s o n a n d W r o b l e w s k i ' s (1984) m o d e l o f w e i g h t - d e p e n d e n t m o r t a l i t y r a t e i n t h e sea desc r ibes w e l l t h e t r e n d o f d e c r e a s i n g m o r t a l i t y r a t e w i t h i n c r e a s i n g size f o r j u v e n i l e a n d a d u l t fishes, p e l a g i c i n v e r t e b r a t e s , a n d w h a l e s ( F i g . 2.1) , b u t i t c o n s i s t e n t l y u n d e r e s t i m a t e s t h e m o r t a l i t y r a t e s o f fish eggs a n d la rvae . T h i s m a y be d u e p a r t l y t o s a m p l i n g p r o b l e m s such as d i f f u s i o n o f t h e o r g a n i s m s o u t o f t h e s a m p l i n g a r e a , o r avo idance o f t h e s a m p l i n g gear by l a r g e r larvae. Howeve r , t h e c o n s i s t e n c y o f t h e d i s c r e p a n c y b e t w e e n t h e o r y a n d o b s e r v a t i o n , a n d t h e f a c t t h a t m a n y egg a n d l a r v a l m o r t a l i t y ra tes are 5 - 1 0 t i m e s h i g h e r t h a n t h a t p r e d i c t e d by t h e i r d r y w e i g h t , suggests t h a t o t h e r p h e n o m e n a m a y be i n v o l v e d . 83 F i s h eggs a n d n e w l y - h a t c h e d la rvae have p o o r l y d e v e l o p e d sensory s y s t e m s , s k e l e t o n , a n d m u s c u l a -t u r e . T h e eggs c a n n o t evade c a p t u r e once a p r e d a t o r h a s fixed i t s a t t e n t i o n o n t h e m a n d n e w l y - h a t c h e d larvae have o n l y a m a r g i n a l l y i m p r o v e d evas ion c a p a b i l i t y . T h e o n l y w a y t o r e d u c e t h e p r o b a b i l i t y o f c a p t u r e is t o r e d u c e t h e p r o b a b i l i t y o f b e i n g f o u n d by a p r e d a t o r . P r e d a t o r s are a t t r a c t e d t o patches o f f o o d because i t is an e f f i c ien t f o r a g i n g s t r a t e g y t o d o so. T h e r e f o r e , r e d u c i n g t h e p r o b a b i l i t y o f b e i n g f o u n d m e a n s d i s p e r s i n g , pass ive ly i n t h e case o f eggs, a n d ac t i ve ly i n t h e case o f larvae. F i s h eggs a n d larvae i n h e r i t a p a t c h y d i s t r i b u t i o n f r o m t h e i r s p a w n i n g p a r e n t s a n d t h i s pa tch iness decreases w i t h age t o a m i n i m u m ( = m a x i m u m d i s p e r s a l ) a f t e r w h i c h i t increases aga in as t h e larvae b e g i n t o s c h o o l , i f t h e y are a pe lag i c species, o r m i g r a t e t o t h e ocean floor, i f t h e y are d e m e r s a l ( T h i s s t u d y : C h a p t e r 1 , F i g . 1.20; H e w i t t 1 9 8 1 ; S m i t h 1973) . A t t h i s age a n d size fish have d e v e l o p e d ef f ic ient p r e d a t o r a v o i d a n c e b e h a v i o u r a n d p a t c h i n e s s is n o l o n g e r a l i a b i l i t y . S t a r v a t i o n m o r t a l i t y m a y o c c u r i n first-feeding l a r v a l fishes ( S h e l b o u r n e 1957: p l a i c e ; O ' C o n n e l l 1980: n o r t h e r n a n c h o v y ; K a s h u b a a n d M a t t h e w s 1984 : f r e s h w a t e r s h a d ; T h i s s t u d y : C h a p t e r 1) . T h e c o n t r i b u t i o n s o f s t a r v a t i o n a n d p r e d a t i o n t o t h e t o t a l m o r t a l i t y r a t e are a s s u m e d t o be a d d i t i v e , n o t m u l t i p l i c a t i v e , f o r reasons t h a t have b e e n d iscussed a b o v e ( C h a p t e r 1 : T h e R o l e o f S t a r v a t i o n ) . The Model E x p o n e n t i a l m o r t a l i t y r a t e is a s s u m e d , a n d t h e t o t a l r a t e , M, is s e p a r a t e d i n t o t h e r a t e d u e t o p r e d a t i o n , Mp, a n d t h e r a t e d u e t o d i r e c t s t a r v a t i o n , M,, (2.1) j.™ = - M = - { M p + M t ) f w h e r e i V = t h e n u m b e r o f l a rvae , a n d i = t i m e (d ) . Mp is a s s u m e d t o fo l l ow P e t e r s o n a n d W r o b l e w s k i ' s (1984) m o d e l o f w e i g h t - d e p e n d e n t m o r t a l i t y , (2 .2) Mv = 5 . 2 6 x l 0- 3 YT*M, w h e r e W= d r y b o d y w e i g h t (g) , a n d s p a t i a l d i s t r i b u t i o n is c o m p l e t e l y r a n d o m , a n d t o inc rease w i t h i n c r e a s i n g p a t c h i n e s s . A s i m p l e a n d a p p r o p r i a t e i n d e x o f p a t c h i n e s s is L l o y d ' s i n d e x ( L l o y d 1967; P i e l o u 1977) , (2 .3) p = 1 + ( w F 1 -l)x~x, 84 w h e r e x —the m e a n d e n s i t y o f eggs o r larvae fo r a c r u i s e , a n d var= t h e var iance o f z . W h e n t h e s p a t i a l d i s t r i b u t i o n is r a n d o m t h e m e a n a n d va r iance are e q u a l a n d p = 1 . T h i s i n d e x is a m e a s u r e o f h o w m a n y m o r e t i m e s m o r e c r o w d e d an average i n d i v i d u a l is re la t i ve t o a n i n d i v i d u a l i n a p o p u l a t i o n w i t h t h e same m e a n d e n s i t y b u t r a n d o m l y d i s p e r s e d . T h e r e f o r e , Mp s h o u l d va ry d i r e c t l y w i t h (l+p). T h e c o m p l e t e m o d e l is (2.4) M = 5 . 2 6 x l 0 - 3 F / - ° - 2 5 ( l + p) + M,. Sources of Data T h e t o t a l m o r t a l i t y ra tes o f fish eggs, la rvae , a n d j u v e n i l e s , a n d o f pe lag i c i n v e r t e b r a t e s were e s t i m a t e d as t h e s lopes o f t h e r i g h t - h a n d l i m b s o f t h e ca tch curves (log^ d e n s i t y o n age: R i c k e r 1975) . T h e c a t c h c u r v e s o f l a r v a l fishes s p a n n e d t h e first-feeding s t a g e . T h e n a t u r a l m o r t a l i t y r a t e s o f a d u l t fishes a n d w h a l e s were c a l c u l a t e d f r o m severa l m e t h o d s : ca tch curves o f v i r g i n p o p u l a t i o n s ; B e v e r t o n a n d H o l t ' s (1957) , P a u l i k ' s (1963) , a n d J o s e p h a n d C a l k i n ' s (1969) t a g - r e c o v e r y m e t h o d s ; regress ions o f t o t a l m o r t a l i t y o n fishing e f fo r t t o find t h e i n t e r c e p t w h e n f i s h i n g e f f o r t was zero ; a n d B e v e r t o n a n d H o l t ' s (1956) m e t h o d o f c a l c u l a t i n g m o r t a l i t y ra tes f r o m t h e p a r a m e t e r s o f t h e g r o w t h e q u a t i o n a n d t h e average l e n g t h o f t h e c a t c h . D r y w e i g h t w a s 2 0 % o f w e t w e i g h t , a n d w e t w e i g h t was c a l c u l a t e d f r o m t h e m i d p o i n t o f t h e l e n g t h r a n g e w i t h a w e i g h t - l e n g t h e q u a t i o n s u p p l i e d b y t h e a u t h o r , o r w i t h a w e i g h t - l e n g t h e q u a t i o n f o r t h e same species f r o m a d i f f e ren t g e o g r a p h i c a rea , o r w i t h a w e i g h t - l e n g t h e q u a t i o n fo r a r e l a t e d spec ies . E g g w e t w e i g h t was ^ir^p, w h e r e r = t h e average r a d i u s o f t h e egg ( c m ) a n d p = t h e spec i f i c g r a v i t y o f t h e eggs ( l g c m - 3 ) . E g g r a d i i were t a k e n f r o m t h e a u t h o r o r f r o m B a g e n a l (1971) , R u s s e l l (1976) , a n d T h e i l a c k e r a n d D o r s e y (1980) . E s t i m a t e s o f p c a m e f r o m va lues c a l c u l a t e d by t h e a u t h o r s , e .g. S m i t h (1973) , H e w i t t (1981) , K o s l o w e t a l . (1985) , H o u d e a n d L o v d a l (1985) , a n d t h i s s t u d y ( C h a p t e r 1 : F i g . 1.20), o r t h e y were c a l c u l a t e d f r o m d e n s i t i e s - a t - s t a t i o n d a t a r e p o r t e d by t h e a u t h o r s , e .g. Far r is (1961) , C o n a n d a n d F a g e t t i (1971) , M a t s u s h i t a e t a l . (1982) , C r o s s l a n d (1980) , B e r r i e n et a l . (1981) , S e t t e (1943) , A n d e r s o n (1984) , a n d C h a v a n c e e t a l . (1985) , o r t h e y were c a l c u l a t e d f r o m s t a t i s t i c s such as t h e coef f ic ient o f v a r i a t i o n o f t h e ca tches s u p p l i e d b y t h e a u t h o r , e .g. H a r d i n g a n d T a l b o t (1973) . M o s t e s t i m a t e s 85 o f p were c a l c u l a t e d f r o m t h e same d a t a used t o c a l c u l a t e m o r t a l i t y r a t e s b u t t h i s was n o t poss ib le i n a l l cases because n o t a l l a u t h o r s r e p o r t e d t h e i r survey dens i t i es . I n these cases p was c a l c u l a t e d f r o m s u r v e y d a t a p u b l i s h e d b y a n o t h e r a u t h o r f o r t h e same species a n d t h e same g e n e r a l r e g i o n . T h e m i d p o i n t o f t h e p range was u s e d . E s t i m a t e s o f Ma f o r la rvae are p r e s e n t l y ava i l ab le fo r t w o species o f fish: i n C h a p t e r 1 i t was c a l c u l a t e d t h a t 5 - 9 0 % o f l a r v a l Pac i f i c h e r r i n g c a p t u r e d i n B a m f i e l d I n l e t were s t a r v i n g w h i c h was e q u i v a l e n t t o a n average m o r t a l i t y r a t e over a 1 m o p e r i o d o f 0 . 0 0 2 - 0 . 0 6 7 d _ 1 or 3 . 1 - 2 3 . 4 % o f t h e t o t a l m o r t a l i t y r a t e o f 0 . 0 6 4 - 0 . 3 0 5 d _ 1 . O ' C o n n e l l (1980) r e p o r t e d t h a t a b o u t 8 % o f la rva l n o r t h e r n a n c h o v y c a p t u r e d i n t h e s o u t h e r n C a l i f o r n i a B i g h t i n t h e s p r i n g o f 1977 were s t a r v i n g w h i c h represents a n M, o f 0.008 d _ 1 or 3 . 6 % o f t h e average t o t a l m o r t a l i t y r a t e o f 0.22 ( S D = 0 . 0 7 ) d " 1 ( T h i s s t u d y : C h a p t e r 1 , T h e R o l e o f S t a r v a t i o n ) . Results T h e p l o t o f t o t a l m o r t a l i t y r a t e o n w e i g h t f o r pe lag ic m a r i n e o r g a n i s m s shows t h a t t h e m o r t a l i t y r a t e m o d e l o f P e t e r s o n a n d W r o b l e w s k i (1984) p r o v i d e s an exce l len t fit t o t h e d a t a f o r pe lag ic i n v e r t e -b r a t e s , j u v e n i l e a n d a d u l t fishes, a n d w h a l e s , over a w e i g h t range o f 14 o r d e r s o f m a g n i t u d e ( F i g . 2.1) . H o w e v e r , i t also c o n s i s t e n t l y u n d e r e s t i m a t e s t h e m o r t a l i t y ra tes o f fish eggs a n d larvae. T h e r e is a s i g n i f i c a n t n e g a t i v e c o r r e l a t i o n b e t w e e n t h e n a t u r a l l o g a r i t h m s o f t h e m i d p o i n t s o f t h e ranges o f p a t c h i n e s s n u m b e r s a n d l o g e W f o r t h e p o o l e d d a t a o f fish eggs a n d la r iae ( F i g . 2 .2) . E x t r a p o l a t i n g t h e f u n c t i o n a l reg ress ion t o p = 1 gives a d r y w e i g h t o f 1 . 7 x l 0 ~ 2 g . T h e regress ion o f l o g e M o n l o g e W f o r t h e same d a t a set was a lso s i g n i f i c a n t a n d nega t i ve (M = 2 . 3 x l 0 ~ 3 W~°59 , r = -0 . 7 2 , P < 0 .001) . T h e h i g h e s t c o r r e l a t i o n coef f ic ient ( r = - 0 . 7 7 , P < 0 .001) was o b t a i n e d by reg ress ing r e s i d u a l m o r t a l i t y (M- 5 . 2 6 x l 0 ~ 3 W~°zs —M,) o n ( 1 + p ) ( F i g . 2.3). T h i s suggests t h a t t h e u n d e r l y i n g c a u s a l r e l a t i o n s h i p is t h e one b e t w e e n m o r t a l i t y a n d pa tch iness . T h e r e s i d u a l m o r t a l i t y a t p = 1 was 0.045 d - 1 , h i g h e r t h a n t h e m o r t a l i t y r a t e o f 0.029 d _ 1 c a l c u l a t e d f r o m a d r y w e i g h t o f 1 . 7 x l 0 ~ 2 g u s i n g e q u a t i o n (2 .2 ) . T h e m o r t a l i t y r a t e s p r e d i c t e d f r o m e q u a t i o n (2.4) are close t o t h e observed m o r t a l i t y r a t e s ( F i g . 2 .4) . T h e s lope o f t h e f u n c t i o n a l reg ress ion o f p r e d i c t e d m o r t a l i t y o n observed m o r t a l i t y was 86 F i g u r e 2 . 1 . P l o t o f i n s t a n t a n e o u s d a i l y m o r t a l i t y ra tes o n d r y w e i g h t f o r m a r i n e o r g a n i s m s . T h e so l id l i ne is t h e p r e d i c t e d m o r t a l i t y r a t e f r o m P e t e r s o n a n d W r o b l e w s k i ' s (1984) m o d e l . N u m b er Species A u t h o r s Invertebrates 2 - 5 6 7 , 8 9, 10 1 1 , 12 1 3 - 2 0 2 1 22 23, 24 25 Fish Eggs 1 , 2 3 - 14 15 1 6 - 2 1 Ilex illecebrosus Thysanoessa raschi Thysanoessa longicaudata Thysanoessa inermis Calanus helgolandicus Acartia tonsa Eurytemora affinus Acartia hudsonii Paracalanidae s p p . Euphausia pacifica Pleurobranchia brachei Melanogrammus aeglefinus Pleuronectes platessa Sardinops sagax Scomber scombrus H u r l e y a n d M o h n (1978) A m a r a t u n g a e t a l . (1978) B e r k e s (1977) L i n d l e y (1978, 1980) L i n d l e y (1978) L i n d l e y (1980) L i n d l e y a n d W i l l i a m s (1980) M u l l i n a n d B r o o k s (1970) H e i n l e (1966) H e i n l e a n d F l e m e r (1975) D u r b i n a n d D u r b i n (1981) N e w b u r y a n d B a r t h o l e m e w (1976) B r i n t o n (1976) L i n d l e y (1978) H i r o t a (1974) Sav i l le (1956) K o s l o w e t a l . (1985) H a r d i n g e t a l . (1978) H a r d i n g a n d T a l b o t (1973) S m i t h ( 1 9 7 3 ) 1 W a r e a n d L a m b e r t (1985) S e t t e (1943) B e r r i e n e t a l . (1981) 87 22 Engraulis anchoita 23 Tautogolabrus adspersus 24 Trachurus symmetric us 25 Sardinops melanostica 26 , 27 Chrysophrys auratus 28 Engraulis japonica 29 , 30 5o /ea so/ea Fish Larvae 1-8 Clupea harengus pallasi 9 - 1 6 Clupea harengus harengus 17, 18 Etrumeus teres 19, 20 Opisthonema oglinum 2 1 Harengula jaguana 22 Engraulis mordax 2 3 - 2 6 Scomber scombrus 27 Scomber japonicus 28 Pseudopleuronectes americanus 2 9 - 3 2 Pleuronectes platessa C i e c h o m s k i a n d C a p p e z z a n i (1973) W i l l i a m s a n d W i l l i a m s (1973) F a r r i s (1961) N a k a i a n d H a t t o r i (1962) C r o s s l a n d (1980) H i y a s h i (1966) -R i l e y (1974) S tevenson (1962) I i z u k a (1966) T h i s s t u d y D a s (1968) D r a g e s u n d a n d N a k k e n (1971a, b ) L o u g h e t a l . (1981) H e n d e r s o n e t a l . (1984) L a u r e n c e (1979) H o u d e (1977a) H o u d e (1977b) H o u d e (1977c) Z w e i f e l a n d S m i t h (1981) H e w i t t a n d M e t h o t (1982) Z w e i f e l a n d L a s k e r (1976) W a r e a n d L a m b e r t (1985) K e n d a l l a n d G o r d o n (1981) W a t a n a b e (1970) P e a r c y (1962a ,b ) B a n n i s t e r e t a l . (1974) R y l a n d (1966) 88 33 34 35 36 3 7 - 3 9 40 4 1 42 43 Sardinops sagax Sardinops melanostica Sardinella aurita Trachuru8 symmetricus Sebastes s p p . Melanogrammus aeglefinus Micromesistius potassou Engraulis japonica Archosargus rhomboidalis Juvenile and Adult Fishes 1 Neothunnus maeropterus 2, 3 Thunnus obesus 5, 6 7 - 1 0 Katsutvonus pelamis Sprattus sprattus Clupea harengus harengus A h l s t r o m (1954) Z w e i f e l a n d L a s k e r (1976) N a k a i a n d H a t t o r i (1954) Z w e i f e l a n d L a s k e r (1976) C o n a n d (1971) Z w e i f e l a n d L a s k e r (1976) F a r r i s (1961) A n d e r s o n (1984) Jones (1973) L a u r e n c e (1979) B a i l e y (1974) L a u r e n c e (1979) H i y a s h i (1966) C h a v a n c e e t a l . (1984) S t e p i e n (1976) H e n n e m u t h (1961) K u m e (1977) L e n a r z (1973) S u d a a n d K u m e (1967) S i l l i m a n (1966) J o s e p h a n d C a l k i n s (1969) H e n n e m u t h (1959) L i n d q u i s t (1978) J o h n s o n (1970) B a i l e y (1980) B u r d a n d B r a c k e n (1965) C u s h i n g a n d B r i d g e r (1966) 89 A a s e n (1952) D r a g e s u n d (1970) 11 Sphyraena argentea P i n k a s (1966) 12, 13 Scomber scombrus P a c i o r k o w s k i e t a l . (1973) I s a k o v (1974) 14 Trisopterus esmarkii R a i t t (1968) 15 Brevoortia tyrannus Schaa f a n d H u n t s m a n (1972) 16 Trachurus japonicus M i t a n i a n d S h o j i m a (1966) 17 Colabis saira H u g h e s (1974) 18 Argentina silus Z u k o w s k i (1972) 19 Sardinops ocellata N e w m a n (1970) 20 Rastrelliger kanagurta S u d j a s t a n i (1974) 2 1 Rastrelliger neglectus H o n g s k u l (1974) 22 , 23 Galtorhinus australis G r a n t e t a l . (1979) 24 Ammodytes tobianus R e a y (1973) 2 5 - 2 8 Sebastes alutus G u n d e r s o n (1977) C h i k u n i (1975) W e s t r h e i m a n d S n y t k o (1974) 2 9 - 3 4 Gadus morhua P i n h o r n (1975) Jones (1966) D i c k i e (1964) Jensen (1959) B a g g e (1974) P a l o h e i m o a n d K o h l e r (1968) K o h l e r e t a l . (1970) M i n e t (1978) 35 Leiognathus splendens P a u l y (1980) 36 Cynoscion nobilis T h o m a s (1968) 37 Nemipterus marginatus P a u l y a n d M a r t o s u b o r o (1980) 90 38 Lethrinus enigmatus L e b e a u a n d C u e f f (1975) 3 9 - 5 0 Pleuronectes platessa K u i p e r s (1977) L o c k w o o d (1980) B e v e r t o n a n d H o l t (1957) 5 1 - 5 4 Pseudopleuronectes americanus P e a r c y (1962b) D i c k i e a n d M c C r a c k e n (1955) H o w e a n d C o a t e s (1975) L u x (1969) 55 Glyptocephalus cynoglossus B o w e r i n g (1977) K o h l e r e t a l . (1970) 56 , 57 Hippoglossoides platessoides P i t t (1973) K o h l e r e t a l . (1970) 58 Rhombosolea plaebeia C o l m a n (1978) , W e b b (1972) 59 , 60 Eopsetta jordani K e t c h e n a n d F o r r e s t e r (1966) 6 1 Pagrus pagrus M a n o o c h a n d H u n t s m a n (1977) 62 Urolophus paucimaculatus E d w a r d s (1980) 63 Merluccius productus N e l s o n a n d L a r k i n s (1970) 64 Gadus macrocephalus K e t c h e n (1964) 6 5 - 6 8 Parophrys vetulus H o U a n d (1969) K e t c h e n (1947) 69 , 70 Gadus minutus M e n o n (1950) 7 1 Merluccius angustimanus M a t t h e w s (1975) 72 Blennius pholis Q a s i m (1957) 73 Paralabrax clathrus Y o u n g (1963) 74 Pseudosciaena diacanthus R a o (1966, 1968) 75 Pseudosciaena manchurica M a k o (1961) 76 Micropogonias undulatus W h i t e a n d C h i t t e n d e n (1977) 77 Cetengraulis mysticetus B a y l i f f (1966) 78 Urophysis chuss R i k h t e r (1974) 9 1 K o h l e r et a l . (1979) 79 Mugil cephalus B r o a d h e a d a n d M e f f o r d (1956) B r o a d h e a d (1953) 80 Etrumeus micropus C h u l l a s o r n et a l . (1977) 8 1 Trichiurus lepturus M i s u l - ( 1 9 6 4 ) 82 Cynoscion nebulosus I v e r s o n a n d M o n e t (1962) 83 Stenotomus chrysops F i n k e l s t e i n (1971) B r i g g s (1968) 84 Saurida tumbil M a k o (1961) 85 Argyrosomus argentatus M a k o (1961) 86 Taius tumifrons S h i n d o (1960) 87 Epinephelus guttatus T h o m p s o n a n d M u n r o (1978) 88 Cephalopholis fulva T h o m p s o n a n d M u n r o (1978) 89 Epinephelus striatus T h o m p s o n a n d M u n r o (1978) 90 Pseudopeneus maculatus M u n r o (1976) 9 1 Notothenia neglecta E v e r s o n (1970) 92 Cheilodactylus macropterus V o o r e n (1977) 93 Fundulus heteroclitus M e r e d i t h a n d L o t r i c h (1979) 94 Notothenia rossi B u r c h e t t a n d R i c k e t t s (1984) W h a l e s 1 , 2 Eschrichtius robustus R i c e a n d W o l m a n (1971) 3 Balaenoptera borealis L o c k y e r (1977a,b) 4 , 5 Physeter catodon G a m b e l l (1974) A l l e n a n d K i r k w o o d (1977) 6 , 7 Megaptera novaeangliae C h i t t l e b o r o u g h (1965) L o c k y e r (1976) 1 S m i t h ' s o r i g i n a l e s t i m a t e was 0 .31 d - 1 , based o n i g n o r i n g t h e las t 24 h o u r s o f t h e ca tch cu rve . T h e reason fo r t h i s s e l e c t i v i t y is u n c l e a r . I chose t h e h i g h e r e s t i m a t e , 0 .61 d — 1 , b a s e d o n t h e ent i re catch c u r v e . 92 io~6 10"4 io~2 1 1 0 2 104 DRY WEIGHT (G) F i g u r e 2.2. F u n c t i o n a l regress ion o f t h e m i d p o i n t o f t h e r a n g e o f pa tch iness n u m b e r o n t h e m i d p o i n t o f t h e r a n g e o f d r y w e i g h t f o r m a r i n e pe lag ic fish eggs a n d larvae. N u m b e r Species A u t h o r s F i s h E g g s 1 Trachurus symmetricus H e w i t t (1981) 2 - 7 Melanogrammus aeglefinus K o s l o w e t a l . (1985) 8 Engraulis japonica M a t s u s h i t a e t a l . (1982) 9 , 10 Pleuronecies platessa H a r d i n g a n d T a l b o t (1973) 1 1 Sardinops sagax S m i t h (1973) 12 Sardinops melanostica T a n a k a (1955) 13, 14 Chrysophrys auratus C r o s s l a n d (1980) 15, 16 Scomber scombrus S e t t e (1943) B e r r i e n e t a l . (1981) F i s h Larvae 1-4 Clupea harengus pallasi T h i s s t u d y 5 Trachurus symmetricus H e w i t t (1981) 6 Engraulis japonica M a t s u s h i t a e t a l . (1982) 8 Pleuronecies platessa H a r d i n g a n d T a l b o t (1973) 9, 10 Sardinops sagax S m i t h (1973) 1 1 , 12 Opisthonema oglinum H o u d e a n d L o v d a l (1985) 13 Scomber scombrus S e t t e (1943) 14 Archosargus rhomboidalis C h a v a n c e e t a l . (1984) 1 5 - 1 7 Sebastes s p p . A n d e r s o n (1984) 18 Sardinella aurita C o n a n d e t F a g e t t i (1971) 94 Ln 50 x o ~o £ 10 to CO a> c o crj Q . Q Fish eggs |~~| Fish larvae i i 11 10 -4 p = 0.193W r=0 .60 P<0.001 •0.402 • • • • • i i i_ - 3 10 Dry Weight (g) F i g u r e 2.3. F u n c t i o n a l regress ion o f r e s i d u a l m o r t a l i t y ra tes o n 1 + p f o r f i sh eggs a n d larvae. T h e n u m b e r s re fe r t o t h e d a t a i n F i g u r e 2.2 on ly . 96 F i g u r e 2.4. P l o t o f m o r t a l i t y ra tes p r e d i c t e d f r o m e q u a t i o n (2.4) a g a i n s t t h e t o t a l m o r t a l i t y r a t e s m e a s u r e d f r o m field p o p u l a t i o n s . T h e b r o k e n l i ne is t h e 45° l i n e o f equa l i t y a n d t h e so l id l i n e is t h e f u n c t i o n a l reg ress ion o f p r e d i c t e d o n o b s e r v e d . T h e n u m b e r s refer, t o t h e d a t a i n F i g u r e 2.2 on ly . 98 66 0.93 ( S E = 0 . 0 8 ) , w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m 1.0 ( t - t e s t , P < 0 .05) . I t c o u l d be m a d e t o a p p r o a c h 1.0 m o r e c losely i f Me was set e q u a l t o 1 0 - 1 5 % o f M f o r fish larvae. Discussion T h e success o f e q u a t i o n (2.4) i n p r e d i c t i n g t h e m o r t a l i t y ra tes o f fish eggs a n d larvae i n t h e sea has i m p l i c a t i o n s f o r t h e s t u d y o f r e p r o d u c t i v e s t r a t e g i e s i n m a r i n e fishes, a n d f o r t h e s u d y o f t h e r e c r u i t m e n t p rocess . T h o s e species w h i c h release eggs i n a h i g h l y p a t c h y p a t t e r n , e.g. Pac i f ic s a r d i n e Sardinops sagax, a n d sea b r e a m , Archosargus rhomboidalis, a re , i n e f fec t , g a m b l i n g t h a t t h e h i g h p r e d a t i o n m o r t a l i t y o f t h e i r eggs a n d larvae is of fset by t h e a d v a n t a g e s o f p a t c h y egg re lease. O n e poss ib le a d v a n t a g e is p r e d a t o r a v o i d a n c e by t h e s p a w n i n g a d u l t s . A c o m p r e h e n s i v e t h e o r y o f r e p r o d u c t i v e s t r a t e g i e s i n fishes m u s t c o m b i n e h y p o t h e s e s o f egg release i n space w i t h h y p o t h e s e s o f egg release i n t i m e ( L a m b e r t a n d W a r e 1984) . T h e m o d e l i m p l i e s t h a t t u r b u l e n t m i x i n g o f t h e u p p e r sea d u e t o s t o r m s , u p w e l l i n g even ts , a n d t i d e s w o u l d p r o m o t e d i s p e r s a l o f eggs a n d larvae a n d t h e r e b y decrease p r e d a t i o n m o r t a l i t y , w h i l e s t r a t i f i c a t i o n o f t h e w a t e r w o u l d t e n d t o r e t a r d d i s p e r s a l a n d so increase p r e d a t i o n m o r t a l i t y . L a s k e r (1985) has p r o p o s e d t h a t s t r a t i f i c a t i o n w o u l d t e n d t o p r o m o t e s u r v i v a l i n l a rva l fishes by a l l o w i n g t h e f o r m a t i o n o f p a t c h e s o f f o o d o r g a n i s m s w i t h su f f i c ien t d e n s i t y t o p r o m o t e success fu l first-feeding. T h e o p t i m a l e n v i r o n m e n t f o r l a r v a l s u r v i v a l m a y b e a b a l a n c e b e t w e e n h i g h d e n s i t i e s o f a g g r e g a t e d f o o d o r g a n i s m s a n d low dens i t i es o f w e l l d i s p e r s e d l a r vae . S u c h an e n v i r o n m e n t o c c u r s w h e n e v e r d i s p e r s i n g larvae d r i f t i n t o a f r o n t b e t w e e n t w o w a t e r masses w h e r e m i x i n g is v i g o r o u s a n d b i o l o g i c a l p r o d u c t i o n is h i g h . T h e s e f r o n t s are p r e s u m e d t o de f ine a n d s u r r o u n d la rva l fish r e t e n t i o n zones ( l ies a n d S i n c l a i r 1982) . 100 C o n c l u d i n g R e m a r k s I b e g a n t h i s s t u d y w i t h t h e o r t h o d o x o p i n i o n t h a t s t a r v a t i o n was a r e a l a n d i m p o r t a n t p h e -n o m e n o n i n l a r v a l fish eco logy. M y research has c o n v i n c e d m e t h a t s t a r v a t i o n does o c c u r i n n a t u r a l p o p u l a t i o n s o f fish, a t least i n l a r va l Pac i f ic h e r r i n g , b u t t h a t i t is n o t t h e m a j o r cause o f d e a t h . T h e m o s t i m p o r t a n t cause o f d e a t h is p r e d a t i o n . I have b e c o m e a t t a c h e d t o t h i s o p i n i o n f o r t w o reasons : first, t h e m e a s u r e d r a t e o f m o r t a l i t y d u e d i r e c t l y t o s t a r v a t i o n is o n l y 1 - 2 3 % o f t h e t o t a l m o r t a l i t y r a t e f o r l a r v a l n o r t h e r n a n c h o v y a n d Pac i f i c h e r r i n g . E v e n w h e n 9 0 % o f c o h o r t s ix 7 - 2 0 m m l o n g larvae were c lass i f ied as s t a r v i n g Me was o n l y 2 3 % o f M. T h i s s u r p r i s i n g r e s u l t makes sense w h e n one cons ide rs t h e w a y i n w h i c h Ms changes w i t h X . T h e d e r i v a t i v e o f M , w i t h r e s p e c t t o X is ( f r o m e q u a t i o n (1.21)) dMe _ 1 d\ ~ < 2 o ( l - X ) ' w h i c h m e a n s t h a t dMa/d\ increases w i t h t h e r e c i p r o c a l o f ( 1 — X ) . T h e r e f o r e , A f , increases \ e r y s lowly w i t h X u p t o a b o u t X== 0 . 8 5 - 0 . 9 0 , a n d o n l y w h e n X > 0 .95 does M, b e g i n t o inc rease e x p o n e n t i a l l y . Me, b y d e f i n i t i o n , can o n l y be i m p o r t a n t w h e n m o r e t h a n 9 5 % o f a la rva l p o p u l a t i o n is s t a r v i n g t o d e a t h . I g r a n t t h a t s u c h c a t a s t r o p h i c s t a r v a t i o n is p o s s i b l e b u t I c a n n o t bel ieve t h a t i t is a c o m m o n even t . I t seems u n r e a s o n a b l e because m o s t m a r i n e fish larvae h a t c h i n t o a n e n v i r o n m e n t t h a t is r i ch i n f o o d o r g a n i s m s . O n e o f t h e s t r o n g e s t i m p r e s s i o n s o f m y field w o r k a t t h e B a m f i e l d M a r i n e S t a t i o n was t h e l u x u r i a n c e o f t h e p l a n k t o n i c l i fe i n t h e n e a r s h o r e pe lag ic zone d u r i n g t h e s p r i n g b l o o m . T h e s e c o n d reason I be l ieve s t a r v a t i o n p lays a m i n o r ro le i n l a r va l p o p u l a t i o n d y n a m i c s is t h a t t h e p r e d a t i o n - p a t c h i n e s s m o d e l is success fu l i n p r e d i c t i n g t h e m o r t a l i t y r a t e s o f fish eggs a n d larvae. T h e i d e a t h a t p r e d a t i o n a n d p a t c h i n e s s are c o r r e l a t e d is a n o l d a n d p o w e r f u l one b u t i t has n o t e n j o y e d m u c h f a v o u r a m o n g l a r v a l fish b i o l o g i s t s w h o are , o n t h e w h o l e , s t i l l firmly a t t a c h e d t o t h e c r i t i c a l p e r i o d p a r a d i g m o f l a r v a l fish s u r v i v a l . T h i s is s u r p r i s i n g because t h e s p a t i a l d i s t r i b u t i o n o f la rva l fishes is easier t o m e a s u r e t h a n t h e i r n u t r i t i o n a l s t a t u s . T h e c r i t i c a l p e r i o d h y p o t h e s i s has e x i s t e d f o r 70 years b u t o n l y i n t h e l as t t e n have ser ious a t t e m p t s b e e n m a d e t o m e a s u r e n u t r i t i o n a l s t a t u s . H o w e v e r , d u r i n g t h i s l o n g 70 year p e r i o d m a n y su rveys have b e e n p e r f o r m e d a r o u n d t h e w o r l d t h a t have d e s c r i b e d i n d e t a i l t h e h o r i z o n t a l a n d v e r t i c a l d i s t r i b u t i o n o f fish la rvae. I t seems r e a s o n a b l e t o 1 0 1 s u p p o s e t h a t p rogress i n l a r v a l fish eco logy w o u l d acce le ra te i f t h e p r e d a t i o n - p a t c h i n e s s hyp o thes is was ass igned e q u a l w e i g h t w i t h t h e c r i t i c a l p e r i o d h y p o t h e s i s . I s p e c u l a t e t h a t t h e r e l a t i o n s h i p b e t w e e n s p a t i a l d i s t r i b u t i o n a n d m o r t a l i t y m a y h o l d f o r j u v e n i l e a n d a d u l t fishes as w e l l as fish eggs a n d la rvae. I f a d u l t fishes d i f fuse o u t w a r d s f r o m a release p o i n t ac-c o r d i n g t o F i c k ' s L a w t h e n f r o m e q u a t i o n 1.20 t h e n a t u r a l m o r t a l i t y r a t e s h o u l d be i nve rse l y c o r r e l a t e d w i t h t h e d i f f u s i o n coe f f i c ien t a n d d i r e c t l y c o r r e l a t e d w i t h t h e square o f t h e d i s p e r s a l v e l o c i t y . D i f f u s i o n coe f f i c ien ts a n d d i s p e r s a l v e l o c i t i e s c a n , i n t h e o r y , be c a l c u l a t e d f r o m t a g - r e c a p t u r e e x p e r i m e n t s i f t h e p o s i t i o n s a t release a n d r e c a p t u r e o f t h e i n d i v i d u a l fish are r e c o r d e d . T h e r e f o r e , i t may b e poss ib le t h a t some o f . t h e v a r i a n c e o f t h e n a t u r a l m o r t a l i t y ra tes t h a t is n o t a c c o u n t e d f o r by d r y w e i g h t m a y be a c c o u n t e d f o r by t h e spec ies-spec i f i c r a t e s o f d i f f u s i o n a n d d i s p e r s a l v e l o c i t y . T h e s e h y p o t h e s e s , a n d o t h e r s t h a t l i n k t h e p o p u l a t i o n p a r a m e t e r s o f a d u l t fishes w i t h t h e i r s p a t i a l d i s t r i b u t i o n , have yet t o b e t e s t e d . 102 Literature Cited A A S E N , 0 . 1952. T h e L u s t e r f j o r d h e r r i n g . F i s k . D i r . S k r . , Ser. H a v u n d e r s . 10(2) . A B L E , K . W . 1978. I c h t h y o p l a n k t o n o f t h e S t . L a w r e n c e e s t u a r y : c o m p o s i t i o n , d i s t r i b u t i o n , a n d a b u n d a n c e . J . F i s h . Res . B o a r d C a n a d a 3 5 : 1 5 1 8 - 1 5 3 1 . A H L S T R O M , E . H . 1954. D i s t r i b u t i o n a n d a b u n d a n c e o f eggs a n d la rva l p o p u l a t i o n s o f t h e Paci f ic s a r d i n e . F i s h . B u l l . , U .S . 5 6 : 8 3 - 1 4 0 . 1976. M a i n t e n a n c e o f q u a l i t y i n f i sh eggs a n d la rvae co l l ec ted d u r i n g p l a n k t o n h a u l s , p . 3 1 3 - 3 1 8 . In H . F . S t e e d m a n [Ed. ] Z o o p l a n k t o n fixation a n d p r e s e r v a t i o n . M o n o g r a p h s i n O c e a n o g r a p h i c M e t h o d o l o g y , v o l u m e 4 . A L D E R D I C E , D . F . a n d A . S. H O U R S T O N . 1985. Fac to rs i n f l u e n c i n g d e v e l o p m e n t a n d s u r v i v a l o f Pac i f i c h e r r i n g (Clupea harengus pallasi) eggs a n d larvae t o t h e b e g i n n i n g o f exogenous f e e d i n g . C a n . J . F i s h . A q u a t . Sc i . 4 2 ( S u p p l . l ) : 5 6 - 6 8 . A L D E R D I C E , D . F . a n d F . P. J . V E L S O N . 1 9 7 1 . S o m e effects o f s a l i n i t y a n d t e m p e r a t u r e o n e a r l y d e v e l o p m e n t o f P a c i f i c h e r r i n g (Clupea pallasi). J . F i s h . Res . B o a r d C a n a d a 2 8 : 1 5 4 5 - 1 5 6 2 . A L L E N , K . R . , a n d G . P. K I R K W O O D . 1977. F u r t h e r d e v e l o p m e n t o f s p e r m w h a l e p o p u l a t i o n m o d e l s . I n t . W h a l i n g C o m m . R e p . 2 7 : 1 0 6 - 1 1 2 . A M A R A T U N G A , T . , M . R O B E R G E , a n d L . W O O D . 1978. A n o u t l i n e o f t h e fishery a n d b i o l o g y o f t h e s h o r t - f i n n e d s q u i d , Ilex illecebrdsus, i n E a s t e r n C a n a d a , p . 2.1-2.17 In N . B a l c h , T . A m a r a t u n g a , a n d R . K . O ' D o r [eds.] P r o c e e d i n g s o f t h e w o r k s h o p o n Hex illecebrosus. T e c h . R e p . F i s h . M a r . Se rv . C a n a d a N o . 833 . A N D E R S O N , J . T . 1984. E a r l y l i fe h i s t o r y o f r e d f i s h (Sebastes spp . ) o n F l e m i s h C a p . C a n . J . F i s h . A q u a t . Sc i . 4 1 : 1 1 0 6 - 1 1 1 6 . A R T H U R , D . K . 1 9 7 6 . F o o d a n d f e e d i n g o f larvae o f t h r e e fishes o c c u r r i n g i n t h e C a l i f o r n i a C u r r e n t , Sardinops sagax, Engraulis mordax, a n d Trachurus symmetricus. F i s h . B u l l . , U . S . 7 4 : 5 1 7 - 5 3 0 . 103 A T C H L E Y , W . R . a n d D . A N D E R S O N . 1978. R a t i o s a n d t h e s t a t i s t i c a l ana lys is o f b i o l o g i c a l d a t a . S y s t . Z o o l . 2 7 : 7 1 - 7 8 . A T C H L E Y , W . R . , G . T . G A S K I N S a n d D . A N D E R S O N . 1976. S t a t i s t i c a l p r o p e r t i e s o f r a t i o s . I . E m p i r i c a l r e s u l t s . S y s t . Z o o l . 2 5 : 1 3 7 - 1 4 8 . B A G E N A L , T . B . 1 9 7 1 . T h e i n t e r r e l a t i o n o f t h e size o f f i sh eggs, t h e d a t e o f s p a w n i n g a n d t h e p r o d u c t i o n cyc le . J . F i s h B i o l . 3 : 2 0 7 - 2 1 9 . B A G G E , 0. 1974. T h e D a n i s h c o d fishery i n t h e B a l t i c 1 9 5 7 - 7 0 . R a p p . P.-v. R e u n . C o n s . in t . E x p l o r . M e r 1 6 6 : 1 0 3 - 1 0 5 . B A I L E Y , K . M . 1 9 8 1 . L a r v a l t r a n s p o r t a n d r e c r u i t m e n t o f Pac i f i c h a k e , Merluccius produetus. M a r . E c o l . P r o g . Ser . 6 : 1 - 9 . 1982. T h e e a r l y l i fe h i s t o r y o f t h e Pac i f i c h a k e , Merluccius produetus. F i s h . B u l l . , U . S . 8 0 : 5 8 9 - 5 9 8 . B A I L E Y , R . S. 1974. T h e l i fe h i s t o r y a n d b i o l o g y o f b l u e w h i t i n g i n t h e n o r t h e a s t A t l a n t i c . I . T h e p l a n k t o n i c phase i n t h e R o c k a l l a r e a . M a r . R e s . ( S c o t l a n d ) 1 9 7 4 ( l ) : l - 2 9 . 1980. P r o b l e m s i n t h e m a n a g e m e n t o f s h o r t - l i v e d pe lag ic fish as e x e m p l i f i e d by N o r t h Sea s p r a t . R a p p . P.-v. R e u n . C o n s . i n t . E x p l o r . M e r 1 7 7 : 4 7 7 - 4 8 8 . B A L B O N T I N , F . S., S. D E S I L V A a n d K . F . E H R L I C H . 1973. A c o m p a r a t i v e s t u d y o f a n a t o m i c a l a n d c h e m i c a l c h a r a c t e r i s t i c s o f r e a r e d a n d w i l d h e r r i n g . A q u a c u l t u r e 2 : 2 1 7 - 2 4 0 . B A N N I S T E R , R . C . A . , D . H A R D I N G , a n d S. J . L O C K W O O D . 1974. L a r v a l m o r t a l i t y a n d subsequen t year class s t r e n g t h i n t h e p la ice (Pleuronectes platesaa L . ) , p . 21-37 . In J . H . S. B l a x t e r [ed.] T h e E a r l y L i f e H i s t o r y o f F i s h . S p r i n g e r - V e r l a g , B e r l i n . B A R N A B E , G . , F . B O U L I N E A U - C O A T A N E A a n d F . R E N E . 1976. C h r o n o l o g i e de l a m o r p h o g e n e s e chez le l o u p au b a r Dicentrarchus labrax ( L . ) (Pisces, S e r r a n i d a e ) o b t e n u p a r r e p r o d u c t i o n a r t i f i -c ie l le . A q u a c u l t u r e 8 : 3 5 1 - 3 6 3 . B A Y L I F F , W . H . 1966. P o p u l a t i o n d y n a m i c s o f t h e a n c h o v e t a , Cetengraulis mysticetus, i n t h e G u l f o f P a n a m a , as d e t e r m i n e d b y t a g g i n g e x p e r i m e n t s . B u l l . I n t e r - A m . T r o p . T u n a C o m m . 1 1 : 1 - 2 8 8 . 104 B E R K E S , F . 1977. P r o d u c t i o n o f t h e e u p h a u s i i d c r u s t a c e a n Thysanoeasa raschi i n t h e G u l f o f S t , L a w r e n c e . J . F i s h . Res . B o a r d C a n a d a 3 4 : 4 4 3 - 4 4 6 . B E R R I E N , P. L . , N . A . N A P L E S f a n d M . R . P E N N I N G T O N . 1 9 8 1 . 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P O P O V A . 1974. A r t i f i c i a l r e a r i n g o f t h e b l a c k sea t u r b o t larvae Scophthalmus maeoticus. A q u a c u l t u r e 4 : 3 2 9 - 3 4 0 . S T E P I E N , W . P., J r . 1976. F e e d i n g o f l a b o r a t o r y - r e a r e d larvae o f t h e sea b r e a m Archosargus rhom-boidalis ( S p a r i d a e ) . M a r . B i o l . 3 8 : 1 - 1 6 . 126 S T E V E N S O N , J . C . 1962. D i s t r i b u t i o n a n d s u r v i v a l o f h e r r i n g larvae (Clupea pallasi Va lc iennes ) i n B r i t i s h C o l u m b i a w a t e r s . J . F i s h . R e s . B o a r d C a n . 1 9 : 7 3 5 - 8 1 0 . S T R U H S A K E R , J . W . , D . Y . H A S H I M O T O , S. M . G I R A R D , F . T . P R I O R a n d T . D . C O O N E Y . 1973. E f f e c t o f a n t i b i o t i c s o n o n s u r v i v a l o f c a r a n g i d fish larvae (Caranx mate r e a r e d i n t h e l a b o r a t o r y . A q u a c u l t u r e 2 : 5 3 - 8 8 . S U D A , A . a n d S. K U M E . 1967. S u r v i v a l a n d r e c r u i t m e n t o f b igeye t u n a i n t h e Paci f ic O c e a n , e s t i m a t e d b y t h e d a t a o f t u n a l o n g l i n e c a t c h . R e p . N a n k e i R e g . F i s h . R e s . L a b . 2 5 : 9 1 - 1 0 3 . S U D J A S T A N I , T . 1974. T h e species of Rastrelliger i n t h e J a v a Sea, t h e i r t a x o n o m y , m o r p h o m e t r y a n d p o p u l a t i o n d y n a m i c s . M . S c . T h e s i s , Z o o l o g y D e p t . , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , B r i t i s h C o l u m b i a , C a n a d a . T A L B O T , G . B . a n d S. I . J O H N S O N . 1972. R e a r i n g Pac i f i c h e r r i n g i n t h e l a b o r a t o r y . P r o g . F i s h . - C u l t . 3 4 : 2 - 7 . T A N A K A , S. 1955. E s t i m a t i o n o f t h e a b u n d a n c e o f t h e eggs o f fish such as s a r d i n e — I I . A b u n d a n c e o f t h e eggs o f t h e Japanese s a r d i n e i n t h e w e s t e r n a rea o f K y u s h u i n 1952. B u l l . J a p . Soc. Sc i . F i s h . 2 1 : 3 9 0 - 3 9 6 . T A N I G U C H I , A . K . 1 9 8 1 . S u r v i v a l a n d g r o w t h o f l a r v a l s p o t t e d s e a t r o u t (Cynoscion nebulosus) i n r e l a t i o n t o t e m p e r a t u r e , p r e y a b u n d a n c e a n d s t o c k i n g dens i t i es . R a p p . P.-v. R e u n . C o n s . i n t . E x p l o r . m e r 1 7 8 : 5 0 7 - 5 0 8 . T A U B E R T , B . D . a n d D . W . C O B L E . 1977. D a i l y r i n g s i n o t o l i t h s o f t h r e e species o f Lepomis a n d Tilapia mossambica. J . F i s h . R e s . B o a r d C a n a d a 3 4 : 3 3 2 - 3 4 0 . T A Y L O R , F . H . C . 1964. L i f e h i s t o r y a n d p resen t s t a t u s o f B r i t i s h C o l u m b i a h e r r i n g s t o c k s . F i s h . Res . B o a r d C a n a d a B u l l . 143 :81p . T H E I L A C K E R , G . H . 1978. E f f e c t o f s t a r v a t i o n o n t h e h i s t o l o g i c a l a n d m o r p h o l o g i c a l c h a r a c t e r i s t i c s o f j a c k m a c k e r e l , Trachurus symmetricus, l a r vae . F i s h . B u l l . , U . S . 76 :403-414 . 127 1980a. C h a n g e s i n b o d y m e a s u r e m e n t s o f l a r v a l n o r t h e r n a n c h o v y , Engraulis mordax, a n d o t h e r fishes d u e t o h a n d l i n g a n d p r e s e r v a t i o n . F i s h . B u l l . , U .S . 7 8 : 6 8 5 - 6 9 2 . 1980b . R e a r i n g c o n t a i n e r size af fects m o r p h o l o g y a n d n u t r i t i o n a l c o n d i t i o n o f l a rva l j ack m a c k e r e l , Trachurus symmetricus. F i s h . B u l l . , U .S . 7 8 : 7 8 7 - 7 9 1 . 1 9 8 1 . E f f e c t o f f e e d i n g h i s t o r y a n d egg size o n t h e m o r p h o l o g y o f jack m a c k e r e l , Trachurus symmetricus, l a r v a e . R a p p . P.-v. C o n s . i n t . E x p l o r . M e r 1 7 8 : 4 3 2 - 4 4 0 . T H E I L A C K E R , G . T . a n d K . D O R S E Y . 1980. L a r v a l fish d i ve rs i t y , a s u m m a r y o f l a b o r a t o r y a n d field r e s e a r c h , p . 1 0 5 - 1 4 2 . In W o r k s h o p o n t h e ef fect o f e n v i r o n m e n t a l v a r i a t i o n o n t h e s u r v i v a l o f l a r v a l pe lag ic fishes, W a s h i n g t o n , D . C . , F A O , I n t e r g o v e r n m e n t a l O c e a n o g r a p h i c C o m m i s s i o n W o r k s h o p R e p o r t N o . 28. T H O M A S , J . C . 1968. M a n a g e m e n t o f t h e w h i t e seabass (Cynoscion nobilis) i n C a l i f o r n i a wa te rs . C a l i f . D e p t . F i s h G a m e , F i s h . B u l l . N o . 142. T H O M P S O N , R . a n d J . L . M U N R O . 1978. A s p e c t s o f t h e b i o l o g y a n d eco logy o f C a r i b b e a n r e e f fishes: S e r r a n i d a e ( h i n d s a n d g r o u p e r s ) . J . F i s h . B i o l . 1 2 : 1 1 5 - 1 4 6 . T O W N S E N D , D . W a n d J. J . G R A H A M . 1 9 8 1 . G r o w t h a n d age s t r u c t u r e o f la rva l A t l a n t i c h e r r i n g , Clupea harengus harengus, i n t h e Sheepsco t R i v e r e s t u a r y , M a i n e , as d e t e r m i n e d by d a i l y g r o w t h i n c r e m e n t s i n o t o l i t h s . F i s h . B u l l . , U .S . 7 9 : 1 2 3 - 1 3 0 . U C H T Y A M A , J . H . a n d P. S T R U H S A K E R . 1 9 8 1 . A g e a n d g r o w t h o f s k i p j a c k t u n a , Katsuwonnus pelamis, a n d y e l l o w f i n t u n a , Thunnus albacares, as i n d i c a t e d b y d a i l y g r o w t h i n c r e m e n t s o f sag i t -t a e . F i s h . B u l l . , U . S . 7 9 : 1 5 1 - 1 6 2 . U M E D A , S. a n d A . O C H O A I . 1975. O n t h e h i s t o l o g i c a l s t r u c t u r e a n d f u n c t i o n o f d igest ive o r g a n s o f t h e f e d a n d s t a r v e d larvae o f t h e y e l l o w t a i l , Seriola quinqueradiata. ( I n J p n . , E n g l , s u m m . ) J a p . J . I c h t h y o l . 2 1 : 2 1 3 - 2 1 9 . U R S I N , E . 1967. A m a t h e m a t i c a l m o d e l o f s o m e aspec ts o f fish g r o w t h , r e s p i r a t i o n , a n d m o r t a l i t y . J . F i s h . R e s . B o a r d C a n a d a 3 2 : 2 5 0 3 - 2 5 1 2 . 128 V I C T O R , B . C . 1982. D a i l y g r o w t h i n c r e m e n t s a n d r e c r u i t m e n t i n t w o c o r a l - r e e f wrasses , Thalaasoma bifasciatum, a n d Haiichoeres birattus. M a r . B i o l . 7 1 : 2 0 3 - 2 0 8 . V L L E L A , M . H . a n d J . J . Z I J L S T R A . 1 9 7 1 . O n t h e c o n d i t i o n o f h e r r i n g larvae i n t h e c e n t r a l a n d s o u t h e r n N o r t h Sea. R a p p . P.-v. R e u n . C o n s . P e r m . i n t . E x p l o r . M e r 1 6 0 : 1 3 7 - 1 4 1 . V O O R E N , C . M . 1977. G r o w t h a n d m o r t a l i t y o f t a r a k i h i (Pisces: C h e i l o d a c t y l i d a e ) i n l i g h t l y fishes p o p u l a t i o n s . N . Z . J . M a r . F r e s h w . Res . 1 1 : 1 - 2 2 . W A R E , D . M . 1975. R e l a t i o n b e t w e e n egg size, g r o w t h , a n d n a t u r a l m o r t a l i t y o f l a r v a l fish. J . F i s h . Res . B o a r d C a n . 3 2 : 2 5 0 3 - 2 5 1 2 . W A R E , D . M . a n d T . C . L A M B E R T . 1985. E a r l y l i fe h i s t o r y o f A t l a n t i c m a c k e r e l (Scomber scombrus) i n t h e s o u t h e r n G u l f o f S t . L a w r e n c e . C a n . J . F i s h . A q u a t . Sc i . 4 2 : 5 7 7 - 5 9 2 . W A R E , D . M . , B . R . D E M E N D I O L A a n d D . S. N E W H O U S E . 1 9 8 1 . B e h a v i o u r o f first-feeding P e r u v i a n a n c h o v e t a l a r v a e , Engraulis ringens. R a p p . P.-v. R e u n . C o n s . i n t . E x p l o r . M e r 178 :467—474. W A T A N A B E , T . 1970 . M o r p h o l o g y a n d eco logy o f e a r l y stages o f l i fe i n Japanese c o m m o n m a c k e r e l , Scomber japonicus H o u t t u y n , w i t h spec ia l re fe rence t o fluctuations o f p o p u l a t i o n s . B u l l . T o k a i R e g . F i s h . R e s . L a b . 6 2 : 1 - 2 8 3 . W E B B , B . F . 1972. F i s h p o p u l a t i o n s o f t h e A v o n - H e a t h c o t e es tua ry . 1 . G e n e r a l ecology, d i s t r i b u t i o n , a n d l e n g t h - f r e q u e n c y . N . Z . J . M a r . F r e s h w . Res . 6 : 5 7 0 - 6 0 1 . W E I N S T E I N , M . P., S. L . W E I S S , R . G . H O D S O N , a n d L . R . G E R R Y . 1980. R e t e n t i o n o f t h r e e t a x a o f p o s t l a r v a l fishes i n a n i n t e n s i v e l y flushed e s t u a r y , C a p e Fear R i v e r , N o r t h C a r o l i n a . U .S . F i s h . B u l l . 7 8 : 4 1 9 ^ 3 6 . W E R N E R , R . G . a n d J . H . S. B L A X T E R . 1980. G r o w t h a n d s u r v i v a l o f l a r va l h e r r i n g (Clupea harengus) i n r e l a t i o n t o p r e y d e n s i t y . C a n . J . F i s h . A q u a t . Sc i . 3 7 : 1 0 6 3 - 1 0 6 9 . W E S T E R N H A G E N , H . v o n a n d H . R O S E N T H A L 1975 . R e a r i n g a n d s p a w n i n g s i g a n i d s (Pisces: Te leos te i ) i n a c losed seawa te r s y s t e m . H e l g o l a n d e r w i s s . M e e r e s u n t e r s . 2 7 : 1 - 1 8 . 129 1 9 8 1 . O n c o n d i t i o n f a c t o r m e a s u r e m e n t s i n Pac i f i c h e r r i n g l a r vae . H e l g o l a n d e r w iss . M e e r e s u n t e r s . 3 4 : 2 5 7 - 2 6 2 . W E S T R H E D v l , S. J . a n d V . A . S N Y T K O . 1974. L e n g t h - w e i g h t r e l a t i o n s o f some Paci f ic ocean perch (Sebastes alutus) i n t h e N o r t h Pac i f i c O c e a n . J . F i s h . Res . B o a r d C a n a d a 3 1 : 3 6 3 - 3 6 6 . W H I T E , M . L . a n d M . E . C H I T T E N D E N , J r . 1977. A g e d e t e r m i n a t i o n , r e p r o d u c t i o n a n d p o p u l a t i o n d y n a m i c s o f t h e A t l a n t i c c r o a k e r , Micropogonias undulatus. F i s h . B u l l . , U . S . 7 5 : 1 0 9 - 1 2 3 . W I L L I A M S , B . K . 1983. Some o b s e r v a t i o n s o n t h e use o f d i s c r i m i n a n t ana l ys i s i n eco logy E c o l o g y 6 4 : 1 2 8 3 - 1 2 9 1 . W I L L I A M S , G . C . a n d D . C . W I L L I A M S . 1973. M o r t a l i t y r a t e s o f p l a n k t o n i c eggs o f t h e c u n n e r , Totogolabrus adspersus ( W a l b a u m ) , i n L o n g I s l a n d S o u n d , p . 181-189. In A . L . P a c h e c o [ed. ] . P r o c e e d i n g s o f a w o r k s h o p o n egg, l a r v a l a n d j u v e n i l e stages o f f i sh i n A t l a n t i c coas t e s t u a r i e s . U .S . N a t i o n a l M a r i n e F i she r i es Serv i ce , M i d d l e A t l a n t i c C o a s t a l F i s h e r i e s C e n t e r T e c h n i c a l P u b l i c a t i o n N o . 1 . W Y A T T , T . 1972. Some effects o f f o o d d e n s i t y o n t h e g r o w t h a n d b e h a v i o u r o f p la ice la rvae. M a r . B i o l . 1 4 : 2 1 0 - 2 1 6 . Y O U N G , P. H . 1963. T h e ke lp bass (Paralabrax elathrus) a n d i t s fishery, 1 9 4 7 - 1 9 5 8 . C a l i f . D e p t . F i s h G a m e , F i s h . B u l l . N o . 172. Z U K O W S K I , C . 1972. G r o w t h a n d m o r t a l i t y o f t h e A t l a n t i c a r g e n t i n e , Argentina silus A s c a n i u s , o n t h e N o v a S c o t i a B a n k s . I C N A F R e s . B u l l . 9 : 1 0 9 - 1 1 5 . Z W E I F E L , J . R . a n d R . L A S K E R . 1976. P r e h a t c h a n d p o s t h a t c h g r o w t h o f fishes—a g e n e r a l m o d e l . F i s h . B u l l . , U . S . 7 4 : 6 0 9 - 6 2 1 . Z W E I F E L , J . R . a n d P. E . S M I T H . 1 9 8 1 . E s t i m a t e s o f a b u n d a n c e a n d m o r t a l i t y o f la rva l anchov ies (1951-75) : a p p l i c a t i o n o f a n e w m e t h o d . R a p p . P.-v. R e u n . C o n s . i n t . E x p l o r . M e r 1 7 8 : 2 4 8 - 2 5 9 . 130 Appendix A Effects of Delayed Feeding and Temperature on the Age of Irreversible Starvation and on the Rates of Growth and Mortality of Larval Pacific Herring Appendix Summary T h e t i m e p e r i o d s f r o m e x h a u s t i o n o f t h e y o l k t o t h e age o f i r revers ib le s t a r v a t i o n f o r Pac i f ic h e r r i n g la rvae were 8.5, 7.0 a n d 6.0 d a t 6 ° , 8 ° , a n d 1 0 ° C , r e s p e c t i v e l y . T h e s e p e r i o d s are w i t h i n t h e r a n g e p r e v i o u s l y m e a s u r e d fo r A t l a n t i c h e r r i n g larvae a n d o t h e r t e m p e r a t e zone fish spec ies ; t h e y are l o n g c o m p a r e d t o t h e p e r i o d s fo r t r o p i c a l spec ies. T h e v a r i a t i o n i n t h e l e n g t h o f t h i s p e r i o d is d u e a l m o s t e n t i r e l y t o t e m p e r a t u r e ; t h e n a t u r a l l o g a r i t h m o f t h e t i m e p e r i o d f r o m f e r t i l i z a t i o n t o i r revers ib le s t a r v a t i o n is h i g h l y c o r r e l a t e d ( r = 0 . 9 1 ) w i t h t h e m e a n r e a r i n g t e m p e r a t u r e f o r 25 species o f p e l a g i c m a r i n e fish la rvae . T h e ra tes o f g r o w t h a n d m o r t a l i t y , m e a s u r e d f o r 26 e x p e r i m e n t a l p o p u l a t i o n s o f Pac i f i c h e r r i n g la rvae rea red a t 6 ° , 8 ° , a n d 10° a n d t e n ages o f de layed first f e e d i n g , decreased a n d i n c r e a s e d , r e s p e c t i v e l y w i t h i n c r e a s i n g age o f first f e e d i n g a n d i n c r e a s i n g t e m p e r a t u r e . T h e s e r a t e s , a d j u s t e d f o r t h e effects o f r e a r i n g c o n d i t i o n s , were c o m p a r e d w i t h t h e ra tes f o r n a t u r a l p o p u l a t i o n s o f h e r r i n g l a r vae . G r o w t h is g e n e r a l l y f a s t e r i n t h e sea t h a n i n e x p e r i m e n t a l enc losures . T w o o f t h e eleven e s t i m a t e s o f n a t u r a l m o r t a l i t y r a t e were h i g h e n o u g h t o i n d i c a t e poss ib le c a t a s t r o p h i c mass s t a r v a t i o n . T h i s is c o n s i s t e n t w i t h H j o r t ' s c r i t i c a l p e r i o d c o n c e p t o f year class f o r m a t i o n a n d i t suggests t h a t m a s s s t a r v a t i o n o c c u r s i n 1 8 - 3 6 % o f t h e n a t u r a l p o p u l a t i o n s o f first f e e d i n g h e r r i n g larvae. Intro duction H j o r t (1914, 1926) p r o p o s e d t h a t c a t a s t r o p h i c s t a r v a t i o n o f first f e e d i n g m a r i n e fish larvae is p r i m a r i l y r e s p o n s i b l e f o r t h e observed v a r i a t i o n i n t h e a b u n d a n c e o f r e c r u i t s . T h i s c r i t i c a l p e r i o d c o n c e p t has severa l c o r o l l a r i e s : first, t h e p r o b a b i l i t y o f s t a r v a t i o n o f a larvae s h o u l d be c o r r e l a t e d w i t h t h e l e n g t h o f t i m e t h a t is ava i l ab le t o t h e larvae t o l e a r n h o w t o feed successfu l ly . S e c o n d , s ince w a t e r t e m p e r a t u r e af fects m e t a b o l i c ra tes i n m a r i n e p o i k i l o t h e r m s , t h e n t e m p e r a t u r e s h o u l d a f fect t h e d u r a t i o n o f t h e l e a r n i n g p e r i o d a n d , t h e r e f o r e , t h e average s u r v i v a l r a t e o f t h e first f e e d i n g larvae. 1 3 1 T h i r d , t h e presence o f i r reve rs ib le s t a r v a t i o n s h o u l d be re f l ec ted as an increase i n t h e s lope o f t h e c a t c h cu rve a t t h e i m m e d i a t e p o s t - y o l k - s a c s tage . . F o u r t h , t h e mass m o r t a l i t y o f i r r e v e r s i b l y s t a r v e d larvae s h o u l d be r e f l e c t e d as a la rge inc rease i n t h e m a g n i t u d e o f t h e average m o r t a l i t y r a t e over t h i s p e r i o d . M a r r (1956) a n d M a y (1974) t e s t e d t h e t h i r d c o r r o l l a r y by e x a m i n i n g t h e p u b l i s h e d su rv i va l cu rves o f n a t u r a l p o p u l a t i o n s o f m a r i n e fish larvae f o r r a p i d increases i n m o r t a l i t y a t t h e e n d o f t h e yo l k -sac s tage . B o t h a u t h o r s f o u n d severa l cases, n o n e o f t h e m h e r r i n g la rvae, i n w h i c h t h e average dens i t i es d i d decrease a b r u p t l y i n t h e i m m e d i a t e pos t - yo l k -sac s tage , b u t t h e y p o i n t e d o u t t h a t t h i s m a y have b e e n p r o d u c e d by e r r o r s i n t h e m e t h o d o l o g y o f s a m p l i n g o r by t h e p a t c h y d i s t r i b u t i o n o f t h e la rvae , as w e l l as b y i r reve rs ib le s t a r v a t i o n . M a y c o n c l u d e d t h a t t h e dens i t i es o f n a t u r a l p o p u l a t i o n s o f m a r i n e fish larvae have r a r e l y b e e n m e a s u r e d w i t h e n o u g h a c c u r a c y t o a l low any r o b u s t c o n c l u s i o n s t o be d r a w n f r o m t h e shape o f t h e s u r v i v a l cu rves . N e i t h e r M a y n o r M a r r used t h e m a g n i t u d e o f t h e average r a t e s o f g r o w t h a n d m o r t a l i t y as a n i n d e x o f s t a r v a t i o n . T h i s a p p e n d i x r e p o r t s a series o f e x p e r i m e n t s des igned t o e x a m i n e t h e first, s e c o n d , a n d f o u r t h co ro l l a r ies o f H j o r t ' s h y p o t h e s i s f o r Pac i f i c h e r r i n g larvae i n p a r t i c u l a r a n d Pac i f i c a n d A t l a n t i c h e r r i n g larvae i n g e n e r a l . T h e first p a r t o f t h e a p p e n d i x r e p o r t s t h e t i m e p e r i o d s f r o m f e r t i l i z a t i o n t o h a t c h , y o l k e x h a u s t i o n , a n d i r r e v e r s i b l e s t a r v a t i o n fo r P a c i f i c h e r r i n g larvae r e a r e d a t t h r e e t e m p e r a t u r e s : 6° , 8 ° , a n d 1 0 ° C . T h e s e p e r i o d s are c o m p a r e d w i t h t hose o f o t h e r species o f pe lag i c m a r i n e fish larvae i n o r d e r t o d e t e r m i n e t h e re la t i ve s u s c e p t i b i l i t y o f Pac i f i c h e r r i n g larvae t o i r r e v e r s i b l e s t a r v a t i o n . T h e second p a r t o f t h i s a p p e n d i x m e a s u r e s t h e r e l a t i o n s h i p s b e t w e e n t h e average ra tes o f g r o w t h a n d m o r t a l i t y a n d t h e degree o f s t a r v a t i o n e x p e r i e n c e d b y e x p e r i m e n t a l p o p u l a t i o n s o f Pac i f i c h e r r i n g la rvae . T h e m a g n i t u d e o f t h e s t a r v a t i o n was v a r i e d b y i n c r e a s i n g t h e age a t first f e e d i n g . T h e g r o w t h a n d m o r t a l i t y r a t e d o f these e x p e r i m e n t a l p o p u l a t i o n s were a d j u s t e d f o r t h e ef fects o f t h e r e a r i n g c o n d i t i o n s a n d t h e n t h e y were c o m p a r e d t o t h e g r o w t h a n d m o r t a l i t y r a t e s o f n a t u r a l . p o p u l a t i o n s o f Pac i f i c a n d A t l a n t i c h e r r i n g la rvae , i n o r d e r t o i n f e r t h e e q u i v a l e n t age o f first f e e d i n g . Materials and Methods E g g I n c u b a t i o n G a m e t e s w e r e o b t a i n e d o n 3 1 M a r c h , 1983, f r o m t h r e e fema les a n d t w o m a l e s t h a t h a d been c a p t u r e d i n t h e S t r a i t o f G e o r g i a by p e r s o n n e l f r o m t h e Paci f ic B i o l o g i c a l S t a t i o n , N a n a i m o , B r i t i s h 132 C o l u m b i a . T h e s e fish were assumed t o b e l o n g t o t h e lower east coast s p a w n i n g s tock ( T a y l o r 1964) . T h e eggs were s t r i p p e d o n t o glass p l a t e s a n d f e r t i l i z e d by d i p p i n g t h e m in to a s o l u t i o n o f m i l t a n d seawate r . T h e y were t h e n s p l i t i n t o t h r e e e q u a l g r o u p s a n d i n c u b a t e d a t 6 ° , 8 ° , a n d 10° C i n a l a b o r a t o r y a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , B . C . T h e s e t e m p e r a t u r e s cover t h e average t e m p e r a t u r e r a n g e e n c o u n t e r e d by Pac i f i c h e r r i n g la rvae, 5-10° C , ( A l d e r d i c e a n d Velsen 1971) , o n t h e B r i t i s h C o l u m b i a coas t . T h e t e m p e r a t u r e o f t h e r e c i r c u l a t i n g seawate r s y s t e m was 6 . ( P C a n d t h i s was r a i s e d t o 8° a n d 10° C b y d e c r e a s i n g t h e flowthrough r a t e i n t o t h e w a t e r t a b l e s t h a t h e l d t h e i n c u b a t i o n a q u a r i a . T h e t e m p e r a t u r e s were k e p t c o n s t a n t by f r e q u e n t a d j u s t m e n t s o f t h e flowthrough r a t e a n d b y h o l d i n g t h e a q u a r i a i n la rge w a t e r t a b l e s so as t o b u f f e r s h o r t - t e r m w a t e r t e m p e r a t u r e changes c a u s e d b y changes i n t h e a i r t e m p e r a t u r e o f t h e l a b o r a t o r y . W a t e r t e m p e r a t u r e s were r e c o r d e d t w i c e d a i l y a n d t h e m e a n s were 6.2 ( S D = 0 . 3 ) , 8.3 ( S D = 0 . 6 ) , a n d 10.3 ( S D = 0 . 7 ) . T h e s a l i n i t y was 2 6%p a n d t h e l i g h t cyc le was 10 h o u r s l i g h t : 1 4 h o u r s d a r k . E x p e r i m e n t a l A p p a r a t u s N e w l y h a t c h e d la rvae were t r a n s f e r r e d b y p i p e t t e f r o m t h e i n c u b a t i o n a q u a r i a t o t h e t h r e e t e s t u n i t s . T h e h a t c h i n g p e r i o d l a s t e d 3 days a n d t r a n s f e r s were d o n e tw ice each day. Each t e s t u n i t c o n s i s t e d o f 12 w h i t e , t r a n s l u c e n t p l a s t i c c o n t a i n e r s i n a w a t e r t a b l e . E a c h c o n t a i n e r h e l d 3 1 a n d t w o h u n d r e d were c o u n t e d i n t o each g i v i n g a d e n s i t y o f 67 1 _ 1 . T h e la rvae i n t h e first 8 b o t t l e s o r t r e a t m e n t s were first f e d a t 0 - 1 4 d p o s t h a t c h a t 2 d i n t e r v a l s , a n a d d i t i o n a l t r e a t m e n t was first f e d a t day 18 i n t h e 6 ° C t e s t u n i t a n d a n o t h e r was first f e d a t day 16 i n t h e 8 ° C t e s t u n i t . T h e larvae i n t h e r e m a i n i n g t h r e e b o t t l e s were s t a r v e d f r o m h a t c h t o d e a t h . O n e o f t h e m was m o n i t o r e d fo r m o r t a l i t y a n d t h e o t h e r t w o w e r e o n l y used as reservo i rs o f s t a r v i n g larvae t o p r o v i d e d a i l y samp les f o r l e n g t h a n d w e i g h t m e a s u r e m e n t . T h e las t t r e a t m e n t was b e g u n o n day 14 because p r e l i m i n a r y obse rva t i ons o f s t a r v i n g la rvae e x p o s e d b r i e f l y t o f o o d a t 10° C h a d s h o w n t h a t f e e d i n g s t o p p e d a f t e r t h e larvae h a d f a l l e n o u t o f t h e w a t e r c o l u m n . F a l l o u t was c o m p l e t e o n day 12 a t 10° C . T r e a t m e n t s 1-8 were g iven e n o u g h n a u p l i i t o m a i n t a i n a p a t c h o f t h e m i n t h e b o t t l e a t a l l t i m e s a f t e r t h e y h a d c o m m e n c e d f e e d i n g . T h e s w i m m i n g a n d f e e d i n g b e h a v i o u r s o f t h e larvae i n each o f t h e t r e a t m e n t s was observed a t i n t e r v a l s d u r i n g each day. Corpses were s i p h o n e d f r o m t h e floors o f t h e b o t t l e s every s e c o n d o r t h i r d day a n d c o u n t e d . A l a r v a was c o n s i d e r e d d e a d w h e n i t d i d n o t r e s p o n d t o w a t e r c u r r e n t s o r 133 gent le p r o b i n g . Feces a n d d e a d Artemia n a u p l i i were r e m o v e d a t t h e same t i m e . O x y g e n a t e d w a t e r was p r o v i d e d b y r e p l a c i n g one h a l f o f t h e seawater i n each b o t t l e w i t h f r e s h seawate r every second day . A t r e a t m e n t was e n d e d w h e n e i t h e r a l l t h e larvae h a d d i e d o r w h e n t h e p e r i o d o f s t a r v a t i o n i n d u c e d m o r t a l i t y h a d e n d e d . T h i s was c o n s i d e r e d t o have o c c u r r e d w h e n t h e m a j o r i t y o f t h e corpses were g r e a t e r t h a n 10 m m i n l e n g t h . L a r v a e less t h a n 10 m m l o n g d i e d o f i r r e w r s i b l e s t a r v a t i o n b u t t h e la rge r ones h a d o b v i o u s l y f e d a n d g r o w n d u r i n g t h e e x p e r i m e n t so t h a t t h e i r d e a t h s m u s t have b e e n caused b y f a c t o r s o t h e r t h a n i r reve rs ib le s t a r v a t i o n . S a m p l i n g S a m p l e s o f n o n - f e e d i n g f i sh were t a k e n f r o m t h e t w o reservo i r b o t t l e s a t each o f t h e t h r e e t e m p e r -a t u r e s each day u n t i l t h e r e were i n s u f f i c i e n t n u m b e r s r e m a i n i n g t o m a k e u p a s a m p l e . T h i s o c c u r r e d a t 20 d a t 6 ° C , 15 d a t 8 ° C , a n d 13 d a t 1 0 ° C . A m i n i m u m o f 10 larvae were t a k e n i n each s a m p l e . T h e f e e d i n g t r e a t m e n t s were s a m p l e d a t t h e e n d o f t h e e x p e r i m e n t a n d 1 0 - 2 0 larvae were t a k e n i n each s a m p l e . T h e la rvae w e r e p i p e t t e d o u t o f t h e r e a r i n g b o t t l e i n t o a s o l u t i o n o f 2% f o r m a l d e h y d e a n d s e a w a t e r ( 2 6 % ). T h e la rvae were s t o r e d fo r a t leas t 1 m o n t h i n o r d e r t h a t t h e d i m e n s i o n s s h o u l d have h a d t i m e t o s t a b i l i z e . S t a n d a r d l e n g t h w a s ' m e a s u r e d f r o m t h e t i p o f t h e s n o u t t o t h e e n d o f t h e n o t o c h o r d w i t h t h e v e r n i e r scale o f a c o m p o u n d m i c r o s c o p e . T h e l a r v a was t h e n r i n s e d i n d i s t i l l e d w a t e r a n d t h e y o l k sac, i f p r e s e n t , was d i ssec ted f r o m t h e b o d y . T h e t w o c o m p o n e n t s , y o l k a n d t i s s u e , were p l a c e d i n s e p a r a t e a l u m i n u m f o i l p a c k e t s a n d d r i e d a t 6 0 ° C f o r 24 h o u r s . T h e p a c k e t s were s t o r e d i n a dess ica to r u n t i l t h e d r y w e i g h t s were m e a s u r e d w i t h a n e l e c t r o b a l a n c e . Results B e h a v i o u r T h e schedu les o f t h e p h y s i o l o g i c a l a n d b e h a v i o u r a l even ts were s t r o n g l y a f fec ted b y t e m p e r a t u r e a n d b y t h e age a t first f e e d i n g . T h e y o l k was c o m p l e t e l y a b s o r b e d i n t h e n o n - f e e d i n g t r e a t m e n t s by d a y 6 a t 6 ° C , b y d a y 5 a t 8 ° C , a n d by day 4 a t 1 0 ° C . T h e age o f c o m p l e t e yo lk a b s o r p t i o n o f t h e f e e d i n g t r e a t m e n t s was a s s u m e d t o have b e e n t h e same as t h a t f o r t h e n o n - f e e d i n g t r e a t m e n t a t each t e m p e r a t u r e . T h e n o n - f e e d i n g fish b e g a n t o show s y m p t o m s o f s t a r v a t i o n o n day 12 a t 6° C , o n day 134 11 a t 8 ° C , a n d o n day 9 a t 1 0 ° C . T h e s e s y m p t o m s i n c l u d e d s lugg i sh s w i m m i n g , h a n g i n g h e a d down in t h e w a t e r c o l u m n , a n d r e s t i n g o n t h e t a n k floor. A l l o f t h e n o n - f e e d i n g larvae h a d fa l l en o u t o f t h e w a t e r c o l u m n a n d were r e s t i n g o n t h e floor o f t h e c o n t a i n e r , w r i g g l i n g feebly, by day 17 a t 6° C , by d a y 13 a t 8 ° C , a n d by day 11 a t 1 0 ° C . T h e s t a r v i n g larvae t h a t s u r v i v e d p a s t t h e age o f c o m p l e t e f a l l o u t o f t e n e x h i b i t e d g ro tesque d e f o r m a t i o n s , some 22 d o l d n o n - f e e d i n g larvae a t 6 ° C h a d t h e i r heads t w i s t e d 90° t o t h e s a g i t t a l ax is o f t h e b o d y . L a r v a e o f t h e t r e a t m e n t s t h a t h a d b e e n f e d b e f o r e t h e age o f c o m p l e t e f a l l o u t d i d n o t , as a g r o u p , f a l l o u t o f t h e wa te r c o l u m n a t any t i m e . A g e o f I r r e v e r s i b l e S t a r v a t i o n T h e m a x i m u m ages o f f i r s t f e e d i n g a t w h i c h some p o r t i o n o f a c o h o r t was ab le t o i n i t i a t e success fu l f e e d i n g a n d t o g r o w were less t h a n 18 d a t 6 ° C a n d less t h a n 16 d a t 8° a n d 10° C . A l l o f t h e 6° C t r e a t m e n t s t h a t were first fed o n o r b e f o r e day 14 h a d s i g n i f i c a n t l y h i g h e r m e a n l e n g t h s a n d d r y w e i g h t s a t age 3 1 d t h a n t h e y d i d a t t h e age o f first f e e d i n g (P < (X01) (F igs . A . l , A . 2 ) . A l l o f t h e 8° C t r e a t m e n t s first f e d o n o r b e f o r e day 10 h a d s i g n i f i c a n t l y h i g h e r m e a n l e n g t h s a t age 20 t h a n t h e y d i d a t t h e age o f first f e e d i n g (P < 0 .05) , w h e r e a s t h e t r e a t m e n t s first f e d o n days 12 a n d 14 h a d m e a n l e n g t h s a t age 20 d t h a t were n o t s i g n i f i c a n t l y d i f f e ren t f r o m t h o s e a t f i r s t f e e d i n g (P > 0 .05) . S i m i l a r r e s u l t s w e r e f o u n d f o r t h e m e a n d r y w e i g h t s e x c e p t t h a t t h e 20 d m e a n w e i g h t f o r t h e t r e a t m e n t first f e d o n d a y 10 was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h e m e a n w e i g h t a t age 10. A l l o f t h e 10° C t r e a t m e n t s t h a t p r o v i d e d s a m p l e s h a d s i g n i f i c a n t l y p o s i t i v e g r o w t h i n b o t h l e n g t h a n d w e i g h t IP < 0 .05) . T h i s i n d i c a t e s t h a t t h e age ranges o f 1 0 0 % i r reve rs ib le s t a r v a t i o n were 1 4 - 1 8 d a t 6° C , 1 0 - 1 5 d a t 8° C , a n d 1 1 - 1 3 d a t 10° C . T h e s e r e s u l t s s u p p o r t t h e b e h a v i o u r a l o b s e r v a t i o n s ; i n g e n e r a l , success fu l first f e e d i n g was n o t poss ib le f o r larvae first o f fe red f o o d a f t e r t h e age o f c o m p l e t e f a l l o u t . G r o w t h R a t e s G r o w t h i n s t a n d a r d l e n g t h was a s s u m e d t o have b e e n l i n e a r w i t h t i m e i n a l l p o p u l a t i o n s , ( A l ) L = Lo + GLt, w h e r e L — s t a n d a r d l e n g t h ( m m ) a t t i m e t ( d ) , Lo— l e n g t h at h a t c h , a n d GL = r a t e o f g r o w t h i n l e n g t h ( m m d - 1 ) . L i n e a r i t y is t h e s i m p l e s t h y p o t h e s i s o f t h e r e l a t i o n s h i p b e t w e e n l e n g t h a n d t i m e 135 F i g u r e A . l . G r o w t h i n m e a n (± 1 S D ) s t a n d a r d l e n g t h o f Pac i f i c h e r r i n g larvae r e a r e d a t 6, 8, a n d 10°C. A is t h e age o f c o m p l e t e y o l k a b s o r p t i o n , B is t h e age a t t h e s t a r t o f f a l l o u t , a n d C is t h e age o f c o m p l e t e f a l l o u t . O n e s t a n d a r d d e v i a t i o n o f t h e m e a n is shown fo r one g r o u p . 136 D A Y S P O S T H A T C H F i g u r e A . 2 . G r o w t h i n m e a n ( ± 1 S D ) t i ssue d r y w e i g h t o f Pac i f i c h e r r i n g larvae r e a r e d a t 6, 8, a n d 1 0 ° C . A, B, a n d C as i n F i g . A . l . O n e s t a n d a r d d e v i a t i o n o f t h e m e a n is shown f o r a one g r o u p . 138 DAYS POST HATCH a n d i t is t h e one used m o s t o f t e n i n l a b o r a t o r y a n d field w o r k o n la rva l h e r r i n g ( B l a x t e r a n d H u n t e r 1982) . D r y w e i g h t was a s s u m e d t o inc rease e x p o n e n t i a l l y w i t h t i m e because w e i g h t is u s u a l l y m o d e l l e d as a p o w e r f u n c t i o n o f l e n g t h , (A.2) W = Wo exp(Gwt), w h e r e W= t i ssue d r y w e i g h t {fig), Wo — w e i g h t a t h a t c h , a n d Gw= t h e r a t e o f g r o w t h i n w e i g h t ( d _ 1 ) . Lo a n d Wo f o r a l l t h e e x p e r i m e n t a l p o p u l a t i o n s were t a k e n f r o m t h e m e a n s a t h a t c h f o r t h e s t a r v e d c o n t r o l s a t each t e m p e r a t u r e . T h e ra tes o f g r o w t h i n l e n g t h a n d w e i g h t d e c l i n e d w i t h i n c r e a s i n g age o f first f e e d i n g , A (Table A . l , F i g s . A . 3 , A . 4 ) . Gi a p p e a r e d t o dec l i ne l i n e a r l y w i t h A a n d a Iwo-way ana lys i s o f -variance ( A N O V A ) w i t h n o i n t e r a c t i o n t e r m i n d i c a t e d t h a t t e m p e r a t u r e was n o t s i g n i f i c a n t (P > 0 .05) . T h e r e f o r e t h e ra tes f r o m a l l t h e t h r e e tes t u n i t s were p o o l e d a n d a s ing le reg ress ion c a l c u l a t e d : ( A . 3 ) GL = 2 . 2 8 x l 0 _ 1 - 7 . 0 0 x l 0 ~ 3 A, n = 23 , r = 0 .98 , P < 0 . 0 0 1 . T h e A N O V A a s s u m e d t h a t t h e r e was n o i n t e r a c t i o n b e t w e e n t e m p e r a t u r e a n d A. T h i s was t e s t e d by p o o l i n g t h e ra tes i n t o t h r e e g r o u p s a t each t e m p e r a t u r e : 0 - 2 , 4 - 8 , 1 0 - 1 4 d a t first f e e d i n g , t o give 2 - 3 va lues p e r ce l l . A t w o - w a y A N O V A o f t h e p o o l e d d a t a i n d i c a t e d t h a t t h e i n t e r a c t i o n t e r m was n o t s i g n i f i c a n t (P > 0 .05) . T h e r e l a t i o n s h i p b e t w e e n Gw a n d A a p p e a r e d t o be n o n - l i n e a r ( F i g . A . 4 ) a n d t h i s n o n - l i n e a r i t y c o u l d n o t b e r e m o v e d w i t h any o f t h e c o m m o n t r a n s f o r m a t i o n s o f Gw • A t h r e e - w a y A N O V A (A, A2, a n d T) w i t h n o i n t e r a c t i o n t e r m s was r u n ; t h e q u a d r a t i c t e r m was i n t r o d u c e d t o a c c o u n t f o r t h e n o n - l i n e a r i t y . B o t h T a n d A were n o t s i g n i f i c a n t (P > 0 .05) , so Gw was regressed o n A 2: (AA) Gw = 4 . 3 2 x l 0 - 2 - 1 . 8 9 x l 0 - 4 A 2 , n = 2 3 , r = 0 .79 , P < 0 . 0 0 1 . T h e a s s u m p t i o n o f n o i n t e r a c t i o n b e t w e e n t h e t h r e e var iab les was t e s t e d b y p o o l i n g t h e r a t e s i n t o t h e t h r e e g r o u p s used f o r t h e p r e v i o u s ana lys i s a n d t h e n r u n n i n g a t h r e e - w a y A N O V A w i t h t h e i n t e r a c t i o n t e r m s AT a n d A2 T. N e i t h e r o f these t e r m s was s i g n i f i c a n t (P > 0 .05) . 140 T A B L E A . l . T h e ra tes o f g r o w t h i n l e n g t h , Gi, t i ssue d r y w e i g h t , Gw, t o t a l m o r t a l i t y r a t e , Mt, m o r t a l i t y r a t e o f t h e f i r s t p e r i o d , Mi, a n d m o r t a l i t y r a t e o f t h e second p e r i o d , M2 , f o r 26 e x p e r i m e n t a l p o p u l a t i o n s r e a r e d a t t h r e e t e m p e r a t u r e s , T, a n d 10 ages o f f i r s t f e e d i n g , A . T A GL Gw Mt M M2 ( ° C ) (d ) ( m m d -1 ) (d" 1 ) ( d -1 ) Id" 1 ) 6 0 0.22 0.038 0.026 0.007 0.018 2 0.19 0.040 0.028 0.012 0.016 4 0.17 0.035 0.027 0.009 0.017 6 0.20 0.043 0.036 0.012 0.024 • .8 0.18 0.036 0.026 0.012 0.013 10 0 .21 0.045 0.042 0.009 0.033 12 0.17 0 .031 0 .031 0.009 0.023 14 0.13 0.020 0.072 0.008 0.064 16 - - - - -18 - - 0.173 0.007 0.167 8 0 0.23 0.042 0.035 0.004 0 .031 2 0.22 0.040 0.056 0.004 0.052 4 0.22 0.037 0.035 0.004 0 .031 6 0 .21 0.036 0.037 0.003 0.034 8 0.18 0.025 0.095 0.006 0.089 10 0.13 0.008 0.124 0.009 0.115 12 0.13 0.005 0.207 0 .010 0.197 14 0 .11 0 .011 0.144 0 .021 0.123 16 - - 0.133 0.004 0.130 10 0 0.22 0.045 0.039 0.009 0.030 2 0.19 0.039 0.059 0 . 0 0 1 0.058 4 0.22 0.049 0.044 0.000 0.044 6 0.20 0.037 0.065 0.002 0.063 8 0.20 0.040 0.088 0.008 0.080 141 10 0.15 0.026 0.147 0.005 0.142 12 0 .11 0.008 0.148 0.004 0.144 14 - - 0 .354 0.007 0.347 142 F i g u r e A . 3 . P l o t o f GL a g a i n s t t h e age o f first f e e d i n g , A, f o r e x p e r i m e n t a l p o p u l a t i o n s r e a r e d a t 6° C (c losed c i rc les ) , 8 ° C (c losed squares) , a n d 10° C (c losed t r i a n g l e s ) . See t e x t f o r t h e reg ress ion e q u a t i o n . 143 0.1 h 0 8 12 16 A (D) 144 F i g u r e A . 4 . P l o t o f Gw a g a i n s t t h e age o f first f e e d i n g , A, f o r e x p e r i m e n t a l p o p u l a t i o n s r e a r e d a t 6, 8, a n d 10°C. See F i g . A . 3 fo r s y m b o l s a n d t h e t e x t f o r t h e regress ion e q u a t i o n . 145 0 . 0 8 r 0 . 0 6 h - 0 . 0 2 1 1 1 — - — J 1 1 1 1 ' 0 4 8 12 16 A (D) 146 M o r t a l i t y R a t e s T h e n u m b e r o f s u r v i v i n g la rvae f o l l o w e d a c o m p l e x t r a j e c t o r y w i t h t i m e i n a l l e x p e r i m e n t a l p o p u l a t i o n s ( F i g . A . 5 ) , an i n i t i a l p e r i o d o f low m o r t a l i t y was f o l l o w e d by a p e r i o d o f mass m o r t a l i t y w h i c h w a s f o l l o w e d by a n o t h e r p e r i o d o f l ow m o r t a l i t y . T h i s p a t t e r n is s i m i l a r t o t h o s e r e p o r t e d by Haegele a n d O u t r a m (1978) a n d S c h n a c k (1981) f o r Pac i f i c h e r r i n g larvae r e a r e d i n enc losu res , a n d b y B l a x t e r a n d H e m p e l (1963) , a n d W e r n e r a n d B l a x t e r (1980) f o r A t l a n t i c h e r r i n g larvae rea red i n enc losures . I t i n d i c a t e s t h a t t h e r e were t w o sources o f m o r t a l i t y . T h e m o r t a l i t y r a t e o f t h e first p e r i o d m a y have been caused b y f a c t o r s assoc ia ted w i t h c o n f i n e m e n t Ln enc losu res , o r a d j u s t m e n t t o c o n f i n e m e n t , or b y t h e d e a t h o f some larvae t h a t h a t c h e d w i t h a b n o r m a l i t i e s . T h e mass m o r t a l i t y o f t h e second p e r i o d was caused by t h e d e a t h o f i r r e v e r s i b l y s t a r v e d larvae. T h e s u r v i v i n g la rvae, w h i c h were p r e s u m a b l y m o r e r e s i s t a n t t o d e l a y e d first f e e d i n g , e n t e r e d a t h i r d p e r i o d o f l o w m o r t a l i t y . T h e r e are severa l r a t h e r c o m p l e x m a t h e m a t i c a l m o d e l s such as t h e W e i b u l l f u n c t i o n ( P i n d e r e t a l . 1978) o r S i le r 's (1979) c o m p e t i n g - r i s k m o d e l t h a t c o u l d be fitted t o t h i s d a t a . However , t h e r e is n o i n f o r m a t i o n o f a n y p r a c t i c a l va lue w h i c h c o u l d be e x t r a c t e d f r o m t h e p a r a m e t e r s o f such m o d e l s t h a t c o u l d n o t be o b t a i n e d b y s e p a r a t i n g t h e d a t a i n t o t w o p e r i o d s based o n t h e s u r v i v o r s h i p curves a n d t h e n fitting t h e d a t a i n each p e r i o d w i t h a s i m p l e e x p o n e n t i a l m o d e l , (A.5) N=N0 e x p ( - M i ) , w h e r e 7 v = t h e n u m b e r o f s u r v i v o r s a t t i m e T, Nq= t h e n u m b e r o f larvae a t t = 0 , a n d M= t h e i n s t a n t a n e o u s m o r t a l i t y r a t e ( d _ 1 ) . T h e m o r t a l i t y r a t e o f t h e first p e r i o d , Mi, was e s t i m a t e d as t h e s lope o f t h e regress ion o f l o g e N o n t i m e f r o m day 0 t o t h e m e a n age o f i r revers ib le s t a r v a t i o n . T h e ages: 1 6 - 1 8 d at 6 ° C , 11 d a t 8 ° C , a n d 9 - 1 0 d a t 1 0 ° C , were chosen f r o m w i t h i n t h e ranges e s t i m a t e d above i n o r d e r t o o b t a i n t h e b e s t fit. T h e r a t e f o r t h e s e c o n d p e r i o d , Mz, was e s t i m a t e d as t h e s lope o f t h e reg ress ion o f l o g e N o n t i m e f r o m t h e m e a n age o f i r revers ib le s t a r v a t i o n t o t h e e n d o f t h e e x p e r i m e n t . T h e t o t a l m o r t a l i t y r a t e , Mt, was c a l c u l a t e d u s i n g t h e n u m b e r s t o c k e d a n d t h e n u m b e r s u r v i v i n g a t t h e e n d o f t h e e x p e r i m e n t . T h e e x p o n e n t i a l m o d e l o f t o t a l m o r t a l i t y does n o t a d e q u a t e l y m o d e l t h e c o m p l e x p a t t e r n o f s u r v i v o r s h i p over t h e course o f t h e e x p e r i m e n t s . I t is u s e d here o n l y as a m e a s u r e o f t h e average response o f a p o p u l a t i o n t o a c o m b i n a t i o n o f d e l a y e d first f e e d i n g a n d t e m p e r a t u r e over t h e p e r i o d o f mass m o r t a l i t y . A t w o - w a y A N O V A o f Mi w i t h n o 147 F i g u r e A.5. S u r v i v a l o f l a r v a l Pac i f i c h e r r i n g a t t h r e e t e m p e r a t u r e s a n d e ight first f e e d i n g t r e a t m e n t s , i n c l u d i n g one p o p u l a t i o n a t each t e m p e r a t u r e t h a t -was s ta rved f r o m h a t c h t o d e a t h . A, B, a n d C as i n F i g . A . l . 148 i n t e r a c t i o n t e r m i n d i c a t e d t h a t i t d i d n o t v a r y s i g n i f i c a n t l y w i t h t e m p e r a t u r e o r w i t h t h e age o f first f e e d i n g (P > 0 .05) . T h e s ign i f i cance o f t h e i n t e r a c t i o n o f t h e t w o f a c t o r s was t e s t e d by p o o l i n g t h e ra tes i n t o t h r e e g r o u p s : 0 - 4 , 6 - 1 0 , a n d 1 2 - 1 8 d a t first f e e d i n g , g i v i n g 2 - 3 values p e r ce l l . A n a l y s i s o f v a r i a n c e i n d i c a t e d t h a t t h e i n t e r a c t i o n t e r m was n o t s ign i f i can t (P > 0 .05) . T h e r e f o r e Mi was c o n s t a n t f o r a l l p o p u l a t i o n s ; t h e m e a n r a t e was 0 .0071 (SD==0.0044) d _ 1 o r 0.7 ( S D = 0 . 4 ) % d _ 1 . T h i s m e a n s t h a t v a r i a t i o n i n Mt was e n t i r e l y t h e r e s u l t o f v a r i a t i o n i n M2. T h e p l o t o f Mt o n A a n d T ( F i g . A . 6 ) shows t h a t t h e r e was a n o n - l i n e a r b e t w e e n t h e t h r e e va r iab les . A t h r e e - w a y A N O V A (A, A?, a n d T) w i t h n o i n t e r a c t i o n t e r m s was r u n a n d b o t h A2 a n d T were f o u n d t o be s i g n i f i c a n t (P < 0 .05) . T h e a s s u m p t i o n o f n o i n t e r a c t i o n b e t w e e n A a n d T was t e s t e d by p o o l i n g t h e m o r t a l i t y ra tes i n t o t h r e e g r o u p s a n d r u n n i n g a t h r e e - w a y A N O V A w i t h i n t e r a c t i o n t e r m s . N e i t h e r o f t h e t w o i n t e r a c t i o n t e r m s w a s s i g n i f i c a n t (P > 0 .05) . T h e m u l t i p l e regress ion of Mt o n A 2 a n d T was: (A.6) Mt == - 1 . 3 3 x l 0 _ 1 + 6 . 1 4 x 1 0 " *A 2 + 2 . 1 1 x l 0 - 2 T, n = 26 , r = 0 .80 , P < 0 . 0 0 1 . Mt was f o u n d t o be n e g a t i v e l y c o r r e l a t e d w i t h b o t h Gi a n d Gw, t h e l i n e a r p r e d i c t i v e regress ions were : (A.7) Mt == 0.254 - l .O lOGz, , n == 2 3 , r = 0 .76 , P < 0 . 0 0 1 , (A.S) Mt = 0 .174 - 3.253 Gw, n = 2 3 , r == 0 .84 , P < 0 . 0 0 1 . Discussion P a c i f i c h e r r i n g la rvae have 6 - 8 . 5 d a t 6 - 1 0 ° C a f t e r t h e e x h a u s t i o n o f t h e y o l k t o l e a r n h o w t o l o c a t e a n d success fu l l y c a p t u r e f o o d b e f o r e t h e y b e c o m e t o o weak t o f e e d . T h i s c o m p a r e s wel l w i t h t h e 5 - 9 d a t 8 - 1 2 ° C fo r A t l a n t i c h e r r i n g larvae r e p o r t e d by B l a x t e r a n d H e m p e l (1963) a n d B l a x t e r a n d E h r l i c h (1974) . T h e t i m e p e r i o d f r o m t h e e x h a u s t i o n o f t h e y o l k t o t h e age o f i r r eve rs ib le s t a r v a t i o n is a n a p p r o x i m a t e i n d e x o f t h e s u s c e p t i b i l i t y o f t h e larvae o f a fish species t o s t a r v a t i o n i n n a t u r e , a n d i t c a n be used t o r a n k species. T a b l e A . 2 l i s ts t h e t i m e p e r i o d s f r o m f e r t i l i z a t i o n t o h a t c h i n g , th, f r o m f e r t i l i z a t i o n t o c o m p l e t e y o l k a b s o r p t i o n , ty, a n d f r o m f e r t i l i z a t i o n t o t h e age o f i r revers ib le s t a r v a t i o n , t , , f o r t h e la rvae o f 25 species o f m a r i n e fishes. T h e r e is a c lear p a t t e r n i n t h e t i m i n g o f these l i fe h i s t o r y e v e n t s : b o t h th a n d ty t e n d t o be c o n s t a n t f r a c t i o n s o f t , , t h e m e a n r a t i o o f th t o t, is 0.37 150 F i g u r e A . 6 . P l o t o f Mt on t e m p e r a t u r e , T, a n d t h e age o f first f e e d i n g , A, f o r 26 e x p e r i m e n t a l p o p u l a t i o n s o f Pac i f i c h e r r i n g l a r vae . T h e c e n t r a l p l a n e is a leas t -squares m u l t i p l e regress ion o f Af t o n T a n d A 2. See t h e t e x t f o r t h e reg ress ion e q u a t i o n . 151 152 T A B L E A . 2 . T i m e p e r i o d f r o m f e r t i l i z a t i o n t o h a t c h i n g , th, t o t h e a b s o r p t i o n o f t h e y o l k , ty, a n d t o t h e age o f i r r e v e r s i b l e s t a r v a t i o n , t,, f o r t h e larvae o f 25 species o f m a r i n e f ishes. T is t h e m e a n r e a r i n g t e m p e r a t u r e . N o . Species h ty t . T A u t h o r (d ) (d) (d ) (°) 1 Engraulis ringens 2.3 5.3 6.8 18.0 M e n d i o l a (1980) c i t e d i n T h e i l a c k e r a n d D o r s e y (1980) L a s k e r (1964) W a r e e t a l . (1981) 2 Anchoa mitchilli 1.0 2.5 3.4 28.0 H o u d e (1974) M a n s u e t i a n d H a r d y (1967) 3 Archosargus rhomhoidalis 1.0 3.1 4.0 26.0 H o u d e (1974) 4 Achirus lineatus 1.0 3.5 4.0 28.0 H o u d e (1974) 5 Melanogrammus aeglefinus 11.0 17.5 22.5 7.0 L a u r e n c e a n d Roges (1976) L a u r e n c e (1974) 6 Pseudopleuronectes 20.0 27.0 33.0 8.0 S c o t t (1929) americanus L a u r e n c e (1975) L a u r e n c e a n d B e y e r (1980) c i t e d i n T h e i l a c k e r a n d D o r s e y (1980) 7 Clupea harengus pallasi 22.0 28.0 36.5 6.0 T h i s s t u d y 16.0 21.0 28.0 8.0 T h i s s tudy , 12.0 16.0 22.0 10.0 T h i s s t u d y 8 Clupea harengus harengus 16.0 26.0 35.0 8.0 N o r w a y , C l y d e a n d K i e l s tocks B l a x t e r a n d H e m p e l (1963) B l a x t e r a n d E h r l i c h (1974) 16.0 20.0 25 .0 12.0 9 Gadus morhua 12.0 18.0 23 .0 7.0 E l l e r t s e n e t a l . (1980, 1981) 10 Pleuronectes platessa 11.8 20 .1 2 8 . 1 10.0 R y l a n d a n d N i c h o l s (1975) W y a t t (1972) 153 11 Engraulis mordax 2.5 6.0 7.5 16.0 T h e i l a c k e r ( u n p u b l . d a t a ) c i t e T h e i l a c k e r a n d D o r s e y (1980) L a s k e r e t a l . (1970) 12 Scomber japonicus 2.3 5.3 6.8 19.0 H u n t e r a n d K i m b r e l l (1980) 13 Solea solea 8.0 15.0 20.5 11.0 R i l e y (1974) B l a x t e r a n d S ta ines (1971) R o s e n t h a l (1966) 14 Trachurus symmetricus 2.5 8.0 10.5 15.0 T h e i l a c k e r (1978, 1981) 15 Sardina pilchardus 2.5 5.8 10.0 17.0 B l a x t e r (1969) 16 Merluccius productus 4.4 6.7 8.0 12.0 B a i l e y (1982) 17 Mugil cephalus 1.5 5.0 9 . 0 1 22.5 N a s h e t a l . (1974) 18 Scophthalmus maeoticus 4.9 9.4 12.5 15.5 S p e c t o r o v a e t a l . (1974) 19 Caranx mate 1.0 5.0 7.4 24.5 S t r u h s a k e r e t a l . (1973) 20 Dicentrarchus labrax 4.7 15.7 30.7 15.0 B a r n a b e e t a l . (1976) 2 1 Chanos chanos 1.3 3.0 5.0 29.0 L i a o e t a l . 81979) 22 Epinephelus tauvina 1.7 5.2 7 . 2 1 28.0 H u s s a i n a n d H i g u k i (1980) 23 Siganus oramin 1.2 3.2 4.2 27.0 W e s t e r n h a g e n a n d R o s e n t h a l 24 Siganus fuscensens 1.1 4.2 5.2 25.0 L a m (1974) 25 Siganus rivulatus 1.3 5.4 6.4 26.5 P o p p e r e t a l . (1973) L a m (1974) 1 E s t i m a t e d f r o m t h e age a t t h e s t a r t o f t h e p e r i o d o f mass m o r t a l i t y a f t e r y o l k a b s o r p t i o n . 154 ( S D = 0 . 1 5 ) a n d t h e m e a n ty/t„ is 0.74 ( S D = 0 . 0 9 ) . A p l o t o f t , o n ty is l i n e a r ( F i g . A . 7 ) a n d i t shews t h a t Pac i f i c h e r r i n g la rvae have values o f t, w h i c h f a l l w i t h i n t h e range o f o t h e r species o f t e m p e r a t e zone pe lag ic fish la rvae . T h e regress ion o f t, o n ty is T e m p e r a t u r e a n d t, are also h i g h l y c o r r e l a t e d ; t h e r e l a t i o n s h i p is b e s t d e s c r i b e d as a negat ive e x p o -n e n t i a l c u r v e ( F i g . A . 8 ) : T h e r e are severa l species o f fish whose la rvae have v e r y h i g h va lues o f f , , va lues t h a t d o n o t fit t h e p a t t e r n s h o w n i n F i g s . A . 7 a n d A . 8 . T h e larvae o f t h e C a l i f o r n i a g r u n i o n , Leuresthes tenuis, (May 1971) a n d t h e s t r i p e d bass , Morone sazatilis, (Rogers a n d W e s t i n 1 9 8 1 ; E l d r i d g e e t a l . 1981) are r e m a r k a b l y r e s i s t a n t t o s t a r v a t i o n , t h e i r t,'s are g r e a t e r t h a n 35 d at 18° a n d 1 5 - 2 4 ° C , r e s p e c t i v e l y . T h e n e w l y - h a t c h e d la rvae o f these t w o species have r e l a t i v e l y l a rge o i l g lobu les as w e l l as y o l k , a n d t h e o i l g l o b u l e is r e t a i n e d f o r l o n g p e r i o d s o f t i m e a f t e r t h e yolk has b e e n c o m p l e t e l y a b s o r b e d . T h i s h e l p s t o p r o l o n g t h e t i m e t o i r reve rs ib le s t a r v a t i o n o r t o a v o i d i t a l t o g e t h e r . T h e va lue o f t h e o i l g l o b u l e t o t h e e n e r g y b u d g e t o f a s t r i p e d bass e m b r y o is s h o w n by t h e f a c t t h a t i t makes u p 5 5 % o f t h e d r y w e i g h t o f a f e r t i l i z e d egg w h e r e a s t h e y o l k m a k e s u p o n l y 3 8 % o f t h e d r y w e i g h t ( E l d r i d g e e t a l . 1982) . T h u s t h e r e a p p e a r s t o be t w o classes o f fish larvae: t h e first c o n t a i n s pe lag i c species t h a t have a r e l a t i v e l y b r i e f p e r i o d a f t e r y o l k e x h a u s t i o n Ln w h i c h t o l e a r n h o w t o feed successfu l ly , a n d t h e second c o n t a i n s i n s h o r e o r e s t u a r i n e species t h a t have m u c h l o n g e r p e r i o d s o f s u r v i v a l because o f t h e presence o f la rge o i l g l o b u l e s . T h e r a t e s o f g r o w t h i n l e n g t h a n d w e i g h t a n d t h e ra tes o f t o t a l m o r t a l i t y o f t h e e x p e r i m e n t a l p o p u l a t i o n s o f Pac i f i c h e r r i n g larvae were s t r o n g l y c o r r e l a t e d w i t h t h e degree o f s t a r v a t i o n i m p o s e d o n t h e m b y delays Ln t h e age o f first f e e d i n g . T e m p e r a t u r e was less i m p o r t a n t t h a n t h e age o f first f e e d i n g , a t least o v e r t h e r a n g e 6 - 1 0 ° C ; i t was c o r r e l a t e d o n l y w i t h t h e m o r t a l i t y r a t e . S i m i l a r r e s u l t s have b e e n r e p o r t e d f o r d e l a y e d f e e d i n g e x p e r i m e n t s w i t h t h e larvae o f o t h e r fish species (Lasker e t a l . 1970 ; M a y 1 9 7 1 ; H o u d e 1974; R o g e r s a n d W e s t i n 1981) . E x p e r i m e n t s i n w h i c h t h e r e was n o de layed first f e e d i n g a n d s t a r v a t i o n was i m p o s e d by v a r y i n g o n l y t h e p r e y d e n s i t y also s h o w e d c o r r e l a t i o n s ( A 9 ) ts = 0.5 + 1 .3 i j „ n = 2 9 , r = 0 .98 , P < 0 . 0 0 1 . ( A L I O ) l o g e f„ = 3.9643 - 0 .0892 T, n = 2 9 , r = 0 . 9 1 , P < 0 . 0 0 1 . 155 F i g u r e A . 7 . P l o t o f t, o n ty f o r t h e larvae o f 25 species o f m a r i n e fishes. T h e c losed c i rc les are Paci f ic h e r r i n g la rvae . T h e n u m b e r s i n t h e o p e n c i rc les re fe r t o t h e r e c o r d s i n Tab le A . 2 . See t h e t e x t f o r t h e regress ion e q u a t i o n . 156 157 F i g u r e A . 8 . P l o t o f ts o n t e m p e r a t u r e f o r t h e larvae o f 25 species o f m a r i n e f ishes. S y m b ols as i n F i g . A . 7 . See t h e t e x t f o r t h e regress ion e q u a t i o n . 158 159 b e t w e e n t h e ra tes o f g r o w t h a n d m o r t a l i t y a n d t h e degree o f s t a r v a t i o n ( H o u d e 1975, 1 9 7 7 d ; Haege le a n d O u t r a m 1978; W e r n e r a n d B l a x t e r 1980; E l d r i d g e e t a l . 1981) . T h e reg ress ion o f Mt o n GL f o r t h e f ive e x p e r i m e n t a l p o p u l a t i o n s r e a r e d by W e r n e r a n d B l a x t e r (1980) was ( A l l ) Mt = 0.202 - 1.217 GL, « = 5, r = 0 .72 , P < 0 . 0 0 1 . T h e i n t e r c e p t o f t h i s regress ion was s i g n i f i c a n t l y l o w e r t h a n t h e i n t e r c e p t f o r t h e same regress ion f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s t u d y , a n d t h e s lope was s i g n i f i c a n t l y h i g h e r ( F i g . A . l l ) . T h e r e s u l t s r e p o r t e d here were n o t u n e x p e c t e d , t h e i r r e a l va lue l ies i n t h e f a c t t h a t t h e y can b e c o m p a r e d w i t h t h e ra tes m e a s u r e d f o r n a t u r a l p o p u l a t i o n s o f h e r r i n g larvae. Such c o m p a r i s o n s assume t h a t t h e r a t e s were n o t b i a s e d by r e a r i n g v a r i a b l e s such as enc losu re v o l u m e , s t o c k i n g d e n s i t y , p r e y t y p e , a n d p r e y d e n s i t y . T h i s a s s u m p t i o n is o b v i o u s l y v i o l a t e d t o some degree i n a l l r e a r i n g e x p e r i m e n t s because a l l c u l t u r e s y s t e m s are p o o r s i m a l c r u m s o f t h e n a t u r a l e n v i r o n m e n t . T h e s t o c k i n g d e n s i t y o f 67 l - 1 t h a t was used i n t h i s s t u d y was h i g h c o m p a r e d t o t h e dens i t i es t h a t are r e c o m m e n d e d f o r e a r l y s tage c l u p e o i d la rvae ( 5 - 1 0 1 _ 1 , B l a x t e r a n d H u n t e r 1982) , a n d t h e t a n k v o l u m e o f 3 1 was low c o m p a r e d t o t h e r e c o m m e n d e d v o l u m e s (20 1, B l a x t e r a n d H u n t e r 1982) . T h e 3 1 t a n k was a c o m p r o m i s e b e t w e e n t h e r e c o m m e n d e d v o l u m e a n d t h e ava i lab le t e s t space ; dens i t ies o f 5 1 _ 1 w o u l d have r e q u i r e d t h e s i m u l t a n e o u s m a i n t e n a n c e o f 36 t a n k s each o f 40 1 v o l u m e , w h i c h is a l a r g e a m o u n t o f space i n any l a b o r a t o r y . T h e s m a l l v o l u m e s also r e d u c e d t h e t i m e a n d e n e r g y r e q u i r e d t o c l e a n t h e m a n d t o m o n i t o r m o r t a l i t y . T w o h u n d r e d la rvae were s t o c k e d i n each t a n k t o ensure t h a t m o s t t r e a t m e n t s h a d e n o u g h s u r v i v o r s t o a l l o w t h e c a l c u l a t i o n o f m e a n l e n g t h s a n d w e i g h t s . T h e ef fects o f s t o c k i n g d e n s i t y a n d t a n k v o l u m e o n t h e t i m e s t o i r r e v e r s i b l e s t a r v a t i o n a n d o n t h e ra tes o f g r o w t h a n d m o r t a l i t y o f h e r r i n g la rvae have n o t y e t b e e n e x a m i n e d i n a c o n t r o l l e d e x p e r i m e n t a l f a s h i o n . T h e r e have b e e n several c o n t r o l l e d e x p e r i m e n t a l s t u d i e s o f t h e effects o f s t o c k i n g d e n s i t y o n t h e r a t e s o f g r o w t h a n d m o r t a l i t y o f t h e la rvae o f o t h e r fish species ( H o u d e 1975,1977; K l e i n - M a c P h e e 1 9 8 1 ; T a n i g u c h i 1981) a n d t h e y have s h o w n t h a t t h e o p t i m a l d e n s i t y var ies b e t w e e n species, b u t t h a t t h e m a x i m u m d e n s i t y a t w h i c h t h e y rea l ize t h e i r p o t e n t i a l ra tes o f g r o w t h a n d s u r v i v a l is a b o u t 30 1 _ 1 . I f s t o c k i n g d e n s i t y a n d t a n k v o l u m e d i d r e d u c e t h e r a t e s o f g r o w t h a n d s u r v i v a l s u r v i v a l o f Pac i f i c h e r r i n g la rvae m e a s u r e d i n t h i s s t u d y t h e n t h e y m u s t b e a d j u s t e d f o r d e n s i t y a n d v o l u m e ef fects be fo re t h e y c a n b e c o m p a r e d w i t h t h e r a t e s m e a s u r e d f o r n a t u r a l p o p u l a t i o n s . F o r t u n a t e l y , a n u m b e r o f e x p e r i m e n t a l s t u d i e s o n t h e g r o w t h 160 a n d m o r t a l i t y o f A t l a n t i c a n d Pac i f i c h e r r i n g have b e e n p e r f o r m e d d u r i n g t h e p a s t t w o decades u s i n g a w i d e r a n g e o f s t o c k i n g dens i t i es a n d t a n k v o l u m e s (Table A . 3 ) . Some o f these s t u d i e s were b a t c h c u l t u r e s i n w h i c h p r e y d e n s i t y a n d s t o c k i n g d e n s i t y we re n o t m e a s u r e d . A l s o , some o f t h e n u m b e r s are q u i t e a p p r o x i m a t e , f o r e x a m p l e t e m p e r a t u r e was h e l d c o n s t a n t i n f e w o f t h e cases, i n s t e a d i t t e n d e d t o r ise d u r i n g t h e r e a r i n g p e r i o d . T h e t e m p e r a t u r e s i n Tab le A . 3 are t h e m i d p o i n t s o f t h e ranges . T h e e s t i m a t e s o f p r e y d e n s i t y i n t h e la rge enc losures are also n o t ve ry a c c u r a t e , f o r e x a m p l e t h e m e a n p r e y d e n s i t y i n t h e 4 . 4 x l O B 1 b a s i n ( O i e s t a d a n d M o k s n e s s 1981) h a d a coef f ic ient o f v a r i a t i o n o f 1 2 4 % w h i c h i n d i c a t e s t h a t t h e p r e y i t e m s were d i s t r i b u t e d p a t c h i l y i n t h e b a s i n . T h e g r o w t h r a t e s a n d t h e t o t a l m o r t a l i t y ra tes o f T a b l e A . 3 were each regressed o n t a n k v o l u m e , s t o c k i n g d e n s i t y , t e m p e r a t u r e , p r e y d e n s i t y a n d p r e y t y p e w i t h t h e B M D P - . 2 R s tepwise m u l t i p l e regress ion p r o g r a m ( D i x o n 1983) . T h i s p r o g r a m en te rs a n d r e m o v e s i n d e p e n d e n t va r iab les i n t o t h e regress ion e q u a t i o n i n a s tepwise m a n n e r u n t i l t h e m a x i m u m a m o u n t o f v a r i a t i o n i n t h e d e p e n d e n t v a r i a b l e has b e e n e x p l a i n e d , s u b j e c t t o t h e c o n s t r a i n t t h a t t h e i n d e p e n d e n t va r iab les m u s t n o t b e h i g h l y c o r r e l a t e d w i t h each o t h e r . P r e y type was g i v e n a v a l u e o f 1 fo r Artemia or m i x t u r e s o f Artemia a n d z o o p l a n k t o n a n d a value o f 2 f o r w i l d z o o p l a n k t o n a l o n e . T h e regress ions o f GL, GW, a n d Mt c o n t a i n e d one o r m o r e o f t h e f o l l o w i n g t h r e e va r i ab les : t a n k v o l u m e , p r e y t y p e , a n d t e m p e r a t u r e , a n d t h e y e x p l a i n e d 4 1 - 8 1 % o f t h e v a r i a t i o n i n t h e r a t e s . T h e c o r r e l a t i o n s b e t w e e n GL, GW a n d Mt a n d t a n k v o l u m e d e p e n d e d heav i l y o n t h e d a t a p o i n t f o r t h e 4 . 4 x l 0 8 1 b a s i n p o p u l a t i o n ; w h e n i t was e x c l u d e d t h e regress ions con ta ined e i t h e r p r e y typ e or t e m p e r a t u r e o r b o t h a n d t h e y e x p l a i n e d 2 8 - 4 9 % o f t h e v a r i a t i o n . T h e lack o f a c o r r e l a t i o n w i t h p r e y d e n s i t y m a y be p a r t l y e x p l a i n e d by t h e h i g h assoc ia ted v a r i a t i o n o f t h e e s t i m a t e s o f p r e y dens i ty f o r t h e la rge enc losu res . A n y c o n c l u s i o n s c o n c e r n i n g t h e c o r r e l a t i o n s o f t h e g r o w t h a n d m o r t a l i t y ra tes w i t h t a n k v o l u m e m u s t r e m a i n t e n t a t i v e because t h e y are c o m p l e t e l y d e p e n d e n t o n a s ing le d a t a p o i n t . E v e n i f t h i s d a t a p o i n t is a c c e p t e d s i g n i f i c a n t increases i n g r o w t h a n d m o r t a l i t y d i d n o t o c c u r un less t h e v o l u m e was l x l O 4 1 o r h i g h e r . T h e m o s t i n t e r e s t i n g r e s u l t s o f t h i s ana l ys i s are t h e r o b u s t c o r r e l a t i o n s b e t w e e n t h e r a t e s o f g r o w t h a n d m o r t a l i t y a n d t h e p r e y t y p e . I n g e n e r a l , h e r r i n g larvae t h a t are first fed Artemia n a u p l i i o r a m i x t u r e o f Artemia a n d w i l d z o o p l a n k t o n have lower m o r t a l i t y ra tes t h a n h e r r i n g larvae fed o n z o o p l a n k t o n a lone ( F i g . A . l l ) . For e x a m p l e , Haege le a n d O u t r a m (1978) f o u n d t h a t t h e m e a n Mt o f Pac i f ic h e r r i n g larvae f e d z o o p l a n k t o n was tw ice as h i g h as t h e m e a n Mt f o r Artemia-ted l a rvae : 0 .100 ( S D = 0 . 0 2 3 , n = 5 ) a n d 0.054 ( S D = 0 . 0 1 5 , n = 7 ) d " 1 , 161 T A B L E A . 3 . T h e l i n e a r r a t e o f g r o w t h i n l e n g t h , GL, t h e e x p o n e n t i a l r a t e o f g r o w t h i n d r y w e i g h t , Gw, a n d t h e t o t a l e x p o n e n t i a l r a t e o f m o r t a l i t y , Mt, o f e x p e r i m e n t a l p o p u l a t i o n s o f h e r r i n g larvae rea red b y a v a r i e t y o f t e c h n i q u e s . T h e t e m p e r a t u r e , T, is t h e m i d p o i n t o f t h e t e m p e r a t u r e r a n g e d u r i n g t h e r e a r i n g p e r i o d . A - z o o p . : Artemia s p p . a n d w i l d z o o p l a n k t o n . N o . Gw Mt T T a n k S t o c k i n g P r e y P r e y A u t h o r V d e n s i t y d e n s i t y t y p e ( m m d - 1 ) ( ° C ) (1) ( I " 1 ) Clupea harengus pallasi 1 0 .31 - - 12.0 100 - - A Ta lb o t a n d J o h n s o n (1972) 2 0.09 - 0.053 9.5 8 264.0 375 1 A Haegele a n d O u t r a m (1978) 2 0.10 - 0.030 9.5 8 216.0 7 5 0 1 A 2 0.18 - 0.087 9.5 8 196.0 375 1 z o o p . 2 0.18 - 0.112 9.5 8 129.0 625 1 z o o p . 2 0.16 - 0.067 9.5 8 149.0 7 5 0 1 z o o p . 2 0.22 - 0.113 9.5 8 172.0 1875 1 z o o p . 2 0.24 - 0.122 9.5 8 208.0 3750 1 z o o p . 2 0.15 - 0.063 9.5 8 249.0 375 1 A - z o o p . 2 0.17 - 0.076 9.5 8 147.0 625 1 A - z o o p . 2 0.15 - 0.043 9.5 8 241 .0 750 1 A - z o o p . 2 0.18 - 0 .061 9.5 8 172.0 1875 1 A - z o o p . 2 0 .21 - 0.053 9.5 8 162.0 3750 1 A - z o o p . 3 0.18 - - 12.1 50 - - A T h i s s t u d y ( A p p . B ) 3 0 . 1 0 2 - - 8.5 25 - - A 3 0 . 2 3 2 - - 8.5 1000 - - A - z o o p . 3 0 . 2 9 2 - - 9.5 2000 - - z o o p . 4 0.25 0.060 0 .151 9.5 6000 0.9 100 z o o p . S d i n a c k (1981) 4 0.23 0.043 0.188 9.5 6 0 0 0 1.0 20 z o o p . 4 0.29 0.024 0.102 9.5 6000 0.9 20 z o o p . 162 4 0.22 0.035 0.144 9.5 6000 0.9 80 z o o p . Clupei a harengus harengus 5 0.30 - - 11.0 200 - - A - z o o p . B l a x t e r (1968) 5 0.24 - - 11.0 200 - - A-zoop. 6 0.10 0.018 0.100 9.0 20 8.0 30 A W e r n e r a n d B l a x t e r (1980) 6 0.12 0.031 0.069 9.0 20 8.0 100 A 6 0.11 0.032 0.034 9.0 20 8.0 300 A 6 0.14 0.034 0.030 9.0 20 8.0 1000 A 6 0.14 0.036 0.036 9.0 20 8.0 3000 A 7 0.33 - - 11.5 400 - - A-zoop. u n p u b l . d a t a , c i t e d i n B l a x t e r a n d H u n t e r (1982) 8 0.112 - - 11.0 120 - - A-zoop. Gef fen (1982) 8 0.122 - - 11.0 120 - - . A - z o o p . 8 0.222 - - 11.0 500 - - j4-zoop. 9 0.293 0.077 0.062 11.5 3.1x10s 0.1 50 z o o p . G a m b l e e t a l . (1981) 9 0.213 0.052 0.033 11.5 3.1x10s 0.1 - z o o p . 10 0.11 0.026 0.083 9.9 1800 0.2 4 z o o p . O i e s t a d a n d M o k s n e s s (1981) 10 0.12 0.042 0.035 9.9 1800 0.2 5 z o o p . 10 0.18 0.058 0.064 9.9 1800 0.2 56 z o o p . 10 0.44 0.120 0.005 9.2 4.4X105 2.3x10" ' 3 749* z o o p . O i e s t a d a n d M o k s n e s s (1981) 1 N u m b e r o f p r e y o f fe red d _ 1 l ~ 1 , n o t average p r e y d e n s i t y . 2 P o p u l a t i o n s s u s p e c t e d o f l o w c o n d i t i o n because t h e o t o l i t h r i n g d e p o s i t i o n r a t e was < 1 d - 1 . 3 L i n e a r r a t e c a l c u l a t e d f r o m a n a s y m p t o t i c g r o w t h c u r v e . 4 M e a n o f a l l d e p t h s over t h e t i m e p e r i o d o f t h e r e a r i n g e x p e r i m e n t . 163 r e s p e c t i v e l y (Tab le A . 3 ) . T h e e x p l a n a t i o n o f t h i s p h e n o m e n o n is t h a t h e r r i n g larvae take several m o r e days t o e s t a b l i s h success fu l first f e e d i n g o n p u r e z o o p l a n k t o n t h a n o n Artemia n a u p l i i (Rosen tha l a n d H e m p e l 1970) a n d so t h e y suf fer a c o r r e s p o n d i n g l y h i g h e r r a t e o f m o r t a l i t y f r o m i r revers ib le s t a r v a t i o n . Artemia n a u p l i i are easier t o c a p t u r e t h a n c o p e p o d n a u p l i i because t h e y are l a rge , slow s w i m m i n g a n d b r i g h t l y c o l o r e d w h e r e a s c o p e p o d n a u p l i i are s m a l l e r , f a s t e r a n d n e a r l y t r a n s p a r e n t . T h i s m e c h a n i s m a lso e x p l a i n s some a p p a r e n t l y p a r a d o x i c a l ef fects r e l a t e d t o p r e y d e n s i t y . Haegele a n d O u t r a m (1978) a n d W e r n e r a n d B l a x t e r (1980) b o t h f o u n d t h a t g r o w t h ra tes i n c r e a s e d w i t h i n c r e a s i n g p r e y d e n s i t y u p t o a n a s y m p t o t e w h i c h lay b e t w e e n 1000 a n d 2000 Artemia 1 _ 1 . Howeve r , t h e h e r r i n g larvae r e a r e d o n w i l d z o o p l a n k t o n i n enc losures la rge r t h a n 1000 1 (Schnack 1 9 8 1 ; G a m b l e e t a l . 1 9 8 1 ; O i e s t a d a n d M o k s n e s s 1981) g r e w r a p i d l y o n p r e y dens i t i es o f o n l y 4 - 7 5 0 1 _ 1 . T h e e x p l a n a t i o n is t h a t t h e p o p u l a t i o n s o f t h e la rge enc losures e x p e r i e n c e d h i g h m o r t a l i t y a n d , t h e r e f o r e , r a p i d se lec t i on f o r h e a l t h y , ac t i ve i n d i v i d u a l s w i t h i n 2 weeks o f h a t c h a n d t h a t these s u r v i v o r s h a d l e a r n e d how t o feed a n d g r o w o n l o w p r e y d e n s i t i e s . I n s u m m a r y , t h e ev idence does n o t s u p p o r t a d j u s t i n g t h e g r o w t h a n d m o r t a l i t y ra tes o f t h e larvae rea red i n t h i s s t u d y f o r t h e effects o f s t o c k i n g d e n s i t y b u t i t does s u p p o r t a d j u s t i n g t h e m f o r t h e effects o f t a n k v o l u m e , p r e y t y p e , a n d t e m p e r a t u r e . C o n s e q u e n t l y , GL, GW a n d Mt we re regressed o n t a n k v o l u m e , V, p r e y t y p e , P T, a n d t e m p e r a t u r e , T, f o r t h e d a t a o f Tab le A . 3 . T h e m u l t i p l e regress ions w e r e : ( A 1 2 ) GL = - 1 . 6 8 x l 0_ 1 + 5 . 6 1 x l 0 - 8 F + 3 . 9 8 x l 0 _ 2 P r + 3 . 0 2 x l 0 ~ 2 T, n = 3 8 , r = 0 .68 , P = 0 . 0 0 1 , ( A 1 3 ) GW = - 5 . 8 5 x l 0- 2 + 1 . 8 9 x l 0 - 8 F + 4 . 7 1 x l O _ 3 P T + 9 . 3 3 x l 0 - 3 T, n = 15, r = 0 . 9 0 , P = 0 .002 , L4 .14) MT = 2 . 5 5 x l 0 _ 1 - 2 . 5 1 x l 0 - 8 V + 6 . 1 3 x l 0 _ 2 P T- 2 . 8 4 x l 0 ~ 2 T, n = 2 7 , r = 0 . 7 1 , P = 0 .008 . T h e g r o w t h a n d m o r t a l i t y ra tes f o r V = 1x10* 1, P T = 2 , a n d T = 6 ° , 8° a n d 10° C are shown i n T a b l e A . 4 w i t h t h e m e a n r a t e s f o r t h i s s t u d y f o r t h e t r e a t m e n t s t h a t were first f e d w i t h i n 4 days o f h a t c h . T h e g r o w t h ra tes c a l c u l a t e d f r o m t h e m u l t i p l e regress ions f o r 6° a n d 8 ° C are 1.5-5.4 t i m e s lower t h a n t h e m e a n g r o w t h ra tes m e a s u r e d f o r t h i s s t u d y b u t t h e c a l c u l a t e d g r o w t h r a t e s a t 10° C are i d e n t i c a l t o t h o s e m e a s u r e d f o r t h i s s t u d y . T h e m o r t a l i t y ra tes c a l c u l a t e d f r o m t h e regress ions f o r 6 ° a n d 8 ° C are 5 - 1 0 t i m e s h i g h e r t h a n t h e m e a n ra tes m e a s u r e d f o r t h i s s tudy , a n d M t c a l c u l a t e d f o r 164 T A B L E A . 4 . T h e m e a n ra tes o f g r o w t h i n l e n g t h , GL, g r o w t h i n d r y w e i g h t , Gw, a n d t o t a l m o r t a l -i t y , Mt, f o r t h e t r e a t m e n t s fed f i r s t d u r i n g t h e yo lk -sac p e r i o d (0—4 d ) a t 6° , 8 ° , a n d 10° C a n d t h e r a t e s c a l c u l a t e d f o r 6 ° , 8 ° , a n d 1 0 ° C f r o m t h e m u l t i p l e regress ions de r i ved f r o m t h e e x p e r i m e n t a l p o p u l a t i o n s o f . h e r r i n g larvae l i s t e d i n T a b l e A . 3 . T M e a n ra tes f o r t r e a t m e n t s M e a n ra tes c a l c u l a t e d f r o m ( ° C ) f i r s t f e d a t 0 - 4 d regress ion e q u a t i o n s GL Gw Mt GL Gw Mt 6 0.19 0.038 0.027 0.09 0.007 0.207 8 0.22 0.040 0.042 0.15 0.026 0.150 10 0 .21 0.044 0.047 0.21 0.044 0.093 165 10° is t w o t i m e s h i g h e r t h a n t h a t m e a s u r e d f o r t h i s s t u d y a t 1 0 ° . T h e ra tes c a l c u l a t e d f r o m t h e m u l t i p l e regress ions a t 6° a n d 8 ° C are c l e a r l y i n e r r o r a n d t h e reason is t h a t t h e r e a r i n g t e m p e r a t u r e s o f T a b l e A . 3 r a n g e f r o m 8.5° t o 1 2 ° C w i t h a m e a n o f 9 . 9 ° C ( S D = 1 . 0 , n = 3 8 ) . C o n s e q u e n t l y , t h e regress ions c a n n o t a c c u r a t e l y p r e d i c t t h e a d j u s t e d g r o w t h a n d m o r t a l i t y r a t e s a t t e m p e r a t u r e s above o r b e l o w 1 0 ° C . T h e s i m i l a r i t y o f t h e t w o sets o f g r o w t h ra tes a t 1 0 ° C i n d i c a t e s t h a t t h e t a n k v o l u m e , s t o c k i n g d e n s i t y , a n d p r e y t y p e t h a t we re used i n t h i s s t u d y d i d n o t l o w e r t h e g r o w t h ra tes , as was s u s p e c t e d . T h e use o f Artemia n a u p l i i i n s m a l l c o n t a i n e r s d i d n o t inc rease t h e m o r t a l i t y , i n s t e a d i t decreased i t b y a f a c t o r o f t w o b e l o w t h a t w h i c h w o u l d have o c c u r r e d i f t h e la rvae h a d f e d o n l y o n w i l d z o o p l a n k t o n . T h e g r o w t h ra tes m e a s u r e d i n t h i s s t u d y c a n be c o m p a r e d d i r e c t l y t o t h o s e m e a s u r e d i n t h e field b u t t h e m o r t a l i t y r a t e s m u s t b e d o u b l e d . T h i s ad hoc ana lys is is c e r t a i n l y n o s u b s t i t u t e f o r a c o n t r o l l e d l a b o r a t o r y s t u d y b u t t h e f a c t r e m a i n s t h a t t h e g r o w t h ra tes m e a s u r e d f o r Paci f ic h e r r i n g i n t h i s s t u d y are e q u a l t o o r h i g h e r t h a n any m e a s u r e d t o d a t e f o r h e r r i n g larvae r e a r e d i n t a n k s less t h a n 1000 1 i n v o l u m e a m d f o r dens i t i es o f 1-8 l - 1 . T h e m o r t a l i t y ra tes were a m o n g t h e lowes t m e a s u r e d f o r any e x p e r i m e n t a l h e r r i n g p o p u l a t i o n s . E s t i m a t e s o f GL a n d Mt f o r f o u r n a t u r a l p o p u l a t i o n s o f Pac i f ic a n d 14 n a t u r a l p o p u l a t i o n s o f A t l a n t i c h e r r i n g la rvae t a k e n f r o m t h e l i t e r a t u r e are l i s t e d i n T a b l e A . 5 a n d p l o t t e d a g a i n s t t h e m i d p o i n t o f t h e t e m p e r a t u r e ranges i n F i g s . A . 9 a n d A . 1 0 . GL was n o t s i g n i f i c a n t l y c o r r e l a t e d w i t h t h e m i d p o i n t s o f t h e t e m p e r a t u r e range (P = 0 .31) , b u t i t was p o s i t i v e l y c o r r e l a t e d w i t h t h e m i d p o i n t o f t h e l e n g t h r a n g e , a l t h o u g h t h e c o r r e l a t i o n was n o t s i g n i f i c a n t (P > 0 . 0 5 ) . T h e t r e n d o f GL w i t h t h e m i d p o i n t o f t h e l e n g t h r a n g e was d u e e n t i r e l y t o t w o v e r y low va lues o f GL (0.05 m m d - 1 ) m e a s u r e d f o r p o p u l a t i o n s 8 a n d 12. E leven o f t h e 18 n a t u r a l p o p u l a t i o n s ( 6 1 % ) h a d average g r o w t h r a t e s t h a t were h i g h e r t h a n t h e h i g h e s t g r o w t h r a t e s t h a t were o b t a i n e d i n t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s t u d y , f o u r ( 2 2 % ) h a d ra tes t h a t were e q u i v a l e n t t o first f e e d i n g a t 0 - 8 d , one ( 6 % ) h a d a r a t e e q u i v a l e n t t o first f e e d i n g a t 8 - 1 2 d , a n d t w o p o p u l a t i o n s ( 1 1 % ) , n u m b e r s 8 a n d 12, h a d g r o w t h r a t e s we l l be low a n y o b t a i n e d i n t h e e x p e r i m e n t a l p o p u l a t i o n s . T h e g r o w t h ra tes o f t h e l a s t t w o n a t u r a l p o p u l a t i o n s m a y have b e e n u n d e r e s t i m a t e d because o f c o n t i n u o u s r e c r u i t m e n t o f n e w l y h a t c h e d larvae d u r i n g t h e s a m p l i n g p e r i o d . G r a h a m a n d C h e n o w e t h (1973) c o n c l u d e d t h a t r e c r u i t m e n t was n e g l i g i b l e i n t h e i r p o p u l a t i o n because t h e yo lk -sac la rvae i n t h e s a m p l e s f e l l f r o m 4 . 7 % t o 0 . 2 % o f t h e s a m p l e s over t h e 5 d s a m p l i n g p e r i o d , a n d because o b s e r v a t i o n o f t h e egg beds by a s u b m e r s i b l e c a m e r a s h o w e d a 166 T A B L E A . 5 . T h e ra tes o f t o t a l m o r t a l i t y , Mt, a n d g r o w t h i n l e n g t h , Gl, f o r n a t u r a l p o p u l a t i o n s o f h e r r i n g l a r vae . B o t h ra tes were c a l c u l a t e d f r o m t h e p e r i o d i n c l u d i n g t h e p e r i o d o f mass m o r t a l i t y t h a t fo l lows c o m p l e t e a b s o r p t i o n o f t h e y o l k . N o . L e n g t h Mt r a n g e GL T A r e a A u t h o r Clupea harengus pallasi 1 8 - 1 5 0 .41 0.30 9 .5 -13 B a r k l e y S o u n d , B r i t i s h C o l u m b i a S t e w n s o n (1962) 1 8 - 1 3 0.25 0.26 9 .5 -13 Q u e e n Cove , B r i t i s h C o l u m b i a 2 7 - 1 7 0.09 0 .21 4 - 6 A k k e s h i B a y , J a p a n I i z u k a (1966) 2 7 - 1 7 0.12 0.32 4 - 6 A k k e s h i B a y , J a p a n Clupea harengus harengus 3 7 - 3 8 - 0.43 7 - 8 C l y d e Sea, S c o t l a n d M a r s h a l l e t a l . (1937) 4 7 - 2 0 - 0.23 1 0 - 1 5 I r i s h Sea, Isle o f M a n B o w e r s (1952) 5 7 - 1 4 0.10 0.28 1 1 - 1 5 Bay o f F u n d y , N o v a S c o t i a D a s (1968) 5 7 - 1 4 0.06 0.28 1 1 - 1 5 B a y o f F u n d y , N o v a S c o t i a 5 6 - 1 4 0 .11 0.28 1 1 - 1 5 B a y o f F u n d y , N o v a S c o t i a 6 9 - 1 3 0.14 0.29 5 .6 -6 .5 N o r w e g i a n coast D r a g e s u n d a n d N a k k e n (1971a) 7 9 - 1 3 0.46 0.33 5 .5 -6 .5 N o r w e g i a n coast D r a g e s u n d a n d N a k k e n (1971b) 8 7 - 1 1 - 0.05 11 -17 N W N o r t h Sea H e m p e l a n d S c h n a c k (1971) 9 9 - 2 1 - 0.16 6 - 1 0 S t . M a r g a r e t ' s B a y , N o v a S c o t i a S a m e o t o (1972) 10 7 - 3 0 - 0.35 1 6 - 2 0 Schle i F j o r d , B a l t i c Sea S c h n a c k (1972, 1974) 11 5 - 3 0 - 0.19 8 - 1 3 Georges B a n k - G u l f o f M a i n e B o y a r e t a l . (1973) 12 5 - 9 0.35 0.05 1 3 - 1 5 Georges B a n k G r a h a m a n d C h e n o w e t h (1973) 13 6 - 3 0 0.04 0.20 1 0 - 1 5 Georges B a n k L o u g h e t a l . (1981) 14 6 - 2 0 - 0.28 8 - 1 3 Georges B a n k L o u g h e t a l . (1982) 167 F i g u r e A.9. P l o t o f GL a g a i n s t t h e m i d p o i n t o f t h e observed t e m p e r a t u r e r a n g e , T, f o r n a t u r a l p o p u l a t i o n s o f Pac i f i c a n d A t l a n t i c h e r r i n g la rvae. T h e n u m b e r s re fe r t o T a b l e A.5 a n d t h e h o r i z o n t a l l ines are t h e assoc ia ted t e m p e r a t u r e r a n g e s . T h e i s o p l e t h s o f age o f first f e e d i n g , A, ware c a l c u l a t e d f r o m t h e regress ion o f GL o n A f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s tudy . See t h e t e x t f o r t h e reg ress ion e q u a t i o n . 168 0.40 169 F i g u r e A . 1 0 . P l o t o f M t a g a i n s t t h e m i d p o i n t o f t h e t e m p e r a t u r e r a n g e , T, f o r n a t u r a l p o p u l a t i o n s o f Pac i f i c a n d A t l a n t i c h e r r i n g la rvae . T h e n u m b e r s i ns ide t h e s y m b o l s re fer t o T a b l e A .5 a n d t h e h o r i z o n t a l l ines are t h e t e m p e r a t u r e r a n g e s . T h e b r o k e n l ines are t h e i s o p l e t h s o f t h e age o f first f e e d i n g , A, c a l c u l a t e d f r o m t h e m u l t i p l e regress ion o f Mt o n A 2 a n d T f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s t u d y a n d d o u b l e d i n o r d e r t o c o m p a r e w i t h t h e n a t u r a l r a t e s . See t h e t e x t f o r t h e regress ion e q u a t i o n . T h e t w o ra tes i n d o u b l e c i rc les are s u s p e c t e d o f h a v i n g b e e n i n f l a t e d by d i s p e r s a l o f t h e la rvae o u t o f t h e s a m p l i n g a rea . 170 0.6 171 t h a t m o s t o f t h e h a t c h i n g h a d s t o p p e d 4 d b e f o r e t h e f i r s t p l a n k t o n samp les were c o l l e c t e d . H e m p e l a n d S c h n a c k (1981) , o n t h e o t h e r h a n d , were n o t ab le t o e s t i m a t e t h e m e a n h a t c h i n g d a t e o f t h e i r p o p u l a t i o n a n d so t h e y c o n c l u d e d t h a t b o t h r e c r u i t m e n t o f n e w l y h a t c h e d larvae a n d i r revers ib le s t a r v a t i o n o f first feeders m a y have b e e n r e s p o n s i b l e f o r t h e low g r o w t h r a t e . O n e firm c o n c l u s i o n can be d r a w n f r o m a c o m p a r i s o n o f t h e g r o w t h r a t e s o f n a t u r a l a n d e x p e r i m e n t a l la rva l h e r r i n g p o p u l a t i o n s : g r o w t h is g e n e r a l l y fas te r i n t h e sea. T h e m e a n GL f o r t h e n a t u r a l p o p u l a t i o n s o f Table A . 5 is 0.27 ( S D = 0 . 0 7 , n = 1 6 ) m m d - 1 c o m p a r e d t o 0.19 ( S D = 0 . 0 7 , n = 6 1 ) m m d - 1 f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f Tab les A . 1 a n d A . 3 . T h i s m a y be i n t e r p r e t e d as ev idence a g a i n s t t h e presence o f i r r e v e r s i b l e s t a r v a t i o n or i t m a y s i m p l y i n d i c a t e t h e ef fect o f s ize-select ive p r e d a t i o n o n h e r r i n g larvae. Mt w a s n o t s i g n i f i c a n t l y c o r r e l a t e d w i t h t h e m i d p o i n t o f t h e t e m p e r a t u r e r a n g e ( P = 0 . 8 7 ) , w i t h t h e la rge e x t r e m e o f t h e l e n g t h r a n g e ( P = 0 . 1 3 ) , o r w i t h t h e m i d p o i n t o f t h e l e n g t h r a n g e ( P = 0 . 2 2 ) . F i v e o f t h e 1 1 e s t i m a t e s ( 4 6 % ) o f Mt were e q u i v a l e n t t o an age o f first f e e d i n g o f 0 - 8 d ( F i g . A . 1 0 ) , b a s e d o n t h e d o u b l e d t o t a l m o r t a l i t y ra tes m e a s u r e d f r o m t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s tudy . F o u r ( 3 6 % ) , o f t h e r e m a i n i n g n a t u r a l ra tes were e q u i v a l e n t t o an age o f first f e e d i n g o f 8 - 1 2 d a n d t w o ( 1 8 % ) were e q u i v a l e n t t o a n age o f 16 d o r g r e a t e r . O n e o f these las t t w o e s t i m a t e s , n u m b e r 1 (Tab le A . 5 ) , a n d a n o t h e r e s t i m a t e e q u i v a l e n t t o an age o f first f e e d i n g o f 8 - 1 2 d , n u m b e r 12, were s u s p e c t e d b y t h e a u t h o r s o f h a v i n g b e e n i n f l a t e d t o a n u n k n o w n degree by d i s p e r s a l o f t h e larvae o u t o f t h e s a m p l i n g a r e a . T h e a c t u a l e q u i v a l e n t ages o f first f e e d i n g were lower t h a n t h o s e i n f e r r e d above because p r e d a t i o n , as w e l l as s t a r v a t i o n , was o p e r a t i n g i n t h e sea. I t is i m p o s s i b l e t o d e t e r m i n e how m u c h l o w e r t h e y a c t u a l l y were because t h e d i s t r i b u t i o n o f t h e m o r t a l i t y r a t e b e t w e e n t h e t w o agents is c o m p l e t e l y u n k n o w n . H o w e v e r , a p l o t o f Mt o n GL f o r t h e cases i n w h i c h b o t h r a t e s were m e a s u r e d shows t h a t seven o f t h e 11 n a t u r a l p o p u l a t i o n s are c l u s t e r e d i n t h e same r e g i o n o f t h e p l o t as a l l t h e e x p e r i m e n t a l p o p u l a t i o n s ( F i g . A . l l ) . T h e r e is n o c o r r e l a t i o n b e t w e e n Mt a n d GL f o r t h e n a t u r a l p o p u l a t i o n s ( P = 0 . 9 0 ) . T h e m e a n Mt f o r t h e n a t u r a l p o p u l a t i o n s is 0 .194 ( S D = 0 . 1 4 9 , n = l l ) d - 1 o r 0.152 ( S D = 0 . 1 3 0 , n = 9 ) d _ 1 i f p o p u l a t i o n s 1 a n d 12 are e x c l u d e d , a n d t h e m e a n r a t e fo r t h e c o m b i n e d e x p e r i m e n t a l p o p u l a t i o n s is 0 .081 ( S D = 0 . 0 6 1 , n = 5 3 ) d - 1 . T h e s e m e a n s are n o t s i g n i f i c a n t l y d i f ferent f r o m each o t h e r ( t - t e s t , P > 0 .05) . I c o n c l u d e t h a t 2 - 4 o f t h e 11 n a t u r a l e s t i m a t e s o f Mt ( 1 8 - 3 6 % ) are h i g h e n o u g h t h a t t h e y m u s t r e p r e s e n t c a t a s t r o p h i c m o r t a l i t y o f those c o h o r t s . T h i s m a y have b e e n c a u s e d b y u n u s u a l l y h i g h p r e d a t o r dens i t i es o r b y i r r e v e r s i b l e s t a r v a t i o n o f t h e first f e e d i n g la rvae. 172 F i g u r e A . 1 1 . P l o t o f Mt o n GL f o r e x p e r i m e n t a l a n d n a t u r a l p o p u l a t i o n s o f A t l a n t i c a n d Paci f ic h e r r i n g la rvae . T h e c losed s y m b o l s are e x p e r i m e n t a l p o p u l a t i o n s o f Pac i f i c h e r r i n g larvae r e a r e d a t 6 ° C (c i rc les) , 8 ° C (squares) , a n d 1 0 ° C ( t r i a n g l e s ) . T h e o p e n s y m b o l s are Paci f ic a n d A t l a n t i c h e r r i n g p o p u l a t i o n s t a k e n f r o m t h e l i t e r a t u r e , t h e c i rc les are n a t u r a l p o p u l a t i o n s , t h e squares are e x p e r i m e n t a l p o p u l a t i o n s f e d Artemia n a u p l i i a n d t h e t r i a n g l e s s are e x p e r i m e n t a l p o p u l a t i o n s fed o n l y z o o p l a n k t o n . T h e n u m b e r s i ns ide t h e o p e n s y m b o l s re fe r t o Tab les A . 3 a n d A . 5 . T h e d o u b l e c i rc les are n a t u r a l p o p u l a t i o n s s u s p e c t e d o f h a v i n g an i n f l a t e d Mt d u e t o d i s p e r s a l o f t h e larvae f r o m t h e s a m p l i n g a rea . A is t h e regress ion o f Mt o n GL f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f W e r n e r a n d B l a x t e r (1980) , B is t h e regress ion f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s t u d y a n d C is t h e regress ion o f t h e d o u b l e d Mt o n GL f o r t h e e x p e r i m e n t a l p o p u l a t i o n s o f t h i s s t u d y . See t e x t f o r t h e regress ion e q u a t i o n s . 173 174 T h i s e v i d e n c e is c o n s i s t e n t w i t h H j o r t ' s c r i t i c a l p e r i o d c o n c e p t t h a t year-class s t r e n g t h is con t ro l l ed b y o c c a s i o n a l c a t a s t r o p h i c s t a r v a t i o n o f f i r s t f e e d i n g la rvae. I t i m p l i e s t h a t 1 8 - 3 6 % o f h e r r i n g year classes are m u c h less a b u n d a n t t h a n t h e average year c lass. I t is i n t e r e s t i n g t o n o t e i n t h i s r e g a r d t h a t t h e r e l a t i v e f requenc ies o f t h e s m a l l e s t year classes f o r Georges B a n k , N o r t h Sea, a n d N o r w e g i a n s p r i n g - s p a w n i n g h e r r i n g s t o c k s are 3 3 , 6, a n d 3 0 % , r e s p e c t i v e l y , f o r t h e years 1 9 5 0 - 1 9 7 7 ( H e n n e m u t h e t a l . 1980) . 175 Appendix B Ring Deposition in the Otoliths of Larval Pacific Herring Appendix Summary T h e f i r s t r i n g i n t h e sag i tae o f l a r v a l Pac i f i c h e r r i n g is d e p o s i t e d a t t h e age o f c o m p l e t e yo lk a b s o r p t i o n . T h e ra tes o f d e p o s i t i o n o f subsequen t r i n g s i n f o u r g r o u p s o f larvae t h a t were fed d a i l y r a n g e d f r o m 0 . 1 2 - 0 . 9 6 r i n g d - 1 , a n d o n l y t w o o f t h e f o u r g r o u p s h a d a d a i l y p a t t e r n . Larvae t h a t were s t a r v e d f r o m h a t c h d e p o s i t e d one r i n g o n day 6 p o s t h a t c h , b u t a l l r i n g d e p o s i t i o n s t o p p e d t h e r e a f t e r . T h e s t a r v a t i o n o f s u b g r o u p s o f la rvae a f t e r 7 d o f f e e d i n g a n d a f t e r 25 d o f f e e d i n g p r o d u c e d d e p o s i t i o n * ra tes t h a t w e r e n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h o s e o f t h e p a r e n t f e e d i n g g r o u p s . T h e average ra tes o f r i n g d e p o s i t i o n were p o s i t i v e l y c o r r e l a t e d w i t h t h e average ra tes o f g r o w t h i n l e n g t h . D a i l y r i n g d e p o s i t i o n i n h e r r i n g la rvae < 20 m m l o n g o c c u r s i n p o p u l a t i o n s w i t h an average g r o w t h r a t e e q u a l t o o r h i g h e r t h a n 0.36 m m d - 1 . Introduction R i n g s o r i n c r e m e n t s i n t h e o t o l i t h s o f fishes have b e e n used t o age w i l d larvae o f severa l species ( R a l s t o n 1976 ; K e n d a l l a n d G o r d o n 1978; M e t h o t a n d K r a m e r 1979; T o w n s e n d a n d G r a h a m 1 9 8 1 ; U c h i y a m a a n d S t r u h s a k e r 1 9 8 1 ; L o u g h e t a l . 1982; V i c t o r 1982) . T h i s m e t h o d has t w o a s s u m p t i o n s : t h a t t h e first r i n g is d e p o s i t e d a t a fixed age i n each species, a n d t h a t t h e r a t e o f r i n g d e p o s i t i o n is c o n s t a n t a t 1 r i n g d - 1 . E v i d e n c e f r o m s t u d i e s o f r i n g d e p o s i t i o n i n e n c l o s u r e - r e a r e d larvae o f t h e A t l a n t i c h e r r i n g , Clupea harengus harengus, (Ge f fen 1982; L o u g h e t a l . 1982) , n o r t h e r n anchovy , Engraulis mordax, ( B r o t h e r s e t a l . 1976) , a n d E n g l i s h sole, Parophrys vetulus, ( L a r o c h e e t a l . 1982) , i n d i c a t e s t h a t these t w o a s s u m p t i o n s m a y n o t b e t r u e i n first-feeding larvae t h a t are s t a r v i n g o r g r o w i n g s low ly . T h e d e p o s i t i o n o f t h e first r i n g m a y b e de layed a n d t h e r a t e o f d e p o s i t i o n o f subsequen t r i n g s m a y b e s i g n i f i c a n t l y less t h a n 1 r i n g d - 1 . T h i s a p p e n d i x r e p o r t s t h a t t h e first r i n g is d e p o s i t e d a t a fixed age i n h e r r i n g larvae a n d t h a t t h i s age is c o i n c i d e n t a l w i t h t h e age a t c o m p l e t e yo lk a b s o r p t i o n . I t a lso c o n f i r m s t h a t t h e subsequen t r a t e o f d e p o s i t i o n is n o t a lways d a i l y b u t t h a t i t is pos i t i ve l y c o r r e l a t e d w i t h t h e r a t e o f g r o w t h i n l e n g t h . 176 Materials and Methods E x p e r i m e n t a l G r o u p s T h e b a t c h e x p e r i m e n t s r e p o r t e d here e m p l o y e d severa l d i f f e r e n t c o n t a i n e r sizes, t e m p e r a t u r e s , a n d p r e y t y p e s ( T a b l e B . l ) . S ix g r o u p s o f Pac i f i c h e r r i n g larvae were rea red f r o m t h e egg: f o u r were fed d a i l y f r o m h a t c h , one was s t a r v e d f r o m h a t c h , a n d one was t e r m i n a t e d 3 d a f t e r h a t c h b e f o r e f o o d was o f fe red . T w o a d d i t i o n a l s t a r v i n g g r o u p s were f o r m e d f r o m s u b - g r o u p s t h a t were r e m o v e d f r o m f e e d i n g t a n k s a f t e r 7 d o f f e e d i n g , a n d a f t e r 25 d o f f e e d i n g , a n d t h e n s t a r r e d t o d e a t h . R e a r i n g C o n d i t i o n s T h r e e g r o u p s , 1 9 8 0 A , 1 9 8 0 C , a n d 1 9 8 0 D , were ra i sed f r o m t h e egg i n 50 1 c i r c u l a r a q u a r i a i n A p r i l -J u n e , 1980. T h e eggs were l a i d o n t h e wa l ls o f a h o l d i n g t a n k by a d u l t h e r r i n g t h a t h a d b e e n c a p t u r e d i n t h e S t r a i t o f G e o r g i a by p e r s o n n e l o f t h e Pac i f i c B i o l o g i c a l S t a t i o n , N a n a i m o , B . C . T h e r e f o r e , t h e eggs c a m e f r o m t h e l o w e r east c o a s t s tock ( T a y l o r 1964) . A f t e r 14 d i n c u b a t i o n a t 7° C t h e eggs were h a t c h e d a n d t h e l a rvae o f 1 9 8 0 A a n d 1 9 8 0 C were t r a n s f e r r e d t o t h e r e a r i n g a q u a r i a . T h e m e a n t e m p e r a t u r e o f t hese t a n k s d u r i n g t h e r e a r i n g p e r i o d was 12.1° C ( S D = 0 . 9 ) . T h e 1 9 8 0 A g r o u p was fed f r o m h a t c h t o t h e e n d o f t h e e x p e r i m e n t a n d 1980C was s t a r v e d f r o m h a t c h t o d e a t h . T h e 1980D g r o u p was r e a r e d a t 7 ° C f o r 3 d b e f o r e i t was a c c i d e n t a l l y d e s t r o y e d . A f o u r t h g r o u p , 1 9 8 0 B , was f o r m e d f r o m a s u b s a m p l e o f 1 9 8 0 A w h i c h was p l a c e d i n i t s o w n 50 1 a q u a r i u m a f t e r 7 d o f f e e d i n g a n d t h e n s t a r v e d f o r 5 d . T w o g r o u p s , 1 9 8 1 A a n d 1 9 8 1 B , were r e a r e d i n A p r i l - M a y o f 1981 a t t h e B a m f i e l d M a r i n e S t a t i o n , B a m f i e l d , B . C . . T h e eggs c a m e f r o m n a t u r a l s p a w n l a i d o n Fucus s p p . i n t h e i n t e r t i d a l zone o f T o q u a r t B a y , B a r k l e y S o u n d , B . C . . T h e r e f o r e , t h e eggs c a m e f r o m t h e l o w e r west coas t s t o c k . T h e first p o p u l a t i o n , 1 9 8 1 A , was ra i sed i n a 1000 1 c i r c u l a r , flowthrough a q u a r i u m . T h e w a t e r t e m p e r a t u r e rose g r a d u a l l y f r o m 8° t o 9 ° C over t h e r e a r i n g p e r i o d . F o o d was a d d e d dai ly . 1 9 8 1 B was r e a r e d i n a c u l t u r e c h a m b e r s u s p e n d e d i n B a m f i e l d I n l e t . T h e c h a m b e r , a 2000 1 c i r c u l a r t a n k ( M a r l i a v e 1981) , floated a t t h e s u r f a c e o f t h e I n l e t (F igs . B . l a n d B . 2 ) . W i l d p l a n k t o n was swept t h r o u g h l o u v r e s o n one s ide o f t h e c h a m b e r b y t i d a l c u r r e n t s a n d was t r a p p e d i n t h e c h a m b e r w h e r e i t served as f o o d f o r t h e l a r vae . T h e r e were n o h e r r i n g larvae i n t h e p l a n k t o n o f t h e I n l e t d u r i n g t h e first 3 weeks so t h e 177 T A B L E B . l . T h e e x p e r i m e n t a l g r o u p s a n d t h e i r r e a r i n g c o n d i t i o n s . G r o u p T a n k R e a r i n g F e e d i n g F o o d V T T r e a t m e n t T y p e (1) ( ° C ) 1 9 8 0 A 50 12.1 fed f r o m day 2 Artemia 1 9 8 0 B 50 12 .1 s ta rved f r o m day 7 n o n e 1 9 8 0 C 50 12 .1 s ta rved f r o m h a t c h n o n e 1980D 50 7 s ta rved f r o m h a t c h n o n e 1 9 8 1 A 1000 8 - 9 fed f r o m h a t c h Artemia, p l a n k t o n 1 9 8 1 B 2000 9 - 1 0 fed f r o m h a t c h p l a n k t o n 1 9 8 2 A 25 8 - 9 fed f r o m h a t c h Artemia 1 9 8 2 B 25 8 - 9 s t a r v e d f r o m day 30 n o n e 178 F i g u r e B . l . D i a g r a m o f t h e i n s i t u c u l t u r e c h a m b e r used t o rear p o p u l a t i o n 1 9 8 1 B . 179 TO ANCHOR F i g u r e B . 2 . D e a t a i l o f t h e c u l t u r e c h a m b e r used t o rear p o p u l a t i o n 1 9 8 1 B s h o w i n g t h e s ide l o u v r e s w i t h t h e screen r e m o v e d a n d t h e holes i n t h e c h a m b e r f l o o r . 1 8 1 182 t a n k p o p u l a t i o n was n o t c o n t a m i n a t e d w i t h w i l d h e r r i n g . T h e su r face w a t e r t e m p e r a t u r e o f t h e I n l e t over t h e r e a r i n g season was 8 - 1 0 ° C . O n e g r o u p , 1 9 8 2 A , was r e a r e d f r o m t h e egg i n t h e l a b o r a t o r y a t t h e S t a t i o n i n A p r i l - M a y , 1982. I t g r e w i n a 25 1 r e c t a n g u l a r a q u a r i a c o o l e d t o 8 - 9 ° C . T h e eggs c a m e f r o m n a t u r a l spawn l a i d on eelgrass, Zostera marinus, i n t h e i n t e r t i d a l zone a t t h e h e a d o f B a m f i e l d I n l e t a n d so t h e y c a m e f r o m t h e lower w e s t coas t s t o c k . T h e fish were fed f r o m h a t c h t o age 30 d a n d t h e n t h e s u r v i v o r s were m o v e d t o a n o t h e r t a n k o f t h e same size w h e r e t h e y were s t a r v e d f o r 8 d . T h i s s u b g r o u p was n a m e d 1982B. T h e l i g h t i n g f o r a l l t h e l a b o r a t o r y g r o u p s was fiourescent a n d ' i t was o n a 10 h o u r l i g h t : 1 4 h o u r d a r k cyc le . T h e cyc le was c u e d t o t h e n a t u r a l p h o t o p e r i o d w i t h l i g h t sensors . T h e wa te r i n a l l o f t h e t a n k s e x c e p t 1 9 8 1 A a n d 1 9 8 1 B was g e n t l y a e r a t e d w i t h a n a i r s t o n e a n d a b o u t one t h i r d o f t h e \ o l u m e was r e p l a c e d w i t h f r e s h seawate r d a i l y . D e a d o r g a n i s m s a n d feces were s i p h o n e d o f f t h e floor o f a l l t a n k s d a i l y e x c e p t 1 9 8 1 B w h i c h d i d n o t a c c u m u l a t e wastes because i t s floor, d r i l l e d w i t h over 1000 s m a l l ho les , was s e l f - c l e a n i n g . H a t c h i n g A l l l a rvae i n a n y s ing le g r o u p were h a t c h e d w i t h i n 24 h o u r s o f each o t h e r . I n 1980 h a t c h i n g was s t i m u l a t e d b y s c r a p i n g t h e eggs o f f t h e w a l l o f a h o l d i n g t a n k . I n 1981 a n d 1982 h a t c h i n g was s t i m u l a t e d b y e x p o s i n g l a te s tage eggs t o a i r f o r 15 m i n u t e s . T h e e x p o s u r e caused a n explos ive h a t c h w h e n t h e eggs were r e t u r n e d t o s e a w a t e r . T h e egg masses were r e m o v e d f r o m t h e t a n k s less t h a n 24 h o u r s a f t e r h a t c h i n g b e g a n . F o o d F o o d f o r t h r e e o f t h e f o u r f e d p o p u l a t i o n s c o n s i s t e d o f f r e s h l y - h a t c h e d Artemia n a u p l i i . O n e o f t h e f e e d i n g g r o u p s , 1 9 8 1 B , fed exc lus i ve l y o n w i l d p l a n k t o n swep t i n t o t h e c h a m b e r by t i d a l c u r r e n t s . A n o t h e r g r o u p , 1 9 8 1 A , was ra i sed o n a d i e t o f Artemia n a u p l i i s u p p l e m e n t e d w i t h w i l d p l a n k t o n c a p t u r e d f r o m t h e su r face o f B a m f i e l d I n l e t w i t h a p l a n k t o n n e t . I n a l l f e e d i n g g r o u p s f o o d was first s u p p l i e d e i t h e r a t h a t c h o r b e f o r e t h e s e c o n d day a f t e r h a t c h , t h e day w h e n Pac i f i c h e r r i n g larvae first b e g i n t o f e e d . B o t h t h e Artemia n a u p l i i a n d t h e w i l d , z o o p l a n k t e r s were a t t r a c t e d t o t h e o v e r h e a d 183 l i g h t a n d t h e y t e n d e d t o c l u s t e r i n a p a t c h a t t h e su r face o f t h e w a t e r . E n o u g h f o o d o r g a n i s m s were a d d e d each d a y t o t h e f e e d i n g g r o u p s t o m a i n t a i n t h e pa tches a t a l l t i m e s . I t is n o t k n o w n w h e t h e r t h e 1981B la rvae i n t h e c u l t u r e c h a m b e r h a d a s i m i l a r o p p o r t u n i t y , b u t t h e r e l a t i v e l y h i g h g r o w t h r a t e o f t h i s g r o u p i n d i c a t e s t h a t f o o d was a b u n d a n t . T h e absence o f f o o d o r g a n i s m s i n t h e w a t e r o f t h e s t a r v i n g g r o u p s was e n s u r e d by filtering seawater t h r o u g h a layer o f glass w o o l b e f o r e i t was a d d e d t o a t a n k . S a m p l e s o f filtered w a t e r were e x a m i n e d u n d e r a m i c r o s c o p e t o v e r i f y t h e absence o f f o o d o r g a n i s m s . S a m p l e s Samp les o f 1 0 - 1 8 larvae were t a k e n f r o m each o f t h e g r o u p s a t i n t e r v a l s o f 2 - 2 0 d . I n 1980 t h e fish were f r o z e n a t - 1 0 ° C a n d i n 1981 a n d 1982 t h e y were preserved i n 3 7 % i s o p r o p y l a l c o h o l . T h e s t a n d a r d l e n g t h was m e a s u r e d f r o m t h e t i p o f t h e s n o u t t o t h e e n d o f t h e n o t o c h o r d w i t h t h e vern ie r scale o f a c o m p o u n d m i c r o s c o p e . S o m e o f t h e larvae were m e a s u r e d l ive b e f o r e p r e s e r v a t i o n , s t o r e d i n d i v i d u a l l y a n d t h e n m e a s u r e d a g a i n 1-6 m o n t h s l a t e r . F reez ing c a u s e d a m e a n sh r inkage o f 6 . 3 % ( S D = 3 . 5 , n = 2 6 ) a n d i s o p r o p y l a l c o h o l caused a m e a n sh r inkage o f 0 . 0 4 % ( S D = 3 . 2 , n = 9 7 ) w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m zero p e r c e n t s h r i n k a g e ( t - t e s t , P > 0 .9 ) . A n e x a m i n a t i o n o f t h e i n d i v i d u a l p e r c e n t s h r i n k a g e s s h o w e d n o t r e n d w i t h l ive s t a n d a r d l e n g t h . T h e f r o z e n l e n g t h s were c o r r e c t e d t o l i ve l e n g t h s b y m u l t i p l y i n g b y t h e f a c t o r 1.063. T h e a l c o h o l - p r e s e r v e d l e n g t h s d i d n o t r e q u i r e c o r r e c t i o n . R i n g C o u n t i n g A f t e r e x t r a c t i o n f r o m t h e s k u l l t h e s a g i t t a e were p l a c e d o n a glass s l ide u n d e r i m m e r s i o n o i l a n d t h e i r d i a m e t e r s were m e a s u r e d w i t h an o c u l a r m i c r o m e t e r . S a g i t t a e are s l i g h t l y f l a t t e n e d s p h e r o i d s i n y o u n g la rvae a n d t h e y t e n d t o b e c o m e m o r e o v a l as t h e fish g rows . T h e d i a m e t e r m e a s u r e d was a lways t h e l o n g e s t ax i s . T h e s a g i t t a e were were p h o t o g r a p h e d a t 4 0 0 - 1 0 0 0 x , t h e d e v e l o p e d film was p r o j e c t e d o n a sc reen , a n d t h e r i n g s were c o u n t e d . A s ing le r i n g c o n s i s t e d o f a d a r k b a n d a n d a n a d j a c e n t l i g h t b a n d . A l l r i n g s , n o m a t t e r h o w f a i n t , were c o u n t e d . T w o classes o f r i n g were obse rved : (1) a g r o u p o f 1-5 t h i n , f a i n t r i n g s c l u s t e r e d a b o u t t h e nuc leus s u r r o u n d e d by (2) w i d e r , d a r k e r r i n g s t h a t c o m p o s e d t h e m a j o r i t y o f t h e r i n g s i n m o s t la rvae. I n some s a g i t t a e t h e second class o f r i n g s 184 were s e p a r a t e d f r o m t h e first b y a d i s t i n c t r i n g w h i c h m a y have b e e n a check d e p o s i t e d i n response t o t h e e x h a u s t i o n o f t h e y o l k . T h e t w o classes c o u l d n o t a lways be c l e a r l y d i s t i n g u i s h e d , p a r t i c u l a r l y i n s l o w - g r o w i n g fish. T h e first class c o r r e s p o n d s t o Ge f fen ' s (1982) ' yo lk sac ' r i ngs a n d t h e second t o h e r ' n o r m a l ' o r ' r e g u l a r ' r i n g s . I n t h i s p a p e r t h e first class w i l l be u n n a m e d because (1) m o s t r i n g s were f o u n d i n la rvae t h a t h a d c o m p l e t e l y a b s o r b e d t h e i r y o l k , a n d (2) i t has n o t b e e n e s t a b l i s h e d t h a t t h e t w o c lasses .o f r i n g s are f u n d a m e n t a l l y d i f f e ren t f r o m each o t h e r so t h e i n t r o d u c t i o n o f n e w t e r m i n o l o g y is p r e m a t u r e . Ge f fen d e f i n e d a ' f i r s t heavy r i n g ' t h a t was f o u n d b e t w e e n t h e o u t e r m a r g i n o f t h e n u c l e u s a n d t h e first n o r m a l r i n g . T h i s t e r m has n o t been used because t h e first n o r m a l r i n g was n o t a l w a y s d i s t i n g u i s h a b l e f r o m s u b s e q u e n t n o r m a l r i n g s . E a c h s a g i t t a w a s c o u n t e d t h r e e t i m e s a n d t h e m e a n o f t h e t h r e e c o u n t s was t a k e n as t h e final c o u n t o f t h a t s a g i t t a . T h e r i n g c o u n t o f a f i s h was t h e m e a n o f t h e final coun ts o f i t s t w o s a g i t t a e . T h e m e a n d i f f e rence i n final c o u n t s b e t w e e n s a g i t t a e o f t h e same fish was 1.3 ( S D = 1 . 4 ) , w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m zero ( t - t e s t , P > 0 .2 ) . T h e s a g i t t a e o f 2 1 la rge larvae (l ive l e n g t h = 14—29 m m , a g e = 2 0 - 5 4 d ) se lec ted r a n d o m l y f r o m several g r o u p s were p h o t o g r a p h e d a n d t h e n fixed t o a glass s l ide w i t h c y a n o a c r y l a t e g lue a n d g r o u n d t o t h e m i d p l a n e w i t h m e t a l l i c l a p p i n g p a p e r . T h e y were r e p h o t o g r a p h e d a n d r e c o u n t e d . T h e m e a n d i f fe rence was 1.1 ( S D = 2 . 0 ) , w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m zero ( t - t e s t , P > 0 .9) . I n s p e c t i o n o f t h e d a t a revealed n o t r e n d o f t h e d i f f e rence w i t h age o r w i t h t h e r i n g c o u n t o f t h e n o n - g r o u n d s a g i t t a e . D a t a A n a l y s i s T h e average ra tes o f r i n g d e p o s i t i o n a n d o f g r o w t h i n l e n g t h were c a l c u l a t e d as t h e s lopes o f l i n e a r p r e d i c t i v e regress ions o f m e a n r i n g n u m b e r a n d m e a n l e n g t h o n age. T h e h o m o g e n e i t y o f t h e va r iances o f t h e m e a n s was t e s t e d w i t h B a r t l e t t ' s t e s t (Sokal a n d R o h l f 1969) a n d i f t h e y were f o u n d t o b e h e t e r o g e n o u s each m e a n was w e i g h t e d w i t h i t s s a m p l e size d i v i d e d by i t s va r iance . Results G r o w t h i n l i ve s t a n d a r d l e n g t h was p o s i t i v e i n a l l g r o u p s e x c e p t 1 9 8 0 C a n d 1 9 8 0 B , i n w h i c h t h e s t a r v i n g l a r v a e s h r a n k . L i n e a r g r o w t h was a s s u m e d f o r t h e p u r p o s e o f o b t a i n i n g average g r o w t h ra tes t o c o m p a r e w i t h t h e average r i n g d e p o s i t i o n r a t e s (Tab le B .2 ) . G r o w t h r a t e was h i g h e s t i n t h e 2000 1 185 T A B L E B .2 . L i n e a r regress ions o f m e a n s t a n d a r d l e n g t h o n age i n 7 g r o u p s o f la rvae. G r o u p i n t e r c e p t s lope S E o f r N o . o f n ( m m ) ( m m d - 1 ) s lope M e a n s 1 9 8 0 A 10.4 0.180 0.030 0.97 4 36 1 9 8 0 B 13.1 -0 .004 0.019 0.19 3 20 1980C 11.2 -0 .107 0 .031 0.90 5 50 1 9 8 1 A 8 . 2 . 0 .231 0 .011 0.99 6 57 1 9 8 1 B 8.4 0.290 0.049 0.96 5 60 1 9 8 2 A 10.6 0.090 0.047 0.89 3 38 1 9 8 2 B 11.4 0.100 0.035 . 0.89 4 39 186 c u l t u r e c h a m b e r a n d lowes t i n t h e 25 1 a q u a r i u m . T h e r e was a p o s i t i v e b u t n o n - s i g n i f i c a n t c o r r e l a t i o n b e t w e e n g r o w t h r a t e a n d c o n t a i n e r size i n t h e f o u r f e d g r o u p s ( r==0.90 , n = 4 , P > 0 .1 ) . T h e t h i n , f a i n t r i n g s o f t h e first c lass were f o u n d i n t h e o t o l i t h s o f m o s t o f t h e 1980 fish t h a t were less t h a n 14 m m l o n g b u t t h e y were n o t f o u n d i n t h e o t o l i t h s o f any 1981 a n d 1982 fish. T h e s e r i n g s m a y h a v e b e e n d e p o s i t e d a t any t i m e b e t w e e n t h e l a t e e m b r y o a n d t h e p o s t y o l k sac s tage . T h e o n l y s a m p l e o f o t o l i t h s f r o m yo lk -sac larvae was a s ing le s a m p l e f r o m 1980D w i t h a m e a n r i n g coun t o f 5.2 ( S D = 0 . 8 , n = 9 ) o n day 1 . T h e r i n g s were n o t observed i n o l d e r , l a r g e r la rvae; t h e y m a y have b e e n p r e s e n t b u t o b s c u r e d by o v e r b u r d e n over t h e n u c l e u s . T h i s p h e n o m e n o n has b e e n observed i n t h e o t o l i t h s o f l a r v a l l a r g e m o u t h bass , Micropterus salmoides, ( M i l l e r a n d S to rck 1982) . T h e first n o r m a l r i n g was d e p o s i t e d i n a l l g r o u p s i n c l u d i n g 1980C by day 6, t h e day a f t e r c o m p l e t e y o l k a b s o r p t i o n . T h i s agrees w e l l w i t h t h e age a t first i n c r e m e n t o f 4.5 ( r a n g e = = 0 - 9 d ) f o u n d f o r A t l a n t i c h e r r i n g b y L o u g h e t a l . (1982) , a n d w i t h t h e age o f 6 d f o u n d f o r t h e same species by Ge f fen (1982) . T h i s i n d i c a t e s t h a t h e r r i n g larvae o f b o t h sub-spec ies have a fixed age a t first i n c r e m e n t d e p o s i t i o n a n d t h a t i t co inc ides w i t h t h e age a t c o m p l e t e yo lk a b s o r p t i o n . T h e r a t e s o f s u b s e q u e n t r i n g d e p o s i t i o n f o r t h e f o u r fed g r o u p s r a n g e d f r o m 0 .12 -0 .96 r i n g d - 1 (Tab le B .3) a n d o n l y 1 9 8 0 A a n d 1 9 8 1 B h a d r a t e s t h a t were n o t s i g n i f i c a n t l y d i f fe ren t f r o m 1 r i n g d - 1 P > 0.9 a n d P > 0 .2 , r e s p e c t i v e l y ) . 1 9 8 1 A h a d a r a t e t h a t was s i g n i f i c a n t l y less t h a n 1 r i n g d - 1 (P > 0 .001) b u t also s i g n i f i c a n t l y g r e a t e r t h a n zero r i n g d - 1 (P < 0 .001) . 1 9 8 2 A h a d a r a t e t h a t was s i g n i f i c a n t l y less t h a n 1 r i n g d - 1 (P > 0 .001) a n d n o t s i g n i f i c a n t l y g r e a t e r t h a n zero r i n g d - 1 ( P > 0 .4) . T h e r a t e o f r i n g d e p o s i t i o n i n 1 9 8 0 C , t h e g r o u p t h a t was s t a r v e d f r o m h a t c h , was -0 .05 r i n g d - 1 , w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m zero (P > 0 .2) . T h i s i n d i c a t e s t h a t t h e s t a r v a t i o n o f first-f e e d i n g l a rvae s t o p p e d r i n g p r o d u c t i o n . 1 9 8 0 B h a d a r a t e w h i c h was n o t s i g n i f i c a n t l y d i f fe ren t f r o m 1 r i n g d - 1 (P > 0 .2) a n d n o t s i g n i f i c a n t l y d i f f e ren t f r o m a r a t e o f zero (P > 0 .9) o r f r o m t h e r a t e o f i t s p a r e n t f e e d i n g g r o u p , 1 9 8 0 A (P > 0 .5 ) . O n e reason f o r these r e s u l t s is t h a t t h e 1 9 8 0 B g r o u p h a d o n l y t h r e e d a t a p o i n t s f o r t h e regress ion a n d so t h e s t a n d a r d e r r o r o f t h e s lope was r e l a t i v e l y h i g h : 1 2 2 % o f t h e s l o p e . I c o n c l u d e t h a t 5 d s t a r v a t i o n a f t e r 6 - 7 d o f f e e d i n g h a s n o ef fect o n t h e r a t e o f r i n g d e p o s i t i o n . 1 9 8 2 B h a d a r i n g d e p o s i t i o n r a t e t h a t was n o t s i g n i f i c a n t l y d i f fe ren t f r o m zero (P > 0 .05 ) , 187 T A B L E B.3 . L i n e a r regress ions o f m e a n n o r m a l r i n g n u m b e r o n age i n 7 g r o u p s o f larvae. G r o u p . i n t e r c e p t s lope S E o f r N o . o f n ( r i n g s ) ( r i n g d - 1 ) s lope M e a n s 1 9 8 0 A -4 .12 0.96 0.06 0.99 4 36 1 9 8 0 B 2.06 0.23 0.28 0.63 3 20 1980C 2.12 -0 .05 0.02 0.83 5 50 1 9 8 1 A - 9 . 3 1 0.63 0.05 0.99 6 57 1 9 8 1 B -5 .60 0.83 0.08 0.99 5 60 1 9 8 2 A 1.45 0.12 0.08 0.83 3 38 1 9 8 2 B 4.90 0.10 0 .11 0.53 4 39 188 a n d w h i c h was n o t s i g n i f i c a n t l y d i f f e r e n t f r o m t h e r a t e o f i t s p a r e n t f e e d i n g g r o u p , 1 9 8 2 A (P > 0.75) . I c o n c l u d e t h a t 8 d o f s t a r v a t i o n a f t e r 25 d o f f e e d i n g has n o ef fect o n t h e r a t e o f r i n g d e p o s i t i o n . T h e average r i n g d e p o s i t i o n r a t e s were s i g n i f i c a n t l y p o s i t i v e l y c o r r e l a t e d w i t h t h e average g r o w t h ra tes ( F i g . B . 3 ) : (B.l) R i n g r a t e = 0.14 + 2 . 4 0 G r o w t h r a t e , n — 7, r = 0.83, P > 0.05. T h e res idua ls o f t h i s regress ion were n o t c o r r e l a t e d w i t h c o n t a i n e r size a n d t h e r e was n o obv ious r e l a t i o n s h i p w i t h p r e y t y p e . H o w e v e r , t h e r e was a s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n w i t h t h e m e a n r e a r i n g t e m p e r a t u r e s ( r = 0 . 8 3 , n = 7 , P > 0 .05) . T h e m u l t i p l e reg ress ion was ( 5 . 2 ) R i n g r a t e = - 1 . 3 9 + 3 . 3 6 G r o w t h r a t e + 0 . 1 4 T e m p e r a t u r e , n = 7, r = 0 .99,P < 0 . 0 0 1 . T h e s e r e s u l t s c o n f i r m t h e c o r r e l a t i o n b e t w e e n r i n g d e p o s i t i o n r a t e a n d g r o w t h r a t e r e p o r t e d f o r A t l a n t i c h e r r i n g la rvae b y Ge f fen (1982) . Ge f fen i n t e r p r e t e d t h e r e l a t i o n s h i p as b e i n g c u r v i l i n e a r a n d l i n e a r i z e d i t b y t r a n s f o r m i n g b o t h var iab les w i t h l o g a r i t h m s . I n o r d e r t o c o m p a r e t h e t w o sets o f d a t a l i n e a r i t y was a s s u m e d . C o v a r i a n c e ana lys i s o f t h e t w o l i n e a r regress ions i n d i c a t e d t h a t t h e r e was n o s i g n i f i c a n t d i f fe rence b e t w e e n t h e s lopes (P > 0 .05) . T h e d a t a f r o m t h i s s t u d y a n d f r o m Gef fen ' s were p o o l e d a s ing le l i n e a r reg ress ion was c a l c u l a t e d , ( B . 3 ) R i n g r a t e = 0.17 + 2 . 1 2 G r o w t h r a t e , n == 12, r = 0 .85 , P < 0 . 0 0 1 . T h e i n f l u e n c e o f t e m p e r a t u r e o n r i n g d e p o s i t i o n r a t e c o u l d n o t b e c o m p a r e d b e t w e e n t h e t w o d a t a sets because Gef fen 's r e a r i n g t e m p e r a t u r e s were n o t c o n s t a n t . Discussion T h e first class o f t h i n r i n g s was f o u n d i n t h e o t o l i t h s o f A t l a n t i c h e r r i n g larvae by G e f f e n (1982) a n d b y L o u g h e t a l . (1982) a n d t h e y have also b e e n d e s c r i b e d i n t h e o t o l i t h s o f l a r va l t u r b o t , Scopthal-mus maximus, (Ge f fen 1982) a n d A r c t o - N o r w e g i a n c o d , Gadus morhua ( G j o s a e t e r a n d T i l s e t h 1982) . I n c r e m e n t s have also b e e n f o u n d i n s i d e t h e nuc leus i n A t l a n t i c h e r r i n g ( L o u g h e t a l . 1982) , a n d i n t h r e e species o f t h e genus Lepomis a n d i n t h e M o z a m b i q u e m o u t h b r e e d e r , Tilapia mossambica, ( T a u b e r t 189 F i g u r e B .3 . R e l a t i o n s h i p b e t w e e n t h e average r i n g d e p o s i t i o n ra tes a n d t h e average g r o w t h ra tes o f seven g r o u p s o f P a c i f i c h e r r i n g la rvae . See t e x t f o r regress ion e q u a t i o n . 1 9 0 1.2 r - 0 . 4 h - 0 . 1 0 . 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 GROWTH RATE (MM/DAY) 191 a n d C o b l e 1977) . I n t h e m u m m i c h o g , Fundulus heteroclitus, these r i n g s are r e g u l a r d a i l y r i n g s t h a t are d e p o s i t e d b e f o r e h a t c h i n g ( R a d t k e a n d D e a n 1982) . L o u g h et a l . (1982) sugges ted t h a t t h e first class o f t h i n r i n g s were r e l a t e d t o t h e i n a b i l i t y o f first-feeding la rvae t o m e e t t h e i r m e t a b o l i c d e m a n d s d u r i n g t h e t r a n s i t i o n t o exogenous f o o d . T h i s a r g u m e n t i m p l i e s t h a t t h e 1980 h e r r i n g larvae were less ab le t o c a p t u r e f o o d t h a n t h e 1 9 8 1 - 8 2 larvae. H o w e v e r , t h i s h y p o t h e s i s does n o t e x p l a i n t h e presence o f f a i n t r i n g s i n t h e 1 9 8 0 C larvae t h a t were s t a r v e d f r o m h a t c h . T h e r e s u l t s o f t h i s s t u d y c o n f i r m Ge f fen ' s o b s e r v a t i o n s t h a t t h e r a t e o f r i n g p r o d u c t i o n is n o t a lways d a i l y a n d t h a t i t is p o s i t i v e l y c o r r e l a t e d w i t h t h e r a t e o f g r o w t h i n b o d y s ize. T h e c o r r e l a t i o n m e a n s t h a t r i n g s c a n n o t be used w i t h c o n f i d e n c e t o age w i l d larvae less t h a n a b o u t 20 m m l o n g un less t h e average g r o w t h r a t e is k n o w n t o be h i g h e r t h a n a b o u t 0.36 m m d - 1 . C o n t a i n e r size, t e m p e r a t u r e , o r p r e y size m a y have ef fects o n t h e r a t e o f r i n g d e p o s i t i o n a p a r t f r o m t h a t w h i c h is e x p l a i n e d b y g r o w t h r a t e . T e m p e r a t u r e e x p l a i n s some o f t h e r e s i d u a l va r iance o f t h e r i n g d e p o s i t i o n r a t e - g r o w t h r a t e reg ress ion . H o w e v e r , t h e p u b l i s h e d e v i d e n c e o n t h e ef fect o f c o n s t a n t t e m p e r a t u r e o n r i n g d e p o s i t i o n does n o t s u p p o r t t h e h y p o t h e s i s t h a t h i g h e r t e m p e r a t u r e s p r o d u c e m o r e i n c r e m e n t s ( N e i l s o n a n d G e e n 1982) . 192 Appendix C Multivariate Analysis of Morphometry and Dry Weight of Larval Pacific Herring Appendix Summary B i v a r i a t e a n d m u l t i v a r i a t e c o n d i t i o n f a c t o r s o f l a r v a l Pac i f i c h e r r i n g were c o m p a r e d i n t e r m s o f t h e i r i n d e p e n d e n c e f r o m size, t h e i r b i o l o g i c a l m e a n i n g , a n d t h e i r o r t h o g o n a l i t y . R a t i o s a n d r e s i d u a l s o f u n i v a r i a t e regress ions were m i x t u r e s o f size a n d s h a p e i n f o r m a t i o n , c o u l d n o t b e i n t e r p r e t e d i n t e r m s o f a l l o m e t r y , a n d were h i g h l y i n t e r c o r r e l a t e d . A l l p r i n c i p a l c o m p o n e n t s , e x c e p t t h e first, were i n d e p e n d e n t o f s ize, t h e i r l o a d i n g p a t t e r n s revealed re l i ab le i n f o r m a t i o n a b o u t a l l o m e t r y , a n d t h e y were c o m p l e t e l y u n c o r r e c t e d w i t h each o t h e r . E x a m i n a t i o n o f t h e l e n g t h a n d w e i g h t d a t a o f r e a r e d a n d w i l d Pac i f i c a n d A t l a n t i c h e r r i n g larvae r e p o r t e d i n t h e l i t e r a t u r e i n d i c a t e d t h a t r e a r e d larvae are heav ie r p e r u n i t l e n g t h t h a n w i l d la rvae, t h a t m o r p h o m e t r y var ies b e t w e e n t h e t w o s u b - s p e c i e s , a n d t h a t t h e effects o f enc losu re a n d gear se lec t i on c o n f o u n d t h e c a l i b r a t i o n o f c o n d i t i o n f a c t o r s w i t h r e a r e d l e a r n i n g s a m p l e s . T h e i m p l i c a t i o n s f o r t h e use o f m o r p h o m e t r i c c o n d i t i o n f a c t o r s i n la rva l fish eco logy are d i scussed . Introduction M o r p h o m e t r i c c h a r a c t e r s a n d d r y w e i g h t have o f t e n b e e n used as va r iab les i n l a r v a l fish c o n d i t i o n f a c t o r s b e c a u s e o f t h e i r ease o f m e a s u r e m e n t ( S h e l b o u r n e 1957; H e m p e l a n d B l a x t e r 1963; B l a x t e r 1965, 1 9 7 1 ; V i l e l a a n d Z i j l s t r a 1 9 7 1 ; A r t h u r 1976; T h e i l a c k e r 1978; W e s t e r n h a g e n a n d R o s e n t h a l 1981) . H o w e v e r , t h e r e are severa l ser ious p r o b l e m s assoc ia ted w i t h t h e i r p r a c t i c a l use as ind i ces o f n u t r i t i o n a l s t a t u s . T h e r e m a y b e d i f fe rences i n m o r p h o m e t r y b e t w e e n w i l d a n d r e a r e d larvae t h a t p r e v e n t t h e a c c u r a t e c a l i b r a t i o n o f c o n d i t i o n f a c t o r s w i t h l e a r n i n g s a m p l e s o f r e a r e d fish ( B l a x t e r 1 9 7 1 ; B a l b o n t i n e t a l . 1973) . C a p t u r e i n a h i g h - s p e e d p l a n k t o n n e t u s u a l l y d i s t o r t s t h e b o d y p r o p o r t i o n s o f fish larvae ( B l a x t e r 1 9 7 1 ; T h e i l a c k e r 1980a ; H a y 1981) , w h i c h f u r t h e r c o n f o u n d s t h e c o m p a r i s o n b e t w e e n r e a r e d a n d field-caught fish. T h e r e m a y also be r a c i a l d i f fe rences i n m o r p h o m e t r y a n d t issue d e n s i t y b e t w e e n larvae f r o m d i f f e r e n t s p a w n i n g s t o c k s ( B l a x t e r 1971) . I f m o r p h o m e t r i c c o n d i t i o n f a c t o r s c a n n o t b e a c c u r a t e l y c a l i b r a t e d w i t h r e a r e d fish t h e y m a y s t i l l b e u s e d as e s t i m a t e s o f ' a p p a r e n t ' c o n d i t i o n , t o 193 be c o r r e l a t e d w i t h b i o t i c or a b i o t i c va r iab les . T h e use o f e i t h e r c a l i b r a t e d o r u n c a l i b r a t e d c o n d i t i o n f a c t o r s requ i res t h a t t h e s t a t i s t i c a l , b i o l o g i c a l , a n d p r a c t i c a l aspec ts o f m o r p h o m e t r i c c o n d i t i o n f a c t o r s be w e l l u n d e r s t o o d . H o w e v e r , these aspects have never b e e n e x p l i c i t l y e x a m i n e d i n t h e fisheries l i t e r a t u r e i n t h e c o n t e x t o f m u l t i v a r i a t e ana lys is o f m o r p h o m e t r i c d a t a . T h e f o l l o w i n g ru les o f c o n d i t i o n f a c t o r s are c o n s i d e r e d se l f -ev iden t : (1) a c o n d i t i o n f a c t o r m u s t be i n d e p e n d e n t o f size so t h a t changes i n t h e f a c t o r w i t h t i m e a n d space c a n be i n t e r p r e t e d u n a m b i g u o u s l y as changes i n n u t r i t i o n a l s t a t u s , (2) a c o n d i t i o n f a c t o r m u s t have some b i o l o g i c a l m e a n i n g i n t h e sense t h a t t h e coef f i c ien ts ass igned t o i t s c o n s t i t u e n t var iab les s h o u l d reveal i n f o r m a t i o n a b o u t a l l o m e t r y , a n d (3) a set o f c o n d i t i o n f a c t o r s m u s t be u n c o r r e l a t e d w i t h each o t h e r so t h a t i f t h e y s h o u l d b e used t o sepa ra te t w o o r m o r e g r o u p s o f a n i m a l s , e i t h e r by o b s e r v a t i o n o r by d i s c r i m i n a n t a n a l y s i s , t h e n t h e y w i l l be se lected o n l y f o r t h e i n f o r m a t i o n t h e y c o n t a i n a n d n o t f o r w h a t t h e y share w i t h o t h e r c o r r e l a t e d f a c t o r s . T h e s e t h r e e r u l e s : s i z e - i n d e p e n d e n c e , b i o l o g i c a l m e a n i n g , a n d o r t h o g o n a l i t y , de f ine a n i d e a l m o r p h o m e t r i c c o n d i t i o n f a c t o r . N o n e o f t h e m o r p h o m e t r i c c o n d i t i o n f a c t o r s t h a t hav e a p p e a r e d i n t h e fisheries l i t e r a t u r e have sa t i s f ied these r u l e s . A l l are h i g h l y c o r r e l a t e d w i t h size a n d , as t h e y are u s u a l l y r a t i o s o r r e s i d u a l s o f u n i v a r i a t e regress ions , t h e i r b i o l o g i c a l m e a n i n g is d i f f i c u l t , i f n o t i m p o s s i b l e , t o i n t e r p r e t e because o n l y t w o d i m e n s i o n s c a n b e c o m p a r e d a t a t i m e . T h e y are also h i g h l y i n t e r c o r r e l a t e d . T h e theses o f t h i s a p p e n d i x a re : (1) t h a t o n l y p r i n c i p a l c o m p o n e n t s ( P C s ) s a t i s f y a l l t h r e e re-q u i r e m e n t s , a n d (2) t h a t t h e o p t i m a l c o n d i t i o n f a c t o r f o r d i a g n o s i n g n u t r i t i o n a l s t a t u s i n fish larvae is a c a n o n i c a l v a r i a b l e c o m p o s e d o f P C s a n d d e r i v e d f r o m a d i s c r i m i n a n t ana lys is o f l e a r n i n g s a m -ples o f fed a n d s t a r v e d fish. T h e first o b j e c t i v e o f t h i s s t u d y was t o p r o v i d e l e a r n i n g s a m p l e s o f f e d a n d s t a r v e d r e a r e d P a c i f i c h e r r i n g la rvae . L e a r n i n g samp les o f r e a r e d A t l a n t i c h e r r i n g la rvae, Clupea harengus harengus, f r o m t h e C l y d e R i v e r e s t u a r y , S c o t l a n d , h a v e a l r e a d y b e e n p r o v i d e d b y B l a x t e r (1971) , E h r l i c h e t a l . (1976) , a n d W e r n e r a n d B l a x t e r (1980) . T h e s e c o n d , a n d m a i n , ob jec t i ve was t o c a l c u l a t e o p t i m a l c o n d i t i o n f a c t o r s . T h e t h i r d o b j e c t i v e o f t h i s s t u d y was t o use t h e c o n d i t i o n f a c t o r s d e r i v e d i n t h i s s t u d y t o c a l i b r a t e t h e m o r p h o m e t r y a n d d r y w e i g h t o f r e a r e d a n d field-caught Pac i f ic h e r r i n g la rvae r e p o r t e d i n t h e l i t e r a t u r e . U n f o r t u n a t e l y , o n l y t w o va r iab les , l e n g t h a n d w e i g h t , have b e e n r e g u l a r l y m e a s u r e d a n d r e p o r t e d i n t h e fisheries l i t e r a t u r e a n d so m u l t i v a r i a t e f a c t o r s c o u l d n o t 194 be a p p l i e d . H o w e v e r , t h e ana lys i s o f t h e l e n g t h a n d w e i g h t d a t a p r o v i d e s some i n s i g h t i n t o r a c i a l d i f fe r -ences a n d d i f fe rences b e t w e e n r e a r e d a n d w i l d larvae t h a t are a p p l i c a b l e t o m u l t i v a r i a t e m o r p h o m e t r i c c o n d i t i o n f a c t o r s . Material and Methods L a r v a e T h r e e e x p e r i m e n t a l g r o u p s were r e a r e d f r o m eggs a t t h e B a m f i e l d M a r i n e S t a t i o n , B a m f i e l d , B r i t i s h C o l u m b i a i n M a r c h - J u n e , 1 9 8 1 . T h e eggs were c o l l e c t e d f r o m n a t u r a l s p a w n f o u n d i n t h e i n t e r t i d a l zone o f T o q u a r t B a y , B a r k l e y S o u n d , a n d i n c u b a t e d a t 8 -10° C . T h e n e w l y - h a t c h e d larvae were t r a n s f e r r e d t o t h r e e b a t c h r e a r i n g c o n t a i n e r s : (1) a 1000 1 flowthrough a q u a r i u m fo r t h e first f e e d i n g g r o u p , 1 9 8 1 A , (2) a 2000 1 c u l t u r e c h a m b e r f o r t h e s e c o n d f e e d i n g g r o u p , 1 9 8 1 B , a n d (3) a 50 1 a q u a r i u m f o r t h e s t a r v i n g g r o u p , 1 9 8 1 C . T h e de ta i l s o f t h e techn iques used t o r e a r t h e 1 9 8 1 A a n d 1 9 8 1 B la rvae are d e s c r i b e d i n t h e M a t e r i a l s a n d M e t h o d s s e c t i o n o f A p p e n d i x B . T h e 1 9 8 1 C larvae were s t a r v e d f r o m h a t c h t o d e a t h a t a c o n s t a n t 10° C . O n e h a l f o f t h e v o l u m e was c h a n g e d every s e c o n d day a n d t h e f r e s h seawa te r was filtered t h r o u g h glass w o o l t o r e m o v e f o o d o r g a n i s m s . S a m p l e s o f t h e w a t e r we re e x a m i n e d u n d e r a m i c r o s c o p e t o e n s u r e t h a t n o f o o d o r g a n i s m s were p resen t . S a m p l i n g T h e la rvae were t a k e n a t t h e r a t e o f 15 d - 1 f r o m days 3 - 1 5 i n t h e t w o f e e d i n g g r o u p s , 1 9 8 1 A a n d 1 9 8 1 B , a n d 10 d _ 1 were t a k e n f r o m days 3 - 1 6 i n t h e s t a r v i n g g r o u p , 1 9 8 1 C . 1 9 8 1 A a n d 1 9 8 1 B s u r v i v e d f o r a n a d d i t i o n a l 32—46 d a n d were s a m p l e d a t i n t e r v a l s o f 2 - 1 4 d d u r i n g t h i s p e r i o d . T h e la rvae were p r e s e r v e d i n a s o l u t i o n o f 2 % f o r m a l d e h y d e a n d seawater ( 3 0 % t f ) a n d s t o r e d f o r a n average o f 50 d a t 20° C i n o r d e r t o a l low t h e d i m e n s i o n s t o s t a b i l i z e . S t a n d a r d l e n g t h was m e a s u r e d f r o m t h e t i p o f t h e s n o u t t o t h e e n d o f t h e n o t o c h o r d w i t h t h e ve rn ie r scale o f a c o m p o u n d m i c r o s c o p e . T h e m o r p h o m e t r i c m e a s u r e m e n t s were t a k e n w i t h an o c u l a r m i c r o m e t e r a n d t h e n each l a r v a was r i n s e d i n f r e s h w a t e r , d r i e d a t 60° C f o r 24 h o u r s , a n d t h e n w e i g h e d w i t h a n e l e c t r o b a l a n c e . 195 S t a t i s t i c a l A n a l y s i s S t u d i e s o n t h e la rvae o f A t l a n t i c h e r r i n g , p l a i c e , Pleuronectes platessa ( E h r l i c h e t a l . 1976) , a n d j a c k m a c k e r e l , Trachurus symmetricus ( T h e i l a c k e r 1978) , showed t h a t s t a r v a t i o n caused a co l lapse i n d e p t h a n d w i d t h o f t h e b o d y . T h e f o l l o w i n g f o u r m o r p h o m e t r i c c h a r a c t e r s were chosen a c c o r d i n g l y : (1) A n a l b o d y d e p t h ( A B D ) , t h e d o r s a l - v e n t r a l d e p t h o f t h e b o d y a t t h e anus, e x c l u d i n g t h e g u t , (2) P e c t o r a l b o d y d e p t h ( P B D ) , m e a s u r e d a t t h e p e c t o r a l g i r d l e , i n c l u d i n g t h e g u t , (3) H e a d W i d t h ( H W ) , m e a s u r e d across t h e d o r s a l su r face o f t h e h e a d i n c l u d i n g t h e eyebal ls , (4) Eye D i a m e t e r ( E D ) . H e a d d e p t h was f o u n d t o be a sens i t i ve i n d i c a t o r o f s t a r v a t i o n i n A t l a n t i c h e r r i n g larvae by E h r l i c h e t a l . (1976) b u t was n o t used i n t h i s s t u d y because i t c o u l d n o t be m e a s u r e d eas i ly a n d c o n s i s t e n t l y i n e a r l y s tage la rvae . T h e m e a n l e n g t h - a t - a g e o f t h e s t a r v e d 1 9 8 1 C larvae was f i t w i t h a one-cyc le G o m p e r t z f u n c t i o n ( Z w e i f e l a n d L a s k e r 1976) , (Cl) L = I o e x p [ ^ ( l - e x p [ - a * ] ) ] , w h e r e Lo= l e n g t h a t h a t c h ( m m ) , AQ = t h e spec i f i c g r o w t h r a t e a t h a t c h ( d _ 1 ) , a n d a = t h e r a t e o f e x p o n e n t i a l decay o f Ac ( d _ 1 ) . T h e m e a n d r y w e i g h t - a t - a g e was m o d e l l e d as a s i m p l e e x p o n e n t i a l decay o f m e a n w e i g h t w i t h t i m e . T h e m e a n l e n g t h s - a n d w e i g h t s - a t - a g e o f t h e 1 9 8 1 A a n d 1 9 8 1 B g r o u p s were fit w i t h t w o - c y c l e G o m p e r t z f u n c t i o n s , A n (C.2) F = F0 exp f — (1 - e x p f - a mm(t, f)]) + -£(1- exp\-8 m a x ( f - f , 0)1)1, a p w h e r e F= l e n g t h ( m m ) o r d r y w e i g h t (jxg) a t t i m e t, Fo = t h e size a t h a t c h ( m m o r ug), BQ — t h e spec i f i c g r o w t h r a t e ( d _ 1 ) a t t h e s t a r t o f t h e s e c o n d cyc le o f g r o w t h , 3= t h e r a t e o f decay o f BQ ( d _ 1 ) , a n d t* = t h e age (d ) o f t h e s t a r t o f t h e second g r o w t h cyc le . T h e t w o - c y c l e G o m p e r t z f u n c t i o n was chosen over t h e one-cyc le v o n B e r t a l a n f f y g r o w t h m o d e l because i t gave m a r g i n a l l y b e t t e r fits t o t h e d a t a a n d because t w o g r o w t h cyc les are m o r e a p p r o p r i a t e f o r t h e g r o w t h o f first-feeding fish l a r vae . T h e first cyc le o f t h e t w o - c y c l e G o m p e r t z f u n c t i o n b e g a n a t h a t c h a n d was f u e l e d by t h e e n e r g y reserves o f t h e y o l k . T h e s e c o n d cyc le b e g a n w h e n t h e fish e s t a b l i s h e d success fu l exogenous f e e d i n g . I n c o n t r a s t , t h e v o n B e r t a l a n f f y m o d e l o f g r o w t h i n l e n g t h assumes t h a t t h e d i m e n s i o n s o f 196 a fish increase monotonically with time from hatch, which does not allow for a period of no growth following the complete absorption of the yolk. The Gompertz functions were fit to the data with the BMDP:3R non-linear, least squares regression program (Dixon 1983). Residuals were calculated from predictive rather than functional linear regressions because the variables were measured with little error and because the correlation coefficients were high enough that the two types of regression were almost identical. PCs were derived with the BMDP:4M factor analysis program (Dixon 1983). The three exper-imental populations were pooled and the six raw variables were linearized with natural logarithms. The six ordinary PCs were extracted from the correlation matrix of the transformed variables rather than the covariance matrix because of the different units (mm and fig) and scales of the raw variables (Pimentel 1979). The PCs were, by definition, uncorrelated with each other so Humphries et al.'s (1981) shearing transformation was not applied. The scores of the ordinary PC's were calculated by multiplying the component coefficients by the standardized variables. The log^-transformed variables were standardized to zero mean and unit standard deviation with z-scores, (C.3) Zij = (xij - Xi)/si, where Zy = the standardized score of case j for variable t, x^ = the raw value of case j for variable t, li = the mean of variable i, and « , = the standard deviation of variable t. Classification functions were calculated with the BMDP:7M stepwise discriminant (SWD) analysis program using only non-yolk-sac larvae because the nutritional status of yolk-sac larvae was obvious by examination. 'Jackknifed' classifications were used to avoid the bias that occurs when the results of the classification are based on the same cases used in developing the classification equations. In the jackknife procedure each case is classified on the basis of equations develop ed from all data except the case being classified. The results are a more realistic estimate of the ability of the predictors to discriminate among groups. 197 Results G r o w t h A t o t a l o f 7 3 1 h e r r i n g larvae were m e a s u r e d f r o m t h e t h r e e g r o u p s o f w h i c h 592 were n o n - y o l k - s a c larvae (Tab le C . l ) . T h e average l i n e a r r a t e o f g r o w t h i n l e n g t h (GL • s lope o f t h e l i n e a r p r e d i c t i v e regress ion o f l e n g t h o n age) was 0.22 m m d - 1 f o r 1 9 8 1 A , 0.28 m m d - 1 f o r 1 9 8 1 B , a n d 0 .01 m m d - 1 f o r 1 9 8 1 C . T h e r a t e f o r 1 9 8 1 C was n o t s i g n i f i c a n t l y d i f f e ren t f r o m zero (P > 0 .2) . T h e g r o w t h r a t e o f 1 9 8 1 A was w i t h i n t h e u p p e r 2 5 . 0 % o f values f o r 6 1 r e a r e d p o p u l a t i o n s o f Paci f ic a n d A t l a n t i c h e r r i n g larvae r e p o r t e d i n t h e l i t e r a t u r e a n d rev iewed i n A p p e n d i x A , a n d w i t h i n t h e l o w e r 3 5 . 0 % o f values f o r 16 n a t u r a l p o p u l a t i o n s . 1 9 8 1 B was w i t h i n t h e u p p e r 1 5 . 0 % o f t h e r e a r e d g r o u p s a n d t h e u p p e r 3 5 . 0 % o f t h e n a t u r a l g r o u p s . T h e e x p o n e n t i a l r a t e o f g r o w t h i n d r y w e i g h t (Gw: s lope o f t h e l i n e a r p r e d i c t i v e reg ress ion o f l o g e W o n age) was 0.067 d _ 1 f o r 1 9 8 1 A , 0.079 d _ 1 f o r 1 9 8 1 B , a n d -0 .039 d _ 1 f o r 1 9 8 1 C . T h e va lues o f 1 9 8 1 A a n d 1 9 8 1 B were a m o n g t h e h i g h e s t r e c o r d e d f o r 15 r e a r e d p o p u l a t i o n s o f Pac i f i c o r A t l a n t i c h e r r i n g larvae ( A p p e n d i x A ) . T h e r e are t o o f e w re l i ab le e s t i m a t e s o f Gw f o r w i l d p o p u l a t i o n s o f h e r r i n g la rvae t o c o m p a r e w i t h t hose d e r i v e d h e r e . I n s u m m a r y , b o t h 1 9 8 1 A a n d 1 9 8 1 B were a m o n g t h e f a s t e s t - g r o w i n g o f t h e rea red g r o u p s r e v i e w e d i n A p p e n d i x A . T h e y o l k - s a c w a s c o m p l e t e l y a b s o r b e d b y d a y 6 i n 1 9 8 1 A a n d 1 9 8 1 B , a n d by day 4 i n 1 9 8 1 C . T h e second G o m p e r t z cyc le o f 1 9 8 1 A b e g a n a t a m e a n age o f 15.3 ( S D = 0 . 8 , n = 2 ) d , w h i c h i n d i c a t e s t h a t t h e l a rvae i n t h i s p o p u l a t i o n were s ta rved d u r i n g t h e first 9 d a f t e r y o l k a b s o r p t i o n (Tab le C . 2 , F i g s . C . l a n d C .2 ) . T h e s e c o n d G o m p e r t z cyc le o f 1 9 8 1 B b e g a n a t a m e a n age o f 6.6 ( S D = 0 . 3 , n = 2 ) d , w h i c h i n d i c a t e s t h a t t h e larvae b e g a n success fu l exogenous f e e d i n g w i t h o u t a n i n t e r v e n i n g p e r i o d o f s e m i - s t a r v a t i o n . T h e 8.7 d d i f fe rence i n t h e s t a r t o f t h e second cyc le b e t w e e n t h e t w o f e e d i n g p o p u l a t i o n s was p r o b a b l y caused b y d i f ferences i n t h e q u a n t i t y o r q u a l i t y o f t h e f o o d t h a t w s ava i l ab le t o t h e l a r v a e . N o n - y o l k - s a c la rvae were d i v i d e d i n t o s t a r v e d ( 7 - 1 5 d i n 1 9 8 1 A , n o n e i n 1 9 8 1 B , a n d 5 - 1 6 d i n 1 9 8 1 C ) a n d f e d ( 1 6 - 6 1 d i n 1 9 8 1 A , 7 - 4 7 d i n 1 9 8 1 B , a n d n o n e i n 1 9 8 1 C ) l e a r n i n g s a m p l e s o n t h e basis o f t*. 198 T A B L E C l . M e a n s ( ± 1 S D ) a t age fo r s t a n d a r d l e n g t h ( L ) , d r y w e i g h t (W), a n a l b o d y d e p t h (ABD), p e c t o r a l b o d y d e p t h (PBD), h e a d w i d t h (HW), a n d eye d i a m e t e r (ED) o f t h r e e p o p u l a t i o n s o f Paci f ic h e r r i n g la rvae . A g e N L w ABD PBD HW ED (d ) ( m m ) fas,) ( m m ) ( m m ) ( m m ) ( m m ) 1 9 8 1 A 3 15 8.8 160 0.24 0.49 0.76 0.30 (0.4) ( 14) (0.01) (0.03) (0.02) (0.02) 4 14 9.3 169 0.24 0.49 0.77 0.32 (0.5) • ( 28) (0.02) (0.04) (0.04) (0.05) 5 15 9.3 156 0.23 0.50 0.79 0.33 (0.5) ( 24) (0.02) (0.03) (0.05) (0.01) 6 15 9.4 156 0.24 0.54 0 .81 0.33 (0.4) ( 25) (0.02) (0 .04) (0.05) (0.03) 7 15 9.6 164 0.24 0.53 0.85 0.37 (0 .4) ( 18) (0.02) (0.07) (0.06) (0.02) 8 15 9.7 163 0.24 0.56 0 .81 0.37 (0.5) ( 29) (0.02) (0 .05) (0.05) (0.03) 9 15 9.8 162 0.24 0.56 0.83 0.37 (0.7) ( 27) (0.01) (0 .05) (0.04) (0.03) 10 15 9.5 151 0.23 0.49 0.84 0.37 (0 .6) ( 32) (0.02) (0 .05) (0.07) (0.03) 11 15 10 .1 186 0.25 0.59 0.86 0.39 (0.6) ( 4 4 ) (0.03) (0 .07) (0.06) (0.04) 12 15 9.9 151 0.23 0 .51 0.84 0.36 (0 .5) ( 30) (0.02) (0 .05) (0.05) (0.02) 13 15 10.4 184 0.25 0.60 0.89 0.39 (0 .7) ( 55) (0 .03) (0 .09) (0 .07) (0.03) 14 15 10.0 174 0.24 0.53 0.86 0.37 ft 199 (0.6) ( 48) (0.03) (0.07) (0.07) (0.03) 15 15 10.0 174 0.24 0.55 0.87 0.37 (0.8) ( 51) (0.03) (0.07) (0.08) (0.03) 16 15 10.2 178 0.23 0.56 0.85 0.38 (0.6) ( 53) (0 .03) (0.08) (0.05) (0.02) 19 13 11.5 304 0.30 0.72 0.95 0.42 (1.3) ( 1 2 7) (0 .06) (0.12) (0.09) (0.03) 24 15 11.5 336 0 .31 0.70 1.05 0.44 (2.0) ( 209) (0 .09) (0.18) (0.15) (0.04) 26 12 13.7 680 0.42 0.97 1.22 0.52 (1.0) ( 339) (0 .11) (0.17) (0 .13) (0.06) 28 15 13.5 690 0.40 0.94 1.16 0.52 (2.4) ( 553) (0.17) (0.22) (0.25) (0.09) 30 15 14.4 864 0.47 1.04 1.36 0.55 (1.8) ( 3 3 4) (0.09) (0.17) (0.09) (0.07) 33 10 15.9 1367 0.66 1.19 1.36 0.62 (1.9) ( 558) (0.18) (0.17) (0.14) (0.09) 40 15 16 .1 1439 0 .61 1.27 1.43 0.65 (1.6) ( 669) (0 .18) (0.20) (0.15) (0.10) 47 11 17.6 2068 0.75 1.48 1.47 0.81 (2.7) (1448) (0.26) (0.33) (0 .15) (0.18) 54 15 18.9 4223 1.17 2.04 1.92 1.09 (2.6) (3179) (0 .39) (0.49) (0.57) (0.2) 6 1 20 2 2 . 1 7575 1.47 2.47 1.91 1.29 (3.3) (5721) (0 .54) (0.79) (0 .24) (0.29) 1 9 8 1 B 3 15 9.1 178 0.26 0.55 0.76 0.30 (0.3) ( 25) (0 .01) (0.04) (0.04) (0.01) 200 4 15 9.5 188 0.25 0.58 0.79 0.31 (0.3) ( 2 2) (0.02) (0.02) (0.04) (0.01) 5 15 9.5 200 0.26 0.62 0.80 0 .31 (0.6) ( 34) (0.02) (0.03) (0.06) (0.01) 6 15 9.7 200 0.27 0.63 0.85 0.32 (0.5) ( 45) (0.02) (0.04) (0.06) (0 .02) 7 15 9.7 226 0.30 0 .71 0.92 0.35 (0.6) ( 35) (0.03) (0.04) (0.06) (0 .02) 8 15 10.5 263 0.33 0.75 1.01 0.38 (0 .5) ( 45 ) (0.04) (0.05) (0.07) (0 .02) 9 15 11.2 277 0.35 0.78 0.96 0.40 (0 .7) ( 32) (0.03) (0 .04) (0.07) (0 .02) 10 15 11.4 349 0.39 0.83 1.03 0.43 (0 .6) ( 7 2) (0.02) (0.05) (0.08) (0.03) 1 1 15 11.9 450 0.40 0.78 0.95 0.40 (0 .6) ( 51) (0.04) (0 .04) (0.05) (0 .03) 12 15 12.8 4 8 1 0 .41 0 .81 1.11 0.44 (0 .8) ( 82 ) (0.03) (0 .07) (0 .07) (0 .05) 13 15 13.7 603 0.51 0.99 1.27 0 .51 (0.4) ( 88) (0.03) (0.04) (0.04) (0 .02) 14 15 13.9 663 0.50 0.99 1.21 0 .51 (0.6) ( 96) (0.05) (0.05) (0.08) (0 .02) 15 15 13.2 673 0.48 0.97 1.22 0.52 (1 .2) ( ! 7 0 ) (0.07) (0.07) (0.17) (0 .06) 19 15 15.5 1112 0.64 1.11 1.43 0.58 (0 .7) ( 220) (0.05) (0 .08) (0.10) (0 .03) 26 10 17.3 1792 0.84 1.34 1.67 0.73 (0 .9) ( 363) (0.10) (0.13) (0.12) (0.05) 33 11 19.2 3093 1.09 1.65 1.64 1.02 2 0 1 (1.0) ( 689) (0.14) (0.15) (0.07) (0.08) 47 10 18.7 2745 1.00 1.69 1.84 1.24 (1.0) ( 557) (0.09) (0.17) (0.13) (0.07) 1 9 8 1 C 3 10 8.7 177 0.24 0.53 0.80 0.33 (0.4) ( 14) (0.01) (0.02) (0 .03) (0.01) 4 10 8.7 160 0.24 0.54 0.76 0.33 (0.3) ( 10) (0.01) (0.02) (0.04) (0.02) 5 10 9.1 172 0.24 0.53 0.76 0 .31 '(0.4) ( 19) (0.01) (0.03) (0.02) (0.02) 6 10 9.3 160 0.24 0.55 0.76 0.30 (0.4) ( 18) (0.02) (0.03) (0 .02) (0.02) 7 10 9.2 168 0.24 0.61 0.79 0.34 (0.4) ( 19) (0.01) (0.02) (0.04) (0.01) 8 10 9.5 155 0.24 0.60 0.79 0.35 (0.5) ( 17) (0.01) (0.03) ' (0 .03) (0.02) 9 10 9.3 133 0.24 0.49 0.75 0.33 (0.5) ( 18) (0.01) (0.03) (0 .04) (0.02) 10 10 9.0 128 0.24 0.58 0.78 0.34 (0.6) ( 31 ) (0.01) (0.02) (0 .05) (0.02) 11 10 9.1 153 0.23 0.56 0 .76 0.35 (0.4) ( 28) (0.02) (0.04) (0 .03) (0.01) 12 10 9.2 145 0.23 0.49 0.77 0.33 (0.5) ' ( 23) (0.01) (0.04) (0 .05) (0.02) 13 10 9.1 102 0.23 0.49 0.72 0.33 (0.4) ( 15) (0.02) (0.05) (0 .04) (0.02) 14 10 9.1 102 0.22 0.50 0.73 0.33 (0.4) ( 20) (0 .02) (0.03) (0.05) (0.02) 15 10 9.3 122 0.23 0.48 0.75 0.33 (0.4) ( 15) (0.01) (0.05) (0.04) (0.02) 16 10 -8.9 113 0.24 0.51 0 .71 0.35 (0.4) ( i o ) (0.01) (0.03) (0.03) (0.02) 203 TABLE C.2. Parameter values of the one-cycle and two-cycle Gompertz growth functions for the standard lengths and dry weights of three populations. Group F0 Bo 0 f Residual M.S. df Length (mm) 1981A 7.2 0.0952 0.2874 0.0249 0.0204 14.68 0.00947 345 1981B 8.1 0.0735 0.3787 0.0655 0.0929 6.80 0.00342 236 1981C 7.5 0.0984 0.4774 - - 0.00247 137 Weight (ug) 1981A 185 -0.0911 0.9166 0.1118 0.0185 15.85 0.15915 345 1981B 258 -0.1230 0.2929 0.2104 0.0688 6.36 0.03825 235 204 F i g u r e C . l . M e a n ( ± 1 S D ) s t a n d a r d l e n g t h o f p o p u l a t i o n s 1 9 8 1 A , 1 9 8 1 B , a n d 1 9 8 1 C . T h e curves are one-cyc le ( 1 9 8 1 C ) a n d t w o - c y c l e ( 1 9 8 1 A a n d 1 9 8 1 B ) G o m p e r t z f u n c t i o n s . See Table C.2 f o r p a r a m e t e r va lues . 205 206 F i g u r e C .2 . M e a n ( ± 1 S D ) d r y w e i g h t o f p o p u l a t i o n s 1 9 8 1 A , 1 9 8 1 B a n d 1 9 8 1 C . T h e curves are t w o -cyc le ( 1 9 8 1 A a n d 1981B) G o m p e r t z f u n c t i o n s a n d a l i n e a r p r e d i c t i v e regress ion ( 1 9 8 1 C ) . See Table C.2 fo r p a r a m e t e r va lues . 207 208 Condi t ion Factors The six log e -transformed variables were highly correlated w i t h each other (P < 0.001,r=0.94-0.98), indicat ing that any one of them could be chosen as the single variable that best encompassed the concept of size. A l l 30 ratios of the six raw variables were significantly correlated (P < 0.001, r=0.20-0.96) w i t h their denominators, indicat ing that they contained a mixture of size and shape information. M o s t of the ratios were also correlated (r=0.00-0.99) w i t h each other. O n l y 9 (2.1%) of the 435 off-diagonal coefficients of the correlation matr ix were not significant (P > 0.05). T h e residuals of the 15 linear predictive regressions based on all 731 larvae were uncprrelated w i t h the independent variable (P > 0.9, r=0.00-0.01) but most were s t i l l correlated w i t h the other five log e -transformed variables (r=0.08-0.35). O n l y four (5.3%) of the 75 coefficients of the correlation matr ix were not significant while 48 (64.0%) were highly significant (P < 0.001). T h i s indicates that the residuals, like the ratios, were mixtures of size and shape informat ion. M o s t of the residuals were also correlated w i t h each other (r=0.01-0.78). O n l y 15 (14.3% of the 105 off-diagonal coefficients of the correlation matr ix were not significant (P > 0.05) while 82 (78.1%) were highly significant (P < 0.001). The residuals of the 15 linear predictive regressions based on the 592 non-yolk-sac larvae had the same properties. Size was not completely removed w i t h univariate regressions because the yolk-sac, starved, and fed learning samples had significantly different slopes. Covariance analysis indicated that the slopes of the regressions of the log e -transformed A B D , P B D , H W , E D , and D W on log .L were highly significantly different (P < 0.001) between the starved and fed groups. The residuals of the regression of log, W on l o g e L , for example, were not correlated w i t h log^L (Fig . C.3) but there was obvious pattern in them; the serial correlation coefficient was 0.58 (a coefficient of 0.00-0.08 indicates no pattern and a coefficient > 0.08 indicates significant pattern at the 5 % probabil ity level). T h e pattern was not removed when the yolk-sac larvae were excluded from the regressions; the coefficient of serial correlation of the residuals of l o g e W on l.og eL for the reduced data set was 0.49. These patterns show that the residuals have discr iminat ion power but it also shows why they remain correlated w i t h size and w i t h other sets of residuals. 209 F i g u r e C.3. S c a t t e r p l o t a n d l i n e a r p r e d i c t i v e regress ion o f log^ W o n l o g j L f o r t h e p o o l e d d a t a o f 1 9 8 1 A , 1 9 8 1 B , a n d 1 9 8 1 C , a n d s c a t t e r p l o t o f t h e r e s i d u a l s o f t h i s regress ion o n l o ^ L . Every f o u r t h l a r v a was se lec ted a t r a n d o m f o r p l o t t i n g . 210 211 TABLE C.3. PC analysis of the correlation matrix of six loj*,- transformed morphometric variables: the coefficients of the six PCs, the eigenvalues (E), the percent of the variance explained (r2 ), and the correlations of the variables with the PCs (r). L ABB PBD HW ED W E r2 PCI -0.060 0.661 2.819 -1.186 -1.037 0.356 5.786 96.4 r 0.99 0.99 0.98 0.98 0.97 0.99 PC2 -0.553 -0.405 -0.297 -0.762 3.034 -0.443 0.074 1.2 r -0.02 -0.08 -0.10 0.05 0.23 -0.07 PC3 -0.567 -0.631 -0.302 3.379 -0.866 -0.493 0.060 1.0 r 0.02 -0.07 -0.04 0.21 -0.09 -0.03 PC4 4.347 -0.872 -1.388 -1.228 -0.879 0.356 0.037 0.6 r 0.15 -0.03 -0.10 -0.05 -0.02 0.05 PC5 -0.326 5.055 -3.208 0.193 -0.578 -0.994 0.028 0.5 r -0.05 0.12 -0.11 0.02 -0.01 0.02 PC6 -2.894 -1.873 -1.969 0.059 0.045 6.670 0.016 0.3 r -0.05 -0.05 -0.01 0.00 0.01 0.10 212 The first principal component (PCl) of the correlation matrix of the log,,-transformed variables accounted for 96.4% of the total variance (Table C.3). The high, positive correlations of the variables with P C l implies a simultaneous increase in all dimensions and indicates that P C l was a size compo-nent. PC2 accounted for 1.2% of the total variance and was mainly a contrast between ED and body depth (ABD and PBD). ED is a morphometric character that does not shrink in response to starvation. Consequently, a starved larva has a larger eye in relation to the rest of its body than a fed larva. PC2 was interpreted as an index of eye allometry. PC3 accounted for 1.0% of the total variance and was mainly a contrast between HW and all other body parts except L. It was interpreted as an index of head width. PC4 accounted for 0.6% of the total variance and was mainly a contrast between L and W on one hand and all other measurements, particularly PBD, on the other. It was interpreted as an index of body depth. PC5 was dominated by a contrast between ABD and PBD and was interpreted as an index of differential body depth. PC6 was dominated by W and was interpreted as an index of tissue density. Scatterplots of PC2 to PC6 on P C l for the pooled data showed that these shape components tended to ordinate the larvae according to their nutritional status. The plot of PC2 on PCl , for example (Fig. C.4), shows that most fed larvae were clustered in the large-size/small-eyed quadrant and most starved larvae were clustered in the small-size/large-eyed quadrant. Note that P C l separates the starved from the fed larvae quite well. This emphasizes the importance of removing size information from condition factors before they are entered into a SWD analysis. Note also that there was a group of fed larvae more big-eyed than the starved larvae. These fish may have belonged to another growth stanza. The means at age of the six PCs for, each of the three experimental groups (Fig. C.5) show that the older (> 30 d) fish of 1981A and 1981B were large-eyed compared to the starved fish of 1981C (the component scores shown in Fig. C.5 were calculated by substituting the mean and standard deviation of each of the loge-transformed variables into the z-scores and multiplying by the component coefficients of Table C.3. The coefficients of the expanded PCs are shown in Table C.4). However, these big-eyed fish were also more wide-headed than the starved larvae (Fig. C.5: PC3), indicating that they were not malnourished. 213 F i g u r e C .4 . S c a t t e r p l o t o f P C 2 o n P C I fo r t h e p o o l e d d a t a o f 1 9 8 1 A , 1 9 8 1 B a n d 1 9 8 1 C . T h e P C s d e r i v e d f r o m t h e s i x - va r i ab le d a t a se t . E v e r y f o u r t h l a r v a was se lec ted a t r a n d o m f o r p l o t t i n g . 214 C\J O o Q . -1 - 2 - 3 A yo lk-sac O starved • fed large-- e y e d O o° o O i fi 2 A O small--eyed small 4 -- 3 - 2 -1 •> large 0 PC1 215 F i g u r e C .5. M e a n s ( ± 1 S D ) a t age o f t h e s ix P C s fo r 1 9 8 1 A , 1 9 8 1 B a n d 1 9 8 1 C . T h e P C s were der ived f r o m t h e s i x - v a r i a b l e d a t a set . 216 1981A 1981B 1981C K*yh \ • • . i i — i • IT i ' ' i ... i f Hjil 11 * * • i 1 • • • i 1— • i : i >- 1 1 — ' \ I— :\v» • * • _ i i _ 1—. 1 — : — • _. ' ' 1 ' ' 20 3 0 4 0 50 0 10 20 3 0 4 0 0 DAYS 217 TABLE C.4. Expanded PCs calculated by substituting the mean and standard deviation of each loge-transformed measurement into the z-scores and then multiplying by the component correlations of Table C.3. L ABD PBD HW ED W constant PCl -4.119 1.290 6.600 -4.137 -2.787 0.337 9.095 PC2 -2.148 -0.790 -0.695 -2.659 8.156 -0.420 13.400 PC3 -2.203 -1.232 -0.707 11.790 -2.328 -0.467 4.765 PC4 16.889 -1.702 -3.248 -4.283 -2.364 0.337 -47.824 PC5 -1.265 9.867 -7.508 0.672 -1.553 -0.942 15.480 PC6 -11.242 -3.656 -4.608 0.207 0.121 6.321 -14.570 218 TABLE C.5. PC analysis of the correlation matrix of log„ L and loge W: the coefficients of the two PCs based on z-scores, the eigenvalues (E), the percent of the variance explained (r2 ), the correlations of the variables with the PCs (r), and the coefficients of the expanded PCs after the mean and standard deviation of the loge- transformed variables were substituted. P C l z-scored r PC2 r expanded P C l PC2 L 3.772 0.995 -3.061 0.103 14.652 11.890 W -3.061 0.995 3.772 -0.103 -2.901 3.575 E 1.979 0.021 r2 98.9 1.1 constant -18.743 8.180 219 A final PC analysis was performed on all 731 larvae using only L and W, the two most commonly measured morphometric variables in larval fish ecology. The first component was a size component (Table C.5) and explained 98.9% of the variance in the data. The second component explained the remaining 1.1% of the variance. The plot of PC2 on PCI resembled the plot of the weight-length residuals on \ogeL (Fig. C.3) because the PC analysis of a two-variable data set is equivalent to a functional regression of one variable on the other. Classification Functions A SWD analysis with the 30 ratios produced a function that correctly classified 92.5% of the non-yolk-sac larvae with one ratio, L/W, and the residuals of the 15 regressions (based on all 731 larvae) produced a function that correctly classified 91.0% of the non-yolk-sac larvae with five sets of residuals, W/ED, ED/L, W/L, W/HW, and PBD/W. The residuals of the regressions based on the 592 non-yolk-sac larvae also classified 91.0% of the cases with the same five sets of residuals. A SWD analysis with the five shape components correctly classified 76.2% of the cases with PC3, PC4 and PC2. The histograms of the canonical variate scores of these and all subsequent SWD analyses followed the bell-shaped appearance of a Gaussian distribution, which indicated that the underlying distributions of the ratios, residuals, and PCs were multivariate normal (Campbell and Atchley 1981). This is an assumption of SWD analysis. The differences in body shape between the small-young and the large-old larvae of 1981A and 1981B suggested that classification could be improved by excluding the larger larvae. A cutoff age of 30 d was chosen which corresponds to the inflexion point of the trends of the five shape components with time (Fig. C.5). All of the starved larvae of 1981C were included plus 279 of the 350 non-yolk-sac larvae of 1981A and 220 of the 241 non-yolk-sac larae of 1981B. SWD analyses correctly classified a total of 91.8% of the cases with two ratios, PBD/L and PBD/W, 91.6% with four sets of residuals, W/ED, W/HW, ED/HW, and W/PBD (based on 731 731 cases), and 78.6% with three shape components, PC3, PC4, and PC2. The residuals based on the 592 non-yolk-sac larvae gave the same results as those based on all 731 larvae. The agreement between this analysis and the first set of SWD runs indicates that the results of the first set were not biased by misclassification of the older, larger larvae. 220 Another possible source of error was the misclassification of the 1981A larvae, particularly those aged 7-14 d. There was no error in the classification of the starved 1981C larvae and the early growth of the 1981B fish was so rapid that few of these larvae were likely to have been misclassified. Four SWD analyses were performed in which all of the 1981A larvae were excluded, leaving only the starved larvae of 1981C and the fed larvae of 1981B. Ratios correctly classified 98.7% of the 301 cases with two variables, ED/W and L/ABD, residuals (based on all 731 fish) classified 97.3% of the cases with four variables, W/ED, W/HW, ED/HW and PBD/L, and PCs classified 85.7% of the cases with two components, PC3 and PC4 (Table C.6). The residuals based on the 595 non-yolk-sac larvae produced results identical to those for the residuals based on all 731 larvae. These results suggest that some of the 7-14 d old 1981A larvae were misclassified and that this reduced the discriminatory power of the first two sets of SWD analyses by an average of 7%. Therefore, this third set of analyses was chosen as the most correct. The canonical variable for the third SWD analysis using PCs was (CA) CVl = -1.197PC3 -0.416PC74. The coefficients of PC3 and PC4 provide the slope of C V l , i.e. -1.197/-0.416 or 2.877 (Fig. C.6). The order of choice of the shape components indicates that starvation in Pacific herring larvae characterized primarily by a decrease in head width and secondarily by a reduction in depth of the body. C V l simplifies to (C.5) ^1=14.191-4.38910^ I,+2.1841oge ABD -+-2.19710& P5X>-12.3311oge HW +3.7701og e£I»+0.4191og < ! W, when the expanded equations for PC3 and PC4 are substituted. A value of C V l < 0 identifies a fed larva and a value of C V l > 0 identifies a starved larva. Pacific herring larvae starved from hatch at 10°C become irreversibly starved about 6 d after complete yolk absorption or on day 10 post-hatch (Appendix A). The corresponding value of C V l , 1.263, was calculated by substituting the mean values of the five morphometric characters and dry weight of the 10 day old 1981C larvae into equation (C.5). A SWD analysis of the non-yolk-sac larvae of 1981B and 1981C correctly classified 78.4% of the cases using only the expanded PC2 derived from the PC analysis of the two-variable (L and W) data set (Table C.6). The canonical variable was-221 T A B L E C . 6 . T h e p e r c e n t o f a l l n o n - y o l k - s a c la rvae o f 1 9 8 1 B a n d 1981C c o r r e c t l y c lass i f ied as s t a r v e d o r f e d w i t h S W D ana lyses o f r a t i o s , res idua ls a n d p r i n c i p a l c o m p o n e n t s . G r o u p P e r c e n t C o r r e c t N u m b e r o f Cases C lass i f i ed i n t o G r o u p S t a r v e d Fed R a t i o s S t a r v e d 100.0 120 0 Fed 97.8 4 177 T o t a l 98.7 124 177 R e s i d u a l s S t a r v e d 97.5 117 3 Fed 97.2 5 176 T o t a l 97.3 122 179 P C s (6 va rs ) S t a r v e d 95.8 115 5 Fed 79.0 38 143 T o t a l 85.7 153 148 P C s (2 v a r s ) S t a r v e d 73.3 88 32 F e d 81.8 33 148 T o t a l 78.4 121 180 222 F i g u r e C .6 . S c a t t e r p l o t o f P C 3 o n P C 4 f o r t h e p o o l e d d a t a o f 1 9 8 1 B a n d 1 9 8 1 C . T h e P C s ware der ived f r o m t h e s i x - v a r i a b l e d a t a set . A l l 3 0 1 n o n - y o l k - s a c larvae were p l o t t e d . C V 1 is t h e c a n o n i c a l va r i ab le t h a t rep resen ts t h e b e s t axis o f d i s c r i m i n a t i o n b e t w e e n s t a r v e d a n d fed larvae. 223 224 (C.6) C F 2 = - 1 . 4 1 5 P C 2 , w h i c h was e q u i v a l e n t t o (C .7 ) CV2 = - 1 1 . 5 7 5 + 16.825 l o g , L - 5 .058 l o g e W, a f t e r t h e e x p a n d e d ve rs ion o f P C 2 was s u b s t i t u t e d i n t o t h e e q u a t i o n . A value o f C V ^ 2 > 0 i n d i c a t e s a s t a r v e d la rvae a n d t h e va lue a t t h e age o f i r r e v e r s i b l e s t a r v a t i o n was 1.548. Size w a s n o t c o m p l e t e l y s e p a r a t e d f r o m s h a p e w i t h r a t i o s o r r e s i d u a l s b u t i t was w i t h t h e s h a p e c o m p o n e n t s . T h e c o u n t e r - i n t u i t i v e b e h a v i o u r o f r a t i o s has been w e l l d o c u m e n t e d ( A t c h l e y e t a l . 1976; A t c h l e y a n d A n d e r s o n 1978; H u m p h r i e s et a l . 1981) . M o s t o f t h e res idua ls r e m a i n e d c o n t a m i n a t e d w i t h size because s ing le regress ion e q u a t i o n s were used t o r e m o v e t h e ef fects o f cova r ia tes f r o m t h r e e l e a r n i n g s a m p l e s , y o l k - s a c , s t a r v e d , a n d f e d , each w i t h s i g n i f i c a n t l y d i f f e r e n t s lopes ( H u m p h r i e s e t a l . 1981) . I t m a y have b e e n poss ib le t o c o m p l e t e l y r e m o v e size w i t h a d i f fe ren t regress ion e q u a t i o n f o r each l e a r n i n g s a m p l e b u t t h i s w o u l d m e a n t h a t a w o r k e r w o u l d have t o k n o w t h e n u t r i t i o n a l s t a t e o f a fish i n o r d e r t o r e m o v e size b e f o r e e n t e r i n g i t i n t o a c l a s s i f i c a t i o n f u n c t i o n , w h i c h de fea ts t h e w h o l e p u r p o s e o f c l a s s i f i c a t i o n . T h e r a t i o s were h i g h l y i n t e r c o r r e l a t e d as w e l l as b e i n g c o r r e l a t e d w i t h s ize, w h i c h m e a n t t h a t t h e y s h a r e d aspec ts o f size a n d shape i n f o r m a t i o n a m o n g each o t h e r . T h e same s i t u a t i o n e x i s t e d w i t h m o s t o f t h e r e s i d u a l s . S W D analyses w i t h such va r iab les are i n t r i n s i c a l l y u n s t a b l e a n d t h e r e f o r e u n r e l i a b l e . T h e u n r e l i a b i l i t y is a p o s i t i v e f u n c t i o n o f t h e average degree o f i n t e r c o r r e l a t i o n a n d a nega t i ve f u n c t i o n o f t h e s a m p l e size ( H u m p h r i e s e t a l . 1 9 8 1 ; W i l l i a m s 1983) . T h e h i g h degree o f i n t e r c o r r e l a t i o n o f t h e r a t i o s ( r = 0 . 0 0 - 0 . 9 9 ) m e a n t t h a t c o m p l e t e l y d i f f e r e n t r a t i o s were se lec ted i n each o f t h e t h r e e sets o f S W D r u n s . T h e l o w e r degree o f i n t e r c o r r e l a t i o n o f t h e r e s i d u a l s ( r = 0 . 0 8 - 0 . 3 5 ) p r o d u c e d m o r e s t a b i l i t y ; t h e set o f res idua ls o f t h e reg ress ion o f l o g g W o n l o g c E D was chosen as t h e b e s t p r e d i c t o r v a r i a b l e i n each o f t h e t h r e e S W D r u n s . H o w e v e r , t h e t h r e e t o f o u r o t h e r sets o f r e s i d u a l s chosen t o a c c o m p a n y W / E D v a r i e d i n t h e i r o r d e r o f s e l e c t i o n . T h e s e o t h e r r e s i d u a l s c o u l d n o t b e e x c l u d e d w i t h o u t s i g n i f i c a n t ( > 1 0 % ) losses o f d i s c r i m i n a t i o n p o w e r . I n c o n t r a s t t o t h e r a t i o s a n d res idua ls t h e Discussion 225 P C s were c o m p l e t e l y u n c o r r e c t e d w i t h each o t h e r a n d so t h e first a n d second c o m p o n e n t s se lec ted i n each o f t h e S W D r u n s , P C 3 a n d P C 4 , r e m a i n e d t h e s a m e . T h e i n t e r c o r r e l a t i o n p r o b l e m also a f fec ted b i o l o g i c a l i n t e r p r e t a t i o n o f t h e r e s u l t s as w e l l as t h e s t a b i l i t y o f t h e se lec t i on process . T h e r a t i o chosen as t h e b e s t p r e d i c t o r i n t h e t h i r d a n d m o s t c o r r e c t S W D r u n was E D / W a n d t h e set o f res idua ls chosen as t h e b e s t p r e d i c t o r was W / E D . P r e s u m a b l y , t h e c o n t r a s t o f E D a n d W c o n t a i n e d m u c h d i s c r i m i n a t i o n p o w e r . Howeve r , t h e S W D r u n s w i t h P C s i d e n t i f i e d P C 3 , a n i n d e x o f h e a d w i d t h , as t h e c o m p o n e n t c o n t a i n i n g t h e m o s t d i s c r i m i n a t i o n p o w e r . T h e c o m p o n e n t i n t e r p r e t e d as a c o n t r a s t b e t w e e n E D a n d a l l o t h e r b o d y d i m e n s i o n s , P C 2 , was n o t se lec ted as a p r e d i c t o r v a r i a b l e i n t h e t h i r d S W D r u n a n d i t was se lec ted t h i r d a n d l a s t i n t h e first t w o r u n s . T h u s t h e resu l t s o f t h e S W D r u n s w i t h r a t i o s a n d res idua ls gave m i s l e a d i n g i n f o r m a t i o n a b o u t t h e bas ic d i f fe rences i n a l l o m e t r y b e t w e e n s t a r v e d a n d fed h e r r i n g larvae. T h e d i f fe rence i n d i s c r i m i n a t i o n p o w e r b e t w e e n t h e c lass i f i ca t i ons based o n r a t i o s a n d t h o s e b a s e d on r e s i d u a l s r a n g e d f r o m 0 . 2 - 2 . 6 % a n d c a n be c o n s i d e r e d n o n - s i g n i f i c a n t f o r p r a c t i c a l p u r p o s e s . T h e 1 2 - 1 6 % d i f fe rence b e t w e e n t h e c lass i f i ca t i ons based o n r a t i o s a n d res idua ls a n d t h a t based o n t h e P C s (de r i ved f r o m t h e s i x - va r i ab le d a t a se t ) were d u e t o t h e size i n f o r m a t i o n t h a t r e m a i n e d i n t h e r a t i o s a n d r e s i d u a l s . T h i s m e a n s t h a t t h e c lass i f i ca t i ons based o n r a t i o s a n d res idua ls are b i a s e d a n d t h a t t h e m o s t r e l i a b l e is t h e one based o n t h e s h a p e c o m p o n e n t s . T h e c l a s s i f i c a t i o n based o n t h e P C 2 o f t h e t w o - v a r i a b l e d a t a set was o n l y 7 . 3 % less success fu l i n c l a s s i f y i n g a l l o f t h e 3 0 1 larvae t h a n t h e t h i r d a n d f o u r t h c o m p o n e n t s o f t h e s i x - va r i ab le d a t a set b u t o n l y 7 3 . 3 % o f t h e s ta rved larvae were success fu l l y c lass i f ied c o m p a r e d t o 9 5 . 8 % fo r t h e s i x -va r iab le c l a s s i f i c a t i o n , a 2 2 . 5 % loss o f d i s c r i m i n a t i o n p o w e r . T h u s t h e a d d i t i o n o f f o u r m o r e m o r p h o m e t r i c c h a r a c t e r s s u b s t a n t i a l l y i nc reased t h e d i a g n o s t i c p o w e r . M o s t a u t h o r s w h o have r e p o r t e d s a m p l i n g r e a r e d o r w i l d h e r r i n g larvae have o n l y r e p o r t e d l e n g t h a n d w e i g h t d a t a , p r e s u m a b l y because t h e r e was n o c o m p e l l i n g reason t o m e a s u r e o t h e r m o r p h o m e t r i c v a r i a b l e s . T h e r e f o r e , t h e m u l t i v a r i a t e c o n d i t i o n f a c t o r s ( P C 2 t o P C 6 a n d C V l ) d e v e l o p e d i n t h i s a p p e n d i x c a n n o t be a p p l i e d t o these p o p u l a t i o n s b u t some i d e a o f t h e p r a c t i c a l uses o f these f a c t o r s i n l a r v a l fish eco logy m a y be g l e a n e d f r o m a n ana lys i s o f t h e ava i l ab le l e n g t h a n d w e i g h t d a t a . T w o s t u d i e s r e p o r t e d l e n g t h a n d w e i g h t d a t a f o r Pac i f i c h e r r i n g la rvae : W e s t e r n h a g e n a n d R o s e n t h a l (1981) m e a s u r e d l ive w i l d larvae c a u g h t a t a n i g h t - l i g h t i n D e p a r t u r e B a y , B r i t i s h C o l u m b i a , a n d 226 S c h n a c k (1981) m e a s u r e d l ive r e a r e d larvae c a p t u r e d f r o m in s i t u c o n t a i n e r s ( v o l u m e = 6 0 0 0 1) l o c a t e d i n D e p a r t u r e B a y . B o t h w o r k e r s d r i e d t h e i r la rvae f r e s h ; W e s t e r n h a g e n a n d R o s e n t h a l (1981) m e a s u r e d t o t a l l e n g t h b u t S c h n a c k (1981) m e a s u r e d s t a n d a r d l e n g t h . T h e s e d a t a were c o m p a r e d w i t h t h a t o f t h i s s t u d y b y a s s u m i n g t h a t s to rage i n 3 - 5 % f o r m a l d e h y d e a n d seawate r causes a 5 % loss i n L ( S c h n a c k a n d R o s e n t h a l 1978; H a y 1982) a n d t h a t L is e q u i v a l e n t t o 9 6 . 5 % o f t o t a l l e n g t h ( M c G u r k , u n p u b l . d a t a ) . H a y (1984) has s h o w n t h a t f i x a t i o n i n 5 % f o r m a l d e h y d e a n d 2 8 % sa l i n i t y seawate r causes a 2 0 - 2 5 % loss i n W i n r e c e n t l y h a t c h e d Pac i f i c h e r r i n g larvae a n d t h a t t h i s p e r c e n t loss decreases w i t h i n c r e a s i n g l a r v a l s ize. B a s e d o n h i s d a t a I a s s u m e d t h a t fixation causes a 2 0 % loss i n live W i n yo lk-sac la rvae , a n d 2 0 % i n p o s t - y o l k - s a c larvae w e i g h i n g 8 0 - 1 0 0 ug a n d t h a t t h i s p e r c e n t decreases l i n e a r l y t o zero a t a fixed W o f 160 fig. T h e w e i g h t - l e n g t h p l o t s o f t h e fed g r o u p s , 1 9 8 1 A a n d 1 9 8 1 B , were g e n e r a l l y l i n e a r f o r larvae > 9.5 m m L b u t t h e y o l k - s a c a n d n o n - y o l k - s a c la rvae < 9.5 m m L were b e s t d e s c r i b e d w i t h a second l i n e a r regress ion ( T a b l e C . 7 , F i g . C .7 ) . T h e w e i g h t - l e n g t h p l o t o f t h e w i l d larvae m e a s u r e d by W e s t e r n h a g e n a n d R o s e n t h a l (1981) e x h i b i t e d t h e same n o n - l i n e a r i t y i n t h e s m a l l , yo lk -sac larvae. T h e r e was n o o b v i o u s e v i d e n c e o f p o o r l y c o n d i t i o n e d p o s t - y o l k - s a c larvae b u t t h e w i l d larvae d i d n o t ach ieve t h e same w e i g h t p e r u n i t l e n g t h as t h e r e a r e d larvae o f 1 9 8 1 A a n d 1 9 8 1 B . T h e r e a r e d larvae o f S c h n a c k (1981) , howeve r , e x h i b i t e d such l o w - w e i g h t p e r u n i t l e n g t h i n la rvae 9.5 - 1 1 . 5 m m l o n g , i n c o m p a r i s o n t o t h e s t a r v e d r e a r e d la rvae o f 1 9 8 1 C , t h a t one m u s t c o n c l u d e t h a t s o m e d i e d o f i r reve rs ib le s t a r v a t i o n . T h e p e r i o d o f s t a r v a t i o n - i n d u c e d m o r t a l i t y was b r i e f because t h e w e i g h t p e r u n i t l e n g t h rose t o m a t c h t h a t o f t h e w i l d la rvae a t a l e n g t h o f 1 0 . 5 - 1 1 . 0 m m . I t is i n t e r e s t i n g t o n o t e i n t h i s r e g a r d t h a t t h e average e x p o n e n t i a l r a t e s o f t o t a l m o r t a l i t y o f S c h n a c k ' s (1981) first f o u r e x p e r i m e n t a l g r o u p s , f r o m w h i c h t h i s w e i g h t - l e n g t h d a t a was t a k e n , were a m o n g t h e h i g h e s t r e c o r d e d f o r p o p u l a t i o n s o f r e a r e d h e r r i n g l a r vae , r a n g i n g f r o m 0 . 1 0 2 - 0 . 1 8 8 d _ 1 ( A p p e n d i x A ) . T h e s e r e s u l t s are s i m i l a r t o t hose r e p o r t e d f o r la rvae o f t h e A t l a n t i c h e r r i n g . T h e w i l d C l y d e a rea h e r r i n g larvae c a p t u r e d by M a r s h a l l e t a l . (1937) , H e m p e l a n d B l a x t e r (1963) , a n d B l a x t e r (1971) were also g e n e r a l l y l i g h t e r p e r u n i t l e n g t h t h a n t h e r e a r e d C l y d e a r e a larvae r e p o r t e d by B l a x t e r (1971) , E h r l i c h et a l . (1976) , a n d W e r n e r a n d B l a x t e r (1980) , espec ia l l y i n fish > 14 m m l o n g . 227 T A B L E C . 7 . P r e d i c t i v e l i n e a r regress ions o f d r y w e i g h t (/xg) o n s t a n d a r d l e n g t h ( m m ) fo r t h r e e g r o u p s o f la rvae . T h e d a t a o f t h e t w o fed g r o u p s , 1 9 8 1 A a n d 1 9 8 1 B , was b e s t d e s c r i b e d w i t h t w o regress ions , one f o r la rvae > 9.5 m m l o n g a n d a n o t h e r fo r la rvae < 9.5 m m l o n g . L e n g t h R a n g e ( m m ) n a b r 1 9 8 1 A 7 .8 -9 .4 8 1 2 .5X10 1 0.799 0 .21 9 .5 -28 .2 254 5 . 4 x l 0 ~ 3 4.486 0.99 1981B 8 . 5 - 9 . 4 3 1 6 . 0 x l ( r -0 .547 0.10 9 .5 -21 .3 175 2 . 4 x l 0 - 2 3.930 0.98 1981C 6 . 6 - 1 0 . 1 120 3.9X102 -0 .480 0.15 228 Figure C.7 . P l o t of fixed live dry weight (ug) on fixed live s tandard length (mm) for reared and w i l d Pacific herring larvae and reared A t l a n t i c herring larvae. A and B are the weight-length regressions for fed and 9-day-starved reared Clyde area At lant ic herring larvae, respectively, reared by Ehr l i ch et al . (1976). Lengths of the At l an t i c herring larvae were reduced by 5% to account for fixation shrinkage. 229 A yOlk-SaC 1 Westernhagen 3 and Rosenthal non-yolk-sacj # non-yolk-sac] scnnack ( 1 9 8 D A yolk-sac O non-yolk-sac 1 9 8 1 C 1 9 8 1 B , 1 9 8 1 A A B 10 20 30 40 SL (MM) 2 3 0 T h e r e are t w o poss ib le reasons f o r t h e r e l a t i v e l y low w e i g h t p e r u n i t l e n g t h o f t h e w i l d larvae c o m p a r e d t o t h e r e a r e d la rvae o f 1 9 8 1 A a n d 1 9 8 1 B . T h e first is t h a t r e a r i n g fish larvae i n enc losures t e n d s t o p r o d u c e heav ie r , d e e p e r - b o d i e d fish w i t h h i g h e r f a t c o n t e n t t h a n w i l d larvae o f t h e same l e n g t h ( B l a x t e r 1 9 7 1 ; B a l b o n t i n e t a l . 1973) . T h e m a g n i t u d e o f t h e d i f fe rences m a y be i nve rse l y r e l a t e d t o t h e size o f t h e enc losu re ( T h e i l a c k e r 1 9 8 0 b ) . T h e r e a p p e a r s t o be n o w a y t o a v o i d t h i s enc losure ef fect a n d s t i l l exerc ise some c o n t r o l over t h e f e e d i n g h i s t o r y o f an e x p e r i m e n t a l g r o u p . T h e second reason is r e l a t e d t o t h e a b i l i t y o f fish larvae t o evade fishing gear , i n t h i s case a n i g h t - l i g h t a n d a s m a l l h a n d - h e l d n e t . R e v e r s i b l y s t a r v e d larvae are n o t ab le t o a p p r o a c h o r m a i n t a i n s t a t i o n a t a n i g h t - l i g h t w i t h t h e same a b i l i t y as success fu l l y f e e d i n g larvae, b u t w h e n t h e y are w i t h i n r a n g e o f t h e n e t t h e y are less ab le t o a v o i d c a p t u r e . A c o m p a r i s o n o f t h i s d a t a w i t h t h e w e i g h t - l e n g t h l ines o f f e d a n d 9 -d -s ta rved r e a r e d C l y d e a r e a A t l a n t i c h e r r i n g larvae r e a r e d b y E h r l i c h et a l . (1976) shows t h a t b o t h w i l d a n d r e a r e d Pac i f i c h e r r i n g larvae are h e a v i e r p e r u n i t l e n g t h t h a n t h e i r C l y d e a r e a c o u n t e r p a r t s ( F i g . C .7 ) . W i l d C l y d e a rea larvae were also l i g h t e r t h a n w i l d Pac i f i c h e r r i n g l a r vae . T h e s e d i f fe rences i n w e i g h t p e r u n i t l e n g t h m a y have b e e n caused b y s t o c k - r e l a t e d d i f fe rences i n egg size o r by s t o c k - r e l a t e d d i f fe rences i n m o r p h o m e t r y a n d d r y w e i g h t . T h e ava i lab le d a t a o n t h e egg d r y w e i g h t o f Pac i f i c h e r r i n g larvae f r o m t h e S t r a i t o f G e o r g i a , B r i t i s h C o l u m b i a , i n d i c a t e s t h a t egg size increases w i t h t h e size o f t h e p a r e n t f e m a l e , as i n A t l a n t i c h e r r i n g , a n d t h a t t h e eggs are g e n e r a l l y heav ier t h a n s p r i n g - s p a w n e d B a l t i c a n d a u t u m n -s p a w n e d M a n x a n d D o g g e r B a n k eggs b u t are t h e same w e i g h t as s p r i n g - s p a w n e d C l y d e a n d N o r w e g i a n h e r r i n g eggs ( K i n g s t o n 1982; H e m p e l a n d B l a x t e r 1967) . T h e r e f o r e , a s tock r e l a t e d d i f fe rence i n egg w e i g h t does n o t a p p e a r t o be a n i m p o r t a n t f a c t o r . I n s u m m a r y , t h e r e a r e d l e a r n i n g s a m p l e s used t o c a l i b r a t e b i v a r i a t e a n d m u l t i v a r i a t e c o n d i t i o n f a c t o r s s h o u l d b e r e a r e d f r o m eggs o f t h e same s p a w n i n g s t o c k , o r a t least t h e same sub-spec ies , f r o m w h i c h s a m p l e s o f w i l d la rvae are t o b e c a p t u r e d . T h i s w i l l r e d u c e t h e b ias i n t r o d u c e d by r a c i a l d i f fe rences i n m o r p h o m e t r y a n d t i ssue d e n s i t y . N a t u r a l l y s p a w n e d eggs s h o u l d b e u s e d , i f p o s s i b l e , i n o r d e r t o a v o i d a n y b ias t h a t m a y b e i n t r o d u c e d f r o m t h e use o f a r t i f i c i a l l y s p a w n e d eggs f r o m p a r e n t fema les t h a t are s m a l l e r o r l a r g e r t h a n t h e m e a n size o f t h e n a t u r a l spawners . L e a r n i n g samp les o f r e a r e d fish s h o u l d be m a i n t a i n e d i n t h e l a rges t enc losers p r a c t i c a l i n o r d e r t o r e d u c e t h e enc losu re 2 3 1 ef fect . F i n a l l y , t h o s e w h o c o m p a r e r e a r e d a n d w i l d fish s h o u l d a lways be aware t h a t t h e c o m b i n a t i o n o f t h e enc losu re ef fect a n d s a m p l i n g p r o b l e m s c a u s e d by gear se lec t i on m a y p r e v e n t c o m p l e t e l y a c c u r a t e c a l i b r a t i o n o f m o r p h o m e t r i c c o n d i t i o n f a c t o r s . D e s p i t e these ser ious q u a l i f i c a t i o n s , c o n d i t i o n f a c t o r s based o n m o r p h o m e t r y a n d d r y w e i g h t have an i m p o r t a n t ro le t o p lay i n l a r v a l fish ecology. T h e y have t h e a d v a n t a g e t h a t t h e i r c o n s t i t u e n t va r iab les are easy t o m e a s u r e a n d d o n o t r e q u i r e any s p e c i a l t e c h n i q u e s o f c o l l e c t i o n a n d p r e s e r v a t i o n , u n l i k e h i s t o l o g y o f t h e v i s c e r a a n d m u s c u l a t u r e ( U m e d a a n d O c h i a i 1975; E h r l i c h et a l . 1976; O ' C o n n e l l 1976, 1980; T h e i l a c k e r 1978; O ' C o n n e l l a n d P a l o m a 1 9 8 1 ; K a s h u b a a n d M a t t h e w s 1984) , o r c h e m i c a l c o m p o s i t i o n ( E h r l i c h 1974a, b , 1975; B u c k l e y 1979, 1980) . T h e s e l a b o r i o u s m e t h o d s c a n n o t be used t o screen m o r e t h a n a s m a l l f r a c t i o n o f any s a m p l e . O f c o u r s e , a l l m e t h o d s o f e s t i m a t i n g c o n d i t i o n m u s t be a p p l i e d t o field-caught la rvae a n d so a l l are s u b j e c t t o t h e same s a m p l i n g p r o b l e m s d iscussed above. O n e s o l u t i o n t o t h e p r o b l e m s o f t h e e n c l o s u r e e f fec t , r a c i a l d i f fe rences i n m o r p h o m e t r y , a n d t h e d i s t o r t i o n c a u s e d b y n e t - c a p t u r e , is t o a v o i d c a l i b r a t i o n e n t i r e l y a n d t r e a t t h e f a c t o r s as r e p r e s e n t i n g ' a p p a r e n t ' c o n d i t i o n . I n t h i s scena r io h i s t o l o g y a n d c h e m i c a l c o m p o s i t i o n c o u l d be used t o assess t h e p r o p o r t i o n o f a l a r v a l c o h o r t t h a t is s t a r v i n g a n d a p p a r e n t c o n d i t i o n f a c t o r s c o u l d b e used t o search fo r r e l a t i o n s b e t w e e n m o r p h o m e t r y a n d e n v i r o n m e n t a l va r i ab les such as w a t e r c h e m i s t r y , w a t e r s t r u c t u r e , p h y t o p l a n k t o n a n d z o o p l a n k t o n d e n s i t y . T h e c o n c e p t s o f s i z e - i n d e p e n d e n c e , b i o l o g i c a l m e a n i n g , a n d o r t h o g o n a l i t y o f c o n d i t i o n f a c t o r s w o u l d s t i l l r e t a i n t h e i r i m p o r t a n c e i n such a n ana lys i s . B o t h l y p es o f f a c t o r , h i s t o l o g i c a l - c h e m i c a l a n d m o r p h o m e t r i c , c o m p l e m e n t each o t h e r a n d b o t h s h o u l d b e m e a s u r e d r o u t i n e l y i n l a r v a l fish s a m p l i n g p r o g r a m s . 232 Appendix D Effects of Net Capture on the Postpreservation Morphometry, Dry Weight, and Condition Factor of Larval Pacific Herring Appendix Summary T h e ef fects o f b e i n g t o w e d i n a p l a n k t o n n e t o n t h e m o r p h o m e t r y a n d d r y w e i g h t o f l a r va l Paci f ic h e r r i n g were m e a s u r e d f o r g r o u p s o f f e d a n d s t a r v e d fish p reserved i m m e d i a t e l y i n 2 % f o r m a l i n a f t e r a t o w i n g t r e a t m e n t . T o w i n g caused s i g n i f i c a n t decreases i n s t a n d a r d l e n g t h a n d d r y w e i g h t , n o change i n eye d i a m e t e r , a n d s i g n i f i c a n t increases b o d y d e p t h a t t h e anus, b o d y d e p t h a t t h e p e c t o r a l g i r d l e , a n d h e a d w i d t h . T h e changes decreased i n m a g n i t u d e w i t h i n c r e a s i n g age a n d size o f t h e fish, a n d t h e y a re e x t r a p o l a t e d t o b e c o m e n o n - s i g n i f i c a n t f o r larvae l onge r t h a n 14.0 m m . T h e e f fec t o f t h e t o w i n g t r e a t m e n t was i n d e p e n d e n t o f t h e d u r a t i o n o f t h e t o w a n d t h e r e was n o s i g n i f i c a n t i n t e r a c t i o n b e t w e e n f e e d i n g s t a t u s ( s ta rved or f e d ) a n d t o w i n g t r e a t m e n t . T h e s e changes i n b o d y d i m e n s i o n s cause s i g n i f i c a n t increases i n t h e a p p a r e n t c o n d i t i o n f a c t o r s . T h e m o r p h o m e t r y a n d d r y w e i g h t o f s m a l l fish la rvae m u s t be c o r r e c t e d f o r t h e ef fects o f n e t c a p t u r e b e f o r e t h e y can b e used t o a c c u r a t e l y m e a s u r e t h e n u t r i t i o n a l s t a t u s o f t h e fish. Intro duction T h e process o f c a p t u r e i n a t o w e d p l a n k t o n n e t causes d a m a g e t o fish larvae f r o m c o n t a c t w i t h t h e su r face o f t h e n e t a n d w i t h o t h e r o r g a n i s m s i n t h e n e t ( A h l s t r o m 1976) . T h e i n j u r i e s t o t h e fish cause loss o f g u t c o n t e n t s (Hay 1981) , s h r i n k a g e i n s t a n d a r d l e n g t h ( T h e i l a c k e r 1980; H a y 1981) , a n d changes i n o t h e r m o r p h o m e t r i c c h a r a c t e r s . T h e s e changes are i n d e p e n d e n t o f any changes i n l e n g t h , d r y w e i g h t o r m o r p h o m e t r y c a u s e d b y s u b s e q u e n t p r e s e r v a t i o n o f t h e fish i n f o r m a l d e h y d e or i n a l c o h o l ( B l a x t e r 1 9 7 1 ; S c h n a c k a n d R o s e n t h a l 1978; T h e i l a c k e r 1980; H a y 1982, 1984) . T h e r e is a n e e d f o r e q u a t i o n s t h a t c a n c o r r e c t t h e b o d y d i m e n s i o n s o f preserved w i l d f i sh larvae f o r t h e effects o f n e t c a p t u r e so t h a t t h e y m a y b e c o m p a r e d w i t h p reserved l a b o r a t o r y - r e a r e d fish la rvae . T h e i l a c k e r (1980) d e r i v e d c o r r e c t i o n e q u a t i o n s f o r five b o d y p a r t s o f l a r va l n o r t h e r n anchovy , Engraulis mordax a n d B l a x t e r (1971) a n d H a y (1981) e x a m i n e d t h e ef fect o f h a n d l i n g o n t h e s t a n d a r d l e n g t h o f la rva l 233 A t l a n t i c herring, Clupea harengus harengus, and Pacific herring, respectively. N o work has been done on the effect of net capture on dry weight for any species of fish larvae, which means that the effect of net capture on Fulton's condit ion factor (Ricker 1975), where 6 is the slope of the regression of log W on l o g L , is unknown. The objectives of this s tudy were: (1) to examine the effects of nett ing on the postpreservation morphometry, dry weight, and condit ion factor of Pacific herring larvae, (2) to derive equations to correct the body measurements and dry weight of preserved larvae, and (3) to examine the possibility that starved and fed herring larvae may be affected differently by towing. T h e effects of towing on live untowed larvae was not examined because field-caught fish larvae are usually preserved immediately after capture in order to maintain their quality. Subsequent analysis of these specimens is always concerned w i t h fixed rather than live body measurements. The effects of preservatives on standard length and dry weight of live larval herring have already been investigated (Schnack and Rosenthal 1978; Hay 1982, 1984). Materials and Methods T h e Pacific herring larvae for these experiments were reared from the egg at the Bamfield M a r i n e S ta t ion , Bamfie ld , B r i t i s h Columbia , in M a r c h - A p r i l 1982. The eggs had been natural ly spawned in Toquart Bay, Bark ley Sound. Newly-hatched larvae were reared in four 50-liter rectangular glass aquaria at a mean temperature of 8 ° C and a salinity of 30%j . The larvae, in two aquaria were fed dai ly w i t h Artemia naup l i i , which they began to eat 2-4 d after hatch. These fish were considered to belong to a single populat ion of fed fish despite being raised in separate containers because they shared the same water table and so experienced the same temperature, light, and chemical environment, and because they were b o t h exposed to a continuous supply of excess food in the form of a school of Artemia naup l i i which was maintained at the surface of the aquaria at a l l t imes. T h e larvae in the (DA) W(mg)xl02/L3(mm), or relative condit ion factor, (D.2) W(mg)xl02/Lb(mm), 234 o t h e r t w o a q u a r i a were a l l o w e d t o s ta rve f r o m h a t c h t o d e a t h , w h i c h o c c u r r e d o n day 15. T h e s e fish were c o n s i d e r e d t o b e l o n g t o a s ingle p o p u l a t i o n o f s t a r v e d larvae because t h e y s h a r e d t h e same wa te r t a b l e . D i v i d i n g t h e fed a n d s ta rved fish i n t o t w o r o u g h l y e q u a l halves was n o t a n a t t e m p t t o r e p l i c a t e t h e t r e a t m e n t s b u t a n a t t e m p t t o d o u b l e t h e t o t a l n u m b e r o f fish ava i lab le f o r t h e s tudy . T h r e e samp les o f 2 0 - 5 0 la rvae each were t a k e n f r o m t h e t w o p o p u l a t i o n s ( fed a n d s t a r v e d ) 1 , 5, 8, 1 1 , a n d 14 d a f t e r h a t c h ( t o t a l = 3 0 s a m p l e s ) , a n d t w o s a m p l e s o f 20-30 larvae were t a k e n f r o m t h e fed p o p u l a t i o n 19, 23 , a n d 30 d a f t e r h a t c h ( t o t a l = 6 s a m p l e s ) , f o r a g r a n d t o t a l o f 36 s a m p l e s . E a c h s a m p l e o f larvae was c a p t u r e d i n one sweep o f a p l a s t i c c u p a n d n o a t t e m p t was m a d e t o c o u n t t h e e x a c t n u m b e r o f la rvae c a p t u r e d i n t h e sweep. T h e first o f t h e t h r e e samp les 1-14 d o l d o r t h e f i r s t o f t h e t w o samp les 19-30 d o l d was t h e e x p e r i m e n t a l c o n t r o l ; i t was i m m e d i a t e l y p reserved i n 2 % f o r m a l d e h y d e i n seawate r ( s a l i n i t y = 3 0 % o ) . T h i s was t h e c o n c e n t r a t i o n o f f o r m a l d e h y d e a f t e r t h e a d d i t i o n o f t h e la rvae . T h e s e c o n d s a m p l e was t a k e n t o a b o a t o n B a m f i e l d I n l e t w i t h i n 5 m i n o f i t s c a p t u r e . T h e r e t h e larvae were re leased i n t o t h e u p t u r n e d m o u t h o f a p l a n k t o n n e t t h a t was t r a v e l l i n g a t a speed o f a p p r o x i m a t e l y 1 m s e c - 1 . T h e n e t was t h e n a l l o w e d t o s i n k t o a d e p t h o f 1 m . T h e n e t was 1.5 m l o n g w i t h a m e s h d i a m e t e r o f 4 7 1 fim, a 40 c m d i a m e t e r m o u t h , a n d a h a r d p l a s t i c c o d e n d w i t h t w o holes o f 4 c m d i a m e t e r c u t i n t o i t s s ides a n d cove red by 73 fim d i a m e t e r m e s h . T h e n e t was p u l l e d f r o m t h e w a t e r a f t e r a t o w o f 5 m i n a n d g e n t l y w a s h e d d o w n w i t h a seawater hose. T h e c o n t e n t s o f t h e c o d e n d were p r e s e r v e d i n 2 % f o r m a l d e h y d e i n seawate r w i t h i n a p e r i o d o f 5 m i n a f t e r t h e n e t was l i f t e d . T h e t h i r d s a m p l e o f t h e 1-14 d o l d fish was t r e a t e d i n a n i d e n t i c a l m a n n e r t o t h e second e x c e p t i t was t o w e d f o r 15 m i n . T h e 19- , 2 3 - , a n d 3 0 - d - o l d fed larvae were s u b j e c t e d t o a 5 m i n t o w only. T h e r e were n o s m a l l ( 8 - 1 2 m m l o n g ) P a c i f i c h e r r i n g la rvae r e s i d e n t i n t h e p l a n k t o n o f B a m f i e l d I n l e t d u r i n g t h e p e r i o d o f t h e e x p e r i m e n t a l t o w s (24 M a r c h - 2 3 A p r i l , 1982) . T h i s was d e t e r m i n e d by s a m p l i n g t h e p l a n k t o n o f t h e I n l e t w i t h p l a n k t o n n e t s a n d w i t h a n i g h t - l i g h t b e f o r e a n d d u r i n g t h e series o f e x p e r i m e n t a l t o w s r e p o r t e d h e r e . P a c i f i c h e r r i n g l a rvae were p rocessed a f t e r 3 m o n t h s s to rage a t 20° C . N o a t t e m p t was m a d e t o c o u n t t h e t o t a l n u m b e r o f la rvae recove red f r o m each t o w . S u b s a m p l e s o f 15 la rvae were t a k e n f r o m each o f t h e 30 s a m p l e s f o r ages 1-14 d a n d s u b s a m p l e s o f 10 larvae were t a k e n f r o m t h e s ix catches f o r ages 1 9 - 3 0 d f o r a t o t a l o f 510 fish. S a m p l e s c o n t a i n i n g 1-d-o ld larvae were s p l i t i n t o one s u b s a m p l e 235 w i t h los t o r d a m a g e d yo lksacs a n d a second w i t h i n t a c t yo lksacs . O n l y i n t a c t 1-d-o ld larvae were m e a s u r e d . L a r v a e 5 - 3 0 d o l d were s u b s a m p l e d r a n d o m l y . S t a n d a r d l e n g t h , or n o t o c h o r d l e n g t h , was m e a s u r e d t o t h e n e a r e s t 0 .1 m m a n d o t h e r d i m e n s i o n s t o t h e n e a r e s t 0 .01 m m u n d e r a c o m p o u n d m i c r o s c o p e . E a c h l a r v a was t h e n r i n s e d i n d i s t i l l e d w a t e r , sealed i n a n a l u m i n u m f o i l p a c k e t a n d d r i e d at 60 ° C f o r 24 h o u r s . T h e p a c k e t s were s t o r e d i n a des i ca to r u n t i l t h e d r y w e i g h t was m e a s u r e d w i t h an e l e c t r o b a l a n c e . I n a d d i t i o n t o s t a n d a r d l e n g t h , f o u r b o d y m e a s u r e m e n t s were t a k e n : (1) d o r s o v e n t r a l b o d y d e p t h j u s t b e h i n d t h e anus ( A B D ) ; (2) b o d y d e p t h a t t h e p e c t o r a l g i r d l e ( P B D ) ; (3) h e a d w i d t h , ( H W ) i n c l u d i n g t h e eyeba l l s ; (4) d i a m e t e r o f t h e eye ( E D ) . T h e d i a m e t e r o f t h e eye was a l w a y s m e a s u r e d a l o n g t h e a n t e r i o r - p o s t e r i o r axis o f t h e o r g a n . T - t e s t s a n d D u n c a n ' s a n d Scheffe's m u l t i p l e r a n g e tes ts were used t o t e s t f o r s i g n i f i c a n t d i f fe rences b e t w e e n t h e m e a n b o d y d i m e n s i o n s a n d c o n d i t i o n o f t h e 5- a n d 1 5 - m i n t o w t r e a t m e n t s a n d t h e con t ro ls a t each age a n d f o o d leve l . A t h r e e - w a y ana lys i s o f va r iance p r o g r a m , G e n l i n ( G r i e g a n d B j e r r i n g 1980) , was used t o t e s t f o r s i g n i f i c a n t i n t e r a c t i o n s o f age, f o o d leve l , a n d t o w t r e a t m e n t o n t h e b o d y d i m e n s i o n s . G e n l i n p e r f o r m e d t h e ana lys i s by fitting va r ious reg ress ion m o d e l s t o t h e d a t a a n d t a k i n g d i f fe rences b e t w e e n t h e s u m s o f squares a b o u t t h e fitted m o d e l s f o r pa i r s o f these m o d e l s . T h i s m e a n t t h a t G e n l i n c o u l d h a n d l e e m p t y cel ls . T h e r e l a t i o n s h i p b e t w e e n c o n t r o l s ize, Y , a n d n e t t e d s ize, X , was m o d e l l e d w i t h a G o m p e r t z e q u a t i o n , (D.Z) Y = Xexpfrap{-ftX)], w h e r e fi is t h e r a t e a t w h i c h X a p p r o a c h e s Y , a n d % is t h e r a t e a t w h i c h J, decays w i t h X . T h e e q u a t i o n was first d e r i v e d by T h e i l a c k e r (1980) . I t was fit w i t h t h e B M D P : A R n o n l i n e a r regress ion p r o g r a m ( D i x o n 1983) . F u l t o n ' s c o n d i t i o n f a c t o r was c a l c u l a t e d because i t is t h e c o n d i t i o n f a c t o r m o s t o f t e n used by w o r k e r s i n l a r v a l fish eco logy (e.g. B l a x t e r 1 9 7 1 ; V i l e l a a n d Z i j l s t r a 1 9 7 1 ; W e s t e r n h a g e n a n d R o s e n t h a l 1981) . T h i s f a c t o r is less t h a n o p t i m a l because : (1) i t is a r a t i o a n d so i t is c o r r e l a t e d w i t h i t s d e n o m i n a t o r a n d , t h e r e f o r e , i t is a m i x t u r e o f size a n d shape i n f o r m a t i o n , (2) t h e a s s u m p t i o n o f 236 isometry (b=3) is incorrect because the weight-length exponent of larval fishes is closer to 4 (Laurence 1979), and, (3) it does not include information on nutritional status contained within the other four body dimensions measured in this study. Relative condition factor has been preferred by some authors (Ehrlich et al. 1976) because 6 is set at a value that reflects the true allometric relationship between weight and length. However, (1) relative condition factor is a ratio with all of the undesirable properties of a ratio, (2) its use assumes the presence of only one group in the data whereas there are four groups (control-fed, control-starved, towed-fed, towed-starved) in the data and each have different weight-length exponents, and (3) it is constructed from only two of the six body dimensions measured. I proposed in Appendix C that only a discriminant function composed of the principal components of a morphometric data set can satisfy the three criteria of an optimal condition factor. The procedure, extraction of components and their use in discriminating between groups, was used in this study to identify those components that best separated control from towed larvae in order to better visualize the effect of towing on herring larvae. The principal components of the morphometric data set were calculated with the BMDP:4M factor analysis program (Dixon 1983). All control and treatment larvae were pooled and the six body dimensions were loge-transformed in order to linearize the relationships between them. The log,-transformed variables were standardized to zero mean and unit standard deviation with z-scores, {DA) ztj = (xi:i - x^/si, where z$ = the standardized score of case j for variable t, x^ - =the value of case j for variable i, xi = the mean of variable t, and a,=the standard deviation of variable i . The six ordinary principal components were extracted from the correlation matrix, rather than the variance-covariance matrix, of the standardized variables because of the different units (mm and ug) of the variables (Pimental 1979). Classification functions were calculated with the BMDP:7M stepwise discriminant analysis program (Dixon 1983). 'Jackknifed' classifications were used to avoid the bias that occurs when the results of the classification are based on the same cases used in developing the classification equations. In the jackknife procedure each case is classified on the basis of equations develop ed from all data except the case being classified. The results are a more realistic estimate of the ability of the predictors to discriminate between groups. 237 Results I c o u l d n o t observe t h e b e h a v i o u r o f t h e e x p e r i m e n t a l fish i m m e d i a t e l y a f t e r t h e tows because t h e s a m p l e s c o n t a i n e d la rge a m o u n t s o f p l a n k t o n . I n o t h e r s t u d i e s w i t h t h e same n e t , w i l d larvae u s u a l l y we re a l i ve a n d s w i m m i n g i n t h e c o d e n d i f catches were s m a l l , a l t h o u g h some s h e w e d t h e w h i t e h e a d c o l o r i n g t h a t i n d i c a t e d a u t o l y s i s a n d o s m o t i c shock . W h e n ca tch dens i t i es were h i g h , as t h e y o f t e n were a f t e r a m a j o r h a t c h o f Pac i f i c h e r r i n g larvae i n t h e I n l e t ( u p t o 155,000 larvae p e r t o w ) , t h e c a p t u r e d la rvae were d e a d a n d c o m p l e t e l y w h i t e w h e n t h e c o d e n d was o p e n e d . I n t h i s s t u d y an average 3 0 % o f 1-d-o ld la rvae h a d r u p t u r e d t h e i r yo lk -sac m e m b r a n e s a n d h a d los t p a r t o r a l l o f t h e i r y o l k sacs a f t e r 5- o r 1 5 - m i n t o w s . B o t h f e d a n d s t a r v e d larvae g r e w i n size d u r i n g t h e yo lk -sac phase ( 0 - 6 d ) (Table D . l ) . T h e fed la rvae c o n t i n u e d t o g r o w d u r i n g t h e p o s t - y o l k - s a c phase ( 7 - 3 0 d ) b u t t h e b o d y p a r t s a n d d r y w e i g h t o f t h e s t a r v e d la rvae decreased . F u l t o n ' s c o n d i t i o n f a c t o r dec reased w i t h age i n b o t h s t a r v e d a n d f e d l a r vae . T h e m e a n b o d y m e a s u r e m e n t s a t age o f t h e 5- a n d 1 5 - m i n t o w t r e a t m e n t s were n o t s i g n i f i c a n t l y d i f f e r e n t (P < 0 .01) , i n d i c a t i n g t h a t t h e ef fect o f n e t t i n g was i n d e p e n d e n t o f t h e d u r a t i o n o f t h e t o w . A c o m p a r i s o n o f t h e p o o l e d n e t t r e a t m e n t d a t a w i t h t h e c o n t r o l d a t a f o r each age a t each f o o d level i n d i c a t e d t h a t t o w i n g caused a r e d u c t i o n i n s t a n d a r d l e n g t h a n d d r y w e i g h t , n o change i n eye d i a m e t e r , a n d an increase i n b o d y d e p t h s a t t h e anus a n d t h e p e c t o r a l g i r d l e a n d i n F u l t o n ' s c o n d i t i o n f a c t o r . T h e ef fect o f t o w i n g was g r e a t e s t f o r s m a l l larvae a n d i t t e n d e d t o decrease w i t h i n c r e a s i n g age a n d size ( F i g . D . l ) . T h e r e is a t r e n d o f dec reas ing pe rcen t change i n F u l t o n ' s f a c t o r w i t h i n c r e a s i n g c o n d i t i o n b u t t h i s was d u e so le ly t o t h e low p e r c e n t changes o f t h e t w o 1-d-old s a m p l e s . T h e changes i n F u l t o n ' s c o n d i t i o n f a c t o r are b e s t s u m m a r i z e d as an average o f + 1 3 . 5 % over t h e l e n g t h r a n g e o f 7 - 1 4 m m . A t h r e e - w a y ana lys i s o f v a r i a n c e s u p p o r t e d t h e o b s e r v a t i o n t h a t t o w i n g h a d s i g n i f i c a n t ef fects o n a l l b o d y d i m e n s i o n s e x c e p t eye d i a m e t e r , a n d o n F u l t o n ' s c o n d i t i o n f a c t o r (Table D .2 ) . F o o d level h a d s i g n i f i c a n t ef fects o n a l l b o d y d i m e n s i o n s b u t n o t o n c o n d i t i o n , a n d age h a d s ign i f i can t ef fects o n a l l b o d y d i m e n s i o n s a n d o n c o n d i t i o n . T h e i n t e r a c t i o n o f t o w i n g a n d f o o d level was n o t s ign i f i can t f o r a n y b o d y d i m e n s i o n o r f o r c o n d i t i o n , i n d i c a t i n g t h a t t h e ef fect o f t o w i n g was i n d e p e n d e n t o f t h e n u t r i t i o n a l s t a t u s o f t h e la rvae . T h e i n t e r a c t i o n o f t o w i n g a n d age was n o t s i g n i f i c a n t f o r b o d y d e p t h s 238 T A B L E D . l . M e a n ( ± 1 S D ) b o d y m e a s u r e m e n t s , d r y w e i g h t s , a n d F u l t o n ' s c o n d i t i o n f a c t o r o f s t a r v e d a n d fed Pac i f i c h e r r i n g la rvae t h a t h a d been t o w e d i n a p l a n k t o n n e t a n d preserved i n 2% f o r m a l i n . D a t a fo r 5 - m i n a n d 1 5 - m i n tows are p o o l e d . Values i n paren theses u n d e r t h e m e a n s are percen t d e v i a t i o n s f r o m u n t o w e d b u t p r e s e r v e d la rvae . A s t e r i s k s i n d i c a t e s i g n i f i c a n t d i f fe rences f r o m c o n t r o l va lues a t * P < 0.05 a n d "P < 0 .01 ( t - t e s t s ) . B o d y d e p t h a t H e a d E y e S t a n d a r d D r y A g e A n u s P e c t o r a l w i d t h d i a m e t e r l e n g t h w e i g h t C o n d i t i o n (d ) N ( m m ) ( m m ) ( m m ) ( m m ) ( m m ) t " g ) E i c t o r S t a r v e d l a r v a e 1 1 30 0 .25(0.02) 0 .51(0 .06) 0 .74(0.06) 0 .31(0 .03) 7.0(0.7) 134(31) 40.0(10.5) ( + 4 . 2 ) (-3.8) (-2.6) (0 .0) (-14.6) * " (-35.0) " ( + 4 . 1 ) 5 30 0 .27(0.02) 0 .62(0.05) 0.85(0.04) 0 .32(0 .02) 8.5(0.4) 150(19) 24.3(3 .6) ( + 3 . 9 ) ( + 5 . 1 ) ( + 1 . 2 ) (-5.9) (-12.4) ( - 2 1 . 5 ) " ( + 1 4 . 7 ) " 8 30 0 .28(0.02) 0 .63(0.05) 0 .89(0.03) 0 .36(0 .02) 8.7(0.4) 133(23) 20.1(2.9) ( + 1 2 . 0 ) * * ( + 1 4 . 6 ) " ( + 8 . 5 ) " ( + 5 . 9 ) (-7.5) " (-23.6) " (-4.8) 11 30 0 .28(0.02) 0 .61(0 .07) 0 .86(0.05) 0 .36(0 .02) 8.4(0.5) 123(19) 21.1(4.6) ( + 7 . 7 ) * * ( + 8 . 9 ) * ( + 8 . 9 ) " ( + 5 . 9 ) (-10.6) " (-12.8) * * ( + 2 3 . 3 ) " 14 30 0 .28(0.02) 0 .60(0 .05) 0 .85(0.05) 0 .36(0 .02) 8.4(0.4) 105(19) 17.7(2.7) ( + 7 . 7 ) " ( + 5 . 3 ) ( + 9 . 0 ) " (0.0) (-8.7) " (-10.3) * ( + 1 6 . 1 ) " F e d l a r v a e 1 1 30 0 .25(0 .02) 0 .54(0 .05) 0 .81(0.05) 0 .32(0 .02) 7.1(0.4) 145(27) 41.2(10.4) ( + 8 . 7 ) " ( + 1 4 . 9 ) " ( + 3 . 9 ) * (0 .0) (-12.4) * * (-26.4) ( + 8 . 9 ) 5 30 0 .27(0 .02) 0 .61(0.06) 0 .86(0.04) 0 .34(0 .02) 8.7(0.3) 126(15) 19.3(3.2) ( + 3 . 9 ) ( + 1 7 . 3 ) " ( + 4 . 9 ) * (-5.6) • (-6.5) " (-34.7) " (-18.8) * * 8 30 0 .27(0.02) 0 .60(0.06) 0 .88(0.05) 0 .35(0 .02) 8.7(0.5) 147(29) 22.1(4 .2) (0.0) ( + 1 . 7 ) ( + 7 . 3 ) " ( + 2 . 9 ) ( - 9 . 4 ) " (-5.8) ( + 2 5 . 0 ) " 11 30 0 .29(0 .03) 0 .65(0.05) 0 .90(0.05) 0 .36(0 .02) 8.9(0.7) 141(45) 19.9(4.3) 239 ( + 3 . 6 ) ( + 1 . 6 ) ( + 3 . 5 ) (-2.7) ( - 1 2 . 8 ) * * ( - 2 4 . 2 ) * * ( + 1 6 . 2 ) * 14 30 0.32(0.03) 0.73(0.12) 0 .94(0.08) 0 .40(0.03) 9.5(0.7) 208(43) 24.6(2.9) ( + 1 0 . 4 ) * * ( + 1 0 . 7 ) * * ( + 8 . 1 ) * * (0.0) (-7.8) * * ( + 1 6 . 9 ) ( + 5 0 . 6 ) * * 19 20 0 .31(0.04) 0.72(0.07) 0 .98(0.03) 0 .41(0.02) 10.5(0.7) 249(63) 21.2(2 .2) ( + 3 . 3 ) ( + 4 . 4 ) ( + 2 . 1 ) ( + 2 . 5 ) (-3.7) ( + 1 3 . 2 ) ( + 2 7 . 9 ) * * 23 20 0 .35(0.06) 0.76(0.14) 1.05(0.05) 0 .44(0.03) 11.1(1.1) 315 (107) 22.1(4 .3) (0.0) (-2.6) ( + 2 . 9 ) ( + 2 . 3 ) (-5.1) (-5.4) ( + 9 . 4 ) 30 20 0 .42(0.03) 0 .93(0.07) 1.14(0.08) 0 .47(0.08) 12.4(0.9) 377(121) 19.1(2.3) ( + 2 . 4 ) ( + 2 . 2 ) (0.0) (-2.1) (-3.9) (-6.9) ( + 3 . 3 ) 1 C o n t r o l s a m p l e s were 15 la rvae each o f ages 1-14 d , a n d 10 larvae each a t ages 1 9 - 3 0 d . 240 F i g u r e D . l . R e l a t i o n s h i p s o f p o s t p r e s e r v a t i o n b o d y d i m e n s i o n s a n d d r y w e i g h t b e t w e e n t o w e d a n d c o n t r o l P a c i f i c h e r r i n g la rvae . C i r c l es are d a t a f r o m t h e p resen t s t u d y , o p e n c i rc les are s t a r v e d larvae a n d c losed c i rc les are fed la rvae . T h e square is d a t a f r o m H a y (1981) a n d t h e t r i a n g l e s are d a t a f r o m B l a x t e r (1971) . T h e b r o k e n l ines are l ines o f e q u a l i t y a n d t h e so l i d curves are fitted G o m p e r t z m o d e l s f o r w h i c h ' e q u a t i o n s are g i v e n . C u r v e s m a r k e d A o r u n m a r k e d fit p r e s e n t d a t a ; B curves are f r o m T h e i l a c k e r (1980) f o r n o r t h e r n a n c h o v y larvae g iven a 5 - m i n s i m u l a t e d t o w . 2 4 1 i ' o v • ' J  1.4 0 .5 0 0.2 0.4 X - D I M E N S I O N O F T O W E D L A R V A E 242 T A B L E D .2 . T h e F - r a t i o s o f t h r e e - w a y analyses o f va r iance o f s ix b o d y m e a s u r e m e n t s a n d F u l t o n ' s c o n d i t i o n f a c t o r . D a t a fo r 5 - m i n a n d 1 5 - m i n t o w are p o o l e d . A s t e r i s k s i n d i c a t e s ign i f i can t d i f fe rences a t * P < 0.05 a n d "P < 0 . 0 1 . B o d y d e p t h a t H e a d Eye S t a n d a r d D r y Sou rce d f A n u s P e c t o r a l w i d t h d i a m e t e r l e n g t h • w e i g h t C o n d i t i o n T o w 2,474 1 7 . 4 " 2 0 . 9 " 35 .4 * * 0.2 138.6** 2 8 . 1 " 14.4** F o o d 1,474 1 7 . 2 " 1 7 . 6 " 58 .5 * * 3 9 . 9 * * 4 4 . 2 " 29 .5 * * 1.2 A g e 7,474 1 0 5 . 1 " 8 8 . 6 " 142 .2* * 1 4 3 . 3 " 224 .5* * 8 9 . 1 * * 170 .2* * T o w x f o o d 2,474 0 .1 0.6 0.3 0.7 0.9 0.3 0.5 T o w x age 11,474 0.5 1.4 3.9** 2 .6** 1.4 3.6* 2.3* F o o d x age 4,474 6 . 7 " 1 5 . 9 " 1 4 . 1 * * 13 .7* * 1 6 . 2 " 20 .6* 7 . 1 * * T o w x f o o d x age 8,474 1.6 2.5* 1.2 1.3 1.2 1.6 4.8** 243 F i g u r e D .2 . P l o t o f t h e fifth o r d i n a r y p r i n c i p a l c o m p o n e n t , P C 5 , o n t h e first o r d i n a r y p r i n c i p a l c o m p o n e n t , P C I , f o r t h e p o o l e d c o n t r o l a n d t o w e d h e r r i n g la rvae. E v e r y f o u r t h l a r v a was p l o t t e d . T h e l i ne a n d t h e e q u a t i o n re fe r t o t h e c a n o n i c a l va r iab le f o r t h e d i s c r i m i n a n t ana lys i s d o n e t o s e p a r a t e t o w e d a n d c o n t r o l g r o u p s . 244 O CL 5 4 3 2 1 0 -1 •2 •3 •4 c o n t r o l : • f e d o s t a r v e d t o w e d : A f e d A s t a r v e d c a n o n i c a l v a r i a b l e = 0 . 6 5 2 P C 1 + 1 . 1 4 6 P C 5 n a r r o w - h e a d e d , l a r g e - e y e d % V & IB w i d e - h e a d e d, s m a l l - e y e d s m a l l <• A. AAO A A= * • A A -> l a r g e - 3 - 2 - 1 0 1 PC1 2 4 5 a t t h e anus a n d t h e p e c t o r a l g i r d l e a n d fo r s t a n d a r d l e n g t h , b u t i t was s i g n i f i c a n t f o r h e a d w i d t h , eye d i a m e t e r , d r y w e i g h t , a n d c o n d i t i o n . I t can b e a s s u m e d w i t h some c o n f i d e n c e t h a t t h e ef fects o f t o w i n g o n b o d y d i m e n s i o n s w i l l dec l i ne w i t h i n c r e a s i n g age a n d size o f a l a r v a because fish develop a m o r e r i g i d s k e l e t o n a n d a t o u g h e r e p i d e r m i s as t h e y g r o w . T h e r e s u l t s p resen ted here s u p p o r t t h i s a s s u m p t i o n b u t t h e ranges o f sizes were n o t s u f f i c i e n t l y la rge t o e s t a b l i s h i t s t a t i s t i c a l l y . For e x a m p l e , t h e p e r c e n t change i n s t a n d a r d l e n g t h d e c l i n e d f r o m a n average o f - 1 3 . 5 % a t day 1 t o - 3 . 9 % a t day 30 b u t because t h e l a t t e r p e r c e n t change was s t i l l s i g n i f i c a n t t h e i n t e r a c t i o n o f t o w i n g a n d age f o r s t a n d a r d l e n g t h was n o t s i g n i f i c a n t . T h e coe f f i c ien ts o f t h e c o r r e l a t i o n s b e t w e e n t h e s i x b o d y d i m e n s i o n s a n d t h e first o r d i n a r y p r i n c i -p a l c o m p o n e n t are a l l h i g h a n d p o s i t i v e , i n d i c a t i n g t h a t i t is a size c o m p o n e n t (Table D .3 ) . T h e l o a d i n g p a t t e r n s o f t h e o t h e r five o r d i n a r y c o m p o n e n t s are b i p o l a r , i n d i c a t i n g t h a t t h e y are a l l s h a p e c o m p o -n e n t s . 7 5 . 1 % o f t h e t o t a l va r iance o f t h e d a t a was e x p l a i n e d as size d a t a a n d 2 4 . 9 % was e x p l a i n e d as s h a p e d a t a . T h e fifth a n d t h e first c o m p o n e n t s were su f f i c ien t t o c o r r e c t l y c lass i fy 8 5 . 3 % o f t h e larvae ( c o n t r o l : 8 8 . 9 % ; t o w e d : 8 3 . 3 % ) u s i n g s tepw ise d i s c r i m i n a n t ana lys i s . T h e o t h e r f o u r c o m p o n e n t s c o m b i n e d o n l y a d d e d a n a d d i t i o n a l 4 . 9 % c o r r e c t l y c lass i f ied a n d so t h e y are n o t d iscussed f u r t h e r . T h e fifth c o m p o n e n t a lone c o r r e c t l y c lass i f ied 7 6 . 7 % o f t h e larvae ( c o n t r o l : 8 4 . 4 % ; t o w e d : 7 2 . 4 % ) a n d t h e first c o m p o n e n t , s ize, o n l y a d d e d a n a d d i t i o n a l 8 . 6 % t o t h e t o t a l c o r r e c t l y c lass i f ied . T h e l o a d i n g p a t t e r n o f t h e fifth c o m p o n e n t i n d i c a t e s t h a t i t is a c o n t r a s t b e t w e e n eye d i a m e t e r , h e a d w i d t h , s t a n -d a r d l e n g t h , a n d b o d y d e p t h a t t h e p e c t o r a l s . B o d y d e p t h a t t h e anus a n d d r y w e i g h t have very low c o r r e l a t i o n s w i t h t h e c o m p o n e n t . T o w e d larvae are c h a r a c t e r i z e d by s m a l l e r re la t i ve eye d i a m e t e r s , l a r g e r r e l a t i v e h e a d w i d t h s , l o n g e r r e l a t i v e s t a n d a r d l e n g t h s , l ower r e l a t i v e b o d y d e p t h s a t t h e p e c -t o r a l s , a n d s m a l l e r s ize, t h a n c o n t r o l larvae o f t h e s a m e age ( F i g . D . 2 ) . T h e key w o r d here is ' r e l a t i v e ' , t h e ana lys i s does n o t suggest t h a t eye d i a m e t e r a c t u a l l y s h r i n k s w i t h t o w i n g o r t h a t s t a n d a r d l e n g t h increases w i t h t o w i n g . R a t h e r , i t m e a n s t h a t t o w i n g increases t h e a p p a r e n t n u t r i t i o n a l s t a t u s o f a fish b y r e d u c i n g i t s a p p a r e n t size i n r e l a t i o n t o i t s a p p a r e n t m o r p h o m e t r y a n d by d i s t o r t i n g t h e d i m e n s i o n s o f t h e m o s t i m p o r t a n t p a r t o f t h e b o d y , t h e h e a d , i n such a w a y t h a t i t m o r e c lose ly resembles t h a t o f a fish w i t h a h i g h e r n u t r i t i o n a l s t a t u s . 246 T A B L E D.3 . T h e mean and standard deviation (SD) of each log^-transformed body dimension for the pooled data (N=510) used to standardize the variables to zero mean and uni t standard deviat ion, and the pr inc ipa l components (PCs) extracted from the correlation matr ix of the six transformed and standardized body dimensions: the coefficients of the six components, the eigenvalues (E), the percent of the variance explained ( r 2 ) , and the correlation of the variables w i t h the components (r). B o d y depth at Head Eye Standard D r y Measure Anus Pectoral w i d t h diameter length weight E r 2 M e a n -1.281 -0.495 -0.149 -1.035 2.191 5.072 S D 0.146 0.173 0.110 0.120 0.147 0.363 P C I -0.140 -0.040 -0.071 -0.090 -0.270 1.292 4.505 75.1 r 0.91 0.87 0.90 0.89 0.88 0.74 P C 2 -0.381 1.658 -0.287 -0.181 -0.207 -0.050 0.588 9.8 r -0.16 -0.27 -0.20 -0.08 0.19 0.64 P C 3 -0.215 -0.181 -0.377 1.745 -0.392 -0.113 0.328 5.5 r -0.19 0.28 0.04 0.35 0.23 -0.18 P C 4 -0.404 -0.360 1.902 -0.441 -0.207 -0.078 0.236 3.9 r -0.09 0.22 0.24 0.11 0.32 -0.11 P C 5 -0.126 -0.206 -0.188 -0.401 1.756 -0.454 0.186 3.1 r -0.04 0.14 -0.24 0.27 -0.17 0.06 P C 6 2.046 -0.669 -0.479 -0.243 -0.122 -0.228 0.157 2.6 r 0.31 -0.16 -0.17 0.01 0.05 -0.05 247 Discussion T h e degree o f s h r i n k a g e o f s t a n d a r d l e n g t h w i t h t o w i n g t h a t was obse rved i n t h i s s t u d y was also obse rved by T h e i l a c k e r (1980) fo r l a r v a l n o r t h e r n a n c h o v y over t h e l e n g t h r a n g e o f 7 - 1 4 m m ( F i g . D . l ) . T h i s s u p p o r t s t h e use o f T h e i l a c k e r ' s e q u a t i o n f o r c l u p e i d l i k e f ishes, e.g. A t l a n t i c h e r r i n g ( L o u g h e t a l . 1982) , as l o n g as spec ies-spec i f ic e q u a t i o n s f o r t h e en t i re l e n g t h r a n g e f r o m h a t c h t o m e t a m o r p h o s i s are s t i l l u n a v a i l a b l e f o r m o s t f ishes. T h e n e t t r e a t m e n t e x p e r i m e n t s o f B l a x t e r (1971) f o r l a r va l A t l a n t i c h e r r i n g a n d o f H a y (1981) f o r l a rva l Pac i f i c h e r r i n g p r o d u c e d sh r inkages o f s t a n d a r d l e n g t h t h a t were a p p r o x i m a t e l y t w i c e as g r e a t as t h o s e observed i n t h i s s t u d y ( F i g . D . l ) . Loss o f d r y w e i g h t w i t h t o w i n g m a y have b e e n c a u s e d b y t h e loss o f b o d y fluids a n d o f f r a g m e n t s o f t h e d e l i c a t e fin f o l d a n d , p e r h a p s , b y t h e loss o f t h e m u c o u s c o a t t h a t n o r m a l l y covers t h e e p i d e r m i s o f a h e r r i n g l a r v a . T h e loss was n o t e n t i r e l y d u e t o a loss o f g u t c o n t e n t s o f t h e f e d - n e t t e d larvae because b o t h t h e s t a r v e d - t o w e d a n d t h e f e d - t o w e d s a m p l e s l os t w e i g h t a t a p p r o x i m a t e l y t h e s a m e r a t e . N e t t r e a t m e n t d i d n o t af fect eye d i a m e t e r p e r h a p s because t h e eye is a r e l a t i v e l y s e l f - c o n t a i n e d o r g a n a n d so is n o t a f fec ted by t h e loss o f b o d y fluids o r b y t h e s h r i n k a g e o f o t h e r b o d y p a r t s . T h e eye c a n be s m a s h e d b y a b r a s i o n i n t h e n e t b u t such d a m a g e is a lways o b v i o u s . T h e i l a c k e r (1980) f o u n d t h a t t h e eye d i a m e t e r o f l a r v a l n o r t h e r n a n c h o v y was n o t a f fec ted by a s i m u l a t e d n e t t i n g t r e a t m e n t b u t t h e l ive eye d i a m e t e r d i d increase w i t h p r e s e r v a t i o n i n 5 % f o r m a l i n . T h e increases i n t h e b o d y d e p t h s a t t h e anus a n d t h e p e c t o r a l g i r d l e were p r o b a b l y caused by t h e s h r i n k a g e i n s t a n d a r d l e n g t h ; t h e b o d y swel led i n d e p t h as i t c o n t r a c t e d i n l e n g t h . A n inc rease i n a n a l b o d y d e p t h was o b s e r v e d b y T h e i l a c k e r (1980) f o r l a r v a l n o r t h e r n a n c h o v y ( F i g . D . l ) . T h e inc rease i n h e a d w i d t h w i t h n e t t i n g was c a u s e d b y t h e l o o s e n i n g o f t h e eyes i n t h e i r socke ts . T h e i n f l a t i o n o f F u l t o n ' s c o n d i t i o n f a c t o r was caused b y s h r i n k a g e i n s t a n d a r d l e n g t h t h a t was n o t b a l a n c e d b y loss o f d r y w e i g h t . T h e s e r e s u l t s are s t r i c t l y a p p l i c a b l e t o h e r r i n g la rvae 7 - 1 4 m m l o n g , b u t t h e t r e n d o f t h e d a t a w i t h age a n d size i n d i c a t e t h a t changes i n b o d y d i m e n s i o n s a n d c o n d i t i o n s h o u l d n o t be s ign i f i can t f o r p r a c t i c a l p u r p o s e s i n h e r r i n g larvae l o n g e r t h a n 14 m m . T h e r e f o r e , t h e r e l a t i v e l y low values o f b o d y d e p t h a n d F u l t o n ' s c o n d i t i o n t h a t B l a x t e r (1971) observed i n C l y d e Sea A t l a n t i c h e r r i n g larvae l o n g e r t h a n 13 m m were p r o b a b l y n o t a r t i f a c t s o f t h e c a p t u r e p rocess . Howeve r , i f one assumes t h a t 248 t h e c o n d i t i o n o f t h e larvae less t h a n 13 m m l o n g was e levated a n average o f 1 3 . 5 % by c a p t u r e t h e n some o f t hose w i l d la rvae m a y have h a d c o n d i t i o n values e q u a l t o or less t h a n t h o s e o f h e r r i n g larvae t h a t we re i r r e v e r s i b l y s t a r v e d i n t h e l a b o r a t o r y . T h i s c o n c l u s i o n also h o l d s fo r t h e s m a l l A t l a n t i c h e r r i n g la rvae c a p t u r e d b y V i l e l a a n d Z i j l s t r a (1971) i n t h e s o u t h e r n a n d c e n t r a l N o r t h Sea. However , d i f fe rences i n t h e d u r a t i o n o f t h e tows a n d i n t h e v o l u m e o f p l a n k t o n c a p t u r e d p e r tow b e t w e e n t h e e x p e r i m e n t a l t o w s r e p o r t e d here a n d those r e p o r t e d by p r e v i o u s a u t h o r s r e n d e r s a l l c o m p a r i s o n s o f t h i s t y p e q u i t e t e n t a t i v e . T h e m a i n c o n c l u s i o n o f t h i s s t u d y is t h a t t h e p rocess o f c a p t u r e i n a p l a n k t o n n e t changes t h e b o d y d i m e n s i o n s , i n c l u d i n g d r y w e i g h t , o f fish larvae. T h o s e w h o i n t e n d t o t o m e a s u r e t h e n u t r i t i o n a l s t a t u s o f field-caught fish larvae u s i n g b o d y d i m e n s i o n s s h o u l d i n c l u d e e x p e r i m e n t a l t o w s o f l a b o r a t o r y - r e a r e d la rvae as p a r t o f t h e process o f c a l i b r a t i n g t h e i r field-caught s a m p l e s . 249 Appendix E Hatching Experiments N a t u r a l l y s p a w n e d h e r r i n g eggs were h a t c h e d i n t h e l a b o r a t o r y i n o r d e r t o e s t i m a t e t h e d u r a t i o n o f t h e h a t c h i n g p e r i o d , t h e m e a n l a r v a l l e n g t h a t h a t c h , t h e m e a n la rva l d r y w e i g h t a t h a t c h , a n d t h e r e l a t i o n s h i p s b e t w e e n these va r iab les a n d t h e d u r a t i o n o f e x p o s u r e t o a i r . H e r r i n g eggs a t t a c h e d t o eelgrass, Zostera marinus, were s a m p l e d f r o m t h e edge o f t h e low t i d e zone a t t h e h e a d o f B a m f i e l d I n l e t o n 4 A p r i l 1982. A p p r o x i m a t e l y e q u a l a m o u n t s by w e i g h t o f s p a w n were p l a c e d i n t h r e e r e c t a n g u l a r glass a q u a r i a i n t h e l a b o r a t o r y o f t h e B a m f i e l d M a r i n e S t a t i o n a n d a c o n t i n u o u s s u p p l y o f 9 - 1 0 ° C seawate r was d i r e c t e d i n t o each a q u a r i a . T h e l i g h t r e g i m e was a 10 L : 1 4 D cyc le c u e d t o t h e n a t u r a l p h o t o p e r i o d w i t h l i g h t sensors . T h e t h r e e t r e a t m e n t s were: (1) u n d i s t u r b e d , la rvae were r e m o v e d b y d r a i n i n g t h e t a n k a n d a l l o w i n g i t t o r e f i l l w i t h i n one m i n u t e , (2) d r a i n e d a n d exposed t o a i r f o r 30 m i n once each day , a n d (3) d r a i n e d a n d exposed t o a i r f o r 30 m i n tw ice each day. T h i s v a r i a t i o n i n t o t a l e x p o s u r e t i m e was des igned t o s i m u l a t e t h e ef fect o f t i d a l e x p o s u r e o n h e r r i n g eggs d e p o s i t e d i n t h e i n t e r t i d a l zone. N e w l y - h a t c h e d larvae were r e m o v e d tw ice each day, a t 1000 h o u r s a n d 1700 h o u r s , b y s i p h o n i n g t h e w a t e r o u t o f each a q u a r i a t h r o u g h a h a n d - h e l d n e t . T h e fish were p rese rved i m m e d i a t e l y i n 2 % f o r m a l d e h y d e a n d seawa te r (30%©) a n d c o u n t e d a n d m e a s u r e d a t leas t 30 d l a t e r . D r y w e i g h t was m e a s u r e d b y r i n s i n g t h e larvae i n f r e s h w a t e r , d r y i n g t h e m a t 60° C f o r 24 h o u r s , a n d t h e n w e i g h i n g t h e m w i t h a n e l e c t r o b a l a n c e . T h e m e a n s t a n d a r d l e n g t h s a n d d r y w e i g h t s a t h a t c h f o r each o f t h e t h r e e e x p o s u r e t r e a t m e n t s were c a l c u l a t e d by w e i g h t i n g each s a m p l e ' s m e a n l e n g t h o r w e i g h t by t h e p r o p o r t i o n o f t h e t o t a l larvae t h a t h a t c h e d a t t h a t d a t e . A l l v i a b l e la rvae h a t c h e d w i t h i n 8 - 1 0 d i n a l l t h r e e ba tches o f n a t u r a l s p a w n i n c u b a t e d i n t h e l a b o r a t o r y ( F i g . E . l ) . T h e d i s t r i b u t i o n o f p e r c e n t h a t c h e d w i t h t i m e was n o r m a l w i t h m a x i m u m h a t c h i n g o c c u r r i n g o n t h e m i d d a t e o f t h e h a t c h i n g p e r i o d . S i m i l a r h a t c h i n g schedules have b e e n o b s e r v e d fo r n a t u r a l a n d a r t i f i c i a l l y s p a w n e d Pac i f i c h e r r i n g eggs (Jones 1972; H o u r s t o n e t a l . 1984) . T h e t w o b a t c h e s o f eggs t h a t h a d b e e n p e r i o d i c a l l y e x p o s e d t o a i r t e n d e d t o h a t c h e a r l i e r t h a n those t h a t h a d b e e n c o n s t a n t l y s u b m e r g e d ; t h e d a t e o f 5 0 % h a t c h i nc reased f r o m 4.2 d a n d 5.4 d t o 5.9 d . T h e s e r e s u l t s agree w i t h t h o s e o f Jones (1972) w h o f o u n d a decrease i n i n c u b a t i o n t i m e f r o m 19.2 d i n c o n s t a n t l y s u b m e r g e d eggs a t 8 ° C t o 18.2 d i n eggs e x p o s e d t o a i r f o r 2 h o u r s each day . 250 F i g u r e E . l . D i s t r i b u t i o n o f h a t c h i n g w i t h t i m e f o r t h r e e g r o u p s o f n a t u r a l l y spawned eggs i n c u b a t e d i n t h e l a b o r a t o r y . 2 5 1 50% hatch Q LU X O < X s o CC LU C L 20 10 0 20 10 no exposure 50% hatch 30 min exposure 0 20 50% hatch 60 min exposure 10 0 • i i — i — i - • i i — - J — " — 1 8 10 12 DAYS 2 5 2 T h e m e a n s t a n d a r d l e n g t h a t h a t c h rose f r o m 6.6 m m t o a b o u t 8.0 m m d u r i n g t h e first 5 d o f t h e h a t c h i n g p e r i o d i n a l l t h r e e g r o u p s ( F i g . E .2 ) . I t s t a y e d a t 8.0 m m o r d e c l i n e d s l i gh t l y d u r i n g t h e r e m a i n i n g 3 -7 d o f t h e h a t c h i n g p e r i o d . A s i m i l a r r ise i n l e n g t h w i t h d u r a t i o n o f t h e h a t c h i n g p e r i o d was observed b y H o u r s t o n e t a l . (1984) f o r larvae h a t c h e d f r o m b o t h n a t u r a l a n d a r t i f i c i a l s p a w n d e p o s i t e d a t d i f fe ren t dens i t i es o n a v a r i e t y o f s u b s t r a t e s . A t w o - w a y ana lys i s o f var iance ( t i m e , e x p o s u r e t i m e ) w i t h a n i n t e r a c t i o n t e r m ( t i m e x e x p o s u r e t i m e ) i n d i c a t e d t h a t s t a n d a r d l e n g t h a t h a t c h v a r i e d s i g n i f i c a n t l y ( P < 0 .001) w i t h t i m e b u t n o t w i t h e x p o s u r e t i m e a n d t h a t t h e r e was n o i n t e r a c t i o n b e t w e e n t i m e a n d e x p o s u r e t i m e . T h e m e a n s t a n d a r d l e n g t h a t h a t c h f o r each o f t h e t h r e e e x p o s u r e t r e a t m e n t s was 7.9, 7.7 a n d 7.7 m m f o r t h e s u b m e r g e d , once e x p o s e d , a n d twice exposed g r o u p s , r e s p e c t i v e l y . S ince m o s t n a t u r a l l y s p a w n e d Pac i f i c h e r r i n g eggs u n d e r g o some degree o f e x p o s u r e t h e l e n g t h a t h a t c h was chosen t o be 7.7 m m . T h e m e a n d r y w e i g h t a t h a t c h was c o n s t a n t a t a b o u t 160 fig f o r a l l t i m e s a n d e x p o s u r e t r e a t m e n t s ( F i g . E . 3 ) . A t w o - w a y ana lys i s o f v a r i a n c e ( t i m e , e x p o s u r e t i m e ) w i t h a n i n t e r a c t i o n t e r m ( t i m e x e x -p o s u r e t i m e ) i n d i c a t e d t h a t d r y w e i g h t d i d n o t v a r y s i g n i f i c a n t l y (P > 0 .05) w i t h t i m e o r e x p o s u r e t i m e a n d t h a t t h e r e was n o i n t e r a c t i o n o f t i m e a n d e x p o s u r e t i m e . T h e m e a n d r y w e i g h t f o r each o f t h e t h r e e e x p o s u r e t r e a t m e n t s was 160, 163, a n d 155 fig f o r t h e s u b m e r g e d , once e x p o s e d , a n d twice exposed g r o u p s , r e s p e c t i v e l y . T h e m e a n d r y w e i g h t f o r t h e p o o l e d d a t a ( w e i g h t e d by a b u n d a n c e ) was 160 fig. 253 F i g u r e E .2 . W h i s k e r a n d b o x p l o t o f t h e s t a n d a r d l e n g t h a t h a t c h fo r t h r e e g r o u p s o f n a t u r a l l y spawned eggs i n c u b a t e d i n t h e l a b o r a t o r y . T h e h o r i z o n t a l b a r s m a r k t h e m e a n l e n g t h , t h e boxes i n d i c a t e one s t a n d a r d d e v i a t i o n o f t h e m e a n l e n g t h , a n d t h e w h i s k e r s i n d i c a t e t h e r a n g e o f s t a n d a r d l e n g t h s . 254' -, i y -1 1 1 1 1 no exposure " "Utrf p i rill - - -• i i i i i 3 0 min exposure U V T V 1 1 1 1 1 1 1 I I I I i 6 0 min exposure v - nl i i i i .... i.. i . J 2 4 6 8 1 0 1 2 DAYS 255 F i g u r e E .3 . W h i s k e r a n d b o x p l o t o f t h e d r y w e i g h t a t h a t c h f o r t h r e e g r o u p s o f n a t u r a l l y spawned eggs i n c u b a t e d i n t h e l a b o r a t o r y . T h e h o r i z o n t a l b a r s m a r k t h e m e a n d r y w e i g h t s , t h e boxes i n d i c a t e one s t a n d a r d d e v i a t i o n o f t h e m e a n w e i g h t s , a n d t h e w h i s k e r s i n d i c a t e t h e r a n g e o f d r y w e i g h t s . 256 2 0 0 1 no e x p o s u r e T - TT T l 1 0 0 T T T O ZD h-X o LU > DC Q • i i i — J — i — — i — i — i — ' — — 1 2 0 0 1 T T I 1 T T 3 0 min e x p o s u r e T T 1 0 0 2 0 0 i i • i • i » i i — i — i — i — ' i 6 0 min e x p o s u r e - r-"1 P 1*1 _ T " y ^  JL r 1 0 0 t I I I I 1 1 1 1 1 1 L. 2 4 6 8 1 0 12 D A Y S 257 Appendix F Net Evasion L a r v a e w e r e f u l l y r e c r u i t e d t o t h e p l a n k t o n - n e t a t h a t c h i n b o t h t h e n i g h t a n d day catches ( F i g . F . l , u p p e r p a n e l ) . L a r v a e l onge r t h a n 18 m m were c a u g h t i n g r e a t e r a b u n d a n c e by t h e n i g h t tows t h a n b y t h e d a y t o w s , i n d i c a t i n g t h a t n e t evasion was a s i g n i f i c a n t f a c t o r i n d a y - c a u g h t larvae o f t h i s size. N e t evas ion b e c a m e a s i g n i f i c a n t f a c t o r i n n i g h t - p l a n k t o n - n e t c a u g h t la rvae l o n g e r t h a n 25 m m . L a r v a e w e r e f u l l y r e c r u i t e d t o t h e n i g h t - l i g h t a t a l e n g t h o f a b o u t 2 1 m m . T h e g e n e r a l absence o f n i g h t - l i g h t e d la rvae g r e a t e r t h a n 35 m m l o n g i n d i c a t e s t h a t t h i s is t h e u p p e r l i m i t o f c a t c h a b i l i t y f o r t h i s gear . T h e ca tches s u m m a r i z e d i n t h e u p p e r p a n e l o f F i g . F . l were t a k e n a t d i f fe ren t s t a t i o n s a n d t h e t o t a l fishing e f f o r t was n o t d i v i d e d e q u a l l y b e t w e e n t h e t h r e e t y p es o f gear . To r e m o v e these f a c t o r s t h e t o t a l c u m u l a t i v e d e n s i t y f o r each l e n g t h class was c a l c u l a t e d f o r p a i r s o f p l a n k t o n - n e t catches t a k e n d u r i n g t h e d a y a n d d u r i n g t h e n i g h t w i t h i n 10 h o u r s o f each o t h e r a t t h e same s t a t i o n . T h e m i d d l e p a n e l o f F i g u r e F . l s u p p o r t s t h e g e n e r a l c o n c l u s i o n s d e r i v e d above ; t h a t t h e r e is l i t t l e d i f fe rence i n t h e l e n g t h a t r e c r u i t m e n t b e t w e e n n i g h t a n d d a y p l a n k t o n - n e t catches b u t t h a t n e t evasion b e c o m e s a s i g n i f i c a n t f a c t o r i n day t o w s f o r la rvae 1 5 - 2 0 m m l o n g . A c o m p a r i s o n o f n i g h t - p l a n k t o n - n e t ca tches t a k e n a t s t a t i o n B w i t h a n i g h t - l i g h t c a t c h t a k e n t h e same e v e n i n g w i t h i n 4 h o u r s ( F i g . F . l , l o w e r p a n e l ) i n d i c a t e s t h a t t h e r e is a c o r r e l a t i o n b e t w e e n t h e d e n s i t y o f t h e p l a n k t o n - n e t catches a n d t h e n u m b e r o f n i g h t - l i g h t e d la rvae , t h a t l a rvae are n o t f u l l y r e c r u i t e d t o t h e n i g h t - l i g h t u n t i l t h e y reach a l e n g t h o f a b o u t 2 0 - 2 1 m m , a n d t h a t n i g h t - p l a n k t o n - n e t catches b e c o m e s e r i o u s l y b i a s e d by n e t evas ion i n l a rvae 24—25 m m l o n g . A l m o s t a l l o f t h e 1981 p l a n k t o n n e t s a m p l e s were t a k e n a t n i g h t . T h e 1 9 8 1 s a m p l i n g p e r i o d f o r t u i t o u s l y b r a c k e t e d t h e p e r i o d f r o m h a t c h i n g t o a b o u t age 56 ( 7 . 7 - 2 9 . 0 m m ) f o r c o h o r t t w o a n d f r o m h a t c h i n g t o a b o u t age 30 ( 7 . 7 - 2 6 . 0 m m ) f o r c o h o r t t h r e e . T h e r e f o r e , i t was a s s u m e d t h a t t h e m e a s u r e d d e n s i t i e s o f these t w o c o h o r t s were n o t s e r i o u s l y b iased by n e t evas ion . M o s t o f t h e day-p l a n k t o n - n e t ca tches t a k e n i n t h i s s t u d y were t a k e n i n t h e first h a l f o f t h e 1982 s a m p l i n g p r o g r a m w h e n t h e la rvae o f c o h o r t s ix were g e n e r a l l y less t h a n 20 m m l o n g . T h e r e f o r e , i t is a s s u m e d t h a t t h e m e a s u r e d d e n s i t i e s o f c o h o r t s ix we re n o t se r ious l y b i a s e d by n e t evas ion. T h e m e a s u r e d dens i t i es 258 F i g u r e . F . l . U p p e r p a n e l : T o t a l s u m m e d dens i t i es o f n i g h t a n d day p l a n k t o n - n e t catches a n d t h e t o t a l n u m b e r o f n i g h t - l i g h t e d ca tches , p l o t t e d a g a i n s t l e n g t h i n 2 m m b i n s . M i d d l e p a n e l : S u m m e d dens i t i es o f n i g h t a n d day p l a n k t o n - n e t catches fo r p a i r s o f s a m p l e s t a k e n at t h e same s t a t i o n w i t h i n 10 h o u r s o f each o t h e r , p l o t t e d a g a i n s t l e n g t h i n L o w e r p a n e l : S u m m e d dens i t i es o f n i g h t p l a n k t o n - n e t ca tches t a k e n a t s t a t i o n B w i t h i n 4 h o u r s o f a n i g h t - l i g h t c a t c h , a n d t h e n i g h t - l i g h t c a t c h , p l o t t e d a g a i n s t l e n g t h i n 2 m m b i n s . 259 TOTAL C A T C H E S 1981 DAY •- NIGHT - NIGHT-LIGHT PLANKTON NET 1 0 2 h day night plankton net c a t c h e s taken at the same stat ions within 10 hours of each other in night plankton net night-light c a t c h e s taken at stat ion B on the same night 15 20 25 30 STANDARD LENGTH (MM) 35 40 260 o f c o h o r t five, h o w e v e r , were p r o b a b l y b iased b y n e t evas ion because m o s t o f t h e c o h o r t five larvae c a p t u r e d were l o n g e r t h a n 13 m m . T h e p l a n k t o n n e t s a m p l e s were n o t c o r r e c t e d fo r n e t evasion because t h e t w o m o s t a b u n d a n t a n d i m p o r t a n t c o h o r t s , n u m b e r s t w o a n d s ix, were r e l a t i v e l y u n a f f e c t e d , as were t h e s a m p l e s o f c o h o r t t h r e e , a n d because t h e d a t a p resen ted i n F i g . F l were t o o c o n f o u n d e d by o t h e r v a r i a b l e s , such as t i m e a n d t i d e level , t o b e used as a re l i ab le basis fo r a w e i g h t i n g scheme. 2 6 1 

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