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UBC Theses and Dissertations

Zooplankton resources and humpback whale (Megaptera novaeangliae) feeding ecology in South-East Alaska Dehalt, Annette Christiane 1986

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ZOOPLANKTON RESOURCES AND HUMPBACK WHALE (MEGAPTERA NOVAEANGLIAE) FEEDING ECOLOGY IN SOUTH-EAST ALASKA by ANNETTE CHRISTIANE DEHALT B.Sc. Texas A&M U n i v e r s i t y , 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT 0: THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e F a c u l t y o f Graduate S t u d i e s (The Department o f Oceanography) 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 the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA May, 1986 (c^ A n n e t t e C h r i s t i a n e D e h a l t , 1986 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I ag r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f (_/ C g _ ^ (A D(q tq(QU The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 Date A^)C']( l°l£L F . - f i ( 2 / 7 9 } ABSTRACT Recent p o p u l a t i o n changes on t h e S E - A l a s k a humpback whale (Megaptera n o v a e a n g l i a e ) f e e d i n g ground may be e x p l a i n e d as b e i n g p r i m a r i l y due t o l a r g e - s c a l e o c e a n o g r a p h i c v a r i a t i o n s t h a t l o c a l l y a f f e c t p l a n k t o n p r o d u c t i v i t y . I t i s s u g g e s t e d t h a t t h e 1978 whale d e c l i n e i n G l a c i e r Bay was due t o l o c a l i z e d n u t r i e n t l i m i t a t i o n caused by c l i m a t e ( E l N i ? i o ) - i n d u c e d changes i n t h i s f j o r d ' s c i r c u l a t o r y p a t t e r n . An assessment of z o o p l a n k t o n i c p r e y i n F r e d e r i c k Sound i n summer 1983 was i n t e g r a t e d i n t o a l o n g - t e r m m o n i t o r i n g p r o j e c t of t h e a r e a , and showed g e n e r a l l y s i m i l a r c o n d i t i o n s as t h e p r e v i o u s season. A s l i g h t i n c r e a s e i n t h e k r i l l p r o p o r t i o n o f p l a n k t o n swarms, s m a l l changes i n k r i l l s p e c i e s c o m p o s i t i o n , and the o c c u r r e n c e o f a S o u t h e r n - o r i g i n copepod s p e c i e s were the n o t a b l e e x c e p t i o n s . A comparison between z o o p l a n k t o n i c f e e d i n g and n o n - f e e d i n g t a r g e t s s u g g e s t e d e u p h a u s i i d biomass ( m a i n l y Thysanoessa r a s c h i i ) t o be t h e most l i k e l y s t i m u l u s f o r whale f e e d i n g a c t i v i t y . E x a m i n a t i o n o f humpback whale f e c a l m a t e r i a l p r o v e d a v a l u a b l e method t o i d e n t i f y d i e t a r y components. The l o c a l d e v e l o p m e n t a l p a t t e r n o f T. r a s c h i i was i n v e s t i -g a t e d w i t h r e g a r d t o i t s noted importance i n humpback whale d i e t . Dominant l i f e h i s t o r y s t a g e s found i n 1983 i n d i c a t e d s u b - o p t i m a l e n v i r o n m e n t a l c o n d i t i o n s , p o s s i b l y r e l a t e d t o i n c r e a s e d c o a s t a l warming. Three s u b - c o h o r t s were i d e n t i f i e d i n t h e s p r i n g spawning c o h o r t , and d e v e l o p m e n t a l t i m i n g appeared t o be c o r r e l a t e d w i t h the w h a l e s' m i g r a t o r y p a t t e r n . i i i TABLE OF CONTENTS Page A b s t r a c t .' i i T a b l e o f C o n t e n t s i i i L i s t of T a b l e s i v L i s t o f F i g u r e s v i Acknowledgements v i i INTRODUCTION 1 PART ONE: HUMPBACK WHALE POPULATION DECLINE IN GLACIER BAY 6 I . BACKGROUND 6 I I . ANALYSIS 8 A. C l i m a t i c C o n d i t i o n s . . 9 B. Water C i r c u l a t i o n 11 C. L o c a l P r o d u c t i v i t y 13 D. Whale F o r a g i n g 15 I I I . CONCLUSIONS 18 PART TWO: ZOOPLANKTONIC PREY IN FREDERICK SOUND 19 I . INTRODUCTION 19 I I . MATERIALS AND METHODS 21 A. F i e l d Techniques 21 B. L a b o r a t o r y Techniques 25 I I I . RESULTS AND DISCUSSION 29 A. Humpback Whale F e e d i n g C o n d i t i o n s i n 1983 29 1. P h y s i c a l E n v i r o n m e n t a l Parameters 29 2. A v a i l a b l e Z o o p l a n k t o n R e s o u r c e s . ; 31 a. Z o o p l a n k t o n C o m p o s i t i o n 31 b. Z o o p l a n k t o n Biomass 38 3. Z o o p l a n k t o n i n Humpback Whale D i e t 40 a. C h a r a c t e r i s t i c s of F e e d i n g T a r g e t s 40 b. D i e t a r y C l u e s from F e c a l Samples 46 B. E c o l o g i c a l S i g n i f i c a n c e of t h e E u p h a u s i i d T . r a s c h i i . . 5 0 1. E c o l o g i c a l N i c h e 50 2. L a r v a l Development 53 3. B r e e d i n g C o h o r t s 57 IV. CONCLUSIONS 65 REFERENCES 67 APPENDIX 72 LIST OF TABLES Ta b l e Page 1. S p e c i e s c o n s i d e r e d d e f i n i t e o r h i g h l y p r o b a b l e p r e y of humpback whales i n S E - A l a s k a a r e a 4 2. E s t i m a t e o f a n n u a l c a l o r i c b a l a n c e o f N o r t h P a c i f i c humpback whale 16 3. E q u a t i o n d e t e r m i n a n t s used i n biomass e s t i m a t i o n s 27 4. V i s u a l s c a l e used t o d e t e r m i n e t h e r e l a t i v e d e n s i t y of b a c k s c a t t e r i n g l a y e r s from SONAR-readings 27 5. S u r f a c e s a l i n i t y and t u r b i d i t y measurements i n F r e d e r i c k Sound d u r i n g J u l y / A u g u s t 1983 29 6. S p e c i e s c o m p o s i t i o n o f s t a n d i n g z o o p l a n k t o n s t o c k i n F r e d e r i c k Sound i n J u l y 1983 32 7. S p e c i e s c o m p o s i t i o n o f s t a n d i n g z o o p l a n k t o n s t o c k i n F r e d e r i c k Sound i n l a t e J u l y / A u g u s t 1983 33 8. Biomass v a l u e s f o r e u p h a u s i i d s and copedpods caught i n s t a n d a r d s i t e tows 34 9. Comparison of s t a n d i n g z o o p l a n k t o n c r o p c o m p o s i t o n , and s a m p l i n g methods used i n F r e d e r i c k Sound August 1982 and 1983 36 10. S p e c i e s c o m p o s i t i o n o f p l a n k t o n s u r f a c e swarms i n August 1983 i n F r e d e r i c k Sound 36 11. Comparison of p l a n k t o n swarm c o m p o s i t i o n , and s a m p l i n g methods used i n F r e d e r i c k Sound 1982 and 1983 37 12. D i s p l a c e m e n t volumes of s t a n d a r d s i t e tows i n F r e d e r i c k Sound l a t e J u l y / A u g u s t 1983 39 13. D i s p l a c e m e n t volumes of tows t h r o u g h s u r f a c e p l a n k t o n swarms i n F r e d e r i c k Sound 1982 and 1983 39 14. Comparison of s u r f a c e f e e d i n g and n o n - f e e d i n g s i t e s i n F r e d e r i c k Sound August 1983 41 15. Comparison of DSL f e e d i n g and n o n - f e e d i n g s i t e s i n F r e d e r i c k Sound i n J u l y 1983 42 16. Comparison of b a c k s c a t t e r c h a r a c t e r i s t i c s a t f e e d i n g and n o n - f e e d i n g s i t e s i n F r e d e r i c k Sound J u l y / August 1983 43 V T a b l e Page 17. Humpback whale f e c a l samples c o l l e c t e d i n F r e d e r i c k Sound d u r i n g t h e 1983 season 47 18. I d e n t i f i e d remains from humpback whale f e c e s c o l l e c t e d i n F r e d e r i c k Sound 1983 47 19. K r i l l c o m p o s i t i o n o f s t a n d i n g z o o p l a n k t o n s t o c k i n F r e d e r i c k Sound J u l y / A u g u s t 1983 51 20. F r e q u e n c i e s o f T. r a s c h i i d e v e l o p m e n t a l s t a g e s caught over t h e s t u d y p e r i o d i n F r e d e r i c k Sound 1983 54 21. Weekly development of spawning s u b - c o h o r t s o f T. r a s c h i i i n F r e d e r i c k Sound 1983 61 v i LIST OF FIGURES F i g u r e * Page 1. The S E - A l a s k a humpback whale f e e d i n g ground 2 2. L o c a t i o n o f t h e endangered humpback whale h a b i t a t G l a c i e r Bay 12 3. Study a r e a o f our 1983 humpback whale p r e y s t u d y , w i t h l o c a t i o n s o f s e l e c t e d z o o p l a n k t o n s a m p l i n g s t a t i o n s 22 4. SONAR-reading s u g g e s t s whales d i v i n g i n t o k r i l l l a y e r a t 60m depth 24 5. S e l e c t e d e u p h a u s i i d p a r t s i d e n t i f i e d from humpback • whale f e c a l m a t e r i a l 48 6. P e r c e n t f r e q u e n c i e s o f e a r l y f u r c i l i a s t a g e s o f T. r a s c h i i i n F r e d e r i c k Sound i n J u l y 1983 56 7. R e l a t i v e p e r c e n t a g e f r e q u e n c i e s o f d e v e l o p m e n t a l groups o f T. r a s c h i i o v e r the t i m e o f t h e s t u d y p e r i o d 58 8. G r a p h i c a n a l y s i s o f T. r a s c h i i development i n F r e d e r i c k Sound over t h e 1983 s t u d y p e r i o d 62 ACKNOWLEDGEMENTS I w i s h t o thank my s u p e r v i s o r , Dr. Timothy R. P a r s o n s , f o r h i s s u p p o r t , s u g g e s t i o n s , and encouragement t h r o u g h o u t t h i s s t u d y , as w e l l as Mr. Gordon M i l b o u r n e f o r f i n a n c i a l s u p p o r t of t h i s s t u d y . The whole "TRP"-Lab, i n c l u d i n g Heather Dovey and Do Kyu Lee, has always been h e l p f u l and s h a l l be remembered f o n d l y . A v e r y s p e c i a l thank you i s o f f e r e d t o B i l l D o l p h i n f o r the o p p o r t u n i t y t o p a r t i c i p a t e i n h i s e x p e d i t i o n t o S E - A l a s k a , f o r t he generous a c c e s s t o h i s d a t a c o l l e c t i o n , and f o r t h e many t h i n g s I l e a r n e d aboard t h e " H v a l f i s k e n . " A warm thank you a l s o t o Jane Rowe, C a r l P a u l s e n , Dan McSweeney, Beth Mathews, L i z Hemmick, L a u r i e M c l v o r , and Ginny Rosenberg f o r t h e i r c o n t r i b u t i o n s t o t h e d a t a s e t used i n t h i s r e p o r t . I am g r a t e f u l t o Dr. John F u l t o n , Y o j i Endo, and Dr. A l Lewis f o r t h e i r v a l u a b l e a d v i c e i n z o o p l a n k t o n i d e n t i f i c a t i o n , and t o Robe r t C a r v e t h and R i c h a r d O'Grady f o r i d e n t i f y i n g n o n - p l a n k t o n i c components i n whale f e c a l samples. Dr. Bruce Wing and Kendra D a l y ( r e p . Dr. Tom E n g l i s h ) i n p a r t i c u l a r d e s e r v e thanks f o r t h e i r d e t a i l e d c o r r e s p o n d e n c e i n answer t o q u e s t i o n s c o n c e r n i n g t h e i r work. The k i n d a s s i s t a n c e o f Dr. Ha r r y Joe o f UBC S t a t i s t i c a l C o n s u l t i n g , who a d v i s e d s u i t a b l e t e s t i n g methods f o r my d a t a s e t , has been v e r y much a p p r e c i a t e d . L a s t but not l e a s t , I thank my f a m i l y and f r i e n d s , e s p e c i a l l y N a t a l i e Dakers, f o r v a r i o u s k i n d s o f s u p p o r t t h a t a i d e d i n p r o d u c i n g t h i s document. 1 INTRODUCTION The humpback whale (Megaptera n o v a e a n g l i a e ) , p r o t e c t e d s i n c e 1966, i s a g l o b a l l y o c c u r r i n g b a l e e n whale s p e c i e s t h a t m i g r a t e s between c o a s t a l low l a t i t u d e b r e e d i n g grounds ( c o l d season) and h i g h l a t i t u d e f e e d i n g grounds (warm season) (Dawbin,1963). The major s e l e c t i v e advantage of t h i s p a t t e r n has been argued t o l i e i n an o v e r a l l c o n s e r v a t i o n o f energy, by t a k i n g advantage o f h i g h e r f o o d c o n c e n t r a t i o n s i n c o l d e r waters w h i l e r e p r o d u c i n g i n a m e t a b o l i c a l l y l e s s demanding, warmer environment (Dawbin,1963; B r o d i e , 1 9 7 5 ; F r o s t and Lowry,1981). The p r e s e n t N o r t h P a c i f i c p o p u l a t i o n has been e s t i m a t e d a t a minimum of 2,100 i n d i v i d u a l s ( D a r l i n g and M o r o w i t z , i n p r e s s ) , w hich s e a s o n a l l y c o n c e n t r a t e on t h r e e r e c o g n i z e d b r e e d i n g and f e e d i n g grounds, r e s p e c t i v e l y (Hoyt,1983). The S E - A l a s k a A r c h i p e l a g o " f e e d i n g ground" ( F i g . l ) f e a t u r e s a m u l t i t u d e o f narrow, f j o r d - t y p e i n l e t s , which have a mean mid-depth of 350 m and a r e c h a r a c t e r i z e d by s h a l l o w thermo- and h a l o c l i n e s ( P i c k a r d , 1 9 6 7 ) . T h e i r s e a s o n a l p r o d u c t i v i t y s u p p o r t s an a n n u a l summer p o p u l a t i o n o f a t l e a s t 365 whales^- ( k r i e g e r and Wing,1984). T r a d i t i o n a l a r e a s w i t h h i g h c o n c e n t r a t i o n s o f humpbacks a r e G l a c i e r Bay (GB), I c y S t r a i t ( I S ) , Lynn C a n a l ( L C ) , and F r e d e r i c k Sound (FS) (Wing and K r i e g e r , 1 9 8 3 ; J u r a s z , 1 9 7 9 a ) . O r i g i n a l e s t i m a t e s o f whale summer p o p u l a t i o n s i n t h e s e r e g i o n s a r e GB:25, LC:15, FS:40-80 1) "whales" s h a l l be used i n t e r c h a n g e a b l y w i t h "humpback wh a l e s " u n l e s s o t h e r w i s e s p e c i f i e d . 2 F i g . 1. The SE-Alaska Humpback Whale Feeding Ground (Map Reprinted from Pickard, 1967). Areas of T r a d i t i o n a l l y High Whale Concentrations are Shaded. 3 (MMC,1980). The ye a r t o y e a r s i t e - f i d e l i t y t o a s p e c i f i c i n l e t by i d e n t i f i e d i n d i v i d u a l s i s r e p o r t e d t o be h i g h ( J u r a s z , 1 9 7 9 a ; MMC,1980; D o l p h i n e t a l . , 1 9 8 3 ) . W i t h i t s r e l a t i v e l y c o a r s e b a l e e n f r i n g e s (Nemoto,1959), and p r e d o m i n a n t l y " g u l p i n g " f e e d i n g mode (Nemoto,1973), the humpback t y p i c a l l y f o r a g e s f o r l a r g e r z o o p l a n k t o n and p l a n k t i v o r o u s f i s h i n c o n c e n t r a t e d d e n s i t i e s . P r e y c o m p o s i t i o n i s known t o v a r y w i d e l y w i t h t i m e and l o c a l i t y ( G a s k i n , 1 9 8 2 ) . T a b . l l i s t s r e p o r t e d p r e y s p e c i e s f o r S E - A l a s k a and v i c i n i t y . F e e d i n g whales i n t h e SE-A l a s k a n i n l e t s have been o b s e r v e d between A p r i l and November, w i t h h i g h e s t f e e d i n g a c t i v i t y o c c u r r i n g i n J u l y and August ( J u r a s z , 1 9 7 9 b ) . The r e c o g n i z e d l o c a l "whale season" f a l l s between June 1 and August 31 (Anon.,1984). S i n c e l a r g e - s c a l e , l a t i t u d i n a l v a r i a t i o n s i n p r e y a v a i l a b i l i t y i n f l u e n c e t h e whales' g l o b a l d i s t r i b u t i o n a l p a t t e r n , one may assume t h a t l o c a l p r e y v a r i a b i l i t y i s a major d e t e r m i n a n t o f whale f r e q u e n c y and movement on a p a r t i c u l a r f e e d i n g ground. However, l i t t l e a t t e n t i o n has been p a i d t o any v a r i a b l e s a f f e c t i n g humpback p r e y i n S E - A l a s k a p r i o r t o 1979. When a p r e v i o u s l y f r e q u e n t e d f o r a g i n g a r e a , G l a c i e r Bay, was d e s e r t e d by whales i n 1978 (MMC,1980), a s e r i e s o f p r e y s u r v e y s were c o n d u c t e d , n o t a b l y by B r y a n t e t . a l . (1981), E n g l i s h ( 1 9 83), and Wing and K r i e g e r (1983 and 1984). Some o f t h e most r e c e n t d a t a on f o o d s o u r c e s and whale f o r a g i n g b e h a v i o r i n S E - A l a s k a have been c o l l e c t e d by W i l l i a m D o l p h i n (unpubl.) 4 SPECIES REFERENCE Thysanoessa raschi Wing and Krieger(1983)*,English(1983),this study* Thysanoessa longipes Bryant(1981),Wing and Krieger(1983) Thysanoessa spini f e r a Nemoto(1965)*,Bryant(1981),Wing and Krieger(1983) Euphausia p a c i f i c a Jurasz(1979b),Earle(1979)*,Bryant(1981), Wing and Krieger(1983) Pandalus borealis Jurasz(1979b),English(1983) Clupea harengus Jurasz(1979b),Wing and Krieger(1983),English(1983) Mallotus v i l l o s u s Wing and Krieger(1983)*,English(1983) Tab. 1. Species Considered Definite (* Based on Stomach Contents or Author's Observation of Feeding Process) or Highly Probable Prey of Humpback Whales i n SE-Alaska Area. d u r i n g a l o n g - t e r m i n v e s t i g a t i o n o f F r e d e r i c k Sound . As p a r t o f t h i s i n v e s t i g a t i o n , I c o l l e c t e d z o o p l a n k t o n samples d u r i n g D o l p h i n ' s 1983 summer f i e l d season ; t h e r e s u l t s o f t h e s e c o l l e c t i o n s form t h e d a t a s e t f o r the second p a r t o f my t h e s i s . The f o l l o w i n g s t u d y w i l l i n v e s t i g a t e t h e i n f l u e n c e of z o o p l a n k t o n i c r e s o u r c e s on humpback whale f e e d i n g and d i s t r i b u t i o n i n S E - A l a s k a . P a r t I w i l l i n v e s t i g a t e a new h y p o t h e s i s r e g a r d i n g t h e d e c l i n e o f t h e G l a c i e r Bay s u b - p o p u l a t i o n and p r o v i d e some i n f o r m a t i o n on the e n e r g e t i c demands and s u p p l i e s o f humpbacks on t h e i r f e e d i n g ground. P a r t I I w i l l a n a l y z e z o o p l a n k t o n i c p r e y c o n d i t i o n s , humpback whale d i e t , and e u p h a u s i i d e c o l o g y i n the F r e d e r i c k Sound f e e d i n g a r e a . 2) " F r e d e r i c k Sound" s h a l l be used t o denote t h e F r e d e r i c k Sound/lower Stephens Passage a r e a . 6 PART ONE; HUMPBACK WHALE POPULATION DECLINE IN GLACIER BAY I . BACKGROUND In t h e r e c e n t p a s t , two d r a s t i c l o c a l humpback p o p u l a t i o n d e c l i n e s were w i t n e s s e d on t h e S E - A l a s k a f e e d i n g ground. Only a few i n d i v i d u a l s each r e t u r n e d t o Lynn C a n a l (LC) a f t e r 1974, and t o G l a c i e r Bay (GB) a f t e r t h e 1978 f e e d i n g season (MMC,1980). W h i l e t h e LC abandonment was r e a s o n a b l y e x p l a i n e d as a f o o d c o m p e t i t i o n problem ( e x t e n s i v e h e r r i n g f i s h e r y 1974-78; c f . MMC,1980), t h e s i t u a t i o n i n GB i s more c o n t r o v e r s i a l , and c a l l s f o r f u r t h e r e x a m i n a t i o n . E u p h a u s i i d s a r e t h e predominant f e e d d u r i n g J u l y and August i n G l a c i e r Bay ( L e i t z e l l , 1 9 7 9 i n E n g l i s h , 1 9 8 3 ; Hale and W r i g h t , 1 9 7 9 ) . I n t h e y e a r s p r e c e e d i n g 1978, a r e g u l a r whale f o r a g i n g p a t t e r n was ob s e r v e d i n GB, which i s documented by J u r a s z (1979a, and 1979 i n E n g l i s h , 1 9 8 3 ) . Two i n f l u x e s , f i r s t a few s i n g l e s and p a i r s i n June, and then a l a r g e group o f around 20 i n d i v i d u a l s i n e a r l y J u l y , were common, t h e l a t t e r c o i n c i d i n g w i t h an i n c r e a s e d c o n c e n t r a t i o n o f f o r a g e i n t h e bay. Whales were o b s e r v e d t o s t a y i n t h e bay a t l e a s t 4-6 weeks ( J u r a s z , 1 9 7 9 a ) . I n 1978, t h e two i n f l u x e s c o n s i s t e d of 4 and 16 wh a l e s , r e s p e c t i v e l y , r e p r e s e n t i n g u s u a l numbers. E x c e p t f o r 3 i n d i v i d u a l s of t h e second group, a l l t h e whales l e f t t h e bay 16 days a f t e r t h e major i n f l u x on J u l y 1 s t ( J u r a s z , 1 9 7 9 a ) . Over the c o u r s e of t h e seas o n , whale f r e q u e n c i e s i n o t h e r SE-Alaskan i n l e t s i n c r e a s e d (MMC,1980), wh i c h can i n p a r t be a t t r i b u t e d t o d i s p l a c e d GB i n d i v i d u a l s ( J u r a s z , 1 9 7 9 a ) . The numbers o f whales 7 r e m a i n i n g i n GB ranged from 1 t o a maximum 7 i n y e a r s f o l l o w i n g (NMFS,1983 and Baker,1983 i n K r i e g e r and Wing,1984). Two major hypotheses have been put f o r w a r d t o e x p l a i n t h e a b o v e - d e s c r i b e d p o p u l a t i o n d e c l i n e : i n c r e a s e d human d i s t u r b a n c e , and d e c r e a s e d f o o d s u p p l y . The impact of i n c r e a s e d v e s s e l t r a f f i c and n o i s e p o l l u t i o n on humpback whales has been d i s c u s s e d e l s e w h e r e (Malme e t . a l . , 1 9 8 2 ; M i l e s and Malme,1983; Herman and B aker,1983). However, t o t a l v i s i t o r days and l a r g e s h i p t r a f f i c had a c t u a l l y d e c r e a s e d between 1977 and 1978, w h i l e o n l y p l e a s u r e c r a f t had i n c r e a s e d ( A n o n 1 9 8 4 ) . F u r t h e r m o r e , i t i s r a r e l y o b s e r v e d t h a t humpbacks l e a v e a r i c h f e e d i n g s i t e i n t h e p r e s e n c e o f a v e s s e l (Anon.,1984; p e r s . o b s e r v . ) . B r y a n t e t . a l . (1981) f i r s t s u g g e s t e d and i n v e s t i g a t e d t h e t h e o r y o f a f o o d s h o r t a g e as t h e cause f o r the p o p u l a t i o n d e c l i n e , s t a t i n g t h a t "the d i s t r i b u t i o n o f humpbacks d u r i n g t h e i r f e e d i n g season may g e n e r a l l y r e f l e c t t h e o c c u r r e n c e and a v a i l a b i l i t y o f p r e y s p e c i e s . " U n f o r t u n a t e l y , no q u a n t i t a t i v e d a t a on p r o d u c t i v i t y or p r e y abundance a r e a v a i l a b l e up t o 1979, which makes a d i r e c t comparison of f o o d p r o d u c t i o n i n GB b e f o r e and a f t e r t h e whale d e c l i n e i m p o s s i b l e . V e r y l i t t l e e f f o r t has been expended t o d i s c o v e r t h e p r o b a b l e causes f o r the h y p o t h e t i c a l d r a s t i c d e c l i n e i n p r o d u c t i o n i n GB around 1978. B r y a n t e t . a l . (1981) c o n c l u d e d t h a t " c l i m a t i c changes might a f f e c t t h e r a t e o f m e l t i n g and c a l v i n g o f g l a c i e r s , w i t h consequent e f f e c t s on t h e s a l i n i t y and t u r b i d i t y . . . t h a t i n t u r n a f f e c t k r i l l abundance." However, he does not s p e c i f y c l i m a t i c changes, nor t h e t y p e o f e f f e c t 8 on e u p h a u s i i d s . Wing and K r i e g e r (1983) compare summer s a l i n i t y v a l u e s i n m i d - G l a c i e r Bay between th e seasons of 1965, ' 79, ' 8 1 a n d '82, and n ote a g e n e r a l s i m i l a r i t y o f c o n d i t i o n s , e x c e p t f o r the 1979 mid-depth v a l u e s by B r y a n t (1981) which t h e y e x p l a i n as p o s s i b l y b e i n g due t o e r r o r (however, see S e c . I I . A . ) . They f u r t h e r d i s c u s s the n e g a t i v e e f f e c t o f i n c r e a s e d thermo- and h a l o c l i n e s on e u p h a u s i i d v e r t i c a l m i g r a t i o n , but do not i m p l y the o c c u r r e n c e o f an i n c r e a s e d p y c n o c l i n e i n GB 1978. The r e l a t i o n s h i p s between o c e a n o g r a p h i c and p r e y a v a i l a b i l i t y a n o m a l i e s i n t h i s f j o r d a r e s t i l l p o o r l y u n d e r s t o o d . I I . ANALYSIS In o r d e r t o e v a l u a t e t h e e f f e c t s o f o c e a n o g r a p h i c f a c t o r s such as a p y c n o c l i n e change on e u p h a u s i i d abundance i n a p a r t i c u l a r ecosystem, t i m e and l o c a t i o n - s p e c i f i c r e l a t i o n s h i p s w i t h i n the system as a whole must be c o n s i d e r e d . My h y p o t h e s i s i s t h a t E l N i n o - S o u t h e r n O s c i l l a t i o n ( E N S O ) - r e l a t e d water d e n s i t y and c i r c u l a t i o n a n o m a l i e s i n GB d u r i n g 1978 p r e v e n t e d any s i g n i f i c a n t n u t r i e n t - r i c h water i n f l u x i n t o t h e bay, t h u s s u p p r e s s i n g k r i l l p r o d u c t i o n below t h r e s h o l d f e e d i n g v a l u e s f o r w h ales. I f u r t h e r s uggest t h a t e u p h a u s i i d abundances l i k e l y never reached a l e v e l where the b a r r i e r e f f e c t o f an i n c r e a s e d p y c n o c l i n e would be a s i g n i f i c a n t cause f o r d e c r e a s e d k r i l l a v a i l a b i l i t y i n upper w a t e r s . I s h a l l d i s c u s s t h i s h y p o t h e s i s by i n t e r c o n n e c t i n g p u b l i s h e d m e t e o r o l o g i c a l , p h y s i c a l and b i o l o g i c a l o b s e r v a t i o n s i n t h e a r e a of c o n c e r n , and by r e l a t i n g them t o t h e c a l c u l a t e d needs of t h e a r e a ' s whale p o p u l a t i o n . 9 A. CLIMATIC CONDITIONS The a n n u a l South American e q u a t o r i a l warming event known as E l N i no i s caused by a weakening of t h e W-E z o n a l p r e s s u r e d i f f e r e n c e ( S o u t h e r n O s c i l l a t i o n ) i n t h e t r o p i c a l P a c i f i c , and o c c u r s w i t h extreme c o n d i t i o n s i n i r r e g u l a r i n t e r v a l s o f s e v e r a l y e a r s . The b e g i n n i n g o f t h e y e a r 1977 marked the s t a r t o f such a warming p e r i o d t h a t peaked i n 1981, t e m p o r a r i l y c o l l a p s e d i n 1982, and d e v e l o p e d i n t o t h e g r e a t e s t r e c o r d e d ENSO-event i n 1983 (Thomson e t . a l . , 1 9 8 4 ) . Northward propaga-t i o n o f a t h e r m o c l i n e d e p r e s s i o n , as w e l l as r e g i o n a l wind f i e l d s h i f t s i n t h e N E - P a c i f i c , t h a t a r e p o s s i b l y i n d u c e d by " a t m o s p h e r i c t e l e c o n n e c t i o n " w i t h e q u a t o r i a l phenomena (Emery and H a m i l t o n , 1 9 8 5 ) , cause c o a s t a l warming a l l t h e way up t o A l a s k a (McLain,1983; Thomson e t . a l , 1 9 8 4 ; Huyer and Smith,1985). As d i s c u s s e d i n d e t a i l by McLain and Ingraham (1980), a s u b s t a n t i a l change i n upper a i r c i r c u l a t i o n (West C o a s t Ridge P a t t e r n ) o c c u r r e d i n t h e w i n t e r s o f 1976/77 and 1977/78 over the c o a s t l i n e from C a l i f o r n i a t o A l a s k a . The f o l l o w i n g a c c o u n t i s based on t h e i r r e p o r t . Winds were more s o u t h e r l y than u s u a l i n A l a s k a ( c f . a l s o Namias,1978), thus i n c r e a s i n g w i n t e r t e m p e r a t u r e s and p r e c i p i t a t i o n d u r i n g t h e 76/77, 77/78, and e a r l y 78/79 w i n t e r s . D u r i n g t h e s e t i m e p e r i o d s , m i l d i c e c o n d i t i o n s p r e v a i l e d i n the A l e u t i a n s down t o I c y Bay (200 mi NW o f G l a c i e r B a y ) , w i t h most i n l e t s b e i n g a l r e a d y i c e - f r e e by March. S p e c i f i c a l l y f o r the 77/78 w i n t e r , i n c r e a s e d onshore t r a n s p o r t o f warm s u r f a c e w a t e r s and d o w n w e l l i n g a r e r e p o r t e d f o r S E - A l a s k a , caused by changes i n the Ekman t r a n s p o r t i n t h e G u l f of A l a s k a ( c f . a l s o Emery and H a m i l t o n , 1 9 8 5 ) . I propose t h a t t h i s i n c r e a s e d d o w n w e l l i n g e x p l a i n s the u n u s u a l l y low midwater s a l i n i t i e s d u r i n g t h e summer o f 1979 r e p o r t e d by B r y a n t (1981), and c r i t i c i z e d by Wing and K r i e g e r (1983). Royer (1983) remarked t h a t s a l i n i t i e s o f lower l a y e r s i n t h i s r e g i o n a r e dependent on up/downwelling r a t h e r than on r u n - o f f . The ENSO phenomenon t h a t began i n t h e w i n t e r o f 1976/77 i n c o n n e c t i o n w i t h t h e N E - P a c i f i c w i n d f i e l d s h i f t , has m a i n t a i n e d an i n s h o r e / o f f s h o r e r e v e r s i o n o f sea s u r f a c e t e m p e r a t u r e (SST) anom a l i e s u n t i l and beyond i t s f u l l development i n w i n t e r 1982/83. SST's a l o n g the c o a s t have g e n e r a l l y been 1° t o 2*C above normal s i n c e 76/77, w i t h peaks i n 1978 and 1981 ( c f . Thomson e t . a l . , 1 9 8 5 ) . C o a s t a l ( w i n t e r ) s a l i n i t y c o n d i t i o n s d u r i n g t h i s warming p e r i o d have been d e s c r i b e d as s l i g h t l y f r e s h e r (Royer,1983; Mysak,1984). O v e r a l l , u n u s u a l ocean c o n d i t i o n s a l o n g t h e West c o a s t a r e r e p o r t e d f o r the w i n t e r s o f 77/78 and 78/79, due t o an a b n o r m a l l y s t r o n g (warm) Davidson C u r r e n t caused by E l Ni n o . Contour maps and weather r e p o r t s from the GB a r e a (Comparative C l i m a t i c Data f o r t h e U.S. t h r o u g h 1981; Mo n t h l y Record o f M e t e o r o l . Observ. N o r t h e r n Canada) s u p p o r t t h e c o n c l u s i o n t h a t i n c r e a s e d c o a s t a l water t e m p e r a t u r e s t o g e t h e r w i t h an i n c r e a s e i n mean monthly a i r t e m p e r a t u r e s and t o t a l p r e c i p i t a t i o n d u r i n g t h e w i n t e r months, s h o u l d have caused a sup r a - n o r m a l r a t e o f g l a c i a l m e l t i n g and a b l a t i o n . Thus the f r e s h w a t e r i n p u t i n t o GB d u r i n g t h e 76/77 and p a r t i c u l a r l y t h e 77/78 c o l d seasons would have been s i g n i f i c a n t l y l a r g e r than u s u a l . B. WATER CIRCULATION G l a c i e r Bay i s a s h a l l o w - s i l l e d f j o r d approximately 100 km i n l e n g t h , t h a t i s surrounded by 40 f a s t r e c e d i n g tidewater g l a c i e r s (Pickard,1967; Matthews,1981) (see F i g . 2 ) . GB i s l o c a t e d i n a geographic area where l i g h t and s t a b i l i t y , r a t h e r than n u t r i e n t s , are the l i m i t i n g f a c t o r s (Parsons e t . al.,1966), p r o v i d e d s u f f i c i e n t t i d a l mixing o c c u r s . However, mixing i n t h i s p a r t i c u l a r i n l e t i s normally of reduced nature (MMC,1980; Matthews,1981), which makes i t s u s c e p t i b l e to n u t r i e n t l i m i t a t i o n (Hale and Wright,1979). Matthews (1981) p r o v i d e s d e t a i l e d i n f o r m a t i o n on the GB c i r c u l a t o r y p a t t e r n , c o n c l u d i n g t h a t "the f j o r d bottom waters tof GB] were renewed a n n u a l l y between November and A p r i l by s a l i n e i n t r u s i o n [from Icy S t r a i t ] over the 69 m deep entrance s i l l " . Icy S t r a i t source water i s d e r i v e d from 60 m depth, and can be expected to be trapped i n GB o n l y i f i t s d e n s i t y (mainly s a l i n i t y - d e p e n d e n t ) i s g r e a t e r than bay water d e n s i t y at s i l l depth. However the p y c n o c l i n e i n GB must not extend below s i l l depth i n order f o r s i g n i f i c a n t deepwater exchange to o c c u r . Icy S t r a i t waters are f r e e l y connected to the North P a c i f i c water mass, and are b e l i e v e d to be the major source of n u t r i e n t s i n GB (Hale and Wright,1979). The degree to which bottom water renewal i s completed, depends on the amount of p r e c i p i t a t i o n and thawing, which can cut o f f water i n t r u s i o n , and r e v e r s e the d i r e c t i o n of flow over the s i l l . A ccording to Matthew's (1981) data, annual bottom water renewal ends with the peak of r u n - o f f due to i c e melt, which i s u s u a l l y around May. F i g . 2. Location of the Endangered Humpback Whale Habitat Glacier Bay. 13 I t can be assumed t h a t i n c r e a s e d f r e s h w a t e r i n p u t d u r i n g the 76/77 and e s p e c i a l l y t h e 77/78 w i n t e r , s u p p o r t e d by t h e s t a b i l i z i n g e f f e c t of t e m p e r a t u r e , caused a q u i c k l y deepening p y c n o c l i n e and i n c r e a s e d water t r a n s p o r t o ut o f t h e bay. T h i s would have e f f e c t e d t h e t e r m i n a t i o n o f n u t r i e n t - r e p l e n i s h i n g deep-water i n t r u s i o n l o n g b e f o r e t h e u s u a l t i m e i n s p r i n g . From t h i s i t i s s u g g e s t e d t h a t bottom water r e n e w a l was i n c o m p l e t e i n 1977, and more th a n l i k e l y n e g l i g i b l e by 1978. C. LOCAL PRODUCTIVITY P r i m a r y p r o d u c t i v i t y has not been measured i n G l a c i e r Bay. In an e v a l u a t i o n o f t h e GB marine ecosystem, r e p r e s e n t a t i v e v a l u e s were g i v e n from P o r t V a l d e z and V a l d e z Arm o f 150 and 220 g C/m 2/yr r e s p e c t i v e l y . T h i s appears t o be a low v a l u e when compared w i t h v a l u e s f o r t h e S t r a i t of G e o r g i a r e g i o n ( H a r r i s o n e t . a l . , 1 9 8 3 ) . However, P i c k a r d (1967) noted g e n e r a l l y reduced b i o l o g i c a l a c t i v i t y i n i n l e t s w i t h g l a c i e r s compared t o g l a c i e r - f r e e i n l e t s i n S E - A l a s k a . Assuming a p r i m a r y p r o d u c t i v i t y o f 200 g C/m 2/yr i n GB under normal c l i m a t i c c o n d i t i o n s , an e c o l o g i c a l e f f i c i e n c y E o f 0.15 (P a r s o n s e t . a l . , 1 9 7 7 ) , and a t r o p h i c l e v e l n of 1.5 and 2.5 f o r z o o p l a n k t o n and p l a n k t i v o r o u s f i s h , r e s p e c t i v e l y , the p r o d u c t i o n e q u a t i o n P = B x E n ( i n which B i s i n i t i a l , and P i s r e s u l t i n g p r o d u c t i v i t y ) y i e l d s t h e f o l l o w i n g a p p r o x i m a t i o n s : Z o o p l a n k t o n P = 11.6 g C/m 2/yr P l a n k t . F i s h P = 1.7 g C/m 2/yr Assuming f u r t h e r a carbon c o n t e n t o f r o u g h l y 6% wet w e i g h t , thebiomass e s t i m a t e s f o r z o o p l a n k t o n and f i s h i n GB a r e 190 and 30 g/m / y r , r e s p e c t i v e l y . In the seasons of the warming e v e n t , GB's n u t r i e n t l i m i t a t i o n , enhanced by a t e m p e r a t u r e - i n d u c e d i n c r e a s e i n water column s t a b i l i t y would be e x p e c t e d t o markedly s u p p r e s s a s p r i n g bloom and subsequent p r o d u c t i v i t y i n t h i s a r e a . T h i s s i t u a t i o n must have been g r e a t l y i n t e n s i f i e d i n t h e second (1978) season o f t h e warming event f o r t h e f o l l o w i n g r e a s o n s : F i r s t l y , a c c o r d i n g t o my h y p o t h e s i s , n u t r i e n t s had a l r e a d y been i n s u f f i c i e n t l y renewed i n t h e p r e c e e d i n g s e a s o n , and were d e p l e t e d below normal l e v e l s . The c o n t i n u e d r i s e o f SST's i n 1978 i n t e n s i f i e d e x i s t i n g c o n d i t i o n s t o a c r i t i c a l l e v e l . S e c o n d l y , t h e i n c r e a s e d d o w n w e l l i n g r e p o r t e d f o r t h e w i n t e r o f 1977/78 a l o n g the S E - A l a s k a c o a s t was p r o b a b l y a s s o c i a t e d w i t h the reduced n u t r i e n t c o n t e n t o f t h e s o u r c e w a t e r . In a d d i t i o n , t h e d e c r e a s e d s a l i n i t y and i n c r e a s e d t e m p e r a t u r e o f t h i s s o u r c e water made i t l e s s l i k e l y t o become t r a p p e d w i t h i n t h e bay. For t h e f o l l o w i n g c o n s i d e r a t i o n s , p r o d u c t i v i t y c o n d i t i o n s i n 1979 w i l l be assumed s i m i l a r t o , and r e p r e s e n t a t i v e o f t h e 1978 season, f o r which no measurements e x i s t . K r i l l d e n s i t i e s i n 1979 i n GB averaged o n l y 5% of k r i l l d e n s i t i e s measured i n FS o f t h a t y e ar ( B r y a n t e t . a l . , 1 9 8 1 ) . I f GB p r o d u c t i v i t y c o n s i d e r e d t o be no l e s s t h a n 50% o f t h a t o f g l a c i e r - f r e e FS d u r i n g non-ENSO y e a r s , t h e n a t l e a s t a t e n - f o l d r e d u c t i o n o f p r o d u c t i v i t y appears t o have o c c u r r e d i n GB d u r i n g t h e d e s c r i b e d c l i m a t i c anomaly, assuming c o n s t a n t FS p r o d u c t i v i t y . Under t h e s e c i r c u m s t a n c e s , a rough e s t i m a t e of biomass i n GB a t t h e n = 2.5 t r o p h i c l e v e l would be around 3 g/m 2/yr. D. WHALE FORAGING Are t h e e n e r g e t i c needs of t h e GB humpbacks c o v e r e d under such i m p a i r e d f e e d i n g c o n d i t i o n s ? In o r d e r t o a s s e s s the amount of p r e y needed by t h e s e w h a l e s , we w i l l have t o c o n s i d e r the f e e d i n g r a t e as w e l l as t h e l e n g t h o f t h e a n n u a l f e e d i n g season. The f o o d i n t a k e of b a l e e n whales on t h e i r f e e d i n g grounds i s g e n e r a l l y e s t i m a t e d a t 30-40 g/kg body w e i g h t / d a y , and a t o n e - t e n t h o f t h i s r a t e d u r i n g the " n o n - f e e d i n g " season ( L o c k y e r , 1 9 8 1 ) . For a c o n s e r v a t i v e e s t i m a t e , I w i l l assume the lower l i m i t of 30g/kg/day i n c a l c u l a t i n g t h e e n e r g e t i c demands of t h e s e whales on t h e GB ecosystem. Assuming a g e n e r a l i z e d d i e t of r o u g h l y o n e - h a l f k r i l l and o n e - h a l f f i s h (Nemoto,1973; Hood,1981), r e p r e s e n t e d by Thysanoessa r a s c h i i a t 0.65 k c a l / g (Mauchline,1980) and s m e l t s (Osmeridae) a t a p p r o x i m a t e l y 1.0 k c a l / g ( G a s k i n , 1 9 8 2 ) , I a r r i v e a t a d a i l y i n t a k e o f a p p r o x i m a t e l y 8.3 x 10^ k c a l p e r average 33 t o n humpback (Whitehead,1985) per day o f f e e d i n g . From L o c k y e r ' s (1981) d a t a , a d a i l y c a l o r i c need of 0.37 x 10^ k c a l f o r an a c t i v e l y moving whale of t h i s s i z e can be deduced. I f an a n n u a l b a l a n c e between e n e r g e t i c i n p u t and o u t p u t i s t o be a c h i e v e d (see Tab.2), a f e e d i n g season o f 140 days a t optimum f e e d i n g r a t e would be n e c e s s a r y . By c o m p a r i s o n , Dawbin (1963) c a l c u l a t e d an average f e e d i n g season o f 5.5 months f o r Southern hemisphere humpbacks, based on c a t c h d a t a o f w h a l i n g s t a t i o n s a l o n g m i g r a t o r y r o u t e s . S i n c e two d i f f e r e n t p o p u l a t i o n s i n d i f f e r e n t h a b i t a t s a r e compared h e r e , s m a l l d i f f e r e n c e s i n t i m i n g s h o u l d not be s u r p r i s i n g . The migratory pattern within populations appears to be f a i r l y predictable and organized, and in case of food shortage, search for higher food l e v e l s would seem more l i k e l y than a prolonged stay in a comparatively unproductive area. By the end of the feeding season, an energy surplus of roughly 64 m i l l i o n kcal i s necessary for use during the migratory/repro-ductive (fasting) season (cf. Tab.2). In order to store t h i s amount of energy, blubber reserves i n the v i c i n i t y of 11 tons are necessary, considering 66% l i p i d in blubber, at 9 kcal/g (Brodie,1981). LENGTH OF SEASON (d) CALORIC INTAKE/ WHALE/SEASON (10 6 kcal) CALORIC OUTPUT/ WHALE/SEASON (10 6 kcal) CALORIC BALANCE/ WHALE/SEASON (10 6 kcal) FEEDING 140 116 52 +64 FASTING 225 19 83 -64 TOTAL 365 135 135 0 Tab. 2. Estimate of Annual Caloric Balance of North P a c i f i c Humpback Whale. With 25 whales confined to GB's area of roughly 1,500 km2, above-mentioned weight gain per whale would equal an annual production of 0.18 g/m2 of whale biomass in t h i s i n l e t . If feeding occurs at the assumed rate and length of time, the prey needed seasonally to cover t h i s population's energetic and storage demands, amounts to an average 2.3 g wet weight/m 2 (This renders an ec o l o g i c a l e f f i c i e n c y E of approximately 0.08 for humpbacks feeding on the nearest t r o p h i c l e v e l ) . I n r e a l i t y , whales a r e known t o use GB s e l e c t i v e l y , and o n l y about o n e - f o u r t h o f t h e bay's a r e a a c t u a l l y q u a l i f i e s as f o r a g i n g t e r r a i n (Hale and W r i g h t , 1 9 7 9 ) , r a i s i n g the demand f o r p r e y p r o d u c t i o n i n t h e s e p a r t s o f t h e bay t o 9.2 g/m2. R e g a r d i n g a s i m p l i f i e d f o o d c h a i n , i n which o n l y p r e y produced a t t h e h i g h e s t t r o p h i c l e v e l i s d i r e c t l y a v a i l a b l e f o r whale consumption, t h e whales' demands can a p p a r e n t l y be s a t i s f i e d under normal c o n d i t i o n s , p r o d u c i n g an e s t i m a t e d 30 g/m 2.(see p r e v i o u s s e c t i o n ) . On t h e o t h e r hand, chances o f e n c o u n t e r i n g the n e c e s s a r y mean p r e y c o n c e n t r a t i o n o f 9.2 g/m2 i n t h e u s u a l f e e d i n g r e g i o n s a r e g r e a t l y r e d u c e d i f bay-wide p r e y p r o d u c t i o n dropped t o 3 g/m2, as e s t i m a t e d f o r the c r i t i c a l y e a r 1978. Food f i n d i n g e f f o r t s and ( i n t e r - and i n t r a - s p e c i f i c ) c o m p e t i t i o n would have i n c r e a s e d beyond o p t i m a l e n e r g e t i c rewards. S i n c e f o o d r e s o u r c e s were assumedly much more p l e n t i f u l i n o t h e r , d e e p e r - s i l l e d SE-Alaskan i n l e t s a t t h a t c r i t i c a l t i me ( c f . B r y a n t e t . a l . , 1 9 8 1 ) , a r e d i s t r i b u t i o n o f humpbacks over the f e e d i n g ground would s i m p l y r e p r e s e n t t h e s e a r c h f o r maximized i n d i v i d u a l f o o d i n t a k e . I t seems p l a u s i b l e t h a t t h e s m a l l number o f humpbacks r e t u r n i n g t o GB s i n c e 1978 c o n s t i t u t e t h e amount of whales (12%) f o r which l o c a l p r o d u c t i o n ( e s t i m . 10% norm) was s t i l l s u f f i c i e n t , r a t h e r than s p e c i f i c i n d i v i d u a l s w i t h d e c r e a s e d s e n s i t i v i t y t o v e s s e l t r a f f i c . I I I . CONCLUSIONS I t has been s u g g e s t e d t h a t the s i g n i f i c a n t p o p u l a t i o n d e c l i n e o f humpback whales i n G l a c i e r Bay s i n c e 1978 was p r i m a r i l y due t o t h e o n s e t o f a major c l i m a t i c change, which d e c r e a s e d n u t r i e n t c i r c u l a t i o n and p r e y l e v e l s i n t h i s p a r t i c u l a r i n l e t . However, s i n c e no measurements o f a c t u a l p r o d u c t i v i t y l e v e l s a r e a v a i l a b l e , t h e ( a d d i t i o n a l ) impact o f 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 cannot be d i s c a r d e d . I t i s a l s o p o s s i b l e t h a t a d i r e c t impact o f hydrodynamic c u e s , such as f l o w a c r o s s GB's s i l l , on whale movement e x i s t s ( J u r a s z , 1 9 7 9 a ; MMC,1980), and may have p l a y e d a r o l e i n t h e o b s e r v e d d i s p l a c e m e n t as w e l l . The r e d i s t r i b u t i o n o f G l a c i e r Bay whales t o o t h e r f e e d i n g a r e a s may be permanent, u n l e s s f e e d i n g c o n d i t i o n s become l e s s f a v o r a b l e i n t h e i r new l o c a l e s . From a r e e v a l u a t i o n of a v a i l a b l e d a t a and e c o l o g i c a l c o n c e p t s , i t has become o b v i o u s t h a t l a r g e - s c a l e m e t e o r o l o g i c a l e v e n t s have perhaps t h e g r e a t e s t p o t e n t i a l t o a f f e c t humpback b e h a v i o r i n a s p e c i f i c a r e a . E n g l i s h (1983) n o t e d t h a t " c y c l e s of whales and t h e i r p r e y w i l l a s s u r e d l y o c c u r i n the f u t u r e " , and l o n g - t e r m , i n t e g r a t i v e e c o l o g i c a l s t u d i e s a r e an apparent n e c e s s i t y f o r l o c a l as w e l l as ocean-wide whale management. PART TWO: ZOOPLANKTONIC PREY IN FREDERICK SOUND I . INTRODUCTION The f o l l o w i n g s t u d y o f p l a n k t o n i c humpback p r e y i n F r e d e r i c k Sound ( F S ) , S E - A l a s k a d u r i n g "whale season" 1983 may i n p a r t be r e g a r d e d as a c o n t i n u a t i o n o f p r e v i o u s p r e y s t u d i e s . I n v e s t i g a t i o n s o f humpback whale r e s o u r c e s on t h i s f e e d i n g ground were c a r r i e d out i n t h e 1979, 1981, and 1982 seasons by B r y a n t e t . a l . ( 1 9 8 1 ) , E n g l i s h (1983), and Wing and K r i e g e r (1983) r e s p e c t i v e l y , a f t e r t h e p o p u l a t i o n d e c l i n e i n G l a c i e r Bay i n 1978 ( c f . P a r t One). FS i s a r e g i o n o f undecimated o r i n c r e a s i n g whale p o p u l a t i o n (MMC,1980), which was r e c e n t l y e s t i m a t e d a t 180 i n d i v i d u a l s ( D o l p h i n and McSweeney,1982). T h i s i n l e t t h u s a l l o w s t h e s t u d y o f p r e y c o n d i t i o n s and f e e d i n g r e q u i r e m e n t s under a p p a r e n t l y u n i m p a i r e d c i r c u m s t a n c e s . Z o o p l a n k t o n r e s o u r c e s i n FS appear t o have v a r i e d between p r e v i o u s seasons under s t u d y . E u p h a u s i i d c o n c e n t r a t i o n s were found t o be h i g h e r i n 1982 t h a n i n e i t h e r 1979 or 1981; t h e a v a i l a b l e d a t a suggest a more than f i v e - f o l d i n c r e a s e i n numbers/100 m^  between 1979 and 1982, which i s p a r t i a l l y a c c o u n t e d f o r by d i f f e r e n c e s i n s a m p l i n g gear (Wing and K r i e g e r , 1 9 8 3 ) . However, the 1981-82 i n c r e a s e i s c o n s i s t e n t w i t h an i n c r e a s e i n b a c k s c a t t e r d e n s i t i e s between t h e s e y e a r s , and i s thought t o r e p r e s e n t a f a c t u a l i n c r e a s e i n z o o p l a n k t o n biomass (Wing and K r i e g e r , 1 9 8 3 ) . The t h r e e above-mentioned s t u d i e s c o n c e n t r a t e d m a i n l y on abundance, c o m p o s i t i o n , and d i s t r i b u t i o n of p o t e n t i a l p r e y s p e c i e s , by s a m p l i n g a t s t a t i o n s o r a l o n g t r a n s e c t s . E n g l i s h (1983) and Wing and K r i e g e r (1983) d i d l i m i t e d s a m p l i n g a t whale f e e d i n g s i t e s , and Wing and K r i e g e r s u g g e s t e d t h a t "the problems e n c o u n t e r e d i n i d e n t i f y i n g and a s s e s s i n g humpback whale p r e y c o u l d be m i n i m i z e d i f t h e s i z e of t h e s a m p l i n g a r e a and s i z e o f t h e water column a r e c o n f i n e d t o a c t u a l humpback whale f e e d i n g a r e a s . " S i n c e t h e u m b r e l l a p r o j e c t o f t h i s p r e y s t u d y i s concerned w i t h humpback f o r a g i n g b e h a v i o r ( D o l p h i n , u n p u b l . ) , and g e n e r a l l y f a v o r e d s a m p l i n g i n t h e v i c i n i t y o f w h a l e s , i t o f f e r e d an i d e a l o p p o r t u n i t y t o f i l l t h i s need f o r d i r e c t p r e y assessment. However, l i m i t e d t ime a l l o t m e n t f o r z o o p l a n k t o n s t a t i o n s reduced the e x p e c t e d d a t a s e t , t h u s p r o h i b i t i n g s t a t i s t i c a l l y s i g n i f i c a n t c o n c l u s i o n s i n c e r t a i n c a s e s . My s t u d y i s concerned w i t h t h r e e major o b j e c t i v e s : 1) To d e t e r m i n e e n v i r o n m e n t a l p a r a m e t e r s , s p e c i e s c o m p o s i t i o n , and abundance of z o o p l a n k t o n i n FS d u r i n g t h e 1983 f e e d i n g s e a s o n , and compare r e s u l t s w i t h t h e p r e v i o u s season (Wing and K r i e g e r , 1 9 8 3 ) as w e l l as t h e 1983 p o s t - s e a s o n (Wing and K r i e g e r , 1 9 8 4 ) whenever p o s s i b l e . 2) To a n a l y z e p r e y s e l e c t i v i t y by comparing t h e c h a r a c t e r i s t i c s o f whale f e e d i n g t a r g e t s w i t h n o n - t a r g e t s , and by i d e n t i f y i n g u n d i g e s t e d p r e y items from f e c a l samples. 3) To i n v e s t i g a t e t h e l o c a l e c o l o g y o f a dominant p r e y s p e c i e s , t h e e u p h a u s i i d Thysanoessa r a s c h i i . I I . MATERIALS AND METHODS A. FIELD TECHNIQUES We were o p e r a t i n g out o f West B r o t h e r I s l a n d , A l a s k a , a t 57° 17' N l a t . and ^ " S l 1 W l o n g , (see F i g . 3 ) . The a r e a w i t h i n which p l a n k t o n samples were t a k e n , ranged from 57°14' t o 57°31' N l a t . and from 133°36' t o 134°10' W l o n g . Our s t a n d a r d s a m p l i n g s i t e f o r b a s e l i n e v a l u e s was chosen t o be a t a p p r o x i m a t e l y 57*15.5' N l a t . and 133°51.5' W l o n g . , f o r i t s c e n t r a l l o c a t i o n i n t h e s t u d y a r e a , and easy a c c e s s i b i l i t y from t h e base camp. The c o l l e c t i o n season l a s t e d from J u l y 11 t o August 28, 1983. Weather c o n d i t i o n s p e r m i t t e d s a m p l i n g on 34 days. For p r a c t i c a l r e a s o n s r e l a t e d t o our whale o b s e r v a t i o n o b j e c t i v e s , s a m p l i n g was g e n e r a l l y l i m i t e d t o d a y l i g h t h o u r s . The d a i l y s t a n d a r d s i t e tow was timed as c l o s e l y as p o s s i b l e t o midday, and ranged between 9:53 and 15:07 h o u r s , w i t h the e x c e p t i o n o f t h r e e tows t a k e n a f t e r 20:00 h o u r s . The t i m i n g of tows r e l a t e d t o whale b e h a v i o r was o p p o r t u n i s t i c . A l l d a t a c o l l e c t i o n was done from aboard a 5.8 m i n f l a t a b l e " Z o d i a c " b o a t , powered by a 90 HP o u t b o a r d e n g i n e . For z o o p l a n k t o n tows, a bongo frame w i t h 40 cm d i a m e t e r openings and 1.5 kg a d d i t i o n a l l e a d w e i g h t was used. Tows were hand-operated from a c o i l o f 170 m p o l y p r o p y l e n e l i n e marked a t 10 m i n t e r v a l s . A c l o s i n g mechanism was t r i e d u n s u c c e s s f u l l y ; t h e r e f o r e a l l tows were c o n t i n u a l l y open. Samples 1 t h r o u g h 27 (7/11/83 - 7/23/83) were t a k e n w i t h N i t e x n e t s o f 200/x mesh s i z e and 170 cm l e n g t h ( t y p e 1 n e t s ) . 22 I I 134' 133*40 F i g . 3. Study Area of Our 1983 Humpback Whale Prey Study, with Locations of Selected Zooplankton Sampling Stations. AI = Akusha I s l . , GI = Gambier I s l . , MD = McDonald Rk., R = Round Rk., SI = S a i l I s l . , SSI = Sunset I s l . , STD = Standard Sit e . T h i s mesh s i z e r e s u l t e d i n c l o g g i n g problems, and was r e p l a c e d by N y l o n n e t s o f 0.8 by 1.1 mm mesh s i z e and 160 cm l e n g t h ( t y p e 2 n e t s ) f o r samples 31 t h r o u g h 61 (7/26/83 - 8/28/83). D u r i n g t h e time o f r e p l a c e m e n t , 3 samples were t a k e n w i t h a d i f f e r e n t bongo frame and 333^a mesh s i z e ( t y p e 3 n e t s ) . Towing depth (z) was c a l c u l a t e d as z = cos a x 1, where a i s t h e e s t i m a t e d t o w i n g a n g l e between t o w l i n e and v e r t i c a l , and 1 i s t h e l e n g t h of the l i n e . The s t a n d a r d s i t e was sampled w i t h v e r t i c a l / o b l i q u e tows from a depth c o r r e s p o n d i n g t o 150 m to w i n g l i n e t o t h e s u r f a c e . Other tows were u s u a l l y aimed a t s o n i c t a r g e t s (SONAR 9 t r a n s d u c e r beam w i d t h , 120 kHz s i g n a l ) , and both o b l i q u e and h o r i z o n t a l tows were employed. Towing speed f o r h o r i z o n t a l tows was a p p r o x i m a t e l y 1.5 k n o t s (approx. 2.8 km/h). C o n c u r r e n t w i t h each tow, a number o f measurements and o b s e r v a t i o n s were t a k e n . The b e h a v i o r o f a l l whales w i t h i n a 500 m r a d i u s o f the tow s i t e was n o t e d . S u r f a c e f e e d i n g b e h a v i o r was c l a s s i f i e d a c c o r d i n g t o J u r a s z (1979b). Repeated d i v i n g i n a r e a s w i t h h i g h b a c k s c a t t e r i n g d e n s i t i e s was a l s o i n t e r p r e t e d as f e e d i n g b e h a v i o r . T h i s assumption i s s t r o n g l y s u p p o r t e d by s e v e r a l SONAR-readings which suggest the pr e s e n c e of whales w i t h i n a k r i l l l a y e r (see F i g . 4 , c o u r t e s y o f Wm. D o l p h i n , u n p u b l . ) . S u r f a c e t r a v e l and s u r f a c e r e s t i n g were c l a s s i f i e d as n o n - f e e d i n g b e h a v i o r . An ARA E t 100 Ma r i n e Temperature Probe was used t o measure a i r t e m p e r a t u r e , and water t e m p e r a t u r e s a t 10, 20, 30, 40, and 50 m d e p t h . However, due t o b a t t e r y problems, t h e s e d a t a were r e n d e r e d u s e l e s s . S u r f a c e s a l i n i t y was measured w i t h a 0 1 • ? } - -•V'- . . . W h a l e s K r i l l l a y e r B o t t o m F i g . 4. SONAR-Reading Suggests Whales ' (Arrows) Diving into K r i l l Layer at 60 m Depth (Courtesy of Wm. Dolphin^unpubl.). r e f T a c t o m e t e r , and t u r b i d i t y w i t h t h e a i d o f a S e c c h i d i s c . The sea s t a t e was noted a c c o r d i n g t o t h e B e a u f o r t s c a l e ; tows were not f e a s i b l e above s t a t e 3. A l l p l a n k t o n samples, as w e l l as whale s c a t samples ( c o l l e c t e d w i t h a s m a l l p l a s t i c b u c k e t ) , were p r e s e r v e d i n 5% b u f f e r e d f o r m a l i n s o l u t i o n . B. LABORATORY TECHNIQUES P l a n k t o n samples were t r a n s f e r r e d t h r o u g h a g r a d i e n t s e r i e s t o a 70% e t h a n o l s o l u t i o n . "Type 2" mesh s i z e was a c c i d e n t a l l y used f o r s t r a i n i n g a l l samples d u r i n g t h i s p r o c e s s , r e s u l t i n g i n some l o s s of s m a l l e r organisms from "type 1" samples. The d i s p l a c e m e n t volume was r e c o r d e d by t r a n s f e r r i n g t h e s t r a i n e d sample t o a measuring c y l i n d e r w i t h a known amount of w a t e r . In o r d e r t o reduce e r r o r i n d u c e d by s p l i t t i n g , t h e samples were p r e - s e l e c t e d f o r r a r e and l a r g e r - t h a n - a v e r a g e o r g a n i s m s . Samples c o n t a i n i n g a p p r o x i m a t e l y 600 or more p l a n k t e r s were s p l i t w i t h a Folsom p l a n k t o n s p l i t t e r . A minimum o f 300 organisms were c o u n t e d and i d e n t i f i e d i n t h o s e samples c o n t a i n i n g more than t h a t number. G r e a t e r a l i q u o t s o f e u p h a u s i i d s t h a n o f o t h e r taxonomic groups were o f t e n a n a l y z e d i n o r d e r t o i n c r e a s e a c c u r a c y of k r i l l c o m p o s i t i o n i n samples w i t h low k r i l l p e r c e n t a g e . The Haasman s p i r a l (Haasman,1983) was used f o r c o u n t i n g a l i q u o t s , and p r o v e d v e r y e f f i c i e n t . E u p h a u s i i d s were i d e n t i f i e d a c c o r d i n g t o McDonald (1928), Boden (1950), and Endo and Komaki (1979). The nomenclature f o r l a r v a l e u p h a u s i i d s was adapted from t h e l a s t - m e n t i o n e d a u t h o r s . Endo's s u g g e s t i o n s ( p e r s . comm.) a i d e d i n i d e n t i f y i n g the u n - d e s c r i b e d l a r v a l forms of Thysanoessa s p i n i f e r a . Rare i r r e g u l a r E uphausia p a c i f i c a i n s t a r s w i t h an even number (2n) of t e l s o n s p i n e s , were combined w i t h c o u n t s o f t h e s t a g e w i t h (2n+l) t e l s o n s p i n e s . P o s t - f u r c i l i a r e u p h a u s i i d s were measured from e y e - c e n t e r t o i n s e r t i o n - o f - t e l s o n (EI l e n g t h ) t o t h e n e a r e s t 0.5 mm. Average l e n g t h s f o r l a r v a l i n s t a r s were t a k e n from above-mentioned l i t e r a t u r e , w h i l e T. s p i n i f e r a l a r v a e were measured d i r e c t l y . L i t e r a t u r e v a l u e s o f t o t a l l e n g t h (TL) were c o n v e r t e d t o E I L by c a l c u l a t i n g t h e EIL/TL p e r c e n t a g e based on drawings by t h e a u t h o r s (% EIL/TL f o r T. r a s c h i i = 0.80, T. l o n g i p e s = 0.77, E. p a c i f i c a = 0.81). Copepods were i d e n t i f i e d a c c o r d i n g t o Gardner and Szabo (1982). Average l e n g t h v a l u e s f o r CV/CVI s t a g e s as w e l l as f o r CI - C I I I s t a g e s of Calanus m a r s h a l l a e and Neocalanus plumchrus were adopted from t h i s r e f e r e n c e , c o n s i d e r i n g o n l y v a l u e s f o r f e m a l e s . C o p e p o d i t e s t a g e s s m a l l e r t h a n 1.3 mm were counted c o l l e c t i v e l y and were a s s i g n e d an average l e n g t h v a l u e o f 0.9 mm f o r l a t e r biomass e s t i m a t e s . A l l o t h e r z o o p l a n k t e r s were i d e n t i f i e d a c c o r d i n g t o Smith (1977) and F u l t o n (1971). The " E I " l e n g t h / w e t w e i g h t r e l a t i o n s h i p s shown by F u l t o n (1971 and 1972) were used f o r biomass e s t i m a t e s o f e u p h a u s i i d s and copepods. C o n v e r s i o n e q u a t i o n s were d e t e r m i n e d w i t h the " c u r v e - f i t t i n g program" on t h e H e w l e t t P a c k a r d 97 C a l c u l a t o r , and a r e shown i n Tab.3. For damaged e u p h a u s i i d s , an average biomass was c a l c u l a t e d based on t h e p r e d o m i n a n t l y caught l i f e COORDINATES* x,y) RANGE(x) CURVE REGR.COEFF . DET^COEFF. (L In mm) TYPE (a,b) (rE2) EU. EIL v s . WW 1.1- 8.0 y=axEb a •= .05 1 .00 b = 2.34 EU. EIL v s . WW 8.5-20.0 y=axEb a = .01 .99 b = 2.96 CO. TL v s . PL .25-5.0 y«a+bx a - -.21 1 .00 b « .83 CO. PL v s . WW .7 -5.0 y=axEb a = .12 1 .00 b " 2.4 1 Tab. 3. Equation Determinants Used i n Biomass Estimations, Accordin to Curves Drawn by Fulton (1971). EU = Euphausiid, CO = Copepod, WW = Wet Weight, EIL = Length from (Mid)Eye to Insertion of Telson, PL = Prosome Length, TL = Total Length. RELATIVE DENSITY 1 2 3 4 5 CLOSEST APPROXIMATION OF AMOUNT OF BACKSCATTER OVER WIDTH OF LAYER 1/8 1/4 1/2 3/4 7/8 Tab. 4. Visual Scale Used to Determine the Relative Density of Backscattering Layers from SONAR-Readings. s t a g e of each s p e c i e s . Whale s c a t subsamples of a p p r o x i m a t e l y 120 ml were examined under d i s s e c t i n g and compound m i c r o s c o p e s f o r i d e n t i f i a b l e remains of f o o d o r g a n i s m s . SONAR p r i n t - o u t s were a n a l y z e d f o r t y p e , d e p t h , v e r t i c a l e x t e n s i o n , and r e l a t i v e d e n s i t y o f b a c k s c a t t e r i n g t a r g e t s . C o n c u r r e n t l y n oted whale (and o c c a s i o n a l l y p r e y ) b e h a v i o r a l l o w e d a c l a s s i f i c a t i o n 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 : a) P l a n k t o n F e e d i n g T a r g e t s b) P l a n k t o n Non-Feeding T a r g e t s c) F i s h T a r g e t s ( e x c l u d e d from a n a l y s i s ) In g e n e r a l , c o n t i n u o u s bands were i n t e r p r e t e d as r e p r e s e n t i n g p l a n k t o n , r a t h e r than f i s h a g g r e g a t i o n s . B a c k s c a t t e r i n g l a y e r s l e s s than 10 m a p a r t were r e g a r d e d as one t a r g e t . B a c k s c a t t e r d e n s i t y was e s t i m a t e d q u a l i t a t i v e l y on a r e l a t i v e s c a l e from 1 t o 5 (see Tab.4). Only r e a d i n g s done on the same m a g n i f i c a t i o n s c a l e c o u l d be i n c l u d e d ; the 100 m i n t e r v a l r e a d i n g s were s e l e c t e d f o r t h e i r predominant use. The UBC MTS Computing System i n c o n j u n c t i o n w i t h t h e "MINITAB" s t a t i s t i c a l program was used f o r n u m e r i c a l d a t a a n a l y s i s . V a l u e s e x p r e s s e d as p r o p o r t i o n (p) were c o n v e r t e d t o the a s i n u s o f the square r o o t o f (p) p r i o r t o a n a l y s i s . A l l d a t a were t e s t e d f o r normal d i s t r i b u t i o n , b e f o r e u n p a i r e d T - t e s t s ( v a r i a n c e non-pooled) or W i l c o x o n two sample rank t e s t s were a p p l i e d a p p r o p r i a t e l y . I f not o t h e r w i s e i n d i c a t e d , a s i g n i f i c a n c e l e v e l o f 0.05 p r o b a b i l i t y may be assumed f o r s t a t e m e n t s about s i g n i f i c a n t d i f f e r e n c e . I I I . RESULTS AND DISCUSSION A. HUMPBACK WHALE FEEDING CONDITIONS IN 1983 1. P h y s i c a l E n v i r o n m e n t a l Parameters The r a n g e s , and where a p p l i c a b l e , mean v a l u e s o f s u r f a c e s a l i n i t i e s and S e c c h i d i s c depths a r e shown i n Tab.5. SURFACE SALINITY Cl) TURBIDITY D-SECCHI(m) study area std. s i t e k r i l l swarms study area std. s i t e k r i l l swarms MEAN — 26.3 27.3 — 6.9 9.8 RANGE 21.0 30.0 23.0 30.0 26.0 29.0 3.2 12.2 3.5 12.2 6.6 11.9 N 61 30 5 60 30 5 Tab. 5. Surface S a l i n i t y and Turbidity Measurements i n Frederick Sound During July/August 1983. The range o f s u r f a c e s a l i n i t i e s measured i n FS i n 1983 f u l l y c o v e r s t h e range measured i n 1982 and 1983 ( f o r a co m p a r i s o n w i t h e a r l i e r seasons see Wing and Krieger,1983). We r e c o r d e d a d d i t i o n a l v a l u e s up t o 0.8%© l o w e r , and 2.1%© h i g h e r i n 1983, which i s l i k e l y due t o more f r e q u e n t measurements, and more s a m p l i n g l o c a l e s . S a l i n i t i e s a t k r i l l s u r f a c e swarmings (see Tab.5) were s l i g h t l y l o wer than t h e minimum s a l i n i t y v a l u e o f 28 % o g e n e r a l l y r e p o r t e d f o r e u p h a u s i i d o c c u r r e n c e s ( M a u c h l i n e and F i s h e r , 1969). I t i s p r o b a b l e t h a t Thysanoessa  r a s c h i i , r e p o r t e d l y a c o a s t a l s p e c i e s , and predominant i n the o b s e r v e d swarms, has s p e c i a l a d a p t a t i o n s t o d e a l w i t h lower s a l i n i t i e s t han most o t h e r E u p h a u s i a c e a . T r a n s p a r e n c y c o n d i t i o n s appear t o be s i m i l a r , i f s l i g h t l y c l e a r e r than c o n d i t i o n s i n 1964/65 d e s c r i b e d by P i c k a r d (1967), who measured a S e c c h i d i s c depth o f 5 m a t " s t a t i o n 10" (near our " s t a n d a r d s i t e " ) , and a range o f 2 - 10 m S e c c h i d i s c depth f o r a l l o f FS. No t r a n s p a r e n c y d a t a a r e a v a i l a b l e from more r e c e n t y e a r s . I t i s o f i n t e r e s t t o note t h a t i n 1983, S e c c h i d i s c depths b e f o r e J u l y 23 were t y p i c a l l y below 6.1 m, and g r e a t e r a f t e r t h i s d a t e , and g e n e r a l l y g r e a t e r a t s u r f a c e swarmings. 31 2. A v a i l a b l e Z o o p l a n k t o n Resources a. Z o o p l a n k t o n C o m p o s i t i o n The same s p e c i e s o f e u p h a u s i i d s and copepods were found as i n t h e 1982 season (see Wing and K r i e g e r , 1983), w i t h t h e e x c e p t i o n o f two o c c u r r e n c e s o f Euchaeta c a l i f o r n i c a . T h i s c a l a n o i d copepod i s of Southern o r i g i n , and r a r e even i n B.C. w a t e r s , where i t i s thought t o denote warm water i n t r u s i o n (Gardner and Szabo,1982). T h i s s p e c i e s * N o r t h e r n d i s p l a c e m e n t may be e x p l a i n e d by t h e 1982/83 ENSO event (McLain,1983). S t a n d i n g s t o c k i n t h i s s t u d y i s r e p r e s e n t e d by t h e " s t a n d a r d s i t e " c r o p , which was sampled r e g u l a r l y t h r o u g h o u t the season. The d i f f e r e n t n e t t y p e s r e t a i n e d d i f f e r e n t sub-p o p u l a t i o n s from t h e water column, as r e s u l t s o f "type 1" and "type 2" n e t s (shown i n Tab.6 and 7, r e s p e c t i v e l y ) i n d i c a t e . As e x p e c t e d , s i g n i f i c a n t l y g r e a t e r p r o p o r t i o n s o f amphipods and c h a e t o g n a t h s were caught w i t h t h e l a r g e r mesh s i z e ( t y p e 2 ) , and a s i g n i f i c a n t l y g r e a t e r p r o p o r t i o n o f copepods w i t h t h e s m a l l e r mesh s i z e ( t y p e 1 ) . Copepod biomass was a l s o s i g n i f i c a n t l y g r e a t e r i n "type 1" samples (see Tab.8). The p r o p o r t i o n o f e u p h a u s i i d s i n numbers i n each sample d i d not v a r y s i g n i f i c a n t l y between th e two n e t t y p e s . However, s i g n i f i c a n t l y more e u p h a u s i i d biomass per volume f i l t e r e d was sampled w i t h "type 1" n e t s (see Tab.8). T h i s can be e x p l a i n e d by t h e f a c t t h a t s i g n i f i c a n t l y more l a r v a l s t a g e s were r e t a i n e d i n " t ype 1" n e t s , w h i l e j u v e n i l e and a d u l t e u p h a u s i i d s were caught i n e q u a l l y s m a l l a b s o l u t e numbers w i t h both mesh s i z e s . To what degree t h e o b s e r v e d 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 m p o s i t i o n between "type 1" and "type 2" net c a t c h e s r e p r e s e n t SAMPLE NO. EUPHAU-SIIDS COPE-PODS AMPHI-PODS ARROW-WORMS TOTAL ZOO PL. 4 766 11,282 178 192 12,796 7 750 22,294 134 320 24,354 8 1,040 4,480 232 30 6,474 10 1,882 6,586 144 24 10,260 16 1,388 9,278 192 30 12,289 18 606 14,230 196 66 16,740 22 402 6,938 278 256 8,350 25 62 5,582 228 80 6,526 27 1,812 16,922 180 88 19,602 X 968 10,844 196 121 13,043 s 586 5,327 42 103 5,780 Tab. 6. Species Composition of Standing Zooplankton Stock i n Frederick Sound i n July 1983, Taken by Oblique Hauls ("Type 1 Nets") Btwn. 100 and 150 m Depth. Values Represent Numbers per Standard Tow, F i l t e r -ing 37.8 m3 Seawater. SAMPLE NO. EUPHAU-SIIDS COPE-PODS AMPHI-PODS ARROW-WORMS TOTAL ZOO PL. 31 42 542 40 28 670 32 108 879 45 20 1,091 33 49 429 37 18 554 35 308 284 85 11 711 36 61 269 57 6 426 37 11 491 16 8 540 38 281 235 69 4 633 39 111 170 67 18 383 40 28 94 56 25 222 42 76 95 59 29 268 43 3 57 24 4 92 50 28 192 79 5 322 51 7 346 247 5 608 53 2 164 126 21 320 56 2 103 364 6 480 61 755 89 160 5 1,019 X 117 277 96 13 521 s 188 212 89 9 262 Tab. 7. Species Composition of Standing Zooplankton Stock i n Frederick Sound i n late July/August 1983, Taken by Oblique Hauls ("Type 2 Nets") Btwn. 100 and 150 Depth. Values Represent Numbers per Standard Tow, F i l t e r i n g 37.8 m^  Seawater. TYPE 1 SAMPLE EUPH.BIOMASS mg/m^  COPE.BIOMASS mg/m^  4 18.34 37.89 7 28.56 68.64 8 12.21 16.92 10 15.78 31.22 16 24.53 73.01 18 9.49 47.68 22 7.25 89.96 25 1.17 33.61 27 17.76 87.49 X 15.01 54.05 s 8.05 24.94 Tab. 8. Biomass Values for Eu-phausiids and Copepods Caught i n Standard Site Tows with Two Different Mesh Sizes During July (Type 1) and Late July/ August (Type 2) 1983 i n Frederick Sound. TYPE 2 SAMPLE EUPH.BIOMASS mg/m^  COPE.BIOMASS mg/m3 31 3.04 20.86 32 4.99 30.87 33 2.62 16.49 35 14.29 11.16 36 2.80 11.56 37 .45 17.89 38 12.12 11.11 39 8.01 7.53 40 1.43 3.73 42 5.35 4.45 43 .20 2.33 50 2.08 9.98 51 .58 12.20 53 .19 6.35 56 .25 4.16 61 103.16 4.71 X 10.10 10.96 s 24.38 7.34 a n a t u r a l s u c c e s s i o n o f p l a n k t o n communities cannot be d e t e r m i n e d from the a v a i l a b l e d a t a , because th e d i f f e r e n t s a m p l i n g methods were a p p l i e d c o n s e c u t i v e l y . Only l a t e - s e a s o n d a t a ("type 2" c a t c h e s ) a r e c o n s i d e r e d f o r t h e comparison w i t h s t a n d i n g c r o p c o m p o s i t i o n d a t a a v a i l a b l e f o r August o f t h e p r e v i o u s season (Wing and K r i e g e r , 1 9 8 3 ) , shown i n Tab.9 . In both s e a s o n s , t h e r a n k i n g o f dominant z o o p l a n k t o n groups by n u m e r i c a l abundance was copepods > e u p h a u s i i d s > c h a e t o g n a t h s . D i f f e r e n c e s i n t h e r e l a t i v e p r o p o r t i o n s o f t h e s e groups i n t h e d i f f e r e n t seasons a r e l i k e l y due, a t l e a s t i n p a r t , t o d i f f e r e n c e s i n s a m p l i n g equipment used ( c f . Tab.9). Because of t h e l a c k of a net c l o s i n g mechanism, o n l y tows th r o u g h swarms a t the s u r f a c e were t a k e n t o r e p r e s e n t h i g h d e n s i t y p l a n k t o n a g g r e g a t i o n s i n t h i s s t u d y . T h e i r c o m p o s i t i o n i s shown i n Tab.10. Wing and K r i e g e r (1983 and 1984) a n a l y z e d s u b s u r f a c e l a y e r s of h i g h b a c k s c a t t e r i n g d e n s i t i e s i n 1982 (summer) and 1983 ( p o s t - s e a s o n ) f o r s p e c i e s c o m p o s i t i o n , and a comparison w i t h my 1983 (summer) d a t a i s shown i n Tab.11. The impact of d i f f e r e n c e s i n net mouth a r e a and mesh s i z e s h o u l d be l e s s e v i d e n t i n c a t c h e s from h i g h d e n s i t y a g g r e g a t i o n s , because of d e c r e a s e d a v o i d a n c e c a p a b i l i t y ( F l e m i n g e r and C l u t t e r , 1 9 6 5 ) and n e t - c l o g g i n g . (Our 1983 s u r f a c e samples appeared t o a c c u r a t e l y r e p r e s e n t t h e p l a n k t o n community as o b s e r v e d from the b o a t . ) T h e r e f o r e , our p l a n k t o n c a t c h e s a r e r o u g h l y comparable w i t h Wing and K r i e g e r ' s r e s u l t s . The dominance of e u p h a u s i i d s ( c o m p r i s i n g 90+ % o f t h e t o t a l c a t c h ) i n p l a n k t o n swarms i s e v i d e n t i n both s e a s o n s , and seems t o be t y p i c a l f o r h i g h d e n s i t y a g g r e g a t i o n s o f the a r e a . AUGUST 1982* N=7 AUGUST 1983 N=16 % EUPHAUSIIDS 19.1 22.4 % COPE PODS 26.3 52.8 % ARROWWORMS 5.1 2.6 TOW TYPE oblique oblique DEPTH RANGE (m) 90-130 106-150 MESHSIZE (mm) .56x.56 .80x1.10 NETMOUTH AREA (m2) .56 .13 (2 X) Tab. 9. Comparison of Standing Zooplankton Crop Composition, and Sampling Methods Used i n Frederick Sound August 1982 and 1983. * Percentages Derived from Total Counts Given i n Wing and Krieger (1983) SAMPLE NO. DEPTH (m) EUPHAU-SIIDS COPE-PODS AMPHI-PODS ARROW-WORMS TOTAL ZOOPL. 52 5 118 11 28 0 189 54 0 21 46 17 9 110 55 0 1,080 264 60 2 1,437 57 0 4,310 8 40 0 4,391 58 0 7,168 0 80 0 7,248 X 1 2,539 66 45 2 2,675 s 2 2,789 100 23 3 2,762 Tab. 10. Species Composition of Plankton Surface Swarms i n August 1983 i n Frederick Sound, Taken by Horizontal Tows with "Type 2 Nets". Values Represent Numbers per 7 Min. Tow at approx. 1.5 Knot Towing Speed, F i l t e r i n g 82 nr* Sea-water. 1982 JULY/AUG. N=9 AUG. N=5 1983 SEPT. N=6 % EUPHAUSIIDS 89.6 94.9 95.3* % AMPHIPODS .7 1.7 not given % ARROWWORMS 2.6 .1 mostly <1 TOW TYPE horizontal 7-9 min. horizontal 7 min. s. 1982 DEPTH RANGE (m) 11-60 0-5 10-126 MESHSIZE (mm) IKMT** .80x1.10 8. 1982 NETMOUTH AREA (m2) IKMT** .13 (x2) s. 1982 Tab. 11. Comparison of Plankton Swarm Composition, and Sampling Methods Used i n Frederick Sound 1982 and 1983. * Denotes Average of Percentages Given for Tows within DSL's by Krieger and Wing (1984) ** For Detailed Description See Aron (1962) There appears t o be a s l i g h t i n c r e a s e o f the e u p h a u s i i d p r o p o r t i o n between 1982 and 1983. The a v a i l a b l e e v i d e n c e s u g g e s t s t h a t arrowworms may be one group of p l a n k t e r s t h a t has p r o p o r t i o n a l l y d e c r e a s e d a t t h e same t i m e , b. Z o o p l a n k t o n Biomass D i s p l a c e m e n t volumes of z o o p l a n k t o n were o n l y f e a s i b l e f o r samples t a k e n w i t h "type 2" n e t s , because of t h e h i g h p h y t o p l a n k t o n c a t c h e s i n "type 1" n e t s . The d i s p l a c e m e n t volumes of s t a n d a r d s i t e tows, r e p r e s e n t a t i v e o f s t a n d i n g z o o p l a n k t o n s t o c k , a r e shown i n Tab.12. Our 1983 mean v a l u e o f 42.7 ml/1000m3 d i f f e r s by more than one o r d e r o f magnitude from the 1982 mean v a l u e o f 810.6 ml/1000 m3 (Wing and K r i e g e r , 1 9 8 3 ) . I n c r e a s e d net a v o i d a n c e o f our s m a l l e r net frame by t h e l a r g e r organisms i s l i k e l y t h e main r e a s o n f o r t h i s d i s c r e p e n c y . K r i e g e r and Wing (1984) r e p o r t no s i g n i f i c a n t d i f f e r e n c e s between b a c k s c a t t e r i n g d e n s i t i e s o f August 1982 and September 1983 i n FS. The d i s p l a c e m e n t volumes i n h o r i z o n t a l tows t h r o u g h h i g h d e n s i t y s u r f a c e a g g r e g a t i o n s o f z o o p l a n k t o n a r e shown i n Tab.13 i n a comparison w i t h s u r f a c e tows t h r o u g h h i g h d e n s i t y a g g r e g a t i o n s i n 1982 by Wing and K r i e g e r (1983). One 1983 sample (no.52, c f . Tab.10) was e x c l u d e d because of i t s h i g h c o n t e n t o f woody d e b r i s , as w e l l as one 1982 sample of m o d i f i e d d e n s i t y (whale b u b b l e - n e t t i n g ) . At a comparable t o w i n g speed and l e n g t h , and by s a m p l i n g a p p r o x i m a t e l y one t e n t h o f the amount of water sampled by the l a r g e r net frame i n 1982, we caught c o n s i d e r a b l y l e s s than o n e - t e n t h of t h e z o o p l a n k t o n amount caught i n 1982 by Wing and SAMPLE MAX.DEPTH VOLUME NO. (m) (ml/l,000m3) 31 148 39.8 32 149 66.3 33 149 46.4 35 148 39.8 36 150 33.2 37 130 39.8 38 106 53.1 39 150 53.1 40 150 26.5 42 150 33.2 43 149 13.1 50 150 46.4 51 150 53.1 53 150 33.2 56 150 53.1 61 150 53.1 X 146 42.7 8 11 12.6 Tab. 12. Displacement Volumes (Adjusted to l,000m3) of Standard S i t e Tows with "Type 2 Nets" i n Frederick Sound late July/August 1983 ( F i l t e r v o l . = 37.8m3). DATE 1982 SAMPLE VOL. DATE 1983 SAMPLE VOL. (ml/30 Min)* (ml/30 Min) (ml/l,000m3) Aug. 20 1,176.9 Aug. 17 3.0 6.1 Aug.. 20 1,375.3 Aug. 17 27.0 76.5 Aug. 20 1,965.3 Aug. 19 72.0 728.3 Aug. 19 147.0 422.3 X 1,505.8 X 62.3 308.3 s 334.8 s 54.8 289.2 Tab. 13. Displacement Volumes (After Exclusion of Large J e l l y f i s h ) of Tows Through Surface Plankton Swarms i n Frederick Sound (1982:IKMT; 1983:"Type 2 Nets"). * Data Taken from Wing and Krieger (1983) K r i e g e r (1983), d e s p i t e our s m a l l e r mesh s i z e ( c f . Tab.13). However, th e p r e s e n t d a t a a r e not s u f f i c i e n t t o suggest a d i f f e r e n c e between seasons i n t h e biomass of h i g h d e n s i t y a g g r e g a t i o n s . S c a r c i t y o f o b s e r v a t i o n s , the s u b j e c t i v i t y i n v o l v e d i n j u d g i n g " h i g h d e n s i t y " o f a t a r g e t , and d i f f e r e n c e s i n equipment a r e p r o b a b l e c o n t r i b u t o r s t o t h e o b s e r v e d d i f f e r e n c e s . 3. Z o o p l a n k t o n i n Humpback Whale D i e t a. C h a r a c t e r i s t i c s o f F e e d i n g T a r g e t s C h a r a c t e r i s t i c v a r i a b l e s o f p l a n k t o n communities w i t h i n l e s s than 100 m o f f e e d i n g whales were compared t o t h o s e i n e q u a l v i c i n i t y o f whales engaged i n a c t i v i t i e s o t h e r than f e e d i n g . S i n c e two d i f f e r e n t s a m p l i n g t e c h n i q u e s ("type 1" n e t s - o b l i q u e tows, and "type 2" n e t s - h o r i z o n t a l tows) were a p p l i e d under t h e s e c i r c u m s t a n c e s , two s e t s o f a n a l y s i s w i l l be c onducted (see Tab.14 and 1 5 ) . Parameters o f samples t a k e n a t s i t e s where whales were f e e d i n g i m m e d i a t e l y p r i o r t o , but not d u r i n g s a m p l i n g , were d i v i d e d i n t o two c a t e g o r i e s : Those t o be u n i n f l u e n c e d by the whales' d e p a r t u r e were i n c l u d e d i n t h e " f e e d i n g " c a t e g o r y ( i . e . p h y s i c a l p a r a m e t e r s , and k r i l l c o m p o s i t i o n ) , and t h o s e t o be i n f l u e n c e d were i n c l u d e d i n the " n o n - f e e d i n g " c a t e g o r y ( i . e . biomass v a l u e s ) . B a c k s c a t t e r i n g c h a r a c t e r i s t i c s from a v a i l a b l e SONAR r e a d - o u t s were compared c o l l e c t i v e l y , i n c l u d i n g b a c k s c a t t e r i n g d a t a from one a d d i t i o n a l f e e d i n g i n c i d e n t ( c f . Tab.16 and A p p e n d i x ) . A l t h o u g h the s c a r c i t y o f d a t a f o r b i d s d e f i n i t e c o n c l u s i o n s , comparisons between f e e d i n g and n o n - f e e d i n g s i t e s SAMPLE NO. WHALE ACTIVITY NO. WH's DEPTH (m) SALINITY <%) TURBIDITY D 8 (m) T.R. RATIO EUPH.BM (mg/m3) COPE.BM (mg/m3) o 55 52 stopped feeding 3 s f c . 27.0 6.6 CO * * M 55 skim-feeding 1 s f c . 27.5 9.8 CO 38.6 4.2 FEE1 57 lunge-feeding 1 s f c . 26.0 9.6 00 187.0 .1 FEE1 58 lunge-feeding 1 s f c . 27.0 11.0 00 387.5 0 DING 49 surface r e s t i n g 1 17 27.0 7.2 CO 0 0 -FEE] 52 surface t r a v e l 3 s f c . * * * 4.3 .1 NON- 54 deep diving 2 s f c . 29.0 11.9 CO .7 .7 SIGNIFICANT P = .1 * * * - -DIFFERENCE P = .2 - - - + -Tab. 14. Comparison of Surface Feeding and Non-Feeding Sites i n Frederick Sound Aug. 1983. Plankton Samples Taken with "Type 2" Horizontal Net Hauls (T.R. RATIO = No. of T. r a s c h i over No. Other K r i l l ; BM = Biomass; + Sign. D i f f . , - No Sign. D i f f . , * Not A p p l i c a b l e ) . WH = Whales. SAMPLE NO. WHALE ACTIVITY NO. WH's DEPTH (m) SALINITY TURBIDITY Ds (m) T.R. RATIO EUPH.BM (mg/m3) COPE.BM (mg/m3) o 20 stopped feeding 5 47 22.0 3.8 25 * * M 21 feeding 10 69 22.0 4.4 00 16.5 41.3 Q W W 24 feeding 2 59 23.0 6.7 112 16.5 34.6 26 stopped feeding 5 78 27.5 6.2 145 * * 26.5 feeding 3 47 no data no data 38 52.7 99.6 o 17 surface travel 2 100 25.5 3.2 4 14.0 162.8 5N-FEEDI1 20 surface t r a v e l 5 47 * * * 9.0 56.1 5N-FEEDI1 23 surface resting 2 80 23.0 5.9 17 8.5 12.6 26 surface t r a v e l 2 78 * * * 8.0 28.0 SIGNIFICANT P = .1 * * * - -DIFFERENCE P = .2 - - + + -Tab. 15. Comparison of DSL Feeding and Non-Feeding Sites i n Frederick Sound i n July 1983. Plankton Samples Taken with "Type 1" oblique Net Hauls. Symbols as i n Tab. 14. SAMPLE DEPTH OF BS THICKN. OF REL. DENSITY TIME OF DAY NO. (m) BS (m) OF BS (1-5) (hrs) 21 21 26 4 20 = 06 24 19 17 3 20:22 z 26.5 29 12 5 20:38 M P 28 31 20 * 20:13 W W 55 0 5 * 16:33 b 57 0 5 * 13 = 37 58 0 5 * 18:13 17 71 30 2 O z 20 21 12 3 o w 23 34 17 1 NON- 26 35 22 * 54 0 8 * [CANT JNCE p = .05 - - * :GNIFI [FFERI p = .1 - - -I—< to r—r Q p = .2 + Tab. 16. Comparison of Backscatter (BS) Characteristics at Feeding and Non-Feeding Sites i n Frederick Sound July/August 1983 (+ Sign. D i f f . , - No Sign. D i f f . , * Not Applicable). from both d a t a s e t s s uggest t h a t e u p h a u s i i d biomass i s the most l i k e l y o f t h e t e s t e d parameters t o t r i g g e r f e e d i n g a c t i v i t y . The t h r e s h o l d k r i l l d e n s i t y p r o b a b l y l i e s between 4.3 and 38.6 mg/m3 (see Tab.14), as sampled w i t h our methods. A c t u a l t h r e s h o l d d e n s i t i e s a r e l i k e l y t o be c o n s i d e r a b l y h i g h e r , s i n c e B r o d i e (1978) e s t i m a t e d a minimum e u p h a u s i i d c o n c e n t r a t i o n around 17.5 g/m3 f o r a s k i m - f e e d i n g f i n w h a l e , and t h e " g u l p i n g method" p r e d o m i n a n t l y used by humpbacks can be assumed t o r e q u i r e even h i g h e r c o n c e n t r a t i o n s . C o i n c i d e n t a l l y , whales were o b s e r v e d s k i m - f e e d i n g d u r i n g tows no. 55 and 57 ( l o w e r c o n c e n t r a t i o n s ) , and g u l p i n g d u r i n g tow no. 58 ( h i g h e r c o n c e n t r a t i o n ; c f . Tab.14). S u r p r i s i n g l y , K r i e g e r and Wing (1984) r e p o r t humpbacks f e e d i n g i n FS on e u p h a u s i i d d e n s i t i e s ( h y d r o a c o u s t i c assessment) between 0.7 and 4.3g/m 3, a d e n s i t y even lower than a s s e s s e d by our l e s s a c c u r a t e net samples. A p r e y d e n s i t y o f 1 g/m3 would r e s u l t i n t h e u n r e a l i s t i c f e e d i n g e f f o r t o f 7,000 " g u l p s " / h , i f t h e d a i l y 1 t o n f o o d r e q u i r e m e n t was t o be f i l l e d on such u n c o n c e n t r a t e d d e n s i t y , a t a g u l p i n g volume of a p p r o x i m a t e l y 6 m 3 ( L o c k y e r , 1 9 8 1 ) . Humpback whales have been known t o employ v a r i o u s methods of c o n c e n t r a t i n g p r e y ( J u r a s z , 1 9 7 9 b ; Hain e t . a l . , 1 9 8 3 ; Hamner,1984a), but a t h r e s h o l d or f i n a l p r e y d e n s i t y f o r any o f t h e s e methods i s not known. No i n d i c a t i o n was found f o r s a l i n i t y , t u r b i d i t y , o r copepod d e n s i t y t o be o f i n f l u e n c e on whale f e e d i n g a c t i v i t y . The f a c t t h a t copepod biomass exceeds e u p h a u s i i d biomass i n the o b l i q u e h a u l s o f both " f e e d i n g " and " n o n - f e e d i n g " c a t e g o r i e s ( c f . Tab.15) appears t o be an a r t i f a c t o f the s a m p l i n g method ( o n l y a s m a l l p o r t i o n of the tow a c t u a l l y sampled t h e p l a n k t o n l a y e r ) . W ith a f r i n g e d i a m e t e r of 0.7 mm (Nemoto,1973), humpback b a l e e n i s c o m p a r a t i v e l y c o a r s e . L a r g e copepods (e.g. C a l a n u s c r i s t a t u s ) have been r e p o r t e d from humpback stomach c o n t e n t s ( P i k e , 1 9 5 0 ; Nemoto,1959), but a r e g e n e r a l l y not c o n s i d e r e d a major f o o d i t e m o f t h i s b a l e e n whale s p e c i e s . R e s u l t s i n Tab.15 suggest t h a t p l a n k t o n a g g r e g a t i o n s w i t h a h i g h T. r a s c h i i p r o p o r t i o n i n i t s k r i l l component a r e more l i k e l y t o become humpback p r e y t h a n t h o s e w i t h r e l a t i v e l y l e s s T. r a s c h i i . S i n c e h i g h T. r a s c h i i p r o p o r t i o n c o i n c i d e s w i t h h i g h e r a b s o l u t e e u p h a u s i i d d e n s i t y i n our samples (Tab.15), a p r e f e r e n c e by whales f o r t h i s p r e y s p e c i e s based on d i e t a r y needs may not be c o n c l u d e d . The e c o l o g i c a l s i g n i f i c a n c e o f t h i s l o c a l l y abundant e u p h a u s i i d w i l l be d i s c u s s e d i n a l a t e r s e c t i o n . B a c k s c a t t e r i n g d a t a a l s o s uggest d e n s i t y (biomass) t o be the most i m p o r t a n t d i s t i n g u i s h i n g f a c t o r between f e e d i n g and n o n - f e e d i n g s i t e s (Tab.16). A l t h o u g h not i n d i c a t e d by our d a t a , the t h i c k n e s s o f a b a c k s c a t t e r i n g l a y e r may w e l l i n f l u e n c e f e e d i n g a c t i v i t y , but s h o u l d be compared w i t h i n c a t e g o r i e s of e q u a l d e n s i t y , i n a l a r g e r d a t a s e t . S i m i l a r l y , t h e depth of the p r e y may p l a y a r o l e i n i n i t i a t i n g f e e d i n g a c t i v i t y . D o l p h i n (1984) found t h a t l a y e r s near s u r f a c e or near bottom a r e more l i k e l y t o be p r e y e d upon by whales than midwater p r e y a g g r e g a t i o n s . A p r e f e r e n c e f o r near s u r f a c e p l a n k t o n i c p r e y i s a l s o i n d i c a t e d by t h e f a c t t h a t most p l a n k t o n - o r i e n t e d f e e d i n g a c t i v i t y was o b s e r v e d d u r i n g t h e l a t t e r p a r t o f the day (Tab.16), which i s i n a c c o r d a n c e w i t h o b s e r v a t i o n s by Nemoto (1973). D i v i n g e n e r g e t i c s ( w i t h r e s p e c t t o t h e v e r t i c a l m i g r a t i o n o f p l a n k t o n ) c o u l d be one o f t h e r e a s o n s f o r t h i s p r e f e r e n c e , but a d d i t i o n a l b e h a v i o r a l and m e t a b o l i c s t u d i e s a r e needed t o c l a r i f y t h i s i s s u e , b. D i e t a r y C l u e s from F e c a l Samples A f t e r stomach samples from dead humpback whales became a r a r i t y i n the l a t e 1960's, a f t e r t h e s p e c i e s ' p r o t e c t i o n , t h e d i r e c t assessment of t h e i r d i e t p r e s e n t e d a problem. A l t h o u g h f e c a l samples from c e t a c e a n s a r e d i f f i c u l t t o c o l l e c t i n t h e f i e l d , and may not be as e a s i l y i d e n t i f i a b l e and r e p r e s e n t a t i v e as stomach c o n t e n t s , t h e y p r e s e n t a f e a s i b l e and p r e f e r a b l e a l t e r n a t i v e t o " c o n t r o l l e d whale h a r v e s t i n g . . . i n S o u t h e a s t A l a s k a " ( E n g l i s h , 1 9 8 3 ) . P r i o r t o summer 1983, no r e p o r t s on the e x a m i n a t i o n o f humpback whale f e c e s a r e a v a i l a b l e t o t h e b e s t o f my knowledge. We c o l l e c t e d 7 f e c a l samples d u r i n g t h e 1983 season (Tab.17), and i d e n t i f i e d p a r t s a r e l i s t e d i n Tab.18. Photographs of s e l e c t e d p a r t s a r e shown i n F i g . 5 . Most of t h e examined m a t e r i a l was w e l l - d i g e s t e d , and o f c l a y - l i k e s t r u c t u r e . A b r i c k - r e d t o red-brown c o l o r was common t o a l l samples, and may be a t t r i b u t e d t o the c a r o t e n o i d s common i n e u p h a u s i i d s ( M a u c h l i n e and F i s h e r , 1 9 6 9 ) . However, K r i e g e r and Wing (1984) p o i n t out t h a t i d e n t i f i c a t i o n o f f o r a g e by f e c a l c o l o r ( k r i l l r r e d , f i s h : g r a y / w h i t e ) i s q u e s t i o n a b l e . They note t h e dominance of d i f f e r e n t t y p e s o f e u p h a u s i i d p a r t s i n t h e i r two d i f f e r e n t i a l l y c o l o r e d f e c a l samples. P a r t s o f c r u s t a c e a n s o t h e r than e u p h a u s i i d s were found i n our samples (cp. Tab.18), and were i n a comparably much l e s s SAMPLE DATE GENERAL LOCATION FIELD OBSERVATIONS 1 7/16 McDonald Rock soft 2 8/04 N of Gambier I s l . soft 3 8/08 Round Rock red, s o l i d clumps 4 8/10 S a i l I s l . soft 5 8/16 S a i l I s l . soft 6 8/19 Gambier I s l . brickred, lumpy 7 8/24 W-Brother I s l . soft Tab. 17. Humpback Whale Fecal Samples Collected i n Frederick Sound During the 1983 Season. CONTENTS FECAL SAMPLE 1 2 3 4 5 6 7 Euphausiid Antennal Scale Euphausiid Mandible Euphausiid Spermatophore Euphausiid 6th Abdominal Segment Euphausiid Uropod + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Brachyuran Zoea Brachyuran Megalops Hyperiid Amphipod Head Hyperiid Amphipod Tailend Crustacean Eye + + + + + + + + + Fish Bone Fish Vertebra +*+ + + + + + Tab. 18. Identified Remains (+) from Humpback Whale Feces Collected i n Frederick Sound 1983. * Herring Dentary a) Mandibles b) Inner Uropod c) Spermatophores d i g e s t e d s t a t e than e u p h a u s i i d p a r t s i n g e n e r a l . Complete B r a c h y u r a n c r a b l a r v a e and c a u d a l p o r t i o n s o f amphipods p o s s e s s e d an a l m o s t undamaged e x o s k e l e t o n . L i m i t a t i o n s i n humpback whale d i g e s t i v e c a p a c i t i e s , and thus i n t h e n u t r i t i o n a l v a l u e of c e r t a i n z o o p l a n k t e r s t o t h e w h a l e s , p o s s i b l y e x i s t . S e v e r a l nematodes of t h e genus A n i s a c i s were found i n one sample (no.3, Tab.18). T h i s genus i s an i n t e s t i n a l p a r a s i t e of v a r i o u s marine mammals, and has been r e p o r t e d t o o c c u r i n the b a l e e n whale genus B a l a e n o p t e r a i n t h e humpback f a m i l y (Yamaguti,1961). I t s o c c u r r e n c e i n Megaptera s h o u l d be n o t e d . The i n f r e q u e n t c o l l e c t i o n s u c c e s s o f f e c a l m a t e r i a l p r e v e n t s a q u a n t i t a t i v e a n a l y s i s o f d i e t a r y c o n s t i t u e n t s . However, q u a l i t a t i v e a n a l y s i s has proven a s u c c e s s f u l means of v e r i f y i n g f i e l d o b s e r v a t i o n s of p r e y s e l e c t i o n , as w e l l as showing p o s s i b l e s e l e c t i v e d i g e s t i o n p r o c e s s e s which may i n f l u e n c e p r e y s e l e c t i o n . For f u t u r e s t u d i e s , c h e m i c a l a n a l y s e s of f a t and p r o t e i n c o n t e n t s e x c r e t e d may shed f u r t h e r l i g h t on e c o l o g i c a l e f f i c i e n c y and e n e r g e t i c s o f f e e d i n g w h a l e s . B. ECOLOGICAL SIGNIFICANCE OF THE EUPHAUSIID T.RASCHII Ve r y l i t t l e i s known about t h e s p e c i f i c e c o l o g y o f e u p h a u s i i d s i n S E - A l a s k a . E n g l i s h (1983) and Wing and K r i e g e r (1983) g i v e day-time depth d i s t r i b u t i o n s f o r each o f t h e f o u r common k r i l l s p e c i e s ( l i s t e d i n T a b . l , t o p ) , and E n g l i s h (1983) has a l s o r e c o r d e d l e n g t h - f r e q u e n c y d i s t r i b u t i o n s f o r s e l e c t e d d e v e l o p m e n t a l s t a g e s o f the f o u r s p e c i e s . Endo ( p e r s . comm.) has r e c e n t l y p r e p a r e d a growth c u r v e f o r Thysanoessa r a s c h i i i n N o r t h e r n S E - A l a s k a , showing a l i f e span of up t o t h r e e seasons i n t h e s e w a t e r s . The l i f e h i s t o r y o f e u p h a u s i i d s i s known t o v a r y i n t r a s p e c i f i c a l l y between d i f f e r e n t l o c a t i o n s ( M a u c h l i n e and F i s h e r , 1 9 6 9 ) , and has not been r e p o r t e d f o r any o f t h e s p e c i e s i n t h e s t u d y a r e a . The r e l a t i v e abundance o f e u p h a u s i i d s p e c i e s i n t h e SE-A l a s k a n k r i l l p o p u l a t i o n has r e c e i v e d l i t t l e a t t e n t i o n i n p r e v i o u s whale p r e y s t u d i e s . 1. E c o l o g i c a l N i c h e I found no s i g n i f i c a n t d i f f e r e n c e i n t h e s p e c i e s c o m p o s i t i o n o f the k r i l l p r o p o r t i o n between "type 1" and "type 2" s t a n d a r d s i t e samples ( c f . Tab.19). The rank of dominance o f k r i l l s p e c i e s i n s t a n d i n g z o o p l a n k t o n c r o p o f FS i n 1983 i s as f o l l o w s : T. r a s c h i i > T. l o n g i p e s > E. p a c i f i c a > T. s p i n i f e r a  Thysanoessa r a s c h i i i s r e p o r t e d as the dominant e u p h a u s i i d s p e c i e s i n FS f o r the 1981 and 1982 seasons as w e l l (Wing and K r i e g e r , 1 9 8 3 ) . Wing ( p e r s . comm.) g i v e s a dominance r a n k i n g of TYPE 1 TYPE 2 SAMPLE T.R. T*L« T»S« £*P« SAMPLE T.R. T.L. T.S. E.P. NO. NO. 4 262 172 4 40 31 12 4 0 24 I 194 104 4 96 32 96 12 0 0 8 344 38 0 2 33 38 8 0 1 10 612 6 0 16 35 298 6 0 0 16 1,126 0 0 6 36 56 1 0 2 18 230 2 0 22 37 3 1 0 6 22 210 0 0 0 38 277 0 0 4 25 14 0 0 16 39 82 6 1 14 27 390 8 0 4 40 23 0 0 2 X 375.8 36.7 .9 22.4 42 59 3 0 1 % EUPH 86.2 8.4 .2 5.1 43 3 0 0 0 50 12 14 0 0 Tab. 19 K r i l l Composition of 51 5 0 0 0 Standing Zooplankton Stock i n Frederick 53 2 0 0 0 Sound July/Aug. 1983. Values Represent Num- 56 0 0 0 2 bers of I d e n t i f i e d Euphausiids per Stan- 61 668 31 0 24 dard Tow. F i l t e r i n g 37.8 Ww % x * ^ » J . » m3 Seawater. X 102.1 5.4 .1 5.0 7o EUPH 90.7 4.8 .1 4.4 T.R. = Thysanoessa r a s c h i , T.L. E.P. = Euphausia p a c i f i c a , EUPH = T. longipes, T.S. = T. s p i n i f e r a , = Total I d e n t i f i e d Euphausiids. . 52 T. r a s c h i i > T. s p i n i f e r a > T. l o n g i p e s > E. p a c i f i c a f o r t h e 1982 s e a s o n , and a r a n k i n g o f T. r a s c h i i > E. p a c i f i c a > T. l o n g i p e s > T. s p i n i f e r a f o r e a r l y f a l l o f 1983. A l t h o u g h h i s r e s u l t s a r e m a i n l y based on h i g h d e n s i t y a g g r e g a t i o n s r a t h e r than r e p r e s e n t i n g t h e whole water column as i n our own s t a n d a r d c r o p samples, th e two 1983 r a n k i n g s appear s i m i l a r . The r e l a t i v e amounts o f E. p a c i f i c a and T. l o n g i p e s may have i n c r e a s e d a t the expense o f T. s p i n i f e r a between 1982 and 1983. The k r i l l p o p u l a t i o n o f t h e sampled s u r f a c e a g g r e g a t i o n s ( c f . Tab.10 and 14) was m o n o s p e c i f i c i n a l l c a s e s , and c o n s i s t e d o f pure c a t c h e s o f T. r a s c h i i . In a l l c a s e s ( e x c e p t sample no.54) whales were o b s e r v e d f e e d i n g on t h e sampled p o p u l a t i o n . A l s o i n t h e p r e s e n c e of f o r a g i n g w h a l e s , f o u r tows t h r o u g h s u r f a c e a g g r e g a t i o n s i n August 1982 and f o u r tows t h r o u g h DSL's (btwn. 60-130 m) i n September 1983, showed a k r i l l c o m p o s i t i o n o f 98% and 70-93% T. r a s c h i i , r e s p e c t i v e l y (Wing, p e r s . comm.). The o n l y s u r f a c e swarm sampled i n t h e absence o f whales i n 1983 ("type 1" n e t s ; not i n c l . i n Tab.10) had r e p r e s e n t a t i v e s o f a l l f o u r common SE-A l a s k a n e u p h a u s i i d s p e c i e s . S p e c i f i c i n f o r m a t i o n on t h e k r i l l c o m p o s i t i o n o f h i g h d e n s i t y a g g r e g a t i o n s i n t h e absence of whales i s not a v a i l a b l e from o t h e r s t u d i e s in- t h e a r e a . T h e r e f o r e , a d i e t a r y p r e f e r e n c e by whales f o r the e u p h a u s i i d T. r a s c h i i would be a premature c o n c l u s i o n ( c f . s e c . A.3a.). N u m e r i c a l abundance and s p e c i e s -s p e c i f i c swarming a r e more l i k e l y causes f o r t h i s s p e c i e s ' dominance i n o b s e r v e d whale f e e d (Wing, p e r s . comm.). 53 D e s p i t e T. r a s c h i i ' s r e p o r t e d dominance i n r e c e n t y e a r s , e a r l i e r l i t e r a t u r e s u g g e s t s t h a t o t h e r e u p h a u s i i d s p e c i e s , n o t a b l y E u p h a u s i a p a c i f i c a , may have p r e v a i l e d i n t h i s a r e a i n seasons p r i o r t o 1981 ( E a r l e , 1 9 7 7 ; J u r a s z , 1 9 7 9 b ; B r y a n t e t . a l . , 1 9 8 1 ) . Wing ( p e r s . comm.) s u s p e c t s m i s i d e n t i f i c a t i o n of j u v e n i l e T. r a s c h i i t o be a p o s s i b l e r e a s o n f o r t h i s , s i n c e h i s own " s p o r a d i c samples from 1962-1975 a l s o show a dominance of T. r a s c h i i i n t h e n o r t h e r n p a r t of S E - A l a s k a . " However, p e r c e i v a b l e changes i n t h e s p e c i e s c o m p o s i t i o n of k r i l l do seem t o o c c u r between seaso n s , and s i n c e t h e s p e c i f i c e c o l o g y of each of t h e f o u r k r i l l s p e c i e s might be q u i t e d i f f e r e n t , a s u c c e s s i o n i n dominance i s l i k e l y t o a f f e c t humpback whale f e e d i n g e c o l o g y as w e l l . The f o l l o w i n g two s e c t i o n s w i l l p r o v i d e f u r t h e r i n f o r m a t i o n on t h e l o c a l e c o l o g y of T. r a s c h i i . 2. L a r v a l Development D u r i n g our s t u d y , o n l y T. r a s c h i i was caught i n s u f f i c i e n t numbers t o a l l o w an e x a m i n a t i o n o f i t s l a r v a l development. E a r l y f u r c i l i a s t a g e s (F(0) t o F(4S1N) i n c l . ) were caught o n l y w i t h "type 1" and "type 3" n e t s , w h i l e l a t e r s t a g e s were r e t a i n e d w i t h a l l mesh t y p e s used. T o t a l numbers o f l i f e h i s t o r y s t a g e s caught over the s t u d y p e r i o d a r e shown i n Tab.20. M a u c h l i n e (1965) n o t e d about the development of T. r a s c h i i : "...a f u r c i l i a l a r v a which has no p l e o p o d s . . . a t t h e n e x t m o u l t , d e v e l o p s 1,2,3,4, or 5 r u d i m e n t a r y n o n - s e t o s e p a i r s o f p l e o p o d s . . . At t h e f o l l o w i n g m o u l t , non-setose p l e o p o d s become s e t o s e and p o s t e r i o r segments w i t h no p l e o p o d s o b t a i n r u d i m e n t a r y n o n - s e t o s e p l e o p o d s . " LIFE HISTORY STAGE COLLECTIVE TERM FREQUENCY F(O) F(O) 1,538 F(1N) 0 F(2N) 18 F(3N) |F(N) 172 F(4N) ) 1,314 F(5N) 393 F(1S4N) 0 F(2S3N) F(3S2N) | F(SN) 18 108 F(4S1N) 807 F(7Tsp)=F(5S) 2,980 F(5Tsp) F(3Tsp) | F ( T 6 P ) 1,030 826 F(lTsp) 4,522 FF FF 7,230 Tab. 20. Frequencies of T. raschi Developmental Stages Caught over the Study Period i n Frederick Sound 1983. T h e r e f o r e , w h i l e a l l l a r v a e d e v e l o p c o n s e c u t i v e l y t h r o u g h the l a t e r f u r c i l i a s t a g e s , a p a r t i c u l a r l a r v a does not complete a l l v a r i a n t s o f e a r l y f u r c i l i a s t a g e s , as was f o r m e r l y b e l i e v e d ( M a u c h l i n e and F i s c h e r , 1 9 6 9 ) . The p e r c e n t f r e q u e n c i e s o f e a r l y f u r c i l i a l a r v a e caught between 11 and 24 J u l y 1983 i n FS w i t h the two s m a l l e r mesh t y p e s a r e shown i n F i g . 6 . A c c o r d i n g t o t h i s e v i d e n c e , t h e dominant d e v e l o p m e n t a l pathway o f T. r a s c h i i i n t h e s t u d y a r e a i n J u l y appears t o be as f o l l o w s : F ( 0) > F(4N) > F(4S1N) (»F4" pathway) Less f r e q u e n t l y o c c u r r i n g pathways, i n t h e o r d e r o f d e c r e a s i n g f r e q u e n c y , i n c l u d e the f o l l o w i n g : F(0) > F(5N) > F(5S) ("F5" pathway) F(0) > F(3N) > F(3S2N) ("F3" pathway) F(0) > F(2N) > F(2S3N) ("F2" pathway) These f i n d i n g s agree w e l l w i t h M a u c h l i n e ' s (1965) d e s c r i p t i o n of t h i s s p e c i e s ' development from t h e C l y d e Sea, where t h e same r a n k i n g o f dominant d e v e l o p m e n t a l pathways was found " i n May and l a t e r . " W h i l e M a u c h l i n e (1965) found a s m a l l number of F(1N) s t a g e l a r v a e and no F(1S4N) specimens, n e i t h e r l i f e s t a g e was e n c o u n t e r e d i n our FS m a t e r i a l , nor i n m a t e r i a l examined by E i n a r r s o n (1945) i n t h e N o r t h A t l a n t i c . Thus, the F(0) > F(1N) > F(1S4N) d e v e l o p m e n t a l pathway seems t o be r a r e i n t h i s e u p h a u s i i d s p e c i e s , i n t h e N o r t h P a c i f i c as w e l l as i n the N o r t h A t l a n t i c where i t was p r e v i o u s l y s t u d i e d . M a u c h l i n e (1980) s u g g e s t s t h a t the d e v e l o p m e n t a l pathway i n c e r t a i n e u p h a u s i i d s p e c i e s i s i n f l u e n c e d by f o o d a v a i l a b i l i t y and o t h e r e n v i r o n m e n t a l c o n d i t i o n s . The genus Thysanoessa i s s a i d t o have a s t r o n g tendency f o r the dominant XT* » »< •"•V • » • • O I N 2 N 3 N 4 N 5 N 1 S 4 N 2 S 3 N 3 S 2 N 4 S 1 N F U R C I L I A S T A G E F C > . 6. Percent Frequencies of Early F u r c i l i a Stages of T. raschi Caught with "Type 1" and "Type 3" Nets i n Frederick Sound i n July 1983. Numbers Indicate Number of Pleopods: N = Non-Setose S = Setose. pathway t o f o l l o w t h e "F5" development under optimum e n v i r o n m e n t a l c o n d i t i o n s ( E i n a r r s o n , 1 9 4 5 ; M a u c h l i n e and F i s h e r , 1 9 6 9 ; M a u c h l i n e , 1 9 8 0 ) . D e v i a t i o n s from t h i s . p a t t e r n , such as a dominant "F4" pathway have been r e p o r t e d f o r T. r a s c h i i , depending on time o f y e a r (Mauchline,1965) and l o c a t i o n ( E i n a r r s o n , 1 9 4 5 ) . In both above-mentioned c a s e s , a p r e v a i l i n g "F4" pathway was a s s o c i a t e d w i t h h i g h e r t e m p e r a t u r e s , a l t h o u g h a p o s i t i v e c o r r e l a t i o n had not been t e s t e d . However, i t i s p o s s i b l e t h a t the t r e n d o f r e c e n t c o a s t a l warming (cp. McLain,1983) i s p a r t i a l l y r e s p o n s i b l e f o r the o b s e r v e d "F4" pathway dominance of T. r a s c h i i i n FS 1983. 3. B r e e d i n g C o h o r t s The development of T. r a s c h i i from egg t o a d o l e s c e n c e ( p o s t f u r c i l i a ) has been r e p o r t e d t o t a k e about two months i n t h e C l y d e Sea ( M a u c h l i n e , 1 9 6 6 ) . For a g e n e r a l o v e r v i e w o f d e v e l o p m e n t a l p r o g r e s s i n FS, l a r v a l s t a g e s l i s t e d i n Tab.20 were d i v i d e d i n t o t h r e e groups: a) E a r l y F u r c i l i a ( E F ) , t o i n c l u d e a l l s t a g e s w i t h an i n c o m p l e t e s e t of p l e o p o d s , i . e . F(0) - F(4S1N) b) L a t e F u r c i l i a ( L F ) , t o i n c l u d e a l l s t a g e s w i t h a complete s e t of 5 s e t o s e p l e o p o d s , but w i t h premature numbers of t e l s o n s p i n e s , i . e . F(7Tsp) - F ( l T s p ) c) P o s t - F u r c i l i a ( P F ) , t o i n c l u d e j u v e n i l e s and a d u l t s The r e l a t i v e p e r c e n t a g e o f each of t h e s e groups i n any o f our p l a n k t o n samples w i t h a t o t a l T. r a s c h i i count >20 was p l o t t e d a g a i n s t time ( F i g . 7 ; f o r d a t e s see Tab.21). Peak o c c u r r e n c e s (>80% of the sampled p o p u l a t i o n ) o f t h e r e s p e c t i v e 58 EF % 120. + 80.+ * 40.+ * 0.+ + -o. LF % 120.+ 10. •2** **2 * * ** 2 * * — + + + +days 20. 30. 40. 50. 80.+ 40.+ + -O. io . 20. PF% 120.+ 80.+ 30. 40. --+days 50. 40.+ 0.+ O. I 10. I 20.J {30. 40. T 2 I 3 I 4 | 5 6 1 7 days week Fi g . 7. Relative Percentage Frequencies of EF, LF, and PF Developmental Groups of T. raschi Over the Time of the Study Period (EF = Early F u r c i l i a , LF «= Late F u r c i l i a , PF = P o s t - F u r c i l i a ; cf. Text). EF Specimens Were Not Retained i n "Type 2 Nets" Used After Week 2 (A). Data Points Expressed as Numbers Denote Multiple Observations. 59 l a r v a l groups were o b s e r v e d i n : mid J u l y - EF group, end J u l y - LF group, end Aug. - PF group, i n d i c a t i n g a d e v e l o p m e n t a l time o f a p p r o x i m a t e l y s i x weeks from e a r l y f u r c i l i a t o p o s t - f u r c i l i a s t a g e s . C o n s i d e r i n g one m o l t per f u r c i l i a i n s t a r e x c e p t f o r t h e F(7Tsp) s t a g e which r e q u i r e s f i v e m o l t s ( M a u c h l i n e and F i s h e r , 1 9 6 9 ; M a u c h l i n e , 1 9 6 5 ) , t h e m o l t i n g r a t e o f T. r a s c h i i i n FS i s e s t i m a t e d t o be a p p r o x i m a t e l y once e v e r y f o u r days. S i n c e s i x i n s t a r s (2 n a u p l i a , 1 m e t a n a u p l i u s , 3 c y r t o p i a s t a g e s ) p r e c e e d t h e f i r s t f u r c i l i a s t a g e , spawning o f the o b s e r v e d c o h o r t s h o u l d have t a k e n p l a c e around mid/end of June. The o b s e r v e d t i m i n g of T. r a s c h i i l a r v a l development i s i n agreement w i t h two e a r l i e r o b s e r v a t i o n s a v a i l a b l e f o r t h i s a r e a ( E n g l i s h , 1 9 8 3 ) : On June 12,1981, o n l y a d u l t specimens ( i n c l . f e m a les w i t h mature eggs) were caught, w h i l e a n o t h e r a n a l y z e d c a t c h from J u l y 20,1981 r e n d e r e d l a r g e amounts of f u r c i l i a l a r v a e and no a d u l t s . An i m p o r t a n t r o l e o f T. r a s c h i i (and o f f o o d organisms w i t h s i m i l a r t i m i n g ) i n t h e e c o l o g y o f Megaptera i n S E - A l a s k a i s i m p l i e d by t h e f a c t t h a t t h e m a j o r i t y o f humpbacks r e p o r t e d l y a r r i v e i n t h e s e w a t e r s a t t h e b e g i n n i n g o f J u l y ( J u r a s z , 1 9 7 9 a ; Anon.,1984), s h o r t l y a f t e r t h e spawning p e r i o d . L i m i t e d p r e d a t i o n on b r e e d i n g a g g r e g a t i o n s i s l i k e l y an e c o l o g i c a l advantage of t h i s t i m i n g . S p r i n g spawning of T. r a s c h i i has been found t o c o r r e l a t e c l o s e l y w i t h t h e s p r i n g p h y t o p l a n k t o n bloom ( E i n a r r s o n , 1 9 4 5 ; Berkes,1976; F a l k - P e t e r s o n and Hopkins,1981), but p r o l o n g e d or m u l t i p l e s p r i n g spawning p e r i o d s a r e r e p o r t e d t o o c c u r i n t h i s s p e c i e s (McDonald,1928; F a l k - P e t e r s o n and Hopki n s , 1 9 8 1 ) . A c c o r d i n g t o Par s o n s e t . a l . (1966), t h e s p r i n g bloom i n SE-A l a s k a n c o a s t a l w a t e r s i s n o r m a l l y e x p e c t e d t o b e g i n around March. Areas of d i a t o m blooms were o b s e r v e d i n FS i n 1983 as l a t e as J u l y 28. A week-by-week a n a l y s i s o f l a r v a l forms r e v e a l e d t h e p a r t i a l l y o v e r l a p p i n g development o f a t l e a s t t h r e e s e p a r a t e s u b - c o h o r t s over t h e s t u d y p e r i o d (see Tab.21 and F i g . 8 ) . The s u b - c o h o r t s a r e each s e p a r a t e d i n development by about one week, o r r o u g h l y two m o l t s . F i g . 8e-f s u g g e s t s a d e c r e a s i n g s t r e n g t h o f s u b - c o h o r t s 1-3. Note the merging o f t h e two s u b - c o h o r t s i n t h e F(7Tsp) s t a g e ( F i g . 8 c ) and t h e p r o g r e s s i v e development of t h e f i r s t s u b - c o h o r t t o t h e next l a r v a l form, w h i l e t h e second and t h i r d s u b - c o h o r t go t h r o u g h f u r t h e r m o l t s i n t h e F(7Tsp) s t a g e ( F i g . 8 d ) . By t h e end o f t h e season ( F i g . 8 g ) , a l l t h r e e o b s e r v e d s u b - c o h o r t s a r e merging i n t o t h e p o s t - f u r c i l i a group. A c c o r d i n g t o l e n g t h measurements by McDonald (1928), t h e mean d a i l y growth r a t e o f the whole T. r a s c h i i s p r i n g c o h o r t was e s t i m a t e d a t 0.11 mm/day. Endo's d a t a ( p e r s . comm.) sugg e s t a s i m i l a r growth r a t e . T h i s v a l u e i s a l s o comparable t o growth e s t i m a t e s o f E. p a c i f i c a s p r i n g c o h o r t s i n B.C. (Heath,1977), and i s between 2 and 7 t i m e s g r e a t e r than the mean d a i l y w i n t e r growth r a t e measured f o r two o t h e r Thysanoessa s p e c i e s o f t h a t r e g i o n ( F u l t o n and L e B r a s s e u r , 1984). WEEK DATES N WEEKLY MOLTING STAGES OF SUB-COHORTS 1st 2nd 3rd 1. 7/11-7/17 8 ,SN 7Tsp 0 N (Calyptopis) 2. 7/18-7/24 13 7Tsp 7Tsp SN 7Tsp 0 N 3". 7/25-7/31 5 7Tsp 7Tsp 7Tsp 7Tsp SN 7Tsp 4. 8/01-8/07 4 5Tsp 3Tsp 7Tsp 7Tsp 7Tsp 7Tsp 5. 8/08-8/14 2 ITsp FF 5Tsp 3Tsp 7Tsp 7Tsp 6. 8/15-8/21 4 FF PF ITsp PF 5Tsp 3Tsp 7. 8/22-8/28 2 FF FF FF PF ITsp FF Tab. 21. Weekly Development of Spawning Sub-Cohorts of T. raschi i n Frederick Sound 1983 (Observed Stages are F u r c i l i a Stages F( ) and Po s t - F u r c i l i a FF). 7 0 -3,2,1 6 0 -c) week 3 5 0 -4 0 -3 0 -2 0 -IO-O (no data) -1 1 r—1 1 r O N SN 7, 5, 3, ITsp PF 1 F i g . 8. Graphic Analysis of T. raschi De-velopment i n Fre-derick Sound over the 1983 Study Pe-r i o d . Numbers 1, 2, 3, Indicate Sub-Cohorts (Cp. Tab. 21) . x-axis: F u r c i l i a F( ) y-axis: % Frequency 70-60-50 40-30-20-lO-O-l d) week 4 70H 60H 50-I 40H 30H 20A l O ^ (no data)  ~i i i i 1—i 1 r— O N SN 7, 5, 3, ITspPF O e) week 5 (no data) "1 1 1 1 1 1 1 1— O N SN 7, 5, 3, ITspPF 70-I 60H 50H 40-I 30H 20-^ lO o f) week 6 (no data) 7 0 H 60-50H 40H 30-I 20-^ l O J 1 1 T ~l 1 O N SN 7, 5, 3, ITspPF g) week 7 (no data) _ n r—\—9-O N SN 7, 5, 3, ITspPF Fi g . 8. (Cont.) I t i s p o s s i b l e t h a t a second b r e e d i n g c o h o r t o r i g i n a t e d towards th e end o f t h e s e a s o n , but t h a t i t s e a r l y s t a g e s were not sampled w i t h t h e l a r g e r mesh s i z e then used. W h i l e McDonald (1928) found e v i d e n c e f o r a second, f a l l c o h o r t o f T. r a s c h i i i n the C l y d e Sea, M a u c h l i n e (1966) and Berkes (1976) r e p o r t o n l y one ( s p r i n g ) spawning f o r t h i s s p e c i e s i n t h e C l y d e Sea and t h e G u l f of S t . Lawrence, r e s p e c t i v e l y . F u r t h e r r e s e a r c h on t h i s e u p h a u s i i d s p e c i e s i n S E - A l a s k a i s n e c e s s a r y , i n o r d e r t o t e s t t h e h y p o t h e s i s of a f a l l b r e e d i n g p e r i o d i n t h i s l o c a l i t y . The p r e s e n c e , and i f so, t h e t i m i n g and a n n u a l r e c r u i t m e n t of a f a l l c o h o r t o f T. r a s c h i i may g r e a t l y i n f l u e n c e t h e e x t e n t o f t h e whale f e e d i n g p e r i o d i n S E - A l a s k a . 65 IV. CONCLUSIONS Our 1983 study g e n e r a l l y showed a s i m i l a r zooplankton composition i n the F r e d e r i c k Sound area as i n the p r e v i o u s season ( c f . Wing and Krieger,1983), c o n s i d e r i n g both s t a n d i n g sto c k and plankton swarms. However, smal l changes i n the k r i l l p o p u l a t i o n were e v i d e n t . The p r o p o r t i o n of e u p h a u s i i d s i n high d e n s i t y aggregations had s l i g h t l y i n c r e a s e d s i n c e 1982, and the s p e c i e s composition of k r i l l showed minor i n t e r a n n u a l f l u c t u a t i o n s i n the r e l a t i v e p r o p o r t i o n s of the f o u r common l o c a l e u p h a u s i i d s , with Thysanoessa r a s c h i i having remained the dominant s p e c i e s . Swarms with high d e n s i t i e s of t h i s e u p h a u s i i d appeared to be p r i m a r i l y preyed upon by humpback whales, l i k e l y due to T. r a s c h i i ' s abundance and swarming behavior. A p r e l i m i n a r y a n a l y s i s of the l o c a l ecology of T. r a s c h i i showed a d e v i a t i o n from t h i s s p e c i e s ' optimum developmental pathway i n 1983. L i k e l y c l i m a t o l o g i c a l causes, as w e l l as p o s s i b l e e c o l o g i c a l e f f e c t s of t h i s circumstance c a l l f o r f u r t h e r i n v e s t i g a t i o n . A b e t t e r understanding of the i n t e r r e l a t i o n s h i p s between atmospheric, oceanographic, and b i o l o g i c a l processes may l e a d to the use of e c o l o g i c a l i n d i c a t o r s (such as sea s u r f a c e temperature or c e r t a i n c h a r a c t e r i s t i c s of the k r i l l p o p u l a t i o n ) i n p r e d i c t i n g and managing f u t u r e whale p o p u l a t i o n changes. The c o n t r i b u t i o n o f , and continued demand f o r , long-term e c o l o g i c a l surveys has been demonstrated, as w e l l as the need f o r s t a n d a r d i z e d sampling equipment i n order to compare seasonal zooplankton p o p u l a t i o n s . Future s t u d i e s are encouraged t o f o c u s on l a r g e - s c a l e comparisons o f f e e d i n g and n o n - f e e d i n g s i t e s , and on the p r o b a b i l i t i e s o f e n c o u n t e r i n g s u f f i c i e n t l y dense swarms a t a g i v e n l o c a l p r o d u c t i v i t y r a t e . 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APPENDIX The f o l l o w i n g two pages show SONAR-readings o f f e e d i n g and n o n - f e e d i n g b a c k s c a t t e r i n g t a r g e t s i n t h e pr e s e n c e o f humpback whales (Megaptera n o v a e a n g l i a e ) i n F r e d e r i c k Sound, S E - A l a s k a , summer 1983 ( c o u r t e s y of Wm. D o l p h i n , u n p u b l . ) . Numbers r e f e r t o c o r r e s p o n -d i n g z o o p l a n k t o n samples, "B" i n d i c a t e s the bottom, and an arrow i n d i c a t e s t h e maximum s a m p l i n g d e p t h . D i a g a n o l t r a c e s denote t h e p a t h o f t h e net as d e t e c t e d by SONAR ( c f . no.'s 17, 21, 23, and 26.5). 21 F E E D I N G 1 *.*. J •;, Li ~ ..... ^ a 17 20 ' i I" 1 : %v.]-.'-' n B 3* 23 N O N - F E E D I N G 

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