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Growth and feeding of juvenile chinook salmon, Oncorhynchus Tshawytscha, in "in situ" enclosures English, Karl K. 1981

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GROWTH AND FEEDING OF JUVENILE CHINOOK SALMON, ONCORHYNCHUS TSHAWYTSCHA, IN "IN SITU" ENCLOSURES. By KARL KRISTOFER ENGLISH B . S c , C o r n e l l U n i v e r s i t y , 1978 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Z o o l o g y ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA November 1981 © K a r l K r i s t o f e r E n g l i s h , 1 981 In 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 of the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree t h a t the 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 reference and study. I f u r t h e r agree t h a t permission f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head of my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood th a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of <dl&0 A*g y  The U n i v e r s i t y of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date DE-6 (2/79) ABSTRACT A f e e d i n g e x p e r i m e n t was d e s i g n e d t o examine how f i s h g r o w t h r a t e s a r e a f f e c t e d by t h e s i z e abundance o f p e l a g i c z o o p l a n k t o n . J u v e n i l e c h i n o o k salmon, O n c o r h y n c h u s t s h a w y t s c h a , were r a i s e d i n 90 m 3 mesh e n c l o s u r e s i n S a a n i c h I n l e t , B.C. The e n c l o s u r e s p e r m i t t e d ample water and z o o p l a n k t o n c i r c u l a t i o n w h i l e r e t a i n i n g 5-6 gram j u v e n i l e s almon. The e n c l o s e d f i s h grew a t an a v e r a g e r a t e of 1.8% wet body w e i g h t / d a y f o r a s i x week e x p e r i m e n t a l p e r i o d . Weekly growth r a t e s r a n g e d from 3.9%/day w h i l e f o o d was ab u n d a n t , t o -0.5%/day when f o o d was s c a r c e . S e v e r a l a n a l y t i c a l methods were u s e d t o e s t a b l i s h a r e l a t i o n s h i p between f i s h gr.owth and t h e s i z e and abundance o f z o o p l a n k t o n i n t h e e n c l o s u r e s . T h e r e i s a s t r o n g r e l a t i o n s h i p between t h e f i s h g rowth r a t e s and t h e abundance of 1.4-4.5mm p r e y . R a t e s of s u c c e s s f u l s e a r c h v a r y d i r e c t l y w i t h t h e s i z e and i n h e r e n t c o n t r a s t of a p r e y i t e m . A minimum r a t e of s u c c e s s f u l s e a r c h o f 2.0m 3/hour was e s t i m a t e d from a f u n c t i o n a l r e s p o n s e c u r v e f o r salmon f e e d i n g on 1.4-4.5mm z o o p l a n k t o n . T h i s v a l u e i s d i s c u s s e d i n r e l a t i o n t o a s a l m o n i d s p h y s i c a l c a p a b i l i t i e s and r e s u l t s f r o m p r e v i o u s f i e l d s t u d i e s and t a n k e x p e r i m e n t s . D a i l y g r o w t h i n c r e m e n t s on t h e o t o l i t h s of t h e e n c l o s e d f i s h were examined w i t h r e s p e c t t o d a i l y v a r i a t i o n s i n wa t e r t e m p e r a t u r e and z o o p l a n k t o n . a b u n d a n c e . E x t r e m e s i n f o o d abundance a p p e a r t o have a s i g n i f i c a n t and c o n s i s t e n t e f f e c t on t h e s p a c i n g of t h e growth r i n g s . However, water t e m p e r a t u r e s w ould have t o be kept c o n s t a n t i n o r d e r t o e s t a b l i s h any c l o s e r i i r e l a t i o n s h i p between f o o d abundance and o t o l i t h g r o w t h r i n g s . i i i i TABLE OF CONTENTS INTRODUCTION . 1 DESCRIPTION OF PROJECT S I T E 4 PART ONE . .•— ". .' 6 The M e t h o d o l o g y 6 The A p p a r a t u s 6 F l o t a t i o n P l a t f o r m 7 Net E n c l o s u r e s 7 P r o t e c t i v e Net 9 L a b o r a t o r y H o l d i n g Tank 10 The P r o c e d u r e 11 S a m p l i n g The Z o o p l a n k t o n 1-1 S a m p l i n g The F i s h 13 G e n e r a l R e s u l t s 13 Q u a n t i t a t i v e D a t a 14 Z o o p l a n k o n Samples 14 F i s h Samples 22 Q u a l i t a t i v e D a t a 30 Summary Of R e s u l t s 32 D i s c u s s i o n 32 PART TWO 35 Growth And F e e d i n g Of A P l a n k t i v o r o u s F i s h •.. 35 Methods 36 Salmon E n e r g e t i c s Model 37 i v M u l t i s p e c i e s D i s c E q u a t i o n 42 R e s u l t s And I n t e r p r e t a t i o n 45 F i s h Growth Vs Z o o p l a n k t o n Abundance 46 F u n c t i o n a l - R e s p o n s e F o r P l a n k t i v o r o u s F i s h .... 49 R e l a t i v e R a t e s Of S u c c e s s f u l S e a r c h 51 R a t e s Of S e a r c h 53 P r e y D i s t r i b u t i o n 57 D i s c u s s i o n 58 PART THREE 63 Growth P a t t e r n s On The O t o l i t h s Of The E n c l o s e d F i s h 63 Methods 63 M e a s u r i n g D a i l y I n c r e m e n t s 64 R e s u l t s 66 D a i l y Growth R i n g s 66 Growth P a t t e r n s On The S a g i t t a e 66 D i s c u s s i o n 70 SUMMARY AND CONCLUSIONS ' 7 5 LITERATURE CITED 7 7 APPENDICIES 83 I . H a n d l i n g The F i s h 83 T r a n s p o r t 83 V a c c i n a t i o n 84 W e i g h i n g And M e a s u r i n g The F i s h 84 B r a n d i n g The F i s h 85 I I . H a n d l i n g The N e t s 86 V Deployment Of N e t s . . . 86 C l e a n i n g The E n c l o s u r e s 87 I I I . C a l c u l a t i o n Of F i s h Growth R a t e s 88 v i L I S T OF TABLES Page T a b l e 1. P r o b a b i l i t y v a l u e s from u n i v a r i a t e and m u l t i v a r i a t e a n a l y s e s o f v a r i a n c e f o r "AM" and "PM" z o o p l a n k t o n s a m p l e s . Symbols: 1 = 9 mm e n c l o s u r e w i t h f i s h . 2 = 19 mm e n c l o s u r e w i t h f i s h . 3 = 19 mm e n c l o s u r e w i t h o u t f i s h . 4 = o u t s i d e t h e e n c l o s u r e s 18 T a b l e 2. The dominant s p e c i e s i n t h e t o p 10 m e t e r s of w a t e r a t t h e e x p e r i m e n t a l s i t e f r o m May 12 t h r o u g h June 29. C i r c l e s i z e i n d i c a t e s l e v e l o f dominance w i t h i n e a c h week 21 T a b l e 3. P r o b a b i l i t y v a l u e s f r o m two way a n a l y s i s o f v a r i a n c e of s t o m a c h c o n t e n t d a t a 27 T a b l e 4. The j u v e n i l e s a l m o n s ' r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h f o r t h e v a r i o u s p r e y f o u n d i n t h e e n c l o s u r e s 52 T a b l e T a b l e T a b l e 5. The c o r r e l a t i o n m a t r i x f o r t h e 9 p r e y g r o u p s f o r w h i c h r a t e s o f s u c c e s s f u l s e a r c h were c a l c u l a t e d . V a l u e s above .85 i n d i c a t e s i g n i f i c a n t c o r r e l a t i o n (p<.05) , 52 S e a r c h r a t e s f o r t h e r a n g e of p r e y s i z e s f o u n d i n t h e e n c l o s u r e s . The maximum s e a r c h r a t e s were d e r i v e d f r o m l a b o r a t o r y m easurements. The p r o b a b l e r a n g e assumes t h a t t h e r e a c t i v e d i s t a n c e f o r f i s h f e e d i n g i n t h e e u p h o t i c zone i n 0.3-0.5 o f t h e l a b o r a t o r y v a l u e , The c o r r e l a t i o n m a t r i x f o r t h e d a i l y g r o w t h i n c r e m e n t s o f s i x f i s h ( A2,A4,A5,Al0,B8,D); t e m p e r a t u r e d a t a (Temp); z o o p l a n k t o n d a t a ( Z o o ) ; and a c o m b i n a t i o n o f t e m p e r a t u r e and z o o p l a n k t o n d a t a (T & Z ) . V a l u e s above .44 a r e s i g n i f i c a n t (p<.05) an d v a l u e s a b o v e .56 a r e h i g h l y s i g n i f i c a n t ( p < . 0 l ) , 57 69 v i i L I S T OF FIGURES Page F i g u r e 1. L o c a t i o n o f o f f s h o r e p l a t f o r m i n S a a n i c h I n l e t , B.C 5 F i g u r e 2. The f i n e mesh e n c l o s u r e 8 F i g u r e 3. F l o t a t i o n p l a t f o r m w i t h t h e p r o t e c t i v e n e t s u r r o u n d i n g t h e f i n e mesh e n c l o s u r e s 10 F i g u r e 4. The s p a t i a l and t e m p o r a l v a r i a t i o n s o f "AM" z o o p l a n k t o n . The s o l i d l i n e r e p r e s e n t s t h e d a t a from o u t s i d e s a m p l e s . S y m b o l s : • 9 mm e n c l o s u r e w i t h f i s h . • 19 mm e n c l o s u r e w i t h f i s h . * 19 mm e n c l o s u r e w i t h o u t f i s h 15 F i g u r e 5. The s p a t i a l and t e m p o r a l v a r i a t i o n s o f z o o p l a n k t o n . The s o l i d l i n e r e p r e s e n t s d a t a f r o m o u t s i d e s a m p l e s . S y m b o l s : • 9 mm e n c l o s u r e w i t h f i s h . • 19 mm e n c l o s u r e w i t h f i s h . * 19 mm e n c l o s u r e w i t h o u t f i s h . 'PM" t h e 16 F i g u r e 6. N o n - p a r a p e t r i c c o r r e l a t i o n c o e f f i c i e n t s . Z o o p l a n k t o n f r o m e a c h e n c l o s u r e were c o r r e l a t e d a g a i n s t samples from o u t s i d e t h e e n c l o s u r e s t h e d a s h e d ( p < . 0 l ) . S y m b o l s : 1 = 2 = 3 = 4 = C o r r e l a t i o n l i n e a r e c o e f f i c i e n t s above h i g h l y s i g n i f i c a n t 9 mm e n c l o s u r e w i t h f i s h . 19 mm e n c l o s u r e w i t h f i s h . 19 mm e n c l o s u r e w i t h o u t f i s h , o u t s i d e t h e e n c l o s u r e s 19 F i g u r e 7. The a v e r a g e d a i l y g r o w t h r a t e f o r i n d i v i d u a l f i s h i n t h e two o f f s h o r e e n c l o s u r e . The i s t h e b e s t e s t i m a t e o f t h e mean d a i l y g r o w t h r a t e f o r a l l f i s h d u r i n g t h a t week 23 F i g u r e 8. C u m u l a t i v e g r o w t h of t h e j u v e n i l e c h i n o o k salmon 24 v i i i F i g u r e 9. The r e l a t i v e i m p o r t a n c e ( I R I ) of t h e v a r i o u s t y p e s o f p r e y f o u n d i n t h e stomachs o f t h e f i s h f r o m t h e 9 mm e n c l o s u r e ( t o p ) and t h e 19 mm e n c l o s u r e ( b o t t o m ) . S ymbols: S = s m a l l p r e y (0.7-1.4 mm) M = medium p r e y (1.4-3.0 mm) L = l a r g e p r e y (3.0-10.0 mm) XL = e x t r a l a r g e p r e y (>10 mm) • = p e l a g i c p r e y . = n o n p e l a g i c p r e y 29 F i g u r e 10. The r e l a t i v e p r o p o r t i o n o f e a c h p r e y g r o u p i n t h e stomach c o n t e n t s o f t h e j u v e n i l e c h i n o o k s a l m o n . • C a l a n u s s p e c i e s C a l l i o p i u s D ecapod l a r v a e E u p h a u s i d s P a r a t h e m i s t o 31 F i g u r e 11. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a s m a l l (0.7-1.4 mm) z o o p l a n k t o n 47 F i g u r e 12. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a medium (1.4-3.0 mm) z o o p l a n k t o n 47 F i g u r e 13. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a l a r g e (>3.0 mm) z o o p l a n k t o n 48 F i g u r e 14. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance of a medium and l a r g e ( 1 . 4 -4.5 mm) z o o p l a n k t o n 48 F i g u r e 15. The f u n c t i o n a l r e s p o n s e o f j u v e n i l e c h i n o o k salmon t o t h e d e n s i t y of 1.4-4.5 mm z o o p l a n k t o n 50 F i g u r e 16. The mean r e a c t i v e d i s t a n c e s ( d a t a ± 95%) o f r a i n b o w t r o u t t o low c o n t r a s t t a r g e t s of v a r i o u s s i z e s (Ware 1973) 55 i x F i g u r e 17. The p a t t e r n of d a i l y growth i n c r e m e n t s d e r i v e d f r o m t h e s a g i t t a e of s i x f i s h r a i s e d i n t h e e x p e r i m e n t a l e n c l o s u r e s 66 F i g u r e 18. C o m p a r i s o n of t h e mean growth i n c r e m e n t s w i t h water t e m p e r a t u r e and z o o p l a n k t o n abundance d a t a 68 F i g u r e 19. Sample p h o t o g r a p h s o f t h e s a g i t t a e f r o m two h a t c h e r y and tank r e a r e d f i s h 72 X ACKNOWLEDGEMENTS Dr. C.A.S. H a l l and a s t u d y by Dr. G.C. L a u r e n c e o r i g i n a l l y s t i m u l a t e d my i n t e r e s t i n t h i s t y p e of f e e d i n g e x p e r i m e n t . I am g r a t e f u l t o D r . T.R. P a r s o n s f o r h i s a s s i s t a n c e and encouragement d u r i n g t h e i n i t i a l p l a n n i n g p h a s e . I am i n d e b t e d t o my w i f e , C i n d y , f o r h e r major c o n t r i b u t i o n s d u r i n g e a c h p h a s e of t h i s p r o j e c t . I would l i k e t o thank Dr. R. H i l b o r n f o r h i s p a t i e n c e and f i n a n c i a l s u p p o r t , and D r . C . J . W a l t e r s f o r h i s v a l u a b l e comments and s u g g e s t i o n s . Many o t h e r i n d i v i d u a l s made i m p o r t a n t c o n t r i b u t i o n s , b u t I woul d e s p e c i a l l y l i k e t o thank Dr. E.B. B r o t h e r s , B. Egan, P. Cahoon, and D. Marmerek. 1 INTRODUCTION Over t h e p a s t 20 y e a r s t h e i n f o r m a t i o n base on m a r i n e p r i m a r y and s e c o n d a r y p r o d u c t i o n and salmon p h y s i o l o g y has grown c o n s i s t e n t l y , y e t c o m p a r a t i v e l y l i t t l e new d a t a has been c o l l e c t e d on t h e c r i t i c a l r e l a t i o n s h i p between young salmon and t h e i r p e l a g i c p r e y . T h i s gap i s l a r g e l y due t o t h e t e c h n i c a l d i f f i c u l t i e s i n v o l v e d w i t h s t u d y i n g p l a n k t i v o r o u s f i s h f e e d i n g on n a t u r a l c o n c e n t r a t i o n s o f z o o p l a n k t o n . Salmon f e e d i n g e x p e r i m e n t s a r e w e l l r e p r e s e n t e d i n t h e l i t e r a t u r e ; however, o n l y a s m a l l p o r t i o n of t h e s e s t u d i e s have examined salmon f e e d i n g on n a t u r a l f o o d s . B r e t t has i n v e s t i g a t e d how g r o w t h r a t e and body c o m p o s i t i o n of j u v e n i l e salmon a r e a f f e c t e d by t e m p e r a t u r e , f i s h s i z e , m e t a b o l i s m , and r a t i o n l e v e l s of v a r i o u s a r t i f i c i a l f o o d s ( B r e t t e t a l . 1969; B r e t t and H i g g s 1970; B r e t t and S h e l b o r n 1975; B r e t t 1976a, 1976b). L e b r a s s e u r e t a l . (1968) were t h e f i r s t t o examine j u v e n i l e salmon f e e d i n g on d i f f e r e n t s i z e s c l a s s e s of p r e y z o o p l a n k t o n , u s i n g 2 hour e x p e r i m e n t s . L e b r a s s e u r (1969) u s e d l o n g e r o b s e r v a t i o n times'' of 8 weeks t o d e t e r m i n e what g r o w t h r a t e s c o u l d be o b t a i n e d when chum salmon were f e d v a r i o u s c o n c e n t r a t i o n s of t h r e e d i s t i n c t n a t u r a l p r e y . In t h e s e e x p e r i m e n t s , p r e y were o f f e r e d t o t h e p r e d a t o r i n 0.25 m3 t a n k s w h i c h m i n i m i z e d , t h e e n e r g y e x pended i n t h e s e a r c h i n g and c a p t u r i n g of a p r e y i t e m . L e b r a s s e u r . c o n c l u d e d t h a t f u r t h e r f e e d i n g t r i a l s were n e c e s s a r y b e c a u s e t h e r e l a t i o n s h i p between f o o d and g r o w t h i s s t r o n g l y d e p e n d e n t on how much e n e r g y i s 2 e x p e nded i n s e a r c h i n g f o r and c a p t u r i n g d i f f e r e n t p r e y . Warren and D a v i s ( 1 9 6 6 ) ; Mann ( 1 9 6 6 ) ; P a l o h e i m o and D i c k i e ( 1 9 6 6 ) ; and K e r r and M a r t i n (1968) a l l s u p p o r t t h i s c o n c l u s i o n . To e s c a p e t h e r e s t r i c t i o n s of tank e x p e r i m e n t s , t h i s s t u d y d e v e l o p e d a new m e t h o d o l o g y i n v o l v i n g " i n s i t u " f e e d i n g e x p e r i m e n t s . The m e t h o d o l o g y i n v o l v e d p l a c i n g j u v e n i l e c h i o o k s a l m o n , O n c o r h y n c h u s t s h a w y t s c h a , i n a semi-open-, e n c l o s u r e i n t h e w a ter column, where t h e i r g r o w t h , s u r v i v a l , and b e h a v i o u r was m o n i t o r e d i n r e l a t i o n t o n a t u r a l z o o p l a n k t o n c o n c e n t r a t i o n s t h a t c h a n g e d as n a t u r a l w a ter masses moved t h r o u g h t h e e n c l o s u r e s . The b a s i c h y p o t h e s i s was t h a t g r o w t h r a t e s a r e d e p e n d e n t on p r e y d e n s i t i e s o v e r t h e r a n g e of p r e y d e n s i t i e s e n c o u n t e r e d n a t u r a l l y . The t h e s i s i s o r g a n i z e d i n t h r e e p a r t s . P a r t one p r o v i d e s a d e t a i l e d d e s c r i p t i o n and e v a l u a t i o n of t h e " i n s i t u " e n c l o s u r e m e t h o d o l o g y . S p e c i a l e mphasis i s p l a c e d on e v a l u a t i n g t h e p e r f o r m a n c e of t h i s a p p a r a t u s . A b r i e f d i s c u s s i o n p r o p o s e s some p r a c t i c a l a p p l i c a t i o n s f o r t h e s e e n c l o s u r e s . P a r t two i n t e g r a t e s q u a n t i t a t i v e and q u a l i t a t i v e d a t a from t h e e n c l o s u r e s w i t h t h e r e s u l t s o f l a b o r a t o r y work by J.R. B r e t t and o t h e r s , i n an a t t e m p t t o r e s o l v e s e v e r a l m a j o r u n c e r t a i n t i e s a b o u t j u v e n i l e f i s h f e e d i n g . T h e s e u n c e r t a i n t i e s a r e : (1) How i s f i s h g r o w t h r e l a t e d t o f o o d a bundance? (2) How a r e g r o w t h r a t e s a f f e c t e d by t h e s i z e of t h e a v a i l a b l e f o o d o r g a n i s m s ? (3) How e f f i c i e n t a r e j u v e n i l e f i s h a t f i n d i n g f o o d ? The s e c t i o n c o n c l u d e s w i t h a d i s c u s s i o n of how t h e f i n d i n g s • o f t h i s s t u d y c o n f i r m or r e f u t e h y p o t h e s e s g e n e r a t e d from 3 p r e v i o u s s t u d i e s . P a r t t h r e e e x a mines r e l a t i v e d a i l y g r o w t h r a t e s , f o r some of t h e e x p e r i m e n t a l f i s h , e s t i m a t e d from t h e d a i l y r i n g s on t h e i r o t o l i t h s . The o b j e c t was t o e s t a b l i s h r e l a t i o n s h i p s between d a i l y g r o w t h and t h e d a i l y f l u c t u a t i o n i n water t e m p e r a t u r e and z o o p l a n k t o n abundance o b s e r v e d i n t h e e x p e r i m e n t a l e n c l o s u r e s . ' 4 DESCRIPTION OF PROJECT S I T E The e x p e r i m e n t a l s i t e was t h a t o f t h e CEPEX e x p e r i m e n t s i n S a a n i c h I n l e t , B r i t i s h C o l u m b i a ( F i g . 1 ) . T h i s s i t e was s e l e c t e d f o r t h e f o l l o w i n g r e a s o n s : (1) t h e i n l e t i s a n a t u r a l f e e d i n g a r e a f o r j u v e n i l e salmon; (2) t h e a r e a i s s h e l t e r e d from major s t o r m s and has low c u r r e n t v e l o c i t i e s ; (3) t h e d e p t h o f t h e water e x c e e d s t h a t o f t h e e u p h o t i c zone; (4) p r o d u c t i o n and s t a n d i n g c r o p l e v e l s a r e r e l a t i v e l y h i g h ; (5) t h e f o o d webs a r e r e l a t i v e l y s i m p l e ( i . e . , r e l a t i v e l y few s p e c i e s ) ; (6) t h e s i t e i s remote from s o u r c e s of p o l l u t i o n ; (7) t h e i n l e t i s deep enough a t t h e s i t e t o accomodate t h e v e r t i c a l m i g r a t i o n of t h e l a r g e r z o o p l a n k t o n ; (8) t h e p h y t o - z o o p l a n k t o n a s s e m b l a g e s a r e w e l l known and most s p e c i e s o c c u r r i n g t h e r e a l s o o c c u r i n t h e open o c e a n ; and (9) some of t h e CEPEX e q u i p m e n t (b u o y s , p l a t f o r m s , e t c . ) g r e a t l y r e d u c e d t h e c o s t o f s e t t i n g up t h e e n c l o s u r e s . These c h a r a c t e r i s t i c s make S a a n i c h I n l e t an e x c e l l e n t s i t e t o t e s t " i n s i t u " e n c l o s u r e s . 5 F i g u r e 1. L o c a t i o n o f o f f s h o r e p l a t f o r m i n S a a n i c h I n l e t , B.C. (Adapted from Barraclough e t a l . 1968) 6 PART ONE • The M e t h o d o l o g y The c o n c e p t of l a r g e c o n t a i n e r s p l a c e d i n t h e water column t o s t u d y p e l a g i c m a r i n e s y s t e m s has r e c e n t l y r e c e i v e d s i g n i f i c a n t a t t e n t i o n ( T a k a h a s h i e t a l . 1975; D a v i e s e t a l . 1975; Gamble e t a l . 1977; G r i c e e t a l . 1977; L a u r e n c e e t a l . 1978). Most of t h e s e s t u d i e s i n v o l v e d e n c l o s i n g a column o f water i n a p l a s t i c bag and m o n i t o r i n g t h e p r o d u c t i v i t y and f o o d c h a i n d y n a m i c s o f t h e c l o s e d s y s t e m . S t u d i e s of f i s h e s i n t h e s e c l o s e d w ater columns have been a l m o s t n o n e x i s t e n t w i t h t h e e x c e p t i o n of K o e l l e r and P a r s o n s ( 1 9 7 7 ) , who d e t e r m i n e d g r o w th r a t e s f o r j u v e n i l e chum salmon f e e d i n g on a s t e a d i l y , d e c l i n i n g number of p r e y z o o p l a n k t o n . L a u r e n c e e t a l . (1978) i n t r o d u c e d a new c o n c e p t where semi-open chambers, made of f i n e n i t e x mesh, were u s e d t o a s s e s s " i n s i t u " g r o w t h r a t e s o f l a r v a l f i s h f e e d i n g on m i c r o - z o o p l a n k t o n . The chambers d e s i g n e d by L a u r e n c e were s m a l l e r and u s e d much f i n e r mesh net t h a n t h e e n c l o s u r e s d e v e l o p e d i n t h i s s t u d y . THE APPARATUS The e x p e r i m e n t a l a p p a r a t u s c o n s i s t e d o f f o u r major components: (1) t h e f l o t a t i o n p l a t f o r m ; (2) t h e f i n e mesh n e t 7 e n c l o s u r e s ; (3) a l a r g e c o a r s e mesh p r o t e c t i o n n e t ; and (4) a l a b o r a t o r y h o l d i n g t a n k . F l o t a t i o n P l a t f o r m The f l o t a t i o n p l a t f o r m (10 m e t e r s i n d i a m e t e r and 1 meter h i g h ) was one of t h r e e c o n s t r u c t e d f o r C o n t r o l l e d E c o s y s t e m P o l l u t i o n E x p e r i m e n t a l (CEPEX) p r o j e c t s . M e n z e l and Chase (1977) d e s c r i b e t h e l a r g e f l o t a t i o n module o r i g i n a l l y u s e d i n CEPEX. The s t r u c t u r e was permamently moored i n 60 m e t e r s o f water i n S a a n i c h I n l e t . Net E n c l o s u r e s The e n c l o s u r e s were d e s i g n e d t o r e t a i n 5-6 g f i s h w h i l e p e r m i t t i n g f r e e movement, i n and o u t , o f s p e c i f i c s i z e r a n g e s of z o o p l a n k t o n . T h r e e mesh s i z e s (1mm, 9mm, and 19mm) were s e l e c t e d t o l i m i t t h e f o o d s i z e a v a i l a b l e t o t h e f i s h i n e a c h e n c l o s u r e . The 1 mm mesh e n c l o s u r e was c o n s t r u c t e d w i t h b l a c k p e r m a s c r e e n i n g ( f l e x i b l e window s c r e e n i n g ) . The 9 mm mesh e n c l o s u r e and t h e two 19 mm mesh e n c l o s u r e s were c o n s t r u c t e d w i t h g r e e n k n o t l e s s n y l o n mesh. F o r t h e p u r p o s e s of t h i s e x p e r i m e n t t h e f o u r e n c l o s u r e s were p l a c e d i n s i d e one of t h e CEPEX f l o t a t i o n p l a t f o r m s . E a c h e n c l o s u r e was r o u g h l y 3.1 m e t e r s i n d i a m e t e r and 12 m e t e r s i n d e p t h ( F i g . 2 ) . The b o t t o m of e a c h e n c l o s u r e was c i r c u l a r and r o u g h l y f l a t ( n o t p u r s e d ) . The s i d e s o f t h e e n c l o s u r e s e x t e n d e d 0.5 m e t e r s -above t h e s u r f a c e of t h e water t o r e t a i n jumping 8 12 meters 3.1 meters F i g u r e 2. The f i n e mesh e n c l o s u r e . 9 f i s h ; t h e r e b y p r e c l u d i n g t h e n e c e s s i t y o f a t o p . A v i a n p r e d a t i o n was not a f a c t o r . T h r e e r i n g s , c o n s t r u c t e d of 38 mm p o l y p i p e , h e l d t h e n e t s open i n a r o u g h l y c y l i n d r i c a l s h a p e . One p o l y p i p e r i n g was f i l l e d w i t h s a n d and g r a v e l and a t t a c h e d t o t h e b o t t o m of t h e n e t . The two r e m a i n i n g r i n g s s u p p o r t e d t h e n e t a t 4 m and a t 8 m below t h e s u r f a c e . The d e p l o y m e n t o f t h e s e e n c l o s u r e s and t h e methods u s e d t o remove p h y t o p l a n k t o n f o u l i n g " a r e d e s c r i b e d i n A p p e n d i x I . P r o t e c t i v e Net A p r o t e c t i v e n e t was d e s i g n e d t o p r e v e n t dog f i s h and o t h e r a q u a t i c p r e d a t o r s from damaging t h e f i n e mesh e n c l o s u r e and d e v o u r i n g t h e j u v e n i l e s almon. The p r o t e c t i v e n e t , c o n s t r u c t e d of 11 cm s e i n e mesh, was 10 m i n d i a m e t e r and 17 m deep. I t was s u s p e n d e d f r o m t h e f l o t a t i o n p l a t f o r m and 16 w e i g h t e d r o p e s h e l d i t s s i d e s away from t h e f o u r e x p e r i m e n t a l e n c l o s u r e s h a n g i n g i n s i d e ( F i g . 3 ) . L a b o r a t o r y H o l d i n g Tank The h o l d i n g t a n k c o n t a i n e d 300 l i t e r s of f i l t e r e d s ea water t h a t was r e c y c l e d a t a c o n s t a n t r a t e and s u p p l i e d w i t h a d e q u a t e oxygen from t h r e e a i r s t o n e s . A c o o l i n g s y s t e m , i n an a d j a c e n t t a n k , m a i n t a i n e d t h e water t e m p e r a t u r e a t 12°C ± 1°C, ( s i m i l a r t e m p e r a t u r e s t o t h o s e i n t h e o f f s h o r e e n c l o s u r e s ) . C o n s i s t e n t d a y - n i g h t l i g h t i n t e r v a l s were m a i n t a i n e d and t h e t a n k s opaque F i g u r e 3. F l o t a t i o n p l a t f o r m w i t h t h e p r o t e c t i v e n e t s u r r o u n d i n g t h e f i n e mesh e n c l o s u r e s . o 11 s i d e s p r e v e n t e d t h e f i s h f r o m b e i n g d i s t u r b e d by r o u t i n e a c t i v i t i e s i n t h e l a b o r a t o r y . THE PROCEDURE On 18 May 1980, a p p r o x i m a t e l y 240 j u v e n i l e c h i n o o k s a l m o n , from C a p i l a n o H a t c h e r y , were w e i g h e d , measured, and b r a n d e d . The f o l l o w i n g day 220 o f t h e s e f i s h were p l a c e d i n two of t h e 90m 3 o f f s h o r e e n c l o s u r e s and 11 were r e t a i n e d i n t h e l a b o r a t o r y h o l d i n g t a n k . The mean i n i t i a l s i z e of t h e j u v e n i l e salmon p l a c e d i n e a c h e n c l o s u r e was v i r t u a l l y i d e n t i c a l : 6.2 g i n w e i g h t and 85 mm i n f o r k l e n g t h . The e n c l o s e d f i s h c o u l d f e e d on n a t u r a l z o o p l a n k t o n w h i l e l a b o r a t o r y f i s h were s t a r v e d . On 26 May, 20 more j u v e n i l e . salmon were added t o t h e l a b o r a t o r y h o l d i n g t a n k t o i n c r e a s e t h e sample s i z e . The w e i g h t and l e n g t h of e a c h s t a r v e d f i s h was r e c o r d e d once a week. The p e r f o r m a n c e of t h e e n c l o s u r e s was e v a l u a t e d w i t h b o t h q u a n t i t a t i v e and q u a l i t a t i v e d a t a . Q u a n t i t a t i v e d a t a were o b t a i n e d f r om d a i l y z o o p l a n k t o n s a m p l e s and w e e k l y f i s h s a m p l e s . Q u a l i t a t i v e o b s e r v a t i o n s o f p l a n k t o n f o u l i n g , z o o p l a n k t o n movement and f i s h f e e d i n g were r e c o r d e d e a c h day d u r i n g t h e s i x week e x p e r i m e n t a l p e r i o d . S a m p l i n g t h e Z o o p l a n k t o n Z o o p l a n k t o n s a m p l e s were c o l l e c t e d on a d a y - n i g h t b a s i s e v e r y 12 h o u r s a t 1000 and 2200 h o u r s t h r o u g h o u t t h e e x p e r i m e n t a l p e r i o d . Two sa m p l e s were o b t a i n e d from a t l e a s t 12 t h r e e of f i v e p o s s i b l e l o c a t i o n s d u r i n g e a c h s a m p l i n g p e r i o d . The f i v e p o s s i b l e l o c a t i o n s f o r t h e p l a n k t o n h a u l s were: (1) ' i n s i d e t h e 9 mm mesh e n c l o s u r e w i t h f i s h . (2) i n s i d e t h e 19 mm mesh e n c l o s u r e w i t h f i s h . (3) i n s i d e t h e 19 mm mesh e n c l o s u r e w i t h o u t f i s h . (4) o u t s i d e t h e e n c l o s u r e s but i n s i d e t h e p r o t e c t i v e n e t . (5) o u t s i d e t h e p r o t e c t i v e n e t . x A v e r t i c a l l y h a u l e d Bongo Net w i t h 202 urn mesh was u s e d t o sample z o o p l a n k t o n a b u ndance. T h i s method was c h o s e n f o r i t s d e m o n s t r a t e d a b i l i t y t o e s t i m a t e z o o p l a n k t o n abundance i n t h e CEPEX b a g s . B a s e d on p r e c i s i o n , a c c u r a c y , and c o m p a r a b i l i t y between e x p e r i m e n t s , v e r t i c a l l y i n t e g r a t e d n e t h a u l s p r o v i d e d t h e b e s t measure of z o o p l a n k t o n abundance i n CEPEX bags (Lawson and G r i c e 1977). Samples were r e t a i n e d i n r e p l a c a b l e c o d ends u n t i l t h e y c o u l d be c a r e f u l l y e m p t i e d and p r e s e r v e d w i t h 15 ml o f f o r m a l i n i n t h e l a b o r a t o r y . The two most r e c e n t s e t s of s a m p l e s were a n a l y z e d e a c h d a y . The s a m p l e s were s p l i t u s i n g a F o l s o m p l a n k t o n s p l i t t e r t o m a x imize t h e p r e c i s i o n of t h e s u b s e q u e n t c o u n t s . Z o o p l a n k t o n c o u n t s were r e c o r d e d f o r t h r e e s i z e g r o u p s : 0.7-1.4 mm; 1.4-3.0 mm; and >3.0 mm. Amphipods and E u p h a u s i a g r e a t e r t h a n 10 mm i n l e n g t h and any medusa or c t e n o p h o r e s were removed and c o u n t e d p r i o r t o m e a s u r i n g t h e wet w e i g h t o f t h e c o u n t e d s ample. The d a t a were r e c o r d e d on 5 x 8 c a r d s a l o n g w i t h o t h e r r e l e v a n t q u a l i t a t i v e i n f o r m a t i o n s u c h as t h e c l a r i t y o f t h e sample i n t e r m s o f m i c r o z o o p l a n k t o n and p h y t o p l a n k t o n ; t h e weather c o n d i t i o n s when t h e sample was t a k e n ; t h e s p e e d o f t h e v e r t i c a l h a u l ; and t h e d a t e and t i m e . 1 3 S a m p l i n g t h e F i s h I n i t i a l l y e v e r y f i s h was w e i g h e d , measured and b r a n d e d u s i n g t h e methods d e s c r i b e d i n A p p e n d i x I . F i s h s a m p l e s were o b t a i n e d once a week w i t h a c o n i c a l s haped n e t 2.5 m i n d i a m e t e r . T h r e e v e r t i c a l tows w i t h t h i s 19 mm mesh n e t would r e c o v e r 90% o f t h e f i s h i n an e n c l o s u r e . O n l y 10 f i s h were sampled i n t h e f i r s t week and none of t h e s e were s a c r i f i c e d . In s u b s e q u e n t weeks f o r t y f i s h f r o m e a c h e n c l o s u r e were t r a n s p o r t e d t o t h e l a b o r a t o r y where t h e y were w e i g h e d and measured. One out of e v e r y 4 f i s h was s a c r i f i c e d and i m m e d i a t e l y p r e s e r v e d i n f o r m a l i n f o r stomach c o n t e n t a n a l y s i s . The r e s t o f t h e f i s h were r e t u r n e d t o t h e i r r e s p e c t i v e e n c l o s u r e s a p p r o x i m a t e l y one hour a f t e r t h e y were removed. The s a c r i f i c e d f i s h were not r e p l a c e d . The f o l l o w i n g day the p r e s e r v e d f i s h were r i n s e d w i t h f r e s h w a t e r , t h e i r stomach c o n t e n t s examined, and t h e i r b o d i e s p r e s e r v e d i n 95% a l c o h o l . G e n e r a l R e s u l t s The f i n e 1 mm mesh p e r m a s c r e e n i n g was not a s u i t a b l e m a t e r i a l f o r an " i n s i t u " s e mi-open e n c l o s u r e . T h i s e n c l o s u r e was t o o e a s i l y t o r n by m o d e r a t e wave and t i d a l a c t i o n , and r a p i d l y c l o g g e d w i t h p h y t o p l a n k t o n g r o w t h . P e r m a s c r e e n i n g mesh would be more s u i t a b l e f o r a s m a l l e r e n c l o s u r e w i t h more s t r u c t u r a l s u p p o r t ( L a u r e n c e e t a l . 1978). The u t i l i t y o f s u c h an e n c l o s u r e w o u l d be l i m i t e d t o a r e a s o r t i m e p e r i o d s o f low 1 4 p h y t o p l a n k t o n p r o d u c t i v i t y . The 9 mm and 19 mm mesh e n c l o s u r e s were much more d u r a b l e and c o u l d be m a i n t a i n e d r e l a t i v e l y • f r e e of p h y t o p l a n k t o n g r o w t h u s i n g t h e methods d e s c r i b e d i n A p p e n d i x II . The i d e a o f u s i n g d i f f e r e n t mesh s i z e s t o l i m i t t h e f o o d s i z e s a v a i l a b l e t o t h e j u v e n i l e f i s h p r o v e d t o be i m p r a c t i c a l . The 1 mm mesh c l o g g e d w i t h p h y t o p l a n k t o n , and t h e 9 mm mesh was not s m a l l enough t o e x c l u d e t h e l a r g e s t z o o p l a n k t o n ( a d u l t E u p h a u s i a ). The 19 mm mesh d i d not s c r e e n o u t any s i z e c l a s s o f z o o p l a n k t o n commonly f o u n d i n S a a n i c h I n l e t . QUANTITATIVE DATA Zooplankon Samples Samples were g a t h e r e d t o a s s e s s s p a t i a l and t e m p o r a l v a r i a t i o n s i n z o o p l a n k t o n c o n c e n t r a t i o n s w i t h r e s p e c t t o s i z e and d o m i n a n t s p e c i e s . F i g u r e 4 i l l u s t r a t e s t h e v a r i a t i o n s i n t h r e e s i z e c a t e g o r i e s of z o o p l a n k t o n g a t h e r e d from more t h a n 113 d a y l i g h t "AM" s a m p l e s . F i g u r e 5 d e p i c t s s i m i l a r d a t a g a t h e r e d from t h e a d d i t i o n a l 86 n i g h t "PM" s a m p l e s . In t h e s e f i g u r e s , t h e d a t a from samples t a k e n o u t s i d e t h e e n c l o s u r e s has been c o n n e c t e d w i t h a s o l i d l i n e . F o r B o n g o . h a u l s , 95% c o n f i d e n c e l i m i t s a r e u s u a l l y 50-200% of an o b s e r v a t i o n (Weibe and H o l l a n d 1968; Lawson and G r i c e 1977). R e p l i c a t e h a u l s were o b t a i n e d , a t e a c h s a m p l i n g l o c a t i o n , s e v e r a l t i m e s d u r i n g t h e e x p e r i m e n t a l p e r i o d . T h e s e s a m p l e s 15 31<m6mai920Z125J72«29 - 192:21222320252621:) 5 6 7 I 9 1011 •Zl^r^lSli JUNE 1RY JUNE Figure 4. The s p a t i a l and temporal variat i o n s of "AM" zooplankton. The s o l i d l i n e represents the data from outside samples. Symbols: • 9 mm enclosure with f i s h . • 19 mm enclosure with f i s h . * 19 mm enclosure without f i s h . F i g u r e 5. The s p a t i a l and t e m p o r a l v a r i a t i o n s o f "PM" z o o p l a n k t o n . The s o l i d l i n e r e p r e s e n t s t h e d a t a f r o m o u t s i d e s a m p l e s . Symbols: • 9 mm e n c l o s u r e w i t h f i s h . • 19 mm e n c l o s u r e w i t h f i s h . * 19 mm e n c l o s u r e w i t h o u t f i s h . 1 7 p r o v i d e an e s t i m a t e of t h e 95% c o n f i d e n c e l i m i t s f o r e a c h s i z e c l a s s of z o o p l a n k t o n . The 95% c o n f i d e n c e l i m i t s were: 50-150% of an o b s e r v a t i o n f o r l a r g e z o o p l a n k t o n ; 49-151% of an o b s e r v a t i o n f o r medium z o o p l a n k t o n ; and 10-180% of an o b s e r v a t i o n f o r s m a l l z o o p l a n k t o n . The 95% c o n f i d e n c e l i m i t s f o r z o o p l a n k t o n c o u n t s were 80-120% of t h e f i r s t c o u n t f o r e a c h s i z e c l a s s . Z o o p l a n k t o n C o n c e n t r a t i o n s The c o m p a r i s o n of z o o p l a n k t o n c o n c e n t r a t i o n s i n s i d e and o u t s i d e t h e e n c l o s u r e s was t h e s i n g l e most i m p o r t a n t a n a l y s i s u s e d t o e v a l u a t e t h e p e r f o r m a n c e e x p e r i m e n t a l e n c l o s u r e s . Two way u n i v a r i a t e and m u l t i v a r i a t e a n a l y s e s of v a r i a n c e were u s e d t o i n v e s t i g a t e t h e s p a t i a l and d a i l y d i f f e r e n c e s i n z o o p l a n k t o n c o n c e n t r a t i o n s . These a n a l y s e s r e v e a l e d h i g h l y s i g n i f i c a n t d i f f e r e n c e s ( p < . 0 l ) between t h e z o o p l a n k t o n c o n c e n t r a t i o n s i n s i d e t h e 'two e n c l o s u r e s w i t h f i s h and c o n c e n t r a t i o n s o u t s i d e t h e e n c l o s u r e s . However, t h e z o o p l a n k t o n c o n c e n t r a t i o n s i n s i d e t h e 19 mm mesh e n c l o s u r e w i t h o u t f i s h were no t s i g n i f i c a n t l y d i f f e r e n t (p<.05) from t h o s e measured o u t s i d e t h e e n c l o s u r e s . These r e s u l t s were c o n s i s t e n t f o r e a c h s i z e c l a s s i n b o t h "AM" and "PM" samples ( T a b l e 1 ) . P a r a m e t r i c and n o n p a r a m e t r i c c o r r e l a t i o n s were a l s o p e r f o r m e d on t h e u n t r a n s f o r m e d d a t a ( F i g . 6 ) . The l a r g e z o o p l a n k t o n (>3.0 mm) i n t h e 9 mm mesh e n c l o s u r e was t h e o n l y c a t e g o r y w h i c h was n o t h i g h l y c o r r e l a t e d ( p < . 0 l ) w i t h i t s c o u n t e r p a r t i n t h e o u t s i d e s a m p l e s . The f o l l o w i n g f a c t s s u g g e s t t h a t t h e f i s h , n o t t h e 18 Samples U n i v a r i a t e A n a l y s i s by S i z e S m a l l Medium L a r g e M u l t i v a r i a t e ( W i l k s Lambda) AM 1 - 4 .0004 .0256 .0202 .001 5 2 - 4 .0010 .0004 .0532 .0006 3 - 4 .2675 . 1 209 .0661 .041 1 PM 1 - 4 .001 1 .0010 .0214 .0048 2 - 4 .0004 .0001 .0118 .0006 3 - 4 .6216 .0907 .8999 T a b l e 1. P r o b a b i l i t y v a l u e s from u n i v a r i a t e m u l t i v a r i a t e a n a l y s e s of v a r i a n c e f o r "AM" "PM" z o o p l a n k t o n s a m p l e s . S y m b o l s : 1 = 9 mm e n c l o s u r e w i t h f i s h . 2 = 19 mm e n c l o s u r e w i t h f i s h . 3 = 19 mm e n c l o s u r e w i t h o u t f i s h . 4 = o u t s i d e t h e e n c l o s u r e s . and and 19 o I— cr .8 + .6 \ .4 + • 2 + RM SAMPLES PM SAMPLES S M L 1 - 4 S M L 2 - 4 S M L 3 - 4 S M L 1 - 4 S M L 2 - 4 S M L 3 - 4 F i g u r e 6. N o n - p a r a p e t r i c c o r r e l a t i o n c o e f f i c i e n t s . Z o o p l a n k t o n from e a c h e n c l o s u r e were c o r r e l a t e d a g a i n s t s a m p l e s from o u t s i d e t h e e n c l o s u r e s . C o r r e l a t i o n c o e f f i c i e n t s above the d a s h e d l i n e a r e h i g h l y s i g n i f i c a n t ( p < . 0 l ) . Symbols: 1 = 9 mm e n c l o s u r e w i t h f i s h . 2 = 19 mm e n c l o s u r e w i t h f i s h . 3 = 19 mm e n c l o s u r e w i t h o u t f i s h . 4 = o u t s i d e t h e e n c l o s u r e s . 20 e n c l o s u r e s , were r e s p o n s i b l e f o r t h e o b s e r v e d d i f f e r e n c e s i n t h e z o o p l a n k t o n c o n c e n t r a t i o n s . The c o n c e n t r a t i o n o f p l a n k t i v o r o u s p r e d a t o r s ( j u v e n i l e f i s h ) was h i g h e r i n s i d e t h a n o u t s i d e t h e e n c l o s u r e s w i t h f i s h . The z o o p l a n k t o n c o n c e n t r a t i o n s measured i n s i d e t h e e n c l o s u r e s w i t h f i s h were c o n s i s t e n t l y l o w e r t h a n t h e z o o p l a n k t o n c o n c e n t r a t i o n s m e asured o u t s i d e t h e e n c l o s u r e s o r i n s i d e t h e e n c l o s u r e w i t h o u t f i s h ( F i g . 4 and 5 ) . Dominant Z o o p l a n k t o n S p e c i e s The d ominant s p e c i e s o v e r t h e e x p e r i m e n t a l p e r i o d f r o m May 12 t h r o u g h June 29 a r e l i s t e d i n T a b l e 2. I t i s r e a d i l y o b v i o u s t h a t C a l a n u s s p e c i e s d o m i n a t e d e a c h s i z e c l a s s t h r o u g h o u t most of t h e e x p e r i m e n t a l p e r i o d . However, a d u l t and l a r v a l E u p h a u s i a were c o d o m i n a n t i n week z e r o ( t h e week b e f o r e t h e f i s h were p l a c e d i n t h e e n c l o s u r e s ) t h r o u g h t h e s e c o n d week. Decapod l a r v a e c o u l d be c o n s i d e r e d c o d o m i n a n t i n t h e s i x t h week. In t h e l a r g e s i z e c l a s s , C a l a n u s s p e c i e s and d e c a p o d l a r v a e were t h e c o d o m i n a n t o r g a n i s m s . Copepod s p e c i e s were dominant o v e r a l l o t h e r s i n t h e medium s i z e c l a s s ; P a r a t h e m i s t o p a c i f i c u s was t h e most common i n d i v i d u a l s p e c i e s . P s e u d o c a l a n u s m i n u t u s was c l e a r l y t h e d ominant s p e c i e s i n t h e s m a l l s i z e c l a s s w h i l e P a r a t h e m i s t o pac i f i c u s was a l s o common, e s p e c i a l l y i n t h e t h i r d and f o u r t h week. T h e r e was o n l y one o b v i o u s d i f f e r e n c e i n t h e s p e c i e s s ampled i n t h e v a r i o u s l o c a t i o n s . A d u l t E u p h a u s i a p a c i f i c u s were n e v e r p r e s e n t i n s a m p l e s t a k e n f r om t h e 19 mm mesh e n c l o s u r e w h i l e s e v e r a l were f o u n d i n s a m p l e s t a k e n f r om t h e 9mm mesh 21 S I Z E RANGE WEEK NUMBER C a l a n u s s p e c i e s D e c a p o d l a r v a e E p i l a b i d o c e r a E u p h a u s i d l a r v a e P a r a t h e m i s t o P s e u d o c a l a n u s 0.7-1.4 mm 1.4-3.0 mm >3.0 mm 0 1 2 3 4 5 6 0 1 2 3 4 5 6 0 1 2 3 4 5 6 9 • • • • • T a b l e 2. The domi n a n t s p e c i e s i n t h e t o p 10 m e t e r s o f water a t t h e e x p e r i m e n t a l s i t e f r o m May 12 t h r o u g h June 29. C i r c l e s i z e i n d i c a t e s l e v e l o f dominance w i t h i n e a c h week. 22 e n c l o s u r e . A l l t h e g e n e r a and s p e c i e s s a m p l e d i n t h e v e r t i c a l tows and stomach c o n t e n t s of t h e f i s h a r e m a j o r z o o p l a n k t o n s p e c i e s i n S a a n i c h I n l e t , i n a c c o r d a n c e w i t h t h e o b s e r v a t i o n s of F u l t o n e t a l . ( 1 9 6 9 ) . F i s h Samples The w e e k l y f i s h samples were u s e d t o e s t i m a t e g r o w th and s u r v i v a l r a t e s , and t h e p r e y o r g a n i s m s consumed by t h e j u v e n i l e f i s h . Growth R a t e s I r r e s p e c t i v e of t h e methods u s e d t o c a l c u l a t e d a i l y g r o w t h r a t e s ( A p p e n d i x I I I ) , t h e p a t t e r n s r e m a i n t h e same ( F i g . 7 ) . The d a i l y g r o w t h r a t e s of t h e f i s h h e l d i n t h e 9 mm mesh e n c l o s u r e were v e r y h i g h f o r t h e f i r s t two weeks, t h e n d r o p p e d d r a s t i c a l l y i n t h e t h i r d week, t h e n i n c r e a s e d i n t h e f o u r t h week, and f i n a l l y d e c l i n e d t o become n e g a t i v e i n t h e l a s t week. The g r o w t h r a t e s o f t h e f i s h i n t h e 19 mm mesh e n c l o s u r e were h i g h f o r t h e f i r s t two weeks, m o d e r a t e f o r t h e n e x t two weeks, and d e c l i n e d i n t h e l a s t two weeks. F i g u r e 8 shows t h e c u m u l a t i v e g r o w th o f t h e f i s h i n .each e n c l o s u r e o v e r t h e e x p e r i m e n t a l p e r i o d . The h i g h e s t g r o w t h r a t e s a c h i e v e d by i n d i v i d u a l s i n t h e s e e n c l o s u r e s (4.9%/day) a r e v e r y c l o s e t o t h e maximum growth r a t e s f o r s i m i l a r s i z e salmon r a i s e d on e x c e s s r a t i o n s i n t h e l a b o r a t o r y . A l s o , P h i l l i p s and B a r r a c l o u g h (1978) c a l c u l a t e d 23 cr o o o CD UJ o CD 5K 9 MM ENCLOSURE — i f 1 r 2 3 4 5 WEEK NUMBER cc a a CD cc CD 19 MM ENCLOSURE 0 • a a o i a ! 0 a § 8 g — i 1 1 r 2 3 4 5 WEEK NUMBER F i g u r e 7. The a v e r a g e d a i l y g r o w t h r a t e f o r i n d i v i d u a l f i s h i n t h e two o f f s h o r e e n c l o s u r e . The i s t h e b e s t e s t i m a t e o f t h e mean d a i l y g r o w t h r a t e f o r a l l f i s h d u r i n g t h a t week. 19 25 I 9 15 25 2 9 M A Y J U N E F i g u r e 8. C u m u l a t i v e g r o w t h o f t h e j u v e n i l e c h i n o o k s a l m o n . 25 s i m i l a r g r o w t h r a t e s ( 4.0%/day) f o r a l l s p e c i e s o f j u v e n i l e salmon r e s i d i n g i n S a a n i c h I n l e t f r o m t h e end of May t h r o u g h t h e m i d d l e of J u n e . ' The j u v e n i l e c h i n o o k s a l m o n , s t a r v e d i n t h e l a b o r a t o r y , d e c l i n e d i n w e i g h t a t an a v e r a g e r a t e of 0.9%/day o v e r t h e same s i x week p e r i o d . The r a t e of w e i g h t l o s s f o r t h e s t a r v e d f i s h was p r o b a b l y c l o s e l y a s s o c i a t e d w i t h t h e i r l e v e l o f a c t i v i t y . T h e s e f i s h were c o n s i s t e n t l y o b s e r v e d m a i n t a i n i n g t h e i r p o s i t i o n i n t h e b o t t o m p o r t i o n of t h e t a n k a g a i n s t a c u r r e n t of a p p r o x i m a t e l y 4cm/sec. S u r v i v a l The s u r v i v a l r a t e s f o r t h e f i s h i n e a c h e n c l o s u r e were, above 90% f o r t h e s i x week e x p e r i m e n t a l p e r i o d . At t h e end of t h e e x p e r i m e n t 106 of t h e 110 f i s h i n i t i a l l y s t o c k e d i n t h e 9 mm e n c l o s u r e , and 97 o f t h e 110 f i s h s t o c k e d i n t h e 19 mm e n c l o s u r e had been r e c o v e r e d a l i v e . Of t h e f i s h i n i t i a l l y s t o c k e d i n t h e 9 mm mesh e n c l o s u r e , 3 had d i e d i n t h e e n c l o s u r e , 40 had been s a c r i f i c e d i n t h e l a b o r a t o y f o r stomach c o n t e n t a n a l y s i s , and 66 had s u r v i v e d t o t h e end of t h e e x p e r i m e n t a l p e r i o d . T h e r e was z e r o n a t u r a l m o r t a l i t y i n t h i s e n c l o s u r e d u r i n g t h e l a s t 4 weeks of t h e e x p e r i m e n t . Of t h e f i s h s t o c k e d i n t h e 19 mm mesh e n c l o s u r e , 41 were s a c r i f i c e d i n t h e l a b o r a t o r y , and 56 s u r v i v e d t h e f u l l 6 week p e r i o d . I t i s h i g h l y p r o b a b l e t h a t most of t h e 13 m i s s i n g f i s h d i d n o t d i e ; r a t h e r , t h e y f o u n d a way out of t h e e n c l o s u r e . Upon d i s a s s e m b l i n g 'the a p p a r a t u s we f o u n d a few p l a c e s where t o r n 26 meshes p r o d u c e d a h o l e t h r o u g h w h i c h f i s h c o u l d e s c a p e . The e s c a p e p l u s n a t u r a l m o r t a l i t y r a t e d u r i n g t h e e n t i r e e x p e r i m e n t a l p e r i o d was o n l y 0.086%/day f o r t h e 9 mm mesh e n c l o s u r e and 0 . 2 8 % / d a y . f o r t h e 19 mm e n c l o s u r e . The s t a r v e d f i s h had s l i g h t l y l o w e r s u r v i v a l r a t e s . Of t h e 11 f i s h s t a r v e d f o r s i x weeks o n l y 5 s u r v i v e d and 13 s u r v i v e d of t h e 20 f i s h s t a r v e d f o r f i v e weeks. The m o r t a l i t y r a t e f o r t h e s t a r v e d f i s h was a p p r o x i m a t e l y 1.0%/day. Stomach C o n t e n t s Stomach c o n t e n t s were examined f o r two r e a s o n s : (1) t o d e t e r m i n e d i f f e r e n c e s between e n c l o s u r e s i n t h e p r e y consumed; and (2) t o e s t i m a t e t h e r e l a t i v e c o n t r i b u t i o n of n o n - p e l a g i c f o o d i t e m s ( f o o d i t e m s a s s o c i a t e d w i t h t h e s i d e s of t h e e n c l o s u r e s ) t o t h e g r o w t h o f t h e j u v e n i l e f i s h . A two way a n a l y s i s of v a r i a n c e was u s e d t o t e s t f o r d i f f e r e n c e s i n t h e p r e y p r e s e n t i n t h e stomach c o n t e n t s between t h e two e n c l o s u r e s f o r f i v e weeks ( T a b l e 3 ) . The stomach c o n t e n t s were s i g n i f i c a n t l y d i f f e r e n t (p<.05) i n o n l y one p r e y c a t e g o r y ; a d u l t E u p h a u s i a , g r e a t e r t h a n 15 mm i n l e n g t h , were more common ( p < . 0 l ) i n t h e stomach c o n t e n t s of t h e f i s h f r o m t h e 9 mm mesh e n c l o s u r e . N o n p e l a g i c f o o d s o u r c e s were not a major c o n t r i b u t o r t o t h e g r o w t h of t h e j u v e n i l e c h i n o o k i n e i t h e r e n c l o s u r e . N i n e of t h e t e n p r e y g r o u p s f o u n d i n s t omachs c o u l d s a f e l y be c o n s i d e r e d p e l a g i c i n o r i g i n ( i . e . n o t . commonly f o u n d a t t a c h e d t o any s u b s t r a t e ) . Amphipods, p r i m a r i l y t h e genus C a l l i o p i u s , were O r g a n i s m E n c l o s u r e t o E n c l o s u r e Week t o Week (>15 mm) E u p h a u s i i d s .0036 .0001 C a l l i o p i u s 1 .0000 .0769 (3.0-15 mm) E u p h a u s i i d s .3190 . 351 3 De c a p o d l a r v a e .1829 .0739 C a l a n u s s p p . .5340 . 1 355 (1.4-3.0 mm) D e c a p o d l a r v a e .3190 .3513 C a l a n u s s p p . .6597 .5291 P a r a t h e m i s t o .1595 .0000 P t e r o p o d a .3496 .0163 (0.7-1.4 mm) P a r a t h e m i s t o .0583 .0000 T a b l e 3. P r o b a b i l i t y v a l u e s f r o m two way a n a l y s i s v a r i a n c e o f s t o m a c h c o n t e n t d a t a . 28 d e s i g n a t e d t h e o n l y n o n p e l a g i c g r o u p . T h e s e o r g a n i s m s were se l d o m c a p t u r e d i n t h e v e r t i c a l h a u l s y e t t h e y were c o n s i s t e n t l y o b s e r v e d on t h e s i d e s o f t h e e n c l o s u r e s . The r e l a t i v e i m p o r t a n c e of t h e v a r i o u s p r e y g r o u p s f o u n d i n t h e stomachs was r a n k e d by means o f an i n d e x o f r e l a t i v e i m p o r t a n c e ( I R I ) . T h i s i n d e x r e f l e c t s t h e sum o f t h e f r e q u e n c y and volume p e r c e n t a g e s , m u l t i p l i e d by t h e p e r c e n t o c c u r r e n c e v a l u e ( P i n k a s e t a l . 1971). F i g u r e 9 shows v e r y c l e a r l y t h e h i g h r e l a t i v e i m p o r t a n c e of n o n p e l a g i c p r e y i n t h e d i e t of t h e j u v e n i l e f i s h d u r i n g t h e l a s t two weeks. These f i g u r e s a l s o show t h e r e l a t i v e i n s i g n i f i c a n c e of t h e s e o r g a n i s m s d u r i n g t h e p r e v i o u s t h r e e weeks. The f o l l o w i n g o b s e r v a t i o n s form t h e b a s i s f o r a s s e s s i n g t h e r e l a t i v e u n i m p o r t a n c e of n o n p e l a g i c f o o d i t e m s t o t h e g r o w th of t h e e n c l o s e d f i s h . (1) The c o n c e n t r a t i o n of amphipods on t h e mesh s t e a d i l y i n c r e a s e d d u r i n g t h e e x p e r i m e n t a l p e r i o d w h i l e t h e g r o w t h r a t e s of t h e f i s h s t e a d i l y d e c r e a s e d . (2) The f i s h e s ' g r o w t h r a t e s were l o w e s t i n b o t h e n c l o s u r e s when amphipods were t h e most i m p o r t a n t component of t h e f i s h stomach c o n t e n t s . (3) V e r y few a l t e r n t i v e p r e y were p r e s e n t i n t h e f i s h e s ' s tomachs d u r i n g t h e l a s t two weeks. (4) The f i s h were n e v e r o b s e r v e d f e e d i n g o f f t h e s i d e s o f t h e e n c l o s u r e s . S e v e r a l o t h e r s t u d i e s have f o u n d t h a t j u v e n i l e c h i n o o k salmon s e l e c t p r e y d r i f t i n g , f l o a t i n g o r swimming i n t h e water column o v e r p r e y a d h e r i n g t o s u b s t r a t e (Engstrom-Heg 1968; B e c k e r 1973; H i g l e y and Bond 1973). 29 INDEX OF R E L A T I V E IMPORTANCE 200 T S N L XL S N L XL 5 M L X L S N L X L S M L XL JLT<£ I JUNE a JUNE IS JUNE 25 JUNE 29 INDEX DF R E L A T I V E IMPORTANCE zoo T 160 4-120 + ao + 40 + S ti L XL JUNE 1 S N L XL JUNE a S M L XL JUNE 15 S M L XL JUNE 2S 5 M L XL JtNE 29 F i g u r e 9. The r e l a t i v e i m p o r t a n c e ( I R I ) o f t h e v a r i o u s t y p e s o f p r e y f o u n d i n t h e stomachs of t h e f i s h f r o m t h e 9 mm e n c l o s u r e ( t o p ) and t h e 19 mm e n c l o s u r e ( b o t t o m ) . Symbols: S = s m a l l p r e y (0.7-1.4 mm) M = medium p r e y (1.4-3.0 mm) L = l a r g e p r e y (3.0-10.0 mm)' XL = e x t r a l a r g e p r e y (>10 mm) | j = p e l a g i c p r e y . = n o n p e l a g i c p r e y . 30 QUALITATIVE DATA S e v e r a l q u a l i t a t i v e o b s e r v a t i o n s s u g g e s t t h a t t h e 9mm mesh e n c l o s u r e d i d not p e r m i t a l l s i z e s of z o o p l a n k t o n -to move t h r o u g h t h e mesh w i t h t h e same e a s e t h a t t h e y moved t h r o u g h t h e 19mm mesh. L a r g e E u p h a u s i a (20-25mm i n body l e n g t h ) were o b s e r v e d swimming i n t o t h e 9mm mesh; y e t , none o f t h e s e E u p h a u s i a were a b l e t o g e t t h e i r a ppendages t h r o u g h t h e 5mm ( i n d i a m e t e r ) h o l e s . However t h e s e E u p h a u s i a were o b s e r v e d swimming f r e e l y t h r o u g h t h e 19mm mesh. N o n e t h e l e s s , more l a r g e E u p h a u s i a were sample d from t h e 9mm e n c l o s u r e t h a n any of t h e f o u r s a m p l i n g l o c a t i o n s . T h e s e f i n d i n g s s u g g e s t t h a t a d u l t E u p h a u s i a may have had d i f f i c u l t y swimming out of t h e 9mm e n c l o s u r e . T h i s c o n c l u s i o n i s s u p p o r t e d by t h e f o l l o w i n g d a t a : (1) t e n meter v e r t i c a l tows t h r o u g h t h e 9mm e n c l o s u r e c a p t u r e d l a r g e E u p h a u s i a d u r i n g the d a y l i g h t h o u r s when t h e s e c r u s t a c e a n s a r e not n o r m a l l y f o u n d i n t h e s u r f a c e w a t e r s ; and (2) f i s h from t h e 9mm e n c l o s u r e had more a d u l t E u p h a u s i a i n t h e i r stomach c o n t e n t s t h a n t h o s e i n t h e 19mm e n c l o s u r e ( F i g . 10). A n o t h e r o b s e r v a t i o n s u g g e s t e d t h a t z o o p l a n k t o n as l a r g e as 3.0 mm, c o u l d move u n a b a t e d t h r o u g h b o t h 9 mm and 19 mm mesh. D u r i n g t h e m o r n i n g sample t a k e n on June 12, s e v e r a l dense p a t c h e s o f E p i l a b i d o c e r a a m p h i t r i t e s were o b s e r v e d moving f r e e l y back and f o r t h t h r o u g h a l l t h e e n c l o s u r e s . One of t h e samples t a k e n t h a t , m o r n i n g p r o d u c e d o v e r 9,000 o r g a n i s m s from one c u b i c meter o f w a t e r . 31 I oo ; FREQUENCY ) VOLUME ) FREQUENCY ; VOLUME ao + 10 + 20 + S ti L XL S ti L XL 9 MM ENCLOSURE L XL S ti L XL 13 MM ENCLOSURE F i g u r e 10. The r e l a t i v e p r o p o r t i o n o f e a c h p r e y g r o u p i n t h e stomach c o n t e n t s o f t h e j u v e n i l e c h i n o o k s a l m o n . [ | = C a l a n u s s p e c i e s = C a l l i o p i u s = Decapod l a r v a e = E u p h a u s i d s = P a r a t h e m i s t o 32 SUMMARY OF RESULTS (1) The 19mm mesh d i d not impede t h e e n t r a n c e o r e x i t of any s i z e c l a s s o f z o o p l a n k t o n f o u n d i n t h e s a m p l e s . (2) C o n c e n t r a t i o n s of a l l s i z e s of z o o p l a n k t o n , i n c l u d i n g a d u l t E u p h a u s i a , i n s i d e t h e 19 mm mesh e n c l o s u r e w i t h o u t f i s h were not s i g n i f i c a n t l y d i f f e r e n t from c o n c e n t r a t i o n s measured o u t s i d e t h e e n c l o s u r e s . (3) Z o o p l a n k t o n c o n c e n t r a t i o n s measured i n s i d e t h e two e n c l o s u r e s w i t h f i s h were 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 c o n c e n t r a t i o n s m easured o u t s i d e , f o r e a c h s i z e c a t e g o r y . (4) J u v e n i l e c h i n o o k salmon were a b l e t o a c h i e v e maximal g r o w t h r a t e s w h i l e f e e d i n g on p e l a g i c z o o p l a n k t o n i n a s e m i - e n c l o s e d water c o l u m n . (5) Food s o u r c e s a s s o c i a t e d w i t h t h e s i d e of t h e e n c l o s u r e s were n o t a major c o n t r i b u t o r t o t h e g r o w t h of t h e j u v e n i l e salmon i n e i t h e r e n c l o s u r e . (6) The 9mm mesh d i d impede t h e e n t r a n c e and e x i t of a d u l t E u p h a u s i a . DISCUSSION T h i s s t u d y has d e m o n s t r a t e d t h e f e a s i b i l i t y and s u i t a b i l i t y of t h e semi-open e n c l o s u r e as an e x p e r i m e n t a l a p p a r a t u s . C l e a r l y t h i s a p p a r a t u s does not p r o v i d e a c o m p l e t e l y n a t u r a l e n v i r o n m e n t f o r p e l a g i c a l l y f e e d i n g f i s h ; however, t h e s e e x p e r i m e n t a l e n c l o s u r e s a p p r o x i m a t e t h e p e l a g i c e n v i r o n m e n t more c l o s e l y t h a n any o t h e r a p p a r a t u s p r e v i o u s l y d e v e l o p e d . The e x c e l l e n t s u r v i v a l and h i g h g r o w t h r a t e s of t h e e n c l o s e d f i s h a r e t e s t i m o n y t o t h e q u a l i t y o f t h e methods u s e d t o sample and h a n d l e t h e j u v e n i l e s a l m o n . The m a j o r drawback t o t h e 19mm e n c l o s u r e was t h a t t h e f i s h 33 c a n n o t p u r s u e p r e y p a s t t h e edge of t h e e n c l o s u r e . The p r o b a b i l i t y o f c a p t u r i n g a p r e y i t e m ( p u r s u i t s u c c e s s ) i s r e d u c e d t o z e r o as t h e p r e y moves out of t h e e n c l o s u r e . T h i s drawback i s n e c e s s a r y i f one w i s h e s t o r e t a i n t h e m a j o r a d v a n t a g e of t h e s e e n c l o s u r e s , i . e . r e t a i n i n g f i s h . Many s t u d i e s have e x p r e s s e d t h e i m p o r t a n c e o f m e a s u r i n g t h e f o o d a v a i l a b l e where t h e f i s h a r e f e e d i n g . O b s e r v e r s a r e s e l d o m c e r t a i n t h a t t h e p r e y c o n c e n t r a t i o n s t h e y measure a r e s i m i l a r t o t h o s e i n t h e v i c i n i t y o f t h e f i s h f e e d i n g i n an open w a t e r c o l u m n . The m e t h o d o l o g y u s e d i n t h i s s t u d y a s s u r e s us t h a t t h e m easured p r e y c o n c e n t r a t i o n s were t a k e n from where t h e f i s h were f e e d i n g , and p r o v i d e s g r o w t h e s t i m a t e s f o r ' t h e f e e d i n g f i s h . The a p p a r a t u s and methods o u t l i n e d i n t h i s p a p e r have p o t e n t i a l f o r h e l p i n g t o r e s o l v e major q u e s t i o n s p e r t i n e n t t o t h e enhancement of salmon s t o c k s . . P o s s i b i l i t i e s a r e : ( 1 ) How i s f i s h g r o w t h r e l a t e d t o z o o p l a n k t o n abundance? ( 2 ) How r a p i d l y do salmon grow a t v a r i o u s t i m e s of t h e y e a r w h i l e f e e d i n g i n t h e p e l a g i c zone of an e s t u a r y ? ( 2 ) A r e h a t c h e r y r e a r e d f i s h more or l e s s e f f i c i e n t f e e d e r s t h a n n a t u r a l l y r e a r e d j u v e n i l e f i s h ? More l a b o r a t o r y e x p e r i m e n t s c o u l d p r o v i d e p a r t i a l a n s w ers t o t h e above q u e s t i o n s but f i e l d s t u d i e s s h o u l d be c o n d u c t e d i n c o n j u n c t i o n w i t h l a b o r a t o r y e x p e r i m e n t s w h e r e v e r p o s s i b l e . T h i s s e c t i o n has d e s c r i b e d a f i e l d m e t h o d o l o g y w h i c h c o u l d be u s e d t o r e v e a l t h e e r r o r s a s s o c i a t e d w i t h e x t r a p o l a t i n g l a b o r a t o r y r e s u l t s t o a n a t u r a l s y s t e m . P a r t two d e s c r i b e s how f i s h g r o w t h r a t e s were r e l a t e d t o p r e y s i z e and abundance i n t h e o f f s h o r e e n c l o s u r e s , and t h e 34 s i m i l a r i t i e s and d i f f e r e n c e s between t h e s e r e s u l t s and r e l a t i o n s h i p s d e r i v e d from t a n k e x p e r i m e n t s . 35 PART TWO Growth and F e e d i n g o f a P l a n k t i v o r o u s F i s h The i m p o r t a n c e of t h e q u a n t i t y and t y p e of f o o d a v a i l a b l e t o t h e g r o w t h r a t e and s u r v i v a l of l a r v a l and j u v e n i l e f i s h e s has been a c k n o w l e d g e d i n many r e p o r t s ( e . g . H j o r t 1914; W i b o r g 1948; A r t h u r 1956; S h e l b o i i r n e 1957; S y s o e v a and D e g t e r e v a 1.965; L e b r a s s e u r e t a l . 1969). O n l y a few s t u d i e s have a t t e m p t e d t o q u a n t i t a t i v e l y e s t a b l i s h t h i s r e l a t i o n s h i p i n a n a t u r a l e n v i r o n m e n t . P r o d u c t i o n s t u d i e s i n t h e S t r a i t of G e o r g i a , p a r t I I I , ( L e b r a s s e u r e t a l . 1969) was aimed l a r g e l y a t d e t e r m i n i n g t h e e x t e n t t o w h i c h t h e e a r l y l i f e s t a g e s of v a r i o u s s p e c i e s of f i s h were r e l a t e d t o t h e p l a n k t o n i c f o o d r e s o u r c e s o f t h e a r e a . The r e s u l t s o f t h i s s t u d y were i n c o m p l e t e , e s p e c i a l l y w i t h r e s p e c t t o t h e n a t u r a l p r e y c o n c e n t r a t i o n s r e q u i r e d f o r t h e maximum s u r v i v a l of l a r v a l f i s h . H y a t t (1976) p r e s e n t s a c o m p r e h e n s i v e r e v i e w o f t h e l i t e r a t u r e p e r t a i n i n g t o f i s h e s ' a c q u i s i t i o n o f f o o d i n t h e n a t u r a l e n v i r o n m e n t . The e x p e r i m e n t a l e n c l o s u r e s d e v e l o p e d i n t h i s s t u d y have p r o v i d e d d a t a t o q u a n t i f y t h e r e l a t i o n s h i p between t h e growth of j u v e n i l e salmon and t h e abundance of n a t u r a l z o o p l a n k t o n . T h r e e l e v e l s o f t h e f i s h - f o o d r e l a t i o n s h i p have been e x a m i n e d : 36 (1) The r e l a t i o n s h i p between f i s h g r o w t h r a t e s and t h e s i z e and abundance of p e l a g i c p r e y ; (2) t h e r e l a t i o n s h i p between f i s h g rowth r a t e s and t h e q u a n t i t y of p r e y consumed; and (3) t h e f u n c t i o n a l components o f t h e r e l a t i o n s h i p between t h e p r e y consumed and t h e abundance of t h o s e p r e y i n t h e w a t e r column. METHODS Weekly f i s h g r o w t h r a t e s were p l o t t e d a g a i n s t t h e c o r r e s p o n d i n g mean z o o p l a n k t o n c o n c e n t r a t i o n s m e a s u r e d i n e a c h e n c l o s u r e . A salmon e n e r g e t i c s model was c o n s t r u c t e d t o c a l c u l a t e t h e minimum number of c a l o r i e s t h a t t h e f i s h must have consumed e a c h day t o s u s t a i n t h e o b s e r v e d g r o w th r a t e s . T hese v a l u e s were used t o e s t a b l i s h a r e l a t i o n s h i p between t h e q u a n t i t y of p r e y consumed and t h e p r e y abundance i n t h e water c o l u m n . H o l l i n g ' s d i s c e q u a t i o n ( H o l l i n g 1959) was u s e d t o f i t a c u r v e t o t h e c o n s u m p t i o n v e r s e s p r e y d e n s i t y d a t a . A m u l t i s p e c i e s d i s c e q u a t i o n (Murdock and O a t e n 1975) was u s e d t o c a l c u l a t e r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h f o r e a c h of t h e 9 p r e y c a t e g o r i e s f o u n d i n t h e stomach c o n t e n t s of t h e j u v e n i l e s a lmon. I t was assumed t h a t p r o p o r t i o n s i n t h e stomach were t h e same as p r o p o r t i o n s a c t u a l l y a t t a c k e d (no d i f f e r e n t i a l r e g u r g i t a t i o n or d i g e s t i o n r a t e s by p r e y t y p e ) . The a n a l y t i c a l methods u s e d t o examine t h e f i s h - f o o d r e l a t i o n s h i p a r e d e s c r i b e d i n t h e f o l l o w i n g two s e c t i o n s . 37 Salmon E n e r g e t i e s Model The p h y s i o l o g i c a l model e s t i m a t e s v a l u e s f o r t h e f i v e major components of t h e e n e r g y budget o f a f i s h . T h e s e v a l u e s p a r t i t i o n t h e e n e r g y consumed i n t o t h e f o l l o w i n g c a t e g o r i e s : e n e r g y l o s s i n f e c e s and n i t r o g e n o u s w a s t e s , e n e r g y f o r s t a n d a r d metabolism,, e n e r g y f o r f e e d i n g m e t a b o l i s m , e n e r g y f o r swimming m e t a b o l i s m , and e n e r g y f o r g r o w t h . Growth was measured i n . t h i s s t u d y , and t h e o t h e r components were e s t i m a t e d from r e l a t i o n s h i p s i n t h e l i t e r a t u r e so as t o f i n a l l y a r r i v e a t e s t i m a t e s of c o n s u m p t i o n . I v l e v ( 1 9 6 1 a ) , P a l o h e i m o and D i c k i e ( 1 9 6 6 ) , L a u r e n c e (1977) and o t h e r s have u s e d s i m i l a r a p p r o a c h e s t o t r a n s l a t e r a t i o n s i z e s i n t o p o t e n t i a l g r o w t h r a t e s . In t h i s model m e t a b o l i c d a t a f o r s o c k e y e salmon i s assumed t o be a p p l i c a b l e t o c h i n o o k s a l m o n . T h i s a s s u m p t i o n i s s u p p o r t e d i n t h e work of E l l i o t (1969) who r e p o r t e d f e e d i n g m e t a b o l i c r a t e s f o r c h i n o o k salmon t h a t were s i m i l a r t o t h o s e m easures f o r s o c k e y e by B r e t t ( 1 9 7 6 ) . E x c r e t i o n B r e t t and G r o v e s (1979) have t h o u g h l y examined t h e l i t e r a t u r e on t h e r a t e s of e n e r g y l o s s t h r o u g h e x c r e t i o n " E r " . They s u g g e s t t h a t f i s h f e e d i n g on i n v e r t e b r a t e s l o s e 25-30% of t h e i r f o o d e n e r g y i n w a s t e s . T h i s v a l u e t a k e s i n t o a c c o u n t b o t h f e c e s and n i t r o g e n o u s w a s t e s and would a p p l y f o r most c o m b i n a t i o n s o f t e m p e r a t u r e and r a t i o n . E l l i o t (1976) f o u n d s i g n i f i c a n t e f f e c t s of t e m p e r a t u r e and body w e i g h t on f e c a l 38 e n e r g y l o s s . However, t h e r a n g e s o f t e m p e r a t u r e and body w e i g h t f o u n d i n t h i s e x p e r i m e n t were n o t s u f f i c i e n t t o n e c e s s i t a t e t h e s e a d j u s t m e n t s . T e m p e r a t u r e e f f e c t s were n o t i n c l u d e d i n any of t h e e q u a t i o n s f o r t h e f o l l o w i n g r e a s o n . A model i n c l u d i n g t e m p e r a t u r e e f f e c t s on m e t a b o l i s m was compared w i t h t h e model d e s c r i b e d i n t h i s ' s e c t i o n . The o u t p u t of t h e two m o d els d i f f e r e d by l e s s t h a n 5%. T h i s was e x p e c t e d b e c a u s e m e t a b o l i c e x p e n d i t u r e s change v e r y l i t t l e between 10 and 15°C and t h e water column t e m p e r a t u r e s were a l w a y s w i t h i n t h i s r a n g e . S t a n d a r d M e t a b o l i s m B r e t t (1965) d e s c r i b e s s e v e r a l e q u a t i o n s r e l a t i n g s t a n d a r d m e t a b o l i s m t o f i s h s i z e and t e m p e r a t u r e . S i n c e t e m p e r a t u r e e f f e c t s a r e m i n o r , t h e f o l l o w i n g e q u a t i o n was u s e d t o c a l c u l a t e s t a n d a r d m e t a b o l i s m : Log(Mb) = -0.63 + 0.078*Log(W) where "W" i s t h e wet w e i g h t of t h e f i s h i n grams and t h e u n i t s f o r s t a n d a r d m e t a b o l i s m "Mb" a r e m i l l i g r a m s of oxygen p e r h o u r . F e e d i n g . M e t a b o l i s m B r e t t m e t a b o l i s m (1976) d e s c r i b e d t h e f o l l o w i n g "Mf" i n terms of r a t i o n s i z e : e q u a t i o n f o r f e e d i n g 39 Mf = ( 92 + 36.6*R ) - Mb where "R" i s t h e d r y w e i g h t of t h e f o o d consumed as a p e r c e n t o f t h e f i s h ' s d r y body w e i g h t . The u n i t s f o r f e e d i n g m e t a b o l i s m a r e m i l l i g r a m s of oxygen p e r k i l o g r a m o f f i s h p e r h o u r . Maximum R a t i o n The f o l l o w i n g e q u a t i o n was u s e d t o c a l c u l a t e t h e maximum r a t i o n w h i c h c o u l d be consumed by a f i s h , d e p e n d i n g on i t s s i z e ( B r e t t , 1971). Rmax = 14.5 - 5.l5*Log(W) where "W" i s the f i s h ' s wet w e i g h t i n grams and "Rmax" has t h e same u n i t s as "R". Swimming M e t a b o l i s m Swimming m e t a b o l i s m or r o u t i n e a c t i v i t y m e t a b o l i s m c an be c a l c u l a t e d i f one knows t h e a v e r a g e d a i l y swimming s p e e d of t h e f i s h ( B r e t t , 1964). Log(Ms) = ( 1.85 + 0.27*V ) - Log(Mb) where "V" i s measured i n f i s h body l e n g t h s p e r s e c o n d and swimming m e t a b o l i s m "Ms" has t h e same u n i t s as f e e d i n g m e t a b o l i sm. 40 ' 1 . . . An e s t i m a t e of t h e minimum a v e r a g e d a i l y swimming s p e e d was u s e d b e c a u s e t h e p r i m a r y f u n c t i o n of t h e model was t o p r o v i d e an e s t i m a t e of t h e minimum number of c a l o r i e s consumed by t h e j u v e n i l e f i s h . H i g h e r swimming s p e e d s would r e q u i r e more f o o d and s u g g e s t even h i g h e r s e a r c h e f f i c i e n c i e s t o s u p p o r t t h e same gr o w t h r a t e . The minimum a v e r a g e d a i l y swimming s p e e d i s d i v i d e d i n t o two c omponents: (1) swimming a s s o c i a t e d w i t h s t r e s s o r n o n f e e d i n g a c t i v i t y and (2) swimming a s s o c i a t e d w i t h f e e d i n g . An e s t i m a t e of t h e n o n f e e d i n g a c t i v i t y was o b t a i n e d from t h e n e g a t i v e g r o w t h r a t e s of t h e s t a r v e d f i s h , -0.9 p e r c e n t body w e i g h t p e r d a y . In t h e model, s t a r v e d f i s h w i t h an a v e r a g e swimming s p e e d o f 1 body l e n g t h p e r s e c o n d l o s e w e i g h t a t a r a t e o f -0.9%/day. T h i s model assumes t h a t e n e r g y e xpended i n s t r e s s or n o n f e e d i n g . a c t i v i t y would be g r e a t e s t f o r a s t a r v e d f i s h and l e a s t f o r f i s h t h a t a c h i e v e t h e i r maximum r a t i o n . H y a t t (1976) f o u n d t h a t t r o u t and kokanee s e a r c h a t s p e e d s of 1-2 body l e n g t h s p e r s e c o n d when f o r a g i n g f o r z o o p l a n k t o n i n t h e w ater c o l u m n . Ware (1978) s u g g e s t s t h a t t h e o p t i m a l f o r a g i n g s p e e d f o r p e l a g i c f e e d i n g f i s h i s a b o u t one body l e n g t h p e r s e c o n d . T h e r e f o r e , one body l e n g t h p e r s e c o n d i s a r e a s o n a b l e e s t i m a t e of t h e minimum a v e r a g e swimming s p e e d a s s o c i a t e d w i t h f e e d i n g . The f o l l o w i n g e q u a t i o n d e s c r i b e s a c o n s e r v a t i v e r e l a t i o n s h i p between swimming s p e e d and r a t i o n s i z e : V = C - ( R/Rmax ) 41 where "C" i s 1.5 body l e n g t h s p e r s e c o n d , and "RTN" and "Rmax" a r e a s d e s c r i b e d a b o v e . T h i s r e l a t i o n s h i p i s c o n s i s t e n t w i t h t h e d e s i g n of t h e model ( t o e s t i m a t e t h e minimum number o f c a l o r i e s w h i c h must have been consumed by t h e f i s h ) . Growth and Food Consumed The e n e r g y a v a i l a b l e f o r growth i s what r e m a i n s o f t h e f o o d e n e r g y i n g e s t e d a f t e r c a t a b o l i s m . In t h e model t h i s i s r e p r e s e n t e d by t h e f o l l o w i n g e g u a t i o n : G = F - F*Er - Mb - Mf - Ms where "F" i s t h e c a l o r i e s consumed and t h e o t h e r v a r i a b l e s a r e as d e s c r i b e d e a r l i e r . A l l v a r i a b l e s i n t h e above e q u a t i o n had t o be t r a n s f o r m e d i n t o t h e same u n i t s ( k i l o c a l o r i e s p e r d a y ) . The o x y c a l o r i f i c e q u i v a l e n t u s e d was 4.8 k i l o c a l o r i e s p e r l i t e r of oxygen ( B r e t t and G r o v e s , 1979). The c a l o r i e s of f o o d consumed "F" c o u l d n o t be c a l c u l a t e d by a d d i n g up c a l o r i e s u s e d f o r gro w t h and m e t a b o l i s m , b e c a u s e b o t h f e e d i n g m e t a b o l i s m , and swimming m e t a b o l i s m a r e p r o p o r t i o n a l t o r a t i o n s i z e . In t h e model, t h e v a l u e f o r t h e a v e r a g e number o f c a l o r i e s consumed e a c h week "F" was a d j u s t e d u n t i l t h e wee k l y g rowth e s t i m a t e s e q u a l l e d t h o s e a c h i e v e d by t h e e n c l o s e d f i s h . The r e s u l t i n g s i x v a l u e s r e p r e s e n t t h e minimum number of c a l o r i e s w h i c h t h e f i s h must have consumed d u r i n g an a v e r a g e day i n ea c h o f t h e s i x weeks t h e y were h e l d i n t h e o f f s h o r e e n c l o s u r e s . The above model can be t r a n s l a t e d i n t o g r o s s g r o w t h 42 e f f i c i e n c i e s of approximately 19% for small rations and 37% for large rations. Biette and Geen (1980) estimate the maximum gross e f f i c i e n c y of food conversion in underyearling sockeye salmon to be 18% and 30% for small and large rations respectively. Therefore, the model probably c a l c u l a t e s the minimum amount of food energy necessary to sustain a given growth rate. Multispecies Disc Equation The Holling multispecies disc equation was f i t t e d for the nine prey groups found in the stomach contents of the juvenile f i s h : Ai * TT * Ni E(Ni) = ---— — — — 1 + ^2 Ai * THi * Ni .where "E(Ni)" i s the amount eaten . of the i t h prey by each predator during time "TT", and "Ni" i s the density of each prey category in the water column. The parameters in the above equation are: "TT" the t o t a l time the predator and prey are exposed to each other each day; "THi" the time spent, by the predator, handling each prey item; and " A i " the predator's rate of successful search. The amount eaten " E ( N i ) n during an entire day was extrapolated from stomach content data using the following equat ion: TT E(Ni) = * SCi Tbs 43 where "SCi" was the mean number of the i t h prey found i n the stomach contents of 10 f i s h , "Tbs" was the number of d a y l i g h t hours before the f i s h were sampled, and "TT" was as d e s c r i b e d above. The primary purpose f o r the above r e l a t i o n was t o standardize the stomach content data f o r the time when the f i s h were sampled. The r e l a t i o n assumes th a t the food eaten, greater than 17 hours before the f i s h were sampled, would not c o n t r i b u t e to the d i s t i n g u i s h a b l e stomach cont e n t s . B r e t t and Higgs (1970) found that j u v e n i l e sockeye salmon h e l d i n 10°C and 15°C water r e q u i r e I9hrs and 11hrs, r e s p e c t i v e l y , to achieve 90% d i g e s t i o n of t h e i r stomach cont e n t s . Nonetheless, the above r e l a t i o n assumes that the enclosed salmon feed at a constant r a t e during the d a y l i g h t hours. Therefore, t h i s r e l a t i o n would overestimate the amount eaten by f i s h that consume l e s s food during each a d d i t i o n a l d a y l i g h t hour. This feeding p a t t e r n would be expected f o r f i s h that achieve t h e i r maximum r a t i o n . However, the average f i s h e s ' stomach was l e s s than h a l f f u l l and the number of d a y l i g h t hours before the f i s h were sampled was always between 6 and 12 hours. Parker and Vanstone (1966) showed that young salmon had a d i u r n a l c y c l e of feeding i n t e n s i t y and that feeding was continuous during d a y l i g h t hours. Under these c o n d i t i o n s , the above r e l a t i o n would provide a reasonable estimate of the amount eaten during an e n t i r e day. The d e n s i t y of each prey item " N i " was d e r i v e d from d a i l y zooplankton samples obtained o u t s i d e the e n c l o s u r e s . Data from samples obtained i n s i d e the enclosures was of l i t t l e value s i n c e 44 i t o f t e n d i d n o t i n c l u d e s e v e r a l of t h e p r e y g r o u p s f o u n d i n t h e stomach c o n t e n t s . I t i s ' p r o b a b l e t h a t t h e f i s h s i g n i f i c a n t l y r e d u c e d t h e number of z o o p l a n k t o n ( e s p e c i a l l y t h e more v i s i b l e s p e c i e s ) i n s i d e t h e e n c l o s u r e s , a s s u g g e s t e d i n P a r t One. B a x t e r (1970) s u g g e s t e d t h a t a l i g h t i n t e n s i t y o f ab o u t 10" 1 m e t e r - c a n d l e s , c o r r e s p o n d i n g t o l a t e dusk, may be u s e d as a g e n e r a l l o w e r t h r e s h o l d f o r v i s u a l f e e d e r s . S i n c e salmon a r e p r i m a r i l y v i s u a l p r e d a t o r s , t h e t o t a l t i m e t h e p r e d a t o r and p r e y a r e e x p o s e d "TT" was e q u a l t o t h e i n t e r v a l between e a r l y dawn and l a t e dusk; a p p r o x i m a t e l y 17 h o u r s i n J u n e . The t i m e s p e n t h a n d l i n g e a c h p r e y i t e m " T H i " i s p r o b a b l y a f u n c t i o n of t h e s i z e of t h e f i s h and t h e s i z e of t h e p r e y . Gazey (1981) has d e m o n s t r a t e d t h e e m p e r i c a l base f o r t h e f o l l o w i n g r e l a t i o n s h i p : TT b = a * W T H i where " a " and "b" a r e p a r a m e t e r s and "W" i s t h e w e i g h t of t h e f i s h . The l e f t hand s i d e of t h e e q u a t i o n r e p r e s e n t s t h e maximum number of e a c h p r e y w h i c h c an be consumed i n t h e t i m e i n t e r v a l "TT". E s t i m a t i o n of t h e p a r a m e t e r s i n t h i s e q u a t i o n was made p o s s i b l e by a s s u m i n g t h a t t h e maximum stomach c a p a c i t y i s a r e a s o n a b l e e s t i m a t e of t h e maximum amount of p r e y w h i c h c an be consumed by a j u v e n i l e salmon i n l e s s t h a n 17 h o u r s . The above e q u a t i o n was f i t t e d t o p h y s i o l o g i c a l d a t a from B r e t t (1971) and t h e " a " and "b" p a r a m e t e r s were e s t i m a t e d a s 0.155 and 0.77 r e s p e c t i v e l y . The stomach c a p a c i t y was d i v i d e d by t h e s i z e of 45 t h e p r e y " P i " t o d e t e r m i n e t h e maximum number of e a c h s i z e o f p r e y w h i c h c o u l d be consumed by a j u v e n i l e salmon e a c h day. The f o l l o w i n g e q u a t i o n d e s c r i b e s t h e h a n d l i n g t i m e f o r e a c h p r e y as a f u n c t i o n of p r e y s i z e and f i s h s i z e : TT * P i T H i = b a*W where a l l t h e v a r i a b l e s and p a r a m e t e r s a r e as d e s c r i b e d e a r l i e r . The r a t e of s u c c e s s f u l s e a r c h " A i " f o r e a c h p r e y g r o u p was e s t i m a t e d u s i n g s e v e r a l n o n l i n e a r p a r a m e t i z a t i o n t e c h n i q u e s . The r e s u l t i n g v a l u e s s h o u l d be c o n s i d e r e d as r e l a t i v e r a t e s o f s u c c e s s f u l s e a r c h b e c a u s e t h e v a l u e s f o r amount e a t e n " E ( N i ) " , e s t i m a t e d from stomach c o n t e n t d a t a , a r e not good e s t i m a t e s of t h e a b s o l u t e number of e a c h p r e y consumed e a c h day. However, the mean stomach c o n t e n t s f o r 10 f i s h p r o b a b l y p r o v i d e a r e a s o n a b l e i n d i c a t i o n of t h e r e l a t i v e numbers of e a c h p r e y t h a t an a v e r a g e f i s h w o u l d consume t h a t d a y . The c o v a r i a n c e and c o r r e l a t i o n m a t r i c e s f o r t h e s e r a t e s of s u c c e s s f u l s e a r c h were examined t o a s s e s s t h e d e g r e e of c o n f o u n d i n g i n e s t i m a t e s due t o l a c k of n a t u r a l c o n t r a s t i n d e n s i t i e s among p r e y g r o u p s . RESULTS AND INTERPRETATION Stomach c o n t e n t s were r e e x a m i n e d t o d e t e r m i n e t h e s i z e s and t y p e s o f z o o p l a n k t o n consumed by t h e j u v e n i l e s a l m o n . F i g u r e 9 shows t h e r e l a t i v e i m p o r t a n c e o f e a c h s i z e g r o u p i n t h e stomach c o n t e n t s of f i s h from e a c h e n c l o s u r e . W i t h t h e e x c e p t i o n of June 46 15 t h e s m a l l s i z e c l a s s i s n o t r e p r e s e n t e d i n t h e s t omach c o n t e n t s o f t h e f i s h from e i t h e r e n c l o s u r e . Engstrom-Heg (1968) and C r a d d o c k e t a l . (1976) a l s o f o u n d t h a t n a t u r a l l y f e e d i n g j u v e n i l e c h i n o o k salmon p r e f e r f o o d i t e m s l a r g e r t h a n 1.4 mm i n l e n g t h . F i g u r e 10 shows t h e r e l a t i v e p r o p o r t i o n of t h e v a r i o u s p r e y t y p e s i n e a c h s i z e c a t e g o r y f o r b o t h e n c l o s u r e s . C a l a n u s s p e c i e s were c o n s i s t e n t l y t h e s m a l l e s t component of t h e stomach c o n t e n t s y e t t h e y d o m i n a t e d t h e s m a l l , medium, and l a r g e s i z e c l a s s e s of t h e z o o p l a n k t o n samples ( T a b l e 2 ) . F i s h Growth v s Z o o p l a n k t o n Abundance The d a t a g a t h e r e d d u r i n g t h e " i n s i t u " e x p e r i m e n t s u g g e s t s t h a t f i s h g r o w t h i s l a r g e l y d e t e r m i n e d by t h e s i z e of t h e a v a i l a b l e f o o d o r g a n i s m s ( F i g . 11-14). The d a t a p o i n t s i n t h e s e f i g u r e s r e p r e s e n t t h e mean g r o w t h r a t e s p l o t t e d a g a i n s t t h e mean z o o p l a n k t o n abundance f o r e a c h week, t h e y - i n t e r c e p t r e p r e s e n t s t h e n e g a t i v e g r o w t h r a t e of t h e s t a r v e d f i s h . The p o i n t where t h e f i t t e d c u r v e c r o s s e s t h e z e r o g r o w t h l i n e r e p r e s e n t s t h e z o o p l a n k t o n c o n c e n t r a t i o n below w h i c h th e f i s h c a n n o t a c h i e v e a m a i n t a n e n c e r a t i o n . The c u r v e s were f i t t e d u s i n g a s a t u r a t i o n f u n c t i o n s i m i l a r t o a d i s c e q u a t i o n . F i g u r e 11 shows no r e l a t i o n s h i p between t h e abundance of s m a l l z o o p l a n k t o n and f i s h g r o w t h r a t e s , w h i l e t h e o t h e r f i g u r e s i n d i c a t e s i g n i f i c a n t r e l a t i o n s h i p s . F i g u r e 14 s u g g e s t s t h a t g r o w t h r a t e s a r e more s t r o n g l y r e l a t e d t o t h e c o m b i n e d c o n c e n t r a t i o n o f medium and l a r g e s i z e c l a s s e s t h a n t o any s i n g l e s i z e c a t e g o r y . 5 2 o c5 ' • 9mm enclosure O 19mm enclosure Maintenance o 100 200 300 400 500 600 Small Zooplankton (organisms/m**) 700 800 900 F i g u r e 11. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a s m a l l (0.7-1.4 mm) z o o p l a n k t o n . • 9 mm enclosure O 19 mm enclosure \P— 10 20 30 40 50 Medium Zooplankton (organisms/m^) o I99 F i g u r e 12. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and th e abundance of a medium (1.4-3.0 mm) z o o p l a n k t o n . • 9 mm enclosure F i g u r e 13. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a l a r g e (>3.0 mm) z o o p l a n k t o n . F i g u r e 14. The r e l a t i o n s h i p s between f i s h g r o w t h r a t e s and t h e abundance o f a medium and l a r g e (1.4-4.5 mm) z o o p l a n k t o n . 49 Wankowski (1979) d e s c r i b e s t h e m o r p h o m e t r i c l i m i t a t i o n s t o t h e r a n g e o f p r e y s i z e s a v a i l a b l e t o j u v e n i l e A t l a n t i c s a lmon. He f o u n d t h a t 10 cm salmon have a maximum mouth gap of 6 mm and a minimum g i l l r a k e r s p a c i n g of 0.8 mm. Wankowski and T h o r p e (1979) f o u n d t h a t j u v e n i l e A t l a n t i c salmon grew most r a p i d l y on f o o d 0.02 t i m e s t h e i r f o r k l e n g t h . T h i s t r a n s l a t e s t o an optimum f o o d s i z e of 1.7 mm t o 2.3 mm f o r t h e j u v e n i l e P a c i f i c salmon r a i s e d i n t h e e n c l o s u r e s . Most of t h e p r e y i n t h e medium and l a r g e s i z e c l a s s e s were between 1.4 mm and 4.5 mm i n l e n g t h . F u n c t i o n a l Response f o r P l a n k t i v o r o u s F i s h The salmon e n e r g e t i c s model e s t i m a t e d t h e minimum amount o f f o o d e n e r g y t h e j u v e n i l e f i s h must have consumed t o s u s t a i n t h e o b s e r v e d g r o w t h r a t e s . The model c o n v e r t s t h e y - c o o r d i n a t e s of t h e d a t a shown i n F i g u r e 14 from p e r c e n t body w e i g h t i n c r e a s e p e r day t o c a l o r i e s consumed p e r day. The f o o d consumed was e x p r e s s e d as a p e r c e n t a g e o f t h e maximum r a t i o n t o a c c o u n t f o r t h e change i n mean f i s h s i z e e a c h week. F i g u r e 15 d e p i c t s t h e f u n c t i o n a l r e s p o n s e of j u v e n i l e c h i n o o k salmon t o t h e d e n s i t y o f 1.4-4.5mm z o o p l a n k t o n . The c u r v e i n F i g u r e 15 r e p r e s e n t s t h e l e a s t s q u a r e s f i t of t h e d a t a t o t h e H o l l i n g s i n g l e s p e c i e s d i s c e q u a t i o n . The i n i t i a l s l o p e of t h i s f u n c t i o n a l r e s p o n s e r e p r e s e n t s a r a t e of s u c c e s s f u l s e a r c h o f 4.0m 3/hr. I f t h e a c t u a l z o o p l a n k t o n c o n c e n t r a t i o n s were t w i c e t h o s e measured ( l i m i t of s a m p l i n g e r r o r ) , t h e minimum r a t e of s u c c e s s f u l s e a r c h w o u l d be 2.0m 3/hr f o r t h i s g e n e r a l p r e y c a t e g o r y . 50 F i g u r e 15. The f u n c t i o n a l r e s p o n s e o f j u v e n i l e c h i n o o k s a l mon t o t h e d e n s i t y of 1.4-4.5 mm z o o p l a n k t o n . 51 The n e x t s e c t i o n compares r a t e s o f s u c c e s s f u l s e a r c h f o r 9 d i s t i n c t p r e y g r o u p s f o u n d i n t h e stomach c o n t e n t s and z o o p l a n k t o n s a m p l e s . R e l a t i v e R a t e s of S u c c e s s f u l S e a r c h The H o l l i n g m u l t i s p e c i e s d i s c e q u a t i o n ( d e s c r i b e d e a r l i e r ) and s e v e r a l n o n l i n e a r o p t i m i z a t i o n r o u t i n e s ( P a t t e r s o n 1978) were u s e d t o c a l c u l a t e r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h f o r e a c h p r e y g r o u p and q u a n t i f y t h e i n t e r r e l a t i o n s h i p s between t h e v a r i o u s p r e y g r o u p s . R a t e s of s u c c e s s f u l s e a r c h d e f i n e a p r e d a t o r ' s c a p a c i t y t o f i n d and c a p t u r e p r e y where t h e d e n s i t y of t h a t p r e y i s low. R e l a t i v e r a t e s of s u c c e s s f u l s e a r c h d i s t i n g u i s h t h e p r e y t h a t were most r e a d i l y c a p t u r e d by t h e p r e d a t o r from t h o s e t h a t were c a p t u r e d l e s s f r e q u e n t l y . The r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h a p p e a r t o v a r y d i r e c t l y w i t h t h e s i z e and i n h e r e n t c o n t r a s t of t h e p r e y i t e m ( T a b l e . 4 ) . The f i s h s e a r c h more e f f e c t i v e l y f o r t h e l a r g e r f o o d i t e m w i t h i n e a c h p r e y g r o u p . F o r example, compare t h e r a t e s of s u c c e s s f u l s e a r c h f o r l a r g e v s . medium v s . s m a l l d e c a p o d l a r v a e . W i t h i n e a c h of t h e s e s i z e c a t e g o r i e s , h i g h e r s e a r c h r a t e s were c a l c u l a t e d f o r h i g h e r c o n t r a s t p r e y . E u p h a u s i a , d e c a p o d l a r v a e , P a r a t h e m i s t o pac i f i c u s and C a l l i o p i u s w i t h t h e i r l a r g e d a r k e y e s and opaque b o d i e s a r e much h i g h e r c o n t r a s t o b j e c t s t h a n t h e t r a n s p a r e n t b o d i e s common t o C a l a n u s s p e c i e s . The r a t e s of s u c c e s s f u l s e a r c h c a l c u l a t e d f o r C a l a n u s s p e c i e s were t h e l o w e s t i n e a c h s i z e c a t e g o r y . C a l a n u s P a r a t h e m i s t o D e capods E u p h a u s i i d s S M L S M S M L L XL ,0 .02 .23 1.50 10.0 .0 .11 .34 .31 2.55 LOW CONTRAST HIGH CONTRAST T a b l e 4. The j u v e n i l e s a l m o n s ' r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h f o r t h e v a r i o u s p r e y f o u n d i n t h e e n c l o s u r e s . 1 1 2 .52 1 3 .05 .04 1 4 .03 .05 .00 1 5 .02 .09 -.00 -.01 1 6 .09 . 1 6 .00 .00 -.01 1 7 . 1 4 . 1 4 -.01 -.00 -.01 .00 1 8 . 1 4 .22 .01 -.01 -.02 -.02 -.02 1 9 .74 .60 .04 .27 .06 .01 .13 .15 1 2 3 4 5 6 7 8 P a r a l i P a r a l Deca C a l Deca C a l Euph - I Amph I 1 1 s m a l l I medium l a r g e 1 I X-T a b l e 5. The c o r r e l a t i o n m a t r i x f o r t h e 9 p r e y g r o u p s f o r w h i c h r a t e s of s u c c e s s f u l s e a r c h were c a l c u l a t e d . V a l u e s above .85 i n d i c a t e s i g n i f i c a n t c o r r e l a t i o n ( p<.05). 53 The c o r r e l a t i o n m a t r i x f o r t h e s e r a t e s o f s u c c e s s f u l s e a r c h , q u a n t i f i e s t h e d e g r e e o f c o n f o u n d i n g i n t h e e s t i m a t e s due t o l a c k o f n a t u r a l c o n t r a s t i n d e n s i t i e s among p r e y g r o u p s . None of t h e p r e y g r o u p s were s i g n i f i c a n t l y c o r r e l a t e d ( T a b l e 5 ) . T h i s a n a l y s i s s u g g e s t s t h a t t h e r e was s u f f i c i e n t c o n t r a s t i n t h e d a t a t o c l e a r l y d e f i n e t h e r e l a t i o n s h i p between t h e p r e y d e n s i t y i n t h e w ater column and t h e amount e a t e n of e a c h p r e y c a t e g o r y . The above a n a l y s e s have p r o v i d e d f u r t h e r s u p p o r t t o my c o n t e n t i o n t h a t t h e e n c l o s e d s a l m o n s ' minimum r a t e of s u c c e s s f u l s e a r c h was p r o b a b l y g r e a t e r t h a n t h e 2.0m 3/hr v a l u e d e r i v e d from F i g u r e 15. The n a t u r e of t h i s s u p p o r t i s as f o l l o w s : (1) The c o r r e l a t i o n m a t r i x and t h e r e l a t i v e . r a t e s o f s u c c e s s f u l s e a r c h s u p p o r t t h e e x c l u s i o n of t h e s m a l l s i z e c l a s s from F i g u r e 15. (2) F i g u r e 15 r e f l e c t s t h e f u n c t i o n a l r e s p o n s e f o r C a l a n u s s p e c i e s more t h a n o t h e r s p e c i e s b e c a u s e C a l a n u s were c o n s i s t e n t l y t h e most abundant o r g a n i s m s . However, the e n c l o s e d s a l m o n s ' r e l a t i v e r a t e s o f e f f e c t i v e s e a r c h f o r C a l a n u s were l o w e r t h a n t h o s e f o r a l l o t h e r p r e y g r o u p s w i t h i n e a c h s i z e c l a s s . R a t e s of S e a r c h The r a t e of s e a r c h r e p r e s e n t s t h e volume o f water an e n c l o s e d f i s h c o u l d s e a r c h p e r u n i t t i m e , c o n s i d e r i n g swimming s p e e d and r e a c t i v e d i s t a n c e t o p o t e n t i a l p r e y ( H y a t t 1978). J u v e n i l e salmon a r e p r i m a r i l y p e l a g i c p r e d a t o r s t h a t depend upon s i g h t t o l o c a t e f o o d i t e m s . P r o t a s o v (1970) p r o p o s e d t h a t a s a l m o n i d ' s v i s i o n i s d i v i d e d i n t o two v i s u a l f i e l d s : t h e f o r w a r d 54 f i e l d u s e d t o l o c a t e p o t e n t i a l f o o d i t e m s w h i l e t h e backward f i e l d warns t h e f i s h o f an a p p r o a c h i n g enemy. P r o t a s o v ' s d i a g r a m s d e p i c t t h e f o r w a r d v i s u a l f i e l d a s roughy t h e shape of a r i g h t a n g l e c o n e ; where t h e a r e a of v i s i o n "AV" i s r e l a t e d t o t h e d i s t a n c e of v i s i b i l i t y "D" i n t h e f o l l o w i n g manner. AV = 1.57 * D 2 The a r e a o f v i s i o n f o r a f e e d i n g f i s h d epends upon t h e f i s h r e a c t i v e d i s t a n c e . Many s t u d i e s have e s t a b l i s h e d t h a t t h e r e a c t i v e d i s t a n c e i s g r e a t l y e f f e c t e d by t h e c l a r i t y of t h e w a t e r , t h e amount o f l i g h t and t h e s i z e and c o n t r a s t of t h e p r e y . Ware (1973) measured t h e r e a c t i v e d i s t a n c e s of rainbow t r o u t t o low c o n t r a s t t a r g e t s of v a r i o u s s i z e s ( F i g . 16). The f o l l o w i n g e q u a t i o n d e s c r i b e s t h e c u r v e f i t t e d t o Ware's d a t a : .44 Dr = 16.34 * P where "Dr" i s t h e r e a c t i v e d i s t a n c e and "P" i s t h e p r e y s i z e i n m i l l i m e t e r s . D a t a f o u n d i n H y a t t ( 1 9 7 6 ) , P r o t a s o v ( 1 9 7 0 ) , and C o n f e r and B l a d e s (1975) s u g g e s t s i m i l a r r e a c t i v e d i s t a n c e s f o r f i s h a t t a c k i n g a v a r i e t y of n a t u r a l p r e y . In a l l of t h e s e s t u d i e s r e a c t i v e d i s t a n c e s were measured i n c l e a r w a ter w i t h i d e a l i l l u m i n a t i o n . The r e a c t i v e d i s t a n c e s f o r f i s h f e e d i n g i n t h e e n c l o s u r e s , as i n most n a t u r a l w a t e r s , would be g r e a t l y r e d u c e d due t o p h y t o p l a n k t o n blooms and s u b - o p t i m a l i l l u m i n a t i o n . Ware (1973) s u g g e s t s t h a t r e a c t i v e d i s t a n c e would 55 E 0 5 10 15 T a r g e t L e n g t h ( m m ) F i g u r e 16. The mean r e a c t i v e d i s t a n c e s ( d a t a ± 95%) o f r a i n b o w t r o u t t o low c o n t r a s t t a r g e t s o f v a r i o u s s i z e s (Ware 1973). 56 be c u t i n h a l f by d o u b l i n g t h e a t t e n u a t i o n c o e f f i c i e n t . I t i s h i g h l y p r o b a b l e t h a t t h e a t t e n u a t i o n c o e f f i c i e n t s f o r t h e e u p h o t i c zone a r e 2-3 t i m e s t h o s e o f c l e a r l a b o r a t o r y w a t e r . The f o l l o w i n g e q u a t i o n c o u l d be u s e d t o e s t i m a t e of t h e a v e r a g e s e a r c h r a t e f o r j u v e n i l e salmon f e e d i n g i n n a t u r a l w a t e r s : 2 .88 SR = 56.52 * v * (.1634 *Ra) * P where "SR" i s t h e r a t e o f s e a r c h i n m 3/hr; "V" i s t h e p r e d a t o r ' s swimming s p e e d i n cm/sec.; "P" i s t h e p r e y s i z e i n m i l l i m e t e r s ; and "Ra" i s t h e a t t e n u a t i o n of l i g h t i n n a t u r a l w ater r e l a t i v e t o t h a t i n c l e a r w a t e r . The o p t i m a l f o r a g i n g s p e e d f o r p e l a g i c f e e d i n g f i s h i s a b o u t one body l e n g t h p e r s e c o n d , as d e s c r i b e d , i n t h e e n e r g e t i c s m odel. T h i s swimming s p e e d was u s e d t o c a l c u l a t e t h e s e a r c h r a t e s f o r t h e r a n g e of p r e y s i z e s f o u n d i n t h e e n c l o s u r e s ( T a b l e 6 ) . The a p p a r a n t v i s u a l c a p a b i l i t i e s s u g g e s t t h a t 2.0m 3/hr i s a r e a s o n a b l e e s t i m a t e f o r t h e minimum r a t e of s u c c e s s f u l s e a r c h f o r p e l a g i c f e e d i n g j u v e n i l e s a l m o n . P r e y D i s t r i b u t i o n P r e y p a t c h i n e s s i s one of t h e m a j o r f a c t o r s w h i c h may c a u s e t e m p o r a l v a r i a t i o n i n t h e r a t e of s u c c e s s f u l s e a r c h . I f t h e p r e y i n s i d e t h e e n c l o s u r e s were clumped i n t o h i g h l y c o n c e n t r a t e d p a t c h e s , t h e f i s h c o u l d have been f e e d i n g i n much h i g h e r c o n c e n t r a t i o n s of p r e y t h a n t h o s e e s t i m a t e d f r o m t h e z o o p l a n k t o n 57 P r e y S i z e (mm) R a t e of S e a r c h (m 3/hr) maximum p r o b a b l e r a n g e 0.7 11 1 . 2 - 2 . 7 1.5 22 2 . 4 - 5 . 4 3.0 40 4.4 - 9.9 4.5 57 6.3 - 14.2 10.0 115 1 2 . 7 - 2 8 . 7 20.0 211 2 3 . 4 - 5 2 . 8 T a b l e 6. S e a r c h r a t e s f o r t h e range of p r e y s i z e s f o u n d i n t h e e n c l o s u r e s . The maximum s e a r c h r a t e s were d e r i v e d f r o m l a b o r a t o r y measurements. The p r o b a b l e r a n g e assumes t h a t t h e r e a c t i v e d i s t a n c e s f o r f i s h f e e d i n g i n t h e e u p h o t i c zone i s 0.3-0.5 o f t h e l a b o r a t o r y v a l u e . 58 s a m p l e s . Such a d i s t r i b u t i o n w o u l d r e s u l t i n an o v e r e s t i m a t i o n of t h e r a t e of s u c c e s s f u l s e a r c h , o n l y i f t h e f i s h o b t a i n a s i g n i f i c a n t p o r t i o n of t h e i r r a t i o n i n a p r e y p a t c h . However, t h e r a t e of s u c c e s s f u l s e a r c h i s d e t e r m i n e d by t h e i n i t i a l s l o p e of t h e f u n c t i o n a l r e s p o n e when b o t h r a t i o n and p r e y numbers i n t h e e n c l o s u r e s were l o w e s t . I f t h e s e few p r e y were h i g h l y c o n c e n t r a t e d , t h e f i s h would s t i l l have t o f i n d t h e s e p a t c h e s and s u c c e s s f u l l y p u r s u e t h e p r e y . Under t h e s e c o n d i t i o n s , t h e salmon may need an even h i g h e r r a t e o f s u c c e s s f u l s e a r c h i n o r d e r t o c a p t u r e t h e p r e y b e f o r e t h e p a t c h d i s p e r s e s or moves out of t h e e n c l o s u r e . One m ight e x p e c t t h a t f i s h , w i t h s u c h h i g h r a t e s of s u c c e s s f u l s e a r c h , c o u l d s i g n i f i c a n t l y r e d u c e t h e c o n c e n t r a t i o n s of f o o d i n s i d e t h e s e e n c l o s u r e s . In f a c t , t h e c o n c e n t r a t i o n s of medium and l a r g e z o o p l a n k t o n i n s i d e t h e e n c l o s u r e s w i t h f i s h were c o n s i s t e n t l y a b o u t 45% and 65% of t h e c o n c e n t r a t i o n s m e asured o u t s i d e t h e s e e n c l o s u r e s f o r day and n i g h t samples r e s p e c t i v e l y . On t h e o t h e r hand, t h e c o n c e n t r a t i o n s o f medium and l a r g e z o o p l a n k t o n i n s i d e t h e e n c l o s u r e s w i t h o u t f i s h , and t h e c o n c e n t r a t i o n s o f s m a l l z o o p l a n k t o n i n e a c h e n c l o s u r e were f r e q u e n t l y above 80% o f t h o s e m easured o u t s i d e . T h e s e r e s u l t s a r e c o n s i s t e n t w i t h t h e c o n t e n t i o n t h a t j u v e n i l e salmon a r e p r i m a r i l y v i s u a l p r e d a t o r s . DISCUSSION Many e x p e r i m e n t s have a t t e m p t e d t o d e t e r m i n e whether a p r e d a t o r consumes p r e y i n r e l a t i o n t o t h e i r a b u n d a n c e . To 59 e s t a b l i s h t h i s r e l a t i o n s h i p one must be c e r t a i n t h a t p r e y c o n c e n t r a t i o n s were measured where p r e d a t o r s , were f e e d i n g . T h i s - i s one of t h e c h i e f a d v a n t a g e s of t h e e n c l o s u r e s . D a t a from t h e s e e n c l o s u r e s r e v e a l e d t h a t j u v e n i l e salmon consumed m o s t l y l a r g e , h i g h c o n t r a s t p r e y ; even when t h e s m a l l , low c o n t r a s t p r e y a r e more a b u n d a n t . Ware (1973) f o u n d t h a t p r e y a c t i v i t y and p r e y e x p o s u r e a c c o u n t e d f o r more o f t h e v a r i a t i o n i n t h e d i e t o f a v i s u a l p r e d a t o r , t h a n p r e y d e n s i t y or p r e y s i z e . B o t h p r e y a c t i v i t y and p r e y e x p o s u r e a r e elements, w h i c h a f f e c t t h e i n h e r e n t c o n t r a s t of t h e p r e y . The b o d y - s i z e p r e d a t i o n h y p o t h e s i s of B r o o k s and Dobson (1965) as w e l l as Z a r e t ' s (1972) m o d i f i c a t i o n o f t h i s t h e o r y , s u p p o r t t h e i m p o r t a n c e of p r e y s i z e and i n h e r e n t c o n t r a s t . Z a r e t f o u n d t h a t t h e s i z e of C l a d o c e r a p e r se may be a l e s s i m p o r t a n t cue t o p l a n k t o p h a g e s , w h i c h hunt v i s u a l l y , t h a n t h e d e g r e e o f p i g m e n t a t i o n a s s o c i a t e d w i t h the eye o r d i g e s t i v e t r a c t of t h e p r e y s p e c i e s . The i m p o r t a n c e of t h e s e t y p e s of v i s u a l c o n t r a s t c u e s was s u p p o r t e d by t h e s a l m o n s ' r e l a t i v e l y h i g h r a t e s o f s u c c e s s f u l s e a r c h f o r a l l p r e y o r g a n i s m s w i t h l a r g e d a r k e y e s . T h i s s e c t i o n has e xamined a s p e c t s of f i s h f e e d i n g t h a t l i e o u t s i d e t h e bounds of c o n v e n t i o n a l tank e x p e r i m e n t s and most " i n s i t u " s t u d i e s . L e b r a s s e u r (1969) s u s p e c t e d t h a t t a n k e x p e r i m e n t s r e d u c e t h e e f f o r t r e q u i r e d f o r c a p t u r i n g p r e y and t h e r e b y mask any r e l a t i o n s h i p s between p r e y s i z e and f i s h g r o w t h . F i g u r e s 11 t h r o u g h 14 c o n f i r m e d h i s s u s p i c i o n s t h a t l a r g e r e n c l o s u r e s and l o w e r p r e y c o n c e n t r a t i o n s would r e v e a l t h e s e r e l a t i o n s h i p s . I v l e v ( 1 9 6 1 b ) , P a r s o n s and L e b r a s s e u r (1970) and o t h e r s 60 have f o u n d t h a t h i g h p r e y c o n c e n t r a t i o n s , w h i c h a r e i n f r e q u e n t l y m easured i n n a t u r e , were n e c e s s a r y t o s u s t a i n p o s i t i v e g r o w t h r a t e s i n t a n k r a i s e d f i s h . They c o n t e n d t h a t t h e s e p r e y c o n c e n t r a t i o n s a r e r e p r e s e n t a t i v e of t h e p a t c h i n e s s of p r e y i n t h e n a t u r a l e n v i r o n m e n t . A c c o r d i n g t o t h e i r t h e o r y , a f i s h w ould have t o m a i n t a i n i t s p o s i t i o n w i t h r e s p e c t t o h i g h c o n c e n t r a t i o n s of p r e y i n o r d e r t o s u s t a i n a h i g h g r o w t h r a t e . The g r o w t h r a t e s of t h e e n c l o s e d f i s h d e m o n s t r a t e t h a t i t i s not n e c e s s a r y f o r p e l a g i c f e e d i n g j u v e n i l e salmon t o f o l l o w p r e y p a t c h e s . T h e s e j u v e n i l e salmon were a b l e t o s u s t a i n h i g h g r o w t h r a t e s w h i l e f e e d i n g o p p o r t u n i s t i c a l l y i n a c o n s t a n t l y c h a n g i n g w ater c o l u m n . The low r a t e s o f s u c c e s s f u l s e a r c h , s u g g e s t e d i n tank e x p e r i m e n t s , a r e c o n f o u n d e d by two f a c t o r s : (1) t h e amount of p r e y a p r e d a t o r c a n consume i s l i m i t e d t o t h e amount of p r e y put i n t h e t a n k , and (2) t h e c o n c e n t r a t i o n s of t h e s e p r e y d e c r e a s e s as t h e p r e d a t o r f e e d s . None of t h e s e f i s h f e e d i n g e x p e r i m e n t s c o n d u c t e d i n t a n k s have removed t h e e f f e c t o f p r e y e x p l o i t a t i o n o r u s e d low enough p r e y c o n c e n t r a t i o n t o a c c u r a t e l y d e s c r i b e t h e i n i t i a l s l o p e of a f i s h e s ' f u n c t i o n a l r e s p o n s e . L a b o r a t o r y and f i e l d work by D.M. Ware and W.E. J o h n s o n p r o v i d e s u p p o r t f o r t h e f u n c t i o n a l r e s p o n s e d e s c r i b e d i n t h i s s t u d y . Ware (1972) p r o v i d e d e s t i m a t e s of r e c o g n i t i o n s u c c e s s and p r e y c a p t u r e s u c c e s s f o r r a i n b o w t r o u t . Ware f o u n d t h a t r e c o g n i t i o n s u c c e s s ( f o r moving p r e y ) was 74% ± 15% and p r e y c a p t u r e s u c c e s s ( p u r s u i t s u c c e s s ) was a t l e a s t 84% ± 16%. The p r o d u c t o f t h e s e two f a c t o r s t i m e s t h e r a t e of s e a r c h e q u a l t h e r a t e o f s u c c e s s f u l s e a r c h . D a t a from Ware 1973 was u s e d t o 61 e s t i m a t e s e a r c h r a t e s o f 4.4-9.9m 3/hr f o r j u v e n i l e salmon f e e d i n g on 3.0mm p r e y i n t h e e u p h o t i c z o n e . T h e s e v a l u e s s u g g e s t t h a t t h e a p p r o p r i a t e minimum r a t e of s u c c e s s f u l s e a r c h w o u l d be 2.7m 3/hr. D a t a p r e s e n t e d i n J o h n s o n 1961 d e s c r i b e s a r e l a t i o n s h i p between t h e g r o w t h o f j u v e n i l e s o c k e y e salmon and t h e abundance of z o o p l a n k t o n i n B a b i n e and N i l k i t k w a L a k e s . In t h e s e l a k e s t h e s o c k e y e w e i g h i n g 0.2 grams i n mid-June grow t o between 1.2 and 5.7 grams by m i d - O c t o b e r (122 d a y s ) , d e p e n d i n g on t h e abundance of z o o p l a n k t o n . The d a t a from J o h n s o n 1961 have been p l o t t e d on F i g u r e 14. The p o i n t s r e p r e s e n t i n g t h e l o w e r g r o w t h r a t e s f o r salmon i n t h e l a k e s a r e v e r y c l o s e t o t h e c u r v e f i t t e d t o my d a t a . U n f o r t u n a t e l y , J o h n s o n ' s d a t a d i d not i n c l u d e o b s e r v a t i o n s f o r v e r y low c o n c e n t r a t i o n s of z o o p l a n k t o n . Few s t u d i e s t o d a t e have a t t e m p t e d t o e s t i m a t e a p r e d a t o r ' s r a t e of s u c c e s s f u l s e a r c h b e c a u s e t h i s component of a f u n c t i o n a l r e s p o n s e i s p r o b a b l y a complex f u n c t i o n of t h e s i z e , m o b i l i t y , and c a m o u f l a g e of p r e y . T h i s s t u d y d i d not a t t e m p t t o e s t i m a t e a b s o l u t e v a l u e s of r a t e of s u c c e s s f u l s e a r c h f o r e a c h p r e y s p e c i e s ; r a t h e r , t h e s t u d y p r o p o s e s a minimum v a l u e f o r t h i s f a c t o r f o r a s p e c i f i c s i z e c l a s s of p r e y o r g a n i s m s . D a t a from p r e v i o u s s t u d i e s a p p e a r s t o s u p p o r t t h i s minimum v a l u e and t h e p r o p o s e d f u n c t i o n a l r e s p o n s e f o r p e l a g i c f e e d i n g j u v e n i l e s a l m o n . A major p r o b l e m i n f i s h f e e d i n g e x p e r i m e n t s i s t h a t c o n v e n t i o n a l methods u s e d t o o b t a i n g r o w t h d a t a r e q u i r e h a n d l i n g of t h e f i s h . In t h i s s t u d y g r o w t h r a t e s were e s t i m a t e d f r o m 62 w e e k l y s a m p l e s i n o r d e r t o m i n i m i z e h a n d l i n g ; however, f o o d abundance d a t a was o b t a i n e d on a d a i l y b a s i s . The i d e a l e x p e r i m e n t a l d e s i g n would p r o v i d e d a i l y e s t i m a t e s o f f i s h g r o w t h t o accompany t h e d a i l y f o o d abundance d a t a . C o n v e n t i o n a l e s t i m a t i o n o f f i s h g r o w t h o v e r s u c h s h o r t i n t e r v a l s would r e q u i r e f r e q u e n t d i s t u r b a n c e of f i s h f e e d i n g . T h e s e d i s t u r b a n c e s w ould s i g n i f i c a n t l y r e d u c e t h e f i s h e s ' a b i l i t y t o f e e d , t h e r e b y , a r t i f i c a l l y a l t e r i n g i t s g r o w t h r a t e . The r e c e n t d i s c o v e r y of d a i l y g r o w t h i n c r e m e n t s on t h e o t o l i t h s of j u v e n i l e s a l m o n i d s may p r o v i d e a means f o r m e a s u r i n g d a i l y g r o w t h w i t h o u t f r e q u e n t d i s r u p t i o n o f f i s h f e e d i n g . P a r t t h r e e e x a mines t h e g r o w t h p a t t e r n s on t h e o t o l i t h of t h e e n c l o s e d f i s h and i n v e s t i g a t e s t h e r e l a t i o n s h i p between d a i l y o t o l i t h growth i n c r e m e n t s and d a i l y z o o p l a n k t o n abundance. 63 PART THREE Growth P a t t e r n s on t h e O t o l i t h s of t h e E n c l o s e d F i s h R e c e n t s t u d i e s have r e v e a l e d t h e e x i s t e n c e o f d a i l y g r o w t h r i n g s i n t h e o t o l i t h s o f many f i s h s p e c i e s ( P a n n e l l a 1971; B r o t h e r s e t a l . 1976; S t r u s a k e r and Uchiyama 1976; T a u b e r t and C o b l e 1977; Barkman 1978; and W i l s o n and L a r k i n 1980). As y e t ' n o s t u d y has a t t e m p t e d t o r e l a t e t h e s e d a i l y growth i n c r e m e n t s t o d a i l y c h a n g e s i n e n v i r o n m e n t a l f a c t o r s . The f o l l o w i n g s e c t i o n d e s c r i b e s methods p e r t i n e n t t o t h e a n a l y s i s of t h e v a r i o u s g r o w t h p a t t e r n s on t h e o t o l i t h s of t h e j u v e n i l e c h i n o o k salmon. METHODS On 5 May 1980 a p p r o x i m t e l y 700 j u v e n i l e c h i n o o k salmon were t r a n s p o r t e d from C a p i l a n o H a t c h e r y t o P a t r i c i a Bay on V a n c o u v e r I s l a n d . T h e r e t h e y were r e t a i n e d i n a h o l d i n g t a n k u n t i l 19 May when 220 were removed t o be r e a r e d i n t h e o f f s h o r e e n c l o s u r e s u n t i l 29 J u n e . The r e s t of t h e f i s h r e m a i n e d i n t h e h o l d i n g t a n k u n t i l t h e y were s a c r i f i c e d on 5 J u n e . The f i s h from t h e h o l d i n g t a n k were p r e s e r v e d by f r e e z i n g . The e n c l o s e d f i s h were f i x e d i n f o r m a l i n t h e n r i n s e d w i t h f r e s h w a ter f o r 24 h o u r s and p r e s e r v e d i n 95% a l c o h o l . A s m a l l random sample o f 20 f i s h f r o m t h e e n c l o s u r e s , . and 64 10 f i s h s a c r i f i c e d on 5 June were u s e d f o r t h e o t o l i t h a n a l y s i s . The s a g i t t a e were removed from e a c h f i s h and s e n t t o D r . Edward B r o t h e r s a t C o r n e l l U n i v e r s i t y . T h e r e t h e o t o l i t h s were g r o u n d and p h o t o g r a p h e d u s i n g t h e methods d e s c r i b e d i n B r o t h e r s e t a l . ( 1 9 7 6 ) . Dr. B r o t h e r s s e l e c t e d t h e c l e a r e s t o t o l i t h p i c t u r e s and l a b e l l e d t h e r i n g s on e a c h p h o t o g r a p h t h a t were, i n h i s o p i n i o n , r e p r e s e n t a t i v e of d a i l y g r o w t h r i n g s . U s i n g a s t e r e o m i c r o s c o p e and a s t a g e m i c r o m e t e r , t h e t h i c k n e s s o f e a c h d a y ' s growth i n c r e m e n t was measured from t h e s e p i c t u r e s . P r i m a r y e m p hasis was p l a c e d on m e a s u r i n g d a i l y g r o w t h i n c r e m e n t s l a i d down when . t h e f i s h were i n t h e o f f s h o r e e n c l o s u r e s . Measur i n q D a i l y I n c r e m e n t s I t i s c l e a r from most of t h e o t o l i t h p i c t u r e s t h a t m e a s u r i n g d a i l y g r o w t h i n c r e m e n t s c a n be a d i f f i c u l t and o f t e n t e n u o u s p r o c e s s . Some of t h e d i f f i c u l t i e s e x p e r i e n c e d a r e l i s t e d b e low: (1) Where does one growth r i n g s t o p and t h e n e x t s t a r t ? (2) What p a r t of t h e d a i l y mark r e p r e s e n t s t r u e growth; t h e t h i c k n e s s of t h e d a r k s e c t i o n ; t h e t h i c k n e s s of t h e l i g h t s e c t i o n ; or t h e i r combined t h i c k n e s s ? (3) How.can one d i s t i n g u i s h between d a i l y and s u b - d a i l y r i n g s ? S i n c e t h e r e a r e no c l e a r a n s w e r s t o t h e above q u e s t i o n s , t h e f o l l o w i n g a p p r o a c h was f o l l o w e d . The d i s t a n c e between t h e c e n t e r o f t h e d a r k e s t p o r t i o n o f two a d j a c e n t d a i l y g r o w t h r i n g s , l a b e l l e d as s u c h by D r . B r o t h e r s , was m e a s u r e d . 65 In c e r t a i n a r e a s of e a c h o t o l i t h , i t , was i m p o s s i b l e t o d i s t i n g u i s h any c l e a r change i n r i n g s p a c i n g . In t h e s e a r e a s , t h e g r o w t h r i n g s were c o n s i d e r e d t o be t h e same d i s t a n c e a p a r t ( s e e f l a t a r e a s o f g r a p h s i n F i g . 17). The r e l a t i v e i n c r e m e n t t h i c k n e s s m e a s u r e d i n o t h e r p a r t s o f t h e o t o l i t h d e p i c t a r o u g h a p p r o x i m a t i o n of t h e m a g n i t u d e o f t h e change i n r i n g s p a c i n g . RESULTS D a i l y Growth R i n g s Of t h e f i s h t h a t were s a c r i f i c e d on 5 J une 1980, s e v e r a l were examined t o d e t e r m i n e t h e number of g r o w th r i n g s w h i c h had been l a i d down on t h e i r o t o l i t h s p r i o r t o t h e s t a r t of t h e e x p e r i m e n t . D r . B r o t h e r s was a b l e t o c o u n t a p p r o x i m a t e l y 197 r i n g s on t h e s e o t o l i t h s . A c c o r d i n g t o C a p i l a n o H a t c h e r y r e c o r d s , t h e s e f i s h were moved from t h e i r i n c u b a t i o n t r a y s t o t h e r e a r i n g t r o u g h s on 20 November 1979. The i n t e r v a l between t h e s e two d a t e s i s 199 d a y s . W i l s o n and L a r k i n (1980) a l s o o b s e r v e d d a i l y r i n g p a t t e r n s i n t h e s a g i t t a e of c h i n o o k s a l m o n . Growth P a t t e r n s on t h e S a g i t t a e P h o t o g r a p h s of s a g i t t a e f r o m s i x f i s h had a c o n t i n u o u s r e c o r d from 19 May t o 14 J u n e . In a l l of t h e s e f i s h , t h e p o r t i o n o f t h e o t o l i t h l a i d down f r o m 15 June t o 29 June had been e r o d e d by c h e m i c a l f i x e r . Even a s h o r t e x p o s u r e t o b u f f e r e d f o r m a l i n 66 i— 3-° I— 3 - ° cr I I I 1 I I I I I I I I I I I I I I I I ! i I I : I I 19 20 21 22 23 24 25 26 27 26 29 30 31 I 2 3 4 5 6 7 6 9 10 11 i2 13 14 MAT JUNE I I I I I I I I I I I I I I I I I I I I I I I 192021 22 2324 2S 26 27 26 29 30 31 1 2 3 4 : 6 7 6 9 10 11 12 13 14 MAT JUNE r _ 5.0. I I I I l l I I I I I I I I I I I i I 1 I I i I : i i 19 20 21 22 23 2 4 25 26 27 28 29 30 31 1 2 3 4 5 6 7 8 9 1011 12 13 14 MAY JUNE i— s - ° I I I I I I I I I I I I I I I I I I I I | | | | | | | 192O21 22232425262726293031 I 2 3 4 5 6 7 6 9 10 I I 12 13 14 MAT JUNE £ 7.0 I— » •» . I I I I I I I I I I I I I I I I I I 192021 22 23242S2627 2829 30 31 I MAT 7 8 9 10 II 12 13 14 JUNE I- S-°. ! ! J i i i i i i I.I M i i i i i i i i i i-1 i 192021 22 2324 25 26 27 28293031 I MAT 5 C 7 6 9 10 I I 12 1 3 1 4 JUNE F i g u r e 17. The p a t t e r n o f d a i l y g r o w t h i n c r e m e n t s d e r i v e d f r o m t h e s a g i t t a e o f s i x f i s h r a i s e d i n t h e e x p e r i m e n t a l e n c l o s u r e s . 67 w i l l d e s t r o y some p a r t o f t h e o t o l i t h r e c o r d . F i g u r e 17 shows t h e g r o w t h p a t t e r n s o b t a i n e d from t h e o t o l i t h s of t h e s e s i x f i s h . T h e s e g r o w t h p a t t e r n s were a n a l y s e d w i t h r e s p e c t t o t e m p e r a t u r e and z o o p l a n k t o n d a t a from t h e o f f s h o r e e n c l o s u r e s ( F i g . 1 8 ) . The t e m p e r a t u r e d a t a r e p r e s e n t s t h e mean w a t e r t e m p e r a t u r e i n t h e t o p 12 m e t e r s d e r i v e d from b a t h i t h e r m o g r a p h r e c o r d s . The z o o p l a n k t o n - d a t a a r e t h e c o n c e n t r a t i o n o f medium and l a r g e z o o p l a n k t o n measured o u t s i d e t h e e x p e r i m e n t a l e n c l o s u r e s . T a b l e 7 i s t h e c o r r e l a t i o n m a t r i x of t h e f i s h g r o w t h i n c r e m e n t d a t a , t e m p e r a t u r e d a t a , and z o o p l a n k t o n d a t a . Most o f t h e f i s h have g r o w t h p a t t e r n s t h a t a r e h i g h l y c o r r e l a t e d w i t h t h o s e of t h e o t h e r f i s h , t h e e x c e p t i o n b e i n g f i s h "D" w h i c h i s o n l y ^ m o d e r a t e l y c o r r e l a t e d w i t h i t s p e e r s . The g r o w t h p a t t e r n s i n t h r e e f i s h (A4,A10,B8) a r e h i g h l y s i g n i f i c a n t l y c o r r e l a t e d ( p < . 0 l ) w i t h t h e t e m p e r a t u r e d a t a , w h i l e o n l y one f i s h (D) i s s i m i l a r l y c o r r e l a t e d w i t h t h e z o o p l a n k t o n d a t a . The r e m a i n i n g two f i s h a r e 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 e i t h e r d a t a s e t . T h e s e r e s u l t s s u g g e s t t h a t a f u n c t i o n . i n c l u d i n g b o t h t e m p e r a t u r e and z o o p l a n k t o n d a t a may more a c c u r a t e l y p r e d i c t o t o l i t h d a i l y g r o w t h i n c r e m e n t s . A m u l t i p l e r e g r e s s i o n was c o n d u c t e d u s i n g t h e f o l l o w i n g r e l a t i o n : OGI = c*RTN*TEMP + d*TEMP + e where "OGI" i s t h e d a i l y o t o l i t h g r o w t h i n c r e m e n t ; "RTN" i s t h e 68 19 20 21 22 23 24 25 26 27 28 2 9 30 31 I 2 3 4 5 6 7 8 9 10 II 12 13 l« MRY JUNE i— »•». 13 23 2] 22 23 24 23 26 2 7 2 6 29 30 3! I 2 3 4 S I 7 8 9 10 II 12 13 |4 MRY JUNE MCDIUn AND Lfi^ CE lOCPLfilJiUO* I I I I I I I I I I I I I I I I 192021 2223242520 2 7 28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 MAY JUNE F i g u r e 18. Comparison of the mean growth i n c r e m e n t s w i t h water t e m p e r a t u r e and z o o p l a n k t o n abundance d a t a . 69 A2 1 A4 .27 1 A5 .32 . 56 1 A1 0 .49 .49 .88 1 B8 .45 .57 .59 .64 1 D . 1 6 .51 .43 .33 . 1 7 1 Zoo .30 .24 .01 -.01 -.01 .72 1 Temp .33 .35 .65 .76 .74 -.03 -.23 A2 A4 A5 A1 0 B8 D Zoo e n c l o s e d f i s h d a t a T a b l e 7. The c o r r e l a t i o n m a t r i x f o r t h e d a i l y g r o w t h i n c r e m e n t s o f s i x f i s h (A2,A4,A5,A10,B8,D); t e m p e r a t u r e d a t a (Temp); z o o p l a n k t o n d a t a ( Z o o ) ; and a c o m b i n a t i o n o f t e m p e r a t u r e and z o o p l a n k t o n d a t a (T & Z ) . V a l u e s above .44 a r e s i g n i f i c a n t (p<.05) and v a l u e s above .56 a r e h i g h l y s i g n i f i c a n t ( p < . 0 l ) . 70 p e r c e n t of t h e maximum r a t i o n a c h i e v e d a t a s p e c i f i c z o o p l a n k t o n c o n c e n t r a t i o n , e s t i m a t e d u s i n g t h e r e l a t i o n s h i p shown i n F i g u r e 15; and "TEMP" i s t h e mean water t e m p e r a t u r e i n t h e t o p 12 m e t e r s , " c " , "d", and "e" a r e c o e f f i c i e n t s e s t i m a t e d by t h e m u l t i p l e r e g r e s s i o n . The above model was b a s e d on t h e a s s u m p t i o n s t h a t o t o l i t h g r o w t h was r e l a t e d t o f i s h g r o w t h , and t h a t t h e f i s h a c h i e v e d c l o s e t o t h e i r maximum r a t i o n d u r i n g t h e weeks d e p i c t e d i n t h e o t o l i t h r e c o r d . F i s h g r o w t h , as d e s c r i b e d e a r l i e r , was f o o d consumed minus m e t a b o l i c l o s s e s . The "RTN*TEMP" t e r m r e p r e s e n t s t h e f o o d consumed, s i n c e maximum r a t i o n was d i r e c t l y r e l a t e d t o t e m p e r a t u r e ( B r e t t 1971). The "TEMP" t e r m r e p r e s e n t s t h e m e t a b o l i c l o s s e s , s i n c e m e t a b o l i s m a l s o i n c r e a s e s w i t h t e m p e r a t u r e ( B r e t t 1971). A l e a s t s q u a r e s r e g r e s s i o n of a l l t h e o t o l i t h d a t a r e v e a l e d t h a t t e m p e r a t u r e and r a t i o n o n l y e x p l a i n 14% of t h e v a r i a n c e i n t h e d a i l y o t o l i t h g r o w t h i n c r e m e n t ; and t e m p e r a t u r e a p p e a r s t o be r e s p o n s i b l e f o r t h e b u l k o f t h e e x p l a i n e d v a r i a n c e . The c o e f f i c i e n t of t e m p e r a t u r e "d" has a v e r y low p r o b a b i l i t y o f b e i n g z e r o (p<.000l) w h i l e t h e c o e f f i c i e n t of t h e r a t i o n -t e m p e r a t u r e t e r m " c " was' not s i g n i f i c a n t l y d i f f e r e n t from z e r o . DISCUSSION T h e s e r e s u l t s a r e n o t s u r p r i s i n g i n l i g h t of r e c e n t r e s e a r c h on s a l m o n i d o t o l i t h s . S e v e r a l a u t h o r s have s u g g e s t e d t h a t t e m p e r a t u r e i s one o f t h e most i m p o r t a n t f a c t o r s a f f e c t i n g t h e d e v e l o p m e n t of g r o w t h r i n g s i n f i s h o t o l i t h s ( e g . T a u b e r t 71 and C o b l e 1977; B r o t h e r s pers.comm.). The p h o t o g r a p h s shown i n F i g u r e 19 p r o v i d e f u r t h e r s u p p o r t f o r t h i s r e l a t i o n s h i p . T h e s e p h o t o g r a p h s d e p i c t two a b r u p t c h a n g e s i n t h e s p a c i n g o f o t o l i t h r i n g s w h i c h were c o n s i s t e n t i n e v e r y f i s h examined. The f i r s t anamoly ( p o i n t 1) o c c u r r e d s e v e r a l d a y s b e f o r e the. f i s h were removed from t h e h a t c h e r y . I f t h e g r o w t h r i n g s on t h e s e o t o l i t h s a r e i n f a c t d a i l y marks, p o i n t 1 would r e p r e s e n t t h e g r o w th i n c r e m e n t f o r A p r i l 26 o r 27. On A p r i l 27, t h e o p e r a t o r s a t C a p i l a n o H a t c h e r y r e c o r d e d a anamalous 0.7 °C r i s e i n w a ter t e m p e r a t u r e . The day t o day change i n t e m p e r a t u r e i s u s u a l l y l e s s t h a n 0.2 °C. The s e c o n d p o i n t l a b e l l e d on F i g u r e 19 i n d i c a t e s t h e end of h a t c h e r y g r o w t h . The g r o w t h r i n g s l a i d down w h i l e t h e f i s h were i n t h e h o l d i n g t a n k a r e s i g n i f i c a n t l y f a r t h e r a p a r t t h a n t h o s e r e p r e s e n t a t i v e of h a t c h e r y g r o w t h . A g a i n t h i s i s p r o b a b l y l a r g e l y a t t r i b u t a b l e t o t e m p e r a t u r e . The water t e m p e r a t u r e i n t h e h a t c h e r y was a r o u n d 6.8 °C w h i l e t h e water t e m p e r a t u r e i n t h e h o l d i n g t a n k was a b o u t 14 °C. T h r o u g h o u t t h e p e r i o d shown i n F i g u r e 19, t h e f i s h were f e d an e x c e s s r a t i o n of Oregon m o i s t p e l l e t s . The above a n a l y s e s and o b s e r v a t i o n s s u g g e s t t h a t d a i l y g r o w t h i n c r e m e n t s r e f l e c t c h a n g e s i n t e m p e r a t u r e more c l o s e l y t h a n t h e y r e f l e c t day t o day v a r i a t i o n i n f o o d abundance; however, t h e mean r e l a t i v e g r o w t h i n c r e m e n t s f o r s i x f i s h ( F i g . 18) s u g g e s t t h a t e x t r e m e s i n f o o d abundance have a s i g n i f i c a n t and c o n s i s t e n t e f f e c t on t h e s p a c i n g of growth r i n g s . T h e s e h i g h f o o d c o n c e n t r a t i o n s , w h i c h p r o b a b l y t r a n s l a t e 72 F i g u r e 19. Sample p h o t o g r a p h s o f t h e s a g i t t a e from h a t c h e r y and t a n k r e a r e d f i s h . 74 i n t o h i g h r a t i o n , a p p a r e n t l y a f f e c t o t o l i t h g r o w t h f o r o n l y a s h o r t p e r i o d of t i m e . T h i s s t u d y has q u a n t i f i e d a r e l a t i o n s h i p between t h e growth of a p e l a g i c f e e d i n g f i s h and f o o d abundance i n t h e water c o l u m n . However, an a t t e m p t t o e s t a b l i s h a r e l a t i o n s h i p between o t o l i t h g r o w t h i n c r e m e n t s and f o o d abundance was i n c o n c l u s i v e . I t a p p e a r s t h a t o t o l i t h growth i s v e r y s e n s i t i v e t o s m a l l c h a n g e s i n t e m p e r a t u r e w h i c h may p a r t i a l l y or c o m p l e t e l y mask any r e l a t i o n s h i p between o t o l i t h g r o w t h and f o o d a b u n d a n c e . These r e s u l t s i n d i c a t e t h a t w a t e r t e m p e r a t u r e would have t o \~ be kept c o n s t a n t i n o r d e r t o e s t a b l i s h any c l o s e r r e l a t i o n s h i p between f o o d abundance and o t o l i t h g r o w t h r i n g s . T h i s r e l a t i o n s h i p w ould be u s e f u l o n l y i f t h e r e i s a c l e a r c o n n e c t i o n between t h e d a i l y growth of t h e o t o l i t h and t h e d a i l y growth of t h e f i s h . To t h i s a u t h o r ' s knowledge, t h i s c o n n e c t i o n has not been e s t a b l i s h e d . 75 SUMMARY AND CONCLUSIONS Mesh e n c l o s u r e s were d e s i g n e d t o i n v e s t i g a t e j u v e n i l e f i s h g r o w t h and f e e d i n g i n a s e m i - n a t u r a l e n v i r o n m e n t . The g e n e r a l r e s u l t s d e m o n s t r a t e d t h a t t h e c o n c e n t r a t i o n o f z o o p l a n k t o n i n s i d e t h e e n c l o s u r e s were s i m i l a r t o t h e c o n c e n t r a t i o n s i n t h e s u r r o u n d i n g w a t e r s . However, t h e s a m p l i n g method u s e d was not c a p a b l e o f d e t e r m i n i n g t h e s p a c i a l a g g r e g a t i o n of p r e y w i t h i n t h e 10 meter water c o l u m n . The s e c o n d s e c t i o n d e s c r i b e d t h e r e l a t i o n s h i p between mean water column z o o p l a n k t o n c o n c e n t r a t i o n and f i s h g rowth r a t e s , and e s t i m a t e d p a r a m e t e r v a l u e s f o r a f u n c t i o n a l r e s p o n s e e q u a t i o n . T h e r e were g e n e r a l t r e n d s i n z o o p l a n k t o n abundance w i t h i n e a c h week which.were r e f l e c t e d i n t h e n e t g r o w t h of t h e e n c l o s e d f i s h . F i g u r e s 11 t h r o u g h 14 s u g g e s t t h a t f i s h g r o w t h was d i r e c t l y r e l a t e d t o t h e abundance of z o o p l a n k t o n g r e a t e r t h a n 1.5mm i n body l e n g t h . F i g u r e 15 d e p i c t e d a f u n c t i o n a l r e s p o n s e c u r v e f o r j u v e n i l e salmon f e e d i n g on z o o p l a n k t o n between 1.5 and 4.5mm i n body l e n g t h . The minimum r a t e of s u c c e s s f u l s e a r c h f o r t h e j u v e n i l e salmon was e s t i m a t e d t o be 2.0m 3/hr f o r t h i s g e n e r a l p r e y c a t e g o r y . The stomach c o n t e n t d a t a and a s s o c i a t e d p r e y d e n s i t i e s were u s e d t o q u a n t i f y t h e p r e d a t o r s r e l a t i v e a b i l i t y ( o r s e l e c t i o n ) t o c a p t u r e d i f f e r e n t p r e y i t e m s . R e l a t i v e r a t e s of s u c c e s s f u l s e a r c h were e s t i m a t e d f o r e a c h p r e y g r o u p by f i t t i n g t h e d a t a t o a m u l t i s p e c i e s d i s c e q u a t i o n . T h i s a n a l y s i s r e v e a l e d t h a t j u v e n i l e salmon a p p e a r t o s e a r c h more e f f e c t i v e l y f o r l a r g e h i g h c o n t r a s t p r e y i t e m s . The 76 r e l a t i v e r a t e s of s u c c e s s f u l s e a r c h and t h e l a c k o f c o v a r i a n c e between p r e y g r o u p s p r o v i d e d f u r t h e r s u p p o r t t o my c o n t e n t i o n t h a t t h e e n c l o s e d s a lmons' minimum r a t e of s u c c e s s f u l s e a r c h was 2.0m 3/hr. R e l a t i o n s h i p s d e r i v e d i n r e c e n t f i s h f e e d i n g s t u d i e s made i t p o s s i b l e t o o b t a i n an i n d e p e n d e n t e s t i m a t e t h e r a t e of s u c c e s s f u l s e a r c h f o r j u v e n i l e s a l m o n . These s t u d i e s s u g g e s t e d t h a t a v i s u a l l y f e e d i n g j u v e n i l e salmon s h o u l d be a b l e t o s u c c e s s f u l l y s e a r c h a t l e a s t 2.7m 3/hr f o r 3.0mm p r e y . The o t o l i t h a n a l y s i s p r e s e n t e d i n s e c t i o n 3 was an a t t e m p t t o s t r e n g t h e n t h e r e l a t i o n s h i p shown i n F i g u r e 15. I t was p o s s i b l e t h a t d a i l y g r o w t h i n c r e m e n t s on a salmon o t o l i t h c o u p l e d w i t h d a i l y e s t i m a t e s of f o o d abundance, would p r o v i d e a more a c c u r a t e e s t i m a t e of a j u v e n i l e s a l mon's f u n c t i o n a l r e s p o n s e . Such a r e l a t i o n s h i p i s b a s e d on t h e a s s u m p t i o n t h a t d a i l y o t o l i t h g rowth i s h i g h l y c o r r e l a t e d w i t h d a i l y f i s h g r o w t h , and o t o l i t h g r o w t h i s not g r e a t l y a f f e c t e d by o t h e r e n v i r o n m e n t a l f a c t o r s . 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D a i l y r i n g s i n o t o l i t h s of t h r e e s p e c i e s of L e p o m i s and T i l a p i a mossambica . J . F i s h . Res. B o a r d Can. 34: 332-340. Wankowski, J.W.J. 1979. M o r p h o l o g i c a l l i m i t a t i o n s , p r e y s i z e s e l e c t i v i t y , and g r o w t h r e s p o n s e of j u v e n i l e A t l a n t i c s a l m o n . J . F i s h B i o l o g y 14: 89-100. Wankowski, J.W.J, and J . E . T h o r p e . 1979. The r o l e of f o o d p a r t i c l e s i z e i n t h e g r o w t h of j u v e n i l e A t l a n t i c s a l m o n . J . F i s h B i o l o g y 14: 351-370. Ware, D.M. 1972. P r e d a t i o n by r a i n b o w t r o u t : t h e i n f l u e n c e of h u n g e r , p r e y d e n s i t y , and p r e y s i z e . J . F i s h . Res. B o a r d Can. 29: 1193-1201. Ware, D.M. 1973. R i s k of e p i b e n t h i c p r e y t o p r e d a t i o n by r a inbow t r o u t . J . F i s h . Res. B o a r d Can. 30: 787-797. Ware, D.M. 1975. Growth, m e t a b o l i s m and o p t i m a l swimming speed of a p e l a g i c f i s h . J . F i s h . Res. B o a r d Can. 32: 33-41. Ware, D.M. 1978. B i o e n e r g e t i e s o f p e l a g i c f i s h : t h e o r e t i c a l c hange i n swimming s p e e d and r a t i o n w i t h body s i z e . J.-F i s h . Res. B o a r d Can. 35: 220-228 82 Warren, C.E., and G.E. D a v i s . 1966. L a b o r a t o r y s t u d i e s on t h e f e e d i n g , b i o e n e r g e t i e s and g r o w t h o f f i s h , p. 175-214. In S.D. G e r k i n g (ed.) Symposium: t h e b i o l o g i c a l b a s i s o f f r e s h w a t e r f i s h p r o d u c t i o n . John W i l e y and Sons, L o n d o n . 495 pp. W i b o r g , R.F. 1948. I n v e s t i g a t i o n s on c o d l a r v a e i n t h e c o a s t a l w a t e r s of n o r t h e r n Norway. O c c u r e n c e o f c o d l a r v a e , and o c c u r e n c e o f f o o d o r g a n i s m s i n t h e stomach c o n t e n t s and i n t h e s e a . Rep. Norw. F i s h . Mar. I n v e s t . V o l . 9: 5-57. W i l s o n , K.H. and P.A. L a r k i n . 1980. D a i l y g r o w t h r i n g s i n t h e o t o l i t h s of j u v e n i l e s o c k e y e salmon. Can. J . F i s h , and A q u a t . S c i . 37: 1495-1498. W i n b e r g , G.G. 1956. R ate o f m e t a b o l i s m and f o o d r e q u i r e m e n t s of f i s h e s . B e l o r u s s i a n S t a t e U n i v e r s i t y , M i n s k . 251 p. F i s h . Res. B o a r d Can. T r a n s l . S e r . No. 194. Z a r e t , T.M. 1972. P r e d a t o r s , p o l y m o r p h i s m i n t h e L i m n o l . O c e a n o g r . 17: i n v i s i b l e p r e y and n a t u r e o f c l a d o c e r a ( c l a s s C r u s t a c e a ) . 171-184. 83 APPENDICIES I . HANDLING THE FISH C h i n o o k salmon from t h e C a p i l a n o h a t c h e r y i n N o r t h V a n c u v e r , B r i t i s h C o l u m b i a were u s e d as t h e e x p e r i m e n t a n i m a l . A l l t h e s e 5-6 g f i s h had been r e a r e d f o r 6 months on Oregon M o i s t P e l l e t s (OMP) p r i o r t o b e i n g t r a n s f e r r e d t o a f r e s h water h o l d i n g t a n k a t t h e Ocean S c i e n c e s I n s t i t u t e a t P a t r i c i a Bay. The young salmon r e m a i n e d i n t h i s 3.2m3 h o l d i n g tank f o r two weeks. D u r i n g t h i s t i m e , t h e f i s h were f e d an e x c e s s r a t i o n of 4 mm OMP and f r e s h l y c a u g h t z o o p l a n t o n w i t h t h e e x c e p t i o n of two i n t e r v a l s , t h e 48 h o u r s b e f o r e v a c c i n a t i o n and t h e 48 h o u r s b e f o r e w e i g h i n g and b r a n d i n g . T r a n s p o r t The f i s h were t r a n s p o r t e d i n 70 l i t r e s of h a t c h e r y water i n f i v e l a r g e g a r b a g e c a n s l i n e d w i t h p l a s t i c g a r b a g e bags. T h r e e OTABS were p l a c e d i n e a c h g a r b a g e c an t o p r o v i d e s u f f i c i e n t oxygen f o r 100 f i n g e r l i n g s . T h e r e was v e r y h i g h m o r t a l i t y i n two of t h e c o n t a i n e r s b e c a u s e o f o v e r c r o w d i n g r e s u l t i n g i n oxygen d e p l e t i o n . The t o t a l m o r t a l i t y was 153 f i s h o u t o f a p p r o x i m a t e l y 700 j u v e n i l e c h i n o o k s a l m o n . 84 V a c c i n a t i o n F i s h s h o u l d be s t a r v e d f o r 48 h o u r s p r i o r t o v a c c i n a t i o n . I n o r d e r t o v a c c i n a t e t h e f i s h a s soon as p o s s i b l e , t h e f i s h were not f e d t h e f i r s t two days t h a t t h e y were i n t h e h o l d i n g t a n k a t P a t r i c i a Bay. An i m m e r s i o n method was u s e d t o g e t t h e v i b r i o v a c c i n e i n t o t h e f i s h . The f i s h were moved i n t o a s m a l l h o l d i n g t a n k where s e v e r a l c o u l d be e a s i l y removed and v a c c i n a t e d . A s h a l l o w c o n t a i n e r was d e s i g n e d t o be t h e w e l l a i r e a t e d v a c c i n e b a t h . The b a t h c o n t a i n e d 50 ml of v i b r i o v a c c i n e ( H i v a x ) m i x e d w i t h 450 ml of f r e s h water a t 14°C. A s m a l l d i p n e t was u s e d t o s e l e c t 10-15 f i s h from t h e s m a l l h o l d i n g t a n k . The f i s h were h e l d i n t h e a i r f o r 10 s e c o n d s ; dunked i n t h e v a c c i n e s o l u t i o n f o r 10 s e c o n d s ; and r e t u r n e d t o t h e l a r g e t a n k t o r e c o v e r . In most c a s e s r e c o v e r y was v e r y r a p i d and t h e r e was no m o r t a l i t y a s s o c i a t e d w i t h t h i s v a c c i n a t i o n p r o c e d u r e . The f i s h were a l l o w e d an i m m u n i z a t i o n p e r i o d of 8 d a y s b e f o r e s a l t water was i n t r o d u c e d i n t o t h e h o l d i n g t a n k . The f r e s h water was r e p l a c e d w i t h 28 p a r t s / t h o u s a n d s a l t water i n a b o u t 4 h o u r s and not a s i n g l e f i s h d i e d . W e i g h i n g and M e a s u r i n g t h e F i s h The f i r s t s t e p was t o a n e s t h e t i z e 4 f i s h by p l a c i n g them i n a s o l u t i o n c o n t a i n i n g 15-20 ml o f 4 m e t h y l 2 p e n t a n o l and 500 ml of s a l t w a t e r . As soon as t h e f i r s t f i s h r o l l e d o n t o i t s s i d e and o p e r c u l u m movement s l o w e d , i t was removed, r o l l e d o v e r l e n s e 85 p a p e r t o remove s u r f a c e m o i s t u r e , and p l a c e d on a M e t i e r E l e c t r o n i c B a l a n c e . I t s w e i g h t was t h e n r e c o r d e d from t h e d i g i t a l r e a d o u t and f o r k - l e n g t h was measured u s i n g a s p e c i f i c a l l y d e s i g n e d measurement t r a y . The measurement t r a y and f i s h were s u b s e q u e n t l y d i p p e d i n a w e l l a e r a t e d r e c o v e r y b u c k e t where t h e f i s h would r e m a i n u n c o n s c i o u s f o r a p e r i o d of 30-60 s e c o n d s . T h i s method r e d u c e d t h e n e c e s s a r y h a n d l i n g of t h e f i s h t o a minimum and i n e v e r y c a s e t h i s p r o c e s s had no o b s e r v a b l e d e t r i m e n t a l e f f e c t on t h e f i s h . B r a n d i n g t h e F i s h D u r i n g t h e i n i t i a l w e i g h i n g and m e a s u r i n g of t h e f i s h , e a c h i n d i v i d u a l was marked w i t h a d i s t i n c t b r a n d . The b r a n d c o n s i s t e d of p a i r s of b a r s "|" or V s "V" o r i e n t e d a t v a r i o u s d i r e c t i o n s i n two of f o u r q u a d r a n t s on one s i d e of t h e f i s h . The f o u r q u a d r a n t s were d e l i n i a t e d by two p h y s i c a l s t r u c t u r e s : t h e d o r s a l f i n and t h e l a t e r a l l i n e . F o r example, one q u a d r a n t would be a n t e r i o r t o t h e d o r s a l f i n and below t h e l a t e r a l l i n e . B o t h b r a n d s were a d m i n i s t e r e d t o t h e same s i d e of t h e i n d i v i d u a l . T h e r e were 6 p o s s i b l e s e t s o f q u a d r a n t s ; 10 p a i r s of b r a n d o r i e n t a t i o n s ; 2 forms of b r a n d s ; and o f c o u r s e , 2 s i d e s t o e v e r y f i s h . The b r a n d i n g implement c o n s i s t e d of a c o p p e r w i r e p r o t r u d i n g from a s m a l l mass of c o p p e r a t t a c h e d t o a wooden h a n d l e . The c o p p e r end was d i p p e d i n a thermos o f l i q u i d n i t r o g e n and t h e n a p p l i e d t o t h e f i s h i n t h e a p p r o p r i a t e q u a d r a n t s . 86 T h i s method of d i s t i n g u i s h i n g e a c h i n d i v i d u a l p r o v e d t o be v e r y s u c c e s s f u l . B r a n d s were e a s i l y r e a d a f t e r 1-2 days and t h e marks d i d not a p p e a r t o e f f e c t t h e f i s h e s ' a b i l i t y t o swim or f e e d . I I . HANDLING THE NETS Deployment o f N e t s The p r o t e c t i v e n e t was t h e f i r s t t o be s e t i n t o p o s i t i o n . The t o p o f t h e n e t was l a s h e d t o t h e f l o t a t i o n p l a t f o r m a t 18 p o s i t i o n s r o u g h l y 2 m a p a r t . A l e a d l i n e and 4 c o r n e r w e i g h t s were a t t a c h e d t o t h e b o t t o m of t h e n e t . The 20 kg c o r n e r w e i g h t s were l o w e r e d u n t i l t h e n e t took on t h e d e s i r e d shape. T h e i r s u p p o r t i n g r o p e s were t h e n t i e d t o t h e f l o t a t i o n p l a t f o r m . T w e l v e more w e i g h t e d r o p e s had t o be p o s i t i o n e d t o h o l d t h e s i d e s o f t h e p r o t e c t i v e n e t i n p l a c e . T h e s e r o p e s were p o s i t i o n e d by t y i n g one end of t h e heavy n y l o n r o p e s t o t h e f l o t a t i o n p l a t f o r m and t o s s i n g t h e r e s t o f t h e rope i n t o t h e p r o t e c t i v e n e t . S u b s q u e n t l y , w i t h t h e h e l p o f t h r e e o t h e r d i v e r s , a l l t h e r o p e s were p u l l e d t h r o u g h t h e bo t t o m of t h e p r o t e c t i v e n e t and a t t a c h e d t o 20 kg w e i g h t s p r o v i d e d from t h e s u r f a c e on e a s i l y d e t a c h e d r o p e s . The f o u r e x p e r i m e n t a l e n c l o s u r e s were a l l d e p l o y e d u s i n g t h e same t e c h n i q u e . F i r s t , f o u r r o p e s were a t t a c h e d t o t h e t h r e e p o l y p i p e r i n g s t o s p a c e t h e r i n g s 4m a p a r t . S e c o n d , t h e r i n g s 87 and r o p e s were p l a c e d i n s i d e t h e mesh n e t s and t h e b o t t o m o f t h e n e t s t r e t c h e d t i g h t t o t h e b o t t o m o f t h e r i n g . N e x t , t h e whole e n c l o s u r e was l i f t e d i n t o a 4.8m aluminum b o a t and t r a n s p o r t e d t o t h e e x p e r i m e n t a l s i t e . T h e r e , f o u r w e i g h t s were a t t a c h e d t o t h e b o t t o m r i n g t o s p e e d up t h e s i n k i n g p r o c e s s , and t h e n e t was t r a n s f e r r e d p a r t l y i n t o a s m a l l r u b b e r b o a t i n s i d e t h e f l o t a t i o n r i n g . The n e t was s e c u r e d t o w a i t i n g g u i d e r o p e s and r e l e a s e d i n t o t h e w a t e r . The r o p e s a t t a c h e d t o t h e r i n g s of p o l y t u b i n g were s e c u r e d t o t h e g u i d e r o p e s once t h e e n c l o s u r e net was f u l l y e x t e n d e d . T h i s t r a n s f e r r e d most of t h e w e i g h t t o t h e g u i d e r o p e s , see F i g u r e 2. A s h o r t d i v e was n e c e s s a r y t o c h e c k on t h e shape and d e p t h of e a c h e n c l o s u r e and t o make t h e n e c e s s a r y a d j u s t m e n t s . D u r i n g t h e same d i v e t h e n e t s were t h o r o u g h l y i n s p e c t e d f o r b r o k e n mesh t h a t would p e r m i t t h e f i s h t o e s c a p e . C l e a n i n g t h e E n c l o s u r e s Two methods were u s e d t o c l e a n t h e e n c l o s u r e s . One method was d e s i g n e d t o remove moderate amounts of f o u l i n g from t h e t o p 4m o f mesh w i t h o u t r e m o v i n g t h e e n c l o s u r e from t h e w a t e r . The s e c o n d method was s u i t a b l e t o remove e x t e n s i v e f o u l i n g , w h e r e v e r i t o c c u r r e d , a f t e r r e m o v i n g t h e e n c l o s u r e . The m o d i f i e d p o o l c l e a n i n g a p p a r a t u s was u s e d t o c l e a n t h e mesh w i t h o u t r e m o v i n g t h e e n c l o s u r e s . A b r u s h , on t h e end o f t h e 4.8m h a n d l e , l o o s e n e d t h e f o u l i n g p h y t o p l a n k t o n w h i l e t h e pump s u c k e d t h e l o o s e n e d clumps of p h y t o p l a n k t o n t h r o u g h t h e vacuum t u b i n g and dumped i t o u t s i d e t h e f l o t a t i o n r i n g . 88 E x t e n s i v e b u i l d u p o f p h y t o p l a n k t o n on t h e mesh n e c e s s i t a t e d t h e r e m o v a l of e a c h e n c l o s u r e , one a t a t i m e , so t h e y c o u l d be t h o r o u g h l y c l e a n e d o u t o f t h e w a t e r . The e n c l o s u r e s were s u s p e n d e d from a l a r g e p i e r a t low t i d e w h i l e t h e f o u l i n g was removed by a c o m b i n a t i o n o f t h e f o l l o w i n g t e c h n i q u e s : (1) The m o d i f i e d p o o l c l e a n i n g a p p a r a t u s , minus t h e 4.8m h a n d l e , was u s e d t o b r u s h and s p r a y t h e f o u l i n g o f f t h e mesh; (2) The n e t was r a i s e d up and down t h r o u g h t h e w ater i n a w a s h i n g machine t y p e a c t i o n ; (3) The n e t was l e f t t o d r y on t h e p i e r o v e r n i g h t and d r i e d p h y t o p l a n k t o n was b r u s h e d o f f t h e n e x t m o r n i n g . E a c h e n c l o s u r e was removed and c l e a n e d once d u r i n g t h e e x p e r i m e n t a l p e r i o d . I t was p o s s i b l e t o remove b e t t e r t h a n 90% of t h e f o u l i n g by t h i s method. I I I . CALCULATION OF FISH GROWTH RATES Two methods were u s e d t o c a l c u l a t e t h e a v e r a g e d a i l y g r o w t h r a t e of t h e f i s h i n e a c h e n c l o s u r e e a c h weeks. B o t h models u s e d i t h e f o l l o w i n g f o r m u l a . GR = 100 X (LOGeGT - LOGeGt) / T In method 1, GT and Gt a r e t h e s i z e s o f an i n d i v i d u a l f i s h a t t h e end and t h e b e g i n n i n g of a week w i t h "T" d a y s . The e s t i m a t e d g r o w t h r a t e (GR) f o r e a c h i n d i v i d u a l c o u l d be combined t o e s t i m a t e t h e mean growth r a t e f o r t h e p o p u l a t i o n t h a t week.' The d i s a d v a n t a g e o f t h i s method i s o b v i o u s when v e r y few i n d i v i d u a l s a r e c a p t u r e d i n two s u c c e s s i v e weeks. F o r example, t h e e s t i m a t e f o r t h e a v e r a g e g r o w t h r a t e o f t h e f i s h i n t h e 9 mm 89 mesh enclosure during the second week is based on only 2 f i s h (Fig. 7).. In method 2, GT and Gt are the average sizes of the f i s h sampled at the end and the beginning of a weeks with "T" days. In t h i s case GR would be the, estimate of the average growth rate for the population that week. This method quickly revealed s i g n i f i c a n t sample bias. Some samples had predominantly larger or smaller than average f i s h . Therefore, i f smaller than average f i s h were sampled one week and larger than average f i s h were sampled the next week, the calculated growth rates would be biased upwards. An estimate of sample bias could be obtained by calcul a t i n g the average growth rate using the average i n i t i a l sizes of the f i s h sampled each week. The best estimate of the mean growth rate o f the population for each week was calculated by subtracting the growth rate a t t r i b u t a b l e to sample bias from the average growth rate estimated in method 2 (Fig. 7). 

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