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Space and food utilization by salmonids in marsh habitats of the Fraser River estuary Dunford, William Errington 1975

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SPACE AND FOOD U T I L I Z A T I O N BY SALMONIDS I N MARSH HABITATS OF THE FRASER RIVER ESTUARY by WILLIAM ERRINGTON DUNFORD B.A., The U n i v e r s i t y o f T o r o n t o , 1972 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e D e p a r t m e n t o f Z o o l o g y We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE UNIVERSITY 'OF B R I T I S H COLUMBIA JANUARY, 19 75 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a i ABSTRACT The temporal u t i l i z a t i o n of space and food by. juvenile P a c i f i c salmon was studied i n selected marsh habitats of the Fraser River Estuary. Two types of marginal habitat were examined- slough habitat (exposed to main current) and channel habitat (backwaters). Chum salmon f r y (Oncorhynchus  keta) and chinook salmon f r y (.0.. tshawytscha) were the most abundant species present i n both habitats, with peak densities occurring i n late A p r i l . Chum and chinook exploited many similar food sources, and the size of prey selected was examined to show a size segregation of the d i e t . Chum tended to select a. greater proportion of smaller, planktonic prey, while chinook ingested a greater proportion of larger, benthic prey. The divergence i n types of prey and prey size selected was greatest during maximum density i n late A p r i l and early May. The density of chinook was greater than chum, except i n early A p r i l . Few chum were taken, a f t e r early June, while chinook were present u n t i l l a te July, showing a steady increase i n length throughout the season. I t i s suggested, that chinook may reside i n the estuarine marsh habitats temporarily each spring and summer. The chum f r y u t i l i z e the habitats for feeding, during migration, but disperse to marine habitats i n a shorter time period than chinook. i i TABLE OF CONTENTS Page ABSTRACT i TABLE OF CONTENTS i i L I S T OF FIGURES i v L I S T OF TABLES v i ACKNOWLEDGEMENTS v i i I . INTRODUCTION 1 I I . STUDY AREA 4 I I I . MATERIALS AND METHODS 10 I V . RESULTS 19 A. P h y s i c a l C h a r a c t e r i s t i c s 19 B. D r i f t O r g a n i s m s 21 1. S l o u g h H a b i t a t 21 2. S i d e C h a n n e l H a b i t a t 21 C. T e m p o r a l a n d S p a t i a l Use . 24 1. S l o u g h H a b i t a t 24 2. S i d e C h a n n e l H a b i t a t 29 D. E s t i m a t i o n o f T o t a l S e a s o n a l Use Of M a r g i n a l H a b i t a t s 29 E. S e a s o n a l C h a n g e s i n S i z e o f J u v e n -i l e Chum a n d C h i n o o k S a l m o n 31 1. F o r k L e n g t h 31 2. M o u t h S i z e 36 F. F o o d a n d F e e d i n g 36 1. S l o u g h H a b i t a t 39 2. S i d e C h a n n e l H a b i t a t 46 3. S i m i l a r i t y o f D i e t s o f Chum an d C h i n o o k F r y 4 8 4. C h i n o o k S m o l t s ( y e a r l i n g s ) .... 48 i i i P a ge 5. J u v e n i l e S o c k e y e S a l m o n 51 G. L a b o r a t o r y F e e d i n g E x p e r i m e n t s .... 52 1. B e h a v i o r O b s e r v a t i o n s 52 2. E x p e r i m e n t a l F e e d i n g R e s u l t s .. 52 V. DISCUSSION AND CONCLUSIONS 59 LITERATURE CITED 65 APPENDICES 6 8 i v L I S T OF FIGURES F i g u r e Page 1. S i x S l o u g h H a b i t a t S i t e s s a m p l e d by B e a c h s e i n e i n S o u t h Arm, F r a s e r R i v e r 5 2. (a) S l o u g h a n d C h a n n e l H a b i t a t s i n S o u t h Arm, F r a s e r R i v e r 6 (b) C h a n n e l H a b i t a t 600 m f r o m c o n f l u e n c e o f C h a n n e l a nd S l o u g h H a b i t a t s o f F i g u r e 2 ( a ) 6 3. (a) F i v e S l o u g h H a b i t a t S i t e s s a m p l e d b y B e a c h s e i n e i n N o r t h Arm, F r a s e r R i v e r 7 (b) L o w e r F r a s e r R i v e r S y s t e m 7 4. D a i l y D i s c h a r g e o f F r a s e r R i v e r a t Hope, f r o m M i d M a r c h t o M i d A u g u s t , 1973 a n d 1974 9 5. T y p i c a l B i - w e e k l y T i d e C y c l e , m e a s u r e d a t mouth o f F r a s e r R i v e r ( S o u t h Arm) 9 6. F o u r S i d e C h a n n e l H a b i t a t S i t e s s a m p l e d b y p o l e n e t i n S o u t h Arm, F r a s e r R i v e r 12 7. (a) L a b o r a t o r y E x p e r i m e n t a l A p p a r a t u s 16 (b) L a r g e H o l d i n g T a n k s - E x p e r i m e n t a l A p p a r a t u s 16 (c) S e v e n s m a l l A q u a r i a f o r F e e d i n g T e s t s .... 17 8. S e a s o n a l C h a nges i n w a t e r t r a n s p a r e n c y i n S l o u g h H a b i t a t , S o u t h Arm, F r a s e r R i v e r 20 9. S e a s o n a l C h a nges i n Mean W a t e r T e m p e r a t u r e o f S l o u g h H a b i t a t a n d S i d e C h a n n e l H a b i t a t , F r a s e r R i v e r 20 10. S e a s o n a l Change o f D e n s i t y o f J u v e n i l e Chum and C h i n o o k i n S l o u g h H a b i t a t , F r a s e r R i v e r E s t u a r y 26 11. S e a s o n a l Change i n D e n s i t y o f J u v e n i l e Chum a n d C h i n o o k i n S i d e C h a n n e l H a b i t a t o f F r a s e r R i v e r E s t u a r y , 1973 30 V F i g u r e Page 12. S e a s o n a l Change i n L e n g t h o f J u v e n i l e Chum f r o m C o m bined S l o u g h a n d S i d e C h a n n e l H a b i t a t i n t h e S o u t h Arm, F r a s e r R i v e r 3 3 13. S i z e o f J u v e n i l e C h i n o o k f r o m C o m b i n e d S l o u g h a n d C h a n n e l H a b i t a t s i n S o u t h Arm 35 14. Change o f Mouth S i z e ( P r e m a x i l l a r y L e n g t h ) w i t h Body S i z e ( F o r k L e n g t h ) o f J u v e n i l e Chum and C h i n o o k 37 15. P e r c e n t a g e b i o m a s s o f m a j o r f o o d c a t e g o r i e s o f J u v e n i l e C h i n o o k a n d Chum S a l m o n i n S l o u g h H a b i t a t , l a t e M a r c h a n d e a r l y A p r i l , 1973 and 1974 ' 40 16. P e r c e n t a g e b i o m a s s o f m a j o r f o o d c a t e g o r i e s o f J u v e n i l e C h i n o o k a n d Chum S a l m o n i n S l o u g h H a b i t a t , l a t e A p r i l , a n d e a r l y May, 19 73 a n d 1974 41 17. P e r c e n t a g e b i o m a s s o f S t o m a c h C o n t e n t s o f J u v e n i l e Chum a n d C h i n o o k i n S l o u g h H a b i t a t , l a t e A p r i l a n d e a r l y May, 1973 a n d 1974 43 18. P e r c e n t a g e b i o m a s s o f m a j o r f o o d c a t e g o r i e s i n s t o m a c h s o f J u v e n i l e C h i n o o k a n d Chum S a l m o n , i n S l o u g h H a b i t a t o f t h e N o r t h Arm 45 19. P e r c e n t a g e b i o m a s s o f f o o d c a t e g o r i e s i n s t o m a c h s o f J u v e n i l e C h i n o o k a n d Chum S a l m o n , i n C h a n n e l H a b i t a t , S o u t h Arm, 1973 47 20. P e r c e n t a g e b i o m a s s o f S t o m a c h c o n t e n t s o f C h i n o o k S a l m o n s m o l t s ( y e a r l i n g s ) i n S l o u g h H a b i t a t , S o u t h Arm, l a t e A p r i l 5 0 21. S t o m a c h c o n t e n t , b i o m a s s o f J u v e n i l e S o c k e y e S a l m o n i n S l o u g h H a b i t a t , S o u t h Arm 50 v i LIST OF TABLES Table Page 1. Estimated number of d r i f t organisms per cubic meter of surface water i n slough habitat of South Arm, Fraser River . 22 2. Estimated number of d r i f t organisms per cubic meter of surface water i n slough habitat of North Arm, Fraser River 23 3. Estimated number of d r i f t organisms per-cubic meter of water i n side channel habitat of South Arm, Fraser River 25 4. A comparison of the t o t a l pink, chum, and chinook salmon f r y migrating population i n the Fraser River at Mission, with an estimate of the t o t a l numbers u t i l i z i n g slough and side channel habitats of marsh area..... 32 5. Size of common prey items found i n stomachs of chum and chinook juveniles from both slough and side : . . channel habitats 38 6. 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 and t values, comparing d i e t of chum.and chinook f r y in the same habitat 49 7. Number of Daphnia, Neomysis, and Chironomous consumed by juvenile chum and chinook when presented with only one prey type per t e s t .... 55 8. Number of Daphnia, Neomysis, and Chironomous consumed by the juvenile chum and chinook salmon when presented with three prey types simultaneously. ; 57 v i i ACKNOWLEDGEMENTS I w i s h , t o e x p r e s s my a p p r e c i a t i o n o f t h e a d v i c e a n d c r i t i c i s m , g i v e n me b y my t h e s i s s u p e r v i s o r D r . T.G. N o r t h c o t e . I a l s o w i s h t o t h a n k Ms. M a r g F i s h e r a n d Mr. K a n j i T s u m u r a f o r t h e i r t e c h n i c a l a s s i s t a n c e a n d e n c o u r a g e -ment. F i n a l l y , I w i s h t o t h a n k my w i f e , L a r c y D u n f o r d , f o r h e r s u p p o r t a n d a s s i s t a n c e a t a l l t i m e s d u r i n g t h e d e v e l o p -ment o f t h i s s t u d y . 1 INTRODUCTION The progeny of a l l species of P a c i f i c salmon (genus Oncor-hynchus) begin l i f e as eggs buried deep i n the gravel of cool, clean streams or occasionally lakes. The incubation of the eggs, the development of alevins, and the emergence of the f r y , together with the environmental factors influencing these events have been well documented (eg. Bams, 1969). Upon emergence from the gravel, the salmon fry w i l l eventually make a downstream migration to r i v e r estuaries and the sea, the timing depending upon the species. On departure from t h e i r natal streams or rearing lakes and i n t h e i r movement toward the ocean, very l i t t l e i s known of the ecology of the P a c i f i c salmon, u n t i l they reach commercial size at sea. The s u r v i v a l rate for most species ( s p e c i f i c a l l y sock-eye) i s measured as the r a t i o of enumerated adults (catch plus escapement) to the number of smolts estimated at the time they leave the lake (Ricker, 1966). At present, there are no quant-i t a t i v e estimates of losses during the downstream migration of the juveniles. Yet losses during t h i s segment of t h e i r l i f e h istory may be considerable. During the downstream migration, i t i s generally accepted that the juvenile of a l l species are ca r r i e d by, and may swim with the current of the r i v e r system. Upon reaching t i d a l water, the a c t i v i t i e s and f i n a l dispersal of juvenile P a c i f i c salmon remain r e l a t i v e l y unknown. An estuary, i n b i o l o g i c a l terms, may be defined as a region of a r i v e r with a variable s a l i n i t y due to the sea (Day, 1951). The term "variable s a l i n i t y " implies both a d i e l v a r i a b i l i t y due to t i d a l influence, and a seasonal v a r i a b i l i t y due to di s -charge of the r i v e r . During the period of juvenile salmon mi-gration, the Fraser River discharge reaches i t s peak, and the surface waters of the estuary are e s s e n t i a l l y freshwater through-out the freshet. A s a l t wedge intrusion, t y p i c a l of a s t r a t -i f i e d estuary such as the Fraser, only penetrates to the mouth of the r i v e r during the freshet. (Hoos & Packman, 1974). Feeding of juvenile P a c i f i c salmon i n r i v e r estuaries and adjacent waters has only recently been studied for pink and chum (Kaczynski et a l . , 1973, and Manzer, 1969), for chum (Mason, 1974, and Sparrow, 1968), for chinook (Reimers, 1973, Stein et a l . , 1972, and Kask, 1972) and for coho (Parker, 1971). The importance of the feeding period i n the estuary was f i r s t emphasized by Henry, 1961, who suggested: that a deficiency of food for a few weeks could cause serious mortality, but s t i l l have only a rather small e f f e c t on the t o t a l f i r s t year growth of the survivors. Growth of juvenile salmon before they encounter sea water most probably w i l l enhance the i r marine s u r v i v a l , and for t h i s rea-son the estuarine feeding i s of great importance. Over three hundred m i l l i o n juvenile P a c i f i c salmon migrate into the Fraser River estuary during certain years (Northcote, ^^2?.,^ K.A. Henry, Racia3_5r?ider^(.fJ:Lcation of Fraser River socke#^^*i$ ^?$vV *almon by means o l | scale's ''and i t s application to salmon, *»«^ '-' management. Inte^nat. Pac. Salm. Fish. Comm. B u l l . 12: 9£?g% • 19 7 4 ) . T h i s phenomenon i s assumed t o o c c u r b e t w e e n t h e m o n t h s o f F e b r u a r y a n d J u l y , w i t h t h e g r e a t e s t a b u n d a n c e o c c u r r i n g i n t h e months o f A p r i l a n d May. I n s p i t e o f t h e m a g n i t u d e o f t h e number o f f i s h e s i n v o l v e d , a n d t h e i m p o r t a n c e o f t h i s s t a g e i n t h e i r l i f e c y c l e , v i r t u a l l y n o t h i n g i s known a b o u t t h e f e e d i n g a n d p o s s i b l e r e s i d e n c e o f t h e s a l m o n i n t h e F r a s e r e s t u a r y . The F r a s e r R i v e r e s t u a r y i s d i v i d e d i n t o two m a i n b r a n c h e s a N o r t h Arm a n d a S o u t h Arm. N e a r t h e mouth o f t h e r i v e r , mar-s h e s a r e a s i g n i f i c a n t f e a t u r e , w i t h t h e l a r g e s t m a r s h e s i n t h e S o u t h Arm. Two t y p e s o f h a b i t a t a r e p r e s e n t i n t h e m a r s h a r e a s s l o u g h h a b i t a t a n d s i d e c h a n n e l h a b i t a t . O n l y s l o u g h h a b i t a t i s p r e s e n t i n t h e s m a l l m a r s h a r e a i n t h e N o r t h Arm. A l a r g e m a r s h a r e a e x i s t s i n t h e S o u t h Arm, i n c l u d i n g b o t h s l o u g h a n d s i d e c h a n n e l h a b i t a t . T h e s e h a b i t a t s w e r e s t u d i e d t o d e t e r m i n e t h e s p a t i a l a n d t e m p o r a l u s e by f i s h e s f r o m e a r l y M a r c h u n t i l e a r l y A u g u s t . The m o s t a b u n d a n t f i s h p r e s e n t i n t h e h a b i t a t s w e r e j u v e n i l e s a l m o n i d s . The f o o d r e s o u r c e e x p l o i t a t i o n b y j u v e n i l e s a l m o n -i d s was e x a m i n e d i n r e l a t i o n t o h a b i t a t t y p e a n d p r e y s i z e s e l e c t i o n . The f o o d s o u r c e s o f o t h e r s p e c i e s u t i l i z i n g t h e h a b i t a t s w e r e a l s o d e t e r m i n e d , and t h e s e r e s u l t s a r e r e c o r d e d i n t h e A p p e n d i x . 4 STUDY AREA A. South Arm The p r i n c i p a l study area was located i n the South Arm of the Fraser River, i n the Duck - Barber - Woodward Island complex, located approximately 6 Km. from the mouth of the r i v e r (Figure 1). This area i s composed of approximately 4 85 hectares (1200 acres) of undisturbed marshland. The c h a r a c t e r i s t i c vegetation of t h i s marshaland i s bulrush (Scirpus americanus), sedge (Carex  lyngbyei) , and c a t t a i l (Typha l a t i f o l i a ) . The substrate i s very so f t , composed of alternating layers of fine s i l t and de-t r i t u s . Two types of habitat predominate i n the South Arm study area. The f i r s t type i s termed slough habitat, which refers to an area exposed to the flow of the r i v e r (Figure 2a). The second i s termed side channel habitat, r e f e r r i n g to the b l i n d channels branching o f f of the main current into the marsh (Figure 2a, b). The flow of water into and out of these narrow channels i s determined largely by the r i v e r height and the tide cycle. B. North Arm The south branch of the North Arm of the Fraser River i s composed almost t o t a l l y of the slough type of habitat (Figure 3). The only area of undisturbed marshland remaining i s the Figure 1: Six slough habitat s i t e s sampled by beach seine i n the South Arm of the Fraser River, approximately 6 km from the mouth. (See Figure 3 b) Scale: 1 cm = 200 m F i g u r e 2 ( a ) : T y p i c a l s l o u g h h a b i t a t ( l e f t ) a n d c h a n n e l h a b i t a t ( r i g h t ) i n t h e S o u t h Arm o f t h e F r a s e r R i v e r . F i g u r e 2 ( b ) : T y p i c a l c h a n n e l h a b i t a t a p p r o x i m a t e l y 600 m f r o m t h e c o n f l u e n c e o f c h a n n e l a n d s l o u g h h a b i t a t shown i n F i g u r e 2 ( a ) . 7 F i g u r e 3 ( a ) : F i v e s l o u g h h a b i t a t s i t e s s a m p l e d b y b e a c h s e i n e i n t h e N o r t h Arm o f t h e E r a s e r - R i v e r . (See F i g u r e 3 (b) ) . S c a l e : 1 cm = 630 m F i g u r e 3 ( b ) : The l o w e r F r a s e r R i v e r s y s t e m , i n c l u d i n g t h e S o u t h Arm m a r s h h a b i t a t (1) and t h e N o r t h Arm m a r s h h a b i t a t ( 2 ) . S c a l e : 1 cm = 14 km 8 small i s l a n d (Swishwash Island) at the mouth of t h i s arm. The vegetation on t h i s i s l a n d i s composed of bulrush (Scirpus amer-icanus) at the lowest l e v e l s , sedge (Carex lyngbyei) at i n t e r -mediate l e v e l s , and c a t t a i l (Typha l a t i f o l i a ) at the higher points (Forbes, 1972). Most of the habitat along the main banks of the North Arm i s a modified slough habitat, having steeper banks on the north side due to the development of Vancouver International Airport, and steep rocky banks on the south side due to elaborate dyking by the Municipality of Richmond. The side channel habitat so prevalent i n the South Arm has been v i r t u a l l y eliminated from the North Arm due to these developments. C. Fraser River Discharge The discharge of the Fraser River w i l l have a measurable e f f e c t on the current speed and the r i v e r height i n the estuary. Over the two seasons that the habitats were studied, the d i s -charge of the r i v e r varied considerably (Figure 4). The t o t a l volume of discharge from mid March to mid August increased from 5.427 b i l l i o n cubic meters i n 1973 to 7.031 b i l l i o n cubic meters i n 1974, an increase of approximately 30% (Water Survey Canada). This discharge i s measured at Hope, B.C., approxi-mately 137 Km upstream from the mouth of the Fraser River. 9 1000000 - T 1974 D i s c h a r g e (CFS) 100000 10000 -March? A p r i l ' May. -28320 D i s c h a r g e 3 J u n e l r J u l y A u g u s t F i g u r e 4: D a i l y d i s c h a r g e o f F r a s e r R i v e r a t Hope, f r o m m i d M a r c h t o m i d A u g u s t , 1973 and 1974. F i g u r e 5: A t y p i c a l b i w e e k l y t i d e c y c l e , m e a s u r e d a t t h e mouth o f t h e F r a s e r R i v e r ( S o u t h A r m ) . S h a d e d a r e a s i n d i c a t e t h e t i m i n g o f s a m p l i n g i n t h e s l o u g h ( l i g h t a r e a ) a n d s i d e c h a n n e l ( d a r k a r e a ) h a b i t a t . 10 MATERIALS AND METHODS A. S l o u g h H a b i t a t 1. S o u t h Arm F i s h w e r e c o l l e c t e d a t b i - w e e k l y i n t e r v a l s f r o m m i d M a r c h u n t i l e a r l y A u g u s t a t s i x s i t e s i n t h e S o u t h Arm ( F i g u r e 1 ) . The b e a c h s e i n e u s e d f o r t h e s e c o l l e c t i o n s was 14 m, l o n g a n d 2 m, d e e p , h a v i n g h e a v y l e a d l i n e (3Kg/m) a l o n g t h e b o t t o m . The s t r e t c h e d mesh s i z e was 6 mm i n t h e c e n t r e o f t h e s e i n e , a n d 12 mm i n a 2.8 m. segment o n b o t h e n d s . B e a c h s e i n i n g was c o n d u c t e d w i t h i n one h o u r o f t h e l o w p o i n t o f t h e b i - w e e k l y t i d e c y c l e ( F i g u r e 5 ) . The b e a c h s e i n e was s e t u s i n g a 5 m a l u m i n u m b o a t p o w e r e d w i t h a 10 h.p. m o t o r , s t a r t i n g f r o m s h o r e a n d c u t t i n g a s e m i c i r c l e , r e t u r n i n g t o t h e same s h o r e a p p r o x i m a t e l y 8 t o 10 m. u p s t r e a m . The a p p r o x i m a t e 2 a r e a c o v e r e d by e a c h b e a c h s e i n e was 30 m , a n d t h e maximum d i s t a n c e f r o m s h o r e s e l d o m e x c e e d e d 2 m e t e r s . The number o f j u v e n i l e chum a n d c h i n o o k t a k e n b y b e a c h 2 s e i n e a r e e x p r e s s e d i n numbers p e r 100 m . S i n c e : s i x b e a c h 2 s e i n e s c o v e r e d 187 m , t h e a c t u a l number c a u g h t a r e m u l t i p l i e d 2 by a f a c t o r o f 0.531 t o make t h e e s t i m a t e p e r 100 m . T h e s e e s t i m a t e s o n l y r e f e r t o t h i s m a r g i n a l s l o u g h h a b i t a t , a n d c a n -n o t be e x t r a p o l a t e d t o t h e t o t a l w e t t e d a r e a . D r i f t o r g a n i s m s w e r e c o l l e c t e d u s i n g a 0.5 m d i a m e t e r tow 11 net with a mesh size of 0.242 mm. Tows were made s l i g h t l y up-stream approximately 6 meters from the shore. The approximate 3 volume of water f i l t e r e d by the tow nets were 21.6 m for the 3 large net (0.5 m i n diameter) and 5.0 m for the small net (0.24 m i n diameter). The organisms c o l l e c t e d were preserved i n 4% formalin. 2. North Arm Five s i t e s i n the North Arm were used for beach seining at bi-weekly i n t e r v a l s from mid May u n t i l early August (Figure 3). The beach seine and technique was i d e n t i c a l to that used i n the South Arm slough habitat. D r i f t organisms were c o l l e c t e d i n the North Arm, using the same tow nets employed i n the South Arm slough habitat. B. Side Channel Habitat 1. South Arm Fish were c o l l e c t e d from four stations i n the South Arm at bi-weekly i n t e r v a l s , on the day before or the day a f t e r the slough habitat sampling (Figure 6) . A pole net was used to catch the f i s h i n the narrow side channels. This hand held device was constructed of two poles 1.8 meters i n height, j o i n -ed by a band of fine nylon mesh (3 mm stretched) 1 m wide and 1 m deep. The bottom edge of the netting was f i t t e d with heavy Figure 6: Four side channel habitat s i t e s sampled by pole net i n the South Arm of the Fraser River. Scale: 1 cm= 140 m (approximately) l e a d l i n e . T h e a p p r o x i m a t e d i s t a n c e s a m p l e d b y p o l e n e t s a t 2 t h e f o u r s t a t i o n s w a s 5 0 m , c o v e r i n g a n a r e a o f a b o u t 3..T. m . T h e n u m b e r o f j u v e n i l e c h u m a n d c h i n o o k c a u g h t b y p o l e n e t o n 2 e a c h d a t e a r e e x p r e s s e d i n n u m b e r s p e r 1 0 0 m , b y m u l t i p l y i n g t h e a c t u a l n u m b e r c a u g h t b y 2. 7 P o l e n e t t i n g w a s c o n d u c t e d a p p r o x i m a t e l y t w o t o t h r e e h o u r s b e f o r e l o w t i d e ( F i g u r e 5 ) , w h e n t h e w a t e r w o u l d b e r u n n i n g o u t o f t h e s i d e c h a n n e l s . T h e u p p e r r e a c h e s o f m a n y o f t h e s e c h a n -n e l s w o u l d b e e x p o s e d a t t h e l o w e s t p o i n t i n a t i d e c y c l e . D r i f t o r g a n i s m s i n t h e s i d e c h a n n e l h a b i t a t w e r e c o l l e c t e d w i t h a n y l o n m e s h (.242 mm) p l a n k t o n n e t , 24 c m i n d i a m e t e r . T h e n e t w a s t o w e d a p p r o x i m a t e l y 5 0 m f o r e a c h s a m p l e , f i l t e r i n g 3 2v3 c u b i c . m e t e r m o f w a t e r . S a m p l e s w e r e p r e s e r v e d i n 4% f o r -m a l i n . C . P h y s i c a l C h a r a c t e r i s t i c s W a t e r t e m p e r a t u r e s w e r e r e c o r d e d a t a l l s a m p l i n g s i t e s i n b o t h h a b i t a t s t o t h e n e a r e s t 0 . 5 C ° , u s i n g a m e r c u r y f i l l e d t h e r m -o m e t e r . L i g h t p e n e t r a t i o n w a s m e a s u r e d i n s l o u g h h a b i t a t u s i n g a s t a n d a r d S e c c h i d i s c , h e l d i n t h e c u r r e n t b y a m e t e r s t i c k . D . L a b o r a t o r y M e t h o d s A l l f i s h w e r e i n i t i a l l y p r e s e r v e d i n 1 0 % f o r m a l i n , a n d a f t e r t w o w e e k s t r a n s f e r r e d t o 37% i s o p r o p y l a l c o h o l . F o r k l e n g t h a n d m a x i l l a r y l e n g t h ( l e n g t h o f u p p e r jaw) w e r e m e a s u r e d t o t h e n e a r e s t 0.1 mm u s i n g d i a l c a l i p e r s . W e i g h t s o f f i s h a n d w e i g h t s o f t h e f o o d b o l u s ( s t o m a c h c o n t e n t s ) w e r e made t o t h e n e a r e s t m i l l i g r a m u s i n g a S a u t e r B a l a n c e , M o d e l 1 6 0 / 0 . 0 0 1 . P r e y i t e m s i n e v e r y s t o m a c h w e r e i d e n t i f i e d a n d c o u n t e d . The l a r g e s t d i a m e t e r o f e a c h p r e y t y p e was m e a s u r e d , a n d t h e means o f t h e s e d i m e n s i o n s w e r e u s e d t o r a n k a l l p r e y i t e m s b y s i z e . A l a r g e number o f e a c h p r e y i t e m w e re w e i g h e d , a n d a mean w e i g h t d e t e r m i n e d . The i n i t i a l b i o m a s s was c a l c u l a t e d b y m u l -t i p l y i n g t h e number o f e a c h p r e y t y p e by t h e mean w e i g h t o f t h e p r e y ( J e n s e n , 1 9 7 4 ) . Then a c o r r e c t i v e f a c t o r was a p p l i e d , by c o m p a r i n g t h e c a l c u l a t e d t o t a l b i o m a s s o f t h e f o o d i t e m s i n e a c h s t o m a c h w i t h t h e a c t u a l m e a s u r e d w e i g h t o f t h e s t o m a c h c o n t e n t s . The c a l c u l a t e d b i o m a s s f o r e a c h p r e y c a t e g o r y w o u l d be s c a l e d up o r down a c c o r d i n g t o t h e d i f f e r e n c e b e t w e e n c a l -c u l a t e d b i o m a s s a nd m e a s u r e d b i o m a s s . D r i f t o r g a n i s m s a m p l e s w e r e f i l t e r e d , t h e n t h o r o u g h l y m i x -e d i n 100 m l o f w a t e r b e f o r e f i v e one m l s u b - s a m p l e s w ere d r a w n . E a c h s u b - s a m p l e was c o u n t e d u s i n g a S e d g e w i c k R a f t e r c e l l . The number o f o r g a n i s m s p e r c u b i c m e t e r o f w a t e r w e r e c a l c u l a t e d . E. L a b o r a t o r y F e e d i n g E x p e r i m e n t s The e x p e r i m e n t a l a p p a r a t u s was a c l o s e d s y s t e m u s i n g F r a s e r R i v e r w a t e r t a k e n n e a r t h e s i t e s o f t h e f i s h c o l l e c t i o n s . The t u r b i d i t y o f t h e w a t e r was m a i n t a i n e d b y t h e c i r c u l a t i n g pumps and a g i t a t i o n i n t h e t e m p e r a t u r e c o n t r o l t a n k . P e r i o d i c a l l y , 15 f i n e s i l t w o u l d be a d d e d t o t h e s y s t e m t o m a i n t a i n t h e l i g h t p e n e t r a t i o n t o a b o u t 2 0 cm, as m e a s u r e d w i t h a s t a n d a r d S e c c h i d i s c i n t h e c o n t r o l t a n k . The w a t e r t e m p e r a t u r e was c o n t r o l l e d b e t w e e n 10 and 11 d e g r e s s c e n t i g r a d e u s i n g a s m a l l r e f r i g e r a t i o n u n i t i n t h e c o n t r o l t a n k ( F i g u r e 7 a ) . J u v e n i l e chum and Chinook w e r e c o l l e c t e d i n the f i e l d u s i n g a b e a c h s e i n e , and transported to the l a b i n l a r g e (100 l i t e r ) p l a s t i c c o n t a i n e r s . No m o r t a l i t y o c c u r r e d d u r i n g t r a n s p o r t . Upon r e a c h i n g t h e l a b , t h e chum a n d C h i n o o k w e r e p o u r e d i n t o t h e h o l d i n g t a n k s ( F i g u r e 7b) and k e p t f o r t h r e e d a y s w i t h o u t f o o d b e f o r e t e s t i n g . The f e e d i n g a q u a r i a w e r e s u p p l i e d w i t h a c o n t r o l l e d f l o w o f w a t e r f r o m t h e l a r g e o b s e r v a t i o n t a n k ( F i g u r e 7 c ) , a n d t h e i n p u t was a l l o w e d t o o v e r f l o w t h e a q u a r i a i n t o t h e s u r r o u n d i n g w a t e r b a t h . An a i r s t o n e was a l s o p l a c e d i n e a c h a q u a r i u m t o m a i n t a i n t h e c i r c u l a t i o n a n d t o m a i n t a i n t h e d i s s o l v e d o x y g e n a t t h e s a t u r a t i o n l e v e l . A e r a t i o n a l s o o c c u r r e d i n t h e l a r g e h o l d i n g t a n k , u s i n g two a i r s t o n e s i n e a c h t a n k . The p r e y i t e m s w e r e a l s o m a i n t a i n e d i n a q u a r i a i n t h e l a b -o r a t o r y . C h i r o n o m i d l a r v a e ( g e n u s C h i r o n o m u s ) a nd N e o m y s i s w e r e c o l l e c t e d f r o m t h e s i t e s o f f i s h c o l l e c t i o n i n t h e F r a s e r E s t u a r y . Some o f t h e D a p h n i a u s e d as p r e y s p e c i e s i n t h e e x -p e r i m e n t s w e r e c o l l e c t e d f r o m c h a n n e l h a b i t a t i n t h e f i e l d , ( D a p h n i a p u l e x - 1.2 mm), a n d a l a r g e r s p e c i e s o f D a p h n i a (3 mm) was c o l l e c t e d i n s m a l l p o n d s on t h e U n i v e r s i t y o f B r i t i s h C o l -u m b i a campus. The p r e y i t e m s w e r e p l a c e d i n t o t h e f e e d i n g a q u a r i a a p p r o x i m a t e l y t e n m i n u t e s b e f o r e t h e a d d i t i o n o f t h e Figure 7 (a): Laboratory experimental apparatus, with temperature control tank on l e f t . Figure 7 (b): Large holding tanks i n foreground were used to maintain chum and chinook juveniles for three days, without food, p r i o r to t e s t i n g . Figure 7 (c): Fish were transferred from large holding tank to seven small aquaria for feeding t e s t s . 18 f i s h . The bottom of each aquarium was covered w i t h a f i n e l a y e r of s i l t (2 mm depth). P r i o r t o the a d d i t i o n of the prey, the i n f l o w of water was d i v e r t e d d i r e c t l y i n t o the surrounding water bath, to prevent the c i r c u l a t i o n of the chironomid l a r v a e d u r i n g the f e e d i n g . Chinook and chum were t r a n s f e r r e d by d i p net from the h o l d -i n g tank to the s m a l l e r t e s t i n g tanks to commence each e x p e r i -ment. A f i n e mesh nylon screen was then p l a c e d over the top of each t e s t i n g tank to prevent escape, and the p r e d a t o r s and prey were l e f t u n d i s t u r b e d f o r f i f t y minutes. At the end of t h i s time p e r i o d , the f i s h were caught with d i p ne t s , a n a e s t h e t i z e d u s i n g MS 222, and put i n t o a 10% f o r m a l i n s o l u t i o n f o r l a t e r stomach content a n a l y s i s . The f e e d i n g tanks were then d r a i n e d through a f i n e mesh screen to remove any remaining prey b e f o r e the next t e s t run. 19 RESULTS A. Physical Characteristics Water transparency was highly variable, dependent on the t u r b i d i t y and mainstem r i v e r discharge. The transparency i n the slough habitat and the side channel habitat was very s i m i l a r . Transparency decreased markedly i n early A p r i l , and remained quite low u n t i l mid July (Figure 8). This time period corres-ponds with the peak abundance of juvenile salmon i n the Fraser estuary. The mean water temperature i n the slough habitat was quite consistent over two sampling seasons, increasing from about 5° C. i n mid March to 13-14° C. i n early July (Figure 9). The mean water temperature i n the side channel habitat varied from 0 - 2 Centigrade degreees warmer than the slough habitat, (Figure 9). The d i e l water temperature i n a shallow side channel fluctuated greatly, with the highest temperature generally corresponding to the minimum water volume (at low t i d e ) . In June or July, side channel temperatures occasionally reached 18 - 20° C. Few salmon were taken at temperatures greater than 15° C. The only species present i n side channels at these elevated temperatures were threespine stickleback and peamouth chub. 20 Surface O-f Secchi Depth (cm) 2CH 40H 60-March A p r i l 1974 May June T-0 -20 -40 -60 July August Figure 8: Seasonal changes i n water transparency i n slough habitat of the South Arm of the Fraser River. Figure 9: Seasonal changes i n mean water temperature of slough habitat and side channel habitat. 21 B. D r i f t Organisms 1. Slough Habitat Cyclopoid, calanoid, and harpacticoid copepods were the most frequent organisms present i n plankton tows from the slough habitat i n the South Arm (Table 1). Very few other organisms were present i n the samples. Cyclopoid copepods reached a max-imum density of 188 per cubic meter of water f i l t e r e d i n late A p r i l . The v i r t u a l absence of Neomysis from these surface samp-les taken i n the main current, compared to the great numbers observed i n every beach seine i n the slough habitat, suggests a near shore, possibly benthic association of these opossum shrimp. Copepods were also dominant i n most plankton tows from slough habitat i n the North Arm (Table 2). Eulachon larvae 3 were very abundant (56/m ) i n the tows i n late May. These larvae are ca r r i e d by the current through the estuary i n ap-proximately a two week period i n late May and early June. Oligochaetes, Nematodes, and the motile Volvox were represented i n the samples from the slough habitat i n the North Arm, but were not present i n s i m i l a r tows i n the South Arm. The low density of d r i f t organisms i n the North Arm slough habitat is-si m i l a r to densities observed i n the South Arm (Table 1). 2. Side Channel Habitat A greater d i v e r s i t y and greater density of organisms were 22 TABLE 1 E s t i m a t e d number o f d r i f t o r g a n i s m s p e r c u b i c m e t e r o f s u r f a c e w a t e r i n s l o u g h h a b i t a t o f t h e S o u t h Arm o f t h e F r a s e r R i v e r . M a r c h 28a A p r i l 24a May 25a J u n e 8a J u l y 4a 1 B o s m i n a i 4 I 1 4 1 C a l a n o i d c o p e p o d s 40 24 8 C y c l o p o i d c o p e p o d s 40 188 4 4 H a r p a c t i c o i d c o p e p o d s 8 8 4 Co p e p o d n a u p l i i 32 4 O s t r a c o d s 12 N e o m y s i s 1 A n i s o g a m m a r u s 4 C o r i x i d s 4 C h i r o n o m i d l a r v a e a - s a m p l e s c o l l e c t e d u s i n g a n y l o n mesh tow n e t , 0.5 m i n d i a m e t e r , mesh s i z e 0.32 mm. T A B L E 2 E s t i m a t e d numbers o f d r i f t o r g a n i s m s p e r c u b i c m e t e r o f w a t e r i n s l o u g h h a b i t a t o f t h e N o r t h Arm o f t h e F r a s e r R i v e r . b a a a b a a a May 1 May 17 May 31 J u n e 2 8 J u l y 2 J u l y 11 J u l y 25 Aug. 2 O l i g o c h a e t e s 2 A 2 2 5 1 Nematodes A l o n a 4 2 8 D a p h n i a 4 50 1 11 5 B o s m i n a C a l a n o i d c o p e p o d s 2 1 2 28 1 2 1 C y c l o p o i d c o p e p o d s 10 1 74 4 3 H a r p a c t i c o i d c o p e p o d s 8 N a u p l i i 2 L e p t o d o r i d a e 1 R o t i f e r s 18 N e o m y s i s 1 A n i s o g a m m a r u s 2 1 C o r o p h i a m C h i r o n o m i d l a r v a e 1 1 1 E u l a c h o n l a r v a e 1 56 V o l v o x 1000 a - t a k e n b y s u r f a c e tow n e t , 0.5 m i n d i a m e t e r , 19 73, mesh s i z e 0.32 mm b - t a k e n b y s u r f a c e tow n e t , 0.24 m i n d i a m e t e r , 19 74, mesh s i z e 0.2 mm K> CO present i n plankton tows i n side channel habitat than i n slough habitat (Table 3) • Cyclopoixl copepods and Daphnia pulex were the most abundant organisms, reaching densities of 322 and 870 ani-3 mals/m respectively. Harpacticoid copepods, calanoid copepods, and Bosmina were frequently present. Neomysis and chironomid larvae and pupae were only occasionally taken. The only organ-ism more numerous i n the slough habitat compared to the side channel habitat were calanoid copepods. C. Temporal and Spatial Use 1. Slough habitat Juvenile salmon were f i r s t taken i n the slough habitat i n mid to late March (Figure 10). Juvenile chum (Oncorhyhchus keta) and juvenile chinook (Oncorhynchus tshawytscha) were the most abundant salmon i n the slough habitat (Table A l , Appendix A). In both years, the juvenile chum salmon preceded the juv-enile chinook salmon into the area, and were i n i t i a l l y more abundant. However, by late A p r i l , the chinook were much more numerous than the chum and were present i n the area over a longer time period. In 1973, the peak density for both species occurred i n late A p r i l , a f t e r which time both species declined i n abundance, the number of chum dropping off at a greater rate than chinook. By that time most of the chinook salmon smolts were taken. In 1974, a d i f f e r e n t pattern occurred. Since the sampling dates i n 1974 TABLE 3 E s t i m a t e d numbers o f d r i f t o r g a n i s m s p e r c u b i c m e t e r o f w a t e r i n s i d e c h a n n e l h a b i t a t o f t h e S o u t h Arm o f t h e F r a s e r R i v e r . D a p h n i a Mar. 2 8 A p r i l 11 A p r i l 24 May 8 ,May 22 J u n e 19 J u l y 4 4 26 13 148 70 113 870 B o s m i n a 4 9 17 9 52 C a l a n o i d c o p e p o d s 9 17 4 4 9 17 C y c l o p o i d c o p e p o d s 109 322 117 48 296 130 148 H a r p a c t i c o i d c o p e p o d s 1 43 65 4 26 4 17 N a u p l i i 2 R o t i f e r s O s t r a c o d s 4 160 N e o m y s i s 1 3 9 A n i s o g a m m a r u s 4 C o l l e m b o l a 4 E p h e m e r o p t e r a 2 C h i r o n o m i d l a r v a e 4 C h i r o n o m i d pupae 4 3 11 1 26 200-1 March A p r i l May June July August # # Chum, South Arm • • C h u m _ N o r t h A r m 0 — Q Chinook, South Arm CP——• Chinook, North Arm Figure 10: Seasonal change of density of juvenile chum and chinook salmon i n slough habitat of the Fraser River Estuary. 27 w e r e a l m o s t i d e n t i c a l t o t h o s e o f 1973, i t i s r e a s o n a b l e t o com-p a r e t h e d e n s i t y o f f i s h t a k e n on e a c h d a t e i n e a c h y e a r . I n 19 74, t h e peak d e n s i t y o f j u v e n i l e chum s a l m o n a g a i n o c c u r r e d i n l a t e A p r i l , b u t were o n l y one f i f t h o f t h e d e n s i t y o f 1 9 7 3 . The j u v e n i l e c h i n o o k , h o w e v e r , e x h i b i t e d a d i f f e r e n t p a t t e r n b e t w e e n t h e two y e a r s . I n 1974, a b i m o d a l p e a k i n a b u n d a n c e o c c u r r e d , t h e f i r s t p e ak i n l a t e A p r i l a n d t h e s e c o n d i n l a t e May. E a c h o f t h e s e p e a k s i s a b o u t one t h i r d o f t h e m a g n i t u d e o f t h e 19 7 3 p e a k . I t s h o u l d be n o t e d , h o w e v e r , t h a n a t h i c k l a y e r o f s i l t a n d f i n e d e t r i t u s , f r e s h l y l a i d down by t h e r i v e r , made s a m p l i n g v e r y d i f f i c u l t i n e a r l y May, and many f i s h w e r e l o s t . I n 19 74, t h e c h i n o o k s a l m o n s m o l t s ( y e a r l i n g s ) e x h i b i t e d a b r o a d e r m i g r a t i o n p e r i o d t h r o u g h t h e s t u d y a r e a a n d many r e m a i n e d i n t h e a r e a d u r i n g J u n e a nd J u l y . I n t h e s l o u g h h a b i t a t o f t h e N o r t h Arm, chum and c h i n o o k w e r e a l s o t h e m o s t a b u n d a n t j u v e n i l e s a l m o n p r e s e n t ( T a b l e A 2 , A p p e n d i x A ) . The d e n s i t y o f chum a n d c h i n o o k was v e r y s i m i l a r t o t h e d e n s i t y o b s e r v e d i n s l o u g h h a b i t a t o f t h e S o u t h Arm o v e r t h e same t i m e p e r i o d ( F i g u r e 1 0 ) . R e l a t i v e l y few j u v e n i l e s o c k e y e s a l m o n w e r e t a k e n i n t h e s l o u g h h a b i t a t , b u t t h e i n d i v i d u a l s p r e s e n t a r e o f i n t e r e s t . I n 1 9 7 3 , 26 v e r y s m a l l (mean l e n g t h 28-31 mm) s o c k e y e f r y were t a k e n f r o m l a t e May t o m i d J u n e . Some o f t h e f r y h a d n o t y e t f u l l y a b s o r b e d t h e i r y o l k s a c , y e t a l l h a d b e e n f e e d i n g t o some e x t e n t . T h e s e f r y w e r e t a k e n o n l y i n s l o u g h h a b i t a t , on t h e S o u t h bank o f t h e e s t u a r y . Two f r y o f t h e same t y p e w e r e a l s o 28 taken i n the North Arm during the same time period. In 19 74, three of these very small sockeye fry were taken i n early June (Table A3, Appendix A). Larger juvenile sockeye fry were also captured i n slough habitat i n 19 73. These juveniles were of intermediate size (48-65 mm), and were taken from early July u n t i l the termina-ti o n of sampling i n early August. Juvenile sockeye salmon smolts were present i n slough habitat i n late A p r i l and Early May, 19 74 (Table A3, Appendix A). The mean length of eleven sockeye taken on these dates was 95.4 mm. An examination of the scales from these sockeye smolts i n d i c a t -ed they were yearling smolts. Only one coho juvenile was taken i n slough habitat i n 1973 and 1974. This single specimen, taken i n the South Arm i n late May, 19 74, was 99.1 mm i n fork length and weighed 11.25 grams. The coho smolts migrating through the estuary probably remain i n deeper water, passing d i r e c t l y through the estuary to Stur-geon and Roberts Banks. Recent sampling at various s i t e s on the Sturgeon and Roberts Banks indicate the coho may remain and feed i n t h i s area for several weeks (Anonymous, 1975). Only three juvenile pink salmon were taken i n slough hab-i t a t i n 19 74 (Table A3, Appendix A). Since pink f r y migrate down the Fraser River at the same time as chum fry (Vernon, 1966), the u t i l i z a t i o n of slough habitat by t h i s species appear n e g l i g i b l e . 29 2. Side channel habitat Juvenile chinook and chum were the only salmon taken i n the side channel habitat (Table A4, Appendix A). The density of chum and chinook i n t h i s habitat corresponds f a i r l y c l o s e l y to the density observed i n the slough habitat (Figure 11). In early A p r i l , the density of chum i n the side channel habitat i s greater than the density i n the slough habitat. The re-verse i s true for the chinook. In late A p r i l , at peak densit-i e s , the chum and chinook are evenly d i s t r i b u t e d i n both habi-t a t s . Throughout May, the density of both chum and chinook i s greater i n the slough habitat. D. Estimation of the Total Seasonal Use of Marginal Habitats An attempt was made to develop an "order of magnitude" approximation of the t o t a l number of juvenile chum and chinook u t i l i z i n g the slough and side channel habitats of the Duck -Barber - Woodward Island complex. These estimates are based on the four beach seine and four pole net catches at bi-weekly in t e r v a l s between Duck Island' and Barber Island (Figure 6). 2 The area covered by four beach seines (125 m ) was extra-polated to the t o t a l area of sim i l a r slough habitat available 2 (76,128 m ). This t o t a l area available was calculated by mul-t i p l y i n g the t o t a l length of shoreline available (17,069 m) by the average maximum distance from shore (4.5 m) sampled by the beach seine. The estimated numbers of salmon for each sampling 30 Q Q Chinook Chum Figure 11: Seasonal change i n density-of juvenile chum and chinook.salmon in. side channel habitat of the Fraser River Estuary, 1973. 31" date (tot a l number x 76,128/125) were then plotted over the whole time period. Assuming that the d a i l y number of salmon passing through the habitat area between any two sampling dates i s equal to the average number taken on those two dates, then the area under the plotted curve w i l l y i e l d an estimate of the t o t a l number of salmon u t i l i z i n g the habitat (Table 4). In the channel habitat, the estimated length of side chan-nels sampled at four pole net s i t e s was approximately 50 m. The t o t a l length of channel habitat available was 12,195 m (probably a low estimate). The number of juvenile salmon taken on each sampling date was mu l t i p l i e d by 244, ,and plotted over the whole time period. Using the same assumptions as the slough estimate, the area under the curve y i e l d s the t o t a l num-ber of salmon u t i l i z i n g the channel habitat. (Table 4). These estimates indicate that a larger proportion of chin-ook salmon fry u t i l i z e these habitats than chum salmon f r y . I t i s also apparent that i n 19 74 a lesser proportion of chum and chinook f r y u t i l i z e d the slough habitat than i n 1973. E. Seasonal changes i n size of juvenile chum and chinook salmon 1. Fork length The mean fork length of the chum salmon f r y from t h e i r f i r s t a r r i v a l i n March u n t i l late May remained between 37 and 38 mm, with a maximum standard deviation i n any sample of 2.31 (Figure 12). The few chum taken aft e r t h i s date were larger (47 mm), 32 TABLE 4 A c o m p a r i s o n o f t h e t o t a l p i n k , chum, and c h i n o o k s a l m o n f r y m i g r a t i n g p o p u l a t i o n i n t h e F r a s e r R i v e r a t M i s s i o n , w i t h an e s t i -mate o f t h e t o t a l numbers u t i l i z i n g s l o u g h and s i d e c h a n n e l h a b i t a t s o f a m a r s h a r e a . 19 7 3 Chum C h i n o o k T o t a l M i g r a t i n g P o p u l a t i o n 109,477,344 13,500,390 S l o u g h h a b i t a t e s t i m a t e 1,900,000 2,600,000 C h a n n e l h a b i t a t e s t i m a t e 412,000 732,000 TOTAL ESTIMATE 2,312,000 3,332,000 % o f T o t a l p o p u l a t i o n 2.1% 24.6% 1974 Chum C h i n o o k T o t a l M i g r a t i n g P o p u l a t i o n 3 130,777,696 16,427,324 S l o u g h h a b i t a t e s t i m a t e 434,000 1,440,000 % o f T o t a l p o p u l a t i o n 0.3% 8. 8% a - F r a s e r & B a i l e y , 1975 C: 33 5 C H Fork Length (mm) 40-30-13 2,3 1 1 March A p r i l May 1974 1 1 June 50H Fork Length (mm) 40H 30- 1—: 1 March A p r i l May June 1973 Figure 12: Seasonal change i n length of juvenile chum salmon from combined slough and side channel habitat i n the South Arm of the Fraser River. number of f i s h i n sample standard deviation mean fork length range i n d i c a t i n g a small proportion of chum would delay t h e i r sea-ward migration to some extent, a t t a i n i n g a greater size before reaching s a l t water. The fact that there was no increase i n length of the chum during the peak migration period (March 15 to May 31) sugggests that any delays i n the estuary for feeding are very b r i e f for the majority of the population. However, the feeding data w i l l show that the marsh areas are u t i l i z e d by the chum for feeding, rather than s t r i c t l y used for migra-tory passage. The mean fork lengths of both chum and chinook f r y from slough and channel habitats were i d e n t i c a l , and both habitats have been combined for analysis. The mean fork length of the juvenile chinook salmon i n 1973 remained between 39 and 40 mm throughout the A p r i l samp-l i n g dates (Figure 13). After t h i s point, the mean length i n -creased steadily u n t i l the chinook migrated out of the estuary. Two individuals taken on July 18 were greater than 80 mm i n length, i n d i c a t i n g a doubling of size over a three month period. Since the downstream migration of juvenile chinook i n the Fraser River, as determined at Mission, terminates about the beginning of June (Todd, 1966), i t i s clear that the juvenile chinook salmon delay t h e i r seaward migration i n the Fraser River Estuary. I t i s also evident from Figure 13, that they exper-ience a rapid growth rate during residence there. The r e l a t i o n -ship between estuarine residence and early marine s u r v i v a l i s an important, but as yet unknown factor. In 19 74, the i n i t i a l mean length of the chinook juveniles (41-42 mm) i n A p r i l was s l i g h t l y greater than that observed i n 35 70-Fork Length (mm) 6(H 50-404 Fork Length (mm) 8 OH 70H 6 OH 50H 40-30-1974 1973 — I 1 1 1 1 Mar. Apr. May June July Aug. Figure 13: Seasonal change i n length of juvenile chinook salmon from combined slough and side channel habitats i n the South Arm of the Fraser River. iji— number of f i s h standard deviation mean fork length — range 36 19 73 (Figure 13). A rapid growth rate was also observed i n 19 74, although the increases were not as dramatic as 1973. In spite of the i n i t i a l larger size of the juvenile chinook i n 19 74, the f i n a l lengths and weights attained were below those reached i n 19 73. 2. Mouth Size Juvenile chinook had a s i g n i f i c a n t l y larger mouth (pre-maxillary length) than juvenile chum of the same fork length (Figure 14). The premaxillary length of chinook 40 mm i n fork length was approximately 20% larger than that of a 40 mm chum. The size of food items consumed by these two species may be segregated by t h e i r d i f f e r e n t mouth size s . F. Food and Feeding Thirteen food categories (prey items) were most frequently found i n the stomachs of juvenile chinook and chum salmon (Table 5). The prey ranged i n size from 0.3 mm i n mean width (Harpac-t i c o i d copepods) to 1.9 mm (Neomysis). The measurements of prey l i s t e d are from the stomachs of juvenile salmon, rather than from prey available. A much greater size range of prey occurred i n the stomachs of other species, such as starry floun-der and p r i c k l y sculpin. The code numbers assigned to each prey type (Table 5) w i l l be referred to i n a l l following f i g -ures . 37 Figure 14: Change of mouth siz e (premaxillary length) with body s i z e (fork length) of juvenile chum and chinook salmon. 38 TABLE 5 S i z e o f common p r e y i t e m s f o u n d i n t h e s t o m a c h s o f J u v e n i l e Chum and C h i n o o k f r o m b o t h S l o u g h and C h a n n e l H a b i t a t s . Tode P r e y I t e m s mm Mean W i d t h mm Range Sample S i z e 1 C o p e p o d a 0.3 0.2-0.4 50 2 C l a d o c e r a 0.5 0.4-0.8 50 3 C o l l e m b o l a 0.6 0.4-0.8 25 4 C h i r o n o m i d l a r v a e 0.7 0.5-0.8 25 5 C h i r o n o m i d pupae 0.9 0.8-1.0 25 6 A d u l t D i p t e r a 1.1 0.9-1.3 25 7 H o m o p t e r a 1.2 0.9-1.6 25 8 E p h e m e r o p t e r a & P l e c o p t e r a 1.4 1.1-1.7 15 9 E u l a c h o n l a r v a e 1.4 1.0-1.5 50 10 A n i s o g a m m a r u s 1.5 0.9-1.8 25 11 C o r o p h i u m 1.6 1.0-2.0 25 12 T a b a n i d l a r v a e 1.7 1.4-2.2 15 13 N e o m y s i s 1.9 1.2-2.5 25 a - T h i s c a t e g o r y i n c l u d e s a b o u t 5% o f o t h e r t e r r e s t r i a l i n s e c t s . 39 1. Slough Habitat In late March 19 73, the predominant organisms consumed by chum were chironomid pupae (65%), the amphipods Anisogammarus (20%), and Corophium spinicorne (10%), the opossum shrimp Neo-mysis (9.5%), and chironomid larvae (7%) (Figure 15). These chum salmon were feeding without the influence of juvenile chin-ook salmon i n the area, and t h i s i s r e f l e c t e d i n the composi-ti o n of t h e i r d i e t . Two weeks l a t e r , as indicated below, a proportion of t h e i r d i e t had s h i f t e d to the smaller prey items. In late March 1974, the few chum and chinook present were both feeding heavily on Chironomid pupae and a Anisogammarus. Under these conditions of low density, there seemed to be a merging of both diets to the same prey types. By early A p r i l , a s l i g h t l y d i f f e r e n t pattern of prey s e l -ection was evident (Figure 15). Both species u t i l i z e d Chiron-omid pupae and Amphipods (Anisogammarus and Corophium) as com-mon food sources, but the chum consumed greater amounts of prey smaller than chironomid pupae (Copepoda and Cladocera), while the chinook consumed greater amounts of larger prey (tab-anid larvae and Neomysis). Cladocera (primarily Daphnia pulex) became very important components of both chum and chinook diets by late A p r i l (Fig-ure 16). The chum consumed proportionately more Daphnia than the chinook, and the remainder of the di e t was composed p r i n -c i p a l l y of.copepods and chironomid pupae. The chinook, i n addition to Cladocera, consumed more of the larger prey such 40 1973 0 C h i n o o k 2 8 C h u m 2 3 4 5 6 P r e y 7 C a t e g o r y -8 9 u 12 13" '1 2 3 2 O 5 P r e y 7 C a t e g o r y 8 9 io:3 11' 12' "in 0 2T 1 L a t e M a r c h 1974 2 C h i n o o k 13 C h u m ~i r 1 r E a r l y A p r i l ,33 17 3 • ZD D 50~ 6 25~ 50 % B i o m a s s C L 0 25 ~T" 50 m T 0 25 % B i o m a s s ~T— 50 F i g u r e 1 5 : P e r c e n t a g e b i o m a s s o f m a j o r f o o d c a t e g o r i e s o f j u v e n i l e c h i n o o k a n d c h u m s a l m o n , , i n . s l o u g h - h a b i t a t l a t e M a r c h a n d e a r l y A p r i l , 1 9 7 3 . a n d . 1 9 7 4 . 41 Prey Category Prey Category Late A p r i l 1973 53 Chinook 47 Chum 1974 46 Chinook 18 Chum 1 7] 1Q] l l j 12 13 55 6 ] 7] 8' 9^  10' «:] ' Q 1 Early May & 1 0 25 l o ~ 0 25 Disproportionate Dd 0 IT ta % Biomass 50 0 25 % Biomass — 50 Figure 16: Percentage biomass of major food- categories i n the stomachs of juvenile chum and chinook salmon in the slough habitat ,in late A p r i l , e a r l y May, 1973 and 1974. 42 a s A n i s o g a m m a r u s , C o r o p h i u m , a n d N e o m y s i s . I n e a r l y May, c h i r o n o m i d l a r v a e and pupae f o r m e d t h e dom-i n a n t p o r t i o n b y b i o m a s s o f b o t h chum a n d c h i n o o k d i e t s . The chum consumed p r o p o r t i o n a t e l y more o f t h e s e i n s e c t s , w i t h t h e r e m a i n d e r o f t h e b i o m a s s c o n s i s t i n g o f c o p e p o d s a n d t e r r e s t r i a l i n s e c t s . The c h i n o o k , h o w e v e r , p r e y e d u p o n l a r g e r o r g a n i s m s as w e l l , w i t h A n i s o g a m m a r u s , C o r o p h i u m , t a b a n i d l a r v a e , a n d Neo-m y s i s f o r m i n g a b o u t 30% o f t h e s t o m a c h c o n t e n t b i o m a s s . The s t o m a c h c o n t e n t s o f t h e chum and c h i n o o k t a k e n i n l a t e May ( F i g u r e 17) w e re s i m i l a r t o t h o s e o f e a r l y May. G r e a t e r t h a n 70% o f t h e f o o d b i o m a s s o f t h e chum c o n s i s t e d o f c h i r o n o -m i d l a r v a e a n d p u p a e , w i t h t h e r e m a i n d e r made up o f l a r g e r p r e y i t e m s s u c h as t e r r e s t r i a l i n s e c t s , E p h e m e r o p t e r a and A m p h i p o d a . A p p r o x i m a t e l y f o r t y p e r c e n t o f t h e c h i n o o k s t o m a c h c o n t e n t b i o m a s s was composed o f t h e c h i r o n o m i d l a r v a e a n d p u p a e , w i t h more t h a n f i f t y p e r c e n t o f t h e r e m a i n d e r made up o f l a r g e r p r e y . T e r r e s t r i a l i n s e c t s , s p e c i f i c a l l y t h e f a m i l y H o m o p t e r a , became an i m p o r t a n t component o f t h e d i e t (> 39%) a n d w e r e com-mon i n a l l s t o m a c h s . T h e s e i n s e c t s a r e p r o b a b l y w a s h e d o f f t h e l u s h e m e r g e n t v e g e t a t i o n o f t h e m a r s h on t h e r i s i n g t i d e a n d t h e n a r e c o n c e n t r a t e d i n t h e s l o u g h s as t h e t i d e e b b s . A c o m p a r i s o n o f t h e b i o m a s s o f f o o d c a t e g o r i e s p r e s e n t i n t h e s t o m a c h s o f chum and c h i n o o k f r o m l a t e May u n t i l e a r l y A u g -u s t i n d i c a t e s an i n c r e a s i n g s i m i l a r i t y i n t h e d i e t s . ( F i g u r e 1 7 ) . The d e n s i t y o f b o t h s p e c i e s , e s p e c i a l l y t h e chum, has b e e n much r e d u c e d b y t h i s t i m e . The r e s u l t s o f t h e e x a m i n a t i o n o f c h i n o o k s t o m a c h s a f t e r 43 L a t e May 1973 4 5 C h i n o o k 5 Chum 4 P r e y C a t e g o r y 9 1Q ]\ 12" 184 1 3 O P r e y 7 C a t e g o r y 8 9 ]0. l l ' 12 13 fcL 1974 3 6 C h i n o o k l 2 C h u m T May t o L a t e J u l y ~lt5 ~50 C) 25 50~ % B i o m a s s 113 0 25 .12 (as a bove) 50 0 % B i o m a s s 2Y 50 F i g u r e 17: P e r c e n t a g e b i o m a s s o f s t o m a c h c o n t e n t s o f j u v e n i l e chum and c h i n o o k i n s l o u g h h a b i t a t , l a t e May a n d f r o m May t o l a t e J u l y . l a t e May s u g g e s t s t h e l a c k o f d o m i n a n c e o f a s i n g l e f o o d c a t -e g o r y . On any g i v e n s a m p l i n g d a t e , a s i n g l e f o o d c a t e g o r y c o u l d p r e d o m i n a t e i n t h e s t o m a c h c o n t e n t b i o m a s s , b u t o v e r an e x t e n d e d p e r i o d o f t i m e (8 w e e k s ) , t h i s d o m i n a n c e c o u l d be r e -d u c e d due t o t h e i n c r e a s i n g a v a i l a b i l i t y o f o t h e r p r e y i t e m s . F o r e x a m p l e , many c h i n o o k j u v e n i l e s t a k e n i n J u l y f e d e x c l u -s i v e l y on e u l a c h o n l a r v a e . . T h e s e l a r v a e w e r e o n l y a v a i l a b l e f o r a b o u t a two week p e r i o d , a n d c h i n o o k t a k e n b e f o r e a n d a f t e r t h i s t i m e c o n t a i n e d no l a r v a e . C h i r o n o m i d pupae w e r e t h e m o s t c o n s i s t e n t p r e y s o u r c e a v a i l a b l e t o t h e c h i n o o k , f o r m i n g a b o u t 2 5% o f t h e consumed b i o m a s s . O t h e r p l a n k t o h i c p r e y commonly t a k e n w e re D a p h n i a and e u l a c h o n l a r v a e . The s e m i - p l a n k t o n i c opossum s h r i m p N e o m y s i s a l s o f o r m e d an i m p o r t a n t component o f t h e d i e t , t o g e t h e r w i t h s e v e r a l b e n t h i c i n v e r t e b r a t e s , s u c h as t h e nymphs o f E p h e m e r o p t e r a a n d P l e c o p t e r a , t h e a m p h i p o d s A n i s -ogammarus and C o r o p h i u m , and c h i r o n o m i d l a r v a e . F o u r t e e n chum s a l m o n j u v e n i l e s e x a m i n e d f r o m m i d May i n t h e s l o u g h h a b i t a t o f t h e N o r t h Arm r e l i e d h e a v i l y on A n i s o g a m -marus as a f o o d s o u r c e ( F i g u r e 1 8 ) . T h e s e a m p h i p o d s f o r m e d more t h a n 70% o f t h e f o o d b i o m a s s . The n e x t m o s t common f o o d c a t e g o r y was c h i r o n o m i d p u p a e , f o r m i n g 14% o f t h e b i o m a s s . The j u v e n i l e c h i n o o k i n t h e N o r t h Arm e x p l o i t e d a w i d e r v a r i e t y .of p r e y t y p e s , w i t h N e o m y s i s , A n i s o g a m m a r u s , a n d c h i r o -n o m i d pupae f o r m i n g a b o u t 60% o f t h e b i o m a s s , ( F i g u r e 1 8 ) . The c h i n o o k o f t h e N o r t h Arm consumed g r e a t e r p r o p o r t i o n s o f N e o m y s i s and a m p h i p o d s t h a n t h e c h i n o o k i n t h e S o u t h Arm ( F i g -u r e 2 0 ) . They a l s o consumed l e s s D a p h n i a . A c o m p a r i s o n o f 45 M i d M a y - M i d A u g u s t 1973 14 C h i n o o k 14 Chum 1. 2 3 4 P r e y C a t e g o r y 8 10 13 7.3 12" 2 5 5 0 2 5 E a r l y May 1974 14 C h i n o o k 6 5 0 B i o m a s s Is 5 0 0 Chum F i g u r e 18: P e r c e n t a g e b i o m a s s o f m a j o r f o o d c a t e g o r i e s i n t h e s t o m a c h s o f j u v e n i l e c h i n o o k a n d chum s a l m o n i i i s l o u g h h a b i t a t o f t h e N o r t h Arm, F r a s e r R i v e r . 46 c h i n o o k o f t h e N o r t h Arm w i t h t h e c h i n o o k o f t h e S o u t h Arm s u g -g e s t s t h a t a g r e a t e r a r r a y o f p r e y t y p e s may be a v a i l a b l e t o t h e c h i n o o k i n t h e s l o u g h h a b i t a t o f t h e S o u t h Arm. 2. S i d e C h a n n e l H a b i t a t C h i r o n o m i d pupae f o r m e d o v e r 60% o f t h e s t o m a c h c o n t e n t b i o m a s s o f c h i n o o k f r y a n d o v e r 40% o f t h e s t o m a c h c o n t e n t b i o -mass o f chum f r y i n s i d e c h a n n e l h a b i t a t i n e a r l y A p r i l ( F i g -u r e 1 9 ) . M o s t o f t h e r e m a i n d e r o f t h e chum d i e t was composed o f h a r p a c t i c o i d c o p e p o d s , w h e r e a s t h e c h i n o o k u t i l i z e d c h i r o n o -m i d l a r v a e , a nd l a r g e r i n s e c t s s u c h as H e m i p t e r a a n d C o l e o p t e r a . H a r p a c t i c o i d c o p e p o d s , w e r e d o m i n a n t i n t h e d i e t o f t h e ..: -chum i n c h a n n e l h a b i t a t i n l a t e A p r i l , f o r m i n g a p p r o x i m a t e l y 70% o f t h e b i o m a s s ( F i g u r e 1 9 ) . The r e m a i n d e r o f t h e p r e y c o n -sumed c o n s i s t e d o f C o l l e m b o l a , c h i r o n o m i d l a r v a e a n d p u p a e , a n d t e r r e s t r i a l i n s e c t s . The c h i n o o k consumed l e s s c o p e p o d s ( 1 6 % ) , a g r e a t e r p r o p o r t i o n o f c h i r o n o m i d p u p a e , t e r r e s t r i a l i n s e c t s a n d a m p h i p o d s , p l u s a l a r g e p r o p o r t i o n (33%) o f N e o m y s i s . D a p h n i a w e r e n o t p r e s e n t i n t h e c h a n n e l h a b i t a t s a m p l e d . I n l a t e May, C o l l e m b o l a w e re an i m p o r t a n t component i n t h e d i e t , f o r m i n g a b o u t f o r t y p e r c e n t o f t h e chum s t o m a c h c o n t e n t b i o m a s s , a n d 13% o f t h e c h i n o o k p r e y b i o m a s s . T h i s s m a l l , s e m i -a q u a t i c i n s e c t i s r e s t r i c t e d t o t h e s t i l l b a c k w a t e r s w h e r e i t h o p s a b o u t on t h e s u r f a c e , c l i n g i n g t o d e b r i s o r o v e r h a n g i n g v e g e t a t i o n . A d u l t D i p t e r a and o t h e r t e r r e s t r i a l i n s e c t s (Homo-Prey Category Prey Category 2 3 4 5 7 8 1Q n 12. 13 E a r l y A p r i l 6 Chinook ^ ^ ^ ^ 3 a 5 6 7 8 9 10J 1l' 12 13 33 L a t e May mm 0 25 L a t e A p r i l 48Chinook 37 Chum 25 50 25 I 50 1^  % Biomass F i g u r e 19: P e r c e n t a g e biomass o f f o o d c a t e g o r i e s o c c u r r i n g i n the stomachs o f chum and ch i n o o k i n c h a n n e l h a b i t a t , South Arm, 1 9 7 3 . 48 optera) were also important i n the di e t of both the chum and chinook. The chinook were also able to u t i l i z e the larger lepidopteran and coleopteran larvae, amphipods, and small fishes (eg. young Gasterosteus). 3. S i m i l a r i t y of diets of Chum and Chinook fry The s i m i l a r i t y of the diets of chum and chinook from slough and channel habitat were calculated, using the Spearman rank cor r e l a t i o n c o e f f i c i e n t (Table 6). The t value for t h i s sta-t i s t i c was calculated and tested for s i g n i f i c a n c e . Only on one occasion (late March, 1974) was the test s i g n i f i c a n t , i n -dicating the independence of the diets on a l l other sampling dates. 4. Chinook smolts (yearlings) In late A p r i l , chinook salmon smolts preyed heavily on the Daphnia i n the slough adjacent to beach seine s i t e s 6 and 7. The remainder of th e i r d i e t (22%) was composed almost en-t i r e l y of chum salmon fry (Figure 20). No chinook salmon fry were observed i n the stomachs of the chinook salmon smolts, and i t i s possible that t h e i r s l i g h t l y larger size could re-move them from the size range open to predation by chinook smolts. In late A p r i l 1974, chinook smolts also u t i l i z e d Daphnia, but t h e i r p r i n c i p l e prey was other juvenile salmon, primarily 49 TABLE 6 The Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t s a n d t v a l u e s , c o m p a r i n g t h e d i e t o f chum a n d c h i n o o k f r y on o c c a s i o n s when b o t h w e r e p r e s e n t i n t h e same h a b i t a t . S l o u g h H a b i t a t . 1973 1974 D a t e C o r r e l a t i o n C o e f f i c i e n t t v a l u e C o r r e l a t i o n C o e f f i c i e n t t v a l u e L a t e M a r c h 0.8303 4.214* E a r l y A p r i l . 1305 .437 0.0030 .009 L a t e A p r i l .1923 .650 .5667 1. 820 ... E a r l y May .3319 1. 219 .4382 1. 824 L a t e May . 1888 .608 E a r l y J u n e .4167 1.213 M i d May Nc .2381 >rth Arm .600 E a r l y A p r i l S i d e C h a n n e l H a b i t a t , 1973 .2440 .616 -L a t e A p r i l .2473 .846 L a t e May .6000 2.121 * s i g n i f i c a n t a t .05 l e v e l 50 P r e y C a t e g o r y L a t e A p r i l , 1973 18 C h i n o o k s m o l t s 2 5 6 •' 71 10 13|] 15 ~~r~ 2 5 L a t e A p r i l , 1974 14 C h i n o o k s m o l t s 2 5 J"~ 5 0 7 5 L a t e May, 8 C h i n o o k 2 5 1974 s m o l t s 5 0 7 5 F i g u r e 20: % B i o m a s s P e r c e n t a g e b i o m a s s o f s t o m a c h c o n t e n t s o f c h i n o o k s a l m o n s m o l t s i n s l o u g h h a b i t a t , i n t h e S o u t h Arm o f t h e F r a s e r R i v e r . P r e y C a t e g o r y 15: chum s a l m o n f r y . 2 3 4 5 6 7 8 10 12 1973 .3 3 S o c k e y e f r y 2 5 5 0 ; 1974 S o c k e y e f r y 2 5 I 5 0 1974 6 S o c k e y e s m o l t s 2 5 5 0 T 75 B i o m a s s F i g u r e 2 1 : P e r c e n t a g e b i o m a s s o f s t o m a c h c o n t e n t s o f j u v e n i l e s o c k e y e s a l m o n i n s l o u g h h a b i t a t , S o u t h Arm, F r a s e r R i v e r . chum salmon f r y . These salmon fry comprised about 65% of the biomass of the smolt d i e t (Figure 2_p) . Eight chinook smolts captured i n late May consumed primarily planktonic prey such as Daphnia and chironomid pupae (Figure 21). The most obvious difference i n the die t of these chinook smolts i s the absence of juvenile chum salmon, which comprised over 60% of the stom-ach content biomass before t h i s date. This i s due to the emigration of the chum fry out of the estuary. 5. Juvenile Sockeye salmon Chironomid pupae were the dominant food source of t h i r t y -three sockeye salmon fry taken i n slough habitat i n 1973. These formed approximately 65% of the prey biomass consumed (Figure 20). Other surface or planktonic invertebrates taken were adult Diptera, Collembola, t e r r e s t r i a l insects (Homoptera) Cladocera, and Copepoda. Very few benthic invertebrates were taken, with the exception of chironomid larvae and Plecoptera. The f i v e juvenile sockeye fry (young of the year) taken i n slough habitat i n late May 19 74, u t i l i z e d a wide variety of food organisms (Figure 21). T e r r e s t r i a l insects, of the families Homoptera and Coleoptera, comprised about 30% of the prey biomass consumed. Ephemeroptera nymphs, tabanid larvae, and chironomid larvae were common benthic organisms selected by these sockeye. Benthic invertebrates made up about 50% of the t o t a l biomass consumed. Noteably absent from a l l the stomach contents were Daphnia and other zooplankton commonly found i n chinook stomachs examined over the same time period. Six of the nine sockeye smolts taken i n late A p r i l had food items i n t h e i r stomachs. These f i s h were a l l taken i n slough habitat on the south bank. The p r i n c i p a l prey consumed was Daphnia, forming 90% of the stomach content biomass (Fig-ure 20). Other prey consumed included chironomid pupae and Anisogammarus. G. Laboratory feeding experiments 1. Behavioral observations The chum salmon juveniles i n the holding tank schooled and swam closer to the surface than the juvenile chinook f r y . The chinook juveniles tended to remain i n an aggregation near the bottom of the tank, with the i n t r a s p e c i f i c distance well defined and constant (about 6 cm). The chinook moved about much less than the chum, and i n general were much more wary than the chum. When chinook and chum were placed together i n the same tank, the chinook remained near the bottom, while the chum schooled and moved a c t i v e l y near the surface. 2. Experimental feeding results Chinook and chum juveniles were f i r s t tested with single prey types (Table 7). The size of the prey types were larger than those normally found i n the stomachs of f i s h c o l l e c t e d i n the f i e l d . Daphnia (type a) were 1.2 mm i n mean length, rang-ing from 0.7 to 1.4 mm. Daphnia (type b) were 3.0 mm i n mean length, ranging from 2.5 to 3.5 mm. Chironomus had a mean body width of 1.6 mm, ranging from 1.0 to 2.1 mm. A wide range of sizes of Neomysis were available, ranging from 1.8 to 4.0 mm i n body width, with a mean size of 2.7 mm. When exposed to a r e l a t i v e l y high density of Daphnia (10/ l i t r e ) , the chum juveniles proved to be more e f f i c i e n t predators, removing as much as 88% of the t o t a l number of Daphnia a v a i l -able. As few as two chum per tank could remove more than 50% of the Daphnia available, over a f i f t y minute period. The chin-ook juveniles were not as e f f e c t i v e as the chum, consuming less than 30% of the Daphnia available. The v a r i a t i o n between i n -dividuals was also greater for the chinook, with only one of every two chinook sel e c t i n g any prey. This r e s u l t c o n f l i c t s with the f i e l d data, since the chinook i n the estuary consumed greater numbers of Daphnia than the chum. The chinook juven-i l e s i n a l l the feeding experiments generally took prey less readily than the chum. Chum salmon exposed to Neomysis as the only available food source did not feed on the Neomysis. On one occasion parts of one Neomysis were found i n three d i f f e r e n t chum stomachs. These prey were generally too large for the chum to handle. The chin-ook juveniles consumed whole Neomysis when i t was the only prey available. Observations of chinook attacks on Neomysis i n d i -cated that only one attempt i n about ten was successful i n cap-turing t h i s prey. Neomysis i s almost transparent, and possesses a darting escape behavior which would remove i t 10-12 cm from t h e i n i t i a l s i t e o f a t t a c k . I n t h e t u r b i d w a t e r , t h i s move-ment w o u l d p r o b a b l y t a k e t h e N e o m y s i s o u t o f t h e s i g h t o f t h e p r e d a t o r . C h i r o n o m u s was t h e o n l y p r e y t e s t e d w h i c h t h e c h i n -ook c a p t u r e d more f r e q u e n t l y t h a n t h e chum. T h e s e p r e y w e r e l a r g e r t h a n t h e c h i r o n o m i d l a r v a e n o r m a l l y f o u n d i n t h e s t o m -a c h s o f chum a n d c h i n o o k f r o m t h e f i e l d c o l l e c t i o n s . The b e n -t h i c n a t u r e o f t h e s e l a r v a e , a n d t h e t e n d e n c y o f c h i n o o k ( i n t h e e x p e r i m e n t a l s i t u a t i o n ) t o r e m a i n n e a r t h e b o t t o m o f t h e t a n k , c o u l d a c c o u n t f o r t h e i n c r e a s e d s e l e c t i o n by t h e c h i n o o k . When t h e t h r e e p r e y t y p e s w e r e p r e s e n t e d a t t h e same t i m e , s i m i l a r r e s u l t s w e r e o b t a i n e d as when p r e s e n t e d i n d i v i d u a l l y , ( T a b l e 8 ). B o t h t h e chum and c h i n o o k consumed a p p r o x i m a t e l y t h e same number o f D a p h n i a as i n t h e p r e v i o u s e x p e r i m e n t . W i t h t h e D a p h n i a a v a i l a b l e , b o t h t h e chum and c h i n o o k c h o s e a l e s s e r p r o p o r t i o n o f c h i r o n o m i d l a r v a e , t h e c h i n o o k c h o o s i n g s l i g h t l y more o f t h e l a r v a e t h a n t h e chum. N e i t h e r t h e chum o r c h i n o o k p r e y e d upon N e o m y s i s , i n d i c a t i n g t h a t t h e o t h e r p r e y s p e c i e s w e r e " p r e f e r r e d " o r e a s i e r t o o b t a i n . 55 T A B L E 7 Number o f Daphnia, Neomysis, and Chironomus consumed by j u v e n i l e chum and chinook when p r e s e n t e d w i t h o n l y one p r e y type p e r t e s t . Number o f f i s h p e r tank S p e c i e s Mean Fork L e n g t h (mm) Number o f each p r e y a v a i l a b l e Number o f each p r e y consumed Prey con-sumed per . f i s h 5 chum 3 8 . 1 2 0 0 Daohnia 1 7 6 35 5 chum 39 .'4 2 0 0 Daphnia 1 4 4 - 29•" 2 chum 4 0 . 9 2 0 0 Daphnia 1 1 1 56 T o t a l 1 2 chum 3 8 . 8 6 0 0 Daphnia 4 3 1 36 5 c h i n o o k 5 1 . 7 2 0 0 Daphnia 1 0 7 2 1 5 c h i n o o k 5 4 . 3 2 0 0 Daphnia 69 14 2 c h i n o o k 5 3 . 7 2 0 0 Daphnia 0 0 T o t a l 1 2 c h i n o o k 5 3 . 3 6 0 0 Daphnia 1 7 6 16 5 chum 4 0 . 2 10 Neomysis . 0 0 2 chum 3 8 . 0 10 Neomysis o 0 5 chum 4 0 . 0 50 Neomysis 1 0 . 2 T o t a l 1 2 chum 3 9 . 8 70 Neomysis 1 0 . 0 8 ' 5 c h i n o o k 4 8 . 6 10 Neomysis 0 0 2 c h i n o o k 4 5 . 8 10 Neomysis 2 1 '• .5 c h i n o o k 5 3 . 0 50 Neomysis 4 0 . 8 T o t a l 1 2 • c h i n o o k 50. 0 70 Neomysis ' 6 0'. 5 ( c o n t . . . . ) TABLE 7 (cont. .. .) 56 Number o f f i s h per tank S p e c i e s Mean Fork Length (mm) Number o f each p r e y a v a i l a b l e Number o f each p r e y consumed P r e y con-sumed p e r f i s h 4 chum 41.9 50 Chironomus 32 8 3 chum 43.5 50 Chironomus 15 ; 5 T o t a l 7 chum 42.5 10 0 Chironomus 47 7 . 5 chinook 52.7 50 Chironomus 41 8.2 5 chinook 53.1 50 Chironomus 41 8.2 T o t a l 10 chinook 52.9 100 Chironomus 82 8.2 57 TABLE 8 Number of Daphnia, Neomysis, and Chironomus consumed by the juvenile chum and chinook salmon when presented with the three prey types simultaneously. Mean Number Fork Number of Number of Prey con-of f i s h . Species Length each prey each prey sumed per per tank (mm) av a i l a b l e consumed f i s h 5 chum 47.8 200 Daphniab 185 1.8 50 Chironomus 9 37 10 Neomysis 0 0 4 chum 45.6 200 Daphnia 80 20 50 Chironomus 24 6 • 10 Neomysis 0 0 5 chum 47.6 200 Daphnia 174 35 50 Chironomus 30 6 10 Neomysis 0 0 To t a l 14 chum 47.0 600 Daphnia 439 31 150 Chironomus 63 4.5 30 Neomysis 0 0 .5 . chinook 55.6 200 Daphnia 45 9 50 Chironomus 23 4.6 10 Neomysis 0 0 (cont....) 58 TABLE 8 ( c o n t . . . . ) Mean Number Fork Number o f Number o f P r e y con-o f f i s h S p e c i e s L e n g t h e a c h prey- e a c h p r e y sumed p e r p e r tank . (mm) a v a i l a b l e consumed f i s h 5 c h i n o o k 59.6 200 Daphnia 158 32 50 Chironomus 30 6 10 Neomysis 0 0. 5 c h i n o o k 58.3 200 Daphnia 75 15 50 Chironomus 20 4 10 Neomysis 0 0 Total 15 c h i n o o k 57.8 600 Daphnia 278 18.5 150 Chironomus 73 4.9 30 Neomysis 0 0 b - A l l t h e Daphnia u s e d i n t h i s s e t o f e x p e r i m e n t s were t h e l a r g e r "b" t y p e , 3.0 mm i n mean l e n g t h . 59 DISCUSSION AND CONCLUSIONS The s l o u g h a n d s i d e c h a n n e l h a b i t a t s o f t h e F r a s e r R i v e r e a t u a r y h a v e b e e n shown t o be i m p o r t a n t f e e d i n g a r e a s f o r j u v -e n i l e chum a n d c h i n o o k s a l m o n . The g r e a t e s t d e n s i t y o f t h e s e s p e c i e s was r e c o r d e d i n l a t e A p r i l , a f t e r w h i c h t i m e t h e d e n s i t y o f chum d e c l i n e d r a p i d l y . Few chum w e r e t a k e n a f t e r e a r l y J u n e . The c h i n o o k , h o w e v e r , w e r e p r e s e n t i n t h e h a b i t a t s u n t i l l a t e J u l y . The c h i n o o k j u v e n i l e s t a k e n a f t e r t h e i r a r r i v a l i n l a t e A p r i l e x h i b i t e d a s t e a d y i n c r e a s e i n l e n g t h u n t i l l a t e J u l y . T h i s g r o w t h s u g g e s t s t h a t c h i n o o k may r e s i d e i n t h e e s t u a r y f o r s e v e r a l months b e f o r e f i n a l d i s p e r s a l . The d e n s i t y o f s a l m o n i d s i n t h e s l o u g h h a b i t a t was s i m i l a r t o t h e d e n s i t y i n t h e s i d e c h a n n e l s i n l a t e A p r i l ( F i g u r e s 10 & 1 1 ) . By e a r l y May, a g r e a t e r d e n s i t y o c c u r r e d i n t h e s i d e c h a n n e l s s u g g e s t i n g a p o s -s i b l e i n c r e a s e i n f o o d a v a i l a b i l i t y i n t h i s h a b i t a t . C h i n o o k a n d chum f r o m s l o u g h a n d s i d e c h a n n e l s e x h i b i t e d a d i f f e r e n t i a l p r e y s e l e c t i o n , i n d i c a t i n g p o s s i b l e d i f f e r e n t i a l a v a i l a b i l i t i e s i n t h e two h a b i t a t s . The s u r f a c e i n s e c t C o l -l e m b o l a f o r m e d a b o u t 13% o f t h e p r e y b i o m a s s o f t h e c h i n o o k a n d chum i n t h e c h a n n e l s , b u t l e s s t h a n 1% i n t h e s t o m a c h c o n t e n t s f r o m t h e s l o u g h s . H a r p a c t i c o i d c o p e p o d s c o m p r i s e d 43% o f t h e consumed p r e y b i o m a s s o f chum f r o m t h e c h a n n e l s , b u t f o r m e d o n l y 14% o f t h e consumed p r e y b i o m a s s i n t h e s l o u g h s . C h i r o n o m i d l a r v a e a n d p u p a e , h o w e v e r , f o r m e d more o f t h e t o t a l b i o m a s s i n t h e f i s h f r o m t h e s l o u g h h a b i t a t t h a n i n f i s h f r o m s i d e c h a n n e l 60 habitat. Chum and chinook u t i l i z e d many common prey types, but chinook and chum taken together i n the same habitat show a d i -vergence i n the prey sizes of the stomach contents. The ten-dency for the chinook to select larger prey than the chum, was i n part related to the larger mouth size of the chinook. Both chinook and chum fed extensively on chironomid pupae and Daphnia when these prey were available i n abundant supply. These prey could be termed the "preferred food item" for both species. The greatest divergence i n the diet of the two f i s h occurs at the extremities of the size range of prey selected. Chum fry fed extensively on copepods and Collembola, e s p e c i a l l y the chum from channel habitats. Chinook fry ingested very few copepods and Collembola, but Neomysis often formed a large proportion of the biomass of t h e i r d i e t . Neomysis was too large a prey to be handled by the chu m>as shown by the feeding experiments, and by the absence of thi s prey item i n the stomach contents of f i e l d c o l l e c t e d specimens. The chum are capable of exp l o i t i n g most of the same food sources as the chinook. In late March, when juvenile chum were not influenced by the presence of chinook, the biomass of the prey types i n the stomach contents was remarkably s i m i l a r to the chinook present i n early A p r i l (Figure 18). As the density of juvenile salmon increased, the divergence i n prey size s e l -ected increased. In late May, when the density of salmonids was reduced, the stomach content biomass of the chum again was more similar to the chinook (Figure 20). I t i s possible that under the conditions of reduced density (in late March and late 61 May), the feeding interactions between chinook and chum would be less frequent and less intense. Juvenile chum salmon have been shown to feed i n small coast-a l streams where they could normally reach the sea i n one night. Mason (19 74) reports chum fry remaining i n a small estuary (Lymn Creek, Vancouver Island, B.C.) u n t i l June 3, feeding on amphipods (Anisogammarus and Corophium), copepods, and insects (Diptera). Observations are s i m i l a r to r e s u l t s obtained i n t h i s s tudy. Feeding of juvenile salmonids i n freshwater habitats p r i o r to marine dispersal has been described for other coastal r i v e r s , and the food sources u t i l i z e d are consistent with the results obtained i n this study. Sparrow (1968) reported chironomids and Daphnia very common i n the stomachs of chum fry i n Somenos Creek, a tributary of the Cowichan River, B.C. Sparrow also reports that chum fry as large as 6 7 mm i n fork length were recorded, remaining i n freshwater as late as June 9. Juvenile chinook salmon fry i n the Somass River Estuary, B.C., have been reported feeding on amphipods (Anisogammarus  confervicolus), f i s h larvae, chironomid larvae, and t e r r e s t r i a l insects (Kask and Parker, 1972). Residence and growth of juvenile chinook (young of the year) has been demonstrated i n the Sixes River, Oregon (Reimers, 1973). Chinook f r y i n t h i s system migrate down into the lower r i v e r i n A p r i l , at a mean length of 43 mm, and reside here u n t i l as late as September, attaining lengths of 80 mm or more. The increasing temperature of the r i v e r was determined to be the 62 c o n t r o l l i n g factor for the timing of f i n a l d i s p e r s a l . Goodman and Vroom (19 72) found that juvenile chinook and chum i n the Squamish River estuary (B.C.) consumed primarily amphipods and mysids. The chum were most abundant i n mid May, and were abundant u n t i l mid June. The chinook were most abun-dant i n mid June, and were present i n early August when sampling terminated. Goodman (1975) reports that Anisogammarus forms the great-est percentage biomass (31.6%) of food items, consumed by chin-ook salmon i n early May i n the Fraser River (South Arm). These f i s h were taken i n slough habitat on the north shore of the r i v e r , due north of Woodward Island (Figure 1). Chironomid l a r -vae and adult Diptera also formed a dominant portion of the prey biomass i n early May and mid June. These results are s i m i l a r to stomach content analysis of chinook taken i n slough habitat i n the Duck - Barber - Woodward Island complex i n 1974. The more frequent occurrence of benthic organisms i n the diet of the chinook suggests that chinook juveniles are p r i -marily benthic oriented. This conclusion i s also supported by the laboratory feeding experiments. The chum f r y , on the other hand, are more pelagic, u t i l i z i n g primarily prey on the surface or i n the water column. As previously discussed, the chinook are not r e s t r i c t e d to benthic invertebrates, but w i l l take ad-vantage of a temporary or l o c a l abundance of pelagic prey such as Daphnia and chironomid pupae. Differences i n the feeding behaviour of chum and chinook probably contributes to some degree of s p a t i a l segregation. This could account for the v e r t i c a l d i s t r i b u t i o n of the species under laboratory conditions, where the chum remain near the sur-face, and the chinook near the bottom, whether i n the same tank or i n separate tanks. Due to the t u r b i d i t y of the water i n the study areas, i t i s not known whether t h i s v e r t i c a l d i s t r i b u t i o n occurs i n the f i e l d . Other species u t l i z i n g the slough habitat were threespine stickleback, p r i c k l y sculpin, peamouth chub, staghorn sculpin, and starry flounder (Appendix B). Only the threespine s t i c k l e -back and p r i c k l y sculpin u t i l i z e d the side channel habitat. The threespine stickleback exploited a wide variety of food resources, with chironomid larvae being most important i n the slough habitat. Copepods and amphipods formed over 70% of the prey biomass of the stickleback i n the side channel habitat. The p r i n c i p a l food sources of the p r i c k l y sculpins were isopods and chironomid larvae. Staghorn sculpin preyed upon isopods, amphipods and juvenile salmon. The peamouth chub taken i n slough habitat were planktivorous, consuming c h i e f l y Daphnia. Starry founders taken i n slough habitat r e l i e d almost exclusive-ly on benthic invertebrates, c h i e f l y amphipods and isopods. The a r r i v a l of juvenile P a c i f i c salmon i n the Fraser River estuary i n late March corresponds with the i n i t i a l presence of other species i n the estuary. In t h i s study, marginal habitat types i n a marsh area have been examined. The habitat has been shown to be an important feeding area for at least three species of juvenile P a c i f i c salmon and f i v e other species. The diverse marsh areas i n the Duck - Barber - Woodward Island com-plex and Ladner Marsh provide suitable habitat for the produc-t i o n of many t e r r e s t r i a l and aquatic invertebrates. These i n -vertebrates i n turn supply a v i t a l food resource for many estu-arine fishes, including the migrating juvenile salmon. Any further degradation of t h i s habitat, by development or p o l l u -t i o n , would further reduce the Fraser River salmon stocks. 65 LITERATURE CITED A l l e n , K.R. 196 9. L i m i t a t i o n s i n p r o d u c t i o n i n s a l m o n i d pop-u l a t i o n s i n s t r e a m s . In_ S a l m o n and t r o u t i n s t r e a m s . H.R. M a c M i l l a n Symp., U n i v . . o f B r i t i s h C o l u m b i a , V a n c o u v e r , B.C., F e b . 1968. Anonymous. Bams, R.A. 1975. F i s h e r i e s S t u d i e s i n t h e F r a s e r R i v e r E s t u a r y i n r e l a t i o n t o p r o p o s e d e x p a n s i o n o f t h e V a n c o u -v e r I n t e r n a t i o n a l A i r p o r t , f e r r y t e r m i n a l l o c a -t i o n a n d e x p a n s i o n o f R o b e r t s Bank P o r t f a c i l i -t i e s . D e p t . o f t h e E n v i r o n . U n p u b l . R e p t . 1969. A d a p t a t i o n s i n s o c k e y e s a l m o n a s s o c i a t e d w i t h i n c u b a t i o n i n s t r e a m g r a v e l s , p. 71-87. I n S a l m o n a n d t r o u t i n s t r e a m s . H.R. M a c M i l l a n Symp., U n i v . o f B r i t i s h C o l u m b i a , V a n c o u v e r , B.C., F e b . 1968. Chapman, D.W. 1966. F o o d and s p a c e as r e g u l a t o r s o f s a l m o n i d p o p u l a t i o n s i n s t r e a m s . Amer. N a t u r . 100: 345-357. Chapman, D.W. and T.C. B j o r n n . 1969. D i s t r i b u t i o n o f s a l m o n -i d s i n s t r e a m s , w i t h s p e c i a l r e f e r e n c e t o f o o d a n d f e e d i n g . I n S a l m o n a n d t r o u t i n s t r e a m s . H.R. M a c M i l l a n Symp., U n i v . o f B r i t i s h C o l u m b i a , V a n c o u v e r , B.C., F e b . 1968. Day, J.H. 1 9 5 1 . The E c o l o g y o f S o u t h A f r i c a n E s t u a r i e s . I.A. R e v i e w o f E s t u a r i n e C o n d i t i o n s i n G e n e r a l . T r a n s . Roy. S o c . S. A f r ; 3 3 : 5 3 - 9 1 . F o e r s t e r , R.E. 196 8. The s o c k e y e s a l m o n . C a n a d a , B u l l . 162, 422 p. F i s h . R e s . Bd. G e r k e , R . J . Goodman, D. H e n r y , K.A. and V.W. K a c z y n s k i . 1972. F o o d o f j u v e n i l e p i n k a nd chum s a l m o n i n P u g e t S o u n d , W a s h i n g t o n . W a s h i n g t o n D e p t . o f F i s h . T e c h . R e p t . 10. and P.R. Vroom. 19 72. I n v e s t i g a t i o n s i n t o F i s h U t i l i z a t i o n o f t h e i n n e r E s t u a r y o f t h e S q u a m i s h R i v e r . D e p t . o f t h e E n v i r o n . T e c h . R e p t . 12 1961. R a c i a l i d e n t i f i c a t i o n o f F r a s e r R i v e r s o c k e y e s a l m o n by means o f s c a l e s a n d i t s ap-p l i c a t i o n t o s a l m o n management. I n t e r n a t . P a c . S a l m . F i s h . Comm. B u l l . 12:97p. 66 Hoar, W.S. Hoar, W.S, Hoos, L.M. 1958. The evolution of migratory behaviour among the juvenile salmon of the genus Oncorhynchus. J. Fish Res. Bd. Canada, 16(6): 835-886. 1951. The behviour of chum, pink and coho salmon in r e l a t i o n to t h e i r seaward migration. J. Fish Res. Bd. Canada, 8(4): 241-263. and G.A. Packman. 19 74. The Fraser River Estuary Status of Knowledge to 1974. Dept. of the En-viron. Special Estuary Series No. 1. Jensen, A.L. Kaczynski, Kask, B.A. McDonald, J. Manzer, J.I, Mason, J.C. Neave, Northcote, 19 74. Predator-prey and competition models with state variables: biomass, number of i n d i v i d u a l s , and average i n d i v i d u a l weight. J.Fish Res. Bd. Canada, 31 (10): 1669-1674. V.W., R.J. F e l l e r , J. Clayton, and R.J. Gerke. 1973. Trophic analysis of juvenile pink and chum salmon i n Puget Sound. J. Fish Res. Bd. Canada, 30: 1003-1008. and R.R. Parker. 1972. Observations on juvenile chinook salmon i n the Somass River Estuary, B.C. Fish Res. Bd. Tech. Rept. 30 8. 1960. The behaviour of P a c i f i c salmon fry during t h e i r downstream migration to freshwater and saltwater nursery areas. J. Fish Res. Bd. Canada, 17(5): 655-676. 1969. Stomach contents of juvenile P a c i f i c s a l -mon i n Chatham Sound and adjacent waters. J. Fish Res. Bd. Canada, 26(8): 2219-2223. 1974. Behavioural ecology of chum salmon fry (Oncorhynchus keta) i n small estuary. J . Fish Res. Bd. Canada, 31: 83-93. 1966b. Salmon of the North P a c i f i c ocean, Part I I I . A review of the l i f e history of North P a c i f i c Salmon. (6) Chum salmon i n B r i t i s h Columbia. Internat. North Pac. Fish. Comm., B u l l . 18, p. 81-85. T.G. 19 74. Biology of the Lower Fraser River: A Review. Westwater Research Centre, Tech. Rept. No. 3, 94 p. 67 P a l m e r , R.N. 1972. F r a s e r R i v e r chum s a l m o n . C a n a d a D e p t . o f E n v i r o n . , F i s h . S e r v . , T e c h . R e p t . 1 9 7 2 - 1 , 284p. P a r k e r , R.R. 1971. S i z e s e l e c t i v e p r e d a t i o n among j u v e n i l e s a l m o n i d f i s h e s i n a B r i t i s h C o l u m b i a i n l e t . J . F i s h R e s . Bd. C a n a d a , 28 ( 1 0 ) : 1 5 0 3 - 1 5 1 0 . P r i t c h a r d , D.W. 1967. What i s an e s t u a r y : p h y s i c a l v i e w p o i n t . I n E s t u a r i e s , G.H. L a w f f ( e d ) , Amer. A s s o c . Adv. S c i . 83: 3-5. R e i m e r s , P.E, R i c k e r , W.E, 1973. The l e n g t h o f r e s i d e n c e o f j u v e n i l e f a l l c h i n o o k s a l m o n i n t h e S i x e s R i v e r , O r e g o n . O r e g o n F i s h . Comm. R e s . R e p t . 4: 2 1966. S a l m o n o f t h e N o r t h P a c i f i c o c e a n . P a r t I I I . A r e v i e w o f t h e l i f e h i s t o r y o f t h e N o r t h P a c i f i c S a l m o n . (4) S o c k e y e s a l m o n i n B r i t i s h C o l u m b i a . I n t e r n a t . N o r t h P a c . F i s h . Comm., B u l l . 18, p. 59-70. S p a r r o w , R.A.H. 1968. A f i r s t r e p o r t o f chum s a l m o n f r y f e e d -i n g i n f r e s h w a t e r o f B r i t h s C o l u m b i a . J . F i s h R e s . Bd. C a n a d a , 2 5 ( 3 ) : 5 99-602. S t e i n , R.A. P.E. R e i m e r s , a n d J.D. H a l l . 1 9 73. S o c i a l i n -t e r a c t i o n b e t w e e n j u v e n i l e c o h o ( O n c o r h y n c h u s  k i s u t c h ) a n d f a l l c h i n o o k s a l m o n ( 0 . t s h a w y t s c h a ) i n t h e S i x e s R i v e r , O r e g o n . J . F i s h . R e s . Bd. C a n a d a , 29 ( 1 2 ) : 1 7 3 7 - 1 7 4 8 . T o d d , I . S . 1966. A t e c h n i q u e f o r t h e e n u m e r a t i o n o f chum s a l m o n f r y i n t h e F r a s e r R i v e r , B.C. Can. F i s h . C u l t u r i s t , 38. V e r n o n , E.H. 1966. E n u m e r a t i o n o f m i g r a n t p i n k s a l m o n f r y i n t h e F r a s e r R i v e r E s t u a r y . I n t e r n a t . P a c . S a l m . F i s h . Comm., B u l l . 19. APPENDIX A . 2 T a b l e A 1: Number o f j u v e n i l e ^ s a l m o n p e r r 100- m o f s l o u g h h a b i t a t , i n t h e S o u t h A r m ' o f t h e F r a s e r R i v e r , 1973. cl Si D a t e p i n k chum c h i n o o k c h i n o o k c o h o s o c k e y e f r y a s m o l t s b Mar. 15 Mar. 29 22 A p r . 12 50 24 A p r . 25 105 257 11 May 9 7 55 1 May 24 2 46 3 J u n . 6 3 27 4 J u n . 2 0 1 20 7 J u l . 4 6 2 J u l . 18 2 4 Aug. 2 1 1 a) y o u n g o f t h e y e a r b) s m o l t s ( y e a r l i n g s ) 69 2 T a b l e A 2: Number o f j u v e n i l e s a l m o n p e r 100 m o f s l o u g h h a b i t a t i n t h e N o r t h Arm o f t h e F r a s e r R i v e r , 1 9 7 3 . D a t e p i n k chum c h i n o o k c h i n o o k c o h o ' s o c k e y e f r y s m o l t s May 17 8 126 1 May 31 1 .31 1 J u n . 13 1 2 4 J u n . 28 8 J u l . 11 3 1 J u l . 25 1 1 Aug. 7 70 Table A 3: Number of juvenile salmon per 100'm2 of slough habitat i n the South and North Arms of the Fraser River, .1974.. South Arm Date p i n k a chuma chinook a ehinook b coho sockeye fr y smolts Mar. 14 1 1 Mar. 28 7 1 Apr. 11 14 7 Apr. 24 21 68 7 5 b May 8° 4 8 3 l b May 22 6 84 2 1 Jun. 5 1 25 3 2 a Jun. 19 1 4 J u l . 4 5 l a J u l . 17 1 l a Middle Arm May 1 22 1 J u l . 2 1 a) young of the year b) smolts (yearlings) c) thick layer of s i l t and fi n e organic material made seining very d i f f i c u l t on t h i s date and many f i s h were probably l o s t . 7 1 T a b l e A 4 : N u m b e r o f j u v e n i l e s a l m o n p e r 1 0 0 m ' o f c h a n n e l . h a b i t a t i n t h e S o u t h A r m o f t h e F r a s e r R i v e r , 1 9 7 3 . D a t e p i n k c h u m c h i n o o k c h i n o o k c o h o s o c k e y e f r y . s m o l t s M a r . 1 4 . M a r . 2 8 3 A p r . 1 1 1 1 1 1 3 A p r . 2 6 1 2 1 2 0 8 M a y 1 0 6 7 2 0 0 M a y 2 5 1 1 1 0 5 J u n . 8 8 8 J u n . 2 1 8 J u l . 4 5 J u l . 1 9 A u g . 3 a ) y o u n g o f t h e y e a r 72 APPENDIX B Species other than salmonids.in the Fraser Estuary Five other species were frequently taken i n the slough and channel habitat of the study area. These species were: threespine stickleback (Gasterosteus aculeatus), p r i c k l y sculpin (Cottus asper), peamouth chub (Mylocheilus caurinus) staghorn s c u l p i n (Leptocottus. armatus)., and starry flounder (Platichthys s'telTatus') . The l a t t e r Jbwo species are marine forms commonly found i n estuarine or brackish waters. Other species taken infrequently by.the sampling gear were: eulachon (Thaleichthys pacif icus.)..,. longfin smelt (Spirinchus  thaleichthys), mountain whitefish (Prosopiunr williamsoni), squawfish (Ptychocheilus oregonensis), redside shiner (Richardsonius balteatus), brassy minnow, (Hybognathus  hankinsoni) , carp (Cyprinis carpio)., and western brook lamprey (Lampetra richardsoni). A. Temporal and s p a t i a l use 1. Slough habitat The i n i t i a l a r r i v a l of other species of f i s h into the slough habitat generally coincided with the a r r i v a l of the juvenile P a c i f i c salmon (Figure B 1 ) . Starry flounder were the most abundant species i n the slough habitat, followed by threespine 73 Number o f F i s h p e r 7 100 m 30H 2 0 -ioH 20H ion 20-4 1973 S t a r r y F l o u n d e r 1974 T 1 r Peamouth Chub i 1 T S t a g h o r n S c u l p i n T~ 1 r P r i c k l y S c u l p i n T T 1 1 r T h r e e s p i n e S t i c k l e b a c k Mar. A p r . May J u n . J u l . Aug. Mar. A p r . May J u n . J u l . F i g u r e B 1: Number o f o t h e r s p e c i e s p e r 100 m o f s l o u g h h a b i t a t i n t h e S o u t h Arm o f t h e F r a s e r R i v e r . 74 stickleback, p r i c k l y sculpin, staghorn sculpin, and peamouth chub, respectively. The number of each of these species, a f t e r an i n i t i a l increase i n A p r i l , did not show any clear trends i n abundance u n t i l sampling terminated i n August. Larger numbers of p r i c k l y sculpin, staghorn sculpin, and starry flounder were present i n the slough habitat of the North Arm (Figure B 2). The p r i c k l y sculpin exhibited a clear migratory pattern, with peak numbers occurring i n mid June. The few threespine stickleback and peamouth chub i n the NorthnArm could be i n d i c a t i v e of a greater marine influence i n t h i s area. 2. Side channel habitat Only two of the f i v e common species other than juvenile salmonids were present i n the channel habitat (Figure B 3 ) . Threespine sticklebacks were the most numerous, u t i l i z i n g these channels as a breeding and rearing area. Small numbers of p r i c k l y sculpin were consistently present i n channel catches. Starry flounder and staghorn sculpin were absent i n t h i s habitat type. B. Food and Feeding 1. Slough habitat. Longfin smelt (Spirinchus thaleichthys): Nine longfin 75 P r i c k l y S c u l p i n S t a g h o r n S c u l p i n May J u n . J u l . A u g. May J u n . J u l . A u g . Peamouth Chub 5H 1 1 r May J u n . J u l . A u g. F i g u r e 3 2: Number o f o t h e r s p e c i e s p e r 100 m o f s l o u g h h a b i t a t i n t h e N o r t h Arm, F r a s e r R i v e r . 76 2 F i c m r e B 3: S e a s o n a l c h a n g e i n numbers p e r 100 m o f o t h e r s p e c i e s i n s i d e c h a n n e l h a b i t a t , S o u t h Arm F r a s e r R i v e r . Q Q T h r e e s p i n e S t i c k l e b a c k A A P r i c k l y S c u l p i n 77 smelt were examined from the slough habitat i n 1973. Almost the entire biomass of the stomach contents (98.4%) consisted of the opossum shrimp (Neomysis mercedis)(Figure B 4) . Although the sample.size i s small (9 stomachs), the longfin smelt was the only species taken who fed almost exclusively on the Neomysis. Since Neomysis were very abundant i n the area, t h i s f i s h species could possess a feeding behaviour or foraging c h a r a c t e r i s t i c which would enable i t to capture t h i s prey, more e f f i c i e n t l y than other species. . Peamouth Chub (Myibcheilus caurinus): Although the number of peamouth chub taken on any date was low, t h i s species can become very concentrated i n the larger backwaters of the estuary at low t i d e s . The peamouth chub were primarily planktivorous, with 56% of the biomass of the stomach contents formed by Cladocera (primarily Daphnia p.mlex.) (Figure B 4) . Ostracods, were also abundant i n the. stomach contents, compris-ing about 20 % of the biomass. Very few true benthic organisms were taken by the peamouth chub, except the chironomid larvae,, forming 11% of the consumed biomass. Starry Flounder (Platyichthys s t e l l a t u s ) : Starry flounder were abundant i n the slough habitat of the South Arm. Although a wide range of sizes were examined, the stomach content analysis yielded consistent r e s u l t s (Figure B 4 ). Benthic 78 P r e y C a t e g o r y 4 5 71 11 12 13 27 T h r e e s p i n e S t i c k l e b a c k • 1] 2D • • ] • 3 25 ~r~ 50 It ] 16 Peamouth Chub 25 — I -50 ft 9 L o n g f i n S m e l t 25 50 75 P r e y C a t e g o r y P r i c k l y S c u l p i n 1 2 4 5 7 11 13 —r 25 50 S t a g h o r n S c u l p i n 75 S t a r r y F l o u n d e r 1 0 25 B i o m a s s - r -50 "T" 25 5 0 F i g u r e B 4: P e r c e n t a g e b i o m a s s o f m a j o r p r e y i t e m s f r o m s i x f i s h s p e c i e s i n s l o u g h h a b i t a t , S o u t h Arm. a O l i g o c h a e t e s t> O s t r a c o d s c d I s o p o d s J u v e n i l e s a l m o n 79 organisms were taken almost exclusively by the flounder, with Isopods (Gnorimosphaeroma)and Amphipods (Corophium and Anisogammarus)- comprising 40.5% and 41.5% of the consumed biomass, respectively. The starry flounder depended on the larger prey to a greater extent than any other species. The remainder of t h e i r d i e t consisted of.ologochaetes, polychaetes, and chironomid larvae. P r i c k l y sculpin (Cottus Asper.).: Thirty three p r i c k l y sculpin from slough habitat were examined. Isopods (Gnorimosphaeroma) and chironomid larvae were predominant food categories, each forming 38% of the stomach content.biomass (Figure B 4). Tabanid larvae and amphipods were also present i n the stomachs. Staghorn Sculpin (Leptocottas arma.tus.).: Thirty three staghorn sculpin were examined from the South Arm slough habitat. The mean size captured was approximately 70 mm i n fork length, which i s about 20 mm greater than the mean size of the p r i c k l y sculpin. This size difference i s re f l e c t e d i n the re s u l t s of the stomach content analysis (Figure B 4). The staghorn sculpin preyed heavily upon benthic organisms such as Isopods (22%) and Amphipods (24%). More importantly, they were of s u f f i c i e n t size to predate upon juvenile P a c i f i c salmon. Juvenile salmon formed 30.5% of the biomass of the stomach contents of the staghorn sculpin. It i s l i k e l y that larger sculpins, not sampled by the gear types used, are present and are an important predator of.juvenile P a c i f i c salmon i n the 80 P r e y C a t e g o r y to 1 2 4 5 6 7 101 11 12 13 14 15 32 T h r e e s p i n e S t i c k l e b a c k ] 25 I 50 I 75 0 B i o m a s s 4 P r i c k l y S c u l p i n - r -25 50 70 F i g u r e B 5 P e r c e n t a g e o f b i o m a s s o f p r e y i t e m s consumed by two s p e c i e s i n s i d e c h a n n e l h a b i t a t , S o u t h Arm, 1973. a O l i g o c h a e t e s 81 Fraser River Estuary. Threespine stickleback (Gasterosteus<aculeatus): Chironomid larvae comprised the largest portion of the biomass (35%) of the stomach contents of threespine stickleback (Figure B 4). Many other benthic prey were present i n the stomachs, such as oligochaetes, amphipods, and tabanid larvae. Copepods, Gladocera, and t e r r e s t r i a l insects were also taken, i n d i c a t i n g the lack of speci a l i z e d feeding behaviour.of Gasterosteus. 2. Side channel habitat Threespine stickleback and.prickly sculpin were the only species other than juvenile chum and chinook salmon taken i n channel habitat i n the South Arm. Of these stickleback were the most common. Copepods and amphipods comprised the greatest portion of the stomach content biomass (70%) of the sticklebacks i n the channel habitat (Figure B 5) . These prey only formed 17%. of the stomach biomass of sticklebacks taken i n the slough habitat. Four p r i c k l y sculpin were examined from the channel habitat. Isopods and Anisogammarus were the dominant prey found i n the stomach contents of these f i s h (Figure B 5). 

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