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Simulation of coho smolt predation on pink and chum fry: the importance of relative size and growth rate Belford, Darlene Lillian 1978

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SIMULATION OF COHO SMOLT PREDATION ON PINK AND CHUM FRY THE IMPORTANCE OF RELATIVE SIZE AND GROWTH RATE by DARLENE LILLIAN BELFORD B.A., U n i v e r s i t y of B r i t i s h Columbia, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES Department of Zoology We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1978 © Darlene L i l l i a n Belford, 1978 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. c Zoology Department of The University of Brit ish Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 August 3, 1978 A b s t r a c t A d e t e r m i n i s t i c s i m u l a t i o n m o d e l i s u s e d t o e x p l o r e t h e r e l a t i o n s h i p b e t w e e n j u v e n i l e p i n k , chum and c o h o s a l m o n g r o w t h a n d s i z e - r e l a t e d s u r v i v a l i n t h e F r a s e r R i v e r e s t u a r y . P a r a m e t e r s m o s t s e n s i t i v e t o c h a n g e a r e i d e n t i f i e d a n d t h e r e s u l t s r e l a t e d t o p r o p o s a l s f o r en h a n c e m e n t . T h e s e r e s u l t s s u g g e s t t h a t i n c r e a s i n g t h e i n i t i a l s i z e o f e n h a n c e m e n t p i n k a n d chum f r y , r e l a t i v e t o t h e s i z e o f w i l d f r y , p r i o r t o s e a w a r d m i g r a t i o n a n d r e l e a s i n g them e a r l y i n t h e s p r i n g may i n c r e a s e t h e i r c h a n c e s o f s u r v i v a l . I f i n c r e a s i n g t o t a l ( e n h a n c e m e n t p l u s w i l d ) f r y d e n s i t y d e c r e a s e s f r y g r o w t h r a t e , t h e p r e s e n c e o f e n h a n c e m e n t f r y i n t h e e s t u a r y c o u l d r e d u c e t h e s u r v i v a l c h a n c e s o f w i l d f r y . The d e c r e a s e i n w i l d s t o c k s u r v i v a l may n o t be a p p a r e n t f r o m e s t i m a t e s o f a d u l t r e t u r n f o r many y e a r s due t o e r r o r s i n m e a s u r e m e n t and t o t h e e f f e c t on s u r v i v a l o f e n v i r o n m e n t a l v a r i a b i l i t y . The m o d e l c a n be u s e d t o i i i suggest and evaluate enhancement proposals. Areas needing further research are also indicated. i v Table of Contents Ab s t r a c t i i Table of Contents l v L i s t of Tables V 1 1 L i s t of Figures 1 X Acknowledgements X 1 1 CHAPTER I . INTRODUCTION 1 1. I n t r o d u c t i o n 1 2. Overview of E x i s t i n g Data 1 3. Purpose of Thesis 10 4. E a r l y L i f e H i s t o r y . . . . . . . . . 11 5. Some D e f i n i t i o n s 14 CHAPTER I I . METHODS 16 1. I n t r o d u c t i o n 16 2. Organization and St r u c t u r e of the Model . . . 17 3. The B i o l o g i c a l Basis of the Model 17 I M i g r a t i o n 17 I I Growth 20 i Growth Rate 20 i i Density 32 i i i Temperature and Density 35 i v Coho Feeding Dynamics 35 V I I I M o r t a l i t y 37 IV Predation 3 8 i General Assumptions 3 8 i i M u l t i s p e c i e s Disc Equation . . . 40 Area Searched and Density of Prey 41 Reactive Distance 41 Distance T r a v e l l e d Per Day . . .. 44 Encounter Rate 49 Pro p o r t i o n of Prey S u c c e s s f u l l y Pursued and K i l l e d 50 T o t a l Searching and Handling Time 58 Handling Time 58 CHAPTER I I I . RESULTS AND DISCUSSION 61 1. I n t r o d u c t i o n 61 2. S e n s i t i v i t y A n a l y s i s 63 I Components of Predation . . . . . . . 63 I I Predator S i z e at M i g r a t i o n i n t o Estuary 66 I I I Timing and Duration of Pink and Chum Fry M i g r a t i o n 6 7 IV Growth Rate 73 V Chum and Pink Size at M i g r a t i o n i n t o the Estuary 78 VI Prey Density 79 VII R e l a t i v e P r o p o r t i o n of Pink to Chum Fry i n the Estuary 84 V I I I Timing and Duration of the Coho Smolt M i g r a t i o n 94 v i IX Non-Coho Na t u r a l M o r t a l i t y 102 X Residence Time and Size at Emigration from the Estuary ...... . . 103 3. Enhancement Experiments . 116 I Changing the Prey:predator Ratio . . 116 I I Enhancement of Pink Salmon 116 4. Examination of Data found i n the L i t e r a t u r e 134 CHAPTER IV. GENERAL DISCUSSION 153 LITERATURE CITED 157 APPENDIX I . Prey Types found i n Salmon Stomachs . 164 APPENDIX I I . L i s t of Parameters and Range of Values t e s t e d i n the Model 165 APPENDIX I I I . Generalized Logic of the Model . ... 167 v i i L i s t of Tables TABLE I . Variances of annual catch ( i n pieces) of various species of P a c i f i c salmon i n North America and A s i a , and variances of various sums of catches of species 3 TABLE I I . Variances of annual catch ( i n weight) of various species o f . P a c i f i c salmon i n North America and A s i a , and variances of various sums of catches of species 5 TABLE I I I . Value of parameters a and b f o r le n g t h -weight equations . . . 19 TABLE IV. Value of parameters a and b f o r growth rate-weight equations 21 TABLE V. S e n s i t i v i t y of model r e s u l t s to changes i n the maximum i n g e s t i b l e prey s i z e 64 TABLE VI. S e n s i t i v i t y . o f model r e s u l t s to changes i n the estimated s t a r t i n g date of the pink and chum f r y m igration 68 TABLE V I I . S e n s i t i v i t y of model r e s u l t s to changes i n estimated pink f r y growth r a t e and f r y migra t i o n date 74 TABLE V I I I . S e n s i t i v i t y of model r e s u l t s to changes i n the estimated s i z e at which pink and chum f r y are assumed to leave the estuary 104 v i i i L i s t of Tables cont'd... TABLE IX. Pink and chum f r y are permitted to leave the model estuary i f t h e i r growth ra t e drops below a s p e c i f i e d value 107 TABLE X. S e n s i t i v i t y of model r e s u l t s to increases i n the d e n s i t y of pink and chum f r y 117 TABLE XI. One example p r e d i c t e d by the model of the negative e f f e c t enhancement pink population may have on w i l d pink and chum populations 132 L i s t of Figures Figure 1 • Total Asian Catch of Salmonids versus Total North American Catch of Salmonids . • 7 Figure 2 • Average Monthly Temperature of Fraser River Estuary 23 Figure 3 . -~ Estimated e f f e c t of Temperature on Growth Rate 25 Figure 4 . Average Weight of Chum Fry in the Estuary . - 28 Figure 5 . Average Weight of Pink Fry i n the Estuary 30 Figure 6 - Estimated E f f e c t of Density on Growth Rate 33 Figure 7 • The " e f f e c t i v e volume" of Water Searched by a predator 42 Figure 8 . Reactive Distance 45 Figure 9 . Relation between Prey Weight and Predator Reactive Distance 47 F.dlgure 10 . Size of Fi s h Prey Found i n Oncorhynchus . . 51 Figure 11 • Strike Distance 54 Figure 12 . Relation Between Strike Distance and Reactive Distance 56 Figure 13 . Proportion of Encountered Prey Successfully Captured and Eaten 59 Figure 14 . Relation Between Fry Density Pattern and Starting Date of Fry Migration . . . .71 Figure 15a . Relation Between Prey:Predator Ratio and Number of Fry Eaten/Coho/Day 8 0 L i s t o f F i g u r e s c o n t ' d . . . x F i g u r e 15b • A n o t h e r E x a m p l e o f R e l a t i o n B e t w e e n P r e y : P r e d a t o r R a t i o a n d Number o f F r y E a t e n / C o h o / D a y 8 2 F i g u r e 16 • R e l a t i o n B e t w e e n C h a n g i n g P i n k a n d Chum F r y A b u n d a n c e a n d Coho S m o l t A b u n d a n c e . . . . 8. 85 F i g u r e 17 . R e l a t i o n B e t w e e n F r y M o r t a l i t y a n d t h e P r o p o r t i o n o f Chum F r y i n t h e T o t a l P r e y P o p u l a t i o n 8"/ 8 7 F i g u r e 18 . An E x a m p l e o f t h e R e l a t i o n B e t w e e n D u r a t i o n o f Coho M i g r a t i o n a n d P i n k and Chum F r y M o r t a l i t y 9 5 F i g u r e 19 • An E x a m p l e o f t h e R e l a t i o n B e t w e e n D a t e Coho E n t e r E s t u a r y a n d P i n k a n d Chum F r y M o r t a l i t y 9 7 F i g u r e 20 . E f f e c t on I n d i c a t o r s o f C h a n g i n g t h e D u r a t i o n o f Coho M i g r a t i o n a n d t h e D a t e o f E n t r y 9 9 F i g u r e 21 . S i z e D i s t r i b u t i o n o f Chum F r y F o u n d i n t h e E s t u a r y E a c h Week 108 F i g u r e 22 . S i z e D i s t r i b u t i o n o f P i n k F r y F o u n d i n t h e E s t u a r y E a c h Week 110 F i g u r e 2 3 . W e e k l y D e n s i t y o f P i n k a n d Chum F r y i n t h e E s t u a r y 114 F i g u r e 24 . E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 16 March) . . . 119 L i s t o f F i g u r e s c o n t ' d . . . x i F i g u r e 25 . E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 1 A p r i l ) 121 F i g u r e 26 . E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 15 A p r i l ) 123 F i g u r e 27 . E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 1 May) 125 F i g u r e 28 . E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d D a t e o f E n t r y o f E n h a n c e m e n t P i n k F r y . 127 F i g u r e 29 . R e l a t i o n B e t w e e n % Chum E g g - t o - F r y S u r v i v a l a n d T o t a l P i n k a n d Chum E g g D e p o s i t i o n 137 F i g u r e 30 . R e l a t i o n B e t w e e n % Chum F r y - t o - A d u l t S u r v i v a l a n d T o t a l P i n k a n d Chum F r y A b u n d a n c e . 14 0 F i g u r e 31 . R e l a t i o n B e t w e e n Age T h r e e Chum R e t u r n s a n d T o t a l P i n k a n d Chum F r y A b u n d a n c e . . 144 F i g u r e 32 . R e l a t i o n B e t w e e n A v e r a g e A d u l t P i n k S a l m o n W e i g h t a n d T o t a l N o r t h A m e r i c a n C a t c h ( i n p i e c e s ) o f O n c o r h y n c h u s S a l m o n . 148 F i g u r e 33 . R e l a t i o n B e t w e e n A d u l t P i n k S a l m o n W e i g h t a n d L e n g t h o f Age T h r e e A d u l t Chum S a l m o n 150 A c k n o w l e d g e m e n t s Numerous p e o p l e i n t h e I n s t i t u t e o f A n i m a l R e s o u r c e E c o l o g y h a v e g i v e n me a s s i s t a n c e d u r i n g t h e c o u r s e o f t h i s s t u d y . I w o u l d e s p e c i a l l y l i k e t o t h a n k R a n d a l l M. P e t e r m a n f o r h i s i n v a l u a b l e s u g g e s t i o n s , e n c o u r a g e m e n t a n d s u p p o r t . My s u p e r v i s o r , C.S. H o l l i n g , C a r l W a l t e r s , B i l l N e i l l a n d M i c h a e l S t a l e y k i n d l y p r o v i d e d many u s e f u l s u g g e s t i o n s and c r i t i c i s m f r o m t h e b e g i n n i n g t o t h e e n d o f t h e s t u d y . I w o u l d a l s o l i k e t o t h a n k B i l l R ees f o r r e a d i n an e a r l y d r a f t o f my t h e s i s , G.W. L i d s t o n e f o r d o i n g t h e f i g u r e d r a w i n g s , L. S t e p h e n s f o r t y p i n g t h e t h e s i s t e x t , a n d S. Rose a n d P. G e o r g e f o r e d i t o r i a l comments on my f i n a l d r a f t . A s p e c i a l t h a n k s t o my f r i e n d s a n d f a m i l y f o r t h e i r c o n t i n u e d s u p p o r t . 1 CHAPTER I . INTRODUCTION 1. I n t r o d u c t i o n The g o a l o f l o n g - t e r m P a c i f i c s a l m o n e n h a n c e m e n t i s " t o d o u b l e t h e p r e s e n t mean a n n u a l c a t c h ( J o h n s o n , 1 9 7 6 ) . " T h i s g o a l i s c o n s i d e r e d b i o l o g i c a l l y a n d t e c h n i c a l l y f e a s i b l e ( L a r k i n , 1974; L a r k i n , 1 9 7 5 ; J o h n s o n , 1 9 7 6 ) . T h i s t h e s i s p r o v i d e s a n o v e r v i e w o f some o f t h e e v i d e n c e s u p p o r t i n g t h e b i o l o g i c a l f e a s i b i l i t y o f s a l m o n e n hancement a n d f o c u s s e s o n wh a t a p p e a r s t o be a c r i t i c a l s t a g e i n t h e l i f e h i s t o r y o f s a l m o n i d s : e a r l y m a r i n e r e s i d e n c e . An a t t e m p t i s made t o s y n t h e s i z e t h e b i o l o g i c a l k n o w l e d g e a n d a s s u m p t i o n s r e g a r d i n g t h i s p e r i o d o f l i f e t o : 1. u n c o v e r a n y s e r i o u s g a p s i n o u r b i o l o g i c a l k n o w l e d g e and t h u s d i r e c t r e s e a r c h p r i o r i t i e s 2. r e l a t e w h a t i s known a b o u t t h e b i o l o g y o f t h e s y s t e m t o p r o p o s e d e n h a n c e m e n t o f s a l m o n i d s . 2. O v e r v i e w o f E x i s t i n g D a t a The f e a s i b i l i t y o f e n h a n c i n g P a c i f i c s a l m o n h a s b e e n e x a m i n e d f r o m a number o f d i f f e r e n t p e r s p e c t i v e s . L o o k i n g f o r i n d i c a t i o n s o f o c e a n l i m i t a t i o n , L a r k i n (1975) r e a s o n e d t h a t i f t h e r e w e r e c o m p e t i t i v e i n t e r a c t i o n s b e t w e e n s p e c i e s o f s a l m o n a t p r e s e n t l e v e l s o f a b u n d a n c e due t o o v e r l a p p i n g 2 d i s t r i b u t i o n s and food l i m i t a t i o n on the high seas, then the variance over time of t o t a l salmonid abundance would be less than the sum of the variances of ind i v i d u a l species' abundance. Using North American and Asian catch s t a t i s t i c s as indices of abundance he found (Table 1): 1. "For each species, the sum of the variances of the North American and Asian catches i s not s i g n i f i c a n t l y d i f f e r e n t from the variance of the combined North American and Asian catch. In some cases, the sum of the variances i s the greater quantity, suggesting possible competitive interactions, but i n other cases the reverse i s true, suggesting that common factors s i m i l a r l y influence catches of various species." 2. For a l l species combined on either side of the P a c i f i c , Larkin found that the variance of the sum was larger than the sum of the variances of the species i n a l l but one case (1950-1959). This suggests that the catches of the various species are p o s i t i v e l y correlated. Larkin concludes that "there i s no obvious evidence that the present abundance of salmon i s s u f f i c i e n t to exploit the potential rearing capacity of the North P a c i f i c . " I applied Larkin's analysis technique to North American and Asian catches expressed as weight (Table 2). Weight seems to be a more useful indicator of competitive i n t e r a c t i o n because: 3 TABLE 1. V a r i a n c e s o f a n n u a l c a t c h ( i n p i e c e s ) o f v a r i o u s s p e c i e s o f P a c i f i c s a l m o n i n N o r t h A m e r i c a a n d A s i a , a n d v a r i a n c e s o f v a r i o u s sums o f c a t c h e s o f s p e c i e s . N o r t h A m e r i c a A s i a Sum o f V a r i a n c e s V a r i a n c e o f Sums 1925-1961" S o c k e y e P i n k Chum Coho Sum o f V a r i a n c e s V a r i a n c e o f Sum 62.61 392.93 12.51 1.62 469.67 740.66 26 .40 2,648.71 137.29 2.09 2,814.49 3,614.90 89 .01 3,041.64 149 .80 3 .71 3,284.16 4,355.56 113.65 4,022.34 142.14 2.91 4,281.04 5,843.61 1925-1949-S o c k e y e P i n k Chum Coho Sum o f V a r i a n c e s V a r i a n c e o f Sum 61.27 244.61 7.92 1.23 315.03 399.29 21. 77 2,899.81 155.31 1.44 3,078.33 4,070.72 83.04 3 ,144.42 163 .23 2.67 3,393 .36 4,470.01 126 .24 3,988.26 165.43 3 .21 4,283.14 6 ,024 .99 1950-1961' S o c k e y e P i n k Chum Coho Sum o f V a r i a n c e s V a r i a n c e o f Sum 15.62 52.72 11.21 2.16 81.71 99 . 89 38.78 1,852.42 109.55 2.81 2,004.56 2,474.24 54.50 1,905.14 120.76 4.97 2,085.27 2,574.13 45.86 2,103.54 84.11 2.43 2,235.94 2,390.43 c o n t ' d . TABLE 1, page 2 N o r t h Sum o f V a r i a n c e A m e r i c a A s i a V a r i a n c e s o f Sums 1950-1969 S o c k e y e 29.17 23.11 52.28 52.91 P i n k 216.10 1,042.50 1,258.60 898.24 Chum 11.76 80.17 91.93 82.43 Coho 3.22 2.55 5.77 5.27 Sum o f V a r i a n c e s 260.25 1,148.33 1,408.58 1,038.85 V a r i a n c e o f Sum 228.04 1,399.02 1,627.06 1,078.49 T a k e n f r o m T a b l e 1 o f L a r k i n , 197 5. R e v i s e d u s i n g d a t a t a k e n f r o m I n t e r n a t i o n a l N o r t h P a c i f i c F i s h e r i e s C o m m i s s i o n (INPFC) s t a t i s t i c a l r e p o r t s f o r 19 5 2 - 1 9 6 9 . N o t e t h a t t h e s e d a t a g r o u p i n g s a r e a s u b s e t o f t h e f i r s t d a t a g r o u p i n g . C h a n g i n g t h e g r o u p i n g d i d n o t c h a n g e t h e g e n e r a l c o n c l u s i o n ( i . e . , t h e sums o f t h e v a r i a n c e s a r e s t i l l s m a l l e r t h a n t h e v a r i a n c e s o f t h e v a r i o u s sums) w h i c h s u g g e s t s , p e r h a p s , t h a t c o n d i t i o n s h a v e r e m a i n e d much t h e same o v e r t i m e . N e v e r t h e l e s s , a n y a n a l y s i s o f t i m e s e r i e s d a t a must be t r e a t e d c a u t i o u s l y due t o t h e e x i s t e n c e o f t r e n d s w h i c h may be c o n f o u n d i n g t h e r e s u l t s . 5 TABLE 2. V a r i a n c e s o f a n n u a l c a t c h ( i n w e i g h t ) o f v a r i o u s s p e c i e s o f P a c i f i c s a l m o n i n N o r t h A m e r i c a a n d A s i a , a n d v a r i a n c e s o f v a r i o u s sums o f c a t c h e s o f s p e c i e s . N o r t h Sum o f V a r i a n c e A m e r i c a A s i a V a r i a n c e s o f Sums 1952-1972 S o c k e y e 240.70 101.19 341.89 318.71 P i n k 493.45 1 ,896.43 2 ,389.88 1,903.28 Chum 197.90 439.13 637.03 573 .09 Coho 37. 72 9.95 47.67 43.79 C h i n o o k 6.48 0.66 7.50 7.25 Sum o f V a r i a n c e s 976.61 2 ,447.36 3 ,423 .97 2,846.12 V a r i a n c e o f Sum 1,064.98 3 ,313.14 4 ,378.12 2,727.04 C a t c h d a t a p r o v i d e d b y ( S e p t e m b e r 1 9 7 6 ) . I N P F C , u n p u b l i s h e d m a n u s c r i p t 1. I t does not assume t h a t i n c r e a s e d c o m p e t i t i o n r e s u l t s i n i n c r e a s e d m o r t a l i t y . 2. I t a l l o w s f o r the p o s s i b i l i t y t h a t i n c r e a s e d c o m p e t i t i o n may r e s u l t i n decreased growth r a t e and an o v e r a l l r e d u c t i o n i n weight of a p o p u l a t i o n below what would have been obtained i n the absence of c o m p e t i t i o n . Looking o n l y a t data from 19 52 to 197 2, I found t h a t among s p e c i e s on each s i d e o f the P a c i f i c the sum of the v a r i a n c e s was s m a l l e r than the v a r i a n c e of the sum. Although the d i f f e r e n c e s were not s i g n i f i c a n t (F-test,-. p> 0.05), they do suggest t h a t wnwhenc .[condition's.-': Lc ao are f a v o u r a b l e , they are f a v o u r a b l e f o r a l l s p e c i e s from t h a t s p e c i f i c c o a s t , w i t h l i t t l e , i f any, negative i n t e r a c t i o n between s p e c i e s . The r e v e r s e was t r u e f o r the whole North P a c i f i c . Although the v a r i a n c e s are again not s i g n i f i c a n t l y d i f f e r e n t , the sum of the v a r i a n c e s i s i n v a r i a b l y the g r e a t e r q u a n t i t y Byggestingesthath.^L c o m p e t i t i v e i n t e r a c t i o n s between s p e c i e s from North America and Asia:may e x i s t . I t i s a l s o p o s s i b l e t h a t the d i f f e r e n c e s i n the v a r i a n c e s , confirmed by the negative c o r r e l a t i o n ( f i g u r e 1, r = -0.57, p<0.01) between North American and A s i a n c a t c h (used as an i n d i c a t o r of abundance), are due to the movement of North American and A s i a n stocks i n the North P a c i f i c r e l a t i v e to i n t e r n a t i o n a l f i s h i n g boundaries and seasons and are not an i n d i c a t i o n of c o m p e t i t i v e i n t e r a c t i o n between s p e c i e s from these two areas. An examination of the p r o p o r t i o n of North 7 FIGURE 1. T o t a l A s i a n C a t c h o f S a l m o n i d s v e r s u s T o t a l N o r t h A m e r i c a n C a t c h o f S a l m o n i d s R e g r e s s i o n o f t o t a l A s i a n s a l m o n i d c a t c h on t o t a l N o r t h A m e r i c a n s a l m o n i d c a t c h ( i n p i e c e s ) . C a t c h y e a r s a r e i n d i c a t e d f o r e a c h d a t a p o i n t . CO American stocks taken by the Asian f l e e t each year r e l a t i v e to North American and Asian catch abundance might reveal whether or not species movement i s responsible for t h i s negative c o r r e l a t i o n . (It should be noted that the annual catches are only an index of oceanic abundance of salmon and a more concise analysis would require escapement as well as age-at-return data.) Walters, et a l . (1977), looking for evidence of food l i m i t a t i o n i n the estuary and along the coast of B r i t i s h Columbia created a simulation model to explore the s p a t i a l and seasonal interactions of migrating juvenile salmon and t h e i r food supplies The authors, using zooplankton biomass as a measure of food supply, concluded that " i t appears that there i s enough food production to support several times the e x i s t i n g abundance of juvenile salmon without noticeable e f f e c t s on growth and s i z e -r e l a t e d s u r v i v a l , even assuming that the useable coastal zone i s very narrow and considering s p a t i a l p osition e f f e c t s within large migrating blocks of f i s h . " Parker (1968) and LeBrasseur, et a l . (1969) also suggest that food supply of juvenile f i s h i s abundant during the time they are i n residence i n the estuary C s p e c i f i c a l l y the B e l l a Coola and Fraser River estuaries). Residence time, however, may be determined by the food supply. I t i s not s u f f i c i e n t , therefore, to judge the a b i l i t y of the food resource to support an increased abundance of juvenile salmon using the abundance of the food supply alone; information on residence time and growth rate i s also required. Peterman C1975) presented data for Skeena River sockeye smolts which seem to indicate that an increased abundance of smolts r e s u l t s 10 in a decreased survival to recruitment. If food production i s not l i m i t i n g t h e i r growth and chances for survival during coastal migration and residence i n the Gulf of Alaska, then something must be happening to l i m i t production either during early estuarine l i f e or during t h e i r r i v e r migration to the sea. Other factors which have not been considered such as disease, parasitism or predator aggregation (Peterman, 1978) may be implicated at any stage. Various authors have suggested that mortality (20% to 85%) from predation during early freshwater and marine l i f e stages l i m i t s the production of salmon (Parker, 1968, 1971; Foerster, 1968; Semko, 1954; Hunter, 1959). Ricker's (1976) review of ocean mortality rates supports the conclusion that early marine mortality of salmon i s more s i g n i f i c a n t than l a t e r high seas mortality. Coho smolts have been i d e n t i f i e d as a major cause of t h i s early freshwater and marine mortality to pink and chum salmon fry (Parker, 1968, 1971; Sibert and Parker, 1972; Bailey, 1974; Hunter, 1959; Semko, 1954). 3. Purpose of Thesis Given the lack of d e f i n i t i v e evidence either supporting or refuting the existence of ocean l i m i t a t i o n of salmonid abundance and given the general agreement that early marine l i f e mortality i s much higher and therefore p o t e n t i a l l y more important than high seas mortality, I decided to focus on the early estuarine l i f e of P a c i f i c chum (Oncorhynchus keta) and pink (Oncorhynchus gorbuscha) salmon. 11 S p e c i f i c a l l y , t h i s thesis addresses three general questions: 1. Can predation by coho (Oncorhynchus kisutch) smolts during early marine l i f e account for the major portion of the observed estimates of fry-to-adult mortality of Fraser River pink and chum salmon? 2. How important to the ultimate survival of pink and chum f r y are r e l a t i v e species' abundance, timing of downstream migration, i n i t i a l size or weight at migration, area of dispersion i n the estuary and s p a t i a l overlap of species, growth rate, and duration of residence in the estuary? 3. How important i s an understanding of these b i o l o g i c a l c h a r a c t e r i s t i c s to proposed enhancement schemes for pink, chum and coho salmon? 4. Early L i f e History 0. gorbuscha (pink salmon) and 0. keta (chum salmon) emerge from the gravel as f r y i n the early s p r i n g — u s u a l l y during early March to mid-May in the Fraser River system—and migrate, immediately to sea. The major spawning areas for pink salmon are found below Hope i n the mainstem of the Fraser River, above the mouth of the Vedder River and i n the Harrison, Chilliwack and Chehalis r i v e r s (Vernon, 1966; Aro and Shepard, 1967). The mainstem of the Fraser accomodates the largest spawn-ing population. Only about twelve percent spawn upstream from 12 Hell's Gate, mainly i n Seton Creek and the Thompson River (Aro and Shepard, 1967). The Fraser has a major odd-year spawning run of pink salmon and a v i r t u a l l y non-existent even-year run (Hurley and Woodall, 1968). Estimates of the number of pink f r y migrants produced between 1964 and 1974 from the odd-year brood year range from 95 m i l l i o n to as many as 266 m i l l i o n (Fraser, 1976). Chum salmon spawn mainly below Hope (Northcote, 1974) u t i l i z i n g the mainstem of the Fraser River and the Chehalis, Chilliwack and Harrison r i v e r s (Aro and Shepard, 1967). Their l i f e cycle i s more variable than the two year l i f e cycle of pink salmon, returning predominantely as three or four year-olds. The dominant age of return varies from year to y e a r — f o r example, between 1960 and 1969, three year-olds composed between 11% and 77% (the average being 34%) of the spawners and four year-olds composed between 22% and 88% (the average being 64.9%) of the spawners (Palmer, 1972). Chum salmon are present i n the r i v e r every year and estimates of chum f r y migrants range from 32 m i l l i o n to as many as 131 m i l l i o n (1964-1974) (Fraser, 1976). L i t t l e i s known about the behaviour of Fraser River pink and chum f r y or about what happens to them during the r i v e r proportion of t h e i r migration to the sea. About t h e i r l i f e during early marine residence, l i t t l e more i s known. Although no evidence has been found of pink f r y feeding i n freshwater, a number of authors have reported that chum f r y feed during down-stream migration (Sparrow, 1968; Bailey, et a l . , 1975). They may also feed i n both freshwater and saltwater once they reach the estuary (Mason, 1974). In the Fraser River, chum f r y 13 apparently u t i l i z e the food resources of the marsh habitats for at least a few weeks (Northcote, 1974). Pink f r y , however, seem to move out into the i n t e r t i d a l zones immediately and perhaps farther a f i e l d (Northcote, 1974; Hurley and Woodall, 1968; Blackburn, personal communication). In the lower Fraser pink f r y form schools when the water i s r e l a t i v e l y clear (Vernon, 1966) whereas chum f r y are s o l i t a r y and aggressive i n freshwater (at l e a s t i n Lynn Creek, Vancouver Island; Mason, 1974). 0. kisutch (coho salmon) are present i n the Fraser system every year. The major portion of coho spawners u t i l i z e the Chehalis and Chilliwack r i v e r s (Aro and Shepard, 1967). Coho f r y spend one or more years i n freshwater although Godfrey (cited by Northcote, 1974) contends that many, i f not the greater proportion go to sea shortly a f t e r emergence. Migrating to sea from mid-April to early May, coho smolts spend an "average of 4 days i n the mainstem of the r i v e r (Bailey, 1974)." After reaching the Fraser estuary, coho smolts appear to move out into the i n t e r t i d a l zones (Northcote, 1974) and are present u n t i l at least the end of June and perhaps longer (Goodman, 1975). Bailey calculated that between 1967 and 1972 the Fraser River system averaged 52,500 coho spawners per year producing an estimated 1,083,000 coho smolts annually (assuming an average fecundity rate and a 10% egg-to-smolt survival r a t e ) . Conversely, Fraser (.197 6) estimated that the Fraser River produces about 2 m i l l i o n coho smolts per year. The stomach contents of juvenile coho indicate that th e i r d i e t i s composed of "marine, estuarine and freshwater organisms. 14 T h i s c o m p o s i t i o n no d o u b t r e f l e c t s t h e movement o f f i s h o n a n d o f f t h e i n t e r t i d a l p o r t i o n o f t h e e s t u a r y w i t h f l o o d i n g a n d e b b i n g t i d e s (Goodman, 1 9 7 5 ) . " I n t e r m s o f b i o m a s s , Goodman r e p o r t s t h a t c o h o s t o m a c h s : 1. u p s t r e a m o f t h e P o r t Mann b r i d g e c o n t a i n e d m a i n l y s a l m o n a n d c h i r o n o m i d l a r v a e , 2. i n t h e N o r t h a n d M i d d l e Arms c o n t a i n e d m a i n l y l a r v a l a n d j u v e n i l e f i s h , 3. i n t h e S o u t h Arm c o n t a i n e d m a i n l y f r e s h w a t e r a n d t e r r e s t r i a l i n v e r t e b r a t e s , 4. o n b o t h S t u r g e o n a n d R o b e r t s B a n k s c o n t a i n e d m a i n l y l a r v a l a n d j u v e n i l e h e r r i n g a n d o t h e r f i s h e s . T h e s e d a t a e s t a b l i s h t h e p o s s i b i l i t y o f a n i m p o r t a n t 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 p i n k , chum and c o h o s a l m o n i n t h e F r a s e r R i v e r . 5. Some D e f i n i t i o n s The t e r m " e s t u a r y " w i l l be u s e d v e r y g e n e r a l l y t o mean t h e a r e a o f f r e s h w a t e r a n d s a l t w a t e r i n t e r f a c e a n d a d j a c e n t a r e a s u t i l i z e d b y f r y d u r i n g t h e i r e a r l y m a r i n e g r o w t h a n d d e v e l o p m e n t s t a g e . T h i s d e f i n i t i o n i s n e c e s s a r i l y v a g u e b e c a u s e o f t h e l a c k o f s p e c i f i c k n o w l e d g e r e g a r d i n g t h e b e h a v i o u r a n d s p a t i a l d i s t r i b u t i o n o v e r t i m e o f t h e s t u d y s p e c i e s — p a r t i c u l a r l y i n t h e F r a s e r R i v e r s y s t e m a n d a d j a c e n t w a t e r s o f t h e G e o r g i a S t r a i t . "The ( F r a s e r ) r i v e r e s t u a r y d o e s n o t o p e n o u t i n t o a l a r g e b a y o r a d e e p p r o t e c t e d i n l e t t y p i c a l o f many e s t u a r i e s but instead flows d i r e c t l y into the marine waters of Georgia S t r a i t , flanked on both sides by extensive shallow mudflats and banks (Northcote, 1976)." The t o t a l area of slough, marsh and foreshore of the Fraser River estuary i s estimated to be 15,319 hectares (Goodman, 1975). For purposes of t h i s study, f i s h "age" i s determined by the number of days an in d i v i d u a l or cohort has spent i n the estuary. "Age c l a s s " , however, i s determined r e l a t i v e to the f i r s t day of seaward migration by f r y , regardless of species. For example, i f seaward migration of pink f r y begins on March 1, a l l f i s h which migrate on that day belong to age c l a s s 1; those which migrate on March 2 belong to age class 2; etc. "Age c l a s s " and "size c l a s s " are considered synonymous. The "size" of an i n d i v i d u a l i n any "age" or "size c l a s s " i s a function of i t s i n i t i a l size at migration and i t s subsequent growth rate while i n the estuary. A l l individuals of the same age, from a single species, are regarded as one "cohort". 16 CHAPTER I I . METHODS 1. I n t r o d u c t i o n To d e t e r m i n e a n d q u a n t i f y t h e b i o l o g i c a l c h a r a c t e r i s t i c s t h o u g h t t o a f f e c t t h e s u r v i v a l o f s a l m o n i d s d u r i n g t h e i r e a r l y m a r i n e l i f e , I d i d a n e x t e n s i v e s e a r c h o f t h e l i t e r a t u r e . The p e r t i n e n t i n f o r m a t i o n was s y n t h e s i z e d i n t o a s i m u l a t i o n m o d e l , a n d t h e m o d e l was u s e d t o e x a m i n e t h e i n t e r - r e l a t i o n s h i p s o f p i n k , chum a n d c o h o s a l m o n d u r i n g t h e i r r e s i d e n c e i n t h e e s t u a r y . W i t h some m o d i f i c a t i o n t h e , m o d e l c o u l d i n c l u d e o t h e r s p e c i e s b u t t h e i n c r e a s e i n c o m p l e x i t y w o u l d be s i g n i f i c a n t . S i n c e I w a n t e d t o e x a m i n e t h e r e l a t i o n s h i p b e t w e e n g r o w t h a n d s i z e - r e l a t e d m o r t a l i t y f r o m c o h o p r e d a t i o n o n p i n k a n d chum f r y , t h e m o d e l o n l y l o o k s i n d e p t h a t t h e e a r l y p e r i o d o f l i f e i n t h e e s t u a r y when t h e f r y a r e v u l n e r a b l e . C o m p l e t e i n f o r m a t i o n d e s c r i b i n g t h e b i o l o g i c a l c h a r a c t e r -i s t i c s o f t h e t h r e e s a l m o n i d s p e c i e s was n o t a v a i l a b l e f o r any one r i v e r . T h us t h e m o d e l i s a c o m p o s i t e o f i n f o r m a t i o n g l e a n e d f r o m many r i v e r s y s t e m s a nd t h e p a r a m e t e r v a l u e s w e r e c h o s e n t o a p p r o x i m a t e t h e b i o l o g i c a l c h a r a c t e r i s t i c s o f t h e F r a s e r R i v e r s y s t e m a s c l o s e l y a s p o s s i b l e . I c h o s e t h e F r a s e r R i v e r s y s t e m t o e v a l u a t e a n d e x p l o r e t h e m o d e l ' s b e h a v i o u r f o r t h r e e m a i n r e a s o n s : 1. T h e r e i s a c o n s i d e r a b l e b o d y o f q u a n t i t a t i v e a n d q u a l i t a t i v e d a t a a v a i l a b l e . 2. T h e r e i s a u n i q u e " n a t u r a l e x p e r i m e n t " o c c u r r i n g i n t h i s s y s t e m s i n c e p i n k s a l m o n f r y a r e p r e s e n t i n s i g n i f i c a n t numbers o n l y i n e v e n c a l e n d a r y e a r s . 3. I t i s a n i m p o r t a n t r i v e r i n t e r m s o f s a l m o n management. W i t h a p p r o p r i a t e c h a n g e s t o t h e p a r a m e t e r v a l u e s , t h e m o d e l c o u l d be u s e d t o e x p l o r e s a l m o n i n t e r a c t i o n s i n a n y r i v e r s y s t e m a s l o n g a s t h e b a s i c p a t t e r n o f e v e n t s i s t h e same. 2. O r g a n i z a t i o n a n d S t r u c t u r e o f t h e M o d e l The s i m u l a t i o n m o d e l i s d e t e r m i n i s t i c a n d m o d u l a r i n f o r m w i t h t h e m o d u l e s c o r r e s p o n d i n g t o t h e m a j o r p r o c e s s c o m p o n e n t s o f t h e b i o l o g i c a l s y s t e m u n d e r s t u d y : m i g r a t i o n , g r o w t h a n d m o r t a l i t y . The m o d e l s i m u l a t e s t h e i n t e r a c t i o n o f t h e s e c o m p o n e n t s on a d a i l y b a s i s . G i v e n t h e q u e s t i o n s b e i n g a s k e d a n d t h e i n f o r m a t i o n a v a i l a b l e on e a c h o f t h e p r o c e s s c o m p o n e n t s , t h i s t i m e s t e p seemed a p p r o p r i a t e t o t h e p r o b l e m . A d e t e r m i n i s t i c m o d e l p e r m i t s a l e s s a m b i g u o u s i n t e r p r e t a t i o n o f t h e r e s u l t s t h a n a s t o c h a s t i c m o d e l ( a l b e i t l e s s r e a l i s t i c ) . E a c h g r o u p ( c o h o r t ) o f s a l m o n m o v i n g i n t o t h e e s t u a r y i s d i f f e r e n t i a t e d b y s p e c i e s a n d a g e . The s i m u l a t i o n e n d s when: a l l p i n k a n d chum f r y h a v e l e f t t h e e s t u a r y , a l l p i n k a n d chum f r y h a v e b e e n e a t e n , o r , a l l p i n k a n d chum f r y a r e no l o n g e r v u l n e r a b l e t o c o h o p r e d a t i o n b e c a u s e t h e y a r e t o o l a r g e . (See A p p e n d i x . I l l f o r d i a g r a m o f m o d e l l o g i c . ) 3. The B i o l o g i c a l B a s i s o f t h e M o d e l I M i g r a t i o n The m o d e l assumes t h a t t h e d o w n s t r e a m j u v e n i l e f i s h m i g r a t i o n i s n o r m a l l y d i s t r i b u t e d . I t d o e s n o t c o n s i d e r y e a r l y v a r i a t i o n s i n t h e s h a p e o f t h e d i s t r i b u t i o n o r v a r i a t i o n s i n a b u n d a n c e on a s h o r t e r t i m e s c a l e t h a n one d a y . A l l f i s h o f a n y one s p e c i e s t h a t m i g r a t e d o w n s t r e a m on a g i v e n d a y a r e assumed t o be e q u a l i n s i z e e v e n t h o u g h t h i s i s known t o be f a l s e ( P a l m e r , 1972) I n t h e e s t u a r y a d i s t r i b u t i o n o f f i s h s i z e i s c r e a t e d due t o f i s h c o m i n g i n a n d t o g r o w t h o f f i s h a l r e a d y t h e r e . C a l c u l a t i n g a d a i l y • d i s t r i b u t i o n o f i n i t i a l f i s h s i z e f o r e a c h s p e c i e s w o u l d g r e a t l y i n c r e a s e t h e c o m p l e x i t y o f t h e m o d e l w i t h o n l y a m a r g i n a l i n c r e a s e i n r e a l i t y a n d p r o b a b l y no a p p r e c i a b l e c h a n g e i n t h e r e s u l t s . The (equatLant i n i t i a l s i z e a s s u m p t i o n a p p l i e s o v e r t h e e n t i r e m i g r a t i o n d u r a t i o n a l t h o u g h a n o p t i o n e x i s t s t h a t a l l o w s p i n k a n d chum f r y t o i n c r e a s e t h e i r i n i t i a l mean s i z e d u r i n g t h e s e a s o n . I n t h e m o d e l , e m i g r a t i o n f r o m t h e e s t u a r y o f p i n k a n d chum f r y i s assumed t o be e i t h e r a f u n c t i o n o f s i z e ( L e B r a s s e u r a n d P a r k e r , 1964; P a r k e r , 1968; A l l e n , 1974) o r a f u n c t i o n o f g r o w t h r a t e ( s e e R e s u l t s a n d D i s c u s s i o n ) . The p a r a m e t e r v a l u e s o f t h e l e n g t h - w e i g h t r e l a t i o n s h i p s u s e d i n t h e m o d e l w e r e e i t h e r t a k e n f r o m t h e l i t e r a t u r e o r c a l c u l a t e d f r o m p u b l i s h e d raw d a t a ( s e e T a b l e 3) a n d a r e assumed t o a p p l y t o F r a s e r R i v e r f i s h . The f o r m o f t h e r e l a t i o n s h i p i s : , ,, , , , T ^1© = a ^10 w h e r e W = w e i g h t ( g ) , L = l e n g t h (mm o r c m ) , a & b a r e two p f i ^ t e d ^ c o n s t a n t s . 19 TABLE 3. Value of parameters a l o g 1 0 W = a + b l o g 1 Q and L = length (mm or pink and chum f r y . and b f o r the equation L, where W = weight (g) cm) f o r coho smolts, LENGTH SPECIES L Coho Pink Chum cm cm mm INTERCEPT a -2.0846 -2.34 -6.2 SLOPE b 3.122 3 .267 AREA & SOURCE 3.642 Chef Creek, Vancouver I s l a n d , B.C., Wickett (unpublished) B e l l a Coola, B.C. , LeBrasseur & Parker (1974) c i t e d by S i b e r t & Parker (1972) Campbell R., Vancouver I s l a n d , B.C.; c a l c u l a t e d from data given i n Goodman & Vroom (19 74) N=39, range 33-10 7 mm 20 II Growth i Growth Rate Growth rate for the three species i n the model i s deter-mined solely by body weight. I t was unnecessary to calculate growth rate as a function of food supply because the dynamics of feeding and growth had already been explored by Walters, et a l . (1977) and they had concluded that food supply during most of the simulated year was abundant enough that the " f i s h a t t a i n near maximum ra t i o n . " Exploration of the e f f e c t of changing growth rate and size (not s p e c i f i c a l l y related to food supply) on the ultimate survival of pink and chum f r y could s t i l l be accomplished without the added complexity of a feeding and growth subroutine. (See separate discussion of coho feeding dynamics.) The form of the growth rate rel a t i o n s h i p used i n the model i s : log G = log a + b log g W where W = weight (g), G = instantaneous growth rate x 100, a & b are two f i t t e d constants. The parameter values were either obtained from the l i t e r a t u r e (Brett and Shelbourn, 1975) or estimated from growth rate data found i n the l i t e r a t u r e (see Table 4). There are several i m p l i c i t assumptions or l i m i t a t i o n s concerning the parameter values given i n Table 4: 1. The parameter values are temperature dependent. 2. The f i s h were assumed to be eating f u l l rations of optimal n u t r i t i o n a l value. The laboratory feeding procedure (e.g., continuous versus i n t e r v a l feeding), however, determines the t o t a l intake of food (Brett, et a l . , 1969; Shelbourn, 21 TABLE 4. Value of parameters a and b f o r the equation log e,. G = lo l o g , , a + b l o g _ n W, where W = weight (g) and G = temperature dependent instantaneous growth r a t e x 100, f o r coho smolts, pink and chum f r y . S i z e and source of v a r i o u s s p e c i e s i n d i c a t e d . Weight Temp I n t e r c e p t Slope SPECIES range (g) C. a b Source Coho Pink Chum 0.3-75.0 15.5 5.53 0.29-10.2 ? (a f n c . of time) 5.334 0.66-7.24 14-16 6.39 -0.34 S t a u f f e r (1973) c i t e d by B r e t t & Shelbourn (1975) -0.384 C a l c u l a t e d u s i n g growth r a t e data found i n LeBrasseur & Parker (1964) f o r C e n t r a l B.C. pink salmon. -0.38 C a l c u l a t e d u s i n g growth r a t e data found i n LeBrasseur (1969) f o r l a b . -r e a r e d j u v e n i l e chum fed Calanus  plumchrus e t a l . , 1973) a n d c o n s e q u e n t l y s h i f t s t h e e s t i m a t e o f g r o w t h r a t e up o r down. 3. The p a r a m e t e r v a l u e s a r e e v a l u a t e d o v e r a s p e c i f i c w e i g h t r a n g e . 4. The p a r a m e t e r v a l u e s a r e c a l c u l a t e d u s i n g n o n -F r a s e r s t o c k s . A s B r e t t a n d S h e l b o u r n (1975) i n d i c a t e " e n v i r o n m e n t a l a n d g e n e t i c d i f f e r e n c e s w o u l d h a v e t h e g r e a t e s t e f f e c t on t h e i n t e r c e p t s " o f t h e r e g r e s s i o n l i n e s t h e r e b y s h i f t i n g t h e e x p e c t e d g r o w t h r a t e up o r down. T h e s e f a c t o r s a r e i m p o r t a n t . As a number o f a u t h o r s ( B r e t t , e t a l . , 1 969; B r e t t , 1 9 7 1 , 1974, 1976; S h e l b o u r n , e t a l . , 1 9 73; B r e t t a n d S h e l b o u r n , 1975) h a v e d e m o n s t r a t e d f o r s o c k e y e s a l m o n , g r o w t h r a t e i s n o t o n l y a f u n c t i o n o f w e i g h t b u t a l s o a f u n c t i o n o f r a t i o n l e v e l , d i e t a n d n u t r i t i o n , f e e d i n g r e g i m e n a n d t e m p e r a t u r e . The m o d e l , h o w e v e r , o n l y c o n s i d e r s e x p l i c i t l y t h e e f f e c t o f t e m p e r a t u r e on g r o w t h r a t e . T e m p e r a t u r e i s assumed t o a f f e c t c o h o , chum a n d p i n k g r o w t h r a t e i n much t h e same way a s i t d o e s s o c k e y e g r o w t h r a t e ( s e e B r e t t , 1 9 7 4 ) . F u r t h e r m o r e , t h e e q u a t i o n s i n T a b l e 4 a r e assumed t o h a v e b e e n d e r i v e d u n d e r o p t i m u m c o n d i t i o n s o f t e m p e r a t u r e (15°C) a n d f o o d a v a i l a b i l i t y . The e f f e c t o f c h a n g i n g e s t u a r i n e t e m p e r a t u r e ( f i g u r e 2) on g r o w t h r a t e i s t h e n s i m u l a t e d b y a p p l y i n g t h e t e m p e r a t u r e - c d e p e n d e n t f u n c t i o n i n f i g u r e 3. The f u n c t i o n i s a p p l i e d e q u a l l y t o a l l t h r e e s p e c i e s i n t h e m o d e l a l t h o u g h s e v e r a l a u t h o r s ( M a r t i n , 1966; H u r l e y a n d W o o d a l l , 1968; B r e t t , 1974) h a v e s u g g e s t e d t h a t t h e o p t i m u m t e m p e r a t u r e f o r p i n k s a l m o n g r o w t h i s l e s s t h a n 15°C,which may r e s u l t i n p i n k g r o w t h r a t e b e i n g u n d e r e s t i m a t e d 23 FIGURE 2. Average Monthly Temperature o f F r a s e r R i v e r E s t u a r y Estimated mean monthly temperature of Fraser River estuary (March-August) used in model. Based on Dunford (1975). FIGURE 3. E s t i m a t e d E f f e c t o f T e m p e r a t u r e on G r o w t h R a t e F u n c t i o n u s e d i n m o d e l t o e s t i m a t e t h e r e l a t i v e e f f e c t o f t e m p e r a t u r e on p i n k , chum and c o h o g r o w t h r a t e s . G r o w t h r a t e @ T°C = G r o w t h r a t e @ 15°C x t e m p e r a t u r e d e p e n d e n t p r o p o r t i o n o f maximum g r o w t h r a t e . T = mean m o n t h l y t e m p e r a t u r e i n t h e e s t u a r y . M o d e l f u n c t i o n i s a c o m p r o m i s e b e t w e e n w h a t i s known a b o u t c o h o a nd s o c k e y e g r o w t h r a t e s ( B r e t t , 1974; B r e t t a n d S h e l b o u r n , 1975) a n d t h e a s s e r t i o n t h a t p i n k f r y a r e a c o l d e r w a t e r s p e c i e s ( B r e t t , 1 9 7 4 ) . lOO-, 0-75-0-50-0 25-0 -i 1 1 i 5-6 10-11 15-16 20-21 Temperature (°C) ro r e l a t i v e t o c o h o g r o w t h r a t e . To d e t e r m i n e t h e p r a c t i c a l i t y o f t h e g r o w t h r a t e e q u a t i o n s i n T a b l e 4, I c o m p a r e d t h e e s t i m a t e d g r o w t h o f p i n k and chum f r y i n t h e m o d e l t o t h a t r e p o r t e d i n t h e l i t e r a t u r e ( f i g u r e 4 and f i g u r e 5 ) . The d a t a i n t h e f i g u r e s w e r e a d j u s t e d t o r e f l e c t a common i n i t i a l s i z e on d a y o f r e l e a s e b u t no a d j u s t m e n t was made f o r v a r i a b i l i t y i n t e m p e r a t u r e o r r a t i o n i n t a k e . O v e r a n e i g h t week p e r i o d , L e B r a s s e u r 1 s (1969) chum f r y grew, on a v e r a g e , b e t w e e n 4.4% a n d 4.8% p e r d a y a t 14 t o 15°C when f e d a b o u t 12% o f t h e i r w e t b o d y w e i g h t p e r d a y . The c o m p a r a b l e g r o w t h r a t e f o r w i l d p i n k s a l m o n was e s t i m a t e d b y L e B r a s s e u r (1969) t o be 4.5% p e r d a y , a l t h o u g h t h e w a t e r t e m p e r a t u r e was p r o b a b l y c o l d e r ( a b o u t 10°C, P a r k e r a n d L e B r a s s e u r , 1 9 7 4 ) . O v e r t h e same l e n g t h o f t i m e a t 10 t o 13°C p i n k f r y f r o m t h e A t n a r k o , r e a r e d i n 29 p a r t s p e r t h o u s a n d s a l i n i t y , g rew a t a b o u t 4.6% p e r d a y , a n d , p i n k f r y f r o m S w e l t z e r C r e e k , r e a r e d i n a n i n c r e a s i n g s a l i n i t y e n v i r o n m e n t , grew a t a b o u t 4.3% p e r d a y , when f e d a b o u t 20% o f t h e i r w e t b o d y w e i g h t p e r day ( b a s e d on d a t a t a k e n f r o m H u r l e y and W o o d a l l , 1 9 6 8 ) . f o r a n e q u i v a l e n t p e r i o d o f t i m e a t 15°C, t h e m o d e l e s t i m a t e s chum g r o w t h t o be a b o u t 5.5% p e r d a y and p i n k g r o w t h t o be a b o u t 5.1% p e r d a y . I f t e m p e r a t u r e d e p e n d e n t g r o w t h i s assumed t o e x i s t , a t a n a v e r a g e t e m p e r a t u r e o f 10°C, chum g r o w t h i s a b o u t 4.6% p e r d a y and p i n k g r o w t h i s a b o u t 4.3% p e r d a y . Thus t h e c o m p a r i s o n b e t w e e n t h e m o d e l and l i t e r a t u r e p i n k a n d chum g r o w t h r a t e s sterns ^ia^ouq^ab-le. 28 FIGURE 4. A v e r a g e W e i g h t o f Chum F r y i n t h e E s t u a r y E s t i m a t e d a v e r a g e w e i g h t o f chum f r y f e d d i f f e r e n t p r e y r a t i o n s ( a s p e r c e n t a g e s o f f i s h w e i g h t s ) a n d e s t i m a t e d w e i g h t o f m o d e l chum f r y o v e r t i m e i n t h e e s t u a r y . L i t e r a t u r e d a t a t a k e n f r o m L e B r a s s e u r , 1969. E.P. = E u p h a u s i a p a c i f i c a ; C P . = C a l a n u s p l u m c h r u s ; P.M. = P s e u d o c a l a n u s m i n u t u s ; E x c e s s = o f f e r e d more f o o d t h a n c o u l d be e a t e n p e r d a y . M o d e l o u t p u t a s sumes a c o n s t a n t t e m p e r a t u r e o f 15°C. 10-, C7> 8 j • O • E-P- 17% - LeBrasseur- 1969 O CP- 17% - LeBrasseur- 1969 D PM- 16% - LeBrasseur- 1969 * Excess LeBrasseur 1969 A Model oulput • . ? 6 -<x> CD C P D CD > < 4H1 8 A § 8 (9 A • ~l— 12 24 36 48 Days since re lease — i — 60 72 84 ro FIGURE 5. A v e r a g e W e i g h t o f P i n k F r y i n t h e E s t u a r y E s t i m a t e d a v e r a g e w e i g h t o f " r e a l " a n d m o d e l p i n k f r y o v e r t i m e i n t h e e s t u a r y . D a t a o f P a r k e r and L e B r a s s e u r a r e b a s e d on r e c o v e r i e s o f m a r k e d f i s h f r o m t h e B e l l a C o o l a R i v e r . D a t a o f H u r l e y and W o o d a l l a r e b a s e d on g r o w t h r a t e - s a l i n i t y e x p e r i m e n t s . P i n k f r y came f r o m t h e A t n a r k o R i v e r a n d S w e l t z e r C r e e k . M o d e l o u t p u t assumes a c o n s t a n t t e m p e r a t u r e EP CD CU CP o > < 10 -, 8 A el 4 i fro* m O 1963- Parker a LeBrasseur- 1974 • 1964 - Parker a LeBrasseur- 1974 A 1965 - Parker a LeBrasseur- 1974 A 1966- Parker a LeBrasseur - 1974 • Atnarko - Hurley a Woodall- 1968 * Model output • Sweltzer - Hurley a Woodall- 1968 o • • • x T r 12 2 4 36 4 8 Days since release 6 0 72 8 4 N e v e r t h e l e s s , p i n k g r o w t h r a t e , r e l a t i v e t o chum g r o w t h r a t e , may be t o o l o w i n t h e m o d e l : R i c k e r (1964) r e p o r t e d t h a t " p i n k s grow f a s t e r t h a n do chums a t c o m p a r a b l e a g e s o r s i z e s . " The p o s s i b l e i m p o r t a n c e o f t h i s f a c t o r t o r e l a t i v e p i n k a n d chum f r y e s t i m a t e s o f m o r t a l i t y i s e x p l o r e d . i i D e n s i t y T h ough W a l t e r s , e t a l . (1977) d i d n o t f i n d a n y i n d i c a t i o n o f f o o d l i m i t a t i o n a l o n g t h e c o a s t o f B r i t i s h C o l u m b i a , d e n s i t y d e p e n d e n t e f f e ' c t s o n g r o w t h c a n n o t be t o t a l l y e l i m i n a t e d , e s p e c i a l l y i f l o c a l e f f e c t s w i t h i n e s t u a r i e s a r e c o n s i d e r e d . F i g u r e 6 shows t h e ' f u f i c t i o n ^ ^ m o d e l u S ^ o u s e d ^ i n ©heemodel^'to explore t h e p o s s i b l e e f f e c t s o f d e n s i t y d e p e n d e n t g r o w t h o n t h e s u r v i v a l o f p i n k a n d chum f r y . The m o d e l assumes t h a t g r o w t h r a t e i s a s i m p l e f u n c t i o n o f d e n s i t y , a l t h o u g h R e i m e r ' s (197 3) w o r k on j u v e n i l e c h i n o o k s a l m o n i n S i x e s R - i v e r , O r e g o n , s u g g e s t s t h a t g r o w t h r a t e i s r e a l l y a c o m p l e x f u n c t i o n o f many i n t e r a c t i n g v a r i a b l e s : 1. c h a n g i n g e s t u a r i n e u t i l i z a t i o n p a t t e r n s b y f i s h 2. i n c r e a s i n g f i s h s i z e 3. c h a n g i n g n u t r i t i o n a l l e v e l and f o o d p r o d u c t i o n i n t h e e s t u a r y 4. c h a n g i n g f i s h d e n s i t y 5. p h y s i o l o g i c a l c h a n g e s a s s o c i a t e d w i t h s m o l t i n g 6. c h a n g e s i n t h e l e v e l o f c o m p e t i t i o n f r o m o t h e r s p e c i e s o f f i s h . 33 FIGURE 6. E s t i m a t e d E f f e c t o f D e n s i t y on G r o w t h R a t e Two f u n c t i o n s u s e d i n t h e m o d e l t o s i m u l a t e t h e e f f e c t o f f r y d e n s i t y on p i n k a nd chum f r y g r o w t h r a t e . M o d e l 1 assumes no d e n s i t y d e p e n d e n t e f f e c t s . M o d e l 2 assumes m o d e r a t e d e n s i t y d e p e n d e n c e ( e s t i m a t e d f r o m R e i m e r s , 1 9 7 3 ) . Number of pink and chum fry per hectare 35 i i i T e m p e r a t u r e a n d D e n s i t y When b o t h t e m p e r a t u r e a n d d e n s i t y a r e h y p o t h e s i z e d t o a f f e c t g r o w t h r a t e , t h e e f f e c t s a r e assumed t o be m u l t i p l i c a t i v e w h i c h p r o b a b l y r e s u l t s i n a more e x t r e m e r e d u c t i o n i n g r o w t h r a t e t h a n w o u l d o c c u r i n r e a l i t y . The a c t u a l r e d u c t i o n i n g r o w t h w o u l d be a c o m p l e x f u n c t i o n o f t e m p e r a t u r e a n d f o o d p r o d u c t i o n i n t h e e s t u a r y and d e n s i t y a n d m e t a b o l i c r e q u i r e m e n t s o f p i n k and chum f r y . i v Coho F e e d i n g D y n a m i c s J u v e n i l e c o h o f e e d i n g d y n a m i c s a r e d e a l t w i t h o n l y i n p a r t . Coho p r e d a t i o n on p i n k and chum f r y i s c a l c u l a t e d e x p l i c i t l y b u t c o h o i n t a k e o f a l t e r n a t i v e f o o d i t e m s s u c h as l a r v a l f i s h e s or zcjopranktorodsiassmedirdinplicitly -tocc)CGurnastfneeded t o make up t h e r e s t o f t h e i r t o t a l d a i l y f o o d requirements. I n t h e m o d e l d a i l y i n t a k e o f f i s h i s d e t e r m i n e d by b o d y w e i g h t : l o g 1 Q R = a + b l o g 1 Q W w h e r e R = c o n s u m p t i o n i n p e r c e n t b o d y w e t w e i g h t , W = w e i g h t ( g ) , a = 1.5, b = - 0 . 3 9 . D e r i v e d by B r e t t (1971]B) f o r s o c k e y e s a l m o n , t h i s f u n c t i o n i s b a s e d on t r i p l e d a i l y f e e d i n g s o f A b e r n a t h y p e l l e t s a t 15°C. I assume t h a t : 1. T h i s r e l a t i o n s h i p a p p l i e s t o c o h o s a l m o n . I n t e r m s o f t h e f e e d i n g r e s p o n s e o f c o h o t o p e l l e t s i n t h e e x p e r i m e n t a l s e t t i n g , t h e r e a p p e a r s t o be n o t much d i f f e r e n c e b e t w e e n s o c k e y e and c o h o ( B r e t t , p e r s o n a l c o m m u n i c a t i o n ) . R i s an e s t i m a t e o f t h e c o n s u m p t i o n o f f i s h i n p e r c e n t b o d y w e t w e i g h t . B r e t t was f o r c e d t o e s t i m a t e f o o d c o n s u m p t i o n i n p e r c e n t b o d y d r y w e i g h t b e c a u s e t h e m o i s t u r e c o n t e n t o f t h e p e l l e t s ( 2 7 . 4 % t o 35%) was d i f f e r e n t f r o m t h e f i s h ( 7 5 % t o 7 8 % ) . A s s u m i n g t h a t a l l s a l m o n i d f i s h e s h a v e t h e same r e l a t i v e m o i s t u r e c o n t e n t , f o o d c o n s u m p t i o n i n p e r c e n t b o d y d r y w e i g h t w i l l be r o u g h l y e q u a l t o p e r c e n t b o d y w e t w e i g h t . U s i n g f i s h a s f o o d i n s t e a d o f p e l l e t s w o u l d n o t c h a n g e t h e p a r a m e t e r e s t i m a t e s o r t h e f o r m o f t h e r e l a t i o n s h i p . T h i s a s s u m p t i o n i s somewhat t e n u o u s . A s B r e t t ( 1 9 7 1 a ; 1971b; p e r s o n a l c o m m u n i c a t i o n ) p o i n t s o u t , t h e r e a r e a number o f f a c t o r s c o n t r o l l i n g a p p e t i t e and h e n c e d a i l y i n t a k e : s t r e t c h r e c e p t o r s i n t h e s t o m a c h (amount a n d s i z e o f f o o d p a r t i c l e s i n g e s t e d ) , e n e r g y demand ( c a l o r i c c o n t e n t o f f o o d i n g e s t e d ) , d i g e s t i o n r a t e o f d i f f e r e n t f o o d p a r t i c l e s . I assume t h a t f i s h p r e y a r e consumed a t t h e same r a t e a s A b e r n a t h y p e l l e t s . The t r i p l e d a i l y f e e d i n g s i n t h e o r i g i n a l e x p e r i m e n t r e s u l t e d i n maximum i n t a k e o f f o o d . A d i f f e r e n t f e e d i n g r e g i m e n w o u l d c h a n g e t h e p r e d i c t i o n o f f o o d i n t a k e p e r d a y ( B r e t t , e t a l . , 1969; B r e t t , 1 9 7 1 a ) . N e v e r t h e l e s s I assume t h a t a n a t u r a l f e e d i n g r e g i m e n w o u l d n o t a l t e r t h e i n t a k e o f f o o d p r e d i c t e d b y t h e e q u a t i o n . 5. The r e l a t i o n s h i p i s temperature independent. B r e t t , et a l . '(1969) show t h a t , f o r sockeye, maximum food int a k e i s a f u n c t i o n of temperature and decreases as temperature decreases or increases from the optimal 15°C. Thus, because Brett; 1 s^experimentstwe'reaperformedpat optimal temperatMEesf^. in t a k e i s probably overestimated. Given these assumptions, over the s i z e range of coho found i n the model estuary, the maximum amount of f i s h ingested ranges between 9% and 11% of coho wet body weight. Coho growth r a t e i s independent of the p r o p o r t i o n of f i s h i n the d i e t . While some st u d i e s show d i f f e r e n c e s i n growth r a t e of salmon fed on p a r t i c l e s of d i f f e r e n t s i z e s (Baloheimo and D i c k i e , 1966) or of d i f f e r e n t n u t r i t i o n a l value ( B r e t t , 1971a), no study shows the e f f e c t of p r o p o r t i o n of f i s h i n the d i e t . Coho are a l s o assumed not to s u f f e r from d e n s i t y r e l a t e d reductions i n growth r a t e , e i t h e r from the presence of competing pink and chum f r y or from increased abundance of coho. I l l M o r t a l i t y The model assumes there i s a f i x e d amount of growth and m o r t a l i t y during downstream migr a t i o n and only deals e x p l i c i t l y w i t h what happens a f t e r the salmon f r y and smolts reach s a l t w a t e r . In the estuary there are two causes of m o r t a l i t y to pink and chum f r y considered i n the model: 1. l o w l e v e l n a t u r a l m o r t a l i t y t h a t i s n o t t h e e x p l i c i t f u n c t i o n o f any s p e c i f i c m o r t a l i t y a g e n t b u t r e p r e s e n t s n o n - c o h o p r e d a t i o n , d i s e a s e , e t c . 2. c o h o s m o l t p r e d a t i o n m o r t a l i t y ( s e e P r e d a t i o n s e c t i o n ) . Coho s m o l t s a r e a l s o assumed t o s u f f e r f r o m n a t u r a l m o r t a l i t y . The d a i l y r a t e s o f n o n - c o h o i n s t a n t a n e o u s m o r t a l i t y t o p i n k , chum a n d c o h o w e r e e s t i m a t e d f r o m d a t a g i v e n i n R i c k e r (1976) a n d a r e , r e s p e c t i v e l y , 0.00053, 0.00043, 0.00043. I V P r e d a t i o n i G e n e r a l A s s u m p t i o n s I n t h e m o d e l p i n k a n d chum f r y a r e i d e n t i f i e d b y s p e c i e s and age c l a s s ( d a t e o f a r r i v a l i n e s t u a r y ) . S p e c i e s d i f f e r e n c e s i n s i z e , g r o w t h r a t e , a b u n d a n c e and l e n g t h o f r e s i d e n c e i n t h e e s t u a r y a r e e x p l i c i t l y e x a m i n e d b u t b e h a v i o u r a l d i f f e r e n c e s t h a t m i g h t r e s u l t i n d i f f e r e n t i a l s u s c e p t i b i l i t y t o p r e d a t i o n , s u c h a s t h e t e n d e n c y o f chum f r y t o h i d e f r o m p r e d a t o r s ( B a k s h t a n s k y , 1964) o r t o s t a y l o n g e r i n t h e l i t t o r a l z o n e s t h a n p i n k f r y (Goodman, 19 75; H u r l e y a n d W o o d a l l , 19 68; D u n f o r d , 19 75; B l a c k b u r n , p e r s o n a l c o m m u n i c a t i o n ) , a r e n o t . The d u r a t i o n a n d amount o f p i n k and chum s p a t i a l o v e r l a p a n d i t s s u b s e q u e n t e f f e c t on s u r v i v a l a r e e x p l o r e d b y c h a n g i n g t h e a s s u m p t i o n s c o n t r o l l i n g e m i g r a t i o n f r o m t h e e s t u a r y . Coho s m o l t s a r e assumed t o r e m a i n i n t h e e s t u a r y u n t i l a l l v u l n e r a b l e - s i z e d p r e y a r e e i t h e r e a t e n o r h a v e m i g r a t e d . Unfortunately, the information does not e x i s t to es t a b l i s h a better numerical response. It might have been more r e a l i s t i c , perhaps, to have had coho begin to migrate out of the estuary afte r some minimum encounter threshold was reached. In one form the model assumes no e x p l i c i t prey refugia. The predator can eventually eat every member of a given age clas s . Another model option allows for predator avoidance, which can be i m p l i c i t l y accounted for by assuming a random d i s t r i b u -t i o n of attacks. Daily survivors of each prey type and size class are estimated by the zero category of the Poisson d i s t r i -bution : EXP (-k.b./a.) x y x where k^ = the number of prey_^ which could be eaten by one predator^ b. = t o t a l number of predators. 1 3 a^ = t o t a l number of prey^ k.b. = t o t a l demand for prey. (This assumes that x j c J x a l l predators., have a constant demand for prey ±.) k.b. i 3 a^ = number of attacks expected by each prey^ in d i v i d u a l (Gilbert, et a l . 1976). No allowance was made i n the model for predator f a c i l i -t a tion or i n h i b i t i o n . 40 i i M u l t i s p e c i e s D i s c Equation A m u l t i s p e c i e s v e r s i o n of the R o l l i n g d i s c equation i s used t o c a l c u l a t e the number o f pink and chum f r y eaten i n each age c l a s s by coho smolts. S p e c i f i c a l l y , NA. = TS a. p. D. 1 1 * i l 1 + V t . a . p . D . i where NAi = number of prey k i l l e d of type i TS = time spent s e a r c h i n g f o r and h a n d l i n g prey a^ = area covered per time s e a r c h i n g = p r o p o r t i o n of prey^. s u c c e s s f u l l y , pursued and k i l l e d D^ = d e n s i t y of prey^ i n the area searched t ^ = the amount of time spent h a n d l i n g each prey^ a t t a c k e d (based on Walters, course notes, 1977) In g e n e r a l , the equation allows each predator to consume pink and chum f r y a c c o r d i n g to t h e i r a v a i l a b i l i t y and p r o b a b i l i t y of b e i ng eaten, up to a maximum imposed by the time a v a i l a b l e and the gut c a p a c i t y of the p r e d a t o r . (For a d i s c u s s i o n of the d e r i v a t i o n and use of a m u l t i s p e c i e s v e r s i o n of the d i s c equation see Eggers, 1976; a d e r i v a t i o n o f the s i n g l e s p e c i e s equation can be found i n Charnov, 1973.) The f o l l o w i n g i s a d i s c u s s i o n o f the v a r i a b l e s i n the equation as they apply i n the model. 41 Area Searched and Density of Prey From f i g u r e 7 i t i s c l e a r t h a t " e f f e c t i v e volume" searched by the predator depends on the p o s i t i o n of the predator below the surface r e l a t i v e to the p o s i t i o n of the prey i n the water column. I t i s simp l e s t to assume that coho, pink and chum are d i s t r i b u t e d i n the same p o r t i o n of the water column ( i . e . at the surface) and that " e f f e c t i v e volume" equals " t o t a l area"searched. Thus, i n the model, area searched and densi t y are c a l c u l a t e d i n terms of a two-dimensional s u r f a c e . 2 That i s , area searched = 2 r DT. + TTr D where r = r e a c t i v e distance (m), 2 r = width of search path, DT_. = distance predator t r a v e l s per day (m) ; TT = 3.14159; and, D. = I 1 A" 2 where 1NL = abundance of prey^, A = area prey occupy (m ) , 2 D^  = number of prey ^ per m . Reactive Distance There i s l i t t l e data a v a i l a b l e on the v i s u a l a c u i t y of f i s h e s , p a r t i c u l a r l y salmon. Therefore, I used the f u n c t i o n c a l c u l a t e d by Kerr (1971) f o r brook t r o u t ( S a l v e l i n u s f o n t i n a l i s ) to estimate r e a c t i v e d istance (radius of sharp perception) of coho smolts. S p e c i f i c a l l y , 1/3 r - c g tan 9 where r = r e a c t i v e d i s t a n c e , tan 9 = 0.0096 (33 min. of a r c ) , c = 0.0124 (assumes s p h e r i c a l p a r t i c l e s of weight g and n e u t r a l d e n s i t y ) , g = prey weight (Kerr, 19 7 1 ) . FIGURE 7. The " e f f e c t i v e v o l u m e " o f w a t e r S e a r c h e d b y a p r e d a t o r , One e x a m p l e o f t h e g e o m e t r i c r e l a t i o n b e t w e e n t h e r a d i u s o f t h e v i s u a l f i e l d ( r ) , t h e d i s t a n c e (s) o f t h e p r e d a t o r ( s o l i d p o i n t ) f r o m t h e s u r f a c e a n d t h e r e s u l t i n g w i d t h o f t h e s e a r c h p a t h (E) and t h e " e f f e c t i v e v o l u m e " o f w a t e r s e a r c h e d by t h e p r e d a t o r , g i v e n t h e l o c a t i o n o f t h e p r e y . E x t r a p o l a t e d f r o m Ware ( 1 9 7 3 ) . 43 searched 44 Even though t h i s r e l a t i o n s h i p was not based on f i s h prey, i t seems to provide a reasonable estimate of r e a c t i v e distance ( f i g u r e 8). The data on distance of "sharp" v i s i b i l i t y of prey of various s i z e s f o r m u l l e t (5.5 cm) and horse mackeral (8.5 cm) was found i n Protasov (1970). The d i f f e r e n c e s between the two f i s h types are a t t r i b u t e d to d i f f e r e n t v i s u a l a c u i t i e s a s s o c i a t e d w i t h t h e i r mode of l i f e . Horse mackeral eat small plankton organisms which r e q u i r e sharp v i s i o n to capture and m u l l e t are mud foragers w i t h a correspondingly reduced heed f o r sharp v i s i o n . Salmon have average v i s u a l a c u i t y ( B r e t t and Groot, 1963). Reactive distance decreases w i t h decreasing water c l a r i t y or ambient l i g h t i n t e n s i t y (Hester, 1968; Duntley, 1963; c i t e d by Ware, 1973). Therefore I assume t h a t the r e l a t i o n s h i p estimates maximum r e a c t i v e distance ( f i g u r e 9) because the Fraser River i s a very t u r b i d r i v e r w i t h "transparency u s u a l l y l e s s than a meter and o f t e n l e s s than h a l f a meter (Northcote, 1976)." F i n a l l y , " v i s u a l a c u i t y i s p r i m a r i l y a f u n c t i o n of p u p i l diameter, which changes r e l a t i v e l y slowly w i t h i n c r e a s i n g body s i z e (Kerr, 1971)." Thus, i n the model, r e a c t i v e distance i s assumed to be independent of predator s i z e . Distance T r a v e l l e d per Day Distance t r a v e l l e d per day by coho i n search of prey depends on the speed of search. In most runs of the model, coho 45 FIGURE 8. R e a c t i v e D i s t a n c e E s t i m a t e d r e a c t i v e d i s t a n c e o f m u l l e t , h o r s e m a c k e r a l and m o d e l c o h o s m o l t s t o p r e y o r m a t e s o f v a r i o u s s i z e s (cm). The l i n e s w e r e f i t t e d b y e y e . Reactive distance (cm) o ro o oo o i ro o i OJ O o _ i o a . to a 2. 3 o 3 a co o < o -» CO CD 3 a o a> CD o o < 47 FIGURE 9. Relation between Prey Weight and Predator Reactive Distance Functional relationship between prey weight (g) and coho smolt reactive distance (m) used i n the model under maximum (clear) and minimum (turbid) v i s i b i l i t y conditions. X Clear • Turbid i — r I 2 T 3 T 4 Prey weight (g) 49 a r e a ssumed t o be s e a r c h i n g a t a r a t e o f f o u r b o d y l e n g t h s p e r s e c o n d , i n d e p e n d e n t o f b o d y s i z e . ( S u s t a i n e d swimming s p e e d o f c o h o o v e r t h e s i z e r a n g e s f o u n d i n t h e e s t u a r y d u r i n g s p r i n g . a n d summer i s a b o u t f o u r t o f i v e b o d y l e n g t h s p e r s e c o n d ( s e e G l o v a , 1 9 7 2 ) . ) S e n s i t i v i t y o f t h e m o d e l t o c h a n g e s i n t h i s p a r a m e t e r i s e x p l o r e d . E n c o u n t e r R a t e P r e y e n c o u n t e r r a t e i s a f u n c t i o n o f a r e a s e a r c h e d a n d d e n s i t y o f p r e y . The m o d e l assumes t h a t p r e y c o n s u m p t i o n r a t e i s d i r e c t l y r e l a t e d t o e n c o u n t e r r a t e e v e n t h o u g h p i n k a n d chum f r y a r e known t o f o r m s c h o o l s ( P a r k e r , 1968; Mason, 1974; F e l l e r , 1974; F e l l e r , e t a l . , 1 9 7 5 ) . S c h o o l s o f p r e y d e c r e a s e t h e p r o b a b i l i t y o f a p r e d a t o r r a n d o m l y e n c o u n t e r i n g a p r e y i t e m and t h u s p r e y e n c o u n t e r r a t e f o r a g i v e n v o l u m e s e a r c h e d w i l l v a r y o v e r t i m e d e p e n d i n g on t h e d e g r e e o f p r e y c o n t a g i o n ( J o n e s , 1 9 7 7 ) . "However, c o n s i d e r e d o v e r a l o n g e n o u g h p e r i o d o f t i m e , t h e a v e r a g e e n c o u n t e r r a t e p e r u n i t t i m e f o r a c o n t a g i o u s p r e y d i s t r i b u t i o n w i l l a p p r o a c h t h e same v a l u e a s w o u l d be t h e c a s e f o r a u n i f o r m p r e y d i s t r i b u t i o n w i t h t h e same mean p r e y d e n s i t y . ( J o n e s t , \ s l 9 7 7 ) . " N e v e r t h e l e s s , t h e r e a r e a number o f p r o b l e m s w h i c h s h o u l d be m e n t i o n e d . I f f o o d a v a i l a b i l i t y i s g r e a t e n o u g h t o q u i c k l y s a t i a t e t h e p r e d a t o r , c o n s u m p t i o n r a t e becomes z e r o w h i l e e n c o u n t e r r a t e r e m a i n s a t t h e same l e v e l ( J o n e s , 1 9 7 7 ) . A s d i s c u s s e d e a r l i e r , t o t a l d a i l y c o n s u m p t i o n d e p e n d s on f e e d i n g p a t t e r n . T h u s , a l t h o u g h t h e l o n g t e r m e n c o u n t e r r a t e p e r u n i t 50 t i m e may s t a y t h e same, r e g a r d l e s s o f p r e y d i s t r i b u t i o n , t h e l o n g t e r m c o n s u m p t i o n r a t e may c h a n g e . F u r t h e r m o r e , s i n c e t h e l o c a t i o n o f s c h o o l s o f p i n k a n d chum f r y i n t h e e s t u a r y may be d e p e n d e n t on f r y s i z e ( L e B r a s s e u r a n d P a r k e r , 1 9 6 4 ) , e n c o u n t e r r a t e o f a p a r t i c u l a r -s i z e d p r e y w i l l be n o n-random i f t h e p r e d a t o r s e l e c t i v e l y s e a r c h e s a n y one a r e a . C o n s u m p t i o n , a t l e a s t i n t e r m s o f numbers o f p r e y , w i l l v a r y a c c o r d i n g t o l o c a t i o n s e a r c h e d . P r o p o r t i o n o f p r e y s u c c e s s f u l l y p u r s u e d a n d k i l l e d O n l y a p r o p o r t i o n o f t h e p r e y e n c o u n t e r e d b y a p r e d a t o r o f a s p e c i f i c s i z e w i l l be s u c c e s s f u l l y p u r s u e d and k i l l e d . A number o f f a c t o r s may d e t e r m i n e t h i s p r o p o r t i o n s u c h a s : t h e r e l a t i v e s i z e o f p r e y and p r e d a t o r , t h e a b i l i t y o f t h e p r e y t o o u t r u n i t s p r e d a t o r , p r e d a t o r p r e f e r e n c e f o r c e r t a i n s i z e d p r e y , t h e a v a i l a b i l i t y o f p r e y t y p e s a n d s i z e s . P h y s i o l o g i c a l l i m i t a t i o n s o f t h e p r e d a t o r d e t e r m i n e t h e maximum s i z e a n d s h a p e o f p r e y e a t e n . F o r c o h o s a l m o n , t h e maximum i n g e s t i b l e p r e y s i z e h a s b e e n e s t i m a t e d a s : 1. 0.044 o f i t s b o d y w e i g h t ( S i b e r t a n d P a r k e r , 1 9 7 2 ) . T h i s means, f o r e x a m p l e , t h a t a 10 cm c o h o c o u l d e a t a chum o r p i n k f r y 42% o f i t s own b o d y l e n g t h . 2. 2. 50% o f i t s b o d y l e n g t h (Semko, 1 9 5 4 ) . F i g u r e 10 shows t h e s i z e o f f i s h p r e y a c t u a l l y f o u n d i n s t o m a c h s o f O n c o r h y n c h u s ( t a k e n f r o m d a t a o f B a r r a c l o u g h , 1967 a n d B a r r a c l o u g h a n d F u l t o n , 1 9 6 7 ) . The l a r g e s t f i s h p r e y FIGURE 10. Size of Fish Prey Found i n Oncorhynchus Size range of f i s h prey found i n stomachs of salmonids (Oncorhynchus). Source: Barraclough, 1967 and Barraclough and Fulton, 1967. (See Appendix I for l i s t of f i s h prey found i n stomachs.) • 0- gorbu scho-o l 0- fcisutch • 0- keta • 0 fshawytscha A 0- nerka • • o k • i • A g l O 1 1 I 1 25 50 75 100 125 o o ~5~0 175 200 225 250 Predator size (mm) 53 f o u n d i n a c o h o s t o m a c h was a P a c i f i c s a n d l a n c e (Ammodytes  h e x a p t e r u s ) — 5 1 . 2 % o f t h e c o h o ' s l e n g t h (162 mm). The i n t a k e o f p r e y b e l o w some t h r e s h o l d s i z e may a l s o be l i m i t e d due t o e n e r g e t i c r e a s o n s o r t o s i z e - s e l e c t i v e p r e d a t i o n ( P r i t c h a r d a n d T e s t e r , 1944; I v l e v , 1 9 6 1 ; K e r r , 1 9 7 1 ; P a l o h e i m o a n d D i c k i e , 1966; W e r n e r , 1974; W e r n e r a n d H a l l , 1974; W e r n e r a n d H a l l , 1 9 7 6 ) . The d i s t a n c e s e p a r a t i n g p r e y a n d p r e d a t o r , t h e i r r e l a t i v e b u r s t s p e e d c a p a c i t i e s a n d t h e i r e n d u r a n c e d e t e r m i n e s t h e a b i l i t y o f a f i s h p r e y t o o u t r u n i t s p r e d a t o r . R e l a t i v e l o c o m o t i v e c a p a c i t y o f f i s h d e c r e a s e s a s f i s h i n c r e a s e i n s i z e ( B r e t t , 1964; G l o v a , 1 9 7 2 ) . F u r t h e r m o r e , t i m e t o f a t i g u e d e c -g . e a s e s s a s v e l o c i t y i i n c r e a s e s . / ; sespeGia-blylat' b u r s t r s p e e d s _ ( B r e t t , 19,64,-);^, T h e s e . f a c t o r y c o m b i n e t o d e t e r m i n e 1 - w h a t ? H o l d i n g , ( p e r s . eomm":) s c a l l s " " strrike.ced-i-sta>ncie-.4t'he: maximum ^ d i s t a n c e - w h i c h c o u l d s e p a r a t e p r e d a t o r a n d p r e y a n d s t i l l r e s u l t i n s u c c e s s f u l c a p t u r e o f t h e p r e y . I n a c r u d e a p p r o x i m a t i o n o f t h e a b o v e f a c t o r s I e s t i m a t e d t h e f u n c t i o n a l r e l a t i o n s h i p b e t w e e n f i s h p r e y s i z e a n d s t r i k e d i s t a n c e ( f i g u r e 1 1 ) . I f r e a c t i v e d i s t a n c e i s a l w a y s l e s s t h a n s t r i k e d i s t a n c e f o r a l l p r e y l e s s t h a n t h e maximum i n g e s t i b l e s i z e ( a s i n t u r b i d w a t e r , f i g u r e 1 2 ) , t h e n f a c t o r s o t h e r t h a n t h e a b i l i t y o f t h e p r e y t o o u t r u n t h e p r e d a t o r ( s u c h a s p r e d a t o r p r e y p r e f e r e n c e ) d e t e r m i n e t h e p r o b a b i l i t y o f p r e y e s c a p e . I n t h e m o d e l , s t r i k e d i s t a n c e i s n o t c o n s i d e r e d b e c a u s e t h e a b o v e c o n d i t i o n i s a l m o s t a l w a y s t r u e . T h u s , i n t h e m o d e l , t h e p r o p o r t i o n o f p r e y e a t e n was d e t e r m i n e d b y p r e y w e i g h t r e l a t i v e t o p r e d a t o r w e i g h t , a n d 54 FIGURE 1 1 . S t r i k e D i s t a n c e E s t i m a t e d r e l a t i o n s h i p b e t w e e n p r e d a t o r s i z e ( c m ) , p r e y s i z e (cm) a n d maximum d i s t a n c e (m) s e p a r a t i n g p r e y a n d p r e d a t o r ( s t r i k e d i s t a n c e ) t h a t w o u l d s t i l l e n e r g e t i c a l l y p e r m i t t h e s u c c e s s f u l c a p t u r e o f t h e p r e y . 56 FIGURE 1 2 . Re : R e l a t i o n . b e t w e e n S.trike'-cSista.'n;G:e:e a n d R e a c t i v e D i s t a n c e R e l a t i o n s h i p b e t w e e n s t r i k e d i s t a n c e a n d r e a c t i v e d i s t a n c e . The l a r g e s t p i n k f r y a 14 cm c o h o . c a n e a t i s a b o u t 1.37 g (5.5 cm) i f t h e maximum p r e y s i z e i s 0.044 ( S i b e r t a n d P a r k e r , 1972) o f c o h o b o d y w e i g h t ; o r a b o u t 2.6 g (6.9 cm) i f t h e maximum p r e y s i z e i s 0.08 5 o f c o h o b o d y w e i g h t ( s e e R e s u l t s ) . Thus t h e a b i l i t y o f c o h o t o c a p t u r e p i n k p r e y ( a n d chum p r e y ) i s n o t s i g n i f i c a n t l y a f f e c t e d b y s t r i k e d i s t a n c e , g i v e n t h e r e a c t i v e d i s t a n c e s u s e d i n t h e m o d e l . •Reactive distance x Strike distance 8 cm- prey Prey wei ght ( g) t h e s h a p e o f t h e f u n c t i o n ( f i g u r e 13) was m o d i f i e d t o e x p l o r e t h e e f f e c t s o f s i z e s e l e c t i v i t y a n d c h a n g e s i n maximum i n g e s t i b l e s i z e . C h a n g e s i n t h e a v a i l a b i l i t y o f p r e y t y p e s a n d s i z e s w e r e assumed n o t t o a l t e r t h e s e f u n c t i o n s . T o t a l S e a r c h i n g a n d H a n d l i n g Time The m o d e l assumes t h a t c o h o s a l m o n s e a r c h f o r p i n k a n d chum f r y t h r o u g h o u t t h e d a y ( b e t w e e n 12 a n d 17 h o u r s ) a t a b o u t t h e same l e v e l o f i n t e n s i t y . T h i s i s b a s e d on a r e p o r t o f c o h o f e e d i n g b e h a v i o u r i n Chatham S o u n d b y M a n z e r ( 1 9 6 9 ) . f;- " i ^ l i H a n d l i n g Time I n f o r m a t i o n o n c o h o h a n d l i n g t i m e o f i n d i v i d u a l p r e y i t e m s was l a c k i n g . I n t h e m o d e l i t was e s t i m a t e d a s : W. TS t . = l l RA . 3 w h e r e t ^ = r e ^ a t i v e ^ t i m e ^ n s p e n t j " handling.---pre'y^ ( h o u r s ) , w^ = w e i g h t o f p r e y ^ (g) , RA.. = e s t i m a t e d maximum d a i l y i n t a k e o f f o o d (g) by p r e d a t o r _ . , TS = t i m e s p e n t s e a r c h i n g a n d h a n d l i n g ( h o u r s ) . T h i s r e l a t i o n s h i p a s s umes t h a t h a n d l i n g t i m e p e r - i n d i v i d u a l • prey i n e r j e a s e s - i n r d i r e c t r p r o p o r . t i - o n to. p r e y s i z e . F u r t h e r m o r e , t h e e q u a t i o n a s sumes t h a t t h e r a t i o o f i n t a k e o f a p a r t i c u l a r p r e y i t e m t o t h e e s t i m a t e d t o t a l d a i l y i n t a k e o f f o o d i s d i r e c t l y p r o p o r t i o n a l t o p r e y s i z e - ( g i v e n a c o n s t a n t r a t e o f s u c c e s s f u l p r e y c a p t u r e o v e r s i z e ) . FIGURE 13. P r o p o r t i o n o f E n c o u n t e r e d P r e y S u c c e s s f u l l y C a p t u r e d a n d E a t e n T h r e e f u n c t i o n s d e s c r i b i n g t h e p r o p o r t i o n ( P i ) o f e n c o u n t e r e d p r e y s u c c e s s f u l l y c a p t u r e d a n d e a t e n . F u n c t i o n 1 assumes t h a t t h e p r o p o r t i o n e a t e n i s a d e c r e a s i n g f u n c t i o n o f i n c r e a s i n g p r e y w e i g h t . F u n c t i o n 2 assumes t h a t a c o n s t a n t p r o p o r t i o n o f a l l p r e y b e l o w a t h r e s h o l d s i z e i s e a t e n ( t h a t i s , t h e y a r e e q u a l l y v u l n e r a b l e t o p r e d a t i o n r e g a r d l e s s o f s i z e ) . F u n c t i o n 3 assumes t h a t p r e d a t o r p r e f e r e n c e f o r l a r g e r p r e y r e s u l t s i n a r e d u c e d c o n s u m p t i o n o f p r e y b e l o w a t h r e s h o l d s i z e . SW = C x PAR w h e r e C = p r e d a t o r s i z e ( g ) , PAR = p a r a m e t e r d e f i n i n g maximum i n g e s t i b l e p r e y s i z e , a n d SW = maximum p r e y s i z e p r e d a t o r c a n e a t . Function Function 2 Function 3 T r SW/2 2SW/3 Prey weight 61 CHAPTER I I I . RESULTS AND DISCUSSION 1. I n t r o d u c t i o n I n s i m u l a t i o n m o d e l l i n g , one o f t h e most i m p o r t a n t t a s k s i s d e t e r m i n i n g w h i c h e l e m e n t s o f t h e m o d e l a r e s e n s i t i v e t o c h a n g e . T h e s e c r i t i c a l e l e m e n t s c o n s t i t u t e a t a r g e t f o r f u r t h e r i n v e s t i g a t i o n , p o l i c y c h a n g e s and m a n i p u l a t i o n ( G a l l o p i n , 1 9 ? ) o f b o t h t h e m o d e l and r e a l s y s t e m . Thus t h e s e n s i t i v i t y o f t h e m o d e l t o c h a n g e s i n a s s u m p t i o n s a nd p a r a m e t e r v a l u e s was e x p l o r e d i n d e p t h . ( F o r a c o m p l e t e l i s t o f t h e p a r a m e t e r s a nd r a n g e o f v a l u e s t e s t e d s e e A p p e n d i x I I . ) I n v i e w o f t h e many s o u r c e s o f m e a s u r e m e n t e r r o r a n d e n v i r o n m e n t a l v a r i a b i l i t y i n h e r e n t i n t h e n a t u r a l s y s t e m , i t seems u n l i k e l y t h a t a 5% o r e v e n a 10% c h a n g e i n t h e m o d e l r e s u l t s , due t o m a n i p u l a t i o n o f some p a r a m e t e r , c o u l d be d e t e c t e d i n t h e r e a l s y s t e m . F o r e x a m p l e , a s s i g n m e n t o f c a t c h a n d e s c a p e m e n t t o t h e F r a s e r R i v e r i s b a s e d on t a g g i n g , ^ c o u n t s a nd t i m i n g o f r u n s w h i c h a c c o u n t f o r a v a r i a b l e s o u r c e and m a g n i t u d e o f e r r o r i n t h e mea s u r e m e n t o f a d u l t r e t u r n . F u r t h e r m o r e , t h e o r i g i n a l e s t i m a t e s o f e g g a a n d j u v e n i l e a b u n d a n c e a r e s u b j e c t t o v a r i o u s f o r m s o f mea s u r e m e n t e r r o r . N e v e r t h e l e s s , a s a s t a r t i n g p o i n t f o r d i s c u s s i o n , I a r b i t r a r i l y c o n s i d e r e d t h e m o d e l s e n s i t i v e i f a c h a n g e i n p a r a m e t e r v a l u e o r a s s u m p t i o n r e s u l t e d i n a g r e a t e r t h a n 5% i n c r e a s e o r d e c r e a s e i n p i n k o r chum f r y m o r t a l i t y . P a r a m e t e r s , . w h i c h c o u l d be m a n i p u l a t e d b y m a n a g e r s r e s p o n s i b l e f o r c o n s t r u c t i o n a n d o p e r a t i o n o f e n h a n c e m e n t f a c i l i t i e s , a r e d i s c u s s e d i n t h a t c o n t e x t . To g a i n some u n d e r s t a n d i n g o f t h e p o s s i b l e c o n s e q u e n c e s o f e n h a n c e m e n t , s e v e r a l p i n k and chum e n h a n c e m e n t e x p e r i m e n t s w e r e done u s i n g t h e m o d e l . T h e s e e x p e r i m e n t s a r e e v a l u a t e d n o t o n l y on t h e b a s i s o f f r y s u r v i v a l o r a d u l t r e t u r n , b u t a l s o , w h e r e p o s s i b l e , o n t h e b a s i s o f w i l d s t o c k , s u r v i v a l v e r s u s e n h a n c e d s t o c k s u r v i v a l . I m p a c t on c o h o s t o c k s i s c o n s i d e r e d o n l y i n t e r m s o f c h a n g e s i n t h e number o f p i n k and chum f r y consumed p e r c o h o . The i n t a k e o f f r y p r e y by c o h o s m o l t s i s assumed t o be a maximum u n d e r e a c h s e t o f s i m u l a t i o n c o n d i t i o n s : 1. The m o d e l d o e s n o t a l l o w f o r p r e y r e f u g i a . 2. The m o d e l assumes 100% o v e r l a p o f p r e y and p r e d a t o r s p a t i a i b u d i S i t r i b u t i o n s . 3. Coho p r e d a t o r s a r e assumed t o p r e f e r f i s h p r e y a n d c o n s e q u e n t l y consume a s many f i s h a s s t o m a c h c a p a c i t y , p r e y a v a i l a b i l i t y a nd v u l n e r a b i l i t y w i l l a l l o w . 4. Coho a r e assumed n o t t o s u f f e r f r o m r e d u c e d g r o w t h o r s u r v i v a l due t o l a c k o f f o o d . 5. T h e r e i s no f e e d i n g i n h i b i t i o n o r i n t e r f e r e n c e . S e v e r a l a v e n u e s o f i n v e s t i g a t i o n s u g g e s t e d b y t h e m o d e l r e s u l t s w e r e e x p l o r e d u s i n g p e r t i n e n t d a t a f o u n d i n t h e l i t e r a t u r e . 2. S e n s i t i v i t y A n a l y s i s I Components of Predation The model r e s u l t s are r e l a t i v e l y i n s e n s i t i v e to most of the components of predation. I found t h a t even comparing extreme combinations of the parameter values (minimum r e a c t i v e d i s t a n c e , 1 body length per second search v e l o c i t y , 45957 hectares search area and 4 hours search time versus maximum r e a c t i v e d i s t a n c e , 5 body lengths per second search v e l o c i t y , 15319 hectares search area and 16 hours search t i m e ) , pink f r y m o r t a l i t y only increased from 32.8% to 37.0% and chum f r y m o r t a l i t y from 9.0% to 10.2%. I n c r e a s i n g the maximum i n g e s t i b l e prey s i z e , however, r e s u l t e d i n a 20 to 23 percent increase (see Table 5) i n pink f r y m o r t a l i t y and a 21 to 26 percent increase i n chum f r y m o r t a l i t y due to the increase i n f r y v u l n e r a b i l i t y . The average number of f r y eaten per coho per day decreased (Table 5) because being able to eat l a r g e f r y , reduced the number of f r y needed to s a t i s f y the coho's d a i l y r a t i o n requirements. In general, the model r e s u l t s were not s e n s i t i v e to changes i n the f u n c t i o n ( f i g u r e 13) used to determine the pro p o r t i o n of encountered pink and chum f r y eaten by coho smolts. However, i f the maximum i n g e s t i b l e prey s i z e was increased, t o t a l chum f r y m o r t a l i t y d i d increase (about 6.1%) using Function 3 versus Function 1 (see Table 5). As chum f r y from any one age c l a s s are g e n e r a l l y l a r g e r than pink f r y from the same age c l a s s , coho preference f o r l a r g e prey (Function 3) has a greater r e l a t i v e impact on chum f r y than TABLE 5. S e n s i t i v i t y o f m o d e l r e s u l t s t o c h a n g e s i n t h e e s t i m a t e d maximum f i s h s i z e Icoho a r e c a p a b l e o f i n g e s t i n g , u s i n g two d i f f e r e n t f u n c t i o n s t o d e s c r i b e t h e p r o p o r t i o n o f e n c o u n t e r e d f i s h p r e y s u c c e s s f u l l y e a t e n . P i n k a n d chum f r y m i g r a t i o n b e g i n s M a r c h 1. P r e y : p r e d a t o r r a t i o i s 11 1 5 : 1 . Chum f r y compose 15% o f t h e t o t a l p r e y p o p u l a t i o n . MAXIMUM INGESTIBLE F R Y ^ S I Z E 0.044 0.085 ( o f c o h o -i ( o f c o h o 2 b o d y w e i g h t ) b o d y w e i g h t ) P i n k % m o r t a l i t y 57 .7 78.2 Chum % m o r t a l i t y 29.6 51.4 FUNCTION 3 F r y e a t e n / c b h o / d a y 3.13 2.51 w EH 1. Maximum # o f < W v u l n e r a b l e d a y s 33 48 O ORTI P i n k % m o r t a l i t y 58 .5 81.5 PH o Chum % m o r t a l i t y 31.0 57 .5 a, •: 3 FUNCTION F r y e a t e n / c o h o / d a y 3.19 2.26 3. Maximum # o f v u l n e r a b l e d a y s 33 54 A b o u t 42% o f c o h o b o d y l e n g t h . A b o u t 50% o f c o h o b o d y l e n g t h . S i m u l a t i o n s assumed d e n s i t y d e p e n d e n t g r o w t h r a t e f o r p i n k a n d chum f r y (mo d e l 2 ) . on p i n k f r y . N e v e r t h e l e s s , p i n k f r y s t i l l s u f f e r a h i g h e r p r e d a t i o n m o r t a l i t y t h a n chum f r y b e c a u s e o f t h e i r g r e a t e r a b u n d a n c e and v u l n e r a b i l i t y (78 t o 82 p e r c e n t v e r s u s 51 t o 58 p e r c e n t , r e s p e c t i v e l y ) . The c o h o ' s p r e f e r e n c e f o r l a r g e r p r e y , r e f l e c t e d i n t h e s h a p e o f F u n c t i o n 3 v e r s u s F u n c t i o n 1, I!>b€ffered" s m a l l p i n k a n d chum f r y f r o m p r e d a t i o n . A l t h o u g h t h e t o t a l number o f p i n k and chum f r y e a t e n was g r e a t e r u s i n g Func«ti6ni:3, c o m p a r e d on a c o h o r t t o c o h o r t b a s i s ( F u n c t i o n 3 v e r s u s F u n c t i o n 1), some c o h o r t s a c t u a l l y h a d a h i g h e r s u r v i v a l r a t e b e c a u s e c o h o p r e f e r e n c e f o r l a r g e f r y g a v e s m a l l f r y a c h a n c e t o grow o u t o f t h e v u l n e r a b l e s i z e r a n g e . U s i n g F u n c t i o n 3 a l s o r e d u c e d t h e a v e r a g e r a t e o f f r y i n t a k e f r o m 2.5 t o 2.3 p e r d a y ( T a b l e 5) b e c a u s e i t t o o k f e w e r l a r g e p r e y t o s a t i s f y t h e d a i l y r a t i o n n e e d s o f t h e c o h o . I n a r e a l s e n s e , t h e c o h o i s " c o n s e r v i n g " l i t - s f o o d s u p p l y : b y . " a l l o w i n g " t h e f r y t o grow, t h e c o h o r e q u i r e s f e w e r p e r d a y and t h e s u p p l y l a s t s l o n g e r ( f r o m 48 t o 54 d a y s ) . ( T h i s a s sumes t h a t t h e f r y r e m a i n a v a i l a b l e a n d a r e n o t e a t e n b y some o t h e r p r e d a t o r . ) T h i s c o n c e p t may a p p l y t o a l l p r e y t y p e s t o some e x t e n t a n d may be e v e n more i m p o r t a n t t o s p e c i a l i s t p r e d a t o r s t h a n t o g e n e r a l i s t p r e d a t o r s l i k e c o h o s a l m o n . N e v e r t h e l e s s , i t s h o u l d be remembered t h a t d i f f e r e n c e s o r c h a n g e s i n p r e y v u l n e r a b i l i t y , r a t h e r t h a n p r e d a t o r p r e y p r e f e r e n c e , s e l e c t i v i t y o r c h a n g i n g s e a r c h i m a g e , e t c . , may a c c o u n t f o r t h e p r e y c o n s u m p t i o n p a t t e r n o f p r e d a t o r s . T h i s f a c t m u s t be c o n s i d e r e d (and o f t e n i s n o t ) when d e s i g n i n g l a b o r a t o r y p r e d a t i o n e x p e r i m e n t s s u c h a s P a r k e r ' s (1971). "The s e l e c t i v i t y o b s e r v e d ( i n t h e e x p e r i m e n t ) w i l l be t h e r e s u l t o f p r e f e r e n c e shown b y t h e a n i m a l f o r t h i s o r t h a t k i n d o f f o o d o n l y i f a l l t h e f o o d c o m p o n e n t s a r e i n a s t a t e i n w h i c h t h e d i f f i c u l t i e s e n c o u n t e r e d b y t h e c o n s u m e r a n i m a l i n p r o c u r i n g them a r e a b s o l u t e l y e q u a l ( I v l e v , 1 9 6 1 , c i t e d b y H y a t t , 1 9 7 6 ) . " W i t h o u t some m e a s u r e o f maximum i n g e s t i b l e p r e y i s i i z e , p r e y v u l n e r a b i l i t y c a n n o t be d e t e r m i n e d . The s e n s i t i v i t y o f t h e m o d e l r e s u l t s t o c h a n g e s i n t h i s p a r a m e t e r s u g g e s t s t h a t t h i s i s a n i m p o r t a n t a r e a f o r f u t u r e r e s e a r c h . A l l o w i n g f o r p r e y a v o i d a n c e o f p r e d a t o r s , u s i n g t h e z e r o c a t e g o r y o f t h e P o i s s o n d i s t r i b u t i o n ( s e e M e t h o d s , g e n e r a l a s s u m p t i o n s o f P r e d a t i o n ) , d i d n o t l e a d t o a s i g n i f i c a n t r e d u c t i o n ( 5 % ) i n p i n k o r chum f r y m o r t a l i t y . I". I l e O a P . r e d a t o r S i z e a t M i g r a t i o n i n t o E s t u a r y F o r l a c k o f a n y b e t t e r i n f o r m a t i o n , mean i n i t i a l s i z e o f c o h o s m o l t s i n t h e m o d e l was 11 cm. Goodman's (1975) d a t a s u g g e s t t h a t t h i s s i z e e s t i m a t e may be t o o h i g h b u t t h e s i z e r a n g e o f c o h o i n h i s s a m p l e s seems t o i n d i c a t e t h e p r e s e n c e o f b o t h f r y a n d y e a r l i n g s a n d p o s s i b l y , s e c o n d y e a r j u v e n i l e c o h o (21-129 mm r a n g e f r o m t h e N o r t h , M i d d l e a n d S o u t h a rms; 38-245 mm r a n g e f r o m S t u r g e o n and R o b e r t s B a n k s ) . To t e s t t h e i m p o r t a n c e o f o v e r e s t i m a t i n g mean c o h o s i z e on t h e e s t i m a t e s o f p i n k a n d chum f r y m o r t a l i t y , I d e c r e a s e d t h e mean i n i t i a l s i z e o f c o h o f r o m 11 cm t o 9.5 cm. P i n k f r y m o r t a l i t y d e c r e a s e d f r o m 81.5% t o 66.6% a n d chum f r y m o r t a l i t y d e c r e a s e d f r o m 57.5% t o 39.3% ( u s i n g F u n c t i o n 3, f i g u r e 1 3 , t o d e t e r m i n e t h e p r o p o r t i o n o f f r y e a t e n ; maximum i n g e s t i b l e p r e y s i z e i s 0.085 o f c o h o b o d y w e i g h t ) . O b v i o u s l y p r e d i c t i o n of the r e l a t i v e and d i r e c t importance of wild and enhancement coho smolt predation on pink and chum f r y w i l l be s i g n i f i c a n t l y affected by the estimated or r e a l average size of the coho. This r e s u l t should be given serious consideration as i n i t i a l size of coho smolts released from enhancement f a c i l i t i e s can be controlled to some extent (Smith, 197 8). I l l Timing and Duration of pink and Chum Fry Migration As Table 6 indicates, the model res u l t s were sensitive to changes i n f r y migration timing c(tfel'afe'ive:Lto ( r e 3 - i - i c -a fixed s t a r t i n g date for coho migration). Although, on any one day, a greater number of both pink and chum f r y are vulnerable to coho predation i f the i r migration i s delayed (consequently shortening the duration and increasing the number of f r y migrating per day), chum f r y mortality a c t u a l l y decreases or remains r e l a t i v e l y constant (e.g. 15.0% versus 12.2%) while pink f r y mortality increases (e.g. 39.8% versus 52.3%). The increased density of vulnerable pink f r y i n the estuary buffers chum f r y from predation. The interaction of b i o l o g i c a l assumptions does not always r e s u l t i n simple additive or m u l t i p l i c a t i v e changes. This makes i t d i f f i c u l t to predict i n advance the di r e c t i o n and magnitude of changes i n model res u l t s due to the addition of or change i n the b i o l o g i c a l assumption. For example, pink and chum f r y may be affected d i f f e r e n t l y (see previous example from Table 6) or the r e l a t i v e change i n mortality may be d i f f e r e n t because of concomitant changes i n density TABLE 6. S e n s i t i v i t y o f m o d e l r e s u l t s t o c h a n g e s i n t h e e s t i m a t e d s t a r t i n g d a t e o f t h e v p i n k and chum f r y m i g r a t i o n a n d t o c h a n g e s i n t h e a s s u m p t i o n s a f f e c t i n g p i n k and chum g r o w t h r a t e . The s t a r t i n g d a t e o f t h e c o h o s m o l t m i g r a t i o n i s c o n s t a n t . F r y m o r t a l i t y i s due t o c o h o s m o l t p r e d a t i o n o n l y a n d o c c u r s d u r i n g t h a t e a r l y p e r i o d o f e s t u a r i n e l i f e when t h e f r y a r e s t i l l a v a i l a b l e a n d v u l n e r a b l e . The maximum i n g e s t i b l e f r y s i z e i s assumed t o be 0.044 o f t h e c o h o ' s body w e i g h t . P r e y : p r e d a t o r r a t i o i s 1 1 5 : 1 . Chum f r y compose 15% o f t h e t o t a l p r e y p o p u l a t i o n . No T e m p e r a t u r e o r D e n s i t y E f f e c t s T e m p e r a t u r e O n l y D e n s i t y O n l y ( m o d e l 2) T e m p e r a t u r e & D e n s i t y :(model 2) MIGRATION BEGINS MARCH 1 % p i n k f r y m o r t a l i t y 29.5 ,3.9. .18 57.7 71.2 % chum f r y m o r t a l i t y 12.8 15.0 29.6 36. 3 c o n t ' d . TABLE 6, P a g e 2. No T e m p e r a t u r e D e n s i t y T e m p e r a t u r e o r D e n s i t y T e m p e r a t u r e O n l y & D e n s i t y E f f e c t s O n l y ( m o d e l 2) ( m o d e l 2) MIGRATION BEGINS MARCH 15 % p i n k f r y 36.9 52.3 74.7 87.7 m o r t a l i t y % chum f r y 10.2 12.2 30.0 37.3 m o r t a l i t y P i n k m i g r a t i o n p e a k s A p r i l 14-15; chum m i g r a t i o n p e a k s A p r i l 1 1 -12; c o h o m i g r a t i o n p e a k s May 1-2. D e n s i t y o f p i n k a n d chum f r y i n t h e e s t u a r y p e a k s a b o u t May 1-2. P i n k m i g r a t i o n p e a k s A p r i l 21; chum m i g r a t i o n p e a k s A p r i l 18; c o h o m i g r a t i o n p e a k s May 1-2. D e n s i t y o f p i n k a n d chum f r y i n t h e e s t u a r y p e a k s a b o u t May 70 (figure 14), temperature (figure 2), etc. Table 6 also provides several examples of th i s l a t t e r e f f e c t (e.g. comparing the increase i n pink f r y mortality due to the added assumption of temperature dependent growth, the r e l a t i v e increase i n pink mortality i s 34.9% i f the fry begin to migrate March 1 and 41.7% i f they migrate March 15.) 71 FIGURE 14. R e l a t i o n B e t w e e n F r y D e n s i t y P a t t e r n a n d S t a r t i n g ©ate o f F r y M i g r a t i o n T o t a l d e n s i t y o f p i n k a n d chum f r y o v e r t i m e , r e l a t i v e t o t h e i r d a t e o f a r r i v a l i n t h e e s t u a r y . D e n s i t y o f c o h o s m o l t s (X10) i s g i v e n f o r c o m p a r i s o n . The F r a s e r R i v e r e s t u a r y i s assumed t o be 15,319 h e c t a r e s . The p r e y : p r e d a t o r r a t i o i s 1 1 5 : 1 . F r y g r o w t h r a t e i s n o t a f f e c t e d b y t e m p e r a t u r e o r d e n s i t y . Pink and Chum fry • March I + March 15 Coho smolts (xlO) © April 23 IV Growth r a t e S e n s i t i v i t y to v a r i o u s parameter changes increases s u b s t a n t i a l l y i f the assumptions c o n t r o l l i n g growth r a t e a l s o change. For example, w i t h no d e n s i t y e f f e c t s on growth, area of d i s p e r s i o n i s not important over the range of values t e s t e d , but w i t h d e n s i t y dependent growth (model 2, f i g u r e 6), i n c r e a s i n g the area from 15319 hectares to 30638 hectares decreased pink f r y m o r t a l i t y 37% (from 74.3% to 37.6%) and chum f r y m o r t a l i t y 19% (from 29.7% to 10.5%). Further increases i n area produced i n s i g n i f i c a n t changes i n m o r t a l i t y r a t e . To explore the s e n s i t i v i t y of the model r e s u l t s to an increase i n estimated pink f r y growth r a t e , I used the r e l a t i o n s h i p found i n B r e t t and Shelbourn (1975) to c a l c u l a t e pink growth r a t e : l o g e G = l o g e 9.7 8 - 0.4 5 l o g e W where G = instantaneous growth r a t e x 100, W = weight (g). The above parameterization seems to overestimate pink f r y growth r a t e (see d i s c u s s i o n of growth r a t e , B i o l o g i c a l B a sis of the model) whereas the parameterization g e n e r a l l y used i n the model (Table 4) may underestimate pink f r y growth r a t e , r e l a t i v e to chum f r y growth r a t e , during t h e i r e a r l y stages of l i f e i n the estuary. Experimetttfa'tfrora (Table Head to: thve f^Mowi'rtgV-ob'S'erVaTtio'ffs +a*n:d 'conclusion's": - .. • •; rlv; 1 js:Un'dea: c e r t a i n assumptions i n c r e a s i n g pink growth rate s u b s t a n t i a l l y decreased TABLE 7. S e n s i t i v i t y o f m o d e l r e s u l t s t o c h a n g e s i n e s t i m a t e d p i n k f r y g r o w t h r a t e a n d f r y m i g r a t i o n d a t e u n d e r v a r i o u s a s s u m p t i o n s a f f e c t i n g p i n k and chum g r o w t h r a t e i n t h e e s t u a r y . P r e y : p r e d a t o r r a t i o i s 1 1 5 : 1 . Chum f r y compose 15% o f t h e t o t a l p r e y p o p u l a t i o n . MARCH 1 MARCH 15 A B A B No 29. 5 19 .1 36 .9 18 .1 P i n k % m o r t a l i t y t e m p e r a t u r e o r d e n s i t y 12. 8 15 .4 10 .2 16 .3 Chum % m o r t a l i t y e f f e c t s 40. 3 27 .7 49 .3 26 .7 # e a t e n / c o h o T e m p e r a t u r e o n l y 39.8 22 .4 52 .3 23 .1 P i n k % m o r t a l i t y 15.0 20 .0 12 .2 23 .2 Chum % m o r t a l i t y 53.9 32 .9 69 .2 34 .6 # e a t e n / c o h o D e n s i t y 57 .7 33 .1 74. 7 44 .5 P i n k % m o r t a l i t y o n l y ( m o d e l 2) 29 .6 34 .0 30. 0 45 .2 Chum % m o r t a l i t y 79 .9 49 .7 10 1 . 8 66 .8 # e a t e n / c o h o c o n t ' d . TABLE 7, Page 2. MARCH 1 MARCH 15 A B A B Temperature 71. 2 44 .1 87. 7 53 .8 Pink % m o r t a l i t y & d e n s i t y (model 2) 36. 3 47 .5 37. 3 56 .7 Chum % m o r t a l i t y 98. 6 66 .7 129. 3 81 .3 # eaten/coho A - Average instantaneous r a t e of pink growth i n weight per day f o r the f i r s t month of l i f e = 0.059033 (about 6.1% per day w i t h no temperature or de n s i t y e f f e c t s ) ; maximum ingestibikesiprey- sizet '• i s 0.044 x predator weight (g) . (Used f o r most s i m u l a t i o n runs described i n the r e s u l t s . ) B - Average instantaneous r a t e of pink growth i n weight per day f o r the f i r s t month of l i f e = 0.085896 (about 9.0% per day). Based on the r e l a t i o n s h i p f o r growth i n B r e t t & Shelbourn (1975) . Maximum ingestiblieKiprey t ' size. - .is i s 0.044 x predator weight (g) . Average instantaneous r a t e of chum growth i n weight per day f o r the f i r s t month of l i f e = 0.06236 (about 6.4% per day) f o r both A & B. (Used i n a l l ; s i m u l a t i o n runs described.) 7 6 pink fry mortality and increased chum f r y mortality. For example, i f f r y migrate March 1 and i f density and temperature a f f e c t growth rate, pink mortality i n the model decreases' from 7 1 . 2 % to 4 4 . 1 % and chum mortality increases from 3 6 . 3 % to 4 7 . 5 % . 2. If pink f r y grow fast enough, they can more than compensate for (compare columns A and B i n Table 7) the advantages chum f r y gain from having a larger i n i t i a l size, a somewhat shorter migration period and a lower encounter rate due to the difference i n pink and chum f r y abundance ( 5 . 7 : 1 ) . 3. The inte r a c t i o n of various assumptions r e s u l t s i n an unpredictable pattern of r e s u l t s , at least i n terms of the r e l a t i v e e f f e c t and sometimes i n terms of the d i r e c t i o n of the e f f e c t . For example, with no temperature or density e f f e c t s on growth rate and changing the date of migration from March 1 to March 1 5 , pink fry mortality increased ( 7 . 4 % ) when average growth rate was 6 . 1 % per day (columns A) but decreased ( 1 % ) when average growth rate was 9.0% per day (columns B). This p a r t i c u l a r r e s u l t i s due to the combined e f f e c t of changed pink f r y v u l n e r a b i l i t y and a v a i l a b i l i t y , changes i n fry density pattern.? and limited coho stomach capacity and abundance. 77 4. IF food supply i s not l i m i t i n g the growth of pink and chum f r y i n the estuary (Parker, 1968; LeBrasseur, et a l . , 1969; Walters, et a l . , 1977) and IF growth rate i s temperature dependent (Brett, et a l . , 1969) and operates as postulated i n the model, THEN, the model predicts that average coho intake of pink and chum f r y during t h e i r residence i n the estuary i s between 32 and 7 0 f r y per coho. (Total average intake was used because the number of days fr y are vulnerable to coho predation during t h i s period of l i f e v aries, depending on the assumptions i n force. Thus the number eaten per day per predator can be misleading). This r e s u l t s i n an estuarine pink and chum mortality rate of 22% to 52% and 12% to 23%, respectively (depending on the assumptions c o n t r o l l i n g migration date, e t c . ) . Thus although coho predation on pink and chum f r y during t h i s early stage of marine l i f e may account for a substantial portion of Fraser River fry-to-adult mortality, i t alone can not account for the observed estimates, given the above conditions (96.6%-99.4%, 1961-1965 brood year chum, Palmer, 1972; 95.0%-99.2%, 1961-1973 brood year pink, IPSFC, 1975). In summary, coho predation i n the model could account for 87.7% of pink f r y and 37.3% of chum f r y mortality under one extreme set of assumptions and 19.1% of pink f r y and 15.4% of chum f r y mortality under the opposite extreme set of assumptions. 78 T h i s c l e a r l y d e m o n s t r a t e s t h e d i f f i c u l t y o f e v a l u a t i n g t h e i m p o r t a n c e o f c o h o p r e d a t i o n o n p i n k a n d chum f r y when t h e r e a r e so many u n c e r t a i n t i e s r e g a r d i n g t h e b a s i c b i o l o g y o f t h e s y s t e m . One more g r o w t h r a t e e x p e r i m e n t , n o t s u m m a r i z e d i n T a b l e 7, a l l o w e d p i n k f r y t o g r o w a t t h e same r a t e a s chum f r y . P i n k m o r t a l i t y d e c r e a s e d f r o m 5 2 . 3 % t o 41.4% a n d chum m o r t a l i t y i n c r e a s e d f r o m 1 2 . 2 % t o 1 5 . 1 % ( a s s u m i n g p i n k a n d chum f r y b e g i n t h e i r m i g r a t i o n on M a r c h 15 and g r o w t h r a t e i s t e m p e r a t u r e d e p e n d e n t ) . Thus t h e r e s u l t s o f t h e m o d e l a r e s e n s i t i v e t o e v e n s m a l l c h a n g e s i n a v e r a g e p i n k f r y g r o w t h . V Chum a n d P i n k S i z e a t M i g r a t i o n i n t o t h e E s t u a r y The i n i t i a l mean s i z e o f chum f r y m o v i n g i n t o t h e F r a s e r R i v e r e s t u a r y i n c r e a s e s o v e r t h e s e a s o n . A l t h o u g h t h i s i n c r e a s e i n mean s i z e may be a s l i t t l e a s 2mm ( P a l m e r , 197 2 ) , i t m i g h t be i m p o r t a n t i f f r y s u r v i v a l i s r e a l l y d e t e r m i n e d b y t h e l e n g t h o f t i m e i t t a k e s t o r e a c h a s i z e t o o b i g f o r c o h o s m o l t s t o e a t . I t e s t e d t h i s h y p o t h e s i s u s i n g t h e m o d e l . I f chum f r y a l o n e i n c r e a s e d i n mean s i z e (2mm o v e r t h e f i r s t lh m o n t h s o f t h e i r m i g r a t i o n ) , chum m o r t a l i t y d e c r e a s e d 3.6% ( i f t h e r e w e r e no d e n s i t y o r t e m p e r a t u r e a f f e c t s o n g r o w t h ) t o 12.4% ( i f b o t h d e n s i t y a n d t e m p e r a t u r e a f f e c t e d g r o w t h r a t e ) b e c a u s e o f t h e i r r e d u c e d v u l n e r a b i l i t y t o c o h o p r e d a t i o n . P r e d a t i o n o n p i n k f r y i n c r e a s e d o n l y m a r g i n a l l y ( < 1 % ) . The i n c r e a s e i n p r e d a t i o n p r e s s u r e o n p i n k f r y i s n o t t h e r e s u l t o f c o h o s w i t c h i n g t o a more v u l n e r a b l e p r e y p e r se 79 b u t s i m p l y t h e r e s u l t o f t h e c o h o s t i l l b e i n g h u n g r y a n d a b l e t o e a t more o f t h e v u l n e r a b l e p i n k f r y e n c o u n t e r e d . The e n c o u n t e r r a t e o f v u l n e r a b l e chum f r y h a s d e c r e a s e d a l t h o u g h t h e o v e r a l l e n c o u n t e r r a t e a c t u a l l y i n c r e a s e s b e c a u s e more chum f r y a r e s u r v i v i n g . V I P r e y D e n s i t y F i g u r e 15a shows two f o r m s , g e n e r a t e d b y t h e m o d e l , o f t h e r e l a t i o n b e t w e e n f r y d e n s i t y a n d t h e number o f f r y s u c c e s s f u l l y e a t e n p e r c o h o p e r d a y . The l o w e r i n t a k e o f chum f r y p e r c o h o i n c u r v e B i s due t o d i f f e r e n c e s i n t h e b i o l o g y o f chum f r y a s o p p o s e d t o p i n k f r y . A l t h o u g h d i f f e r e n c e s i n m i g r a t i o n t i m i n g a n d g r o w t h r a t e a r e p a r t l y r e s p o n s i b l e , t h e m a j o r f a c t o r c o n t r i b u t i n g t o t h e l o w e r i n t a k e o f f r y i s t h e l a r g e r i n i t i a l s i z e o f chum f r y , c o u p l e d w i t h t h e c o h o 1 s s t o m a c h c a p a c i t y l i m i t a t i o n s . The f o r m o f t h e r e l a t i o n b e t w e e n f r y d e n s i t y and c o h o i n t a k e o f f r y a l s o d e p e n d s on t h e b i o l o g i c a l a s s u m p t i o n s d e f i n i n g t h e m o d e l s y s t e m ( e . g . f i g u r e 1 5 b ) . F o r e x a m p l e , i f f r y g r o w t h r a t e i s assumed t o be a f u n c t i o n o f t e m p e r a t u r e and d e n s i t y , t h e i n c r e a s e i n a v e r a g e i n t a k e o f f r y p e r c o h o i s more s e v e r e w i t h i n c r e a s e s i n f r y d e n s i t y . C o m p a r i n g t h e s h a p e . o f C u r v e A i n f i g u r e 15b t o c u r v e A i n f i g u r e 1 5 a , i n c r e a s i n g t h e p r e y : p r e d a t o r r a t i o f r o m 50:1 t o 200:1 r e s u l t e d i n a 365% v e r s u s 127% i n c r e a s e i n t h e a v e r a g e number o f f r y e a t e n p e r c o h o p e r d a y . The r e d u c t i o n i n f r y g r o w t h r a t e due t o d e n s i t y a n d t e m p e r a t u r e e f f e c t s r e s u l t s i n f r y t h a t a r e s m a l l e r , o n a n y g i v e n d a y , t h a n f r y n o t s u f f e r i n g f r o m r e d u c e d g r o w t h . Thus t h e a v e r a g e number o f f r y n e e d e d b y c o h o t o 80 FIGURE 15a. Relation Between Prey;Predator Ratio and Number of Fry Eaten/Coho/Day Two forms of the functional r e l a t i o n between the prey: predator r a t i o and the average number of f r y (prey) eaten per coho per day. In curve A, chum f r y compose 15% of the t o t a l prey population. In curve B, chum f r y compose 100% of the prey population. Fry migration begins March 15. Fry growth rate i s not affected by temperature or density. 82 FIGURE 15b. Another Example of Relation Between Prey:Predator Ratio and Number of Fry Eaten/Coho/Day Two more examples of the functional r e l a t i o n between the prey: pre'dator r a t i o and the average number of f r y eaten per coho per day. In curve A, f r y growth rate i s affected by temperature and density (model 2). In curve B, f r y growth rate i s affected by density only (model 2). Chum f r y compose 15% of the t o t a l prey population. Fry migration begins March 1. Average no- of fry eaten per day per coho ro oJ cn £8 84 s a t i s f y t h e i r d a i l y r a t i o n requirements in c r e a s e s . Figure 16 shows the k i n d of change i n pink and chum m o r t a l i t y t h a t can be expected w i t h increases i n e i t h e r t o t a l f r y abundance or coho smolt abundance (assuming no temperature or d e n s i t y e f f e c t s on growth). For example, f o r low l e v e l s of f r y abundance ( l e s s than 120 m i l l i o n ) , the number of pink and chum f r y eaten i s almost constant, r e g a r d l e s s of the number of coho, because m o r t a l i t y i s being l i m i t e d by prey a v a i l a b i l i t y and v u l n e r a b i l i t y . The system i s at the low end (prey:predator r a t i o 60:1) of the coho f u n c t i o n a l response curve (see f i g u r e 15a).. As the number of f r y inc r e a s e s , m o r t a l i t y begins to be l i m i t e d not only by f r y a v a i l a b i l i t y and v u l n e r a b i l i t y but a l s o by coho abundance and stomach c a p a c i t y . For example, i f there are 2 m i l l i o n coho, i n c r e a s i n g t o t a l f r y abundance from 200 to 360 m i l l i o n r e s u l t s i n a 10% decrease i n pink m o r t a l i t y , whereas, i n c r e a s i n g t o t a l f r y abundance from 360 to 520 m i l l i o n (an equal, absolute increase) r e s u l t s i n a greater than 15% decrease i n pink m o r t a l i t y . Thus, coho are operating f a r t h e r out on the limb of the f u n c t i o n a l response curve ( r e f e r to f i g u r e 15j.},. V I I R e l a t i v e P r o p o r t i o n of Pink to Chum Fry i n the Estuary The r e l a t i v e p r o p o r t i o n of pink to chum f r y i n the estuary v a r i e s from year to year i n the n a t u r a l environment. Figure 17a shows the e f f e c t on expected t o t a l f r y m o r t a l i t y r a t e , under three d i f f e r e n t assumptions, of changing t h e i r r e l a t i v e p r oportions i n the model: FIGURE 16. Relation Between Changing Pink and Chum Fry Abundance and Coho Smolt Abundance The combined e f f e c t on the indicators shown of changing both the coho smolt abundance and the t o t a l pink and chum f r y abundance. Fry migration begins March 15. Fry growth rate i s not affected by temperature or density. 8 6 - 6 Average no- of fry eoten Pink fry mortality (xlO ) Chum fry mortality (xlO ) per coho per day FIGURE 17. R e l a t i o n b e t w e e n F r y M o r t a l i t y a n d t h e P r o p o r t i o n o f Chum F r y i n t h e T o t a l B r e y P o p u l a t i o n F i g . 1 7 a . R e l a t i o n b e t w e e n p e r c e n t p i n k a n d chum f r y m o r t a l i t y a nd p r o p o r t i o n o f chum f r y i n t h e t o t a l p i n k and chum f r y p o p u l a t i o n . I n c u r v e A t h e r e i s a d e c r e a s i n g p r e y : p r e d a t o r r a t i o ; chum a b u n d a n c e i s c o n s t a n t (30 m i l l i o n ) . I n c u r v e B t h e r e i s a c o n s t a n t p r e y : p r e d a t o r r a t i o ( 1 1 5 : 1 ) . I n c u r v e C t h e r e i s a n i n c r e a s i n g p r e y : p r e d a t o r r a t i o ; p i n k a b u n d a n c e i s c o n s t a n t (195.5 m i l l i o n ) . P i n k a n d chum f r y m i g r a t i o n b e g i n s M a r c h 15. F r y g r o w t h r a t e i s n o t , a f f e c t e d b y t e m p e r a t u r e o r d e n s i t y . 8 0 ~\ (a) E =3 6 0 H - o cr >v ^ o 4 0 - | . _ i _ CL O - £ c a> o O - O - O 0J CL O 2 0 i— 8 0 0 —i— 20 4 0 6 0 8 0 100 % of total prey population composed of chum fry CO 00 FIGURE 17. R e l a t i o n B e t w e e n F r y M o r t a l i t y and t h e P r o p o r t i o n o f Chum F r y i n t h e T o t a l P r e y P o p u l a t i o n F i g . 17b. R e l a t i o n b e t w e e n p e r c e n t p i n k f r y m o r t a l i t y a n d p r o p o r t i o n o f chum f r y i n t h e t o t a l p i n k a n d chum f r y p o p u l a t i o n . See f i g u r e 17a f o r d e s c r i p t i o n o f c u r v e s A, B, and C and c o n d i t i o n s o f s i m u l a t i o n . F i g . 1 7 c . R e l a t i o n b e t w e e n number o f p i n k f r y e a t e n a n d p r o p o r t i o n o f chum f r y i n t h e t o t a l p i n k a n d chum f r y p o p u l a t i o n . See f i g u r e 17a f o r d e s c r i p t i o n o f c u r v e s A, B a n d C and c o n d i t i o n s o f s i m u l a t i o n . 90 91 1. In curve A the proportion of chum f r y i n the prey population i s altered by changing the abundance of pink fry (either by enhancing or depleting the t o t a l pink salmon population). 2. In curve B, the ov e r a l l prey:predator r a t i o remains constant while the proportion of chum fry in the prey population increases. 3. In curve C the i n i t i a l abundance of pink f r y remains constant while the proportion of chum fry in the prey population i s increased by enhancing the t o t a l chum salmon population. The shape of curve A (figure 17a) i s due to the interaction of several variables: r e l a t i v e abundance and vu l n e r a b i l i t y of prey species and predator abundance and stomach capacity. When the number of pink f r y i n the estuary i s high, mortality i s largely determined by predator stomach capacity, abundance and the length of time prey remain vulnerable to predation. When the number of pink f r y i n the estuary i s low, mortality i s largely determined by prey a v a i l a b i l i t y and v u l n e r a b i l i t y . As the prey:predator r a t i o decreases, a greater proportion of the fry of each species (e.g. figure 17b) i s eaten but the increase i n the proportion of t o t a l pink and chum f r y eaten stops, and ac t u a l l y begins to decrease (right limb of figure 17a), because of the r e l a t i v e increase i n abundance of the less vulnerable chum f r y and the general decrease i n the number of f r y eaten (refer to the discussion of the coho functional response to changes i n prey density, figures 15 and 16). Thus, although increasing the abundance of pink f r y i n the estuary tends to buffer chum f r y from predation (for example, decreasing the proportion, not the number, of chum in the prey population from 8 0% to 5%, decreased chum f r y mortality 2 0.3%)>: a s i g n i f i c a n t proportion of any increase in pink abundance i s eaten. For example, when the number of pink f r y i n the model estuary was increased from 7.5 to 4 5.0 m i l l i o n (chum proportion of prey population 80% and 40%, respectively), 57% (19.7 million) of the added pink f r y were eaten (see figure 17c). The decreasing l e f t limb of curve A (figure 17a) indicates tthat^theTpr6por<fe£ond6jfdadded pink f r y surviving predation i s now greater than the proportion dying. Although species s p e c i f i c mortality increases (e.g. curve B, figure 17b) when the abundance of chum f r y i n the prey population increases (curve B, figure 17a preyrpredator r a t i o constant), the increases are not s u f f i c i e n t to o f f s e t the net decrease i n t o t a l pink and chum f r y mortality. Chum fry are not only less susceptible to predation than pink f r y , but also t h e i r larger si z e , combined with t h e i r increased a v a i l a b i l i t y , reduces the average intake of f r y per coho (see figure 15, curve B). Species s p e c i f i c chum f r y mortality increases because there are more vulnerable chum available and less pink f r y to buffer them; species s p e c i f i c pink f r y mortality increases because the t o t a l number of vulnerable pink and chum f r y decreases, with the increase i n abundance of less-vulnerable chum, thereby increasing the predation pressure on the remaining vulnerable f r y . I t i s n e c e s s a r y t o m e a s u r e a d u l t r e t u r n b e f o r e t h e r e l a t i o n s h i p b e t w e e n f r y s u r v i v a l a n d r e l a t i v e a b u n d a n c e o f chum t o p i n k f r y c a n be e v a l u a t e d . A l t h o u g h p i n k s a l m o n i n t h e m o d e l a r e more v u l n e r a b l e t o p r e d a t i o n d u r i n g t h e i r e a r l y s t a g e s o f l i f e , t h e y o n l y s p e n d one y e a r i n t h e o c e a n a s o p p o s e d t o two o r t h r e e y e a r s f o r chum s a l m o n . A c r u d e c a l c u l a t i o n o f t o t a l p i n k a n d chum a d u l t r e t u r n i n d i c a t e d t h a t r e t u r n was h i g h e r (115.8 v e r s u s 115.6 m i l l i o n ) , a l b e i t i n s i g n i f i c a n t l y , when chum f r y a c c o u n t e d f o r o n l y 5% v e r s u s 95% o f t h e o r i g i n a l f r y p o p u l a t i o n . (The l o w e s t n e t r e t u r n o f a d u l t p i n k and chum s a l m o n (113.3 m i l l i o n ) o c c u r r e d when chum f r y a c c o u n t e d f o r 50% o f t h e p r e y p o p u l a t i o n . ) I f w e i g h t o f a d u l t r e t u r n was c a l c u l a t e d i n s t e a d d o f n u m b e r s , h o w e v e r , t h e r e s u l t s w o u l d be c o m p l e t e l y d i f f e r e n t ( i n g e n e r a l , a d u l t chum s a l m o n w e i g h more t h a n a d u l t p i n k s a l m o n ) . T h u s , c o r r e c t e v a l u a t i o n o f t h e s e r e s u l t s a n d t h e i r p e r t i n e n c e t o e n h a n c e m e n t w o u l d r e q u i r e i n f o r m a t i o n o n t h e r e l a t i v e e c o n o m i c i m p o r t a n c e o f e a c h s p e c i e s , g i v i n g due c o n s i d e r a t i o n t o t h e i r d i f f e r i n g b i o l o g i c a l c h a r a c t e r i s t i c s . T o t a l c o m b i n e d m o r t a l i t y rfco p i n k a n d chum f r y i n c u r v e C ( f i g u r e 1 7 a ) , a s w e l l a s s p e c i e s s p e c i f i c m o r t a l i t y ( e . g . c u r v e C, f i g u r e 1 7 b ) , d e c r e a s e s . I n c r e a s i n g t h e number o f chum f r y i n t h e e s t u a r y n o t o n l y b u f f e r s p i n k f r y f r o m c o h o p r e d a t i o n , b u t a l s o r e d u c e s c o h o i n t a k e o f f r y b e c a u s e f e w e r chum f r y a r e r e q u i r e d t o s a t i a t e e a c h c o h o ( s e e d i s c u s s i o n o f c u r v e B and d i s c u s s i o n o f c o h o f u n c t i o n a l r e s p o n s e t o i n c r e a s i n g p r e y d e n s i t y ) . I n summary, t h e s h a p e o f t h e c u r v e s d e p i c t e d i n f i g u r e 17, a n d t h e r e f o r e t h e a b o v e d i s c u s s i o n , d e p e n d s on t h e 94 assumption t h a t f r y growth r a t e i n the e s t u a r y i s independent of f r y d e n s i t y . N e v e r t h e l e s s , these r e s u l t s should be c o n s i d e r e d b e f o r e any attempt i s made to e s t a b l i s h an even brood year pink run i n the F r a s e r R i v e r . Even though the presence of pink f r y may reduce chum f r y m o r t a l i t y (assuming no adverse d e n s i t y e f f e c t s ) , i t may be more p r o f i t a b l e to enhance on l y chum salmon. VI I I Timing and Duration of the Coho Smolt M i g r a t i o n The t i m i n g and d u r a t i o n of the cb.ho smolt m i g r a t i o n i n t o the F r a s e r R i v e r e s t u a r y are u n c e r t a i n . Figuresl ;lSliand 19 i l l u s t r a t e the e f f e c t on pink and chum m o r t a l i t y r a t e s of changing these parameters i n the model. In f i g u r e 18, i n c r e a s i n g the d u r a t i o n of the coho m i g r a t i o n i n t o the e s t u a r y from 16 to 48 days ( f i r s t day of e n t r y and t o t a l abundance c o n s t a n t ) , reduced pink and chum m o r t a l i t y 46% and 72%, r e s p e c t i v e l y . Coho d e n s i t y i n the e s t u a r y b u i l d s up over a longer time i n t e r v a l thereby r e d u c i n g the d a i l y p r e d a t i o n p r e s s u r e and p r o v i d i n g the f r y w i t h time to outgrow the coho which have not y e t a r r i v e d . Changing the date o f coho e n t r y ( f i g u r e 19) gave the f r y time to grow, making them l e s s v u l n e r a b l e to p r e d a t i o n when the coho f i n a l l y entered the e s t u a r y . F i g u r e 20 shows the complete range of f r y m o r t a l i t y r a t e s obtained by v a r y i n g both the time of e n t r y and d u r a t i o n of the coho smolt. m i g r a t i o n i n t o the e s t u a r y . The o n l y i n f o r m a t i o n a v a i l a b l e f o r F r a s e r R i v e r coho suggests t h a t they enter the e s t u a r y over a p e r i o d of about two weeks, beginning i n l a t e A p r i l ( Fraser, 197 6). Based on FIGURE 18. An E x a m p l e o f t h e R e l a t i o n B e t w e e n D u r a t i o n o f Coho M i g r a t i o n a n d P i n k a n d Chum F r y M o r t a l i t y An e x a m p l e o f t h e r e l a t i o n b e t w e e n t h e d u r a t i o n o f t h e c o h o s m o l t m i g r a t i o n ( i n # o f d a y s ) and m o d e l e s t i m a t e s o f p i n k a nd chum f r y m o r t a l i t y . F r y and c o h o m i g r a t i o n b e g i n s M a r c h 15 and A p r i l 9, r e s p e c t i v e l y . I n i t i a l p r e y : p r e d a t o r r a t i o i s 1 1 5 : 1 . F r y g r o w t h r a t e i s s n o t a f f e c t e d b y t e m p e r a t u r e o r d e n s i t y . I n i t i a l mean s i z e o f f r y i s c o n s t a n t o v e r t h e s e a s o n . 16 days | j 24 days 99-4 Pink Chum 97 FIGURE 19. An E x a m p l e o f t h e R e l a t i o n B e t w e e n D a t e Coho E n t e r E s t u a r y a n d P i n k a n d Chum F r y M o r t a l i t y An e x a m p l e o f t h e r e l a t i o n b e t w e e n t h e d a t e c o h o s m o l t s a r e assumed t o b e g i n e n t e r i n g t h e e s t u a r y and m o d e l e s t i m a t e s o f p i n k a n d chum f r y m o r t a l i t y . F r y m i g r a t i o n b e g i n s M a r c h 15. I n i t i a l p r e y r p r e d a t o r r a t i o i s 1 1 5 : 1 . F r y g r o w t h r a t e i s n o t a f f e c t e d b y t e m p e r a t u r e o r d e n s i t y . Coho s m o l t m i g r a t i o n i n t o t h e e s t u a r y l a s t s 24 d a y s . I n i t i a l mean s i z e o f f r y i s c o n s t a n t o v e r t h e s e a s o n . Pink Chum CO CO FIGURE 20. E f f e c t on Indicators of Changing the Duration of Coho Migration and the Date of Entry The combined e f f e c t on the indicators shown of changing both the date of coho entry into the estuary and the duration of coho migration. Start of coho entry into estuary lagged (in # of days) from March 15. I n i t i a l preyrpredator r a t i o i s 115:1. Fry migration begins March 15. Fry growth rate i s not affected by temperature or f r y density. Chum fry mortolily (xlO6) co >% a c o 48 -r 40 + 32 + 24 + 16 % chum fry mortality WW \ % chum adult return Average no- of fry eaten per coho per day 3 *o c o o l_ CP E o JZ: o O Pink fry mortality (xlO ) 4 8 T 40 32 + 24 + 16 4-180 \ 100 \ to ^ % pink fry mortality 10 2 0 30 40 50 % pinVc adult return 10 20 30 40 50 Total average no- of fry eaten per coho 10 20 30 40 50 1 4 4 - / \ 108^ 72 \ 36 I26J 90 \ 54 \ 18 -I f 10 20 30 40 5* Number of days coho entry lagged from March 15 o o 101 th i s information, the model predicts that wild coho populations from the Fraser River could eat about 37% of the pink f r y and 10% of the chum f r y r e s i d i n g i n the estuary (assuming the fry begin migrating on March 15 and growth i s not affected by temperature or density). In contrast, Parker (1968f estimated that 55% to 77% of pink f r y from Hooknose Creek did not survive their f i r s t 4 0 days i n the estuary. Most of t h i s mortality he attributed to coho predation. If coho smolts are to be produced using enhancement f a c i l i t i e s , the tradeoff between the costs (such as increased feeding and maintenance) of delaying the time of release and the benefits of minimizing the r i s k to pink and chum f r y would have to be evaluated. An a l t e r n a t i v e method of coho enhancement might be to accelerate the growth of coho f r y such that they reach smolt size i n the late f a l l or early winter and thus go to sea during their f i r s t year (Smith, 1978). This would eliminate predation by enhancement coho on pink and chum fry during their period of estuarine l i f e . Survival, however, of the enhanced coho may be low due to adverse environmental conditions found in late f a l l or early winter. Coho returning to the Qulf of Georgia are of major importance as a sports f i s h . Thus, any attempt to reduce or eliminate coho predation on pink and chum f r y must be evaluated not only i n terms of the estimated increase i n production of pink and chum but.also in terms of the possible negative impact on coho production. 102 IX Non-Coho Natural Mortality In the model pink and chum f r y were subjected to a low le v e l of natural mortality i n addition to mortality from coho predation. The s e n s i t i v i t y of the model r e s u l t s , p a r t i c u l a r l y the rate of coho predation, to changes i n t h i s parameter was tested. (The following experiments assume that f r y migration begins March 15.) With no density e f f e c t s on growth rate, there was v i r t u a l l y no change i n coho predation rate when pink and chum fry instantaneous natural mortality rate was increased from 0.0002 to 0.004 per day (about 1.9 f r y were eaten per day per coho). Nevertheless, the number of surviving pink and chum fry decreased from 122.1 to 104.3 m i l l i o n and from 30.7 to 26.4 m i l l i o n , respectively, due to the increase i n non-coho natural mortality. Using density model 2 and the same range of non-coho instantaneous mortality rates, mortality from coho predation decreased from 75.3% to 69.2% (about 12 million) for pink f r y and from 30.2% to 26.9% (about 1.1 million) for chum f r y . The average number of f i s h eaten per. day per coho decreased marginally (4.0 to 3.7). Pink and chum f r y surviving t h i s period of l i f e , decreased from 47.4 to 43.1 m i l l i o n and from 23.8 to 20.9 m i l l i o n , respectively. By increasing the non-coho mortality rate s t i l l further to 0.01 per day, the number of surviving pink and chum f r y decreased another 7 and 4 m i l l i o n , respectively. Although the average.number of f ry eaten per day per coho only dropped to about. 3.3, pink and chum mortality due to coho predation decreased another 7.6% and 3.9%, respectively. 103 T h u s , a l t e r n a t i v e m o r t a l i t y a g e n t s h a v e t h e p o t e n t i a l t o s u b s t a n t i a l l y r e d u c e t h e " r e a l i z a b l e " i m p a c t o f c o h o p r e d a t i o n on p i n k and chum f r y . X R e s i d e n c e T ime and S i z e a t E m i g r a t i o n f r o m t h e E s t u a r y T h e r e i s c o n s i d e r a b l e u n c e r t a i n t y a s t o t h e l e n g t h o f t i m e p i n k a n d chum f r y r e m a i n i n t h e e s t u a r y . I n a l l o f t h e r u n s d i s c u s s e d so f a r p i n k a n d chum f r y h a v e b e e n assumed t o r e m a i n i n t h e e s t u a r y u n t i l t h e y a r e g r e a t e r t h a n e i g h t c e n t i m e t e r s i n l e n g t h ( L e B r a s s e u r a n d P a r k e r , 1964; P a r k e r , 1968; A l l e n , 1 9 7 4 ) . T h i s c o r r e s p o n d s t o a m o d e l r e s i d e n c e t i m e o f a b o u t 8 weeks - i f f g g o w t h h r a c t e e i s o h o t e . r e d u c e d y b y e d e n s i t y o r t e m p e r a t u r e e f f e c t s . To e v a l u a t e t h e e f f e c t o f t h i s a s s u m p t i o n o n e x p e c t e d m o r t a l i t y r a t e s due t o p r e d a t i o n , I e x p e r i m e n t e d w i t h p i n k a n d chum r e s i d e n c e t i m e (and c o n s e q u e n t l y prey, s p e c i e s m s p ^ c c o m p o s i t i o n ) b y c h a n g i n g t h e s i z e a t w h i c h t h e y w e r e assumed t o l e a v e t h e e s t u a r y . Coho a r e assumed t o r e m a i n i n t h e e s t u a r y u n t i l a l l o f t h e v u l n e r a b l e p i n k and chum f r y a r e e a t e n o r h a v e l e f t . T h e r e a r e f i v e m a j o r p o i n t s t o n o t e a b o u t t h e r e s u l t s shown i n T a b l e 8: 1. I f b o t h p i n k a n d chum f r y l e a v e t h e e s t u a r y a f t e r t h e y r e a c h 4.0 cm (a r e s i d e n c e t i m e o f 1 t o 2h w e e k s ) , t h e n g r o w t h r a t e o f p i n k o r chum f r y i s n o t a f f e c t e d b y f r y d e n s i t y ( m o d e l 2) a s e v i d e n c e d by t h e c o n s t a n t f r y m o r t a l i t y r a t e s ( 2 1 . 4 % a n d 7.3%, r e s p e c t i v e l y ) . TABLE 8 S e n s i t i v i t y o f m o d e l r e s u l t s t o c h a n g e s i n t h e e s t i m a t e d s i z e a t w h i c h p i n k a n d chum f r y a r e assumed t o l e a v e t h e e s t u a r y . F r y a r e assumed t o b e g i n e n t e r i n g t h e e s t u a r y M a r c h 15. P r e y : p r e d a t o r r a t i o i s 1 1 5 : 1 . Chum f r y compose 15% o f t h e t o t a l p r e y p o p u l a t i o n . 1 2 3 4 No t e m p e r a t u r e T e m p e r a t u r e , o r d e n s i t y ^ & d e n s i t y e f f e c t s T e m p e r a t u r e D e n s i t y e f f e c t s A B o t h m i g r a t e a t 4 . 0 cm. 21.4 29.0 21 .4 34 .8 Q. "5 p i n k m o r t a l i t y 7.3 6.7 7 .3 6 .6 g. "5 chum m o r t a l i t y B P i n k f r y m i g r a t e a5 4 .0 cm; chum 20.7 27.9 21 - 23 42 .4 g, "o p i n k m o r t a l i t y a t 5 . 0 cm. 16.4 22.8 16 — 17 40 .0 a "o chum m o r t a l i t y C P i n k f r y m i g r a t e -a t 5 . 0 cm.; 37". 4 53.2 61 - 66 81 - 82 a *o p i n k m o r t a l i t y chum a t 4.0 cm. 3.9 3.0 5 .0 7 .6 a chum m o r t a l i t y D B o t h m i g r a t e 36.9 52.2 67 _ 75 86 - 88 o. "5 p i n k m o r t a l i t y 10.2 12.2 23 — 30 36 - 37 a "o chum m o r t a l i t y Density model 2 105 2. The p r e s e n c e o f p i n k f r y i n t h e e s t u a r y t e n d s t o b u f f e r chum f r y f r o m c o h o p r e d a t i o n (compare f o r e x a m p l e B I a n d D l — c h u m m o r t a l i t y i s r e d u c e d 6 . 2 % ) . N e v e r t h e l e s s , u n d e r a d i f f e r e n t s e t o f h y p o t h e s e s , t h i s b u f f e r i n g e f f e c t c a n be r e v e r s e d (compare f o r e x a m p l e B3 a n d D 3 — c h u m m o r t a l i t y a c t u a l l y i n c r e a s e s 7 t o 13 p e r c e n t ) b e c a u s e t h e i n c r e a s e d d e n s i t y o f f r y i n t h e e s t u a r y r e s u l t s i n r e d u c e d f r y g r o w t h r a t e and c o n s e q u e n t l y l e n g t h e n s t h e p e r i o d o f v u l n e r a b i l i t y t o p r e d a t i o n . 3. The p r e s e n c e o f chum f r y i n t h e e s t u a r y d o e s l i t t l e t o r e d u c e p i n k f r y m o r t a l i t y (compare f o r e x a m p l e A l a n d B I o r A2 a n d B2 o r C I a n d D l — p i n k m o r t a l i t y i s r e d u c e d 1 . 2 % ) . 4. The i m p o r t a n c e o f t h e p a r a m e t e r c o n t r o l l i n g t h e l e n g t h o f p i n k a n d chum r e s i d e n c e i n t h e e s t u a r y i s d e m o n s t r a t e d b y t h e r a n g e o f m o d e l e s t i m a t e s o f p i n k and chum f r y m o r t a l i t y due t o c o h o p r e d a t i o n ( a s s u m i n g t h a t t h e c o h o do n o t f o l l o w t h e i r p r e y ) . F o r e x a m p l e , a s s u m i n g t e m p e r a t u r e a nd d e n s i t y a f f e c t g r o w t h r a t e , m i g r a t i n g e a r l y ;(A1) c a n r e d u c e p i n k f r y m o r t a l i t y 53% and chum f r y m o r t a l i t y 30%. N e v e r t h e l e s s , i f t h e f r y l e a v e t h e e s t u a r y a t a s m a l l s i z e , m o r t a l i t y f r o m a g e n t s o t h e r t h a n c o h o may i n c r e a s e s u c h t h a t a n y r e d u c t i o n i n m o r t a l i t y a c h i e v e d b y e s c a p i n g c o h o may be more t h a n c o m p e n s a t e d f o r . 5. A t . a n y one t i m e d i f f e r e n t f a c t o r s may be l i m i t i n g c o h o c o n s u m p t i o n o f f r y p r e y . F o r e x a m p l e , i n C2 106 p i n k f r y m o r t a l i t y i s l i m i t e d b y t h e i r a v a i l a b i l i t y a n d v u l n e r a b i l i t y a s w e l l a s by t h e c o h o 1 s s t o m a c h c a p a c i t y . However, chum f r y m o r t a l i t y f r o m c o h o p r e d a t i o n i s m a i n l y l i m i t e d b y t h e i r a v a i l a b i l i t y due t o t h e i r e a r l y e m i g r a t i o n f r o m t h e e s t u a r y . A n o t h e r m e c h a n i s m w h i c h may i n d u c e f r y m i g r a t i o n f r o m t h e e s t u a r y , m i g h t be r e d u c e d g r o w t h r a t e due t o f o o d l i m i t a t i o n o r o t h e r d e n s i t y r e l a t e d e f f e c t s . T h i s h y p o t h e s i z e s t h a t f i s h h a v e some way o f m o n i t o r i n g t h e i r own g r o w t h r a t e . T a b l e 9 shows t h a t i n m o s t c a s e s f r y m o r t a l i t y f r o m c o h o p r e d a t i o n i s n o t s i g n i f i c a n t l y r e d u c e d b e l o w v a l u e s d e r i v e d u s i n g a b o d y s i z e o n l y movement t r i g g e r ( c o n t r o l ) , u n l e s s f r y b e g i n m i g r a t i n g when t h e i r g r o w t h r a t e d r o p s b e l o w 3% p e r d a y ( e . g . , a s s u m i n g d e n s i t y d e p e n d e n t g r o w t h r a t e ( m o d e l 2 ) , p i n k and chum f r y m o r t a l i t y i s r e d u c e d 11.4% and 1 0 . 8 % , r e s p e c t i v e l y ) . The t a b l e a l s o shows, a s e v i d e n c e d by t h e c o n s t a n t f r y m o r t a l i t y r a t e s , t h a t g r o w t h r a t e n e v e r d r o p s b e l o w 3% u n l e s s d e n s i t y i s p o s t u l a t e d t o a f f e c t f r y g r o w t h r a t e . The m o s t i n t e r e s t i n g a s p e c t o f t h i s e x p e r i m e n t was n o t t h e §d^e.efexbiifj^ryi%morHtali4t^"^a;t^ :) ibut^l : the3;s>fczei;di-.s^r;ibutl'Om i o f f r y i n t h e e s t u a r y . F i g u r e s 21 and 22 i n d i c a t e t h e t r u e mean s i z e a n d s i z e r a n g e o f chum and p i n k f r y f o u n d i n t h e m o d e l e s t u a r y d u r i n g t h e s e a s o n . ( S t a n d a r d d e v i a t i o n was riot c a l c u l a t e d b e c a u s e f r y s i z e d i s t r i b u t i o n i n t h e m o d e l e s t u a r y i s n o t n o r m a l , e s p e c i a l l y d u r i n g t h e f i r s t s i x weeks.) T h e s e f i g u r e s d e m o n s t r a t e a number o f i m p o r t a n t f a c t o r s : 1. The p o t e n t i a l e f f e c t o f f r y i n - m i g r a t i o n on t h e mean s i z e o f f i s h s a m p l e s t a k e n f r o m t h e n a t u r a l e n v i r o n m e n t i s a p p a r e n t f r o m t h e a l m o s t c o n s t a n t TABLE 9. p i n k and chum f r y a r e p e r m i t t e d t o l e a v e t h e e s t u a r y i f t h e i r g r o w t h r a t e d r o p s b e l o w a s p e c i f i e d v a l u e o r i f t h e y r e a c h a l e n g t h g r e a t e r t h a n 8.0 c e n t i m e t e r s . O t h e r c o n d i t i o n s a r e t h e same as t h o s e i n T a b l e 8. No t e m p e r a t u r e T e m p e r a t u r e o r d e n s i t y ^ & d e n s i t y 1 e f f e c t s T e m p e r a t u r e D e n s i t y e f f e c t s M i g r a t e o n l y i f s i z e 36.9 52.3 74.7 87.7 P i n k % m o r t a l i t y 8.0 cm. ( C o n t r o l ) 10.2 12.2 30.0 37.3 Chum % m o r t a l i t y M i g r a t e i f g r o w t h 36.9 52.3 74.7 87.7 P i n k % m o r t a l i t y r a t e l e s s t h a n 1% 10.2 12.2 30.0 37.3 Chum % m o r t a l i t y p e r d ay o r s i z e 8.0 cm. M i g r a t e i f g r o w t h 36.9 52.3 72.9 81.8 P i n k % m o r t a l i t y l e s s t h a n 2% p e r d a y 10.2 12.2 27.8 31.8 Chum % m o r t a l i t y o r s i z e 8.0 cm. M i g r a t e i f g r o w t h 36.9 52.3 63.3 63.9 P i n k % m o r t a l i t y r a t e l e s s t h a n 3% 10.2 12.2 19.2 21.8 Chum % m o r t a l i t y p e r d a y o r s i z e 8.0 cm. D e n s i t y model 2 108 EIGURE 21. Size D i s t r i b u t i o n of Chum Fry Found i n the Estuary Each Week Mean size and size range, of chum f r y found i n the model estuary each week since the beginning of the f r y migration on March 15. Each week i s i d e n t i f i e d by a sample number. I n i t i a l prey:predator r a t i o i s 115:1. Fry growth rate i s affected by pink and chum f r y density (model 2). Fry leave estuary i f growth rate less than 3% per day or fry length greater than 8.0 cm. range mean size Sample number FIGURE 22. Size D i s t r i b u t i o n of Pink Fry Found i n the Estuary Each Week Mean size and size range of pink f r y found i n the model estuary each week since the beginning of the f r y migration on March 15. Each week i s i d e n t i f i e d by a sample number. I n i t i a l prey:predator r a t i o i s 115:1. Fry growth rate i s affected by pink and chum f r y density (model 2). Fry leave the estuary i f growth rate less than 3% per day or fry length greater than 8.0 cm. range 112 mean s i z e o f t h e f r y f o r t h e f i r s t f i v e weeks ( s a m p l e s 1 t o 6 ) . R e p r e s e n t a t i v e s a m p l e s o f f i s h t a k e n d u r i n g t h i s t i m e p e r i o d w o u l d s u g g e s t t h a t t h e f r y w e r e n o t s t a y i n g i n t h e e s t u a r y f o r a n y l e n g t h o f t i m e . I f t h e s a m p l i n g t e h h n i q u e was b i a s e d i n f a v o u r o f l a r g e r f i s h , s u b s t a n t i a l l y d i f f e r e n t e s t i m a t e s o f g r o w t h r a t e a n d r e s i d e n c e t i m e c o u l d be i n f e r r e d . The e f f e c t o f a n o t h e r k i n d o f b i a s i s d e m o n s t r a t e d by t h e r e s u l t s o f s a m p l e 6 and 7: o u t - m i g r a t i o n , o f t h e l a r g e r f i s h due t o a d r o p i n t h e i r g r o w t h r a t e . The e s t i m a t e d mean s i z e o f f i s h f r o m s a m p l e s 7 and 8 i s s t i l l b e i n g b i a s e d b y i n - m i g r a t i o n b u t t h i s i s p a r t i a l l y o o f f s e t b y p r e d a t i o n on s m a l l -s i z e d f i s h . T h u s , t h e mean s i z e o f t h e s a m p l e d f r y r e m a i n s a b o u t t h e same a l t h o u g h t h e v a r i a b i l i t y h a s d e c r e a s e d s u b s t a n t i a l l y . An i n v e s t i g a t o r , o b s e r v i n g t h e t o t a l p a t t e r n o f mean s i z e , m i g h t be t e m p t e d t o s p e c u l a t e t h a t t h e f r y i n t h e e _ s t u a r y b§4.ustoppgd g r o w i m g d u ^ i n g g t b h e l a s f e t t w o o w e e k s s o f Z A p r i l . On t h e c o n t r a r y , a l l f i s h f o u n d i n t h e e s t u a r y a r e g r o w i n g a t a r a t e g r e a t e r t h a n 3% p e r d a y . The i n c r e a s e i n mean s i z e o b s e r v e d i n s a m p l e s 9 t o 12 i s d u e t o t h e i n c r e a s i n g number o f l a r g e r f i s h r e m a i n i n g i n t h e e s t u a r y . G r o w t h r a t e o f t h e l a r g e r f i s h i s a g a i n h i g h e r t h a n t h e e m i g r a t i o n t h r e s h o l d o f t h r e e p e r c e n t b e c a u s e f r y d e n s i t y h a s b e e n r e d u c e d b y o u t - m i g r a t i o n and m o r t a l i t y . 113 A s t h e s m a l l - s i z e d i n - m i g r a n t s a r e e a t e n , t h e mean s i z e becomes i n c r e a s i n g l y b i a s e d u p w a r d . 3. D e n s i t y ( f i g u r e 23) o f p i n k a n d chum f r y i n t h e e s t u a r y f o l l o w s t h e w e l l - k n o w n p a t t e r n o f i n c r e a s e and e v e n t u a l d e c r e a s e o v e r t i m e ( t h e r e s u l t o f i n -a n d o u t - m i g r a t i o n and m o r t a l i t y ) . T h i s d e n s i t y p a t t e r n w o u l d t e n d t o l e n d s u p p o r t t o t h e c o n t e n t i o n t h a t g r o w t h had s t o p p e d f o r t h e l a s t two weeks o f A p r i l . 4. F r y f r o m t h e e a r l y and m i d d l e p a r t o f t h e r u n m i g r a t e d t o s e a a t a s m a l l e r s i z e t h a n f r y f r o m t h e l a t e r p a r t o f t h e r u n . R e i m e r s (197 3) o b s e r v e d t h a t j u v e n i l e c h i n o o k w h i c h s t a y e d i n t h e e s t u a r y o v e r t h e summer and r e d g h e d a l a r g e r s i z e p r i o r t o s e a w a r d m i g r a t i o n t h a n e a r l y m i g r a t i n g c h i n o o k , had a h i g h e r s u r v i v a l r a t e . T h i s s u p p o r t s a n e a r l i e r c o n t e n t i o n t h a t m o r t a l i t y due t o a g e n t s i n t h e o c e a n may more t h a n c o m p e n s a t e f o r a n y r e d u c t i o n i n c o h o p r e d a t i o n a c h i e v e d by m i g r a t i n g e a r l y . M a r k i n g o f f r y , a n d r e - s a m p l i n g o v e r t i m e i n t h e e s t u a r y , w o u l d d e c r e a s e t h e p r o b l e m s m e n t i o n e d i n #1 o f e s t i m a t i n g g r o w t h r a t e , b u t o n l y i f f i s h w e r e m a r k e d o v e r a s h o r t p e r i o d o f t i m e o r i f d i f f e r e n t m a r k s w e r e u s e d t o e s t a b l i s h t h e i r d a t e o f m i g r a t i o n . I n a n e s t u a r y a s l a r g e a s t h e . F r a s e r , a l a r g e number o f f i s h w o u l d h a v e t o be m a r k e d t o i n s u r e a r e a s o n a b l e c h a n c e o f r e c o v e r i n g a s i g n i f i c a n t number. 114 FIGURE 23. Weekly Density of Pink and Shurn Fry i n the Estuary Combined <nenvbety of pink and chum f r y per hectare of estuary f((15,319 hectares). Conditions are the same as those described in figure 20. Sample number 116 3. Enhancement Experiments I Changing the Prey:Predator Ratio I f pink and chum growth r a t e i n the estuary i s d e n s i t y dependent (as i n model 2) , then predation may r e s u l t i n compensatory m o r t a l i t y i f pink or chum f r y are enhanced. For example, i n the model, i n c r e a s i n g the t o t a l number of pink and chum f r y e n t e r i n g the estuary from 23 0 (prey:predator rationll5:1) to 460 (230:1) m i l l i o n u l t i m a t e l y reduced pink and chum a d u l t r e t u r n by 23.8 and 0.4 m i l l i o n , r e s p e c t i v e l y (Table 10). The increased d e n s i t y of f r y i n the estuary reduced growth and extended the length of time f r y were vuln e r a b l e to predation from 33 to 57 days, thus i n c r e a s i n g f r y m o r t a l i t y . As the t a b l e i n d i c a t e s , t h i s e f f e c t may completely negate some enhancement attempts, e s p e c i a l l y l a r g e s c a l e ones. I I Enhancement of Pink Salmon I t has been shown, using the model, that r e l a t i v e timing^of migration? ; i n i t i a l 'sizejland: abundance may bepdmportant determinants of pink and chum f r y s u r v i v a l during e a r l y e s t u a r i n e l i f e . To examine the e f f e c t on s u r v i v a l of changing these parameters, pink salmon were enhanced i n the model. The enhanced pink population was t r e a t e d as a separate stock so t h a t the s u r v i v a l of both the " w i l d " and enhanced population could be determined. Thus the enhanced pink population i s assumed toJcome from a f a c i l i t y where abundance, time of m i g r a t i o n , d u r a t i o n and s i z e a t m i g r a t i o n can be manipulated. TABLE 10. S e n s i t i v i t y o f m o d e l r e s u l t s t o i n c r e a s e s i n t h e d e n s i t y o f p i n k a n d chum f r y . F r y g r o w t h r a t e i s a f u n c t i o n o f d e n s i t y m o d e l 2. F r y m i g r a t i o n b e g i n s M a r c h 1. A v e r a g e i n s t a n t a n e o u s m o r t a l i t y r a t e a t s e a i s assumed t o be 0.00053 p e r d a y f o r p i n k s a l m o n and 0.00043 p e r d a y f o r chum s a l m o n ( b a s e d on R i c k e r , 1 9 7 6 ) . P i n k s a l m o n a r e assumed t o s p e n d a maximum o f 410 d a y s a t s e a . T w e n t y - t w o p e r c e n t o f t h e chum f r y a r e assumed t o s p e n d 840 d a y s a t s e a ; t h e r e m a i n d e r , 1200 d a y s . P r e y : p r e d a t o r r a t i o 57.57-,l 1 115:1 230:1 % p i n k f r y m o r t a l i t y 33.8 57 .7 /85.2 % chum f r y m o r t a l i t y 15.6 29.6 64.3 p i n k a d u l t ^ r e t u r n (#'s) 50.3 63.2 39.4 % p i n k a d u l t r e t u r n 51.6 32.4 10.1 chum a d u l t ^ r e t u r n ( l ' s ) 8.8 14.6 14.2 % chum a d u l t r e t u r n 51.1 42.3 20.6 ^ I n i t i a l number o f c o h o p r e d a t o r s i s c o n s t a n t (2 m i l l i o n ) . A d u l t r e t u r n i s i n m i l l i o n s o f f i s h . 118 For these model experiments, the enhanced f r y m i g r a t i o n i n t o the e s t u a r y was assumed to l a s t one week. the abundance of the enhanced stock was v a r i e d but kept r e l a t i v e l y s m a l l . The model's p r e v i o u s r e s u l t s suggested t h a t , any decrease i n m o r t a l i t y due to an i n c r e a s e i n the prey:pr e d a t o r ratio,, may be more than o f f s e t by the i n c r e a s e i n p r e d a t i o n m o r t a l i t y due to d e n s i t y r e l a t e d decreases i n f r y growth r a t e . The w i l d pink and chum f r y are assumed to begin t h e i r m i g r a t i o n on March 1, to i n c r e a s e i n mean s i z e over the d u r a t i o n o f t h e i r m i g r a t i o n i n t o the est u a r y , and to experience temperature and d e n s i t y (model 2) r e l a t e d r e d u c t i o n s i n growth r a t e . The i n i t i a l abundance of w i l d pink and chum stocks i s constant f o r each s i m u l a t i o n (195.5 m i l l i o n pink f r y and 34.5 m i l l i o n chum f r y ) . The complete r e s u l t s of t h i s experiment are g r a p h i c a l l y d i s p l a y e d i n f i g u r e s 2$ to 2'.8. F i g u r e s 2[4 to 287 show the r e s u l t s , f o r fo u r separate m i g r a t i o n s t a r t i n g dates, of changing both the abundance and i n i t i a l f r y s i z e o f . t h e enhanced pink p o p u l a t i o n . In f i g u r e 2!4 (enhancement m i g r a t i o n beginning 16 March) , the i n i t i a l s i z e of enhancement pink f r y has no e f f e c t on the estimate of enhanced f r y m o r t a l i t y (0%) over the e n t i r e range of enhanced pink abundance. Regardless of t h e i r i n i t i a l s i z e or any r e d u c t i o n i n growth r a t e due to d e n s i t y - r e l a t e d e f f e c t s , they are s t i l l too b i g to eat when the coho smolts reach the es t u a r y . N e v e r t h e l e s s , i n c r e a s i n g t h e i r i n i t i a l s i z e may improve t h e i r s u r v i v a l chances i f they have to enter the es t u a r y l a t e r i n the season. For example, i n f i g u r e 25 FIGURE 24?. E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 16 M a r c h ) The c o m b i n e d e f f e c t on t h e i n d i c a t o r s shown o f c h a n g i n g b o t h t h e i n i t i a l mean s i z e o f t h e e n h a n c e m e n t p i n k f r y and t h e i r i n i t i a l a b u n d a n c e . M o r t a l i t y a n d a d u l t r e t u r n o f e n h a n c e m e n t p i n k ("enhanced p i n k " ) a n d " w i l d " p i n k a n d chum a r e c a l c u l a t e d s e p a r a t e l y . E n h a n c e m e n t p i n k f r y b e g i n t o e n t e r t h e e s t u a r y on M a r c h 16. W i l d f r y m i g r a t i o n b e g i n s M a r c h 1. The i n i t i a l a b u n d a n c e o f w i l d p i n k , chum and c o h o i s c o n s t a n t ( 1 9 5 . 5 , 3 4 . 5, and 2 m i l l i o n , r e s p e c t i v e l y ) . F r y g r o w t h r a t e i s a f f e c t e d b y t e m p e r a t u r e and d e n s i t y f(*model 2) . Enhanced pink fry mortality (xlO 6) 24 T 18 12 oo • 0 0 Wild chum fry mortality (xlO6) 24 18 J-12 -120 - II-S • no -10-5 -i Wild pink fry mortality (xlO6) 24 t •148 I8| 12 • 144 140 136 % enhanced pink fry mortality Enhanced pink adult return (xlO 6 ) 0 0 0 0 % wild chum fry mortality 36 34 32 • 30 % wild pink fry mortality — 76 •74 -72 •70 18 • 14 10 Wild chum odult return (xlO 6) I 3-1 13-5 1 4 0 -4 Wild pink odult return (xlO 6) " -34 -.36 r 38 - 4 0 - 42 - 44 1 3-35 3-55 3-75 3-35 3-55 3-75 3-35 3-55 3-75 % enhanced pink adult return - 8 0 S -+-•80-3 % wild chum odult return 3 8 39 4 0 41 % wild pink adult return •18 •20 -22 3-35 3-55 3-75 Mean size (cm) of enhanced pink f r y - - e n t e r March 16 121 FIGURE 25. E f f e c t on Indicators of Changing Mean Size and Abundance of Enhancement Pink Fry (Migration Begins 1 April) The combined e f f e c t on the indicators shown of changing both the i n i t i a l mean size of the enhancement pink f r y and thei r i n i t i a l abundance. Mortality and adult return of enhancement pink ("enhanced pink") and "wild" pink and chum are calculated separately. Enhancement pink f r y begin to enter the estuary on A p r i l 1. Wild f r y migration begins March 1. The i n i t i a l abundance of wild pink, chum and coho i s constant (195.5, 34.5, and 2 m i l l i o n , r e s p e c t i v e l y ) . Fry growth rate i s affected by temperature and density (model 2). Enhanced pink fry mortality (xlO6) 2 4 T I 4 10 O O O 0~ O a o c o T 3 C 3 JD O c: Wild chum fry mortality (xlO ) 2 4 -I8t 122 12 + Wild pink fry mortality (xlO 6) C L 2 4 T c a x: cr . Lul 18 + 12 + 3-35 % enhanced pink fry mortality T63 49 35 21 7 % wild chum fry mortality % wild pink fry mortality Enhanced pink adult return (xlO 6) Wild chum adult return (xlO 6) 13-6 1 4 0 Wild pink adult return (xlO 6) 36 . 3-35 3-5 5 3-75 3-35 3 55 375 Mean size (cm) of enhanced pink f r y - - e n t e r Apri l I % enhanced pink adult return T I 3 6 0 ; % wild chum adult return 4L 3 9 . 42 — I % wild pink adult return 19 18. 2 3 , 3 35 3-55 3-75 ro ro FIGURE 2'6. E f f e c t on Indicators.of Changing Mean Size and Abundance of Enhancement Pink Fry (Migration Begins 15 April) The combined e f f e c t on the indicators shown of changing both the i n i t i a l mean size of the enhancement pink f r y and the i r i n i t i a l abundance. Mortality and adult return of enhancement pink ("enhanced pink") and "wild" pink and chum are calculated separately. Enhancement pink f r y begin to enter the estuary on A f r i l 15. Wild f r y migration begins March 1. The i n i t i a l abundance of wild pink, chum and coho i s constant (195.5, 34.5, and 2 m i l l i o n , r e s p e c t i v e l y ) . Fry growth rate i s affected by temperature and density (model 2). Enhanced pink fry mortality 24 r (xlO6) 18 to b o o o~ o o a> o c a -o c jQ O T3 <D O C a sz c UJ 12 + • 22 -18 -14 -II - 7 — 1 1 e Wild chum fry mortality (xlO ) 2 4 T 181 12 •10-4 -t-101 -I (xlO 6) Wild pink fry mortality 24 18 + 12 + 136 135 134 -133 3-35 3-55 3-75 % enhanced pink fry mortality 98 8 98-9 % wild chum fry mortality • 30-o -f-•29-3 -I % wild pink fry mortality 70 -68 3-35 3-55 3-75 Enhanced pink adult return (xlO3) Wild chum odult return --- 14-Z • -1 4-4 1 1 Wild pink adult return (xlO 6 ) 44 •45 "46 47. 335 3-55 3-75 % enhanced pink adult return less than 1% 1— % wild chum adult return 4 | _ "42 -t-% wild pink adult return "23 •24 3-35 3-55 3-75 Mean size (cm) of enhanced pink f ry - -enter April 15 ro FIGURE 2B. E f f e c t on I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d A b u n d a n c e o f E n h a n c e m e n t P i n k F r y ( M i g r a t i o n B e g i n s 1 May) The c o m b i n e d e f f e c t o n t h e i n d i c a t o r s shown o f c h a n g i n g b o t h t h e i n i t i a l mean s i z e o f t h e e n h a n c e m e n t p i n k f r y and t h e i r i n i t i a l a b u n d a n c e . M o r t a l i t y a n d a d u l t r e t u r n o f e n h a n c e m e n t p i n k ("enhanced p i n k " ) a nd " w i l d " p i n k a n d chum a r e c a l c u l a t e d s e p a r a t e l y . E n h a n c e m e n t p i n k f r y b e g i n t o e n t e r t h e e s t u a r y on May 1. W i l d f r y m i g r a t i o n b e g i n s M a r c h 1. The i n i t i a l a b u n d a n c e o f w i l d p i n k , chum and c o h o i s c o n s t a n t ( 1 9 5 . 5 , 3 4 . 5, a n d 2 m i l l i o n , r e s p e c t i v e l y ) . F r y g r o w t h r a t e i s a f f e c t e d b y t e m p e r a t u r e a n d d e n s i t y ( m o d e l 2 ) . Enhanced pink fry mortality % enhanced pink fry Enhanced pink adult return % enhanced pink odult (xlO 6) mortality (xlO 3) return D H 1 1 H 1 1 J 1 1 4 1 1 3 35 3-55 3-75 3 35 355 3-75 3-35 355 3-75 3 35 3 55 3-75 Mean size (cm) of enhanced pink fry —enter May I ro FIGURE 28. E f f e c t o n I n d i c a t o r s o f C h a n g i n g Mean S i z e a n d D a t e o f E n t r y o f E n h a n c e m e n t P i n k F r y The c o m b i n e d e f f e c t on t h e i n d i c a t o r s shown on c h a n g i n g b o t h t h e i n i t i a l mean s i z e o f t h e e n h a n c e m e n t p i n k f r y and t h e i r i n i t i a l d a t e o f . e n t r y i n t o t h e e s t u a r y . S t a r t o f e n h a n c e d p i n k f r y e n t r y i n t o e s t u a r y l a g g e d ( i n # o f d a y s ) f r o m 1 M a r c h ! . F i g u r e 29 was c r e a t e d f r o m i n f o r m a t i o n t a k e n f r o m f i g u r e s 25 t o 28 f o r an e n h a n c e d p i n k f r y i n i t i a l a b u n d a n c e o f 18 m i l l i o n . Enhanced pink fry mortality % enhanced pink fry Enhonced pink adult return % enhanced pink adult U IO 6 ) mortality (x lO 6 ) return 61 r I T T Mean size (cm) of enhanced pink fry m o r t a l i t y o f e n h a n c e d p i n k f r y r a n g e s f r o m l e s s t h a n 7% f o r f r y 3.7 5 cm t o g r e a t e r t h a n 63% f o r f r y 3.3 5 cm. I n f i g u r e 2t]l t h e e n h a n c e d f r y m i g r a t e t o o l a t e f o r t h e i n c r e a s e i n s i z e t o i m p r o v e t h e i r c h a n c e s f o r s u r v i v a l . T h e y a c t a s a n a l t e r n a t i v e p r e y i t e m a t a t i m e when v u l n e r a b l e w i l d f r y a r e a l r e a d y i n s h o r t s u p p l y . The t o t a l a n n i h i l a t i o n o f t h e s e f r y i s due t o t h e m o d e l ' s a s s u m p t i o n s o f no p r e y r e f u g i a , t o t a l o v e r l a p o f p r e y a n d p r e d a t o r s p a t i a l d i s t r i b u t i o n s a n d t h e c o n t i n u e d e s t u a r i n e r e s i d e n c e o f a l l c o h o s m o l t s . T h e s e a s s u m p t i o n s , a l t h o u g h u n r e a l i s t i c , do n o t i n v a l i d a t e t h e d e m o n s t r a t e d r e l a t i o n s h i p b e t w e e n s u r v i v a l and m i g r a t i o n t i m i n g , e t c . F i g u r e 2 8 i l l u s t r a t e s t h e r e l a t i o n s h i p b e t w e e n e n h a n c e d f r y i n i t i a l s i z e , d a t e o f m i g r a t i o n and m o r t a l i t y f o r a c o n s t a n t a b u n d a n c e (18 m i l l i o n ) o f e n h a n c e m e n t p i n k f r y . I f t h e e n h a n c e m e n t p i n k f r y e n t e r t h e e s t u a r y e a r l y a s i n f i g u r e 2'fy, m o r t a l i t y t o w i l d p i n k and chum f r y i n c r e a s e s ( e . g . w i l d p i n k f r y m o r t a l i t y i n c r e a s e d f r o m l e s s t h a n 7 0% t o g r e a t e r t h a n 76%) a s t h e a b u n d a n c e o f e n h a n c e m e n t p i n k f r y i n c r e a s e s . The i n c r e a s e d t o t a l d e n s i t y o f f r y i n t h e e s t u a r y d e p r e s s e s t h e g r o w t h r a t e o f t h e e n t i r e r u n o f w i l d f r y , t h e r e b y i n c r e a s i n g t h e number o f f r y and l e n g t h o f t i m e t h e y a r e v u l n e r a b l e t o p r e d a t i o n . H owever, i n f i g u r e s 25 t o 2% t h e e n h a n c e d p i n k s t o c k s a r e e n t e r i n g t h e e s t u a r y l a t e r i n t h e s e a s o n . T h u s t h e i n c r e a s e i n t o t a l f r y a b u n d a n c e a n d t h e r e s u l t i n g d e n s i t y - r e l a t e d r e d u c t i o n i n w i l d f r y g r o w t h r a t e h a s l e s s o f a n i m p a c t on t h e w i l d f r y a l r e a d y i n t h e e s t u a r y . W i l d f r y m o r t a l i t y r e t u r n s a l m o s t t o t h e p r e - e n h a n c e m e n t l e v e l o f 67 a n d 28 p e r c e n t , r e s p e c t i v e l y , i n f i g u r e 27>. T h i s 130 p a t t e r n o f r e s u l t s o c c u r s f o r t h r e e r e a s o n s : 1. The o v e r a l l p a t e r n o f f r y d e n s i t y i n t h e e s t u a r y c h a n g e s i n r e s p o n s e t o t h e e n h a n c e d f r y e n t r y d a t e , t h e i r t o t a l a b u n d a n c e a n d t h e l e n g t h o f t i m e t h e i r p r e s e n c e i n t h e e s t u a r y o v e r l a p s w i t h t h a t o f t h e w i l d f r y . A s d i s c u s s e d f o r f i g u r e 2%, t h i s c h a n g i n g d e n s i t y p a t t e r n i s r e f l e c t e d i n t h e g r o w t h r a t e o f w i l d f r y , i n t h e l e n g t h o f t i m e w i l d f r y r e m a i n i n t h e e s t u a r y , a n d i n t h e number o f w i l d f r y a v a i l a b l e and v u l n e r a b l e a t a n y g i v e n t i m e . W i t h t h e l a t e r i n t r o d u c t i o n o f e n h a n c e d f r y , more o f t h e w i l d f r y h a v e e i t h e r l e f t t h e e s t u a r y o r a l r e a d y o u t g r o w n t h e p r e d a t o r . F o r e x a m p l e , f o r one p i n k c o h o r t , i t t o o k 56 d a y s t o r e a c h 8.1 cm u n d e r one s e t o f d e n s i t y c o n d i t i o n s and 8 0 d a y s t o r e a c h o n l y 6.3 cm u n d e r a n o t h e r s e t o f d e n s i t y c o n d i t i o n s . ( U n f o r t u n a t e l y t h i s e x a m p l e r e l a t e s s p e c i f i c a l l y t o t h e m o d e l e x p e r i m e n t d i s c u s s e d p r e v i o u s l y (where t h e p r e y : p r e d a t o r r a t i o was i n c r e a s e d f r o m 57.5:1 t o 230:1) b e c a u s e I d i d n o t r e c o r d t h i s i n f o r m a t i o n f o r t h e s p r e s e n t i e T x p e E i m e n t s . N e v e r t h e l e s s , t h e e f f e c t s a r e c o m p a r a b l e , a l t h o u g h l e s s e x t r e m e b e c a u s e t h e d e n s i t y i n c r e a s e i s l e s s e x t r e m e a n d d i s t r i b u t e d d i f f e r e n t l y o v e r t h e s e a s o n . ) 2. S i n c e a l l o f t h e e n h a n c e d f r y c a n no l o n g e r o u t g r o w t h e i r c o h o p r e d a t o r s b e f o r e t h e y r e a c h t h e e s t u a r y , t h e y a r e now s u b j e c t t o p r e d a t i o n 131 m o r t a l i t y a n d t h u s b u f f e r w i l d p i n k a n d chum f r y t o some e x t e n t f r o m p r e d a t i o n . F o r e x a m p l e , w i l d p i n k f r y m o r t a l i t y i s r e d u c e d f r o m 77.6% i n f i g u r e 24 t o 70% i n f i g u r e 26, f o r a c o n s t a n t i n i t i a l a b u n d a n c e (24 m i l l i o n ) o f e n h a n c e m e n t p i n k s a l m o n . 3. The i n c r e a s e d s i z e o f e n h a n c e m e n t p i n k f r y m i g r a t i n g l a t e i n t h e s e a s o n d o e s n o t s u b s t a n t i a l l y r e d u c e t h e i r v u l n e r a b i l i t y t o p r e d a t i o n r e l a t i v e t o w i l d f r y b e c a u s e t h e i n i t i a l s i z e o f w i l d f r y a l s o i n c r e a s e s o v e r t i m e . T h us t h e p o t e n t i a l i n c r e a s e i n e n h a n c e d f r y s u r v i v a l , a c h i e v e d b y t h e r i g h t c o m b i n a t i o n o f m i g r a t i o n t i m i n g a n d s i z e a t m i g r a t i o n , i s c o n f i r m e d b y t h i s e x p e r i m e n t . The most i m p o r t a n t r e s u l t o f t h e s e e x p e r i m e n t s , h o w e v e r , i s t h e p o s s i b l e n e g a t i v e i m p a c t on w i l d p i n k a n d chum f r y p o p u l a t i o n s due t o t h e p r e s e n c e o f t h e e n h a n c e d s t o c k . I n t h e e x a m p l e shown i n T a b l e 1 1 , w i l d p i n k a n d chum f r y m o r t a l i t y i n c r e a s e s 2.4 t o 9.5 p e r c e n t and 1.8 t o 8.4 p e r c e n t , r e s p e c t i v e l y . The s u b s e q u e n t d e c r e a s e s i n w i l d p i n k a n d chum i a d u i f c r r . e t u r a i : a r e b a r e l y c o m p e n s a t e d f o r by t h e i n c r e a s e i n t o t a l a d u l t s a l m o n r e t u r n due t o t h e e n h a n c e m e n t p r o j e c t (0.8 t o 2.9 m i l l i o n i n c r e a s e i n a d u l t r e t u r n s ) . N e v e r t h e l e s s , t h e p r o j e c t w o u l d be j u d g e d a s u c c e s s i f t h i s w e r e b a s e d on t h e s u r v i v a l o f e n h a n c e d f i s h a l o n e . I t i s d o u b t f u l , g i v e n t h e n a t u r a l v a r i a b i l i t y o f t h e " r e a l " s y s t e m , i f d e c r e a s e s o f t h e m a g n i t u d e shown i n T a b l e 11 i n w i l d p i n k a n d chum a d u l t r e t u r n w o u l d be n o t i c e d o r e v e n a t t r i b u t e d t o t h e e n h a n c e m e n t p r o j e c t . I t h a r d l y n e e d s t o be s a i d how i m p o r t a n t t h i s r e s u l t i s : C r e a t i n g c o n d i t i o n s w h i c h 132 TABLE 11. One example predicted by the model of the negative e f f e c t enhancement pink populations may have on wild pink and chum populations. . Enhanced f i s h migrate March 16 - March 22. Results were independent of size at migration. Both temperature and density (model 2) were assumed to a f f e c t f r y growth rate. Wild pink and chum f r y increase i n i n i t i a l mean size over time. The i n i t i a l wild prey:predator r a t i o i s 115:1. Wild f r y migration begins March 1. Number of fry eaten and adult return are i n m i l l i o n s of f i s h . Predicted wild pink and chum adult returns are much higher than actually observed i n the 'real' system. Nevertheless the basic message of the experiment i s s t i l l v a l i d . cont'd. TABLE 11, P a g e 2. E n h a n c e d P i n k S t o c k A b u n d a n c e ( m i l l i o n s ) 0.02 6.0 12.0 18.0 24.0 # P i n k 1 f r y e a t e n 131.0 135.6 140.2 144.9 149.5 % P i n k f r y e a t e n 67.1 69.5 71.9 74.3 76.6 # Chum 1 f r y e a t e n 9.6 10.2 10.9 11.6 12.5 % Chum f r y e a t e n 27.8 29.6 31.6 33.8 36.2 # P i n k 1 a d u l t r e t u r n 48.2 44.6 41.0 37.3 33.7 % P i n k a d u l t r e t u r n 24.7 22.9 21.0 19.1 17.3 # Chum 1 a d u l t r e t u r n 14.8 14.4 14.0 13.6 13.1 % Chum a d u l t r e t u r n 43.0 31.9 40.7 39.4 37.9 # E n h a n c e d p i n k a d u l t r e t u r n 0.0 4.8 9.6 14.4 19.2 . 3 T o t a l n e t increase i n f i s h r e t u r n s 0.0 0.8 1.6 2.3 ;.2v9 " W i l d " p i n k a n d chum p o p u l a t i o n s . C o n t r o l T o t a l n e t i n c r e a s e i n f i s h r e t u r n s e q u a l s e n h a n c e d p i n k r e t u r n m i n u s t h e d e c r e a s e i n w i l d p i n k and chum a d u l t r e t u r n , a s c o m p a r e d t o t h e c o n t r o l ( i . e . , no e n h a n c e m e n t s t o c k ) . 134 increase the l i k e l i h o o d of survival of enhancement stocks may re s u l t i n a decrease i n the survival of natural stocks and could lead to their eventual destruction. 4. Examination of Data found i n the Literature The res u l t s of experimentation with the model suggest that: 1. the presence of pink f r y i n the estuary may buffer chum f r y from predation, or 2. the presence of pink f r y i n the estuary may r e s u l t i n density-related reductions i n chum growth rate/ with a subsequent increase i n predation mortality.; because small f r y are subject to predation for a longer period of triime and more of them are required to satiate the predator.. I looked for evidence i n the l i t e r a t u r e to support either 1 or 2. Fraser River pink f r y are produced i n s i g n i f i c a n t numbers only during odd brood years and thus create a "natural" experiment. I encountered a number of problems-,! ho.wewe'2t,erwh?env r-».a'fe'fc'emp^ edirtr6:i.use>ft&£s> -ver, whs-ap.p.r.oachui to use th.-.s .approach: 1. Estimates of f r y production and survival are v i r t u a l l y non-existent,in the l i t e r a t u r e or cover such a limited time span they are of l i t t l e use. 2. There seems to be no coordination or consistent method of data gathering or reporting by the a g e n c i e s r e s p o n s i b l e f o r t h e d i f f e r e n t s p e c i e s o f s a l m o n f o u n d i n t h e F r a s e r R i v e r , a n d no a t t e m p t i s made t o s y n t h e s i z e t h e d a t a g a t h e r e d . C o n s e q u e n t l y , i t was d i f f i c u l t t o o b t a i n t h e n e c e s s a r y d a t a f o r b o t h p i n k a n d chum s a l m o n o v e r a s u f f i c i e n t l y l o n g t i m e s p a n . 3. The two t o f i v e y e a r l i f e h i s t o r y c y c l e o f chum s a l m o n makes a n a l y s i s d i f f i c u l t . 4. F r y - t o - a d u l t m o r t a l i t y e s t i m a t e s i n c l u d e t h e p e r i o d o f e s t u a r i n e a n d o c e a n i c l i f e . A l t h o u g h i t h a s g e n e r a l l y b e e n a c c e p t e d t h a t ocean'mortality r a t e s i a r e y m c h t l o w e r r t h a n j e s ^ ^ 1976') / v a r i a b i l i t y i n jocean . m o r t a l i t y c o u l d i l e a d t o ;mis-rleadingiTiconclusiqns7 G"cEgg-t©,-t£ry frortald'tya estimates cover cthecegg and'part o f the freshwater f r y stages o f l i f e . 5. E s t i m a t e s o f f r y - t o - a d u l t s u r v i v a l d e p e n d on t h e o r i g i n a l e s t i m a t e s o f e g g - t o - f r y s u r v i v a l . T h u s , a n y c o n c l u s i o n s b a s e d o n e s t i m a t e s o f f r y - t o -a d u l t s u r v i v a l may be a n a r t i f a c t o f e r r o r s made i n t h e o r i g i n a l e s t i m a t e s o f e g g - t o - f r y s u r v i v a l . F o r e x a m p l e , g i v e n a c o n s t a n t number o f r e t u r n i n g a d u l t s , a 5% v e r s u s a 10% e s t i m a t e o f e g g - t o - f r y s u r v i v a l r e s u l t s i n a 100% i n c r e a s e i n t h e e s t i m a t e o f f r y - t o - a d u l t s u r v i v a l . T h u s t h e f o l l o w i n g a n a l y s i s s h o u l d o n l y be c o n s i d e r e d s u g g e s t i v e o f f u t u r e a v e n u e s o f i n v e s t i g a t i o n . I p o s t u l a t e d t h a t i f t h e p r e s e n c e o f p i n k f r y w e r e t o r e d u c e t h e s u r v i v a l r a t e o f chum f r y , t h e n t h i s w o u l d be e v i d e n t f r o m a c o m p a r i s o n o f e v e n a n d o d d b r o o d y e a r e s t i m a t e s 136 of chum s u r v i v a l . (This assumes that the only difference between odd- and even-year brood years i s the presence or absence of pink fry.) I f i r s t looked at freshwater egg-to-fry chum survival because what happens at t h i s l i f e stage i s important to the analysis of the marine l i f e stage. Pink and chum salmon share the same major spawning areas i n the Fraser River below Hope and migrate to sea at about the same time. Major concentrations of coho are also found i n these areas. Using data provided by Fraser (1976) for brood years 1964 to 1974, I found that mean chum egg-to-fry su r v i v a l was lower during even, non-pink brood years than during odd, pink brood years .(11.64%yversus 16.25%). Although the difference was not s i g n i f i c a n t (arc sin square root transform of data, t-test,p'> 0005) , i t suggests that chum fry may be buffered from predation by the presence of pink f r y . Figure 29 seems to support t h i s contention: chum mortality during the egg-to-fry l i f e stage appears to be depensatory although the relat i o n s h i p between t o t a l egg abundance and chum egg-to-fry survival was not s i g n i f i c a n t (t-test,p>0.05). The poten t i a l benefit of increasing the abundance of f r y migrating downstream at any one •time iirayybe)<masked<<teQ Spmeh^^teMefc^^^e^ScOlr^i^hj^ S^f11 deposition due to non-predator mortality on the spawning grounds (such as egg suffocation or egg displacement by late spawners). The reverse sit u a t i o n was true for chum fry-to-adult s u r v i v a l . Using a combination of data taken from Palmer (197 2) and Fraser (1976) for brood years 1961 to 1970, I found that mean chum fry-to-adult survival was higher during even, non-pink FIGURE 29. Relation Between % Chum Egg-to-Fry Survival and Total Pink and Chum Egg Deposition Relation between percent egg-to-fry survival of Fraser River chum salmon and the estimated t o t a l egg deposition of Fraser River pink and chum salmon (brood years 1964 to 1974). Fraser River pink fry are produced only during odd brood years. Brood years are indicated for each data point. Source of data: Fraser (1976). 2 4 2CH > CO I O •4— I CP CP CD e 3 SZ O 16-J 12 8 A 4-\ r = 0 - 4 8 4 p r 0 0 5 • 70 .67 '71 >68 T 4 8 12 16 20 2 4 28 8 3Estimated pink and chum abundance in eggs (xlO ) 00 139 brood years than during odd, pink brood years (1.54% versus 0.91%). Again the difference i s not s i g n i f i c a n t (are s i n square root transform of data, t - t e s t , p > 0.05) but i t does suggest that the presence of pink salmon may have a negative e f f e c t on chum survival a f t e r they leave the r i v e r . A l t e r n a t i v e l y , perhaps i f the abundance of pink and chum f r y were increased even more, the percent mortality would decrease due to predator saturation (assuming there was not a concomitant increase i n mortality due to other sources such as disease). Figure 3 0 suggests that chum fry-to-adult survival may be related more to the t o t a l abundance of pink and chum f r y i n the estuary than to the presence or absence of pink f r y per se. There was no rel a t i o n s h i p between chum fry-to-adult survival and chum fry abundance alone over the range of chum abundances examined. Thus the increase i n t o t a l f r y abundance during pink years may have a net negative e f f e c t on the survival of chum salmon. Any increase i n sur v i v a l due to pink buffering during the early egg-to-fry stage may be more than compensated for by the increase i n mortality occurring l a t e r . Whether the increase i n mortality occurs i n the estuary or during a l a t e r period of l i f e can not be determined from these data. A l t e r n a t i v e l y , t h i s change from a lower average even brood year chum egg-to-fry survival i n a higher average even brood year chum fry-to-adult survival (com-pared to odd brood years) could be due to measurement error i n the estimates of egg-to-fry survival ( i . e . , #5, p. 135)! Further-more, even without measurement error, i t i s very d i f f i c u l t to obtain "evidence of s i g n i f i c a n t e f f e c t s " from a short series of observations (see discussion i n Ricker, 1975). Thus the 140 FIGURE 3®. Relation Between % Chum Fry-to-Adult Survival and Total Pink and Chum Fry Abundance Relation between percent fry-to-adult survival of Fraser River chum salmon and the t o t a l abundance of Fraser River pink and chum fry (brood years 1964 to 1970). Fraser River pink salmon are produced only during odd brood years. Brood years are indicated for each data point. Source of data: Fraser (1976) . 3 H • • 6 8 • 65 I H 7 0 ^ * 6 6 • 6 9 167 1 1 1 1 1 1 1 1 100 2 0 0 3 0 0 4 0 0 Estimated pink and chum fry abundance (xlO ) 142 suggestions as to what might be occurring during each l i f e - s t a g e are speculative and require further investigation. If the decrease i n chum survival i s a d i r e c t r e s u l t of density dependent decreases i n growth rate either i n the estuary or l a t e r i n l i f e , then one might expect to be able to observe at l e a s t one of the following: 1. A decrease i n the mean size of chum salmon produced from high density brood years and a subsequent decrease i n the proportion of age three adult returns. (This assumes that age of return i s related to size or growth rate as Foerster (.1968) suggests i t i s for sockeye.) Thus, the mean size of chum which do return as three year olds may not show any s i g n f i c i a n t decrease. 2. A decrease i n the v a r i a b i l i t y of size at return and an increase, rather than a decrease, i n mean size at return due to the increased s u s c e p t i b i l i t y and mortality of small-sized chum during high density brood years. This selection by predators of slower-growing f i s h could also lead to a decrease i n mean age at return, i f the assumption made i n #1 i s true. It should be noted, however, that experi-ments conducted by Jones (1958) and Ricker (1969) (both c i t e d by Ricker, 1975) suggest that any change i n the shape of the size d i s t r i b u t i o n or the v a r i a b i l i t y of the frequency d i s t r i b u t i o n due to even quite severe non-linear s i z e - s e l e c t i v e mortality 143 i s l i k e l y to be "too l i t t l e to be detectable i n practice (Ricker, 1975)." 3. An o v e r a l l increase i n mean size of chum salmon produced during high density brood years because the increase' i n mortality may actually r e s u l t i n improved growth of the chum which survive. I found that the mean length of age three, male chum salmon was s i g n i f i c a n t l y larger for chum produced during odd brood years (73.8 cm versus 70.7 cm; t - t e s t , p < 0.02). The difference i n mean length between odd and even brood year, age three female chum salmon was not s i g n i f i c a n t (68.8 cm versus 67.3, respectively; t - t e s t , p > 0.05). For age four chum salmon the differences i n mean length, between odd and even brood year f i s h , were also i n s i g n i f i c a n t . This i s due, perhaps to the possible masking e f f e c t of one extra year of growth. (The analysis was done on data taken from Palmer $1972) for brood years 1957 to 1966.) Thus, although there may be a r e a l increase i n the mean size of age three chum salmon produced from odd brood years, the reason for t h i s increase i s not apparent. There were i n s u f f i c i e n t data to ascertain i f there was a re l a t i o n s h i p between the proportion of chum returning at age three and t h e i r s i z e . There did not appear to be any rela t i o n s h i p between the proportion of chum returning at age three and chum fry-to-adult survival for brood years 1961 to 1970. (These data were taken from Anderson (1976), Palmer (197 2) and Fraser (1976). 143a Although figure 31 suggests an i n t r i g u i n g r e l a t i o n s h i p between the proportion of chum returning at age three and the t o t a l abundance of pink and chum f r y , I can not explain i t based on the information available for those years. Godfrey (1959) looked at the average annual weight of pink salmon i n B r i t i s h Columbia and southeastern Alaska and found that pink salmon from the even-year cycle ( l i k e Fraser River male chum salmon) were consistently smaller than those of the odd-year cycle. Furthermore, during t h i s time period i n both B r i t i s h Columbia and southeastern Alaska, odd-year cycle pink salmon were more abundant than the even-year cycle which suggested that i n t r a s p e c i f i c competition for available food was not a factor i n the decreased size of even-year cycle f i s h (Godfrey, 1959). The s i m i l a r i t y i n the trend (1944-1958) of average size among f i v e d i s t i n c t geographical areas, extending from southern B r i t i s h Columbia to southeastern Alaska, suggests that "at lea s t during that phase of t h e i r ocean residence which i s most important i n determining th e i r f i n a l s i z e , the several stocks of B r i t i s h Columbia pink salmon have l i v e d and fed either i n the same ocean area, or i n adjacent areas s i m i l a r l y affected by variations i n oceanographic conditions (Godfrey, 1959)." Size differences, however, can occur without food l i m i t a t i o n . Brown (1957) found that "when groups of fishes of 144 FIGURE 31. Relation Between Age Three Chum Returns and Total Pink and Chum Fry Abundance Relation between the proportion of Fraser River chum returning at age three and the t o t a l abundance of Fraser River pink and chum f r y (brood years 1964 to 1971). Fraser River pink fry are produced only during odd brood years. Brood, years are indicated for each data point. Percent age three chum return for 1971 i s based on incomplete data (5 yearsolds had not yet returned). Age three chum salmon return to spawn aft e r spending two years at sea. Source of data: Anderson (1976) and Fraser (1976). Q Chum adult return percentage o o ro o _ o * o O =r = O - h o age three ro o _L_ O J _ CD O o • cn CD CD cn cn ^ cn o o 146 one species are kept together, i t commonly happens that the dispersion i n size between the largest and smallest individuals increases as they grow larger." Furthermore, Blaxter (1965), studying the feeding and ecology of herring larvae, found that "at the end of a period of two to three months afte r hatching the largest larva i n a tank may be twice the length of the shortest, although abundant food has been offered and the larvae came from the same parents." They both suggest that t h i s increase i n size v a r i a b i l i t y i s due to "size-hierarchy" e f f e c t s — l a r g e r f i s h being more aggressive and there by i n h i b i t i n g the feeding response of smaller f i s h . The greater abundance, hence increased estuarine density, of odd-year cycle pinks may accentuate t h i s e f f e c t . Martin (1966) found that size differences within a population of pink salmon from Alaska could r e s u l t from differences i n timing of migration (food supply c o n t r o l l e d ) . He found that early migrants not only were s i g n i f i c a n t l y greater i n size by the time late migrants entered the estuarines but also retained t h i s r e l a t i v e size difference. If survival i s p o s i t i v e l y related to si z e , any negative e f f e c t s on growth caused by the greater abundance of odd-year cycle pinks may be masked by the decreased survival of small f i s h . This i s very l i k e l y i f Martin's (.1966) observations are correct and i f late migrants are more affected than early migrants by the increase i n abundance: r e l a t i v e l y more early migrants would contribute to the f i n a l return of adult pink salmon. 147 Thus t h e h i g h e r mean s i z e o f t h e o d d - y e a r c y c l e p i n k s a l m o n c o u l d be t h e r e s u l t o f t h e s e c o m b i n e d e f f e c t s . I t i s a l s o p o s s i b l e t h a t i n t e r s p e c i f i c r a t h e r t h a n i n t r a s p e c i f i c c o m p e t i t i o n f o r a v a i l a b l e f o o d i s c a u s i n g t h e r e d u c e d s i z e o f e v e n - y e a r c y c l e f i s h . T h e r e i s e v i d e n c e ( R o y c e , e t a l . , 1968, c i t e d b y L a r k i n , 1975) t h a t t h e f i v e s p e c i e s o f O n c o r h y n c h u s f r o m N o r t h A m e r i c a h a v e o v e r l a p p i n g s p a t i a l a n d t e m p o r a l d i s t r i b u t i o n s i n t h e N o r t h P a c i f i c . U s i n g t o t a l N o r t h A m e r i c a n c a t c h (1952-1972) o f O n c o r h y n c h u s a s a n i n d e x o f a b u n d a n c e , I f o u n d t h a t t h e a v e r a g e w e i g h t o f p i n k s a l m o n was n e g a t i v e l y c o r r e l a t e d w i t h t o t a l N o r t h A m e r i c a n s a l m o n catovh (r=-0.516) an d t h a t t h i s c o u l d a c c o u n t f o r a s i g n i f i c a n t p r o p o r t i o n o f t h e v a r i a n c e ( F - t e s t , p<.025, f i g u r e 3 2 ) . T hus t h e d i f f e r e n c e i n w e i g h t b e t w e e n o d d - and e v e n - y e a r c y c l e p i n k s a l m o n may be d u e , i n p a r t , t o s p e c i e s i n t e r f e r e n c e o r c o m p e t i t i o n f o r f o o d i n t h e o c e a n d u r i n g y e a r s o f h i g h O n c o r h y n c h u s d e n s i t y r a t h e r t h a n p i n k s a l m o n d e n s i t y p e r s e . T h i s i n t e r p r e t a t i o n i s v a l i d o n l y i f t o t a l N o r t h A m e r i c a n c a t c h t e n d s t o be g r e a t e r i n e v e n y e a r s t h a n odd y e a r s ; a t r e n d t h a t a p p e a r s l i k e l y f r o m f i g u r e 3%. A l t e r n a t i v e l y , one c o u l d a r g u e , e s p e c i a l l y i f o n l y F r a s e r R i v e r p i n k s a l m o n w e r e c o n s i d e r e d , t h a t t h e i n c r e a s e d a v e r a g e w e i g h t o f o d d - y e a r c y c l e p i n k s was due t o g e n e t i c d i f f e r e n c e s a n d t h e c o r r e l a t i o n w i t h t o t a l N o r t h A m e r i c a n c a t c h s p u r i o u s . ( F r a s e r R i v e r p i n k s a l m o n t e n d t o be l a r g e , e v e n f o r o d d - y e a r c y c l e f i s h ( G o d f r e y , 1 9 5 9 ) . ) F i g u r e 33, h o w e v e r , shows t h a t mean s i z e o f a d u l t p i n k a n d age t h r e e chum s a l m o n , p r o d u c e d d u r i n g t h e same b r o o d y e a r , a r e p o s i t i v e l y c o r r e l a t e d ( r = 0 . 7 9 5 , F - t e s t , p < 0 . 0 1 ) ; w i t h f i s h f r o m o d d - b r o o d 148 FIGURE 32. Relation Between Average Adult Pink Salmon Weight and Total North American Catch (in pieces) of Oncorhynchus Salmon Relation between B r i t i s h Columbia average pink adult weight , and abundance of North American Oncorhynchus catch (catch years 1952 to 1972). Fraser River pink salmon are only present i n the catch during odd catch years. Source of data: INPFC (1976, unpublished manuscript) and B.C. Catch S t a t i s t i c s . FIGURE 33. Relation Between Adult Pink Salmon Weight and Length of Age Three Adult Chum Salmon Relation between B r i t i s h Columbia average pink adult weight and average length of age three Fraser River chum salmon (brood years 1957 to 1966). Data include both males and females. Fraser River pink salmon are produced and caught only during odd years. Brood years are indicated for each data point. Age three chum salmon return to spawn after spending two years at sea. Source of data: Palmer (1972) and B.C. Catch S t a t i s t i c s . CD cn k_ — CD > D r-1 1 5-J C < 3 CD 5 ' r = 0 - 7 9 5 p k O O l 62* 5 7 . 61 T ~r~ 58 62 66 7 0 7 4 78 Age three chum average length ( c m ) T T T 152 y e a r s b e i n g l a r g e r , i n g e n e r a l . U n l e s s t h e d i f f e r e n c e i n s i z e b e t w e e n e v e n - a n d o d d - y e a r c y c l e chum i s a l s o g e n e t i c , t h i s r e s u l t s u g g e s t s t h a t p i n k a n d chum s a l m o n a r e b e i n g a f f e c t e d by s i m i l a r f a c t o r s a t s e a . Due t o t h e l i f e h i s t o r y c h a r a c t e r i s t i c s o f F r a s e r R i v e r p i n k and age t h r e e chum, F r a s e r R i v e r p i n k s a l m o n p o t e n t i a l l y c o h a b i t w i t h o d d - and e v e n - y e a r c y c l e F r a s e r R i v e r chum o n l y d u r i n g t h e chum's f i r s t o r s e c o n d y e a r o f m a r i n e l i f e , r e s p e c t i v e l y . I f t h e l e n g t h i n c r e m e n t f o r chum s a l m o n d u r i n g t h e f i r s t o c e a n y e a r i s a p p r e c i a b l y l a r g e r t h a n t h a t o f s u b s e q u e n t y e a r s , a s i t i s f o r s o c k e y e s a l m o n ( F o e r s t e r , 1 9 6 9 ) , t h e n c o n d i t i o n s d u r i n g t h i s f i r s t y e a r a t s e a may l a r g e l y d e t e r m i n e t h e u l t i m a t e s i z e o f age t h r e e chum s a l m o n . A l t h o u g h t h e d a t a s u g g e s t t h a t i n t e r - s p e c i e s i n t e r a c t i o n s a r e o c c u r r i n g , t h e e v i d e n c e i s weak diiie t o t h e p a u c i t y o f d a t a a v a i l a b l e a n d t h e c o m p l e x i t y o f t h e p r o b l e m . I t m i g h t p r o v e w o r t h w h i l e , h o w e v e r , t o e x a m i n e some o f t h e i s s u e s r a i s e d i n g r e a t e r d e p t h . F o r e x a m p l e , a c o m p a r i s o n o f o d d - a n d e v e n - y e a r c y c l e , age t h r e e chum s c a l e s m i g h t d e t e r m i n e i f o c e a n g r o w t h i s r e a l l y d i f f e r e n t d u r i n g t h e i r f i r s t y e a r a t s e a . D e t e r m i n i n g t h e p o s s i b l e a v e n u e s o f i n t e r a c t i o n b e t w e e n s p e c i e s a n d t h e i r e f f e c t s on g r o w t h and s u r v i v a l may p r o v e t o b e v e r y i m p o r t a n t i n v i e w o f f u t u r e e n h a n c e m e n t p r o p o s a l s . F o r e x a m p l e , w o u l d r e s t o r a t i o n o f an e v e n - y e a r p i n k r u n t o t h e F r a s e r R i v e r h a v e a n e t b e n e f i c i a l o r n e g a t i v e e f f e c t on t h e s u r v i v a l a n d g r o w t h o f chum s a l m o n ? 153 CHAPTER I V . GENERAL DISCUSSION The p u r p o s e o f a n a l y s i s i s t o "make e x p l i c i t t h e c o m p l e x i t y t h a t i s h i d d e n by t h e more a b b r e v i a t e d c h a r a c t e r o f t h e i r [ i e . a s s e r t i o n s , h y p o t h e s e s , e t c . ] u s u a l v e r b a l f o r m u l a t i o n ( Q u i n t o n , 1 9 7 7 ) . " As t h i s t h e s i s c l e a r l y d e m o n s t r a t e s , s i m u l a t i o n m o d e l l i n g c a n be a u s e f u l t o o l f o r d o i n g t h i s . F r om j u s t t h e i n i t i a l p h a s e o f d a t a s y n t h e s i s u s e d t o b u i l d t h e m o d e l , I was a b l e t o i d e n t i f y a r e a s n e e d i n g f u r t h e r r e s e a r c h . F o r e x a m p l e , t h e r e l a t i v e p o s i t i o n s o f p r e y and p r e d a t o r i n t h e w a t e r c o l u m n d e t e r m i n e n o t o n l y t h e d e n s i t y o f p r e y and p r e d a t o r p e r u n i t v o l u m e o f w a t e r b u t a l s o t h e " e f f e c t i v e v o l u m e " o f w a t e r s e a r c h e d by t h e p r e d a t o r . The t h e o r e t i c a l e f f e c t o n p r e y e n c o u n t e r r a t e o f d i f f e r e n t a s s u m p t i o n s r e g a r d i n g t h e i r r e l a t i v e p o s i t i o n s i n t h e w a t e r c o l u m n s h o u l d be s t u d i e d . a n d c o m p a r e d t o l a b o r a t o r y s t u d i e s o f e n c o u n t e r r a t e . I was a l s o a b l e t o u s e t h e m o d e l t o i d e n t i f y t h e p a r a m e t e r s w h i c h w e r e m o s t s e n s i t i v e t o c h a n g e a n d t o r e l a t e t h e s e r e s u l t s t o p r o p o s a l s f o r e n h a n c e m e n t , e v e n t h o u g h t h e r e a r e w e a k n e s s e s i n t h e m o d e l due t o t h e p a u c i t y o f d a t a a v a i l a b l e t o d e s c r i b e many o f t h e b i o l o g i c a l p r o c e s s e s . F u r t h e r m o r e , 154 the potential exists for using t h i s model to a s s i s t managers i n making decisions regarding future enhancement proposals. Enhancement managers have been given the mandate to increase the abundance of salmonid stocks (Johnson, 1976). The results of the s e n s i t i v i t y analysis and model enhancement experiments could be used to suggest alternative ways of achieving the "best" compromise between c o n f l i c t i n g objectives. For example, while the manager may be given the e x p l i c i t objective to increase the abundance of salmonid stocks, he usually must also consider less-defined but very r e a l " i m p l i c i t " objectives (ie. maximize d o l l a r return on investment costs of f r y production; minimize any possible negative e f f e c t s on wild stocks). While he may only be able to manipulate to some extent such parameters as enhanced f r y abundance, i n i t i a l s i z e , timing and duration of migration, he needs some method for evaluating the r e s u l t s of such manipulations. The model r e s u l t s showed that: 1. Increasing i n i t i a l size and migrating early i n the season may increase the likel'ihoodi.of pink. . and chum fry surviving estuarine coho predation. 2. Increasing the abundance of f r y entering the estuary may subs t a n t i a l l y increase f r y survival i f the prey:predator r a t i o also increases 155 s u f f i c i e n t l y ( i e . reach predator saturation). 3. S u s c e p t i b i l i t y to predation may depend f i r s t on the b i o l o g i c a l c h a r a c t e r i s t i c s of the prey species ( i e . growth rate) and second on the r e l a t i v e proportion of that species i n the prey population. 4. Wild populations of pink and chum may be negatively affected by decisions regarding the enhancement stock ( i e . the possible negative impact at c r i t i c a l times during the season of increased f r y density on wild f r y growth r a t e s ) . 5. Decisions insuring the maximization of t o t a l f r y s u r v i v a l during the estuarine stage of l i f e may c o n f l i c t with the i m p l i c i t objective to maximize d o l l a r return on investment costs of fry production ( i e . not only the r e l a t i v e number and weight of pink and chum adult returns are important but also t h e i r r e l a t i v e market value). 6. Parameters beyond the control of managers (such as timing of wild coho migration, the e f f e c t of temperature on growth rate) can greatly a f f e c t the predictions of f r y survival during t h i s l i f e stage. Using the model to analyse these r e s u l t s i n r e l a t i o n to 156 management objectives could r e s u l t i n s p e c i f i c enhancement proposals ( i e . what species to enhance, how many to produce, etc.) that would take advantage of the li m i t e d a b i l i t y of the manager to manipulate cert a i n parameters. The major problem w i l l be measuring the "success" of these manipulations. Any system or method of "monitoring for hazard e f f e c t s (ie any negative e f f e c t s enhancement stocks may have on wild stocks) may be completely incapable of d i f f e r e n t i a t i n g s i g n i f i c a n t change from natural, but unpredictable, fluctuations (Clark, 1978)." Nevertheless t h i s should not be considered a reason for not taking the r i s k to enhance. It only means that any evaluation of a proposal to enhance should be evaluated with due consideration given to t h i s inescapable s i t u a t i o n . Additional research i s needed to determine more e f f e c t i v e methods of monitoring the "state" of the system ( i e . i d e a l l y one should be able to distinguish enhanced stocks from wild stocks so that separate growth and survival rates, at the various stages of l i f e , could be determined). 157 LITERATURE CITED A l l e n , B r i a n . 1974. E a r l y m a r i n e l i f e h i s t o r y o f B i g Q u a l i c u m R i v e r chum s a l m o n . I n : P r o c e e d i n g s o f t h e 1974 N.E. P a c i f i c p i n k and chum s a l m o n w o r k s h o p . D.R. H a r d i n g , e d . pp. 137-148. A n d e r s o n , A.D. 1976. The 1974 r e t u r n o f e v e n y e a r p i n k s a l m o n s t o c k s t o t h e J o h n s t o n e S t r a i t s t u d y a r e a and p r o s p e c t s f o r 1976. T e c h . R e p t . S e r . PAC/T-76-6. E n v i r o n m e n t C a n a d a . F i s h e r i e s a nd M a r i n e S e r v i c e . P a c i f i c R e g i o n S o u t h e r n O p e r a t i o n s B r a n c h . 12 pp. A r o , K.V. and M.P. S h e p a r d . 1967. S a l m o n o f t h e N o r t h P a c i f i c OSean. P a r t I V . S p a w n i n g p o p u l a t i o n s o f N o r t h P a c i f i c S a l m o n . 5. P a c i f i c S a l m o n i n C a n a d a . I n t . N o r t h P a c i f i c F i s h . C o m m i s s i o n B u l l . 2 3 . pp. 2 2 5-327. B a i l e y , J a c k E., B r u c e L. W i n g and C h e s t e r R. M a t t s o n . 1975. Z o o p l a n k t o n a b u n d a n c e a n d f e e d i n g h a b i t s o f f r y o f p i n k s a l m o n , O n c o r h y n c h u s . k e t a , i n T r a i t o r s C o v e , A l a s k a , w i t h s p e c u l a t i o n s on t h e c a r r y i n g c a p a c i t y o f t h e a r e a . F i s h e r y B u l l e t i n . V o l . 7 3 . #4. pp. 8 4 6 - 8 6 1 . B a i l e y , M i k e . 1974. Some t h e o r e t i c a l c o n s i d e r a t i o n s r e g a r d i n g t h e i m p a c t o f h a t c h e r y c o h o s m o l t s on b o t h w i l d a nd a r t i f i c i a l l y p r o d u c e d chum a n d 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 s y s t e m . I n : P r o c e e d i n g s o f t h e 197 4 N.E. P a c i f i c p i n k and chum s a l m o n w o r k s h o p . D.R. H a r d i n g , e d . pp. 121-132. B a k s h t a n s k y , E.L. 1964. 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R e i m e r s , P a u l 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 S i x e s R i v e r , O r e g o n . R e s e a r c h r e p o r t s o f t h e F i s h C o m m i s s i o n o f O r e g o n . V o l . 4. #2. 43 pp. R i c k e r , W.E. 1964. O c e a n g r o w t h a n d m o r t a l i t y o f p i n k a n d chum s a l m o n . J . F i s h . R e s . B d . o f Ca n a d a 21 (5). pp. 905-931. R i c k e r , W.E. 1976. R e v i e w o f t h e r a t e o f g r o w t h a n d m o r t a l i t y o f P a c i f i c s a l m o n i n s a l t w a t e r , a n d n o n -c a t c h m o r t a l i t y c a u s e d b y f i s h i n g . J . F i s h . R e s . B d . o f C anada 33 (7). pp. 1483-1524. R i c k e r , W.E. 1975. Computation and i n t e r p r e t a t i o n o f b i o l o g i c a l s t a t i s t i c s , o f f i s h p o p u l a t i o n s . F i s h . Res. Bd. o f Canada B u l l . 191. 382 pp. 163 Semko, R.S. 1954. A m e t h o d f o r d e t e r m i n i n g t h e c o n s u m p t i o n by p r e d a t o r s o f t h e y o u n g o f P a c i f i c s a l m o n d u r i n g t h e e a r l y s t a g e s o f d e v e l o p m e n t . F i s h . R e s . Bd. o f C a n a d a T r a n s l a t i o n S e r i e s . #215. S h e l b o u r n , J . E . , J.R. B r e t t a n d S. S h i r a h a t a . 1 9 7 3 . E f f e c t o f t e m p e r a t u r e a n d f e e d i n g r e g i m e o n t h e s p e c i f i c g r o w t h r a t e o f s o c k e y e s a l m o n f r y ( O n c o r h y n c h u s n e r k a ) w i t h a c o n s i d e r a t i o n o f s i z e e f f e c t . J . F i s h . R e s . Bd. o f C a n a d a 30. pp. 1191-1194. S i b e r t , J o h n a n d R.R. P a r k e r . 1972. A m o d e l o f j u v e n i l e p i n k s a l m o n g r o w t h i n t h e e s t u a r y . F i s h . R e s . Bd. o f C a n a d a . T e c h n i c a l R e p o r t 321. 62 pp. S m i t h , S t a n l e y D. 1978. M a r i c u l t u r e o f c o h o s a l m o n ( O n c o r h y n c h u s k i s u t c h ) . i n San F r a n c i s c o B a y . MSc T h e s i s . U n i v . o f San F r a n c i s c o S t a t e . 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 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 i s h C o l u m b i a . J . F i s h . R e s . Bd. o f C a n a d a 25 ( 3 ) . pp. 5 9 9 - 6 0 2 . 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 P S F C B u l l e t i n 14. 83 pp. W a l t e r s , G . J . , R. H i l b o r n , R.M. P e t e r m a n , a n d S t a l e y , M.J. 197 7. A m o d e l f o r e x a m i n i n g e a r l y o c e a n l i m i t a t i o n o f P a c i f i c s a l m o n p r o d u c t i o n . I n p r e s s , J . F i s h . R e s . Bd. C a n a d a . Ware/ D.M. 1 9 7 3 . R i s k o f e p i b e n t h i c p r e y t o p r e d a t i o n b y r a i n b o w t r o u t ( S a l m o g a i r d n e r i ) . J . F i s h . R e s . Bd. o f C a n a d a 30. pp. 78 7 - 7 9 7 . W e r n e r , E a r l E. 1974. The f i s h s i z e , p r e y s i z e , h a n d l i n g t i m e r e l a t i o n i n s e v e r a l s u n f i s h e s a n d some c o m p l i c a t i o n s . J . F i s h . R e s . B o a r d o f C a n a d a 3 1 . pp. 1 5 3 1 - 1 5 3 6 . W e r n e r , E a r l E. a n d D o n a l d J . H a l l . 1974. O p t i m a l f o r a g i n g and t h e s i z e s e l e c t i o n o f p r e y b y t h e b l u e g i l l s u n f i s h (ILepomis m a c r o c h i r u s ) . E c o l o g y . V o l . 55. #5. pp. 1 0 4 2 - 1 0 5 2 . W e r n e r , E a r l E. a n d D o n a l d J . H a l l . 1976. N i c h e s h i f t s i n s u n f i s h e s : e x p e r i m e n t a l e v i d e n c e a nd s i g n i f i c a n c e . S c i e n c e . V o l . 1 9 1 . pp. 404 - 4 0 6 . W i c k e t t , W. P e r c y . L e n g t h a n d w e i g h t s t u d i e s o f c o h o a t C h e f C r e e k . A b s t r a c t . U n p u b l i s h e d . F i s h e r i e s R e s e a r c h B o a r d o f C a n a d a , N a n a i m o , B.C. 164 APPENDIX I P r e y T y p e s f o u n d i n S a l m o n S t o m a c h s Number 1. C l e v e l a n d i a i o s (Arrow-Goby) 2 2. C l u p e a p a l l a s i i ( P a c i f i c h e r r i n g ) 289 3. S e b a s t o d e s s p . l a r v a e ( R o c k f i s h l a r v a e ) 42 ±4. M e r l u c c i u s p r o d u c t u s ( P a c i f i c hake) 32 5. T h a l e i c h t h y s p a c i f i c u s ( E u l a c h o n ) 670 6. L e u r o g l o s s u s s t i l b i u s ( N o r t h e r n s m o o t h t o n g u e ) 55 7. G o b i i d a e ( G o b i e s ) 1 8. Ammodytes h e x a p t e r u s ( P a c i f i c s a n d l a n c e ) 40 9. L y o p s e t t a e x i l i s ( S l e n d e r s o l e ) 1 10. G a s t e r o s t e u s a c u l e a t u s ( T h r e e s p i n e s t i c k l e b a c k ) 3 11. S t i c h a i i d a e ( P r i c k l e b a c k s ) 7 12. O p h i o d o n e l o n g a t u s ( L i n g c o d ) 23 13. T h e r a g r a c h a l c o g r a m m u s ( W h i t i n g o r P o l l o c k ) 6 14. U n i d e n t i f i e d f i s h l a r v a e 17 S o u r c e : B a r r a c l o u g h , 1967 a n d B a r r a c l o u g h and F u l t o n , 1967. Tows done i n A p r i l , J u n e a n d J u l y . APPENDIX I I P a r a m e t e r C r u i s i n g v e l o c i t y o f p r e d a t o r T u r b i d i t y ( r e a c t i v e d i s t a n c e ) A r e a o f d i s p e r s i o n H o u r s s p e n t s e a r c h i n g a n d h a n d l i n g P r o p o r t i o n e a t e n o f t h o s e e n c o u n t e r e d D e n s i t y - g r o w t h r a t e f u n c t i o n s Maximum p r e y s i z e p r e d a t o r c a n i n g e s t Coho s m o l t i n i t i a l s i z e S t a r t o f p i n k a n d chum f r y m i g r a t i o n Number o f d a y s c o h o e n t r y l a g g e d b e h i n d p i n k and chum f r y e n t r y i n t o t h e e s t u a r y A v e r a g e p i n k f r y g r o w t h r a t e D u r a t i o n o f c o h o m i g r a t i o n i n t o t h e e s t u a r y N on-coho n a t u r a l m o r t a l i t y t o p i n k a n d chum f r y i n t h e e s t u a r y P i n k a n d chum f r y s i z e a t s e a w a r d m i g r a t i o n f r o m t h e e s t u a r y Range o f V a l u e s 1 b o d y l e n g t h / s e c o n d - 5 b o d y l e n g t h s / s e c o n d 0.2 ( v e r y t u r b i d ) - 1.0 ( c l e a r ) 15,319 h e c t a r e s ( a p p r o x i m a t e a r e a o f f o r e s h o r e , m a r s h & s l o u g h ) - 45,957 h e c t a r e s 4 h o u r s - 20 h o u r s se e f i g u r e 13 s e e f i g u r e 6 0.044 - 0.085 o f p r e d a t o r ' s b o d y w e i g h t 9.5 cm, 11.0 cm M a r c h 1, M a r c h 15 0 . - 5 0 d a y s 6.1%, 6.4%, 9.0% p e r d a y d u r i n g e a r l y l i f e i n e s t u a r y 16 - 48 d a y s 0.0002 - 0.02 i n s t a n t a n e o u s r a t e p e r d a y 4.0 - 9.0 cm Parameter Range of Values Pink and chum f r y a l s o allowed to migrate to sea i f growth r a t e dropped below a pre-set value T o t a l abundance of pink . and chum f r y T o t a l abundance of coho smolts I n i t i a l s i z e of enhanced pink f r y Number of days enhanced pink f r y lagged behind " w i l d " pink and chum f r y entry i n t o estuary Abundance of enhanced pink f r y Percent chum f r y of t o t a l pink and chum f r y population Average chum f r y growth ra t e I n i t i a l s i z e of pink f r y I n i t i a l s i z e of chum f r y Non-coho n a t u r a l m o r t a l i t y to coho smolts i n estuary Coho smolt m i g r a t i o n begins Pink f r y m i g r a t i o n ends Chum f r y m i g r a t i o n ends 1%, 2%, 3% per day 40 - 520 m i l l i o n 2 - 4 m i l l i o n 3.35 - 3.75 cm 16 - 61 days 6 - 24 m i l l i o n 5% - 100% 6.4% per day during ear] l i f e i n estuary 3.35 - 3.55 cm 3.68 - 3.88 cm 0.00043 instantaneous r a t e per day about A p r i l 2 3 about May 2 5 about May 22 APPENDIX I I I G e n e r a l i z e d L o g i c o f M o d e l I n i t i a l i z e v a r i a b l e s M i g r a t e i n t o e s t u a r y Grow C a l c u l a t e b a s e l i n e m o r t a l i t y f o r a l l s p e c i e s C a l c u l a t e number o f p i n k a n d chum f r y e a t e n b y c o h o s m o l t s A r e a l l p i n k & chum f r y e a t e n ? A r e a l l p i n k & chum f r y t o o b i g t o e a t ? Have a l l p i n k & chum f r y m i g r a t e d YES C a l c u l a t e p i n k a n d chum a d u l t r e t u r n a s s u m i n g b a s e l i n e m o r t a l i t y r a t e d u r i n g t i m e a t s e a . C a l c u l a t e a n d p r i n t s t a t i s t i c s R e s e t p a r a m e t e r s a nd b e g i n a new s i m u l a t i o n ? NO S t o p 

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