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The effects of experience on the acquisition of food by juvenile chum salmon, Oncorphynchus Keta, in… Levy, David Alan 1977

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THE EFFECTS OF EXPERIENCE ON THE ACQUISITION OF FOOD BY JUVENILE CHOM SALHON, ONCORHYNCHUS KETA , IN A TIDAL CREEK OF THE SQUAHISH RIVER ESTUARY, B.C., By DAVID ALAN LEVY B . S c , M c G i l l U n i v e r s i t y , 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Dept. of Zoology) 5Je accept t h i s t h e s i s as conforming t o the r e g u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1977 David Alan Levy, 1977 In present ing th is thes is in p a r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f r ee ly ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th is thes is for s c h o l a r l y purposes may be granted by the Head of my Department or by h is representa t ives . It is understood that copying or p u b l i c a t i o n of th is thes is for f i n a n c i a l gain sha l l not be allowed without my writ ten pe rm i ss i on . Department of ZOOLOGY The Un ivers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date September 30. 1977 A b s t r a c t The f e e d i n g behaviour of j u v e n i l e chum salmon, Oncorhynchus keta , was analysed using a combination l a b o r a t o r y and f i e l d tecfanigue. The e f f e c t s of experience with a s i n g l e prey type were si m u l a t e d by f e e d i n g animals i n the l a b o r a t o r y with one of the f o l l o w i n g food types - the amphipod Anisogammarus c o n f e r v i c o l u g , the mysid Heomysis l e r e e d i s , or Oregon H o i s t P i s h P e l l e t s . , A f t e r 30 days of l a b o r a t o r y e x p e r i e n c e , the experimental animals were marked and r e l e a s e d i n t o an i n t e r t i d a l creek of the Squamish R i v e r estuary, and subsequently r e c a p t u r e d . A n a l y s i s o f t h e stomach contents o f i n t r o d u c e d f i s h showed that the p r o p o r t i o n of Neomysis i n mysid-conditioned f i s h was g r e a t e r than the p r o p o r t i o n of Neomy.sis i n both the other experimental groups and n a t u r a l l y o c c u r i n g chum j u v e n i l e s i n the t i d a l creek. In c o n t r a s t , t h e r e was no d i f f e r e n c e i n the p r o p o r t i o n o f Anisogammarus i n the d i e t of amphipod-conditioned f i s h compared to the other experimental groups. Only very few amphipods were a c g u i r e d by experimental animals compared to n a t u r a l l y o c c u r r i n g chum j u v e n i l e s . , R e l a t i v e numbers o f e p i b e n t h i c i n v e r t e b r a t e s present i n the water column were assessed by means of morning and evening plankton tows i n the t i d a l creek c l o s e t o the time of the experimental i n t r o d u c t i o n s . Anisogammarus was shown to undergo a d i e l v e r t i c a l m i g r a t i o n and was a p p a r e n t l y u n a v a i l a b l e to f i s h p r e d a t o r s i n the t i d a l creek at the time of the i n t r o d u c t i o n s . The l a c k of a measurable treatment e f f e c t i n amphipod-conditiqned f i s h was a t t r i b u t e d to t h i s f a c t o r . i i i The p r o p o r t i o n of Neomyjsis i n the d i e t of experimental f i s h was d i f f e r e n t a c r o s s a l l treatment groups on two c o n s e c u t i v e i n t r o d u c t i o n dates. The higher r e a l i z e d a v a i l a b i l i t y of Negmysis on the second i n t r o d u c t i o n date i n d i c a t e d that d i f f e r e n c e s i n the r e l a t i v e abundance of v a r i o u s prey types occurred on a d a i l y b a s i s i n the t i d a l creek. i v T a ble 'Of Contents Ab s t r a c t ................................... ... ............ i i LIST OF FIGURES V LI ST OF TABLES v i ACKNOWLEDGESENTS . . . . . w.. :,.;,.>>•;.•.„••,... ... ..... . . . ... , v i i i INTRODUCTION 1 HETHODS AND HATERIALS ., ...V 4 Regular Sampling . • 4 Laboratory C o n d i t i o n i n g *. 6 F i e l d I n t r o d u c t i o n s 11 Benthic Sampling . .... ..... ........ ..•< «. 13 Laboratory Stomach A n a l y s i s 14 RESULTS .. . . . . 16 Regular Sampling .............................. 16 C o n d i t i o n i n g Experiments .............................. 19 Benthic Prey Samples 33 DISCUSSION ,.y*-.yv>,.-.>>:.,^  36 E f f e c t s Of Experience 36 Prey A v a i l a b i l i t y In The T i d a l Creek ^ y , , 4 3 Food Of Chum Salmon In The Sguamish Es t u a r y 46 LITERATURE CITED ..... . . . . . . . . , . . y , . r . l? 50 APPENDICES . .. . ... . . ....... . . .. . ,. .. v,-.y,:.^.vV..cvV ,•....:/ 53 V LIST OF FIGORES Fi g u r e 1. L o c a t i o n Of The T i d a l Creek Study Area In The Squamish E s t u a r y . 5 F i g u r e 2. Two Of The Common I n t e r t i d a l Crustacea Found In The Sguamish E s t u a r y . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Fig u r e 3. A J u v e n i l e Chum Salmon, Qncorhy.nchus k e t a • , In A Tank With The E s t u a r i n e Mysid, Neomy.sis mercedis . ....8 Fig u r e 4. View Of The T i d a l Creek At Successive Tide L e v e l s . , • ,. .... 12 Fi g u r e 5. Diet Of J u v e n i l e Chum Salmon In The T i d a l Creek Of The Sguamish Estuary On A p r i l 21 And May 26,1976. ... 17 Fig u r e 6. D i e t Of J u v e n i l e Chum Salmon In The T i d a l Creek Of The Squamish Estuary On June 8 And J u l y 1,1976 18 F i g u r e 7., Comparison Of The D i e t Of Wild Chum J u v e n i l e s And S e l e c t e d Experimental Groups Released Into The T i d a l Creek On J u l y 15/76. ...................................22 F i g u r e 8. Comparison Of The Diet Of Wild Chum J u v e n i l e s And S e l e c t e d Experimental Groups Released Ipto The T i d a l Creek On J u l y 16/76 , 23 v i liIST OF TABLES Table 1. S i z e s Of D i f f e r e n t Food Types Used I n C o n d i t i o n i n g Experiments. ... .. •. 9 Table 2. S i z e s Of J u v e n i l e Chum Salmon Sampled From The T i d a l Creek Of The Squamish Estuary. .................... .9 Table 3. Percentage Recapture Success And The Percentage Of Animals Which Fed During T i d a l Creek I n t r o d u c t i o n s On J u l y 15 And 16,1976....................................20 Table 4. Average Length, Height, And C o n d i t i o n F a c t o r Of Experimental Animals Recaptured From The Two Combined T i d a l Creek I n t r o d u c t i o n s . .,. . . .... .... . . .. .............. 21 Table 5. C o r r e l a t i o n Between R e s u l t s Of ^Volume And ^Occurrence Methods Of Stomach A n a l y s i s For Combined I n t r o d u c t i o n s 1 And 2. ...25 Table 6. Occurrence of Prey In The Stomach Contents of J u v e n i l e Chum Salmon f o r Combined I n t r o d u c t i o n s 1 And 2. ...................................................,.27 Table 7. R e s u l t s From 3-way G - t e s t Of Independence For C o n d i t i o n i n g H i s t o r y (C) X Prey Type (P) X Occurrence (0) . 28 Tab l e 8. R e s u l t s From 3-way G-test of Independence For Prey Type (P) X I n t r o d u c t i o n Date (I) X Occurrence (0) For J u v e n i l e Chum Salmon Co n d i t i o n e d To Feed On Large And Small Amphipods. .... ........ ........... .... ..... .......28 Tabl e 9. Res u l t s From 3-way G-test Of Independence For C o n d i t i o n i n g H i s t o r y (C) X I n t r o d u c t i o n Date (I) X Occurrence Of Mysids (O) For J u v e n i l e Chum Salmon Introduced Into The T i d a l creek. . . 28 Table 10. The average Number And V a r i a t i o n In Number Of Prey C a t e g o r i e s Consumed By D i f f e r e n t Experimental Groups. ................................................30 Table 11. The Average S i z e And V a r i a t i o n In Length Of Mysids Consumed By The D i f f e r e n t Experimental Groups. ..32 Tabl e 12. Numbers Of E p i b e n t h i c I n v e r t e b r a t e s Caught In Plankton Tows In E a r l y Morning And Late Evening P r i o r To And A f t e r T i d a l Creek I n t r o d u c t i o n s 34 Table 13. Two-way A n a l y s i s Of Variance On Numbers (Square-Root Transformed) Of Anisogammarus , Neomysis , gnoriroosphaeroma , And I n s e c t Larvae Caught In Plankton Tows ........................... .......................,35 Table 14. Numbers Of Amphipods Per Gram Dry Height Of Fueus Caught In Basket Traps Before And A f t e r T i d a l Creek I n t r o d u c t i o n s ................................,.........35 v i i i ACKNOWLEDGEMENTS Many people c o n t r i b u t e d to the development of t h i s t h e s i s . My s u p e r v i s o r . Dr. J.D. MacPhail, c o n s t a n t l y provided c o n s t r u c t i v e c r i t i c i s m and encouragement. Dr.C.p.Levings i n t r o d u c e d me t o the Sguamish e s t u a r y and e n t h u s i a s t i c a l l y supported t h e r e s e a r c h . During the f o r m a t i v e stages o f t h i s work, K.Hyatt gave much h e l p f u l a d v i c e . Dr.C.F.fehrhahn f r e g u e n t l y gave s t a t i s t i c a l a d v i c e . An e a r l y v e r s i o n o f t h i s manuscript was reviewed and s u b s t a n t i a l l y improved by Drs.T. G.Northcote and W.E . N e i l l . I thank these i n d i v i d u a l s f o r t h e i r h e l p f u l n e s s . , Thanks are a l s o due t o the many graduate students from the I n s t i t u t e o f Animal Resource Ecology, as w e l l as E.Scanlan and J . Kaats who p a r t i c i p a t e d i n v a r i o u s s t a g e s of the f i e l d work. N.McDaniel s u p p l i e d the photographs f o r the t h e s i s and a s s i s t e d i n the f i e l d i n t r o d u c t i o n s . T h i s study would not have been f e a s i b l e without access t o the e x c e l l e n t l a b o r a t o r y f a c i l i t i e s at the P a c i f i c Environment I n s t i t u t e , West Vancouver. The s t a f f members there are thanked f o r t h e i r constant w i l l i n g n e s s to a s s i s t me i n my r e s e a r c h . I acknowledge the f i n a n c i a l support o f the N a t i o n a l Research C o u n c i l o f Canada, as w e l l as the XXV Salmon Research S o c i e t y of B r i t i s h Columbia. F i n a l l y , I would l i k e to thank my parents f o r t h e i r unceasing moral support. 1 INTRODUCTION Chum salmon , Oncorhynchus keta , i n the P a c i f i c Northwest have evolved a l i f e h i s t o r y t h a t i n v o l v e s e x t e n s i v e m i g r a t i o n s through a v a r i e t y o f h a b i t a t s . Fry hatch out of the g r a v e l i n r i v e r s and streams and migrate down to an est u a r y where some p r o p o r t i o n of the p o p u l a t i o n r e s i d e s and grows before moving i n t o marine l i t t o r a l areas, and e v e n t u a l l y i n t o o f f s h o r e marine areas. Feeding can take place i n f r e s h water (Sparrow, 1968), but most f r y are thought t o begin f e e d i n g o n l y a f t e r r e a c h i n g the estu a r y . S e v e r a l s t u d i e s document the f e e d i n g h a b i t s of chum j u v e n i l e s i n e s t u a r i e s ( Goodman and Vrooa, 1972 ; Mason, 1974; Dunford, 1975) and i n near-shore marine environments (Kaczynski e t a l . , 1 9 7 3 ; F e l l e r et a l . , 1975).; From the r e s u l t s of these i n v e s t i g a t i o n s i t i s apparent that e p i b e n t h i c crustaceans are important as a food source d u r i n g the e a r l y phases of j u v e n i l e e x i s t e n c e . Many f e e d i n g s t u d i e s suggest t h a t f i s h t y p i c a l l y a c g u i r e , as food, o n l y a s m a l l subset of the t o t a l s e t of p o t e n t i a l food organisms i n t h e i r environment. E x p l a n a t i o n s to account f o r density-independent e x p l o i t a t i o n i n c l u d e p e r c e p t u a l or be h a v i o u r a l s e l e c t i o n on the pa r t of the predator, as well as d i f f e r e n c e s i n the a v a i l a b i l i t y of prey t y p e s . One mechanism t h a t might account f o r the changes i n fe e d i n g a b i l i t y when there a r e repeated experiences with a p a r t i c u l a r prey type i s the formation of a " s p e c i f i c s e arch image" (Tinbergen,1960). Here 2 the predator l e a r n s to r e c o g n i z e morphological c h a r a c t e r i s t i c s of the prey and t h e r e f o r e " l e a r n s to see" the prey.. A v a i l a b l e l a b o r a t o r y evidence i n d i c a t e s that f i s h possess a l e a r n i n g a b i l i t y (eg. O'Connell,1960) and can improve t h e i r f e e d i n g a b i l i t y on a given prey with experience (Ivlev,1960; Beukema,1968; Ware,1971; Bryan,1973). Moreover f i s h stomachs f r e q u e n t l y c o n t a i n "runs" of one or a s m a l l number of prey types and C u r i o (1976) i n t e r p r e t s t h i s as c i r c u m s t a n t i a l evidence f o r a l e a r n i n g a b i l i t y on the p a r t of the f i s h t o improve t h e i r s earching a b i l i t y f o r s p e c i f i c prey.. Apart from l a b o r a t o r y s t u d i e s , as w e l l as t h e o r e t i c a l c o n s i d e r a t i o n s ( R o l l i n g , 1 9 6 5 ) i o n l y one f i s h study (Bryan and Larkin,1972) a s s e s s e s the importance of predator experience i n the f i e l d environment. G i l b e r t e t al.,(1976) d i s c u s s the value of f i e l d experimentation i n e c o l o g i c a l r e s e a r c h and argue t h a t , although d e t a i l and s i m p l i c i t y are s a c r i f i c e d i n a f i e l d experiment, compared to l a b o r a t o r y work, g r e a t e r c o n f i d e n c e i n the g e n e r a l i z a t i o n s a r r i v e d at more than compensates f o r t h i s . , Goodman and Vroom (1972) r e p o r t that i n the Sguamish e s t u a r y , B.C., chum salmon j u v e n i l e s feed on mysids, amphipods, c y c l o p o i d s , and t e r r e s t r i a l i n s e c t s . Compared with the r e l a t i v e l y g e n e r a l i z e d f e e d i n g h a b i t s of f i s h i n most temperate freshwater ecosystems (Larkin,1956), chum salmon i n the Squamish e s t u a r y a c q u i r e a r e l a t i v e l y low d i v e r s i t y of food types. Because of the r e l a t i v e l y low s p e c i e s d i v e r s i t y i n e s t u a r i e s (Odum,1971) e s t u a r i n e p r e d a t o r s , such as j u v e n i l e chum salmon, a r e l i k e l y to have repeated encounters with a s i n g l e , or only a few, prey types. The experiments i n the present study were 3 t h e r e f o r e designed as an extension of p r e v i o u s l a b o r a t o r y work on the e f f e c t s of predator e x p e r i e n c e , with a p a r t i c u l a r prey type, on subsequent f e e d i n g behaviour. To assess the r o l e of experience i n j u v e n i l e chum salmon, experimental animals were c o n d i t i o n e d to feed on one of s e v e r a l prey t y p e s , then marked and r e l e a s e d i n t o a t i d a l creek i n the Sguamish e s t u a r y . C o n d i t i o n i n g i n the present study r e f e r s to the process of a s s o c i a t i v e l e a r n i n g i n an animal which i s manifested by a change i n some aspect of i t s behaviour. Thus a " f i s h c o n d i t i o n e d to feed on a s p e c i f i c prey item" r e f e r s t o an animal which has l e a r n e d , through e x p e r i e n c e , t o search f o r , approach,„ handle, and i n g e s t that prey item. Laboratory i n f o r m a t i o n {Ware,1971) suggests that a f t e r a f i n i t e number of experiences, a f i s h e s * s e a r c h i n g e f f i c i e n c y i s maximized, and i t i s presumed t h a t s i m i l a r e f f e c t s occur on the animals* i n g e s t i o n and h a n d l i n g e f f i c i e n c y . A f t e r a p e r i o d of time, e x p e r i m e n t a l l y i n t r o d u c e d animals were r e c a p t u r e d and t h e i r stomach contents analysed. The primary aim of the experiment was to t e s t whether experimental animals , i n the f i e l d , would o v e r - e x p l o i t prey animals o f the type they had experienced p r e v i o u s l y , r e l a t i v e to p r e d a t o r s l a c k i n g such experience. The technique a l s o provided a means f o r a s s e s s i n g the r e l a t i v e a v a i l a b i l i t y o f d i f f e r e n t prey types on subsequent i n t r o d u c t i o n dates, as well as a means f o r d e t e r m i n i n g the e f f e c t o f prey behaviour on the v u l n e r a b i l i t y of the prey to the f i s h . 4 METHODS AND MATERIALS To e v a l u a t e c o n d i t i o n i n g i n j u v e n i l e chum salmon, a mark-recapture experiment was performed u s i n g f i s h whose feed i n g h i s t o r y was p r e v i o u s l y manipulated and t h e r e f o r e known. Experimental animals were i n t r o d u c e d i n t o a t i d a l creek i n the Squamish Estuary ( F i g . 1 ) , l o c a t e d a t the head of Howe Sound about 45 km. north o f Vancouver,B. C. F o l l o w i n g r e c a p t u r e , the d i e t of these •'conditioned" f i s h was compared to t h e d i e t of f i s h samples taken i n the same t i d a l creek p r i o r to the i n t r o d u c t i o n , as w e l l as b e n t h i c samples taken d u r i n g and a f t e r the i n t r o d u c t i o n . . , l§aalar Sampl.ins Before the experiment a beach se i n e (2.4m x 36.6m, with 130 micron mesh i n the two wing panels and 65 micron mesh i n the bag s e c t i o n ) was used to c o l l e c t monthly samples of j u v e n i l e salmon from the t i d a l creek. The l o c a t i o n of the t i d a l creek i n the e s t u a r y i s shown i n Fig.1. T h i s channel i s i n t e r - t i d a l and so d r a i n s completely when the t i d e i s below the 1.5m. l e v e l . T h i s allowed a beach s e i n e t o be used as a passive sampler and c o n c e n t r a t e a l l the f i s h i n t o a r e l a t i v e l y s m a l l area. These were then d i p n e t t e d or seined when the t i d e dropped s u f f i c i e n t l y . S i m i l a r methods were used by C a i n and Dean (1976) i n an i n t e r t i d a l creek i n a South C a r o l i n a e s t u a r y . 6 Sampling dates sere chosen so t h a t a r a p i d drop i n t i d e l e v e l o ccurred during the morning hours. The net was p o s i t i o n e d across the mouth of the t i d a l creek a t h i g h t i d e (about 3.7m. l e v e l ) and a f f i x e d i n p o s i t i o n by two stakes on e i t h e r s i d e of the t i d a l creek. When the water l e v e l dropped s u f f i c i e n t l y , a subsample of 10-15 f i s h was d i p n e t t e d and immediately preserved i n a 10% formaldehyde s o l u t i o n f o r l a t e r l a b o r a t o r y a n a l y s i s . Laboratory C o n d i t i o n i n g The animals used i n the experiments were obtained from the estu a r y i n e a r l y June i n t h e same manner as r e g u l a r samples, and t r a n s p o r t e d i n p l a s t i c garbage p a i l s from the e s t u a r y to the aquarium f a c i l i t i e s a t the P a c i f i c Environment I n s t i t u t e , Best Vancouver, B.C. During t h e s e t r a n s f e r s , and a l l subsequent t r a n s f e r s , water temperature was maintained a t about 10°C by adding blocks of i c e t o the water. The f i s h were watched f o r any abnormal behaviour t h a t might suggest oxygen d e f i c i e n c y , eg. con g r e g a t i n g at the s u r f a c e , and, i f t h i s was e v i d e n t , pure oxygen was bubbled i n t o the c o n t a i n e r s f o r about a one minute p e r i o d . T h i s was u s u a l l y s u f f i c i e n t to r e l i e v e symptoms of apparent oxygen s t r e s s . A few f i s h d i e d d u r i n g t r a n s p o r t and h a n d l i n g , but never more than 551 o f the t o t a l . The f i s h were maintained i n c i r c u l a t i n g freshwater i n 125 l i t e r f i b e r g l a s s tanks at d e n s i t i e s o f about 400 i n d i v i d u a l s per tank. Before, and d u r i n g c o n d i t i o n i n g treatments, a l l animals were f e d Oregon H o i s t P e l l e t s coated with Terramycin t o c o n t r o l V i b r i o s i s d i s e a s e . T h i s d i s e a s e was known t o be c a r r i e d by some 7 of the wi l d f i s h . Two s p e c i e s of e s t u a r i n e crustaceans, c o l l e c t e d by beach s e i n e and a plankton net from the Squamish e s t u a r y , formed three of the prey types used i n the c o n d i t i o n i n g experiments. The two sp e c i e s were: the mysid, Neomjsis mergedis (Holmes) , and the other the amphipod, Anisoqammarus c o n f e r v i c o l u s (Stimpson) (Figs.2 and 3)..Both were extremely abundant over c e r t a i n areas o f the estu a r y and i t was u s u a l l y p o s s i b l e t o a c q u i r e enough i n d i v i d u a l s on any one sampling t r i p to provide adequate numbers f o r about 5 days of food c o n d i t i o n i n g . Two d i f f e r e n t s i z e c l a s s e s o f amphipods were o b t a i n e d with a s e r i e s of 3 submerged s e i v e s (2.0mm, 1.19mm, and 0.5mm mesh diameter)., A f t e r d e p o s i t i n g about one thousand amphipods on the uppermost (c o a r s e s t ) s e i v e , water was siphoned away from around the s e i v e s and the h y d r o p h i l i c amphipods would then crawl through the s e i v e screens u n t i l t h e i r body diameter was too grea t t o a l l o w f u r t h e r downward p e n e t r a t i o n . The amphipods remaining on two of the screens, 0.5mm and 1.19mm, were then used as food i n the s m a l l and l a r g e amphipod treatment groups r e s p e c t i v e l y . In a d d i t i o n to the t h r e e l i v e prey types, f i s h i n two of the tanks r e c e i v e d only Oregon Moist P e l l e t s . F i s h were f e d one of two s l i g h t l y d i f f e r e n t s i z e d p e l l e t s . A summary of the s i z e s of the d i f f e r e n t food types i s given i n Table 1. Lengths of the crustaceans were measured with an ocu l a r micrometer by gently s t r e t c h i n g t h e animals under a d i s s e c t i n g microscope. Appendages, eg. antennae and r o s t r a , were not i n c l u d e d i n any le n g t h measurements. During the f i r s t two weeks of l a b o r a t o r y c o n d i t i o n i n g a l l 8 F i g u r e 2. Two of the common i n t e r t i d a l C r u s t a c e a found i n the Squamish e s t u a r y . The d o r s o - v e n t r a l l y f l a t t e n e d s p e c i e s i s the i s o p o d Gaorimosphaeroma o r e g o n q n s i s and t h e l a t e r a l l y f l a t t e n e d s p e c i e s i s the amphipod Anisoqammarus c o n f e r v i c o l u s . F i q u r e 3. A j u v e n i l e chum salmon, Oncorhynchus keta i n a tank wit h the e s t u a r i n e mysid, l e o m y s i s tnercgdis . 9 •+-PELLET TYPE A PELLET TYPE B SMALL AHPHIPOD LARGE AMPHTPOD M YS ID +-Number Measured Mean Length mm 50 1.9 50 1.6 50 5. 1 50 7.9 50 11.9 | Standard I D e v i a t i o n 11 0-73 1 0.40 | 0.87 | 1.00 | 1.91 | i Mean I Diameter | mm 1 1 0.8 | 1 . 3 1 - 1 - -j Standard I D e v i a t i o n n 1 I 0.04 | r t • 0.07 | - | . . M M * f i > Table 1. ; S i z e s experiments. of d i f f e r e n t food types used i n c o n d i t i o n i n g \ Sampling |I I Date || A p r i l 21/76 | May 26/76 | June 8/76 | J u l y 1/76 | I N It 15 | 9 | 15 | 9 | | Mean ) | | Length | | | mm || 41.7 I 40.7 | 48.4 | 49.4 | I Mean || I Height | | I g II 0.6 3 | 0.63 | 0.98 | 1. 12 | I Mean | | | K f a c t o r * H t _ .._ i i -0.0081 | _. _ . _. a~ 0.0085 | 0.0082 | _ i - • — L _ 0.0090 | ._" .. i *K=wt/0.1L3 Table 2. S i z e s of j u v e n i l e chum salmon sampled from the t i d a l creek o f the Sguamish e s t u a r y . 10 f i s h were given as much p e l l e t food, three times per day, as co u l d be consumed i n a 10 minute p e r i o d . Food was presented twice i n the morning, and once i n the e a r l y a f t e r n o o n . P e l l e t s were shaken i n a beaker and then i n t r o d u c e d v i a the i n f l o w i n t o the tank, a s m a l l amount a t a time. C o n d i t i o n i n g s t a r t e d on June 10,1975. Two groups were maintained on one of the two p e l l e t types, and the other t h r e e groups on a combination of one of the l i v e food types and the p e l l e t food. Animals c o n d i t i o n e d on l i v e food r e c e i v e d as many prey as could be consumed i n a 10 minute p e r i o d f o r t h e i r f i r s t meal o f t h e day, and f i s h p e l l e t s f o r the two subsequent meals. One day's c o n d i t i o n i n g experience was s a i d t o occur whether or not any feed i n g t o o k place. When f e e d i n g d i d not take p l a c e w i t h i n 10 minutes, which happened on s e v e r a l o c c a s i o n s near the s t a r t of the experiment, the prey were removed with a dipnet a f t e r 10 minutes. Three gaps o f 1-2 days d u r a t i o n i n the c o n d i t i o n i n g schedule were unavoidable due t o the l a c k of a v a i l a b l e l i v e food items. On these days the f i s h r e c e i v e d an a d d i t i o n a l meal of p e l l e t food as a replacement f o r the l i v e food meal. In t o t a l , t he f i s h r e c e i v e d 30 days of c o n d i t i o n i n g experience spread out over a 34 day p e r i o d , from June 10/76 to J u l y 13/76. At the end of 30 days o f c o n d i t i o n i n g experience, the f i s h were i n d i v i d u a l l y marked by f i n - c l i p p i n g ( e i t h e r one or a combination of a n a l , caudal, or d o r s a l f i n s were c l i p p e d ) . Before marking, the f i s h were a n a e s t h e t i z e d with HS-222. The mark was obtained by c u t t i n g o f f the t i p of a f i n or f i n s with a s c a l p e l blade. The maximum number o f f i n c l i p s an experimental animal r e c e i v e d was two. F i v e groups of f i s h were de p r i v e d o f 11 food f o r two days before t h e i r i n t r o d u c t i o n i n t o the t i d a l creek. In a d d i t i o n , two other experimental groups were obtained by s t a r v i n g some o f the p e l l e t - t r a i n e d f i s h f o r a t o t a l of 7 days i n s t e a d of 2 days. Beukema (1968) showed t h a t i n s t i c k l e b a c k s , the l e n g t h o f food d e p r i v a t i o n can have a marked e f f e c t on the f e e d i n g r a t e during the i n i t i a l hour a f t e r the beginning of a feeding experiment. I used a long d e p r i v a t i o n p e r i o d f o r some o f t h e p e l l e t c o n d i t i o n e d f i s h i n an attempt to o b t a i n p r e d a t o r s which would be maximally r e a c t i v e t o the prey items i n the t i d a l creek. Thus t h e r e were a t o t a l of 7 d i f f e r e n t treatment groups used i n the experiment. f i e l d I n t r o d u c t i o n s a f t e r s e v e r a l t r i a l i n t r o d u c t i o n s and r e c a p t u r e s of f i s h i n t o the t i d a l creek, I decided t h a t a f a i r l y long i n t r o d u c t i o n p e r i o d , about 12 hours, would be necessary t o overcome e f f e c t s due to h a n d l i n g or d i e l and t i d a l changes. Fig.4 shows the magnitude of the t i d a l changes d u r i n g the course of the t i d a l creek i n t r o d u c t i o n s . The procedure f o l l o w e d was t o t r a n s p o r t the experimental f i s h by means of t r u c k and boat to the e s t u a r y , and, a f t e r t h e beach s e i n e was i n p l a c e at the mouth of the t i d a l c r e e k , r e l e a s e them i n t o the enclosed area. The e n c l o s u r e extended 75 meters i n l e n g t h and was 20 meters wide at the mouth. The behaviour of the f i s h at the time of r e l e a s e was a p p a r e n t l y normal { they formed s c h o o l s a t the s u r f a c e and c o u l d be observed a f t e r s u n r i s e a t t a c k i n g both l i v e and inanimate o b j e c t s ). One of the advantages o f u s i n g f a i r l y s m a l l f i s h f o r 12 F i g u r e U. View of the t i d a l c reek i n t h e Squamish e s t u a r y a t s u c c e s s i v e t i d e l e v e l s . A beach s e i n e i s i n p l a c e a t the mouth r e s t r i c t i n g the movements o f i n t r o d u c e d f i s h . 13 the c o n d i t i o n i n g experiments (50mm) was t h e i r b e h a v i o u r a l p l a s t i c i t y - the animals proved t o be adaptable t o handl i n g and d i d not appa r e n t l y r e g u i r e a l o n g adjustment p e r i o d t o the t i d a l creek environment b e f o r e s t a r t i n g t o feed. Handling e f f e c t s would probably be more s i g n i f i c a n t f o r l a r g e r f i s h . F i s h were re c a p t u r e d at low t i d e i n the afternoon by 'herding* them i n t o the bag s e c t i o n o f the net and using a d i p n e t to r e t r i e v e them. During one of the i n t r o d u c t i o n s the f i s h were recovered by dragging a s m a l l beach s e i n e i n s i d e the e n c l o s u r e . F o l l o w i n g r e c a p t u r e , the animals were immediately preserved i n a 10% formaldehyde s o l u t i o n and s t o r e d f o r subsequent l a b o r a t o r y a n a l y s i s . Benthic Sampling During the p e r i o d o f f i s h i n t r o d u c t i o n s two methods were used t o o b t a i n i n f o r m a t i o n on the r e l a t i v e abundance of d i f f e r e n t prey types i n the t i d a l creek. One of these i n v o l v e d the use of basket t r a p s f o r a s s e s s i n g the numbers of Anisoqammarus c o n f e r v i c o l u s (Levings, 1976) . The oth e r method found t o be e f f e c t i v e was a 0.25mz,350 micron SCOR/UNESCO plankton net used as a be n t h i c sampler by towing beside the sedge mats along the margins of the t i d a l creek., R e p l i c a t e wire baskets (20cm x 20cra x 20cm) s t u f f e d with Fucus d i s t i c h u s were suspended a t about the 3.1m t i d e l e v e l near th e mouth of the t i d a l creek. These were then removed at v a r i o u s i n t e r v a l s d u r i n g and a f t e r the the course of the experiment. The numbers of amphipods caught were expressed per gram dry weight 14 of Fucus . Plankton tows were made on two mornings b e f o r e , and on one evening a f t e r the experiment, by dragging the net along the edge of the sedge mat f o r the e n t i r e l e n g t h of the t i d a l c r e e k . Much sedge d e t r i t u s was c o l l e c t e d by t h i s method and some of the organisms were probably adhering t o sedge l e a v e s or rhizomes a t the time of sampling. The plankton samples were preserved i n a 10S? formaldehyde s o l u t i o n and subsequently i d e n t i f i e d and counted. , Laboratory Stomach A n a l y s i s The methods used f o r stomach a n a l y s i s were the same f o r the f i s h o b t ained throuqh r e g u l a r sampling and the exp e r i m e n t a l f i s h from the two i n t r o d u c t i o n s . , The preserved i n d i v i d u a l s were r i n s e d i n t a p water, b l o t t e d dry, and then weighed to the nearest O.Q1g on a M e t t l e r H65 balance. They were then measured under a d i s s e c t i n g microscope t o the nearest mm and the f i n s examined f o r f i n c l i p s . A l l animals t h a t c o u l d not be p o s i t i v e l y i d e n t i f i e d as to t h e i r c o n d i t i o n i n g h i s t o r y were omitted from subsequent a n a l y s i s . F o l l o w i n g i d e n t i f i c a t i o n , the stomach was d i s s e c t e d from the gut by i n c i s i o n s a t the esophagus and the j u n c t i o n of the p y l o r i c caeca with the stomach. The stomach con t e n t s were then spread out on a p e t r i d i s h , i d e n t i f i e d , and counted. Amphipods and mysids were measured by o c c u l a r micrometer to the nearest 0,Imm^  The r e l a t i v e importance of the d i f f e r e n t prey was approximated by v i s u a l l y e s t i m a t i n g the volu m e t r i c displacement o f each prey type under the b i n o c u l a r 15 microscope. Percent occurrence values were obtained by summing the number of occurrences o f a l l items and then s c a l i n g the values f o r the i n d i v i d u a l prey t o a percentage b a s i s . A d d i t i o n a l l y , the numbers of a l l prey types i n t h e d i e t were counted and percent frequency v a l u e s o b t a i n e d . Thus t h r e e independent measurements of stomach contents (percent volume, percent occurrence, and percent frequency) were determined. 16 RESULTS Regular Sampling The average l e n g t h , weight, and c o n d i t i o n f a c t o r ( weight/length 3) s t a t i s t i c s f o r the f i s h sampled i n the t i d a l creek before the i n t r o d u c t i o n s are shown i n Table 2. These data i n d i c a t e an i n c r e a s e i n the average s i z e of the f i s h captured i n the t i d a l creek over time. F i g u r e s 5 and 6 show the r e s u l t s from the t h r e e methods of stomach a n a l y s i s a p p l i e d t o the r e g u l a r samples of f i s h obtained i n the t i d a l creek. On two of the sampling dates, A p r i l 21 and May 26, th e r e appears t o be l a r g e d i f f e r e n c e s i n the r e s u l t s from the percent frequency a n a l y s i s o f the prey items and the other two methods. T h i s d i s c r e p a n c y can be e x p l a i n e d by the high r e p r e s e n t a t i o n of c y c l o p o i d s i n the d i e t and the s m a l l s i z e (0.5-1.Omm i n length) of these organisms. yThe percent frequency method o v e r e s t i m a t e s t h e r e l a t i v e importance o f t h i s prey group. The other two methods, percent volume and percent occurrence, show c l o s e agreement and subsequent d i e t a r y comparisons are based on the r e s u l t s o f the percent volume a n a l y s i s . From F i g u r e s 5 and 6, i t can be seen that many of the prey organisms f i e . ftPisogammarus c o n f e r v i c o l q s , t e r r e s t r i a l i n s e c t s , and cy c l o p o i d s ) make up d i f f e r e n t p r o p o r t i o n s of the d i e t over time. 17 100 • 75... SO. ES. 0. % FREQUENCY H—h—1- H 1 !• 5- 3- 4- 5- G« 7- B- 9.10-100 v 75. 50. 25.1 0 % OCCURRENCE -+-100 v 75. 50-ES.l 1- S- 3- 4> 5- G. 7- B. 9>10. % VOLUME . - I— I !• 5- 3- 4. 5- G- 7. B- 9-10-100 v 75. 50-es.l o % FREQUENCY 4=1- 1 1 JL» £> a« 4« 5« 6- 7. B' 9-10 1O0-75... so... ES... 0>._ 100. 75... SO. E5.I % OCCURRENCE 1» E> 3- 4- 5. E' 7' S- 9'10. % VOLUME !• E' 3- 4. 5. G' 7- B- 9-10. PREY TYPE APRIL 21/76 N = l 5 o .5 a Z E e 2 o o o c c a E g-O M . .3 o 2 H 0 u H 1 1 1 1 1 1 1 1 !• E< 3' 4. 5. 6- 7. 8< 9-10-PREY TYPE MAY 26/76 N«=9 PREY TYPE F i g u r e 5. Diet of juvenile chum salmon in the ti d a l creek of the Squamish estuary on A p r i l 21 and May 26, 1976. 18 100 75.1 SO ES.j. 0 % FREQUENCY ! • 5- 3. 4- 5. G« 7- B' 9.10 100. 75... 50... ES... % OCCURRENCE ! • S- 3. 4. 5. G> 7- B. 9-10 100. 75... 50... 55... % VOLUME ! • 2. 3- A- 5. E« 7. B> 9-10 PREY TYPE JUNE 8/76 N = 15 a. 3 E _ E 2 O h « c Z h> £ E u u o J 100 v 75 50... ES... % FREQUENCY H—I 1—I h ! • E« 3> 4. 5. G' 7- B- 9.10. 100.T 75 50 E5.I % OCCURRENCE 100 75. 50. ES.I H 1 1 1. B« 3- 4- 5. G- 7. B' 9-10-% VOLUME 1. £• 3-' 4.' 5.' G.' 7.' B.' 9.'i0.' PREY TYFE « JULY 1/76 o N = 9 t i i i — i — i — y !• E« 3- 4.' 5.' 6« 7.' 0.' g.'io.' PREY TYPE F i g u r e 6. Diet of juvenile chum-salmon in the tidal creek of the Squamish estuary, on June 8 and J u l y 1, 1976. 19 C o n d i t i o n i n g Experiments Recapture r a t e s of experimental animals f o r two 4-hour t r i a l i n t r o d u c t i o n s i n t o the t i d a l creek on A p r i l 21,1976 (no. introduced=123) and J u l y 1,1976 (no., introduced-9) were 63% and 44% r e s p e c t i v e l y . These r e c a p t u r e r a t e s are s u b s t a n t i a l l y higher than the 16% ( J u l y 15/76) and 2 1 % ( J u l y 16/76) average r e c a p t u r e r a t e s d u r i n g t h e a c t u a l experiments which each l a s t e d f o r a 14-hour time p e r i o d . S u b s t a n t i a l l o s s e s of experimental f i s h o c c u r r e d around the edges of t h e t i d a l creek e n c l o s u r e , as w e l l as through the spaces between the beach s e i n e f l o a t s and the net. In a d d i t i o n ^ staghorn s c u l p i n s , - L e p t o c o t t n s armatus, trapped i n the e n c l o s u r e , were observed p r e d a t i n g on the experimental f i s h . The two processes, leakage of f i s h around the e n c l o s u r e , and p r e d a t i o n by s c u l p i n s , account f o r the apparent i n v e r s e r e l a t i o n s h i p between the r e c a p t u r e r a t e of experimental f i s h and the l e n g t h of time o f the experimental introduction..„ The r e c a p t u r e r a t e s and the percentage of animals t h a t fed du r i n g the two experimental i n t r o d u c t i o n s , along with l e n g t h , weight, and c o n d i t i o n f a c t o r s t a t i s t i c s are given i n T a b l e s 3 and 4. Comparison of the stomach contents (percent volume method) of w i l d chum j u v e n i l e s and s e l e c t e d experimental groups are shown i n F i g u r e s 7 ( J u l y 15/76) and 8 (July 16/76). Appendices I and I I o u t l i n e the d e t a i l e d r e s u l t s of stomach a n a l y s i s of the experimental f i s h and show a l l three methods of stomach a n a l y s i s - percent volume, percent occurrence, and percent frequency. There i s good agreement between the percent volume 20 ~rr-r NO. f INTRODUCED CONDITIONING HISTORY LENGTH OF FOOD DEPRIVATION RECAPTURED FED I n t r o d u c t i o n 1 J u l y 15/76 Mysid Small Amph Large Amph P e l l e t Type A P e l l e t Type B P e l l e t Type A P e l l e t Type B 2 days 2 days 2 days 2 days 2 days 7 days 7 days 90 95 90 75 75 35 40 • i, i 26% 1515 8% 11% 12% •, 29% 18% 74% 93% 86% 88% 100% 100% 86% Mysid Small Amph Large P e l l e t Type A P e l l e t Type B P e l l e t Type A P e l l e t Type B I n t r o d u c t i o n 2 J u l y 16/76 - + +_ ; ; H , 2 days 2 days 2 days 2 days 2 days 7 days 7 days 125 120 110 85 105 40 55 i i 24% 23% 15% 18% 24% 18% 9% 90% 96% 88% 100% 92% 86% 100% Tab l e 3. Percent r e c a p t u r e success and the percentage of animals which fed du r i n g t i d a l creek i n t r o d u c t i o n s on J u l y 15 and 16,1976. 21 a - ~ ~ r r -f CONDITIONING | | | HISTORY || LENGTH OP | FOOD | DEPRIVATION | — | r : N | AVE. LENGTH mm "TT I AVE. | WEIGHT i g - 1 — "S | AVE. | | KFACTOR 1| I Mysid |1 2 days \ 53 | 5 7 . 9 | 1 .76 f 0 . 0 0 8 8 | I Small | J 1 Amph | | 2 days J 42 | 5 3 . 5 | 1.41 J 0 . 0 0 8 7 | I Large j j 1 Amph | | 2 days 1 24 | 5 0 . 8 I 1 .18 J 0 . 0 0 8 4 j | P e l l e t | | J Type A |j 2 days | 23 | 5 5 . 0 1 1 . 4 7 I 0 . 0 0 8 4 | J P e l l e t 11 1 Type B M 2 days | 34 J 5 2 . 1 I 1 .26 I 0 . 0 0 8 3 | I P e l l e t | | J Type A | | 7 days | 17 I 51 . 5 I 1 .13 | 0 . 0 0 7 8 | I P e l l e t || | Type B 19 7 days j 12 | 5 3 . 8 1 1 .29 I 0 . 0 0 8 0 J t. — - i a.. ' ..«, a ...... ,. -X _ _ J iK=Wt/0.1L3 Table 4. Average l e n g t h , weight, and c o n d i t i o n f a c t o r of experimental animals r e c a p t u r e d from the two combined t i d a l creek i n t r o d u c t i o n s . 22 iOOv 75 50 4 55 0 J U N E 8/76 N = 15 n n !• E» 3' 4- 5« 6> 7. 8- 9-10. 100 75 50... E5... 0 J U L Y 1/76 N=9 H 1 1 1 h 1' £• 3- 4. 5' 6> 7. 8- 9«10« A PREY TYPE A. e e £ 5 « u. c ° £ o Z H O U U J £ < U O I 1 1 1 1 1 1 r 1 1 1 !• E> 3- 4. 5- B- 7- B« 9-10. • 100. 75-1 50..: E5... O MYSID C O N D I T I O N E D J U L Y 15/76 N=17 -i i n 100. 75... 50. ES. .. < 1 1 1 1. £• 3> 4- 5- E« 7- 8> 9.10. S M A L L A M P H I P O D C O N D I T I O N E D J U L Y 15/76 N = 13 !• E« 3- 4« 5. 6- 7. B- 9-10. 100-^ 75 SO ES.j: 0 P E L L E T T Y P E A C O N D I T I O N E D J U L Y 15/76 N=7 H 1 1 h 4=1- i 1 1' E> 3. 4. 5. 6- 7. 8. 9.10 A PREY TYPE PREY'TYPE, F i g u r e 7. C o m p a r i s o n of the diet of wild chum juveniles and selected e x p erimental groups r e l e a s e d into the tidal c r e e k on J u l y 15/76. H i s t o g r a m s r e p r e s e n t percent volume r e s u l t s . 23 75-1 J U N E 8/76 N = l 5 ~1 -n lOO. lOO-75. 50. ES-1 . E- 3- 4- 5- G- 7« 8' 9-10. J U L Y 1/76 N=9 H 1 1 1 H—I 1. E« 3- 4. 5. 6> 7- B« 9-10. Jk PREY TYPE A 6 -3' -to 2 t £ rt « £ IS £ E 2 o u V V Z H I I I .e .e o u u H 1 1 H 5 £ £ 2" C S e 5 ' S g •5 .2 t. o i. c o c ° K < O O H 1 1 1 1 « E- 3- 4« 5- G. 7. B> 9'10-JL. PREY TYPE MYSID C O N D I T I O N E D 75.. J U L Y 16/76 N = 27 50-. E5-. o. i ! • E« —1 i — I — I — i i — I — 3- 4. 5. 6. 7- 8' 3'iO-100. ""SMALL A M P H I P O D C O N D I T I O N E D " J U L Y 16/76 •-N = 27 =1 1 1 1 H 1 1—1 i . £. 3< 4- 5. G- 7- 6- 9.10. 100 75 50 ES.J: P E L L E T T Y P E A C O N D I T I O N E D J U L Y 16/76 N = 15 -+—I—I—I—-I—-H—I 1» E- 3- 4« 5- G» 7« B> 9-10' A. PREY TYPE A F i g u r e 8. C o m p a r i s o n of the diet of wild chum juveniles and selected e x p e r i m e n t a l groups r e l e a s e d into the t i d a l c r e e k on J u l y 16/76. H i s t o g r a m s r e p r e s e n t percent volume r e s u l t s . 24 and percent occurrence methods and Spearman rank c o r r e l a t i o n c o e f f i c i e n t s (Table 5} which t e s t f o r the l a c k of c o r r e l a t i o n between the two methods, a r e s i g n i f i c a n t f o r a l l treatment groups. T h i s i m p l i e s a good g u a l i t a t i v e agreement i n the r e s u l t s o f the two methods. Thus the percent volume r e s u l t s are c o n s i d e r e d to be a v a l i d r e p r e s e n t a t i o n of the d i e t s of the d i f f e r e n t experimental groups. From the r e s u l t s i n F i g u r e s 7 and 8, as w e l l as Appendices I and I I , the f o l l o w i n g t r e n d s are e v i d e n t . F i r s t , animals c o n d i t i o n e d t o feed on mysids a c q u i r e d a higher p r o p o r t i o n , of mysids i n the d i e t than those c o n d i t i o n e d to feed on e i t h e r amphipods or p e l l e t s . Second, f i s h c o n d i t i o n e d to feed on e i t h e r s m a l l or l a r g e amphipods a p p a r e n t l y d i d not a c q u i r e a higher p r o p o r t i o n of amphipods i n the d i e t than the other treatment groups. T h i r d , there were no d i f f e r e n c e s i n d i e t between the groups c o n d i t i o n e d on d i f f e r e n t types o f f i s h p e l l e t s . F o u r t h , t h e r e were no l a r g e d i f f e r e n c e s i n d i e t between the p e l l e t - f o o d groups deprived of food f o r d i f f e r e n t l e n g t h s of time. L a s t l y , there appear t o be d i f f e r e n c e s i n the r e l a t i v e p r o p o r t i o n s of v a r i o u s components , notably geomys.is , i n the d i e t , f o r the two i n t r o d u c t i o n dates. To a s s e s s s t a t i s t i c a l l y the d i f f e r e n c e s between the treatment groups, I used t h e occurrence data i n a three-way c l a s s i f i c a t i o n G - t e s t f o r independence as o u t l i n e d i n Sokal and Bohlf (1969). The s t a t i s t i c was employed i n two d i f f e r e n t ways: f i r s t , t o assess the e f f e c t s due t o c o n d i t i o n i n g I lumped the animals of s i m i l a r treatment groups from the two i n t r o d u c t i o n dates, and second, by comparing the d i e t of i n d i v i d u a l treatment groups f o r the two d i f f e r e n t i n t r o d u c t i o n dates. The f i r s t 25 # - — '• | CONDITIONING | HISTORY I| LENGTH OF |J FOOD || DEPRIVATION -T——— j SPEAR HAN RANK | CORRELATION | COEFFICIENT J SSVOL VS. %OCC " i — | DF -r — • -1 T •  .—i I Mysid ! | 2 days | 0.8542 1 7 | 4 .346 * * | 1 Small I Amph II 2 days | 0.8152 | 8 | 3.980 **j I Large I Amph 1! 2 days | 0.8482 1 5 1 3.581 * 1 | P e l l e t j Type a II 2 days I 0.9732 1 5 | 9.466 * * | | P e l l e t | Type B 1 1 2 days | 0.7818 1 8 | 3.547 * * | j P e l l e t 1 Type A 1 1 7 days | 0.8631 | 6 | 4.186 * * | I P e l l e t | Type B i , , 1 1 7 . j . ! . - . days | 0.8875 i , . ' _ 1 7 A I 5.096 .a. _ * * j *=.01< P < .05 **= P < .01 T a b l e 5 . C o r r e l a t i o n between r e s u l t s of ^volume and %occurrence netbods of stomach a n a l y s i s f o r combined i n t r o d u c t i o n s 1 and 2. T t e s t e v a l u a t e s the n u l l hypothesis t h a t the c o r r e l a t i o n between the two methods i s zero., 26 comparison uses the occurrence data presented i n T a b l e 6 and examines the independence or l a c k t h e r e o f of c o n d i t i o n i n g e f f e c t s (C) ",- prey type e f f e c t s (P) , and occurrence e f f e c t s (0) * I t was necessary i n t h i s a n a l y s i s t o omit the prey c l a s s e s which had low expected v a l u e s s i n c e t h e i r i n c l u s i o n would have l e d to e r r o r i n the computed G-value. S i n c e the r e s u l t s of the a n a l y s i s (Table 7) show an o v e r a l l l a c k of independence (G-value f o r CxPxO independence = 339.252) G-values f o r the v a r i o u s two-way t e s t s of independence^ as w e l l as the CxPxO i n t e r a c t i o n , were computed. Note that a G-value f o r the PxC independence t e s t c o u l d not be computed due t o the way the experiment was designed ( i e . the sum o f the occurrences and non-occurrences was i d e n t i c a l f o r the d i f f e r e n t prey t y p e s ) . The i n t e r p r e t a t i o n s one can draw from the r e s u l t s i n T a b l e 7 i n c l u d e the f o l l o w i n g : 1. CxO independence- there was no s i g n i f i c a n t d i f f e r e n c e i n the t o t a l number of occurrences of prey items f o r the d i f f e r e n t treatment groups. 2. PxO independence- t h e r e was a s i g n i f i c a n t e f f e c t of prey type on the occurrence of prey. Thus the d i f f e r e n t prey types were not e q u a l l y r e p r e s e n t e d i n the d i e t . . The high G-value ( 284.146) accounts f o r much of the o v e r a l l |CxPxO) l a c k of independence. ., • • • 3. CxPxO i n t e r a c t i o n - s i n c e the CxO t e s t i s not s i g n i f i c a n t , and the PxC t e s t was not performed, a s i g n i f i c a n t t h i r d order i n t e r a c t i o n c o n s t i t u t e s evidence f o r an e f f e c t of c o n d i t i o n i n g . Thus the l a c k of PxO independence i s d i f f e r e n t a c r o s s the v a r i o u s c o n d i t i o n i n g treatment groups. 27 CONDITIONING HISTORY PREY TYPE NO. OF OCCURRENCES NO.OF ABSENCES Mysid Mysids 31 T e r r . I n s e c t 26 Amphipods 2 Ins.Larvae 3 Ins. Pupae 6 13 18 42 41 38 TOTALS 44 44 44 44 44 68 152 220 Small Amph Mysids 13 T e r r . I n s e c t 34 Amphipods 5 Ins.Larvae 6 Ins. Pupae 11 27 6 35 34 29 40 40 40 40 40 69 131 200 Large Amph Mysids 7 T e r r . I n s e c t 19 Amphipods 5 Ins.Larvae 2 Ins. Pupae 6 14 2 16 19 15 21 21 21 21 21 39 66 105 P e l l e t Food Mysids 18 36 54 2-day T e r r . I n s e c t 49 5 54 d e p r i v a t i o n Amphipods 5 49 5 4 Ins.Larvae 6 48 54 Ins.Pupae 19 35 54 97 173 270 P e l l e t Food 7-day d e p r i v a t i o n Mysids 10 T e r r . I n s e c t 24 Amphipods 4 Ins. l a r v a e 6 Ins. Pupae 11 17 3 23 21 16 27 27 27 27 27 55 80 135 TOTALS 328 602 930 Table 6. Occurrence o f prey i n the stomach contents o f j u v e n i l e chum salmon f o r combined i n t r o d u c t i o n s 1 and 2. (Terr. Ins. = T e r r e s t r i a l I n s e c t ; I n s . Larvae=Insect Larvae;Ins. Pupae= I n s e c t Pupae.) 28 HYPOTHESIS TESTED DF CxO independence PxO independence PxC independence CxPxO i n t e r a c t i o n CxPxO independence 4 3. 868 4 284.146 ** 16 not test e d 16 51.24 .** 40 33 9.252 ** ** = P< .01 Table 7. R e s u l t s from 3-way G-test of independence c o n d i t i o n i n g h i s t o r y (C) x prey type (P) x occurrence CO). f o r r — | HYPOTHESIS TESTED DF G — > I 1x0 independence 1 1,808 | PxO independence 3 76.980 ** J Pxl independence 3 not t e s t e d I PxIxO i n t e r a c t i o n 3 1. 170 | PxIxO independence 10 79.956 ** a **=P< .01 Table 8. R e s u l t s from 3-way G - t e s t of independence f o r prey type (P) x i n t r o d u c t i o n date (I) x occurrence (0) f o r j u v e n i l e chum salmon c o n d i t i o n e d t o feed on l a r g e and s m a l l amphipods. HYPOTHESIS TESTED DF CxO independence 4 18.692 ** IxO independence 1 6.002 * IxC independence 4 7.836 CxIxO i n t e r a c t i o n 4 8.264 CxIxO independence 13 40.794 ** *=.01 < P < .05 **=P< .01 Ta b l e 9. R e s u l t s from 3-way G-test of independence f o r c o n d i t i o n i n g h i s t o r y (C) x i n t r o d u c t i o n date (I) x occurrence of mysids (0) f o r j u v e n i l e chum salmon i n t r o d u c e d i n t o the t i d a l creek of the Sguamish Estuary. 29 S i m i l a r a n a l y s e s were performed comparing the d i e t s of i n d i v i d u a l treatment groups i n the two d i f f e r e n t i n t r o d u c t i o n s . Again i t was necessary t o pool the r e s u l t s from more than one treatment group to achieve adequate sample s i z e s . The r e s u l t s of the comparison i n d i e t f o r the amphipod-conditioned f i s h (combined s m a l l and l a r g e amphipod groups) f o r the two d i f f e r e n t i n t r o d u c t i o n dates are g i v e n i n Table 8. Since the PxIxO i n t e r a c t i o n i s not s i g n i f i c a n t , t here i s a p p a r e n t l y no e f f e c t o f i n t r o d u c t i o n date on the d i e t . S i m i l a r r e s u l t s e x i s t f o r mysid-conditioned f i s h and the p e l l e t - c o n d i t i o n e d f i s h d e p r i v e d of food f o r two days. Thus no d i f f e r e n c e s i n the o v e r a l l d i e t a r e a t t r i b u t a b l e t o the i n t r o d u c t i o n date. Since a comparison o f F i g s . , 7 and 8 suggest d i f f e r e n t r e p r e s e n t a t i o n of mysids i n the d i e t f o r a l l treatment groups, a 3-way G-test of independence was performed on c o n d i t i o n i n g h i s t o r y (C) x i n t r o d u c t i o n date (I) x occurrence of mysids (0). The r e s u l t s of t h i s a n a l y s i s (Table 9) i n d i c a t e an o v e r a l l l a c k of independence a t t r i b u t a b l e t o s i g n i f i c a n t CxO and 1x0 G-values. Thus t h e r e i s a s i q n i f i c a n t c o n d i t i o n i n g e f f e c t on the number of mysid-occurrences i n the d i e t , as w e l l as a s i g n i f i c a n t e f f e c t of i n t r o d u c t i o n date on the occurrence of mysids. T h i s r e s u l t c onfirms the t r e n d apparent i n F i g s . 7 and 8 th a t t h e r e i s a higher r e p r e s e n t a t i o n of mysids i n the d i e t o f j u v e n i l e chum salmon from the second i n t r o d u c t i o n date ( J u l y 16/76). Summary s t a t i s t i c s f o r the mean number of prey types consumed by the v a r i o u s treatment groups are provided i n Table 10. The prey types c o n s i d e r e d a r e those shown i n the key on 30 r " — — J CONDITIONING | HISTORY -TT : | | LENGTH OF i | FOOD i j DEPRIVATION i i "T— N — i — . - r-| MEAN NO 1 | OF PREY | i TYPES I | CONSUMED | STANDARD | DEV IN | NO OF | PREY | TYPES | CONSUMED J T i i ! Mysid || 2 days J nn | 1.70 5 | 0.878 | I Small | Amph 11 2 days j no I 2.025 J 1.050 | 1 Large 1 Amph II 2 days j 21 | 2.000 | 1.183 | I P e l l e t I Type A I | 2 days j . 22 | 1.636 | 0.789 | I P e l l e t I Type B || 2 days ! 32 1 2.250 | 1.077 J | P e l l e t 1 Type A I | 7 days i 16 1 2. 188 J 1.328 | I P e l l e t J Type B || 7 days -XI , .. „. X .„, 11 I 2.818 | _ .JL 1.779 | _ ••':J."_-ii,r 1 Table 10. The average number and v a r i a t i o n i n number o f prey c a t e g o r i e s consumed by the d i f f e r e n t e xperimental groups . P r e y c a t e g o r i e s c o n s i d e r e d were those l i s t e d i n f i g u r e 1 and c a l c u l a t i o n s are based on the combined r e s u l t s from the two i n t r o d u c t i o n dates. 31 Figs.5-8. One way a n a l y s i s o f v a r i a n c e i n d i c a t e s the d i f f e r e n c e i n the mean number of prey types consumed i s s i g n i f i c a n t (F=2.358,P < 0.05). With two e x c e p t i o n s , the mean number of prey c a t e g o r i e s consumed was g r e a t e r f o r p e l l e t - c o n d i t i o n e d than f o r l i v e - p r e y - c o n d i t i o n e d animals (Table 10) . The p e l l e t - t y p e A group (2-day d e p r i v a t i o n ) and the small amphipod group were the o n l y groups i n c o n s i s t e n t w i t h t h i s g e n e r a l i z a t i o n . ; • To assess d i f f e r e n c e s i n p r e y - s i z e d i s t r i b u t i o n f o r the va r i o u s treatment groups, i n g e s t e d mysids were measured and the r e s u l t s pooled f o r each group. Thus n=10 f o r the large-amphipod group (Table 11) i m p l i e s t h a t a t o t a l of 10 mysids were consumed by the group as a whole. S i n c e the v a r i a n c e s i n mysid l e n g t h were extremely heterogenous ( i n d i c a t e d by the l a r g e d i f f e r e n c e s i n the standard d e v i a t i o n column i n Table 11) , the procedure f o r t e s t i n g the d i f f e r e n c e i n mean s i z e o f i n g e s t e d mysids was an approximation o u t l i n e d i n Sokal and Hohlf (1969). The procedure weights the means according t o the r e c i p r o c a l of the va r i a n c e of the sample from which they were taken. The r e s u l t s o f t h i s a n a l y s i s i n d i c a t e a s i g n i f i c a n t d i f f e r e n c e (F=8.91,P < .01) i n the mean s i z e o f mysids attacked. -It can be seen (Table 11) t h a t , with one e x c e p t i o n , f i s h c o n d i t i o n e d to feed on mysids a c q u i r e d l a r g e r mysids as prey items i n the t i d a l creek than e i t h e r amphipod or p e l l e t - c o n d i t i o n e d f i s h . 32 r - " TT~ •• — r - T " i CONDITIONING || LENGTB OF | NO OF MEAN | STANDARD | HISTORY 1) FOOD | MYSIDS LENGTH | DEV IN | { | DEPRIVATION | CONSUMED I OF MYSIDS | MYSID | 1 1 | | CONSUMED | LENGTHS | 1 I | | MM | i 1 l i i i_ i l ! r T Mysid | | 2 days | 80 J 14.1 | 2.39 | Small || 2 days | 36 J 14.0 | 0.81 | Amph | | ! j J Large 11 2 days | 10 \ 13.0 | 1. 09 | Amph | | J \ J P e l l e t 11 2 days | 13 j 14.2 | 3.06 | Type A | J J ! P e l l e t 11 2 days | 29 j 11.6 | 1.61 | Type B M J J j P e l l e t 11 7 days | 3 ! 11.4 | 4.31 | Type A | | \ j J P e l l e t | | 7 days | 12 \ 12.7 | 2 . 80 | Type B || 1 i ] i , . J U L . * . _ — ,i. _ j „ . Table 11. The average s i z e and v a r i a t i o n i n length of mysids consumed by the d i f f e r e n t e x p e r i m e n t a l groups . M y s i d s were pooled from stomachs of a l l f i s h from the two i n t r o d u c t i o n dates. 33 Benthic Prey. Sjyy>les A summary of the numbers of organisms caught i n the plankton net, b e f o r e and a f t e r t h e i n t r o d u c t i o n s i s given i n T a b l e 12. To determine the magnitude of d i e l e f f e c t s a 2-way a n a l y s i s of v a r i a n c e on s p e c i e s and sampling time was performed comparing the abundance of the f o u r most numerous organisms along the southern margin o f the t i d a l creek (Table 13). A square r o o t t r a n s f o r m a t i o n was a p p l i e d t o normalize the d i s t r i b u t i o n of sample v a l u e s , and the data pooled f o r J u l y 13 and J u l y 14 t o provide an estimate of the daytime abundance. The r e s u l t s of t h i s a n a l y s i s i n d i c a t e s i g n i f i c a n t d i f f e r e n c e s i n both s p e c i e s and sampling times (day vs.night) as well as s i g n i f i c a n t f i r s t - o r d e r i n t e r a c t i o n of s p e c i e s and sampling time. These d i f f e r e n c e s can be a t t r i b u t e d to a d i e l v e r t i c a l m i g r a t i o n which i s e s p e c i a l l y apparent i n Anisogammarus c o n f e r v j c o l u s , Snorimosphaeroma Oregonensis , and the chironomid l a r v a e i n the t i d a l creek (Table 12)., The numbers of amphipods caught i n ; the suspended basket samplers are shown i n Table 14. Since the values f o r the l a t t e r 4-day samples ( J u l y 16-20) are much higher ( t - v a l u e = 27. 406,P < 0.01) than the i n i t i a l 4-day samples ( J u l y 12-16) , i t i s e v i d e n t t h a t , i n a d d i t i o n to d i e l v a r i a t i o n , there e x i s t s a l o n g e r term v a r i a t i o n i n amphipod numbers, probably on a time s c a l e o f days or weeks., 34 1 1 MORNING EVENING r i • 1-4— JULY 13/76 • J0LY 1 4/76 I JULY 19/76 | SAMPLING \ TIHE(HHS) r t 1 l 0740 | 0750 0710 • T x _ 0720 ! 2155 ! 2210 f i \ Anisogammarus 1 c o n f e r v i c o l a s ! T -4-4— 6 I 10 ! 3 T I 1 _ i _ 866 I 1012 I Neomjsis I mereedis T T ^ .11 904 1 | 890 984 T _ i _ 768 T _ 1 104 4 ! 844 1 Gnorimosphaeroma 1 oreqonensis T I _11 34 I 27 T 5 + _ 1 _ . . 7 82 ! 62 • I I n s e c t Larvae II— 4 | 1 1 5 T 4 i 43 i 49 | 1 Corophium \ s p i n i c o r n e !! t J 1 | 1 f 0 i 0 a 0 - i 1 I Hydracarina J . J . . 1 | 1 - j — • . J . . 0 1 1 - i — 0 0 T" I 0 "I 1 - J Table 12. Numbers of epibenthic invertebrates caught i n plankton tows i n early morning and l a t e evening prior to and a f t e r t i d a l creek introductions. 35 r — !  • f - - -• T" j SOURCE o? | DF | SS | MS | F | VARIATION J | | ,. 1 . 1 i i 1 1 T ] I Subgroups j 7 j 3786*0768 J ] Time | 1 505. 0519 | 505.0519 | 278.0907 * * I J Species 3 2639.4947 } 879.8316 I 484.4512 ** | I Time X Species 3 641.5302 | 213. 8434 | 117.746 1 ** | I Within ( e r r o r ) 16 29.0583 I 1.8161 i I T o t a l ! 23 I 3815.1351 1 1 * . J — . ;. 1 „ 1 **=P < .01 Table 13. Two-way a n a l y s i s of v a r i a n c e on numbers of benthic organisms c o l l e c t e d i n the plankton net a t d i f f e r e n t sampling times. A sguare r o o t t r a n s f o r m a t i o n was performed and o n l y the four most abundant groups - Anisogaamarias , Neomvsis , Gnorimosphaeroma . and i n s e c t l a r v a e were co n s i d e r e d i n the a n a l y s i s . . SAMPLING DATES NO. OF REPLICATES MEAN NO. OF AMPHIPODS PER GRAM DRY WEIGHT OF FUCUS STANDARD DEVIATION JULY 12-20 1976 6.8 3.25 JULY 12-16 1976 I JULY 16-20 | 1976 1.1 0.07 I 6.7 0. 28 Tabl e 14. Numbers o f amphipods per gram dry weight o f Fucus caught i n basket t r a p s b e f o r e and a f t e r t i d a l creek i n t r o d u c t i o n s . 36 DISCUSSION Effects Of Experience Experience i n the f i s h conditioned to feed on Neomvsis for 30 days before t h e i r introduction into the t i d a l creek was manifested by the f i s h acquiring a larger proportion of mysids in the diet (Figs.7 and 8) than those groups of f i s h conditioned to feed on either amphipods or p e l l e t food. In addition, the s i g n i f i c a n t G-value f o r the CxPxO interaction (Table 7) constitutes evidence for an e f f e c t of conditioning across a l l treatment groups. The r e s u l t s of the experiment therefore demonstrate that experience with a given palatable prey type increases the feeding a b i l i t y of a predator on that prey, through learning, r e l a t i v e to other prey types i n the environment. The lack of a higher proportion of Anisoqammarus in the diet of the amphipod-conditioned f i s h compared to the other experimental groups <Figs.7 ; and 8) contradicts t h i s generalization. There are several possible reasons why t h i s occurred. F i r s t , i f Anisoqamm ar us i s r e l a t i v e l y unpalatable, the f i s h would not be expected to improve t h e i r feeding a b i l i t y on t h i s prey type. Second, the amphipod-conditioned f i s h probably would not show an increase i n feeding a b i l i t y on amphipods when the density of Anisogammarus i s very low r e l a t i v e to alternate prey. Thus i f amphipods were r e l a t i v e l y unavailable in the t i d a l creek at the time of the introduction, a conditioning e f f e c t 37 might not be apparent. There are s e v e r a l reasons why the f i r s t a l t e r n a t i v e i s u n l i k e l y . Anisogammarus i s a c c e p t a b l e as food by chum salmon i n the Squamish and other e s t u a r i e s ( F i g s . 5 and 6; Goodman and Vroom, 1972; Dunford, 1975) and at times t h i s s p e c i e s makes up a high p r o p o r t i o n of t h e i r d i e t . A l s o , i f amphipods were r e l a t i v e l y u n p a l a t a b l e , the amphipod-conditioned f i s h would be expected t o a c q u i r e a lower p r o p o r t i o n of amphipods than the other experimental groups, s i n c e , with e x p e r i e n c e , the f i s h would be expected t o l e a r n t o a v o i d u n p a l a t a b l e prey ( H o l l i n g , 1 9 6 5 ) , p r o v i d e d a l t e r n a t e prey were a v a i l a b l e . A comparison of the amphipod-conditioned f i s h with t h e other treatment groups (Figs.7 and 8) shows no evidence f o r a decreased responsiveness of amphipod-conditioned f i s h towards amphipods- these prey occur i n a l l treatment groups i n low but e q u i v a l e n t p r o p o r t i o n s . ,:• T h i s supports the c o n t e n t i o n t h a t Anispgammarus i s a p a l a t a b l e prey item and l e a v e s open the p o s s i b i l i t y t h a t the s p e c i e s was not present i n the t i d a l creek i n s u f f i c i e n t abundance f o r t h e amphipod-conditioned f i s h to express a c o n d i t i o n i n g e f f e c t . E f f e c t s of e x p e r i e n c e i n other f i s h s p e c i e s have been documented i n both l a b o r a t o r y s t u d i e s ( I v l e v , 1961; Beukema,1968; Ware,1971; Bryan,1973) and a f i e l d study (Bryan and Larkin,1972). Bryan and L a r k i n showed, by r e p e a t e d l y sampling the stomach c o n t e n t s of marked rainbow t r o u t , t h a t i n d i v i d u a l s s p e c i a l i z e d on d i f f e r e n t prey items and t h a t t h i s s p e c i a l i z a t i o n c o u l d p e r s i s t f o r a t l e a s t h a l f a year. Thus these animals were r e p e a t e d l y h a r v e s t i n g a s m a l l subset of the t o t a l s e t o f food types and becoming more capable a t f e e d i n g on those prey animals 38 Ivlev (1961) reported that i n carp, the number of pri o r t r a i n i n g periods has an influence on the e l e c t i v i t y value, E (proportion of food i n the diet r e l a t i v e to the environment) and that "the habit of feeding on certain food continues even with the option of a much wider choice." In sticklebacks, Beukema (1968) demonstrated that with experience, the r i s k to prey increased due to a higher chance of discovery a f t e r the prey had been previously encountered. In addition, the f i s h became more responsive to inedible objects which resembled the prey. Studies on rainbow trout show that trout can develop a " t r a i n i n g bias" (Bryan,1973). This means that when given a choice between f a m i l i a r and novel food, the f i s h w i l l acquire the type of food that they have eaten previously. Ware (1971) , also working with rainbow trout, reported that experimental animals became more responsive to the prey that they had experienced previously due to an increase in the reactive distance of the f i s h f or the prey type. Only a low l e v e l of reinforcement (6 encounters/48 hours) was necessary for the f i s h to show an increased responsiveness and Ware suggests that the c h a r a c t e r i s t i c s shown by rainbow trout allow them to learn to discover r e l a t i v e l y scarce polymorphic prey. In addition to the l i s t e d studies, there i s some circumstantial evidence from a study by LeBrasseur (1969) on juvenile chum salmon which supports the idea of an increased feeding a b i l i t y on previously experienced prey types. LeBrasseur used dif f e r e n t size-groups of sorted l i v e zooplankton i n feeding and growth studies and found that euphausiids were acquired only by f i s h which had previously fed on euphausiids. Thus 39 LeBrasseur's f i n d i n g s are i n accordance with the r e s u l t s of the t i d a l creek experiment which show t h a t j u v e n i l e chum salmon can l e a r n to i n c r e a s e t h e i r f e e d i n g a b i l i t y on a p r e v i o u s l y experienced prey type. During t h e b e h a v i o u r a l c y c l e which makes up a predator-prey i n t e r a c t i o n , the f o l l o w i n g components are i n v o l v e d IdeHuiter,1966): 1) Search- s t i m u l i t h at inform predator as to exact l o c a t i o n of prey are absent 2) Approach- l o c a t i o n o f prey known, prey o u t s i d e g r a s p i n g range 3) Capture^- prey w i t h i n g r a s p i n g range 4) I n g e s t i o n - c o n t a c t s t i m u l a t i o n from prey To assess t h e mechanism whereby experience i n c r e a s e s a pr e d a t o r ' s f e e d i n g a b i l i t y , i t i s necessary t o r e l a t e the change i n f e e d i n g a b i l i t y t o one or more of the above components. Most hypotheses suggest t h a t t h e change i n f e e d i n g a b i l i t y with experience i s mediated through an i n c r e a s e d s e a r c h i n g e f f i c i e n c y of the predator f o r a s p e c i f i c prey. The e a r l i e s t e x p l a n a t i o n which was invoked t o account f o r time l a g s between the t h e occurrence o f i n s e c t l a r v a e i n high abundance, and t h e i r subsequent appearance i n the food of s e v e r a l s p e c i e s o f song b i r d s , P ar us sp. , was proposed by Tinbergen (1960). Tinbergen invokes a mechanism i n v o l v i n g a p e r c e p t u a l change on the p a r t of the predator which a f f e c t s t h e i r s e a r c h i n g a b i l i t y f o r a p a r t i c u l a r prey. The " s e a r c h i n g image h y p o t h e s i s " assumes: 1)that s p e c i f i c c h a r a c t e r s are used i n the se a r c h f o r prey; 40 2) t h a t these s p e c i f i c c h a r a c t e r s a r e a s s i m i l a t e d i n a kind of l e a r n i n g process by means of which the b i r d s adopt a " s p e c i f i c s e a r c h i n g image", and 3) t h a t one member of a p a i r {ma t i n g - p a i r ) , adopts the s e a r c h i n g image of i t s mate when seeing the prey c o l l e c t e d by the l a t t e r . f Predators are thought t o s e l e c t i v e l y f i l t e r out v i s u a l s t i m u l i r e a c h i n g t h e i r r e t i n a , and thus can i n c r e a s e t h e i r s e a r c h i n g a b i l i t y f o r s p e c i f i c prey. Adoption of a s e a r c h i n g image i s thought t o be through a process of c o n d i t i o n i n g t h a t takes p l a c e a f t e r encounters with a new s p e c i e s o f prey. Dawkins (1971) provided some experimental evidence c o n s i s t e n t with the "se a r c h i n g image h y p o t h e s i s " by showing t h a t with experience domestic c h i c k s can improve t h e i r s e a r c h i n g a b i l i t y f o r c r y p t i c a l l y c o l o u r e d g r a i n , and t h a t t h i s i s l i k e l y due to a p e r c e p t u a l change. Hoyama (1970) c r i t i c i z e d the s e a r c h i n g image hypothesis and proposed an a l t e r n a t e mechanism t o e x p l a i n the i n c r e a s e d s e a r c h i n g e f f i c i e n c y of g r e a t t i t s on the i n s e c t l a r v a e they r e p e a t e d l y acq.ui.re as food. According to Royama's h y p o t h e s i s , a predator l e a r n s t o r e s t r i c t i t s s e a r c h i n g e f f o r t i n a p a r t i c u l a r h a b i t a t , and a c q u i r e s a l l of the prey types o c c u r r i n g t h e r e i n a more-or-less random f a s h i o n . Onder Royama^s hy p o t h e s i s there i s no n e c e s s i t y t h a t a s i e v i n g mechanism of the v i s u a l s t i m u l i v i a the r e t i n a be developed or t h a t the predator become more res p o n s i v e t o a p a r t i c u l a r prey. Rather, the predator i s predisposed t o capture c e r t a i n prey due to i t s d i s p r o p o r t i o n a t e s e a r c h i n g e f f o r t i n p a r t i c u l a r h a b i t a t s . 41 a s e r i e s of experiments on c a r r i o n crows f e e d i n g on b a i t covered by mussel s h e l l s o f d i f f e r e n t c o l o u r allowed Croze (1970) t o assess the change i n the crows' s e a r c h i n g behaviour with experience, c r o z e i n t e r p r e t s h i s r e s u l t s i n terms o f s e a r c h i n g image formation but acknowledges the importance of l e a r n i n g where t o s e a r c h . Thus the s p e c i f i c c h a r a c t e r s of the prey, as w e l l as the h a b i t a t are both l e a r n e d and "form j o i n t l y the p e r c e p t u a l template of a Searching Image." In the t i d a l creek experiments i t i s u n l i k e l y t h a t the j u v e n i l e salmon l e a r n e d where t o c o n c e n t r a t e t h e i r s e a r c h i n g e f f o r t t o maximize t h e i r s e a r c h i n g e f f i c i e n c y , s i n c e a l l p r e v i o u s experiences with prey occurred i n l a b o r a t o r y tanks where the prey are not a s s o c i a t e d with p a r t i c u l a r f e a t u r e s of the h a b i t a t {eg,sedge rhizomes or sediment as i n the t i d a l c r e e k ) . Thus, assuming that the f i s h c o u l d not l e a r n to respond to raicrohabitat d i f f e r e n c e s i n the l a b o r a t o r y tanks, the only c h a r a c t e r i s t i c s the f i s h c o u l d l e a r n were a s s o c i a t e d with the s p e c i f i c morphology of the preyi Although j u v e n i l e salmon are thought to be v i s u a l p r e d a t o r s (Hoar,1958) there i s evidence from at l e a s t one experiment (McBride e t al.,1962) t h a t o l f a c t o r y p e r c e p t i o n i s s i g n i f i c a n t i n j u v e n i l e sockeye salmon. E x t r a c t s of n a t u r a l foods, at c o n c e n t r a t i o n s as low as 1 p a r t i n 80;000,000, were d e t e c t a b l e by f i s h t h a t had p r e v i o u s l y experienced the food. I t i s p o s s i b l e t h a t i n the t i d a l creek experiments j u v e n i l e chum salmon c o u l d improve t h e i r s e a r c h i n g a b i l i t y f o r p a r t i c u l a r prey by l e a r n i n g t o d i s c r i m i n a t e o l f a c t o r y cues emerging from the prey types on which they were c o n d i t i o n e d to feed. 42 The d i s c u s s i o n thus f a r c o n s i d e r s the p o s s i b l e e f f e c t s of experience on the s e a r c h i n g behaviour of p r e d a t o r s and i g n o r e s t h e i n t e r a c t i o n s between experience and the handling components of p r e d a t i o n i n the b e h a v i o u r a l c y c l e : approach, c a p t u r e , and i n g e s t i o n . An i n c r e a s e i n f e e d i n g a b i l i t y with experience a t t r i b u t a b l e t o a g r e a t e r h a n d l i n g e f f i c i e n c y can be formulated as the " h a n d l i n g hypothesis". The l i v e prey items used i n the c o n d i t i o n i n g experiments were l a r g e r e l a t i v e to the s i z e of the j u v e n i l e salmon predator ( F i g . 3 ) . During the course of the c o n d i t i o n i n g treatments, the salmon were observed to change t h e i r h a n d l i n g behaviour towards both mysids and amphipods. With experience, the p r e d a t o r s l e a r n e d t o manipulate mysids i n t h e i r mouths so t h a t they were i n g e s t e d t a i l - f i r s t or h e a d - f i r s t . A l t e r n a t i v e l y , mysids were grasped i n the mid-dorsal r e g i o n i n such a way t h a t the s u c t i o n c r e a t e d by expansion o f the b u c c a l c a v i t y caused the abdomen of the mysid to f o l d down onto the thorax thus r e d u c i n g i t s s i z e and c r e a t i n g a more e a s i l y i n g e s t i b l e p a r t i c l e . Near the beginning of the c o n d i t i o n i n g schedule amphipods were r e p e a t e d l y i n g e s t e d and e x p e l l e d from the mouth. However, as the number of experiences i n c r e a s e d , the freguency of e x p u l s i o n s decreased. T h i s suggests t h a t j u v e n i l e chum salmon-increase t h e i r h a n d l i n g e f f i c i e n c y when c o n d i t i o n e d to feed on s p e c i f i c prey items. F u r t h e r support f o r the " h a n d l i n g h y p o t h e s i s " are the r e s u l t s i n Table 11. This t a b l e compares the s i z e d i s t r i b u t i o n o f i n g e s t e d mysids..If t h e r e i s an e f f e c t of experience on the p e r c e p t u a l a b i l i t y of the predator, then f i s h c o n d i t i o n e d t o feed on mysids should be more res p o n s i v e towards s m a l l e r , more c r y p t i c i n d i v i d u a l s , than f i s h 43 conditioned on f i s h p e l l e t s or amphipods. The observed s i z e d i s t r i b u t i o n however, i s opposite that predicted on the basis of perceptual discriminatory a b i l i t y . Juvenile salmon conditioned to feed on mysids attacked larger mysids in the t i d a l creek than other treatment groups. This supports the hypothesis that experienced f i s h learned to manipulate the prey better than f i s h conditioned on other food types. ft comparison of the s i z e d i s t r i b u t i o n of ingested amphipods for the small- and large-amphipod conditioned groups of f ish :was not possible due to the small number of amphipods eaten by the f i s h during the t i d a l creek introductions. Prey flyailability In The T i d a l Creek Many f i e l d studies dealing with the feeding of f i s h are concerned with making inferences about prey a v a i l a b i l i t y (the perceived abundance of prey organisms to the f i s h ) . For example, Allen (1941) defines absolute a v a i l a b i l i t y as the proportion of the population which, i n a t y p i c a l habitat would be v i s i b l e to, and of suitable s i z e and taste to be eaten by a f i s h of the type under consideration, i f the f i s h had the whole area under consideration. Any estimate of t h i s parameter requires a detailed understandinq of a predators* physiological and behavioural c a p a b i l i t i e s as well as an accurate assessment of the number, behaviour, and d i s t r i b u t i o n a l pattern of prey i n the environment. F i e l d investigators rarely, i f ever, have t h i s information at t h e i r disposal. More operational terms have been defined by Hyatt {in press) who defined " r e a l i z e d a v a i l a b i l i t y " to i n d i c a t e the prey items present i n the d i e t of a given sample of p r e d a t o r s , " p o t e n t i a l a v a i l a b i l i t y " as t hat s e t of prey organisms t h a t are p h y s i c a l l y present and which t h e predators can d e t e c t , capture, handle, i n g e s t , and a s s i m i l a t e i n a given time i n t e r v a l , as w e l l as "apparent a v a i l a b i l i t y " to r e f e r t o a l l of the organisms t h a t appear t o an i n v e s t i g a t o r to be p h y s i c a l l y present and which he t h i n k s the predator should be capable of d e t e c t i n g , c a p t u r i n g , h a n d l i n g , i n g e s t i n g , and a s s i m i l a t i n g . P e r u s a l of the r e s u l t s from the stomach content a n a l y s i s ( F i g s . 7 and 8) shows t h a t the p r o p o r t i o n of mysids i n the d i e t was higher on * the second i n t r o d u c t i o n date (July 16) f o r a l l treatment groups. The r e s u l t s from the 3-way G-test o f independence (Table 9) c o n f i r m t h a t there was a s i g n i f i c a n t e f f e c t of i n t r o d u c t i o n . d a t e on the occurrence of mysids. Thus t h e r e was a d i f f e r e n c e i n the r e a l i z e d a v a i l a b i l i t y of mysids i n the t i d a l creek on the two i n t r o d u c t i o n dates. In c o n t r a s t to anisogammarus which remain near the sedge rhizomes when the t i d e i s low (Levings,1973), Neomysis moves i n and out of the t i d a l creek with each f l o w i n g and ebbing t i d e . T h i s migration of mysids over a s h o r t time s c a l e probably r e s u l t s i n a h i g h l y v a r i a b l e mysid d e n s i t y i n t h e t i d a l creek from day to day. Conseguently, the p o t e n t i a l a v a i l a b i l i t y of mysids changes on a d a i l y b a s i s , and i t i s understandable t h a t the r e a l i z e d a v a i l a b i l i t y o f mysids i s d i f f e r e n t f o r the two i n t r o d u c t i o n dates. One of the u n a n t i c i p a t e d r e s u l t s of the t i d a l creek i n t r o d u c t i o n s was the low freguency o f Anisogammarus i n the 45 d i e t , p a r t i c u l a r l y s i n c e r e g u l a r samples of f i s h from the t i d a l creek showed t h i s amphipod to be an important food item. These cru s t a c e a n s were c e r t a i n l y present i n the v i c i n i t y of the t i d a l creek, although there i s a s u g g e s t i o n from the basket t r a p data (Table 14) t h a t t h e i r d e n s i t y was low at the time of the i n t r o d u c t i o n s . Examination of the plankton tow data (Table 12) shows a marked d i f f e r e n c e i n the abundance of amphipods a t d i f f e r e n t sampling times and t h i s shows up i n the a n a l y s i s of v a r i a n c e (Table 13) as a s i g n i f i c a n t time e f f e c t . Thus, i t i s l i k e l y t h a t Anisogammarns has a s t r o n g d i e l migration p a t t e r n , and t h a t t h i s a f f e c t s t h e i r p o t e n t i a l a v a i l a b i l i t y as food f o r f i s h . Recently Davis and Holton (1976) present evidence from the Columbia River Estuary t h a t shows t h a t Anisoqammarus migrates v e r t i c a l l y on a d i e l b a s i s and was most v u l n e r a b l e t o t h e i r sampling d e v i c e , an e p i b e n t h i c s l e d , on a low s l a c k t i d e between 1600 and 2400 hours. I f t h i s r e l a t i o n s h i p i s v a l i d f o r the t i d a l creek i n the Sguamish e s t u a r y , then i t would e x p l a i n the absence of amphipods i n the stomach c o n t e n t s . Since j u v e n i l e chum salmon were i n t r o d u c e d a f t e r the peak migrat i o n p e r i o d (1600-2400 hours) the amphipods were apparently u n a v a i l a b l e t o the f i s h . Moreover, t h i s d i e l m i g r a t i o n p a t t e r n i m p l i e s t h a t the amphipods which one observes i n chum salmon stomachs ( F i g s . 5 and 6) sampled i n the morning hours (060 0-0900 hours) were eaten 6-17 hours p r e v i o u s l y . A v a i l a b l e i n f o r m a t i o n on the r a t e of evacuation of chum salmon f r y stomachs i n d i c a t e s a 10 hour eva c u a t i o n a t 12.8°C ( B a i l e y et a l . ,1975) . Since the temperature of the e s t u a r y was lower than 12.8°C on most sampling dates, and the corresponding evacuation r a t e t h e r e f o r e l o n g e r than 10 46 hours, the data are c o n s i s t e n t with the hypothesis t h a t the amphipods observed i n the stomachs of chum j u v e n i l e s were a c q u i r e d on the evening b e f o r e sampling. Food Of. Clvum Salmgn In The Squamish Estuary. The r e s u l t s of the stomach a n a l y s i s of f i e l d samples from the t i d a l creek ( F i g s . 5 and 6) show much v a r i a t i o n with time, and although c e r t a i n prey organisms (eg. Anisogammarus and t e r r e s t r i a l i n s e c t s ) occur r e p e a t e d l y i n d i f f e r e n t p r o p o r t i o n s , an understanding of t h e d i e t on one o c c a s i o n cannot be used to p r e d i c t subsequent f e e d i n g behaviour. One p o s s i b l e reason f o r t h e observed changes i s due t o the r e l a t i o n s h i p between predator s i z e and prey s i z e . S i n c e t h e j u v e n i l e chums were l a r g e r during t h e l a t t e r two sampling p e r i o d s (Table 2) .the d i f f e r e n c e i n d i e t might r e f l e c t a change i n t h e f e e d i n g behaviour of the predator through a "developmental s w i t c h " mechanism. Thus as the pred a t o r s grew l a r g e r , they might exclude s m a l l e r organisms from t h e i r d i e t and i n c l u d e a higher p r o p o r t i o n of l a r g e forms. The r e d u c t i o n i n the percent frequency of c y c l o p o i d s (small prey) over time (Figs.5 and 6 ) , and t h e i n c r e a s e i n the percent volume °f H§2I2§i§ ( l a r g e prey) i s evidence s u p p o r t i n g t h i s mechanism. A second reason f o r a change i n the p r o p o r t i o n o f d i f f e r e n t components i n the d i e t might be due t o a change i n the p o t e n t i a l a v a i l a b i l i t y o f the d i f f e r e n t prey types. F i s h i n the l a b o r a t o r y are q u i t e s e n s i t i v e to changes i n the d e n s i t y of a l t e r n a t e prey types (Murdoch et al.,1975) and the r e s u l t s i n T a b l e 11 show t h a t , a t l e a s t f o r some prey organisms, t h e r e are d i f f e r e n c e s i n 47 t h e i r p o t e n t i a l a v a i l a b i l i t y . I t i s l i k e l y t h a t i n the t i d a l creek, both the developmental s w i t c h mechanism, and the changed p o t e n t i a l a v a i l a b i l i t y of prey types c o n t r i b u t e d t o the high v a r i a b i l i t y i n d i e t . S i n c e Neomysis was found to be an a c c e p t a b l e food type i n the l a b o r a t o r y and i t was observed to be an important, i f not the dominant, c o n s t i t u e n t o f the i n v e r t e b r a t e biomass i n the t i d a l creek on a l l sampling o c c a s i o n s {Table 12), i t i s s u r p r i s i n g t h a t t h i s c r u s t a c e a n d i d not make up a g r e a t e r p r o p o r t i o n of the d i e t from the f i e l d samples. One mechanism to account f o r a low u t i l i z a t i o n of an a p p a r e n t l y h i g h l y p r o f i t a b l e prey type by a predator, i s f o r the prey type to become u n p r e d i c t a b l e i n i t s abundance and d i s t r i b u t i o n p a t t e r n s over time. Since Neomy.sis migrates i n t o d i f f e r e n t p a r t s of the e s t u a r y at s u c c e s s i v e t i d a l s t a g e s , t h i s might e f f e c t i v e l y allow the p e r s i s t e n c e o f a h i g h , prey d e n s i t y i n an area o f high predator d e n s i t y . Due t o t h e i r temporal and s p a t i a l v a r i a b i l i t y , i t might be d i f f i c u l t f o r j u v e n i l e chum salmon t o form a search image f o r these prey. The r e s u l t s o f the stomach a n a l y s i s of the p e l l e t - c o n d i t i o n e d f i s h on the two i n t r o d u c t i o n dates can be used as a s i m u l a t i o n of the d i e t of naive chum f r y feeding i n the e s t u a r y f o r the f i r s t time. Since these groups show a higher v a r i a b i l i t y i n the number o f prey types consumed {Table 10) than l i v e p r e y - c o n d i t i o n e d f i s h , the i n i t i a l e n t r y of f r y i n t o the e s t u a r y i s l i k e l y t o be a period when a r e l a t i v e l y high d i v e r s i t y of prey are a g u i r e d . Naive p r e d a t o r s a r e l i k e l y t o e x p l o i t prey i n a more random f a s h i o n than experienced 48 p r e d a t o r s , u n t i l a s u f f i c i e n t number of encounters cause the formation of a search image. ., Of s i g n i f i c a n c e , the number of sea r c h i n g images t h a t a pr e d a t o r can possess a f f e c t s i t s f o r a g i n g a b i l i t y i n the n a t u r a l environment , and t h i s w i l l be c o n t r o l l e d by the r e l a t i v e r a t e s o f l e a r n i n g and f o r g e t t i n g of search images. A v a i l a b l e evidence i n d i c a t e s t h a t crows (Croze,1970) can form more than one s e a r c h image, but i n rainbow t r o u t , a l t e r n a t e food does not a f f e c t the d i s t a n c e of r e a c t i o n of an experienced p r e d a t o r f o r the prey type i t i s c o n d i t i o n e d to feed on (Hare,1971), I t i s not known how many search images can be s i m u l t a n e o u s l y r e t a i n e d by f i s h . Recently Mendelson (1975) p u b l i s h e d a d e t a i l e d account of the f e e d i n g h a b i t s of the minnow Notrop.is i n p o o l s of Roxbury Creek, Wisconsin....His aim was t o assess resource p a r t i t i o n i n g i n f o u r sympatric s p e c i e s . , He suggests the f o l l o w i n g p o s s i b l e a l t e r n a t i v e mechanisms t h a t allow c o e x i s t e n c e : 1) Pr e d a t o r s are adapted t o the capture o f s p e c i f i c kinds of prey, and they f r e g u e n t c e r t a i n p l a c e s because t h e i r prey r e s i d e t h e r e . 2) Predators are adapted t o p a r t i c u l a r h a b i t a t s , to r e g i o n s i n which they f u n c t i o n most e f f e c t i v e l y , and i n these regions they prey i n d i s c r i m i n a t e l y on whatever animals of a s u i t a b l e s i z e are a v a i l a b l e . , On the b a s i s of the s p a t i a l d i s t r i b u t i o n of the predators and prey and an examination of stomach c o n t e n t s , Mendelson concludes t h a t t h e second a l t e r n a t i v e i s more l i k e l y . From the r e s u l t s o f many f i e l d and l a b o r a t o r y s t u d i e s (eg. Beukema,1968; 4 9 Ivlev,1961) however, the evidence suggests t h a t , c o n t r a r y to Mendelson's c o n c l u s i o n , f i s h are h i g h l y d i s c r i m i n a t e i n t h e i r f e e d i n g p a t t e r n s and r a r e l y , i f ever, a c q u i r e whatever animals are a v a i l a b l e i n a density-dependent fashion..Moreover, i n the t i d a l creek experiments I demonstrated t h a t s i m i l a r p r e d a t o r s can be c o n d i t i o n e d t o respond d i f f e r e n t l y t o an i d e n t i c a l set of food organisms i n the t i d a l creek. Thus, the r e s u l t s of the present study s t r o n g l y favour the f i r s t a l t e r n a t i v e and demand a reassessment of the problem., 50 LITESAIfllE CITED Allen,K.R. 1941. S t u d i e s on t h e b i o l o g y o f the e a r l y s t a g e s of the salmon ( S a l m o s a l a r ). J. Anim. E c o l . 10:47-76. 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The predatory behaviour o f rainbow t r o u t ( S a l m o g a i r d n e r i ). Ph.D. T h e s i s . Dept. Zoology. Univ. Of B.C.,Vancouver, B.C. 185p. APPENDICES 54 A P P E N D I X I. Diet of experimental f i s h r e l e a s e d into the tida l c r e e k on J u l y 15/7 6. 100 75.1 50. £5.1 0 % FREQUENCY 1 — F = h = 1— h -I—I—I i . E« 3- 4- 5- 6« 7- 8. a.10. 100 75-1 50 25.1 % F R E Q U E N C Y i» £• 3. 4> 5. G> 7. B- 9-10. IJOO. 75... 50. E 5 4 0 lOOv 75 50-1 ES. % O C C U R R E N C E 1. E- 3« 4. 5. E< 7- 8- 9-10. % V O L U M E H h H—-I—I—I 1. E- 3- 4. 5- B. 7- B- 9-10. 100. 75.| SO. ES-1 O 100. 75.. 50-.. £5.1 % O C C U R R E N C E !• B' 3« 4« 5. 6« 7« 8' 9>10-% V O L U M E 1. £• 3- 4. 5. B- 7- 8- 9-10. • PREY TYPE MYSID 2-day July 15/76 N = 17 E „ c 3 0. E E PREY TYPE S M A L L A M P H 2- day July 15/76 N = 13 x. U o J u a I — i — i — i — I — I — l — i — i — i — i 1. E» 3' 5. G- 7- B- 9-10. PREY TYPE Diet of juvenile chum salmon conditioned to feed on mysids and small amphipods (2-day food deprivation) during first tidal creek introduction- July 15/76. 55 A P P E N D I X I. [CONT'D] 1D0-75... 50... £5 0 % FREQUENCY H h—1 1 h !• E« 3> A' 5« 6- 7- B- 9>10. 100 75 50... ES... 0 100v 75 50 254 0 % OCCURRENCE H 1 !• 2- 3« A' 5« 6- 7. B« 9«10. % V O L U M E . . -i 1—I—I—I—I—I—I 1. E« 3- 4 . 5. E« 7. B« 9<10-1O0. 75... 50... E5... 0:~. % F R E Q U E N C Y H 1 H 1 1. E« 3« 4 . 5- 6' 7. B- 9>10. 100-T 75 50 ES 0 % O C C U R R E N C E H — 1 . . H — f -1. E- 3> 4- 5- £• 7. B> 9 -10 . 100. 75... SO-. E5..r 0... % V O L U M E H 1 r—+- 4=1 H 1 !• E- 3- 4. 5. E> 7. B- 9-10. PREY TYPE L A R G E A M P H 2-day July 15/76 N = 6 " 2 v •a v *> a C u o o ri £ £ t .S I 2. I S" S -6 « 2 2 - -g j E- E !'! J t E .£ 2 c 5 £ .2 S g o o o n « j i P o ^ •> C C D . - ; u M >-e «> ' o o o ? « o „ „ •I , i j • o v -e J= ^ « c .° , \ ° U U U > J X < <-> U | 1 1 1 1 1 1 1 1 1 1 1. 2. 3> 4. 5. G« 7« B« 3<10. to PREY TYPE P E L L E T T Y P E A 2- day July 15/7 6 N=7 PREY TYPE Diet of juvenile chum salmon conditioned to feed on large amphipods and pellet typc-A (2-day food deprivation) during first tidal creek introduction- July 15/76. 56 A P P E N D I X I. [CONT'D] 100. 75... 50... % FREQUENCY H 1 !• 2« 3- 4. 5« 6> 7. 8- 9.10« 75 50... 25... % OCCURRENCE 3=F H 1 100 v 75-50-25.1 !• 2. 3. 4> 5. G> 7- 8- 9-10. % V O L U M E H 1 1. 2« 3^ 4«' 5. G« 7. B" 9-10. 100. 75... 50... 25... % F R E Q U E N C Y 1O0. 75... SO-BS •! 0 2. 3. 4« 5. 6- 7- 8- 9.10-% O C C U R R E N C E H 1 1 . 2. 3- 4- 5. 6. 7. B- 9-10. 100 v 75 50... 25... % V O L U M E 7- 8. 9-10-PREY TYPE P E L L E T T Y P E B 2-day July 15/76 N=9 • E -.2 X E E o o o 5 E c u o o o « ? ° o i. « e • x. x. s- « v. c ° •= Z f-1 O U O -J X < <J u I 1 1 1 1 1 1 1 1 1 1 1 . 2- 3- 4. 5- G- 7« B- 9-10-PREY TYPE P E L L E T T Y P E A 7 -day July 15/76 N = 10 PREY TYPE Diet of juvenile chum salmon conditioned to feed on pellet type-B(2-day food deprivation) and pellet type-A (7-day food deprivation) during first tidal creek introduction- July 15 /76. A P P E N D I X I. [CONT'D] 100 v 75 50 2S.J. 0 % FREQUENCY !• E> 3« 4. 5. 6« 7.' 9.10.' lOOv 75 SO B5.I 100 75. 50... ES... % OCCURRENCE 1' E« 3> 4« 5« 6. 7. B* 9«10. % V O L U M E 0 < M - n u i ~i i i i i !• £• 3> 4. 5. B> 7. B» 9-10. PREY TYPE P E L L E T T Y P E B 7-day July 15/76 N = 6 t l CL —< j t i i f l o o »- V. . c c p « o o Z H U U J o U I 1 1 1 h !• E« 3-•+- H (- H 1 5> G. 7- B« 9<10-PREY'TYPE Diet of juvenile chum salmon conditioned to feed pellet type-B(7-day food deprivation) during first tidal creek introduction- July 15/7 6. 58 A P P E N D I X II. Diet of experimental f i s h r e l e a s e d into the tida l c r e e k on Ju l y 16/76. 1 0 0 7 5 . . . 5 0 . . . E S . . : % FREQUENCY - F = l — I — h — 1 — I — I — I ! • E« 3> 4 . 5 . £ • 7 . 8- 9 - 1 0 . 1 0 0 . } 75.X 5 0 . 2 5 . % F R E Q U E N C Y -I 1 1 h •H 1 ! • E« 3 . 4 . 5» G» 7 . B - 9 - 1 0 . 1 0 0 . 7 5 . . . 5 0 . E5-. % OCCURRENCE H—I I I—I—I 1 0 0 . 7 5 . . . S O . . . E 5 . ! • E> 3« 4- 5 - G- 7 . B» 9 - 1 0 . % V O L U M E H 1—h H — I 1 0 0 . 7 5 . . . S O . . . 2 5 . . . % O C C U R R E N C E 1 0 0 . 7 5 . . . 5 0 . . . 2 5 . -f 1 I I H 1 1- E« 3 . 4 . 5 . G - 7 . 8 - 9 . 1 0 . % V O L U M E 1- E« 3« 4« 5 . G> 7« B> 9 . 1 0 -=1 1 I 1 1 1 1-—l ! • £ • 3 - 4 - 5 . G - 7 . S- 9 . 1 0 . PREY TYPE MYSID 2-day July 16/76 N=27 £ £ 2 £ O 0 o C C D . - ; 0 0 0 ? Z H t I-o o u J H 1 1 h u u £ s £ t» v .c .c « - s* c H h .S £ a. v » rt ™ _ -5 » £ a c •2 I " •S E ° a. GO U O 1 . £ • 3 . 4 . 5 . G . 7 . B« 9 - 1 0 . PREY. TYPE S I / A L L A M P H 2-day July 16/76 N = 27 PREY TYPE Diet of juvenile chum salmon conditioned to feed on mysids and small amphipods (2-day food deprivation) during second tidal creek introduction- July 16/76. 59 A P P E N D I X II. [CONT'D] 100 v 75. so.1 ES. 0-% FREQUENCY •i 1 h -i—I 1. E« 3' 4. 5- E« 7- B. 9.10-100 75-.. 50-.. ES.. % FREQUENCY =1 1 1 >—I 1 1 1« E« 3. 4 . 5. B> 7- 8- 9-10-100. 75... 50... E5._ % OCCURRENCE 1" E« 3- 4 - S. 6« 7. B- 9-10. 100. 75>. 50. ES.I % VOLUME I I I r~i i 1 !• E» 3- 4 . 5- G> 7. B> 9-10 100. 75-. SO-ES. % OCCURRENCE 1 P=l 1—I !• E« 3- 4 . 5- 6» 7- B- 9«10. 100.^ 75 50... ES-.r % VOLUME 1=1-+. -I 1 r—( 1 1 1- E« 3- 4- 5- 6. 7. B' 9>10. PREY TYPE LARGE AMPH 2- day July 16/76 N = 15 E o U O o o £ E E .2 c - E g O O O "3 rt c c a y M rt C E ° c o X <. U O H 1 1 1 1 1 1 1 1 1 !• E« 3- 4 - 5. 6- 7. B- 9-10. PREY TYPE P E L L E T T Y P E A 2-day July 16/76 N=l 5 PREY TYPE Diet of juvenile chum salmon conditioned to feed on large amphipods and pellet type-A (2-day food deprivation) during second tidal creek introduction- July 16/76. A P P E N D I X II. [CONT'D] 60 1 0 0 V 75 SO 55.1 0 100.,. 75 50... ES... 0 100. I 75.| 50 25.1 % FREQUENCY -i 1 1 1 1 I I !• £• 3- 4 . 5« G- 7. 8- 9.10-% OCCURRENCE -f=F !• 2« 3« 4« 5« 6* 7« 8. 9«10« % VOLUME - t — I — ( — + • !• 2- 3> 4 . 5- B« 7. 8- 9.10. too. 75... 50... 25... 0..: 100. 75... 50... 25v. 0... 100- T 75 50.1 25-% FREQUENCY H 1 I I i 1 !• 2- 3- 4 - 5« 6> 7. B> 9-10 % OCCURRENCE H 1 I 1 1 1 . 1. g. 3. 4 . 5. E- 7. 8- 9«10. % VOLUME 1- 2» 3- H - -+- H h 5- E> 7. B> 9'10-PREY TYPE P E L L E T TYPE B 2-day J u l y 16/76 N=23 6 o o Z H 3 P. i t E E X. X. >• u o o O. ... U) o i. u L. O I. O C O u o I — i — i — i — i — I — i — i — - t — ^ J.. E- 3' 4. 5. G« 7. B- 9-10. PREY TYPE •PELLET T Y P E A 7 - d a y J u l y 16/76 N=6 PREY"TYPE D i e t of j u v e n i l e c h u m s a l m o n c o n d i t i o n e d to f e e d on p e l l e t t y p e - B ( 2 - d a y food d e p r i v a t i o n ) and p e l l e t t y p e - A (7-day f o o d d e p r i v a t i o n ) d u r i n g s e c o n d t i d a l c r e e k i n t r o d u c t i o n - J u l y 16/76. A P P E N D I X II. [CONT'D] 100. SO ES-l % FREQUENCY H (-1. E« 3« 4. S- 6- 7. 8« 9>10. lOOv 75. SO-E3. O. 100-I 75.J SO-55-1 % OCCURRENCE H h . . . . !• £• 3« 4« 5- 6- 7- B- 9.10' m % V O L U M E - t — I — t - -t- -i 1« 5« 3' A- 5. 6* 7. B> 9.10. PREY TYPE P E L L E T T Y P E B 7 -day-July 16/76 N = 5 £ ~ £ E o u. V V .5 ... « £ 2 o O J2 u u I—I—I—I—I—I—I—(-£ P. u o 1. E> 3. . -I- . 5- 5. 7. B- 9-10-PREY TYPE Diet of juvenile chum salmon conditioned to feed on pellet type-B(7-day food deprivation) during second tidal creek introduction- July 16/76. 

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