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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 o f 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 o f Zoology  We a c c e p t t h i s t h e s i s as c o n f o r m i n g 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 B r i t i s h 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.  Department of c  Zoology  The University of B r i t i s h Columbia  2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5 A u g u s t 3,  1978  Abstract  A deterministic the  relationship  growth  between  and s i z e - r e l a t e d  estuary.  initial  migration increase  juvenile survival  and the r e s u l t s  enhancement.  relative  model  These size  of wild  and r e l e a s i n g their  (enhancement  chances  plus wild)  chum a n d c o h o River  to proposalsf o r  suggest that  increasing  a n d chum f r y ,  fry,prior  them e a r l y  to  seaward  i n the spring  of survival. f r ydensity  may  I f increasing  total  decreases f r y growth  rate,  t h e presence o f enhancement f r y i n t h e e s t u a r y  could  reduce  decrease  the survival  i n wild  stock  estimates of adult  chances  of wild  fry.  The  s u r v i v a l may n o t b e a p p a r e n t  return  f o r many  i n measurement and t o t h e e f f e c t environmental v a r i a b i l i t y .  salmon  t o change a r e  o f enhancement p i n k  to the size  to explore  i n the Fraser  related  results  i s used  pink,  Parameters most s e n s i t i v e  identified  the  simulation  y e a r s due t o  from  errors  on s u r v i v a l o f  The model c a n be u s e d t o  iii  suggest and e v a l u a t e enhancement p r o p o s a l s . needing f u r t h e r r e s e a r c h  are a l s o  indicated.  Areas  iv Table of Contents  Abstract  i i  Table o f C o n t e n t s  l v  L i s t o f Tables  V  L i s t of Figures  1  1 X  Acknowledgements CHAPTER I .  1  X  INTRODUCTION  1  1  1  1.  Introduction  1  2.  Overview o f E x i s t i n g Data  1  3.  Purpose o f T h e s i s  4.  Early Life History  5.  Some D e f i n i t i o n s  CHAPTER I I .  10 . . . . . . . . .  11 14  METHODS  16  1.  Introduction  16  2.  O r g a n i z a t i o n and S t r u c t u r e o f t h e Model  3.  The B i o l o g i c a l B a s i s o f t h e Model  17  I  Migration  17  II  Growth  20  i  Growth Rate  20  ii  Density  32  iii  Temperature and D e n s i t y  35  iv  Coho F e e d i n g Dynamics  35  ...  17  V  III  Mortality  37  IV  Predation  38  i  G e n e r a l Assumptions  38  ii  M u l t i s p e c i e s Disc Equation  ...  40  Area Searched and D e n s i t y o f Prey  41  Reactive Distance  41  D i s t a n c e T r a v e l l e d P e r Day Encounter  . . ..  Rate  P r o p o r t i o n o f Prey S u c c e s s f u l l y Pursued and K i l l e d  44 49 50  T o t a l S e a r c h i n g and H a n d l i n g  CHAPTER I I I .  Time  58  H a n d l i n g Time  58  RESULTS AND DISCUSSION  61  1.  Introduction  61  2.  Sensitivity Analysis  63  I  Components o f P r e d a t i o n . . . . . . .  63  II  Predator Size a t Migration i n t o Estuary Timing and D u r a t i o n o f P i n k and Chum  66  Fry M i g r a t i o n  67  IV  Growth Rate  73  V  Chum and P i n k S i z e a t M i g r a t i o n i n t o  III  VI  the E s t u a r y  78  Prey D e n s i t y  79  V I I R e l a t i v e P r o p o r t i o n o f P i n k t o Chum V I I I FTiming r y i n and t h e ED su tr ua at ri yo n o f t h e Coho Smolt M i g r a t i o n  84 94  vi  IX  Non-Coho N a t u r a l M o r t a l i t y  X  Residence Time and S i z e a t  102  E m i g r a t i o n from t h e E s t u a r y ...... . . 3.  4.  Enhancement Experiments  .  I  Changing the P r e y : p r e d a t o r R a t i o  II  Enhancement o f P i n k Salmon  103 116  . .  116 116  E x a m i n a t i o n o f Data found i n t h e Literature  CHAPTER IV.  134  GENERAL DISCUSSION  153  LITERATURE CITED  157  APPENDIX I .  164  Prey Types found i n Salmon Stomachs .  APPENDIX I I . L i s t of Parameters and Range of V a l u e s t e s t e d i n t h e Model APPENDIX I I I . G e n e r a l i z e d L o g i c o f t h e Model  165 . ... 167  vii L i s t of Tables  TABLE I .  V a r i a n c e s o f annual 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 salmon i n N o r t h America and A s i a ,  and 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  of s p e c i e s TABLE I I .  3  V a r i a n c e s o f annual c a t c h ( i n weight) 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 salmon i n N o r t h America and A s i a ,  and 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  of species TABLE I I I .  5 V a l u e o f parameters a and b f o r l e n g t h -  weight e q u a t i o n s TABLE IV.  . . .  19  V a l u e o f parameters a and b f o r growth  rate-weight equations TABLE V.  S e n s i t i v i t y o f model r e s u l t s  21 t o changes  i n the maximum i n g e s t i b l e prey s i z e TABLE V I .  64  S e n s i t i v i t y . o f model r e s u l t s t o changes  i n t h e e s t i m a t e d s t a r t i n g date o f t h e p i n k and chum fry migration TABLE V I I .  68  S e n s i t i v i t y o f model r e s u l t s t o changes  i n e s t i m a t e d p i n k f r y growth r a t e and f r y m i g r a t i o n date TABLE V I I I .  74  S e n s i t i v i t y o f model r e s u l t s t o  changes i n the e s t i m a t e d s i z e a t which p i n k and 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  104  viii L i s t of Tables cont'd...  TABLE I X .  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  the model e s t u a r y i f t h e i r growth r a t e drops below a s p e c i f i e d value TABLE X.  S e n s i t i v i t y o f model 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 and chum f r y TABLE X I .  107  117  One example p r e d i c t e d by t h e model o f t h e  n e g a t i v e e f f e c t enhancement p i n k p o p u l a t i o n may have on w i l d p i n k and chum p o p u l a t i o n s  132  L i s t of F i g u r e s Figure  1 •  T o t a l A s i a n Catch of Salmonids  versus  T o t a l North American Catch o f Salmonids . • Figure  2 •  Average Monthly Temperature o f F r a s e r River Estuary  F i g u r e 3 . -~ Estimated  23  e f f e c t o f Temperature on  Growth Rate Figure 4 .  25  Average Weight o f Chum F r y i n the Estuary  Figure 5 .  . -  28  Average Weight o f Pink F r y i n the Estuary  Figure 6 -  Estimated  30 E f f e c t o f Density on Growth  Rate Figure 7 •  7  33  The " e f f e c t i v e volume" o f Water Searched by a predator  42  Figure 8 .  R e a c t i v e Distance  45  Figure 9 .  R e l a t i o n between Prey Weight and Predator  R e a c t i v e Distance  47  F.dlgure 10 .  S i z e o f F i s h Prey Found i n Oncorhynchus . . 51  F i g u r e 11 •  S t r i k e Distance  F i g u r e 12 .  R e l a t i o n Between S t r i k e Distance and  54  Reactive Distance F i g u r e 13 .  56  P r o p o r t i o n o f Encountered Prey S u c c e s s f u l l y Captured and Eaten  F i g u r e 14 .  R e l a t i o n Between F r y Density and  F i g u r e 15a .  59  Pattern  S t a r t i n g Date o f F r y M i g r a t i o n  R e l a t i o n Between Prey:Predator  . . . .71  Ratio  and Number o f F r y Eaten/Coho/Day  80  List  of Figures  Figure  15b •  cont'd...  x  A n o t h e r Example o f R e l a t i o n Prey:Predator Fry  Figure  16 •  Ratio  82  R e l a t i o n Between Changing Pink and  Abundance 17 .  a n d Number o f  Eaten/Coho/Day  Chum F r y A b u n d a n c e  Figure  Between  a n d Coho S m o l t  . . . .  An Example Duration and  Figure  19 •  8"/  87  o f Chum F r y i n t h e T o t a l  Prey Population 18 .  85  R e l a t i o n Between F r y M o r t a l i t y and t h e Proportion  Figure  8.  of the Relation  o f Coho M i g r a t i o n  Between and Pink  Chum F r y M o r t a l i t y  95  An Example o f t h e R e l a t i o n Date Coho E n t e r  Estuary  Between  and Pink and  Chum F r y M o r t a l i t y Figure  20 .  97  E f f e c t on I n d i c a t o r s o f Changing t h e Duration  o f Coho M i g r a t i o n  and t h e  Date o f E n t r y Figure  21 .  Size Distribution Found  Figure  22 .  23 .  Figure  24 .  the Estuary  Weekly Density in  o f Chum F r y  i n the Estuary  Size Distribution in  Figure  99  E a c h Week  of Pink  108  F r y Found  E a c h Week of Pink  110  a n d Chum F r y  the Estuary  114  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 Size  and Abundance  of  Enhancement  Pink  F r y (Migration Begins  16 M a r c h )  . . .  119  List  of Figures  Figure  25 .  cont'd...  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 Size Fry  Figure  26 .  and Abundance  and Abundance  Figure  29 .  121  Pink  15 A p r i l )  123  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  Fry 28 .  1 April)  o f Enhancement  (Migration Begins  Size  Figure  Pink  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  Fry 27 .  o f Enhancement  (Migration Begins  Size  Figure  x i  and Abundance  o f Enhancement  (Migration Begins  Pink  1 May)  125  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 Size  and Date o f E n t r y  Pink  Fry .  Enhancement 127  R e l a t i o n Between Survival  of  % Chum  and T o t a l Pink  Egg-to-Fry a n d Chum E g g  Deposition Figure  30 .  137  R e l a t i o n Between Survival  % Chum  Fry-to-Adult  and T o t a l Pink  a n d Chum F r y  Abundance Figure  31 .  R e l a t i o n B e t w e e n A g e T h r e e Chum and  Figure  32 .  Total Pink  Salmon Weight and T o t a l N o r t h Catch Figure  33 .  ( i npieces)  . .  144  Pink American  o f Oncorhynchus Salmon  R e l a t i o n Between A d u l t  Pink  .  148  Salmon  Weight and L e n g t h o f Age Three Chum S a l m o n  14 0  Returns  a n d Chum F r y A b u n d a n c e  R e l a t i o n Between Average A d u l t  .  Adult 150  Acknowledgements  Numerous p e o p l e Ecology this  h a v e g i v e n me  study.  Peterman  Neill  Michael  a s s i s t a n c e during the  and  s u p e r v i s o r , C.S.  like  Resource  course  to thank  and  the  I would  study.  draft  criticism  drawings,  and  Rose and  final  draft.  A  their  continued  L. P.  from  also like  o f my  figure  Holling,  Staley kindly  suggestions  S.  of Animal  of  Randall  M.  f o r h i s i n v a l u a b l e suggestions, encouragement My  early  Institute  I would e s p e c i a l l y  support.  an  i n the  thesis, Stephens  George  special support.  Carl  Walters,  p r o v i d e d many the  beginning  t o thank G.W.  Bill  Lidstone  for editorial  thanks  t o my  to the  end  thesis  comments on and  of  for readin  for doing  friends  Bill  useful  Rees  f o r t y p i n g the  and  the  text, my  family for  1 CHAPTER I .  1.  INTRODUCTION  Introduction The  "to  goal  of long-term  double  the present  goal  i s considered  This  Pacific  mean a n n u a l  salmon enhancement i s catch  biologically  1974; L a r k i n , 1975; Johnson,  provides  an overview  i n the l i f e  history of  e a r l y marine residence.  An attempt  i s made t o  knowledge and assumptions  uncover  2.  relate  Overview of E x i s t i n g The  examined  of  regarding  direct  research  feasibility  enhancement o f  of enhancing  Pacific  o f ocean l i m i t a t i o n ,  i f t h e r e were c o m p e t i t i v e  salmon a t present  levels  salmonids.  Data  f r o m a number o f d i f f e r e n t  indications  priorities  what i s known a b o u t t h e b i o l o g y o f t h e  system t o proposed  that  on  any s e r i o u s gaps i n o u r b i o l o g i c a l  knowledge and thus  for  supporting the  period of l i f e t o : 1.  2.  thesis  stage  synthesize the biological this  This  feasible  o f salmon enhancement and f o c u s s e s  what a p p e a r s t o be a c r i t i c a l salmonids:  1976).  o f some o f t h e e v i d e n c e  feasibility  1976)."  and t e c h n i c a l l y  (Larkin,  biological  (Johnson,  salmon has been  perspectives. Larkin  (1975)  i n t e r a c t i o n s between  Looking reasoned species  o f abundance 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 h i g h seas, then the v a r i a n c e over time o f t o t a l salmonid  abundance would be l e s s  than the sum o f the v a r i a n c e s of i n d i v i d u a l s p e c i e s ' abundance. Using North American and A s i a n c a t c h s t a t i s t i c s as i n d i c e s o f abundance he found 1.  (Table 1 ) :  "For each s p e c i e s , the sum o f the v a r i a n c e s o f the North American and A s i a n catches  i s not s i g n i f i c a n t l y  different  from the v a r i a n c e o f the combined North American and Asian catch.  In some cases, the sum o f the v a r i a n c e s  i s the g r e a t e r q u a n t i t y , suggesting p o s s i b l e c o m p e t i t i v e i n t e r a c t i o n s , but i n other cases the r e v e r s e i s t r u e , suggesting t h a t common f a c t o r s s i m i l a r l y i n f l u e n c e catches o f v a r i o u s s p e c i e s . " 2.  For a l l s p e c i e s combined on e i t h e r s i d e of the P a c i f i c , L a r k i n found  t h a t the v a r i a n c e of the sum was l a r g e r  than the sum o f the v a r i a n c e s o f the s p e c i e s i n a l l but one  case  (1950-1959).  T h i s suggests  t h a t the catches o f  the v a r i o u s s p e c i e s a r e p o s i t i v e l y c o r r e l a t e d . L a r k i n concludes  t h a t "there i s no obvious  evidence  that the present abundance o f salmon i s s u f f i c i e n t t o e x p l o i t the p o t e n t i a l r e a r i n g c a p a c i t y of the North P a c i f i c . " I a p p l i e d L a r k i n ' s a n a l y s i s technique and A s i a n catches expressed  as weight  (Table 2 ) . Weight seems  to be a more u s e f u l i n d i c a t o r o f c o m p e t i t i v e because:  t o North American  interaction  3 T A B L E 1.  Variances o f annual catch ( i npieces) o f various s p e c i e s o f P a c i f i c salmon i n North America and 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 of species. North America  Asia  Sum o f Variances  Variance o f Sums  1925-1961" Sockeye  62.61  26 .40  89 .01  113.65  2,648.71  3,041.64  4,022.34  149 .80  142.14  Pink  392.93  Chum  12.51  137.29  1.62  2.09  Sum o f Variances  469.67  2,814.49  3,284.16  4,281.04  Variance o f Sum  740.66  3,614.90  4,355.56  5,843.61  61.27  21. 77  83.04  126 .24  Pink  244.61  2,899.81  3 ,144.42  3,988.26  Chum  7.92  155.31  163 .23  165.43  Coho  1.23  1.44  2.67  3 .21  Sum o f Variances  315.03  3,078.33  3,393 .36  4,283.14  Variance o f Sum  399.29  4,070.72  4,470.01  6 ,024 .99  Sockeye  15.62  38.78  54.50  45.86  Pink  52.72  1,852.42  1,905.14  2,103.54  Chum  11.21  109.55  120.76  2.16  2.81  4.97  2.43  Sum o f Variances  81.71  2,004.56  2,085.27  2,235.94  Variance o f Sum  99 . 89  2,474.24  2,574.13  2,390.43  Coho  3 .71  2.91  1925-1949Sockeye  1950-1961'  Coho  84.11  cont'd.  TABLE  1, p a g e 2  North America  Sum o f Variances  Asia  Variance o f Sums  1950-1969 Sockeye  29.17  23.11  52.28  52.91  Pink  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  Variances  260.25  1,148.33  1,408.58  1,038.85  Variance o f Sum  228.04  1,399.02  1,627.06  1,078.49  Sum  of  Taken from Table Revised  1 of Larkin,  using data  Fisheries  taken  Commission  1 9 7 5.  from  (INPFC)  International statistical  North  Pacific  reports for  1952-1969. Note  that these  data  data  grouping.  Changing  general  conclusion  still  smaller than  which  suggests,  the  same o v e r  series of  data  groupings  (i.e.,  the grouping  first  d i d n o t change t h e  t h e sums o f t h e v a r i a n c e s a r e sums)  t h a t c o n d i t i o n s have remained  N e v e r t h e l e s s , any a n a l y s i s  must be t r e a t e d c a u t i o u s l y  t r e n d s w h i c h may  of the  the variances of the various  perhaps,  time.  are a subset  be c o n f o u n d i n g  of  much  time  due t o t h e e x i s t e n c e  the results.  5  TABLE  2. Variances species Asia, of  o f annual  of Pacific  catch  ( i nweight)  salmon i n North  of various  America  and  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  species.  North America  Asia  Sum o f Variances  Variance o f Sums  1952-1972 Sockeye  240.70  101.19  341.89  318.71  Pink  493.45  1 ,896.43  2 ,389.88  1,903.28  Chum  197.90  439.13  637.03  5 7 3 .09  Coho  3 7 . 72  9.95  47.67  43.79  6.48  0.66  7.50  7.25  976.61  2 ,447.36  3 ,423 .97  2,846.12  1,064.98  3 ,313.14  4 ,378.12  2,727.04  Chinook Sum o f Variances Variance o f Sum  Catch  data  (September  p r o v i d e d by INPFC, u n p u b l i s h e d 1976).  manuscript  1.  I t does n o t results  2.  assume t h a t i n c r e a s e d  i n increased mortality.  I t allows  f o r the p o s s i b i l i t y  competition and  an  competition  may  result  overall  that  increased  i n decreased  growth  r e d u c t i o n i n weight of a  b e l o w what w o u l d have b e e n o b t a i n e d of Looking  among s p e c i e s on  are  suggest  smaller  than  Although the  sum  the v a r i a n c e  significant  for a l l species  i f any,  The  negative  r e v e r s e was  sum  of the  of  by  sum.  (F-test,-. p >  not  Asia:may  the  the n e g a t i v e  Although they  favourable,  they  coast,  international indication  Asian  stocks  fishing  Pacific.  greater  different, quantity species  exist.  of competitive areas.  An  (figure  Asian  r =  and  variances, -0.57,  (used  t o t h e movement o f  interaction  examination  1,  catch  i n the North P a c i f i c  boundaries  with  species.  i n t e r a c t i o n s between  correlation  i n d i c a t o r o f a b u n d a n c e ) , a r e due  that  0.05),  significantly  i s invariably  p < 0 . 0 1 ) between N o r t h A m e r i c a n and  A m e r i c a n and  absence  the  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  confirmed  two  the  i n t e r a c t i o n between  competitive  f r o m N o r t h A m e r i c a and  these  I found  t r u e f o r the whole N o r t h  the v a r i a n c e s  Byggestingesthath.^L  It  i n the  from t h a t s p e c i f i c  the v a r i a n c e s are again of  t o 197 2,  t h a t wnwhenc .[condition's.-': Lc ao a r e  favourable  little,  f r o m 19 52  each s i d e o f the P a c i f i c  t h e d i f f e r e n c e s were n o t do  population  competition. only a t data  v a r i a n c e s was  rate  as  North  relative  s e a s o n s and  an  are not  between s p e c i e s  of the p r o p o r t i o n of  to an  from North  7  FIGURE  Total Total  Regression of American indicated  Asian Catch  of Salmonids  North American  total  salmonid f o r each  1.  Catch  Asian salmonid  catch data  of  Salmonids  c a t c h on  (in pieces). point.  versus  Catch  total  North  years  are  CO  American stocks taken by the A s i a n f l e e t each year  relative  to North American and A s i a n c a t c h abundance might r e v e a l whether or not s p e c i e s movement i s r e s p o n s i b l e f o r t h i s correlation.  negative  ( I t should be noted t h a t the annual catches  are  o n l y an index of oceanic abundance of salmon and a more c o n c i s e a n a l y s i s would r e q u i r e escapement as w e l l as a g e - a t - r e t u r n data.) Walters,  e t a l . (1977), l o o k i n g f o r evidence  of food  l i m i t a t i o n i n the e s t u a r y and along the c o a s t of B r i t i s h Columbia c r e a t e d a s i m u l a t i o n model to e x p l o r e the s p a t i a l and  seasonal  i n t e r a c t i o n s of m i g r a t i n g j u v e n i l e salmon and t h e i r food s u p p l i e s The authors, u s i n g zooplankton supply, concluded  biomass as a measure of  food  t h a t " i t appears t h a t t h e r e i s enough food  p r o d u c t i o n to support  s e v e r a l times the e x i s t i n g abundance o f  j u v e n i l e salmon without  n o t i c e a b l e e f f e c t s on growth and  size-  r e l a t e d s u r v i v a l , even assuming t h a t the useable c o a s t a l zone i s very narrow and c o n s i d e r i n g s p a t i a l p o s i t i o n e f f e c t s w i t h i n l a r g e m i g r a t i n g b l o c k s of f i s h . " et a l . (1969) a l s o suggest  Parker  (1968) and  LeBrasseur,  t h a t food supply of j u v e n i l e f i s h  i s abundant d u r i n g the time they are i n r e s i d e n c e i n the C s p e c i f i c a l l y the B e l l a Coola and F r a s e r R i v e r Residence time, however, may  estuary  estuaries).  be determined by the food  supply.  I t i s not s u f f i c i e n t , t h e r e f o r e , to judge the a b i l i t y of the food resource t o support an i n c r e a s e d abundance of j u v e n i l e salmon u s i n g the abundance o f the food supply alone;  information  on r e s i d e n c e time and growth r a t e i s a l s o r e q u i r e d .  Peterman  C1975) presented  data f o r Skeena R i v e r sockeye smolts which  seem to i n d i c a t e t h a t an i n c r e a s e d abundance of smolts  results  10 i n a decreased  s u r v i v a l to recruitment.  I f food p r o d u c t i o n i s  not l i m i t i n g t h e i r growth and chances f o r s u r v i v a l d u r i n g c o a s t a l m i g r a t i o n and r e s i d e n c e i n the Gulf o f A l a s k a , then  something  must be happening t o l i m i t p r o d u c t i o n e i t h e r d u r i n g e a r l y e s t u a r i n e l i f e o r d u r i n g t h e i r r i v e r m i g r a t i o n t o the sea. Other f a c t o r s which have not been c o n s i d e r e d p a r a s i t i s m o r predator aggregation  such as d i s e a s e ,  (Peterman, 1978) may be  i m p l i c a t e d a t any stage. V a r i o u s authors have suggested  t h a t m o r t a l i t y (20% t o 85%)  from p r e d a t i o n d u r i n g e a r l y freshwater l i m i t s the p r o d u c t i o n o f salmon 1968;  stages  (Parker, 1968, 1971; F o e r s t e r ,  Semko, 1954; Hunter, 1959).  ocean m o r t a l i t y r a t e s supports  and marine l i f e  Ricker's  (1976) review o f  the c o n c l u s i o n t h a t e a r l y marine  m o r t a l i t y o f salmon i s more s i g n i f i c a n t than l a t e r high seas mortality. of  Coho smolts have been i d e n t i f i e d as a major cause  t h i s e a r l y freshwater  and marine m o r t a l i t y t o pink and chum  salmon fry (Parker, 1968, 1971; S i b e r t and Parker, 1974;  Hunter, 1959; Semko, 1954).  3.  Purpose o f T h e s i s Given the l a c k of d e f i n i t i v e evidence  either  1972; B a i l e y ,  supporting  or r e f u t i n g the e x i s t e n c e of ocean l i m i t a t i o n o f salmonid abundance and given the g e n e r a l agreement t h a t e a r l y marine l i f e m o r t a l i t y i s much higher and t h e r e f o r e p o t e n t i a l l y more important  than high seas m o r t a l i t y , I decided t o focus on the  e a r l y e s t u a r i n e l i f e o f 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 t h e s i s addresses three  general  questions: 1.  Can  p r e d a t i o n by coho (Oncorhynchus k i s u t c h )  smolts  d u r i n g e a r l y marine l i f e account f o r the major p o r t i o n of the observed estimates  of f r y - t o - a d u l t m o r t a l i t y  of F r a s e r R i v e r pink and chum salmon? 2.  How  important  to the u l t i m a t e s u r v i v a l of  pink  and chum f r y are r e l a t i v e s p e c i e s ' abundance, t i m i n g of downstream m i g r a t i o n ,  s i z e or weight a t  m i g r a t i o n , area of d i s p e r s i o n i n the e s t u a r y  and  s p a t i a l o v e r l a p of s p e c i e s , growth r a t e , and  duration  of r e s i d e n c e i n the 3.  initial  How  important  estuary?  i s an understanding  of these  biological  c h a r a c t e r i s t i c s to proposed enhancement schemes f o r pink, chum and coho salmon?  4.  Early L i f e History 0. gorbuscha  (pink salmon) and 0. keta  (chum salmon)  emerge from the g r a v e l as f r y i n the e a r l y s p r i n g — u s u a l l y d u r i n g e a r l y March to mid-May i n the F r a s e r R i v e r migrate, immediately to sea.  system—and  The major spawning areas f o r pink  salmon are found below Hope i n the mainstem of the F r a s e r R i v e r , above the mouth of the Vedder R i v e r and C h i l l i w a c k and C h e h a l i s r i v e r s 1967). ing  (Vernon, 1966;  i n the Aro and  Harrison, Shepard,  The mainstem of the Fraser accomodates the l a r g e s t spawn-  population.  Only about twelve percent  spawn upstream from  12 H e l l ' s Gate, mainly i n Seton Creek and the Thompson R i v e r (Aro and Shepard,  1967).  The F r a s e r has a major odd-year spawning  run of pink salmon and a v i r t u a l l y n o n - e x i s t e n t even-year (Hurley and Woodall, migrants produced  1968).  run  Estimates of the number of pink f r y  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  ( F r a s e r , 1976).  Chum salmon spawn mainly below Hope (Northcote,  1974)  u t i l i z i n g the mainstem of the F r a s e r R i v e r and the C h e h a l i s , C h i l l i w a c k and H a r r i s o n r i v e r s  (Aro and Shepard,  1967).  Their  l i f e c y c l e i s more v a r i a b l e than the two year l i f e c y c l e of pink salmon, r e t u r n i n g predominantely  as three or f o u r y e a r - o l d s .  The dominant age of r e t u r n v a r i e s from year to y e a r — f o r example, between 1960 and 77%  and 1969,  three y e a r - o l d s composed between 11%  (the average being 34%)  of the spawners and f o u r y e a r -  o l d s composed between 22% and 88% of the spawners (Palmer, 1972).  (the average being 64.9%) Chum salmon are p r e s e n t i n the  r i v e r every year and estimates of chum f r y migrants range 32 m i l l i o n t o as many as 131 m i l l i o n Little  from  (1964-1974) ( F r a s e r , 1976).  i s known about the behaviour of F r a s e r R i v e r pink  and chum f r y or about what happens  to them d u r i n g the r i v e r  p r o p o r t i o n of t h e i r m i g r a t i o n t o the sea.  About t h e i r  d u r i n g e a r l y marine r e s i d e n c e , l i t t l e more i s known.  life Although  no evidence has been found of pink f r y f e e d i n g i n freshwater, a number of authors have r e p o r t e d t h a t chum f r y feed d u r i n g downstream m i g r a t i o n (Sparrow, 1968; may  B a i l e y , e t a l . , 1975).  They  a l s o feed i n both freshwater and s a l t w a t e r once they reach  the e s t u a r y (Mason, 1974).  In the F r a s e r R i v e r , chum f r y  13 a p p a r e n t l y u t i l i z e the food r e s o u r c e s of the marsh h a b i t a t s f o r a t l e a s t a few weeks (Northcote, 1974).  Pink f r y , however,  seem to move out i n t o the i n t e r t i d a l zones immediately farther a f i e l d  (Northcote, 1974;  Hurley and Woodall,  Blackburn, p e r s o n a l communication).  and  perhaps  1968;  In the lower F r a s e r pink  f r y form s c h o o l s when the water i s r e l a t i v e l y c l e a r  (Vernon,  1966)  whereas chum f r y are s o l i t a r y and a g g r e s s i v e i n freshwater (at l e a s t i n Lynn Creek, Vancouver I s l a n d ; Mason, 1974). 0. k i s u t c h (coho salmon) are present i n the F r a s e r system every year.  The major p o r t i o n of coho spawners u t i l i z e  the C h e h a l i s and C h i l l i w a c k r i v e r s  (Aro and Shepard, 1967).  Coho f r y spend one or more years i n freshwater although ( c i t e d by Northcote, 1974)  contends  t h a t many, i f not the g r e a t e r  p r o p o r t i o n go t o sea s h o r t l y a f t e r emergence. from m i d - A p r i l to e a r l y May,  Godfrey  M i g r a t i n g to sea  coho smolts spend an "average  4 days i n the mainstem of the r i v e r  ( B a i l e y , 1974)."  of  After  r e a c h i n g the F r a s e r e s t u a r y , coho smolts appear t o move out the i n t e r t i d a l zones (Northcote, 1974)  and are p r e s e n t u n t i l a t  l e a s t the end of June and perhaps longer B a i l e y c a l c u l a t e d t h a t between 1967 R i v e r system averaged  (Goodman, 1975). and 1972  52,500 coho spawners per year  the F r a s e r producing  an estimated 1,083,000 coho smolts a n n u a l l y (assuming f e c u n d i t y r a t e and a 10% egg-to-smolt  into  survival  an  average  rate).  Conversely, F r a s e r (.197 6) estimated t h a t the F r a s e r R i v e r produces about 2 m i l l i o n coho smolts per year. The  stomach contents of j u v e n i l e coho i n d i c a t e t h a t t h e i r  d i e t i s composed of "marine, e s t u a r i n e 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 off  the intertidal  ebbing  tides In  portion  (Goodman,  upstream  Goodman r e p o r t s t h a t c o h o  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  i n the North larval  3.  terrestrial 4.  on both larval  These d a t a interaction  River.  5.  Some The  invertebrates,  Sturgeon  and Roberts  and j u v e n i l e establish  herring  Banks c o n t a i n e d and o t h e r  the possibility  term  "estuary" w i l l  be used  by f r y d u r i n g t h e i r  development  stage.  of  of specific  spatial in  distribution  This definition  important salmon  i nthe  very generally  "The  e a r l y marine  t o mean  and adjacent growth  i s necessarily  and  vague  knowledge r e g a r d i n g t h e behaviour  over  t h e F r a s e r R i v e r system  Strait.  fishes.  o f an  p i n k , chum a n d c o h o  mainly  Definitions  utilized  the lack  mainly  f r e s h w a t e r and  the area o f freshwater and s a l t w a t e r i n t e r f a c e areas  mainly  fish,  Arm c o n t a i n e d m a i n l y  between j u v e n i l e  Fraser  stomachs:  larvae,  and M i d d l e Arms c o n t a i n e d  and j u v e n i l e  i n the South  and  1975)."  salmon and chironomid 2.  on and  of the estuary with flooding  terms o f biomass,  1.  t h e movement o f f i s h  time  of the study  and  species—particularly  and adjacent waters  (Fraser) r i v e r  because  of the Georgia  e s t u a r y does n o t open o u t i n t o  l a r g e bay o r a deep p r o t e c t e d i n l e t  typical  o f many  a  estuaries  but i n s t e a d flows d i r e c t l y i n t o the marine waters of  Georgia  S t r a i t , f l a n k e d on both s i d e s by e x t e n s i v e shallow mudflats banks (Northcote, 1976)." and  The  and  t o t a l area of slough, marsh  f o r e s h o r e of the F r a s e r R i v e r e s t u a r y i s estimated to be  15,319 h e c t a r e s  (Goodman, 1975).  For purposes of t h i s study, f i s h "age"  i s determined  by  the number of days an i n 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 m i g r a t i o n by f r y , r e g a r d l e s s of s p e c i e s . For example, i f seaward m i g r a t i o n of pink f r y begins on March 1, a l l f i s h which migrate on t h a t day belong to age c l a s s 1;  those  which migrate on March 2 belong to age c l a s s 2; e t c . "Age The  c l a s s " and  " s i z e c l a s s " are c o n s i d e r e d synonymous.  " s i z e " of an i n d i v i d u a l i n any  "age"  or " s i z e c l a s s " i s  a f u n c t i o n of i t s i n i t i a l s i z e a t m i g r a t i o n and growth r a t e while i n the e s t u a r y . age,  from a s i n g l e  i t s subsequent  A l l individuals  s p e c i e s , are regarded  as one  of the same  "cohort".  16 CHAPTER  1.  determine and q u a n t i f y t h e b i o l o g i c a l  thought t o a f f e c t early marine  the survival  life,  search  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  pink,  estuary. species  chum a n d c o h o With  Since  their  of the literature.  into  a  simulation  t o examine t h e i n t e r - r e l a t i o n s h i p s  salmon d u r i n g  their  some m o d i f i c a t i o n t h e , m o d e l  but the increase  characteristics  o f salmonids during  I d i d an e x t e n s i v e  m o d e l , a n d t h e m o d e l was u s e d of  METHODS  Introduction To  The  II.  i n complexity  residence could  w o u l d be  i nthe  include  significant.  I wanted t o examine t h e r e l a t i o n s h i p between  growth and s i z e - r e l a t e d m o r t a l i t y from coho p r e d a t i o n and  chum f r y , t h e m o d e l o n l y  period  of life Complete  istics any  one r i v e r .  information  t o approximate  Fraser  River  the  1.  There and  2.  species  information  systems and t h e parameter v a l u e s  system t o evaluate  f o r three  main  i s a considerable  this  system  in  significant  of the  and  explore  reasons: body o f q u a n t i t a t i v e  data a v a i l a b l e .  i s a unique  in  characteristics  were  as possible.  River  qualitative  There  character-  was n o t a v a i l a b l e f o r  i s a composite o f  system as c l o s e l y  model's behaviour  i n depth a t the e a r l y  the biological  chose t h e Fraser  pink  when t h e f r y a r e v u l n e r a b l e .  Thus t h e model  chosen  on  describing the biological  salmonid  f r o m many r i v e r  I  looks  i n the estuary  of the three  gleaned  other  "natural experiment"  since pink  salmon  numbers o n l y  occurring  f r yare  present  i n even calendar  years.  3.  I t i s an important  river  i n terms o f salmon  management. With appropriate  changes t o the parameter v a l u e s , t h e  model  c o u l d be u s e d t o e x p l o r e  river  system as long  salmon i n t e r a c t i o n s i n any  as t h e b a s i c p a t t e r n o f events  i s the  same.  2.  Organization  and S t r u c t u r e o f t h e Model  The s i m u l a t i o n model form w i t h  i s d e t e r m i n i s t i c and modular i n  t h e modules corresponding  components  of the biological  growth and m o r t a l i t y .  process  system under study:  The m o d e l  simulates  asked  and t h e i n f o r m a t i o n a v a i l a b l e on each o f t h e time  A d e t e r m i n i s t i c model of  the results  than  Each group is  and  a l l pink  chum  large.  3.  by s p e c i e s  vulnerable  less  into  realistic).  the estuary  the estuary,  o r , a l l pink  t o coho p r e d a t i o n  Basis  process  The s i m u l a t i o n  f r y have l e f t  being  interpretation  (albeit  ends  a l l pink  a n d chum  f r yare  because they  are too  (See A p p e n d i x . I l l f o r d i a g r a m o f model  The B i o l o g i c a l I  and age.  of  to the problem.  ambiguous  o f salmon moving  f r y have been eaten,  no l o n g e r  a less  a s t o c h a s t i c model  a n d chum  the questions  seemed a p p r o p r i a t e  permits  (cohort)  differentiated  when:  step  Given  the interaction  components  this  basis.  migration,  these  components,  on a d a i l y  t o the major  logic.)  o f the Model  Migration The m o d e l assumes t h a t t h e downstream  juvenile  fish  migration  i s normally  variations in  given  is  fish  o f any one s p e c i e s  known t o be f a l s e  greatly  size  increase  the results.  size  i n reality  the entire migration  that  allows  pink  size  during  the season.  Parker,  1964; P a r k e r ,  growth rate The used  initial  a i n and  would only  a  no a p p r e c i a b l e assumption  change  applies  an o p t i o n  exists  their  initial  mean  from the estuary  of pink  and  a function of size  (LeBrasseur  1974) o r a f u n c t i o n o f  (see R e s u l t s and D i s c u s s i o n ) .  parameter values  from p u b l i s h e d  assumed t o a p p l y relationship  of the length-weight r e l a t i o n s h i p s  i s :  ,  where W = weight  taken  raw data  to Fraser  River  ,,  ^1©  a  species  size  1968; A l l e n ,  i n t h e model were e i t h e r  calculated  f o r each  duration although  emigration  on  this  coming  o f t h e model w i t h  chum f r y i s a s s u m e d t o b e e i t h e r and  due t o f i s h  a n d chum f r y t o i n c r e a s e  t h e model,  even though  In the estuary  and probably  T h e (equatLant  downstream  Calculating a daily •  the complexity  over  In  there.  fish  one day.  i n size  1972)  yearly  or variations  that migrate  i s created  already  of i n i t i a l  increase  marginal  (Palmer,  of fish  growth of f i s h  distribution  in  s c a l e than  day a r e assumed t o be e q u a l  distribution to  I t does n o t c o n s i d e r  i n t h e shape o f t h e d i s t r i b u t i o n  abundance on a s h o r t e r time All  a  distributed.  from the l i t e r a t u r e (see Table  fish.  , , , =  a  (g), L = length  & b a r e two p f i ^ t e d ^ c o n s t a n t s .  or  3) a n d a r e  The form o f t h e T  ^10 (mm o r c m ) ,  19  TABLE 3. V a l u e o f parameters a and b f o r the e q u a t i o n log  1 0  W = a + b log  1 Q  L, where W = w e i g h t (g)  and L = l e n g t h (mm o r cm)  f o r coho s m o l t s ,  p i n k and chum f r y .  SPECIES  LENGTH L  INTERCEPT a  SLOPE b  AREA & SOURCE Chef Creek, Vancouver I s l a n d , B.C., W i c k e t t (unpublished) B e l l a C o o l a , B.C. , LeBrasseur & Parker (1974) c i t e d by S i b e r t & P a r k e r (1972) Campbell R., Vancouver I s l a n d , B.C.; c a l c u l a t e d from d a t a g i v e n i n Goodman & Vroom (19 74) N=39, range 33-10 7 mm  Coho  cm  -2.0846  3.122  Pink  cm  -2.34  3 .267  Chum  mm  -6.2  3.642  20 II  Growth i  Growth Rate  Growth r a t e f o r the t h r e e s p e c i e s i n the model i s d e t e r mined s o l e l y by body weight.  I t was  unnecessary  to c a l c u l a t e  growth r a t e as a f u n c t i o n of food supply because the dynamics of f e e d i n g and growth had a l r e a d y been e x p l o r e d by Walters, e t a l . (1977) and they had concluded simulated year was maximum r a t i o n . " and  size  t h a t food supply d u r i n g most of the  abundant enough t h a t the " f i s h a t t a i n E x p l o r a t i o n of the e f f e c t of changing  near growth r a t e  (not s p e c i f i c a l l y r e l a t e d to food supply) on the u l t i m a t e  s u r v i v a l of pink and chum f r y c o u l d s t i l l be accomplished  without  the added complexity of a f e e d i n g and growth s u b r o u t i n e .  (See  separate d i s c u s s i o n of coho f e e d i n g dynamics.) The  form of the growth r a t e r e l a t i o n s h i p used i n the  model i s : log  G = log  where W = weight a & b are two  a + b log  g  W  (g), G = instantaneous growth r a t e x  fitted  constants.  The parameter v a l u e s were e i t h e r o b t a i n e d from the ( B r e t t and Shelbourn,  1975)  found i n the l i t e r a t u r e  literature  or estimated from growth r a t e data  (see Table 4).  There are s e v e r a l i m p l i c i t assumptions or concerning the parameter v a l u e s g i v e n i n Table  limitations  4:  1.  The parameter v a l u e s are temperature  2.  The f i s h were assumed to be e a t i n g f u l l of optimal n u t r i t i o n a l value. f e e d i n g procedure  dependent.  (e.g., continuous  (Brett, et a l . ,  rations  The l a b o r a t o r y versus  i n t e r v a l f e e d i n g ) , however, determines i n t a k e of food  100,  1969;  the  total  Shelbourn,  21  TABLE 4. Value lo  o f p a r a m e t e r s a and b f o r t h e e q u a t i o n  log, , a + b l o g _ temperature  n  W, where W = w e i g h t  dependent i n s t a n t a n e o u s  f o r coho s m o l t s ,  Weight SPECIES  range  (g)  Coho  0.3-75.0  Pink  0.29-10.2  Chum  0.66-7.24  e  (g) and G =  g r o w t h r a t e x 100,  p i n k a n d chum f r y .  of various species  log ,. G =  S i z e and s o u r c e  indicated.  Temp C. 15.5  Intercept a 5.53  ? 5.334 (a f n c . o f time)  14-16  6.39  Slope b  Source  -0.34  S t a u f f e r (1973) c i t e d by B r e t t & S h e l b o u r n (1975)  -0.384  Calculated using growth r a t e d a t a found i n LeBrasseur & P a r k e r (1964) f o r C e n t r a l B.C. p i n k salmon.  -0.38  Calculated using growth r a t e d a t a 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  3.  et  al.,  1973) a n d  of  growth  The p a r a m e t e r weight  4.  As B r e t t  have t h e g r e a t e s t  the regression  factors  (Brett,  et al.,  et a l . ,  1973; B r e t t  sockeye  growth  growth  rate  and temperature.  growth rate  rate  of ration  the effect  i s assumed t o a f f e c t  1974).  temperature  then in  figure  species Hurley  3.  and  nutrition,  however,  coho,  only rate.  chum a n d p i n k sockeye  growth  Furthermore, the equations i n Table under  optimum  (15°C) a n d f o o d a v a i l a b i l i t y .  estuarine  simulated  diet  o f t e m p e r a t u r e on g r o w t h  i n m u c h t h e same w a y a s i t d o e s  (see B r e t t ,  changing  level,  demonstrated  a function of  The model,  4 a r e assumed t o have been d e r i v e d of  As a number o f a u t h o r s  i s not only  feeding  Temperature  up o r down.  1971, 1974, 1976; S h e l b o u r n ,  a function  explicitly  differences  on t h e i n t e r c e p t s "  a n d S h e l b o u r n , 1975) have  salmon,  (1975)  thereby s h i f t i n g the  are important.  weight but also  considers  and Shelbourn  effect  lines  rate  1969; B r e t t ,  regimen  specific  using non-  "environmental and genetic  expected These  over a  values are calculated  stocks.  indicate  of  up o r down. values are evaluated  The p a r a m e t e r  would  the estimate  range.  Fraser  for  rate  consequently shifts  temperature  by a p p l y i n g The f u n c t i o n  (figure  conditions  The e f f e c t o f  2) o n g r o w t h  rate i s  the temperature-cdependent  function  i s applied  equally  to a l l three  i n t h e model a l t h o u g h s e v e r a l  authors  ( M a r t i n , 1966;  and W o o d a l l , 1968; B r e t t ,  the optimum temperature f o r p i n k 1 5 ° C , w h i c h may  result  i n pink  1974) have salmon  growth  suggested  growth  rate  i s less  that than  being underestimated  23  FIGURE 2.  Average Monthly Temperature o f F r a s e r R i v e r  Estuary  Estimated mean monthly temperature of F r a s e r R i v e r (March-August) used i n model.  estuary  Based on Dunford (1975).  FIGURE  Estimated  Function  used  temperature rate  E f f e c t o f Temperature  i n model  on p i n k ,  @ T°C = G r o w t h  proportion temperature  to estimate  chum a n d coho rate  o f maximum g r o w t h  rate.  i n the estuary.  Model  what i s known a b o u t  (Brett,  1974; B r e t t  pink  on Growth  coho  Rate  the relative growth  effect of  rates.  @ 15°C x t e m p e r a t u r e  between  that  3.  T = mean function  and sockeye  Growth  dependent monthly  i s a  compromise  growth  rates  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  f r y are a colder  water  species  (Brett,  1974).  lOO-, 0-750-500 250  -i 5-6  1  10-11 Temperature  1  15-16 (°C)  i  20-21  ro  relative  t o coho growth  To  determine  equations and  rate.  the practicality  i n Table  4, I c o m p a r e d  o f t h e growth  t h e estimated growth  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  (figure  4 and f i g u r e  adjusted  to reflect  5).  rate  i n the literature  The d a t a i n t h e f i g u r e s  a common i n i t i a l  size  of pink  were  on d a y o f r e l e a s e  b u t n o 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 ration  intake. O v e r a n e i g h t week p e r i o d ,  grew, on a v e r a g e , when f e d a b o u t  LeBrasseur s 1  (1969)  chum f r y  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  12% o f t h e i r  wet body weight p e r day.  f o r wild  p i n k salmon  The  comparable  growth  rate  LeBrasseur  (1969)  t o b e 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 LeBrasseur, Over  was e s t i m a t e d b y  ( a b o u t 10°C, P a r k e r a n d  1974). t h e same l e n g t h o f t i m e a t 1 0 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 grew a t about reared 4.3% day  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 ,  i n an i n c r e a s i n g  20% o f t h e i r  grew a t about  wet body w e i g h t p e r  (based on d a t a taken from H u r l e y and W o o d a l l , an e q u i v a l e n t p e r i o d  e s t i m a t e s chum g r o w t h growth  t o be about  growth  i s assumed  chum g r o w t h 4.3%  s a l i n i t y environment,  p e r d a y , when f e d a b o u t  for  literature  t o be about  to exist,  5.5% p e r d a y a n d p i n k I f temperature  a t an average  Thus t h e comparison  dependent  t e m p e r a t u r e o f 10°C,  4.6% p e r d a y a n d p i n k g r o w t h  p i n k a n d chum g r o w t h  1968).  o f t i m e a t 15°C, t h e m o d e l  5.1% p e r d a y .  i s about  per day.  salinity,  i s about  between t h e model and  rates  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  Estimated rations weight  average  weight  (as percentages  o f chum of fish  o f m o d e l chum f r y o v e r  Literature data  taken  E.P.  = Euphausia  P.M.  = Pseudocalanus  than could constant  from  pacifica;  weights)  time  prey  and e s t i m a t e d  i n the estuary.  L e B r a s s e u r , 1969. CP.  minutus;  be e a t e n p e r d a y .  temperature  f r yfed different  o f 15°C.  = Calanus  Excess  plumchrus;  = offered  more  Model o u t p u t assumes  food a  10-,  E-P- 17% - LeBrasseur- 1969  8j  17% - LeBrasseur- 1969  D  PM-  16% - LeBrasseur- 1969  *  LeBrasseur 1969  Model oulput  •  C7>  CP-  Excess  O  O  A •  • . ?  <x>  (9  6-  A  CD CP D  CD  > <  • 4H  1  A §  8  8 — i —  ~l—  12  24  36  Days since  48  release  60  72  84 ro  FIGURE  Average  Estimated time  average  Weight  Data  on  recoveries  of marked  of  H u r l e y and  Woodall  experiments. Sweltzer  of Pink Fry i n the Estuary  weight of  i n the estuary.  5.  "real"  and  model p i n k f r y over  o f P a r k e r and  fish  from  are based  on  LeBrasseur are  the B e l l a growth  Coola River.  rate  -  Model  o u t p u t assumes a c o n s t a n t  Data  salinity  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  Creek.  based  and  temperature  10 -,  8A  O  1 9 6 3 - Parker a LeBrasseur-  1974  •  1964 - Parker a LeBrasseur-  1974  A  1965 - Parker a LeBrasseur-  1974  A  1 9 6 6 - Parker a L e B r a s s e u r - 1974  •  Atnarko - Hurley a Woodall-  *  Model output  •  Sweltzer - Hurley a Woodall- 1968  el EP  •  CD  •  CU CP  o  o  4 i  x  •  >  < m  fro* T  r  12  24  36  48  Days since release  60  72  84  1968  Nevertheless, may  growth r a t e , r e l a t i v e  be t o o l o w i n t h e model:  "pinks The  pink  grow f a s t e r  than  p o s s i b l e importance  chum f r y e s t i m a t e s  i i  food  (1964) r e p o r t e d  d o chums a t c o m p a r a b l e a g e s o r of this  factor to relative  e t a l . (1977) d i d n o t f i n d  along  the coast  of British  dependent effe'cts on g r o w t h c a n n o t be t o t a l l y  Figure the  i flocal  effects  possible effects  any  indication density  eliminated,  within estuaries are considered. ©heemodel^'to  explore  o f d e n s i t y dependent growth on t h e s u r v i v a l  a n d chum f r y .  The of  and  Columbia,  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  of pink  pink  sizes."  Density  limitation  especially  that  of mortality i s explored.  Though W a l t e r s , of  Ricker  t o chum g r o w t h r a t e ,  model assumes t h a t growth r a t e  density, although  Reimer's  ( 1 9 7 3)  salmon  i n S i x e s R-iver, Oregon,  really  a c o m p l e x f u n c t i o n o f many changing  2.  increasing fish  3.  changing n u t r i t i o n a l in  function  work on j u v e n i l e  suggests  1.  i s a simple  chinook  t h a t growth r a t e i s  interacting variables:  estuarine utilization  patterns  by  fish  size level  and food  production  the estuary  4.  changing  fish  density  5.  p h y s i o l o g i c a l changes a s s o c i a t e d w i t h  6.  changes  i n the level  species  of  fish.  of competition  smolting  from  other  33  FIGURE  Estimated Effect  6.  of Density  Two  f u n c t i o n s used i n the model  fry  d e n s i t y on p i n k  on Growth  to simulate  Rate  the effect  and chum f r y g r o w t h r a t e .  Model  1  a s s u m e s no d e n s i t y d e p e n d e n t e f f e c t s .  Model  moderate d e n s i t y dependence  from Reimers, 1973).  (estimated  2  of  assumes  Number of pink and chum fry per hectare  35 i i i  to  and  Density  When b o t h t e m p e r a t u r e a n d  density  affect  Temperature  growth  multiplicative reduction actual  rate,  which  in growth  reduction  t e m p e r a t u r e and  the e f f e c t s  a r e assumed  probably results rate  than would  in growth  would  be  part.  coho  larval  t o m a k e up In  on  The  a complex  of  function  or  density  chum f r y .  Dynamics  p i n k and  but coho i n t a k e  fishes  extreme  occur in r e a l i t y .  feeding dynamics  Coho p r e d a t i o n  explicitly  be  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  Coho F e e d i n g  Juvenile  to  i n a more  and 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  iv  are hypothesized  are dealt with  only  in  chum f r y i s c a l c u l a t e d  of alternative  food  items such  as  z c j o p r a n k t o r o d s i a s s m e d i r d i n p l i c i t l y -tocc)CGurnastfneeded  the r e s t  of their  the model d a i l y  total  intake  daily  of f i s h  food  requirements.  is determined  by  body  weight: log  1  R = a + b log  Q  where R = consumption W  = weight Derived  is  based  15°C.  on  i n p e r c e n t body wet  1.5,  by  (1971]B)  Brett  triple  daily  b =  weight,  -0.39. f o r sockeye  salmon,  feedings of Abernathy  this  pellets  function at  that:  This relationship of  W  Q  (g), a =  I assume 1.  1  applies  the feeding response  experimental difference personal  setting,  between  t o coho  salmon.  o f coho t o p e l l e t s  there appears  sockeye  communication).  and  coho  t o be  In  terms  in  the  not  (Brett,  much  R  i s an  estimate of  percent  body wet  estimate weight  fishes food be  to  to  equal  fish  as  change the  tenuous.  factors  different  moisture  estimates  or  assumption (1971a;  1971b;  a p p e t i t e and  of  particles  rate of  assume t h a t f i s h rate The  as Abernathy triple  resulted feeding food  feeding  of  form  of  the  personal a number  of  daily  stomach  (amount  energy  food  particles.  a r e consumed a t the  I  same  pellets. feedings  i n the  original  food.  A  experiment  different  regimen would change the p r e d i c t i o n day  (Brett,  Nevertheless regimen would  p r e d i c t e d by  not  food i n g e s t e d ) ,  i n maximum i n t a k e o f  intake per  1971a).  food  daily  the  ingested),  different prey  would  hence  and  content  will  weight.  there are  receptors i n the  digestion  content,  i s somewhat  stretch  (caloric  the  that a l l salmonid  intake:  demand  from  instead of pellets  points out,  food  the  body wet  controlling  size  of  dry  to percent  Brett  communication)  body  body d r y weight  This  in to  i n percent  parameter  As  content  Assuming  food  relationship.  was  fish  forced  i n percent  same r e l a t i v e  consumption  Using  35%)  78%).  have the  roughly  B r e t t was  the moisture  (27.4%  (75%  weight.  consumption  because  pellets fish  food  the consumption of  the  et a l . ,  1969;  of  Brett,  I assume t h a t a n a t u r a l not  alter  equation.  the  intake  of  5.  The r e l a t i o n s h i p i s temperature independent. B r e t t , e t a l . '(1969) show t h a t , f o r sockeye, maximum food i n t a k e i s a f u n c t i o n o f temperature and d e c r e a s e s as temperature d e c r e a s e s or i n c r e a s e s from the o p t i m a l 15°C.  Thus, because  Brett; s^experimentstwe'reaperformedpat o p t i m a l 1  temperatMEesf^. i n t a k e i s p r o b a b l y o v e r e s t i m a t e d . G i v e n t h e s e assumptions, over the s i z e range o f coho found i n the model e s t u a r y , the maximum amount o f f i s h  ingested  ranges between 9% and 11% o f coho wet body w e i g h t . Coho growth r a t e i s independent o f the p r o p o r t i o n o f f i s h i n the d i e t .  W h i l e some s t u d i e s show d i f f e r e n c e s i n  growth r a t e o f salmon f e d on p a r t i c l e s o f d i f f e r e n t (Baloheimo and D i c k i e , 1966) o r o f d i f f e r e n t  sizes  nutritional  v a l u e ( B r e t t , 1971a), no study shows the e f f e c t o f p r o p o r t i o n of  f i s h i n the d i e t .  Coho a r e a l s o assumed n o t t o s u f f e r  from d e n s i t y r e l a t e d r e d u c t i o n s i n growth r a t e , e i t h e r the  from  p r e s e n c e o f competing p i n k and chum f r y o r from i n c r e a s e d  abundance o f coho.  Ill  Mortality The model assumes t h e r e i s a f i x e d amount o f growth and  m o r t a l i t y d u r i n g downstream m i g r a t i o n and o n l y d e a l s 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 s m o l t s r e a c h saltwater. In the e s t u a r y t h e r e a r e two causes o f m o r t a l i t y t o p i n k and chum f r y c o n s i d e r e d i n the model:  1.  low  level  explicit  n a t u r a l m o r t a l i t y that i s not function of  agent but  any  represents  the  specific mortality  non-coho p r e d a t i o n ,  disease,  etc. 2.  coho smolt  p r e d a t i o n m o r t a l i t y (see  Predation  section). Coho s m o l t s The pink,  are  daily  chum and  (1976)  a l s o assumed t o  and  rates of  age  the  General  residence  (date  littoral  explored from  the  by  Ricker  0.00043.  identified  i n estuary).  are  explicitly  zones  as  (Bakshtansky, than  pink  Dunford,  are  such  not.  fry  19 7 5 ;  The  length  examined  the  in  or  Blackburn,  of  differential  to  of  chum f r y  stay  longer  ( G o o d m a n , 19 7 5 ;  d u r a t i o n and  species  but  tendency  1964)  by  Species  r a t e , abundance and  to predation,  Hurley  personal  amount o f  overlap  and  i t s subsequent e f f e c t  changing  the  assumptions  on  controlling  pink  and  survival  are  emigration  estuary.  Coho s m o l t s all  arrival  estuary  19 6 8 ;  communication), chum s p a t i a l  chum f r y a r e  growth  from predators  Woodall,  and  differences that might r e s u l t  susceptibility to hide  of  in size,  i n the  behavioural  and  in  Assumptions  model pink  class  differences  the  given  Predation  In  in  from data  m o r t a l i t y to  r e s p e c t i v e l y , 0.00053, 0.00043,  i  and  from n a t u r a l m o r t a l i t y .  non-coho i n s t a n t a n e o u s  coho were e s t i m a t e d  are,  IV  suffer  are  assumed  v u l n e r a b l e - s i z e d prey  are  to remain either  i n the  eaten  or  estuary have  until  migrated.  U n f o r t u n a t e l y , the i n f o r m a t i o n does not e x i s t t o e s t a b l i s h a b e t t e r numerical response.  I t might have been more r e a l i s t i c ,  perhaps, t o have had coho begin t o migrate out o f the e s t u a r y after  some minimum encounter t h r e s h o l d was reached. In one form the model assumes no e x p l i c i t prey r e f u g i a .  The p r e d a t o r can e v e n t u a l l y e a t every member o f a g i v e n age class.  Another model o p t i o n a l l o w s f o r p r e d a t o r avoidance, which  can be i m p l i c i t l y accounted f o r by assuming a random d i s t r i b u tion of attacks.  D a i l y s u r v i v o r s of each prey type and s i z e  c l a s s a r e estimated by the zero category o f the P o i s s o n d i s t r i bution : EXP (-k.b./a.) x y x where k^ = the number o f prey_^ which c o u l d be eaten by one predator^ b. = t o t a l number of p r e d a t o r s . 1 3 a^ = t o t a l number o f prey^ k.b. = t o t a l demand f o r prey. x j x c  J  (This assumes t h a t  a l l predators., have a constant demand f o r prey .) ±  k.b. i 3 a^ = number o f a t t a c k s expected by each prey^ individual (Gilbert,  e t a l . 1976).  No allowance was made i n the model f o r p r e d a t o r tation  or i n h i b i t i o n .  facili-  40 ii  Multispecies Disc  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 is  used  to calculate  in  e a c h age c l a s s NA.  =  1  disc  equation  t h e number o f p i n k and chum f r y e a t e n  by coho s m o l t s .  Specifically,  TS a. p. D. 1* i l 1  + V t.  a. p. D.  i where N A i = number o f p r e y k i l l e d TS  = time  a^  = area covered =  spent  s e a r c h i n g f o r and h a n d l i n g p e r time  = d e n s i t y of prey^  t^  = t h e amount o f t i m e prey^  In g e n e r a l , the equation  i n the area  each  course  notes,  availability  1977)  t o consume  and p r o b a b i l i t y available  (For a d i s c u s s i o n o f  and u s e o f a m u l t i s p e c i e s v e r s i o n o f t h e d i s c  e q u a t i o n c a n be f o u n d  model.  handling  up t o a maximum imposed by t h e t i m e  see Eggers,  discussion  searched  a l l o w s each p r e d a t o r  the gut c a p a c i t y of the predator.  equation  the  spent  on W a l t e r s ,  p i n k a n d chum f r y a c c o r d i n g t o t h e i r  the d e r i v a t i o n  searching  attacked (based  and  prey  killed  D^  eaten,  i  p r o p o r t i o n o f prey^. s u c c e s s f u l l y , pursued and  of being  o f type  1976; a d e r i v a t i o n i n Charnov,  of the v a r i a b l e s  1973.)  o f the s i n g l e  species  The f o l l o w i n g i s a  i n the equation as they  apply i n  41  Area Searched  and D e n s i t y o f 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 p r e d a t o r depends on the p o s i t i o n o f t h e p r e d a t o r below t h e s u r f a c e r e l a t i v e t o the p o s i t i o n o f the prey i n the water column.  I t i s s i m p l e s t t o assume t h a t coho, p i n k  and chum a r e d i s t r i b u t e d i n t h e same p o r t i o n o f the water column ( i . e . a t t h e s u r f a c e ) and t h a t " e f f e c t i v e volume" e q u a l s " t o t a l area"searched.  Thus, i n the model, a r e a s e a r c h e d and  d e n s i t y are c a l c u l a t e d i n terms o f a t w o - d i m e n s i o n a l  surface.  2  That i s ,  a r e a searched = 2 r DT. + T T r D  where r = r e a c t i v e d i s t a n c e (m), 2 r = w i d t h o f s e a r c h p a t h , DT_. = d i s t a n c e p r e d a t o r t r a v e l s p e r day (m) ; TT = 3 . 1 4 1 5 9 ; and, D. = 1  I  A"  2  where 1NL = abundance o f p r e y ^ , A = a r e a prey occupy (m ) , 2  D^ = number o f prey ^ per m .  Reactive Distance There i s l i t t l e d a t a a v a i l a b l e on t h e v i s u a l a c u i t y o f f i s h e s , p a r t i c u l a r l y salmon. c a l c u l a t e d by K e r r  (1971)  T h e r e f o r e , I used t h e f u n c t i o n  f o r brook t r o u t  (Salvelinus  f o n t i n a l i s ) t o e s t i m a t e r e a c t i v e d i s t a n c e ( r a d i u s o f sharp p e r c e p t i o n ) o f coho s m o l t s .  Specifically,  r - c g tan  1/3 9  where r = r e a c t i v e d i s t a n c e , t a n c =  0.0124  9 =  0.0096  (33  min. o f a r c ) ,  (assumes s p h e r i c a l p a r t i c l e s o f w e i g h t g and  n e u t r a l d e n s i t y ) , g = prey w e i g h t  ( K e r r , 19 7 1 ) .  FIGURE  The  One of  "effective  of water  example o f t h e geometric the visual  (solid of  volume"  field  7.  Searched by a  relation  ( r ) , the distance  predator,  between t h e r a d i u s (s) o f t h e p r e d a t o r  point)  from  t h e s u r f a c e and t h e r e s u l t i n g  the search  path  (E) a n d t h e " e f f e c t i v e  searched  by t h e p r e d a t o r ,  Extrapolated  f r o m Ware  given  (1973).  volume"  the location  width of water  of the prey.  43  searched  44  Even though t h i s r e l a t i o n s h i p was n o t based on f i s h p r e y , i t seems t o p r o v i d e a r e a s o n a b l e e s t i m a t e o f r e a c t i v e distance (figure 8).  The d a t a on d i s t a n c e o f "sharp"  v i s i b i l i t y o f prey o f v a r i o u s 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 P r o t a s o v  (1970).  The  d i f f e r e n c e s between t h e two f i s h t y p e s a r e a t t r i b u t e d t o 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 o f l i f e . Horse mackeral  e a t s m a l l p l a n k t o n organisms w h i c h r e q u i r e  sharp v i s i o n t o c a p t u r e and m u l l e t a r e mud f o r a g e r s w i t h a c o r r e s p o n d i n g l y reduced heed f o r sharp v i s i o n . average v i s u a l a c u i t y ( B r e t t and G r o o t ,  Salmon have  1963).  R e a c t i v e d i s t a n c e d e c r e a s e s w i t h d e c r e a s i n g water c l a r i t y o r ambient l i g h t i n t e n s i t y 1963;  c i t e d by Ware, 1973).  ( H e s t e r , 1968; D u n t l e y ,  T h e r e f o r e I assume t h a t t h e  r e l a t i o n s h i p e s t i m a t e s maximum r e a c t i v e d i s t a n c e ( f i g u r e 9) because t h e F r a s e r R i v e r i s a v e r y t u r b i d r i v e r w i t h " t r a n s p a r e n c y 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 ( N o r t h c o t e , 1976)." F i n a l l y , "visual acuity i s primarily a function of p u p i l d i a m e t e r , which changes r e l a t i v e l y s l o w l y w i t h i n c r e a s i n g body s i z e  ( K e r r , 1971)."  Thus, i n t h e model, r e a c t i v e d i s t a n c e  i s assumed t o be independent o f p r e d a t o r  size.  D i s t a n c e T r a v e l l e d p e r Day D i s t a n c e t r a v e l l e d p e r day by coho i n s e a r c h o f prey depends on t h e speed o f s e a r c h .  I n most runs o f t h e model, coho  45  FIGURE  Reactive  Estimated and  The  Distance  r e a c t i v e distance of m u l l e t , horse  model coho  (cm).  8.  smolts  lines  were  t o prey fitted  o r mates by  eye.  mackeral  of various  sizes  Reactive o  ro o  distance  (cm) ro  oo o i  OJ  O o  o  _i  i  o o a.  2.  to a  3  o  3  -» CO CD a co o <  3 a o  a>  CD o o <  47  FIGURE 9.  R e l a t i o n between Prey Weight and Predator R e a c t i v e D i s t a n c e  F u n c t i o n a l r e l a t i o n s h i p between prey weight smolt r e a c t i v e d i s t a n c e  (g) and coho  (m) used i n the model under maximum  ( c l e a r ) and minimum (turbid) v i s i b i l i t y  conditions.  X Clear • Turbid  i  I  —r  T  2  3  Prey weight (g)  T 4  49 are  assumed  t o be  per  second,  independent  speed  of coho over  spring.and second  o f body  the s i z e  summer i s a b o u t  in this  Encounter Prey density  pink  and  size.  ranges four  to five  Sensitivity  The  i s a  related  body  Feller,  1974;  g i v e n volume  searched w i l l  function  Feller,  i t e m and  enough p e r i o d  per  unit  the  same v a l u e a s w o u l d with  the  Nevertheless, s h o u l d be  though  1975).  of a predator  randomly  thus prey encounter  vary over  mentioned.  satiate  discussed  the case  rate  time depending  the  encounter will  rate  approach  f o r a uniform prey  same m e a n p r e y d e n s i t y . ( J o n e s t , \ s l 9 7 7 ) . "  I f food a v a i l a b i l i t y  the p r e d a t o r , consumption  earlier,  on  for a  "However, c o n s i d e r e d  of time, the average  be  1968;  Schools  t h e r e a r e a number o f p r o b l e m s  encounter rate  pattern.  even  schools (Parker, et a l . ,  and  consumption  time f o r a contagious prey d i s t r i b u t i o n  distribution  to  of area searched  of prey c o n t a g i o n (Jones, 1977).  quickly  lengths per  of the model  to encounter rate  a prey  while  i n the estuary during  model assumes t h a t p r e y  encountering  over a long  swimming  i s explored.  prey decrease the p r o b a b i l i t y  degree  (Sustained  found  chum f r y a r e known t o f o r m  1974;  o f f o u r body l e n g t h s  Rate  of prey.  i s directly  Mason,  parameter  encounter rate  rate  As  at a rate  (see G l o v a , 1972).)  changes  of  searching  remains total  Thus, a l t h o u g h the  at the daily long  which  i s g r e a t enough  to  rate  becomes  zero  same l e v e l  (Jones,  1977).  consumption  depends on  term encounter r a t e  per  feeding unit  50 time  may  stay the  long  term  same, r e g a r d l e s s o f p r e y  c o n s u m p t i o n r a t e may  Furthermore,  s i n c e the  chum f r y i n t h e  e s t u a r y may  (LeBrasseur  Parker,  sized  prey  searches  and  w i l l be  any  one  Only of A  a  number o f  the  relative  prey  size  prey,  may  encounter  fry  size  rate of  a  the  prey  least  i n terms  pursued  determine and  this  and  the  availability  and  of prey  limitations  shape of prey prey  0.044 o f 1972). could  size  of  by  pursued  the  types  ability  and  For  (Sibert  a chum o r p i n k  killed.  the  certain  salmon,  the the  as: Parker,  that a of  of  for  and  f r y 42%  as:  determine  coho  T h i s means, f o r example, eat  predator  sizes.  been e s t i m a t e d  i t s body weight  a  and  the predator  eaten.  has  killed  p r o p o r t i o n such  predator,  of  searched.  encountered  successfully  particular-  selectively  i t s predator, predator preference  maximum i n g e s t i b l e 1.  and  d e p e n d e n t on  successfully  of prey  Physiological maximum s i z e  be  of  according to location  w i l l be  factors  to outrun  sized  of prey  size  location  Consumption, a t  a proportion of  specific  schools of pink  change.  1964),  w i l l vary  Proportion  the  non-random i f the p r e d a t o r  area.  numbers o f p r e y ,  distribution,  10  i t s own  cm  coho  body  length. 2.  2.  Figure  10  50%  of  i t s body  shows t h e  size  of  length fish  (Semko,  prey  actually  stomachs of Oncorhynchus  (taken from  1967  F u l t o n , 1967).  and  Barraclough  and  1954).  data  of The  found  in  Barraclough, largest  fish  prey  FIGURE 10.  S i z e of F i s h Prey Found i n Oncorhynchus  S i z e range o f f i s h prey found i n stomachs of (Oncorhynchus). and F u l t o n ,  Source:  1967.  found i n stomachs.)  B a r r a c l o u g h , 1967  salmonids and B a r r a c l o u g h  (See Appendix I f o r l i s t of f i s h prey  •  0-  ol  0- fcisutch  •  0- keta  •  0  A  0- nerka  •  •  o k  • 1  25  50  gorbu scho-  o  fshawytscha  o  i • 1  75  I  100  1  Agl  O  ~5~0 175 125 Predator size (mm)  200  225  250  53 found  i n a coho stomach was a P a c i f i c  hexapterus) The be  —51.2%  o f the coho's length  i n t a k e o f prey below  limited  predation  Paloheimo  Hall,  1974; Werner and H a l l ,  relative  and D i c k i e ,  b u r s t speed  1966; Werner,  1974; Werner and  1976).  capacities  of a fish  locomotive capacity  prey  i t s predator.  Furthermore,  19,64,-);^, T h e s e . f a c t o r y  determines Relative  increase i n size  time t o fatigue dec-  v e l o c i t y i i n c r e a s e s . / ; sespeGia-blylat'  s  their  endurance  decreases as f i s h  1964; G l o v a , 1972).  g.eases as  and t h e i r  to outrun  of fish  also  1961; K e r r ,  d i s t a n c e s e p a r a t i n g prey and predator,  the a b i l i t y  (Brett,  s i z e may  or to size-selective  and T e s t e r , 1944; I v l e v ,  1971;  (Ammodytes  ( 1 6 2 mm).  some t h r e s h o l d  due t o e n e r g e t i c r e a s o n s (Pritchard  The  sandlance  burstrspeeds _ (Brett,  combine t o determine -what? Holding,  (pers.  1  eomm":) s c a l l s " " strrike.ced-i-sta>ncie-.4t'he: m a x i m u m ^ d i s t a n c e - w h i c h separate p r e d a t o r and prey and s t i l l  result  could  i n successful  capture of the prey. In a crude the  functional  distance than  ingestible other  relationship  (figure  strike  a p p r o x i m a t i o n o f t h e above  11).  between  I f reactive  distance f o ra l lprey size  fish  of the prey  less  because  I n t h e model,  strike  t h e above c o n d i t i o n  Thus, in t h e model, determined  by prey weight  than  figure  size  and  strike less  t h e maximum 12), then  factors  t o outrun the predator  as p r e d a t o r p r e y p r e f e r e n c e ) determine escape.  prey  I estimated  d i s t a n c e i s always  (as i n t u r b i d water,  than the a b i l i t y  factors  the probability  of prey  distance i s not considered  i s almost  always  the proportion relative  true.  o f prey  eaten  (such  was  t o predator weight, and  54  FIGURE  Strike  Estimated  relationship  size  and  (cm)  predator permit  the  Distance  between p r e d a t o r  maximum d i s t a n c e  (strike  11.  distance)  (m)  of  (cm),  separating prey  t h a t would  successful capture  size  the  still prey.  prey and  energetically  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 ;  and  Relationship The  largest pink  (5.5  cm)  Parker, if  between  strike  Distance  distance and r e a c t i v e distance.  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  i f t h e maximum p r e y  size  1972) o f c o h o body w e i g h t ;  t h e maximum p r e y  Results). (and  Reactive  given  ( S i b e r t and  o r a b o u t 2.6 g  ( 6 . 9 cm)  i s 0.08 5 o f c o h o b o d y w e i g h t ( s e e  Thus t h e a b i l i t y  chum p r e y )  distance,  size  i s 0.044  o f coho t o capture  i snot significantly  pink  a f f e c t e d by  the reactive distances  prey  strike  used i n t h e model.  •Reactive distance x Strike distance  8 cm- prey  Prey  wei ght  ( g)  the  shape o f t h e f u n c t i o n ( f i g u r e  the  effects  ingestible and  sizes  of size size.  were  Total  Changes  i n the availability  assumed n o t t o a l t e r these  Searching  chum f r y t h r o u g h o u t  and Handling  Time  f o rpink and  i n Chatham  i s based  a t about  on a r e p o r t o f  Sound by Manzer  (1969).  Time  Information items  This  types  functions.  t h e d a y ( b e t w e e n 1 2 a n d 17 h o u r s )  feeding behaviour  f;- " i ^ l i H a n d l i n g  o f prey  t h a t coho salmon search  same l e v e l o f i n t e n s i t y .  coho  to explore  s e l e c t i v i t y a n d c h a n g e s i n maximum  The m o d e l assumes  the  13) was m o d i f i e d  on coho h a n d l i n g  was l a c k i n g .  time  of individual  prey  I n t h e m o d e l i t was e s t i m a t e d a s : t. l  =  W. l  TS 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^ w^  = weight  o f prey  maximum d a i l y TS = t i m e This  relationship  item  assumes  (g) b y p r e d a t o r _ . ,  that handling  t i m e p e r - i n d i v i d u a l • prey the  that the ratio of intake of a particular  prey  proportional  t o prey  prey  over  total  to. p r e y  (hours).  Furthermore,  to the estimated  capture  estimated  searching and handling  inerjeases-inrdirectrpropor.ti-on equation  ( g ) , RA.. =  intake o f food  spent  assumes  ^  (hours),  daily  size.  intake o f food  size- (given a constant  size).  i sdirectly  rate of successful  FIGURE 13.  Proportion  o f Encountered Captured  Three  functions describing  prey  successfully  that  the proportion eaten  increasing  Prey  and Eaten  the proportion (Pi) of  c a p t u r e d and eaten.  prey weight.  Successfully  F u n c t i o n 1 assumes  i s a decreasing function of F u n c t i o n 2 assumes  that  constant p r o p o r t i o n o f a l l prey below a threshold eaten  (that  i s , they a r e equally of size).  F u n c t i o n 3 assumes t h a t  preference  f o rlarger  prey  prey  predator  below a t h r e s h o l d size  ingestible can e a t .  results size.  size,  size i s  predator  i n a reduced  consumption  SW = C x P A R w h e r e C =  ( g ) , PAR = p a r a m e t e r  prey  a  vulnerable to predation  regardless  of  encountered  defining  a n d SW = m a x i m u m p r e y  maximum size  predator  Function  Function 2  Function 3  T  SW/2  Prey weight  r  2SW/3  61 CHAPTER  1.  tasks  simulation modelling,  i s determining  change.  further  DISCUSSION  the  one o f t h e most  These c r i t i c a l  elements c o n s t i t u t e a target f o r changes and  was e x p l o r e d  i n depth.  t h e parameters and range o f v a l u e s I n v i e w o f t h e many  environmental  variability  seems u n l i k e l y  sources  detected  i n the real  tested  system.  or  River  to various  could and that  i n pink  operation context.  i s based  on  point  tagging,  fora variable  o f eggaand  source  return.  juvenile  fordiscussion, I  arbitrarily  s e n s i t i v e i f a change i n parameter than  o r chum f r y m o r t a l i t y .  be m a n i p u l a t e d  be  forms o f measurement e r r o r .  assumption r e s u l t e d i n a greater  decrease  could  For example, assignment o f  estimates  as a s t a r t i n g  t h e model  i n t h e model  i n t h e measurement o f a d u l t  the original  abundance a r e s u b j e c t  considered  see Appendix I I . )  o f some p a r a m e t e r ,  ^counts and t i m i n g o f runs which account magnitude o f e r r o r  list  i n the n a t u r a l system, i t  and escapement t o t h e F r a s e r  Nevertheless,  (For a complete  t h a t a 5% o r e v e n a 1 0 % c h a n g e  due t o m a n i p u l a t i o n  Furthermore,  Thus  o f measurement e r r o r and  inherent  results,  and  system.  o f t h e model t o changes i n assumptions and  parameter values  catch  manipulation  19? ) o f both t h e model and r e a l  sensitivity  important  which elements o f t h e model a r e s e n s i t i v e  investigation,policy  (Gallopin,  of  R E S U L T S AND  Introduction In  to  III.  5% i n c r e a s e o r Parameters,.  by managers r e s p o n s i b l e  o f enhancement f a c i l i t i e s ,  value  which  f o r construction  are discussed  i n  To of  gain  some u n d e r s t a n d i n g  enhancement,  several pink  were done u s i n g  the  not  basis  only  also,  on  the  model. of  where p o s s i b l e , on  versus  enhanced  considered  only  stock  smolts  i s assumed  and  the  coho.  possible  consequences  chum e n h a n c e m e n t  experiments  These experiments are  basis  survival.  t o be  the  fry survival  i n terms of  chum f r y consumed p e r  of  or  adult return,  of w i l d  I m p a c t on  changes The  i n the  stock, coho  stocks  f r y prey  each  but  survival  number o f  intake of  a maximum u n d e r  evaluated  set of  is  pink by  and  coho  simulation  conditions: 1.  The  model does not  2.  The  m o d e l a s s u m e s 100%  predator 3.  consequently  capacity, will 4.  growth or There  Several results  prey  are  assumed  of  prey  to prefer  consume as availability  assumed not survival  i s no  avenues of  were e x p l o r e d  literature.  overlap  refugia. and  fish  many f i s h and  as  prey stomach  vulnerability  allow.  Coho a r e  5.  f o r prey  spatiaibudiSitributions.  Coho p r e d a t o r s and  allow  feeding  to  due  s u f f e r from to  lack of  inhibition  or  food. interference.  i n v e s t i g a t i o n suggested  using  pertinent data  reduced  found  by in  the the  model  2.  Sensitivity Analysis I  Components o f P r e d a t i o n  The model r e s u l t s a r e r e l a t i v e l y i n s e n s i t i v e t o most of t h e components o f p r e d a t i o n . extreme c o m b i n a t i o n s  I found t h a t even comparing  o f t h e parameter v a l u e s (minimum r e a c t i v e  d i s t a n c e , 1 body l e n g t h p e r second s e a r c h v e l o c i t y , 45957 h e c t a r e s s e a r c h area and 4 hours s e a r c h time v e r s u s maximum r e a c t i v e d i s t a n c e , 5 body l e n g t h s p e r second s e a r c h v e l o c i t y , 15319 h e c t a r e s s e a r c h a r e a and 16 hours s e a r c h t i m e ) , p i n k f r y m o r t a l i t y o n l y i n c r e a s e d from 32.8% t o 37.0% and chum f r y m o r t a l i t y from 9.0% t o 10.2%. I n c r e a s i n g t h e 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 t o 23 p e r c e n t i n c r e a s e (see T a b l e 5) i n p i n k f r y m o r t a l i t y and a 21 t o 26 p e r c e n t i n c r e a s e i n chum f r y m o r t a l i t y due t o t h e i n c r e a s e i n f r y v u l n e r a b i l i t y .  The  average number o f f r y eaten p e r coho p e r day d e c r e a s e d (Table 5) because b e i n g a b l e t o e a t l a r g e f r y , reduced t h e number o f f r y needed t o s a t i s f y t h e coho's d a i l y r a t i o n requirements. I n g e n e r a l , t h e model r e s u l t s were n o t s e n s i t i v e t o changes i n t h e f u n c t i o n ( f i g u r e 13) used t o determine t h e p r o p o r t i o n o f encountered smolts.  p i n k and chum f r y eaten by coho  However, i f t h e maximum i n g e s t i b l e prey s i z e was  i n c r e a s e d , t o t a l chum f r y m o r t a l i t y d i d i n c r e a s e (about  6.1%)  u s i n g F u n c t i o n 3 v e r s u s F u n c t i o n 1 (see T a b l e 5 ) . As chum f r y from any one age c l a s s a r e g e n e r a l l y l a r g e r than p i n k f r y from t h e same age c l a s s , coho p r e f e r e n c e f o r l a r g e prey ( F u n c t i o n 3) has a g r e a t e r r e l a t i v e impact on chum f r y than  T A B L E 5.  Sensitivity  o f model r e s u l t s  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 ,  two d i f f e r e n t encountered fry  functions  fish  migration  1115:1.  t o changes i n t h e estimated  prey  to describe  the proportion of  s u c c e s s f u l l y eaten.  b e g i n s M a r c h 1.  Pink  Prey:predator  Chum f r y c o m p o s e 1 5 % o f t h e t o t a l  prey  population.  FRY^SIZE  0.085 (of coho 2 body w e i g h t )  % mortality  57 .7  78.2  Chum % m o r t a l i t y  29.6  51.4  Fry eaten/cbho/day  3.13  2.51  33  48  ORTI  0.044 ( o f c o h o -i body weight)  a n d chum  ratio i s  MAXIMUM I N G E S T I B L E  Pink  using  Pink  % mortality  58 .5  81.5  PH  Chum % m o r t a l i t y  31.0  57 .5  Fry eaten/coho/day  3.19  2.26  33  54  FUNCTION w  3  1.  EH < W  Maximum # o f vulnerable  days  O  o  a,•:  FUNCTION  3  3.  Maximum # o f vulnerable  days  About  42% o f coho body  length.  About  50% o f coho body  length.  Simulations pink  assumed  d e n s i t y dependent growth r a t e f o r  a n d chum f r y ( m o d e l 2 ) .  on  pink  fry.  Nevertheless,  predation m o r t a l i t y than  pink  The  on  coho's preference  a cohort  preference  the  for larger Function  to cohort  greater  versus  51 t o  had a h i g h e r  f o r l a r g e f r ygave  5) b e c a u s e ration  1, I!>b€ffered" the total  survival  small  small  i ttook  Using  2.5  Function  3 also  t o 2.3  needs o f t h e coho.  In a real  supply:  (from  48  t o 54 d a y s ) .  sense,  t h e coho  apply  types  t o a l l prey  Nevertheless, or changes preference, account  i n prey  like  coho  selectivity  predator.)  t o some e x t e n t a n d predators  than  be remembered  that differences  r a t h e r than  or changing  search  predator  image, e t c . ,  consumption pattern of predators.  f a c t must be c o n s i d e r e d  to  salmon.  vulnerability,  f o r the prey  laboratory  to specialist  i t should  lasts  ( T h i s assumes t h a t t h e f r y  This concept  predators  reduced  by ."allowing" t h e f r yt o  b y some o t h e r  generalist  coho  to satisfy the  and a r e n o t eaten  may b e e v e n m o r e i m p o r t a n t  1),  per day  remain a v a i l a b l e may  compared  r a t e because  Function  large prey  lit-s food  pink  number o f  grow, t h e coho r e q u i r e s fewer p e r day and t h e s u p p l y longer  i n the  f r y a chance t o grow o u t  fewer  "conserving"  reflected  (Function 3 versus  average r a t e o f f r y i n t a k e from  daily  higher  w a s g r e a t e r u s i n g Func«ti6ni:3,  basis  actually  prey,  Although  the v u l n e r a b l e s i z e range.  (Table  is  3 versus  a n d chum f r y e a t e n  some c o h o r t s  of  (78 t o 82 p e r c e n t  chum f r y f r o m p r e d a t i o n .  pink  a  respectively).  shape o f F u n c t i o n and  suffer  chum f r y b e c a u s e o f t h e i r  abundance and v u l n e r a b i l i t y 58 p e r c e n t ,  f r ys t i l l  ( a n d o f t e n i s n o t ) when  predation experiments  such  prey may This  designing  as Parker's  (1971).  "The  selectivity  result kind  observed  ( i n t h e experiment)  o f p r e f e r e n c e shown b y t h e a n i m a l  which  in  p r o c u r i n g them a r e a b s o l u t e l y  Hyatt,  of  the d i f f i c u l t i e s  1976)." prey  this  category  f o rprey  lack  suggest  size  range  1961, c i t e d  that  The  parameter  prey  sensitivity  suggests  (seeMethods, to a  at Migration into  general  significant  this  size  juvenile  coho  arms;  3 8 - 2 4 5 mm  test  range  range  Goodman's  and p o s s i b l y ,  mortality  decreased  decreased  from  determine  o f coho  from  second  Sturgeon  and Roberts  Banks).  o f o v e r e s t i m a t i n g mean c o h o  from  year  t h e N o r t h , M i d d l e and  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 , size  (1975)  seems t o i n d i c a t e t h e  from  from  the importance  t h e mean i n i t i a l  size  e s t i m a t e may b e t o o h i g h b u t t h e  f r y and y e a r l i n g s  ( 2 1 - 1 2 9 mm  Estuary  i n f o r m a t i o n , mean i n i t i a l  o f coho i n h i s samples  of both  size  by  o f predators, using the zero  d i d not lead  o f any b e t t e r  presence  prey  animal  f o r future research.  avoidance  of Predation),  data  to  i n this  s m o l t s i n t h e m o d e l w a s 1 1 cm.  To  state  ( 5 % ) i n p i n k o r chum f r y m o r t a l i t y .  For  on  (Ivlev,  c a n n o t be d e t e r m i n e d .  t o changes  IleOaP.redator S i z e  South  or that  by t h e consumer  equal  of the Poisson distribution  reduction  coho  encountered  i s an important area  assumptions  I".  forthis  some m e a s u r e o f m a x i m u m i n g e s t i b l e  vulnerability  Allowing  of  Without  t h e model r e s u l t s  that  be t h e  o f food o n l y i fa l l t h e food components a r e i n a  in  isiize,  will  I  1 1 cm t o 9.5 cm.  size  decreased Pink f r y  8 1 . 5 % t o 6 6 . 6 % a n d chum f r y m o r t a l i t y  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 h e p r o p o r t i o n o f f r y e a t e n ; maximum  i s 0.085 o f c o h o b o d y w e i g h t ) .  Obviously  ingestible prediction  of  the r e l a t i v e and d i r e c t importance  o f w i l d and enhancement  coho smolt p r e d a t i o n 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  a f f e c t e d by the estimated or r e a l average s i z e o f the coho. T h i s r e s u l t should be given s e r i o u s c o n s i d e r a t i o n as i n i t i a l s i z e o f coho smolts r e l e a s e d from enhancement f a c i l i t i e s can be c o n t r o l l e d t o some e x t e n t  Ill  (Smith, 197 8 ) .  Timing and D u r a t i o n o f pink and Chum F r y M i g r a t i o n  As T a b l e 6 i n d i c a t e s , the model r e s u l t s were s e n s i t i v e to changes i n f r y m i g r a t i o n t i m i n g c(tfel'afe'ive:Lto ( r e 3 - i - i c  a f i x e d s t a r t i n g date f o r coho m i g r a t i o n ) .  Although, on  any one day, a g r e a t e r number o f both pink and chum f r y a r e v u l n e r a b l e to coho p r e d a t i o n i f t h e i r m i g r a t i o n i s delayed (consequently  s h o r t e n i n g the d u r a t i o n and i n c r e a s i n g the number  of  f r y m i g r a t i n g per day), chum f r y m o r t a l i t y a c t u a l l y  or  remains r e l a t i v e l y c o n s t a n t  (e.g. 15.0% versus 12.2%)  w h i l e pink f r y m o r t a l i t y i n c r e a s e s (e.g. 39.8% versus The  decreases  52.3%).  i n c r e a s e d d e n s i t y of v u l n e r a b l e pink f r y i n the e s t u a r y  b u f f e r s chum f r y from p r e d a t i o n . The  i n t e r a c t i o n o f b i o l o g i c a l assumptions does not  always r e s u l t i n simple a d d i t i v e or m u l t i p l i c a t i v e changes. T h i s makes i t d i f f i c u l t t o p r e d i c t i n advance the d i r e c t i o n and magnitude o f changes i n model r e s u l t s due to the a d d i t i o n of  o r 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 a f f e c t e d d i f f e r e n t l y  (see p r e v i o u s  example from Table 6) o r the r e l a t i v e change i n m o r t a l i t y may be d i f f e r e n t because o f concomitant  changes i n d e n s i t y  TABLE  6.  Sensitivity v  pink and  o f model r e s u l t s  t o changes  a n d 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 chum g r o w t h r a t e .  The s t a r t i n g d a t e  constant.  Fry mortality  that  period of estuarine  early  vulnerable.  T h e maximum  coho's body weight. the  i n the estimated  total  prey  ingestible  Prey:predator  o f t h e coho  smolt  predation  f r ysize  i s assumed  i s 115:1.  pink  migration i s  only  when t h e f r y a r e s t i l l  ratio  of the  i n the assumptions a f f e c t i n g  i s due t o coho smolt life  s t a r t i n g date  and occurs  available  during  and  t o b e 0.044 o f t h e  Chum f r y c o m p o s e 1 5 % o f  population.  No Temperature or Density Effects  Temperature Only  Density Only ( m o d e l 2)  Temperature & Density ( m o d e l 2) :  MIGRATION B E G I N S MARCH 1 % pink f r y mortality  29.5  ,3.9. .18  57.7  71.2  % chum f r y mortality  12.8  15.0  29.6  36. 3  cont'd.  TABLE  6, P a g e 2.  No Temperature or Density Effects  Temperature Only  Density Only ( m o d e l 2)  Temperature & Density ( m o d e l 2)  MIGRATION B E G I N S MARCH 15 % pink f r y mortality  36.9  52.3  74.7  87.7  % chum f r y mortality  10.2  12.2  30.0  37.3  Pink  m i g r a t i o n peaks A p r i l  m i g r a t i o n p e a k s May a b o u t May  Pink  1-2.  Density  chum m i g r a t i o n of pink  peaks A p r i l  11-12;  coho  a n d chum f r y i n t h e e s t u a r y  peaks  1-2.  m i g r a t i o n peaks A p r i l  p e a k s May  14-15;  1-2.  Density  2 1 ; chum m i g r a t i o n p e a k s A p r i l  of pink  18; coho  a n d chum f r y i n t h e e s t u a r y  peaks  migration about  May  70 ( f i g u r e 14), temperature  (figure  p r o v i d e s s e v e r a l examples the  2), e t c .  Table 6 a l s o  of t h i s l a t t e r e f f e c t  (e.g. comparing  i n c r e a s e i n pink f r y m o r t a l i t y due t o the added  assumption  of temperature dependent growth, the r e l a t i v e i n c r e a s e i n pink m o r t a l i t y i s 34.9% and 41.7%  i f the f r y b e g i n to migrate March 1  i f they migrate March  15.)  71  FIGURE  14.  R e l a t i o n Between F r y D e n s i t y and  Starting  Pattern  ©ate o f F r y M i g r a t i o n  Total  density of pink  a n d chum f r y o v e r  their  date  i n the estuary.  (X10)  i s given  of arrival  f o r comparison.  time, Density  The F r a s e r  relative o f coho  River  smolts  estuary i s  assumed  t o be 15,319 h e c t a r e s .  115:1.  F r y growth r a t e i s n o t a f f e c t e d by temperature o r  density.  The p r e y : p r e d a t o r  to  ratio i s  Pink and Chum fry • March I + March 15 Coho smolts (xlO) © April 2 3  IV  Growth r a t e  S e n s i t i v i t y t o v a r i o u s parameter changes i n c r e a s e s s u b s t a n t i a l l y i f the assumptions a l s o change.  c o n t r o l l i n g growth r a t e  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 i m p o r t a n t over the range o f v a l u e s 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 a r e a from 15319  h e c t a r e s t o 30638 h e c t a r e s  decreased p i n k f r y m o r t a l i t y 37% chum f r y m o r t a l i t y 19%  (from 74.3%  (from 29.7%  t o 37.6%) and  t o 10.5%).  Further  i n c r e a s e s i n a r e a 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 rate. To e x p l o r e the s e n s i t i v i t y o f the model r e s u l t s t o an i n c r e a s e i n e s t i m a t e d p i n k 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) t o c a l c u l a t e  p i n k growth r a t e : log  e  G = log  e  9.7 8 - 0.4 5 l o g  e  W  where G = i n s t a n t a n e o u s growth r a t e x 100, W = weight  (g).  The above p a r a m e t e r i z a t i o n seems t o o v e r e s t i m a t e p i n k f r y growth r a t e (see d i s c u s s i o n o f growth r a t e , B i o l o g i c a l B a s i s o f the model) whereas the p a r a m e t e r i z a t i o n g e n e r a l l y used i n the model (Table 4) may  u n d e r e s t i m a t e p i n k f r y growth r a t e ,  r e l a t i v e t o chum f r y growth r a t e , d u r i n g t h e i r e a r l y  stages  o f l i f e i n the e s t u a r y . Experimetttfa'tfrora  (Table  Head to: th e f^Mowi'rtgV-ob'S'erVaTtio'ffs a*nd 'conclusion's": v  +  - .. • •; rlv; 1 js:Un'dea: pink  certain  growth  rate  :  assumptions  increasing  substantially  decreased  T A B L E 7. Sensitivity pink  f r y growth  various rate  o f model r e s u l t s  i n the estuary.  No temperature or density effects  Temperature only  Density only ( m o d e l 2)  r a t e and f r y m i g r a t i o n  assumptions a f f e c t i n g  Chum f r y c o m p o s e  t o changes  pink  ratio  prey  MARCH 1  MARCH 1 5  A  A  B  date  a n d chum  Prey:predator  15% o f t h e t o t a l  i n estimated under growth  i s 115:1.  population.  B  29. 5  19 .1  36 .9  18 .1  Pink  12. 8  15 .4  10 .2  16 .3  Chum % m o r t a l i t y  40. 3  27 .7  49 .3  26 .7  #  39.8  22 .4  52 .3  23 .1  Pink  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  #  57 .7  33 .1  74. 7  44 .5  Pink  29 .6  34 .0  30. 0  45 .2  Chum % m o r t a l i t y  79 .9  49 .7  101. 8  66 .8  #  % mortality  eaten/coho  % mortality  eaten/coho  % mortality  eaten/coho  cont'd.  TABLE 7, Page 2.  MARCH 1  Temperature & density (model 2)  MARCH 15  A  B  A  B  71. 2  44 .1  87. 7  53 .8  Pink % m o r t a l i t y  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 i n s t a n t a n e o u s r a t e o f p i n k growth i n w e i g h t p e r day f o r t h e f i r s t month o f l i f e = 0.059033 (about 6.1% per  day w i t h no temperature o r d e n s i t y e f f e c t s ) ; maximum  i n g e s t i b i k e s i p r e y - sizet '•  i s 0.044 x p r e d a t o r w e i g h t (g) .  (Used f o r most s i m u l a t i o n r u n s d e s c r i b e d i n t h e r e s u l t s . )  B - Average i n s t a n t a n e o u s r a t e o f p i n k growth i n w e i g h t p e r day f o r t h e f i r s t month o f l i f e = 0.085896 (about 9.0% per  day).  Based on t h e r e l a t i o n s h i p f o r growth i n  B r e t t & S h e l b o u r n (1975) .  Maximum ingestiblieKiprey t '  size. - .is i s 0.044 x p r e d a t o r w e i g h t (g) .  Average i n s t a n t a n e o u s r a t e o f chum growth i n w e i g h t p e r day f o r t h e f i r s t month o f l i f e = 0.06236 (about 6.4% p e r day) f o r b o t h A & B. described.)  (Used i n a l l ; s i m u l a t i o n runs  76  pink  f r y m o r t a l i t y and i n c r e a s e d chum f r y m o r t a l i t y .  For example, i f f r y migrate March 1 and i f d e n s i t y and  temperature a f f e c t growth r a t e , pink m o r t a l i t y  i n the model decreases' from 7 1 . 2 % t o 4 4 . 1 % and chum m o r t a l i t y i n c r e a s e s from 3 6 . 3 % to 4 7 . 5 % . 2.  I f pink  f r y grow f a s t enough, they can more than  compensate f o r (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  s i z e , a somewhat s h o r t e r  migration  p e r i o d and a lower encounter r a t e due t o the d i f f e r e n c e i n pink and chum f r y abundance (5.7:1) .  3.  The i n t e r a c t i o n o f v a r i o u s assumptions r e s u l t s i n an u n p r e d i c t a b l e  pattern of r e s u l t s , a t l e a s t i n  terms of the r e l a t i v e e f f e c t and sometimes i n terms o f the d i r e c t i o n of the e f f e c t .  For example,  with no temperature or d e n s i t y e f f e c t s on growth r a t e and changing the date of m i g r a t i o n 1 t o March 1 5 , pink (7.4%)  fry mortality  from March  increased  when average growth r a t e was 6 . 1 % per day  (columns A ) but decreased  ( 1 % ) when average  growth r a t e was 9.0% per day (columns B ) . p a r t i c u l a r r e s u l t i s due to the combined o f changed pink  This  effect  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 f r y d e n s i t y pattern.? and l i m i t e d coho stomach c a p a c i t y and abundance.  77 4.  IF food supply i s not l i m i t i n g the growth o f pink and chum f r y i n the e s t u a r y (Parker, 1968; LeBrasseur, e t a l . ,  1969; Walters, e t a l . ,  and IF growth r a t e i s temperature et  al.,  1977)  dependent  (Brett,  1969) and operates as p o s t u l a t e d i n the model,  THEN, the model p r e d i c t s t h a t average coho i n t a k e o f pink and chum f r y d u r i n g t h e i r r e s i d e n c e i n the e s t u a r y i s between 32 and 7 0 f r y per coho. average fry of  (Total  i n t a k e was used because the number o f days  are v u l n e r a b l e t o coho p r e d a t i o n d u r i n g t h i s p e r i o d l i f e v a r i e s , depending  on the assumptions  i n force.  Thus the number eaten per day per predator can be misleading).  T h i s r e s u l t s i n an e s t u a r i n e pink and  chum m o r t a l i t y r a t e o f 22% t o 52% and 12% to 23%, respectively  (depending on the assumptions  m i g r a t i o n date, e t c . ) .  controlling  Thus although coho p r e d a t i o n  on pink and chum f r y d u r i n g t h i s e a r l y stage of marine l i f e may account f o r a s u b s t a n t i a l p o r t i o n o f F r a s e r R i v e r f r y - t o - a d u l t m o r t a l i t y , i t alone can not account f o r the observed e s t i m a t e s , g i v e n 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 for  summary, coho p r e d a t i o n i n the model c o u l d account  87.7% o f pink f r y and 37.3% o f chum f r y m o r t a l i t y under one  extreme s e t o f assumptions  and 19.1% o f pink f r y and 15.4% o f  chum f r y m o r t a l i t y under the o p p o s i t e extreme s e t o f assumptions.  78 This  clearly  demonstrates the d i f f i c u l t y  importance o f coho p r e d a t i o n  on p i n k  so many u n c e r t a i n t i e s r e g a r d i n g  a n d chum f r y when t h e r e a r e  the basic  One m o r e g r o w t h r a t e e x p e r i m e n t , 7, a l l o w e d  pink  of evaluating the  b i o l o g y o f t h e system.  n o t summarized  f r y t o g r o w a t t h e same r a t e a s c h u m f r y .  mortality  decreased  increased  from 12.2% t o 15.1% (assuming p i n k  their  migration  dependent). small  Thus t h e r e s u l t s  River  initial  estuary  i n mean  of  time  I  tested If  first  i ttakes this  t o reach  hypothesis  chum f r y a l o n e  ( i f there  the Estuary  the season. a s 2mm  i s really a size using  into  Although  (Palmer, determined  predation.  197 2 ) ,  increase  i t might  t o o b i g f o r coho  smolts  toeat.  t h e model.  increased  i n mean  migration),  size  because o f t h e i r Predation  o f coho  on pink  (2mm o v e r t h e  chum m o r t a l i t y d e c r e a s e d  i n predation  switching  affected  reduced v u l n e r a b i l i t y f r yincreased pressure  be  by t h e l e n g t h  were 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 on  The i n c r e a s e  result  the Fraser  this  t o 12.4% ( i f b o t h d e n s i t y and t e m p e r a t u r e  growth rate)  (<1%).  into  o f chum f r y m o v i n g  over  i ff r ysurvival  i s temperature  f r y growth.  be a s l i t t l e  lh m o n t h s o f t h e i r  growth)  the  increases  s i z e may  important  size  a n d chum f r y b e g i n  o f t h e model a r e s e n s i t i v e t o even  Size at Migration  mean  Pink  5 2 . 3 % t o 4 1 . 4 % a n d chum m o r t a l i t y  on M a r c h 15 a n d g r o w t h r a t e  Chum a n d P i n k  The  3.6%  from  changes i n average pink  V  i n Table  only  marginally  on p i n k  t o a more v u l n e r a b l e  t o coho  f r yi s not prey  p e r se  79 but to  simply  e a t more o f t h e v u l n e r a b l e  encounter the  t h e r e s u l t o f t h e coho s t i l l  rate  of vulnerable  o v e r a l l encounter  rate  pink  being  hungry  and  f r y encountered.  chum f r y h a s d e c r e a s e d  actually increases  able  The although  because  more  chum f r y a r e s u r v i v i n g .  VI  Prey  Figure the  relation  successfully fry of  15a shows two f o r m s , g e n e r a t e d between  f r ydensity  by t h e model, o f  and t h e number o f f r y  e a t e n p e r coho p e r day.  The l o w e r  p e r coho i n c u r v e B i s due t o d i f f e r e n c e s chum f r y a s o p p o s e d  migration major  timing  factor  larger  intake  and growth  t h e model  growth  rate  and  density,  o f chum  i n the biology differences i n  are partly responsible, intake  f r y , coupled with  form o f t h e r e l a t i o n  fry  Although  intake  the  of f r yi s the the coho s 1  limitations.  of f r yalso  defining  fry.  rate  s i z e o f chum  capacity  The  t o pink  c o n t r i b u t i n g t o the lower  initial  stomach  is  Density  f r y density  depends on t h e b i o l o g i c a l system  (e.g. figure  i s assumed  the increase  more s e v e r e w i t h  between  i n average  increases  assumptions  15b).  t o be a f u n c t i o n intake  and coho  For example, i f  o f temperature o f f r y p e r coho  i n f r ydensity.  Comparing the  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 , increasing in  the prey:predator  a 365% v e r s u s  127% i n c r e a s e  eaten p e r coho p e r day. to  density  ratio  from  i n t h e a v e r a g e number o f f r y  The r e d u c t i o n  and temperature  50:1 t o 200:1 r e s u l t e d  i n f r y growth r a t e  due  effects results i n f r ythat are  smaller,  on any given  day, than  f r y n o t s u f f e r i n g from  reduced  growth.  Thus t h e a v e r a g e number o f f r y needed by coho t o  80  FIGURE 15a.  R e l a t i o n Between Prey;Predator R a t i o and Number of F r y Eaten/Coho/Day  Two forms o f the f u n c t i o n a l r e l a t i o n between the prey: predator r a t i o and the average number o f 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 p o p u l a t i o n . of the prey p o p u l a t i o n .  In curve B, chum f r y compose 100% F r y m i g r a t i o n begins March 15.  F r y growth r a t e i s not a f f e c t e d by temperature  or d e n s i t y .  82  FIGURE 15b.  Another Example of R e l a t i o n Between  Prey:Predator  R a t i o and Number o f F r y Eaten/Coho/Day  Two more examples of the f u n c t i o n a l 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. temperature  In curve A, f r y growth r a t e i s a f f e c t e d by  and d e n s i t y (model 2 ) .  In curve B, f r y growth  r a t e i s a f f e c t e d by d e n s i t y o n l y (model 2). compose 15% of the t o t a l prey p o p u l a t i o n . begins March 1.  Chum f r y  Fry migration  Average no- of fry eaten per day per coho ro  £8  oJ  cn  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 increases. F i g u r e 16 shows t h e k i n d o f change i n p i n k and chum m o r t a l i t y t h a t can be e x p e c t e d w i t h i n c r e a s e s i n e i t h e r t o t a l f r y abundance o r coho smolt abundance (assuming no temperature o r d e n s i t y e f f e c t s on growth).  F o r example, f o r  low l e v e l s o f f r y abundance ( l e s s than 120 m i l l i o n ) , t h e number o f p i n k and chum f r y e a t e n i s almost c o n s t a n t ,  regardless  o f the number o f coho, because m o r t a l i t y i s b e i n g 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 . low end ( p r e y : p r e d a t o r response c u r v e  ratio  The system i s a t t h e  60:1) o f the coho f u n c t i o n a l  (see f i g u r e 15a).. As t h e number o f f r y  i n c r e a s e s , m o r t a l i t y b e g i n s t o be l i m i t e d n o t o n l y 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 b u t a l s o by coho abundance and stomach c a p a c i t y .  F o r example, i f t h e r e a r e 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 t o 360 m i l l i o n  results  i n a 10% d e c r e a s e i n p i n k 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 t o 520 m i l l i o n  (an e q u a l ,  absolute  i n c r e a s e ) r e s u l t s i n a g r e a t e r than 15% decrease i n p i n k mortality.  Thus, coho a r e o p e r a t i n g f a r t h e r o u t on t h e l i m b  of t h e f u n c t i o n a l response c u r v e  VII  ( r e f e r t o f i g u r e 15j.},.  R e l a t i v e P r o p o r t i o n o f P i n k t o Chum F r y i n t h e Estuary  The r e l a t i v e p r o p o r t i o n o f p i n k t o chum f r y i n t h e e s t u a r y v a r i e s from year t o year i n t h e n a t u r a l environment. F i g u r e 17a shows t h e e f f e c t on e x p e c t e d t o t a l f r y m o r t a l i t y r a t e , under t h r e e d i f f e r e n t assumptions, o f c h a n g i n g t h e i r r e l a t i v e p r o p o r t i o n s i n t h e model:  FIGURE 16.  R e l a t i o n Between Changing Pink and Chum Fry Abundance and Coho Smolt Abundance  The combined e f f e c t on the i n d i c a t o r s shown of changing  both  the coho smolt abundance and the t o t a l pink and chum f r y abundance.  F r y m i g r a t i o n begins March 15.  i s not a f f e c t e d by temperature  or  density.  F r y growth r a t e  86  Pink fry mortality (xlO  -  )  Chum fry mortality (xlO  6  )  Average no- of fry eoten per coho per day  FIGURE 17.  Relation Proportion  Fig. and  17a.  between F r y M o r t a l i t y  o f Chum F r y i n t h e T o t a l B r e y  R e l a t i o n between percent  p r o p o r t i o n o f chum  population. ratio;  I n curve  chum a b u n d a n c e  there  i s a constant  there  i s an i n c r e a s i n g  constant March 15. density.  and t h e  p i n k a n d chum f r y m o r t a l i t y  f r yi n the total A there  pink  a n d chum f r y  i s a decreasing  i s constant  prey:predator  Pink  prey:predator  (30 m i l l i o n ) . ratio  prey:predator  (195.5 m i l l i o n ) .  Population  (115:1).  ratio;  I n curve I n curve  B C  p i n k abundance i s  a n d chum f r y m i g r a t i o n  F r y growth r a t e i s n o t , a f f e c t e d by temperature  begins or  8 0 ~\  (a)  60 H  E =3 -o  cr  ^  >v  o  . _  i _  CL  O  c a> o  £  0J CL  O-O-O  40-|  20  O  0  —i— 20  40  60  i—  8 8 00  100  % of total prey population composed of chum fry CO 00  FIGURE 17.  R e l a t i o n Between Proportion  Fig.  F r y M o r t a l i t y and t h e  o f Chum F r y i n t h e T o t a l  Prey  Population  17b.  R e l a t i o n between percent  pink  f r y m o r t a l i t y and  proportion  o f chum f r y i n t h e t o t a l  pink  a n d chum f r y  population.  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  B, a n d C a n d c o n d i t i o n s  Fig.  17c.  proportion population.  of  simulation.  R e l a t i o n b e t w e e n number o f p i n k o f chum f r y i n t h e t o t a l  pink  f r y eaten  of  simulation.  and  a n d chum f r y  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  B and C and c o n d i t i o n s  A,  A,  90  91 1.  In curve A the p r o p o r t i o n o f chum f r y i n the prey p o p u l a t i o n i s a l t e r e d by changing the abundance of pink f r y ( e i t h e r by enhancing  or d e p l e t i n g the  t o t a l pink salmon p o p u l a t i o n ) . 2.  In curve B, the o v e r a l l p r e y : p r e d a t o r r a t i o remains c o n s t a n t w h i l e the p r o p o r t i o n o f chum f r y i n the prey p o p u l a t i o n i n c r e a s e s .  3.  In curve C the i n i t i a l abundance o f pink f r y remains constant w h i l e the p r o p o r t i o n o f chum f r y i n the prey p o p u l a t i o n i s i n c r e a s e d by enhancing the t o t a l chum salmon p o p u l a t i o n .  The shape of curve A ( f i g u r e 17a) i s due t o the i n t e r a c t i o n of s e v e r a l v a r i a b l e s :  r e l a t i v e abundance and  v u l n e r a b i l i t y o f prey s p e c i e s and p r e d a t o r abundance and stomach c a p a c i t y .  When the number o f pink f r y i n the e s t u a r y  i s high, m o r t a l i t y i s l a r g e l y determined  by p r e d a t o r stomach  c a p a c i t y , abundance and the l e n g t h o f time prey remain vulnerable to predation.  When the number o f pink f r y i n the  e s t u a r y i s low, m o r t a l i t y i s l a r g e l y determined 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 .  by prey  As the prey:predator  ratio  decreases, a g r e a t e r p r o p o r t i o n of the f r y o f each s p e c i e s (e.g. f i g u r e 17b) i s eaten but the i n c r e a s e i n the p r o p o r t i o n of t o t a l pink and chum f r y eaten stops, and a c t u a l l y begins t o decrease  ( r i g h t limb o f f i g u r e 17a), because o f the r e l a t i v e  i n c r e a s e i n abundance o f the l e s s v u l n e r a b l e chum f r y and the g e n e r a l decrease i n the number o f f r y eaten  ( r e f e r t o the  d i s c u s s i o n o f the coho f u n c t i o n a l response t o changes i n prey d e n s i t y , f i g u r e s 15 and 16).  Thus, although  i n c r e a s i n g the abundance o f pink f r y i n  the e s t u a r y tends t o b u f f e r chum f r y from p r e d a t i o n ( f o r example, d e c r e a s i n g the p r o p o r t i o n , not the number, o f chum i n the prey p o p u l a t i o n from 8 0% t o 5%, decreased  chum f r y  m o r t a l i t y 2 0.3%)>: a s i g n i f i c a n t p r o p o r t i o n o f any i n c r e a s e i n pink abundance i s eaten.  F o r example, when the number o f  pink f r y i n the model e s t u a r y was i n c r e a s e d from 7.5 t o 4 5.0 million  (chum p r o p o r t i o n o f prey p o p u l a t i o n 80% and 40%,  r e s p e c t i v e l y ) , 57% (19.7 m i l l i o n ) o f the added pink f r y were eaten  (see f i g u r e 17c).  The d e c r e a s i n g l e f t limb o f curve A  ( f i g u r e 17a) i n d i c a t e s tthat^theTpr6por<fe£ond6jfdadded pink f r y s u r v i v i n g p r e d a t i o n i s now g r e a t e r than the p r o p o r t i o n dying. Although  s p e c i e s s p e c i f i c m o r t a l i t y i n c r e a s e s (e.g.  curve B, f i g u r e 17b) when the abundance o f chum f r y i n the prey p o p u l a t i o n i n c r e a s e s  (curve B, f i g u r e 17a p r e y r p r e d a t o r  r a t i o c o n s t a n t ) , the i n c r e a s e s are not s u f f i c i e n t t o o f f s e t the n e t decrease  i n t o t a l pink and chum f r y m o r t a l i t y .  Chum  f r y are not o n l y l e s s s u s c e p t i b l e to p r e d a t i o n than pink f r y , but a l s o t h e i r l a r g e r s i z e , combined with t h e i r i n c r e a s e d a v a i l a b i l i t y , reduces the average i n t a k e o f f r y per coho (see f i g u r e 15, curve B ) .  Species s p e c i f i c chum f r y m o r t a l i t y  i n c r e a s e s because there are more v u l n e r a b l e chum a v a i l a b l e and l e s s pink f r y t o b u f f e r them; s p e c i e s s p e c i f i c pink f r y m o r t a l i t y i n c r e a s e s because the t o t a l number o f v u l n e r a b l e pink and chum f r y decreases,  w i t h the i n c r e a s e i n abundance  of l e s s - v u l n e r a b l e chum, thereby pressure on the remaining  i n c r e a s i n g the p r e d a t i o n  vulnerable f r y .  It  i s necessary  t o measure a d u l t  relationship  between  chum t o p i n k  f r y c a n be e v a l u a t e d .  the  f r y s u r v i v a l and r e l a t i v e  model a r e more v u l n e r a b l e  stages  of life,  they only  opposed t o two o r t h r e e calculation  of total  r e t u r n was h i g h e r insignificantly, 95%  adult  pink  adult  the  evaluation would of  each  species,  biological Total C  fry  versus  net return  numbers,  salmon). pertinence  when  I f weight however,  Thus,  adult correct  t o enhancement importance  g i v i n g due c o n s i d e r a t i o n  to their  differing  characteristics. c o m b i n e d m o r t a l i t y rfco p i n k  i n the estuary  not only  but also  a n d chum f r y i n c u r v e  specific  pink  intake  t h e number o f chum  f r y from  coho  o f f r ybecause  t o s a t i a t e each coho o f coho  m o r t a l i t y (e.g.  Increasing  buffers  reduces coho  curve B and d i s c u s s i o n  fewer  (see d i s c u s s i o n o f  f u n c t i o n a l response  to increasing  density). In  17,  5%  economic  chum f r y a r e r e q u i r e d  prey  f o r only  on t h e r e l a t i v e  figure 17b), decreases.  predation,  that  albeit  d i f f e r e n t ( i ngeneral,  ( f i g u r e 17a), as w e l l as species  c u r v e C,  indicated  population.)  adult pink  early  crude  (113.3 m i l l i o n ) o c c u r r e d  be c o m p l e t e l y  information  their  A  (The l o w e s t  o f these r e s u l t s and t h e i r  require  salmon i n  during  115.6 m i l l i o n ) ,  f o r 50% o f t h e p r e y  salmon w e i g h more t h a n  pink  return  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  r e s u l t s would  chum  a n d chum a d u l t  a n d chum s a l m o n  abundance o f  f o r chum s a l m o n .  f r ypopulation.  the  i n the ocean as  when chum f r y a c c o u n t e d  chum f r y a c c o u n t e d of  spend one y e a r  years  pink  Although  to predation  (115.8 v e r s u s  of the original  of  return before  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  and t h e r e f o r e  i n figure  t h e above d i s c u s s i o n , depends on t h e  94 assumption t h a t f r y growth r a t e i n the of f r y d e n s i t y .  Nevertheless,  considered  b e f o r e any  brood year  pink run  presence of pink no  attempt  The  changing  and  t i m i n g and  illustrate  the  i t may  Duration  estuary  I n f i g u r e 18, into  e n t r y and  total  mortality  46%  the  (assuming  be more p r o f i t a b l e  o f t h e Coho S m o l t  on p i n k  and  migration  f r o m 16  ;  t o 48  days  respectively.  e s t u a r y b u i l d s up  over  a longer  (figure  19)  and  thereby  p r o v i d i n g the  gave t h e  reducing time the  f r y t i m e t o grow, finally  Figure  20  shows t h e c o m p l e t e r a n g e  of  f r y m o r t a l i t y rates obtained  by  v a r y i n g both  entry  and  d u r a t i o n o f t h e coho smolt. m i g r a t i o n The  suggests two  estuary.  the  Changing  m a k i n g them l e s s v u l n e r a b l e t o p r e d a t i o n when t h e coho the  of  chum  f r y with  t o o u t g r o w t h e coho w h i c h have n o t y e t a r r i v e d . o f coho e n t r y  day  Coho d e n s i t y i n  time i n t e r v a l  and  coho  (first  abundance c o n s t a n t ) , r e d u c e d p i n k  the d a i l y p r e d a t i o n p r e s s u r e  into  F i g u r e s l l S l i a n d 19  i n c r e a s i n g the d u r a t i o n of the  the e s t u a r y  Migration  model.  72%,  entered  to  chum m o r t a l i t y r a t e s o f  and  date  even  Even though  are u n c e r t a i n .  parameters i n the  migration  be  i s made t o e s t a b l i s h an  d u r a t i o n o f t h e cb.ho s m o l t  effect  these  should  salmon.  Timing  the F r a s e r R i v e r  i s independent  r e d u c e chum f r y m o r t a l i t y  adverse d e n s i t y e f f e c t s ) ,  VIII  results  i n the F r a s e r R i v e r .  f r y may  enhance o n l y chum  these  estuary  only  into  the  time of  the  estuary.  information a v a i l a b l e for Fraser River  t h a t they  enter  weeks, b e g i n n i n g  the  estuary  in late April  over  a period of  ( F r a s e r , 197 6 ) .  coho about  Based  on  FIGURE  An Example Duration Pink  of the Relation  15 a n d A p r i l  ratio  i s 115:1.  the season.  the duration  ( i n # o f days) and model  of the  estimates of  F r y and coho m i g r a t i o n  9, r e s p e c t i v e l y .  F r y growth rate  temperature or density. over  between  f r ymortality.  March  and  a n d Chum F r y M o r t a l i t y  smolt migration  p i n k a n d chum  Between  o f Coho M i g r a t i o n  An example o f t h e r e l a t i o n coho  18.  Initial  Initial  issnot  begins  prey:predator  affected  by  mean s i z e o f f r y i s c o n s t a n t  16  | 99-4  Pink  Chum  j  days  2 4 days  97  FIGURE 19.  An Example o f t h e R e l a t i o n Between Coho E n t e r  Estuary Fry  An are  estimates begins Fry  t o begin  of pink  March 15.  a n d Chum  Mortality  example o f t h e r e l a t i o n assumed  and Pink  Date  between t h e date  entering the estuary  preyrpredator  Fry migration  ratio  growth r a t e i s n o t a f f e c t e d by temperature  Coho s m o l t mean s i z e  migration into  the estuary  o f f r yi s constant  over  the  smolts  and model  a n d chum f r y m o r t a l i t y . Initial  coho  lasts  i s 115:1. or density.  24 d a y s .  season.  Initial  Pink  Chum CO  CO  FIGURE  20.  E f f e c t on I n d i c a t o r s of Changing the Duration of Coho M i g r a t i o n  and  the Date of E n t r y  The combined e f f e c t on the i n d i c a t o r s shown of changing the date of coho e n t r y i n t o the e s t u a r y and coho m i g r a t i o n .  115:1.  the d u r a t i o n of  S t a r t o f coho e n t r y i n t o e s t u a r y  ( i n # of days) from March 15.  both  lagged  I n i t i a l preyrpredator r a t i o i s  F r y m i g r a t i o n begins March 15.  F r y growth r a t e i s  not a f f e c t e d by temperature or f r y d e n s i t y .  Chum fry mortolily  (xlO ) 6  %  chum fry mortality  %  chum adult return  Average no- of fry eaten per coho per day  48 -r 40 +  co >% a  32 + 24 +  c o  WW \  16  3  *o c o o  Pink fry mortality (xlO )  l_  48  E  40  %  pink fry  %  mortality  pinVc adult return  Total average no- of fry eaten per coho  T  CP o JZ: o  O  32 + 1 4 4  24 + 16  -/  \ 108^ 72 \ 36 I26J 90 \ 54 \  410  180 \  20  100 \  to 30 40 ^50  10  20 30  40  50  10  20  30  40 50  -I  10  18  f  20  30  40 5*  Number of days coho entry lagged from March 15 o o  101 t h i s i n f o r m a t i o n , the model p r e d i c t s t h a t w i l d coho  populations  from the F r a s e r R i v e r c o u l d e a t about 37% of the pink f r y and  10% o f the chum f r y r e s i d i n g i n the e s t u a r y  fry  begin m i g r a t i n g on March 15 and growth i s not a f f e c t e d by  temperature o r d e n s i t y ) .  In c o n t r a s t , Parker  (assuming the  (1968f  estimated  t h a t 55% t o 77% o f pink f r y from Hooknose Creek d i d not s u r v i v e t h e i r f i r s t 4 0 days i n the e s t u a r y .  Most o f t h i s  m o r t a l i t y he a t t r i b u t e d t o coho p r e d a t i o n . I f coho smolts a r e to be produced u s i n g enhancement facilities,  the t r a d e o f f between the c o s t s  (such as i n c r e a s e d  f e e d i n g and maintenance) of d e l a y i n g the time o f r e l e a s e and the b e n e f i t s o f minimizing  the r i s k t o pink and chum f r y would  have to be evaluated. An a l t e r n a t i v e method o f coho enhancement might be t o a c c e l e r a t e the growth of coho f r y such t h a t they reach  smolt  s i z e i n the l a t e f a l l or e a r l y winter and thus go t o sea d u r i n g t h e i r f i r s t year  (Smith,  1978).  T h i s would e l i m i n a t e  p r e d a t i o n by enhancement coho on pink and chum f r y d u r i n g p e r i o d of e s t u a r i n e l i f e .  their  S u r v i v a l , however, o f the enhanced  coho may be low due t o adverse environmental c o n d i t i o n s found in  late f a l l  or e a r l y w i n t e r .  Coho r e t u r n i n g to the Qulf o f Georgia importance as a s p o r t s f i s h .  are o f major  Thus, any attempt t o reduce or  e l i m i n a t e coho p r e d a t i o n on pink and chum f r y must be evaluated not o n l y i n terms o f the estimated  increase i n production of  pink and chum b u t . a l s o i n terms o f the p o s s i b l e impact on coho p r o d u c t i o n .  negative  102 IX  Non-Coho N a t u r a l  Mortality  In the model pink and chum f r y were subjected  t o a low  l e v e l o f n a t u r a l m o r t a l i t y i n a d d i t i o n t o m o r t a l i t y from coho predation.  The s e n s i t i v i t y o f the model r e s u l t s ,  the r a t e o f coho p r e d a t i o n , was t e s t e d . migration  particularly  t o changes i n t h i s parameter  (The f o l l o w i n g experiments assume t h a t f r y  begins March 15.)  With no d e n s i t y e f f e c t s on growth r a t e , there was v i r t u a l l y no change i n coho p r e d a t i o n  r a t e when pink and chum  f r y instantaneous n a t u r a l m o r t a l i t y r a t e was i n c r e a s e d  from  0.0002 t o 0.004 per day (about 1.9 f r y were eaten per day per coho).  N e v e r t h e l e s s , the number o f s u r v i v i n g pink and chum  f r y decreased from 122.1 t o 104.3 m i l l i o n and from 30.7 to 26.4  m i l l i o n , r e s p e c t i v e l y , due t o the i n c r e a s e  natural  i n non-coho  mortality.  Using d e n s i t y model 2 and the same range of non-coho instantaneous m o r t a l i t y r a t e s , m o r t a l i t y from coho  predation  decreased from 75.3% to 69.2% (about 12 m i l l i o n ) f o r pink f r y and  from 30.2% t o 26.9% (about 1.1 m i l l i o n ) f o r chum f r y .  The  average number o f f i s h eaten per. day per coho decreased  marginally  (4.0 to 3.7). Pink and chum f r y s u r v i v i n g  period of l i f e , 23.8  this  decreased from 47.4 to 43.1 m i l l i o n and from  t o 20.9 m i l l i o n , r e s p e c t i v e l y .  mortality rate s t i l l  By i n c r e a s i n g the non-coho  f u r t h e r t o 0.01 per day, the number o f  s u r v i v i n g pink and chum f r y decreased another 7 and 4 m i l l i o n , respectively.  Although the average.number o f f r y eaten per  day  per coho only dropped t o about. 3.3, pink and chum m o r t a l i t y  due  t o coho p r e d a t i o n  respectively.  decreased another 7.6% and 3.9%,  103 Thus, a l t e r n a t i v e to  substantially  predation  X  mortality  agents have t h e p o t e n t i a l  reduce the " r e a l i z a b l e "  on p i n k  impact  o f coho  a n d chum f r y .  Residence  Time and S i z e a t E m i g r a t i o n  from the  Estuary  There  i s considerable u n c e r t a i n t y as t o the length of  time  pink  runs  discussed  remain  a n d chum f r y r e m a i n  i n the estuary  centimeters Allen,  1974).  time  o f about  composition) leave  have  time  of this  (and c o n s e q u e n t l y  the estuary.  1964; P a r k e r ,  t o a model  residence  assumption on  the size  expected  w i t h pink and  prey, s p e c i e s m  sp^c  a t which they were  Coho a r e assumed  t o remain  a l l of the vulnerable pink  assumed  i n the  a n d chum f r y a r e e a t e n  left.  There a r e f i v e shown i n T a b l e 1.  eight  ggowthhracteeisohote.reducedybyedensity  the effect  by changing  estuary u n t i l or  and P a r k e r ,  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  chum r e s i d e n c e  to  than  effects.  To e v a l u a t e mortality  are greater  corresponds  8 weeks - i f f  temperature  they  (LeBrasseur This  In a l l of the  a n d chum f r y h a v e b e e n a s s u m e d t o  until  i n length  1968;  or  so f a r p i n k  i n the estuary.  about the r e s u l t s  8:  I f both they  pink  reach  weeks), not by  major p o i n t s t o note  a n d chum f r y l e a v e  4.0 cm  then  affected  time  growth r a t e o f pink by f r yd e n s i t y  the constant  7.3%,  (a r e s i d e n c e  the estuary  f r ym o r t a l i t y  respectively).  after  of 1 to  2h  o r chum f r y i s  ( m o d e l 2) a s rates  (21.4%  evidenced and  TABLE 8 Sensitivity fry  o f model r e s u l t s  a r e assumed t o l e a v e  March  15.  Prey:predator  t o changes i n t h e e s t i m a t e d  the estuary. ratio  size  a t which  F r y a r e assumed t o b e g i n  i s 115:1.  Chum f r y c o m p o s e  pink  a n d chum  entering the estuary  15% o f t h e t o t a l  prey  population. 1 2 No t e m p e r a t u r e or density effects Temperature A  B  C  D  Both migrate a t 4 . 0 cm.  3  4 Temperature, ^ & density Density effects  21.4 7.3  29.0 6.7  Pink fry migrate a 5 4 .0 cm; chum a t 5 . 0 cm.  20.7 16.4  27.9 22.8  21 16  —  Pink fry migrate a t 5 . 0 cm.; c h u m a t 4.0 cm.  37". 4 3.9  53.2 3.0  61  - 66  81  Both migrate  36.9 10.2  52.2 12.2  67 _ 75 23 30  86 36  Density model 2  21 .4 7 .3  - 23  17  5 .0  —  34 .8 6 .6  Q. "5 g. "5  pink m o r t a l i t y chum m o r t a l i t y  42 .4 40 .0  "o a "o  g,  pink m o r t a l i t y chum m o r t a l i t y  - 82 7 .6  a *o a  pink m o r t a l i t y chum m o r t a l i t y  - 88 - 37  o. "5 a "o  pink m o r t a l i t y chum m o r t a l i t y  105 2.  The p r e s e n c e o f p i n k buffer  f r yi n the estuary  chum f r y f r o m c o h o p r e d a t i o n  tends t o  (compare f o r  example B I and D l — c h u m m o r t a l i t y i s reduced 6.2%).  Nevertheless,  hypotheses,  this  under a d i f f e r e n t  buffering effect  set of  c a n be  reversed  (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 actually  increases  7 t o 13 p e r c e n t )  because the  increased density of f r yi n the estuary in  reduced  lengthens 3.  f r y growth r a t e and  4.  does  i s reduced  Dl—pink  1.2%).  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 length is  of pink  a n d chum r e s i d e n c e  demonstrated  pink  little  f r y m o r t a l i t y (compare f o r example  a n d B I o r A 2 a n d B2 o r C I a n d  mortality  to predation.  o f chum f r y i n t h e e s t u a r y  to reduce pink Al  consequently  the period of vulnerability  The p r e s e n c e  results  the  i n the estuary  by t h e range o f model e s t i m a t e s  a n d chum f r y m o r t a l i t y d u e t o c o h o  predation  ( a s s u m i n g t h a t t h e coho do n o t f o l l o w t h e i r For  example, assuming  affect  mortality estuary other  reduction may 5.  e a r l y ;(A1) c a n  f r y m o r t a l i t y 53% a n d chum f r y  30%.  Nevertheless,  a t a small  than  prey).  temperature and d e n s i t y  growth r a t e , migrating  reduce pink  of  c o h o may  size,  i fthe f r y leave the  m o r t a l i t y from  increase  such t h a t any  i n m o r t a l i t y achieved  be more t h a n  A t . a n y one time  agents  by escaping  coho  compensated f o r . different  f a c t o r s may b e  coho consumption o f f r y prey.  limiting  F o r example,  i n C2  106 pink and  fry mortality vulnerability  capacity.  Another the  that  fish  using  early  be  reduced  or other density  Table  some way  a body  day  (e.g., assuming  density  table  constant  fry mortality  below  unless density  3% The  the coho s  their  due  growth  growth  fry mortality values  (control),  rate  drops  11.4%  shows, as that  aspect of  from  rate  unless  this  3%  (model  per 2),  10.8%,  never  to affect  coho  derived  e v i d e n c e d by  growth  rate.  below  and  i s postulated  most i n t e r e s t i n g  This hypothesizes own  below  from  food  i s reduced  rates,  coho  the estuary.  rate  also  from  availability  to  effects.  reduced  stomach  1  dependent growth  chum f r y m o r t a l i t y The  availability  f r y migration  rate  o n l y movement t r i g g e r when t h e i r  respectively).  growth  i n most cases  begin migrating  and  by  induce  related  fry  pink  their  e m i g r a t i o n from  significantly  size  by  of monitoring their  9 shows t h a t  i s not  as  limited  m e c h a n i s m w h i c h may  have  predation  i s mainly  to their  estuary, might  limitation  as w e l l  by  H o w e v e r , chum f r y m o r t a l i t y  predation due  i s limited  the drops  f r y growth  experiment  was  rate.  not  t h e §d^e.efexbiifj^ryi%morHtal 4 ^"^ ^ ibut^l:the3;s>fczei;di-.s^r;ibutl'Om i o f i  fry  i n the estuary.  size  and  estuary  size  d u r i n g the  calculated is  range  because  not normal,  figures 1.  The  a;t  :)  F i g u r e s 21 o f chum and  and  22  indicate  p i n k f r y found  season.  (Standard d e v i a t i o n  fry size  distribution  especially  demonstrate  t  during the  a number o f  potential  mean s i z e  effect  of f i s h  environment  of  i s apparent  i n the was  riot  These  factors:  taken from  from  mean  model  s i x weeks.)  f r y in-migration  samples  true  i n the model e s t u a r y  first  important  the  the  the almost  on  the  natural constant  TABLE  9.  pink  a n d chum f r y a r e p e r m i t t e d  below a s p e c i f i e d Other  value  to leave  o r i fthey  reach  c o n d i t i o n s a r e t h e same a s t h o s e No t e m p e r a t u r e or density effects Temperature  the estuary a length  i n Table  greater  than  growth r a t e 8.0  drops  centimeters.  8.  ^ Density  i ft h e i r  Temperature & density 1 effects  Migrate only i fsize 8.0 cm. ( C o n t r o l )  36.9 10.2  52.3 12.2  74.7 30.0  87.7 37.3  Pink % m o r t a l i t y Chum % m o r t a l i t y  M i g r a t e i fgrowth r a t e l e s s t h a n 1% per day o r s i z e 8.0 cm.  36.9 10.2  52.3 12.2  74.7 30.0  87.7 37.3  Pink % m o r t a l i t y Chum % m o r t a l i t y  M i g r a t e i fgrowth l e s s t h a n 2% p e r d a y or size 8.0 cm.  36.9 10.2  52.3 12.2  72.9 27.8  81.8 31.8  Pink % m o r t a l i t y Chum % m o r t a l i t y  M i g r a t e i fgrowth r a t e l e s s t h a n 3% per day o r s i z e 8.0 cm.  36.9 10.2  52.3 12.2  63.3 19.2  63.9 21.8  Pink % m o r t a l i t y Chum % m o r t a l i t y  Density  model 2  108  EIGURE 21.  S i z e D i s t r i b u t i o n o f Chum F r y Found i n the E s t u a r y Each Week  Mean s i z e and s i z e range, o f chum f r y found  i n the model  estuary each week s i n c e the beginning o f the f r y m i g r a t i o n 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.  a f f e c t e d by pink and chum f r y d e n s i t y e s t u a r y i f growth r a t e l e s s than g r e a t e r than 8.0 cm.  F r y growth r a t e i s (model 2 ) . F r y leave  3% per day or f r y l e n g t h  range mean size  Sample number  FIGURE 22.  S i z e D i s t r i b u t i o n o f Pink F r y Found i n the E s t u a r y Each Week  Mean s i z e and s i z e range o f pink f r y found  i n the model  estuary each week s i n c e the beginning o f the f r y m i g r a t i o n 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.  a f f e c t e d by pink and chum f r y d e n s i t y  F r y growth r a t e i s (model 2 ) . F r y  leave the e s t u a r y i f growth r a t e l e s s than f r y l e n g t h g r e a t e r than 8.0 cm.  3% per day or  range  112 mean s i z e  of the f r y f o rthe f i r s t  (samples 1 t o 6 ) . taken the  during  this  Representative time  suggest  f r y were n o t s t a y i n g i n t h e e s t u a r y of time.  I f t h e sampling  biased  i n favour  of larger f i s h ,  different time The  estimates  could  be  effect  of  the larger fish  7 and 8 i s s t i l l  mean s i z e  being  biased  Thus,  has  decreased  tempted  of fish  samples  on s m a l l -  the v a r i a b i l i t y  An i n v e s t i g a t o r ,  p a t t e r n o f mean s i z e ,  to speculate  might  t h a t t h e f r y i n t h e e_stuary  du^inggtbhelasfettwooweekssofZ  On t h e c o n t r a r y ,  estuary  a r e growing a t a rate greater  The i n c r e a s e  from  o f t h e sampled  April.  day.  growth  by i n - m i g r a t i o n b u t  although  substantially.  b§4.ustoppgd g r o w i m g  i n their  t h e mean s i z e  r e m a i n s a b o u t t h e same  the total  out-migration,  by p r e d a t i o n  fry  observing  residence  i s demonstrated  6 a n d 7:  due t o a drop  i spartiallyooffset fish.  was  substantially  kind of bias  o f sample  The e s t i m a t e d  sized  that  f o rany  tehhnique  o f growth r a t e and  of another  the results  this  fish  inferred.  by  rate.  weeks  samples o f  p e r i o d would  length  be  five  a l l fish  i n mean s i z e  found  i nthe  than  observed  3% p e r  i n samples  9 t o 12 i s d u e t o t h e i n c r e a s i n g n u m b e r o f l a r g e r fish the  remaining larger fish  threshold has  i n the estuary. i s again  of three  been reduced  higher  percent  Growth r a t e o f than  because  by o u t - m i g r a t i o n  the emigration  fry density and m o r t a l i t y .  113 As  the  size 3.  small-sized in-migrants  becomes i n c r e a s i n g l y b i a s e d  Density  (figure  estuary  f o l l o w s the  23)  and  eventual  and  out-migration  contention  of  over  and  stopped  f o r the  e a r l y and  prior  to  sea  over  chinook,  at a  part of that  to  middle part  smaller  the  run.  had  earlier  in  the  the  summer a n d  a  higher  contention  run  fry  from  stayed a  the  size  migrating  rate.  This  t h a t m o r t a l i t y due  more t h a n compensate achieved  in  larger  than e a r l y  i n coho p r e d a t i o n  last  (197 3)  redghed  survival  density  the  than  j u v e n i l e chinook which  o c e a n may  reduction  size  of i n -  the  of  Reimers  seaward m i g r a t i o n  an  (the r e s u l t  t h a t g r o w t h had  the  the  increase  to  from  estuary  of  support  to  Fry  observed  chum f r y i n  lend  tend  April.  later  time  mean  upward.  This  weeks of  the  and  the  mortality).  two  migrated  pink  eaten,  well-known pattern  decrease  p a t t e r n would  4.  are  to  for by  supports agents  any  migrating  early. Marking of would  decrease  the  growth r a t e , but of  time or  f r y , and  re-sampling  problems mentioned  only  i f fish  over i n #1  of  were marked over  i f d i f f e r e n t marks were used  of migration.  I n an  estuary  number o f  fish  would  h a v e t o be  chance of  recovering  a  time  as  significant  estuary,  estimating a  short  period  to e s t a b l i s h their  l a r g e as marked  i n the  the. F r a s e r ,  to  number.  insure a  a  date  large  reasonable  114  FIGURE 23.  Weekly D e n s i t y o f Pink and Shurn F r y i n the E s t u a r y  Combined <nenvbety o f pink and chum f r y per hectare o f e s t u a r y f( 15,319 h e c t a r e s ) . (  i n f i g u r e 20.  C o n d i t i o n s are the same as those d e s c r i b e d  Sample number  116  3.  Enhancement Experiments  I  Changing the P r e y : P r e d a t o r  Ratio  I f p i n k and chum growth r a t e i n the e s t u a r y i s d e n s i t y dependent (as i n model 2) , then p r e d a t i o n may  result in  compensatory m o r t a l i t y i f p i n k 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 o f p i n k and chum f r y e n t e r i n g the e s t u a r y from 23 0 r a t i o n l l 5 : 1 ) t o 460  (230:1) m i l l i o n u l t i m a t e l y reduced p i n k  and chum a d u l t r e t u r n by 23.8 (Table 10).  The  (prey:predator  and  0.4  million, respectively  i n c r e a s e d d e n s i t y of f r y i n the e s t u a r y reduced  growth and extended the l e n g t h of time f r y were v u l n e r a b l e to  p r e d a t i o n from 33 t o 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 some enhancement a t t e m p t s ,  II  completely  negate  e s p e c i a l l y l a r g e s c a l e ones.  Enhancement of P i n k Salmon  I t has been shown, u s i n g the model, t h a t r e l a t i v e t i m i n g ^ o f m i g r a t i o n ? i n i t i a l 'sizejland: abundance may ;  determinants  bepdmportant  of p i n k and chum f r y s u r v i v a l d u r i n g e a r l y  estuarine l i f e .  To examine the e f f e c t on s u r v i v a l o f changing  these parameters, p i n k salmon were enhanced i n the model. The  enhanced p i n k p o p u l a t i o n was  t r e a t e d as a s e p a r a t e  stock  so t h a t the s u r v i v a l of b o t h the " w i l d " and enhanced p o p u l a t i o n c o u l d be d e t e r m i n e d .  Thus the enhanced p i n k p o p u l a t i o n 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. Sensitivity of  pink  density  o f model  results  a n d chum f r y . model  2.  F r y growth r a t e  Fry migration  instantaneous mortality rate 0.00053 p e r d a y f o r p i n k chum s a l m o n assumed  to increases  (based  i s a function of  begins March  1.  a t s e a i s assumed  Average t o be  s a l m o n and 0.00043 p e r d a y f o r  on R i c k e r ,  1976).  Pink  salmon a r e  t o s p e n d a maximum o f 410 d a y s a t s e a .  p e r c e n t o f t h e chum f r y a r e assumed sea;  i n the density  t o spend  Twenty-two  840 d a y s a t  t h e r e m a i n d e r , 1200 d a y s .  Prey:predator  ratio  57.57-,l  115:1  1  230:1  % pink f r y mortality  33.8  57 .7  /85.2  % chum f r y mortality  15.6  29.6  64.3  pink adult ^ r e t u r n (#'s)  50.3  63.2  39.4  % pink return  51.6  32.4  10.1  8.8  14.6  14.2  51.1  42.3  20.6  adult  chum a d u l t ^ return (l's) % chum return  adult  ^ Initial Adult  number o f  return  coho  predators i s  i s i n millions  of  fish.  constant  (2  million).  118 For  t h e s e model experiments,  t h e enhanced  t h e e s t u a r y was assumed t o l a s t  small.  t h a t , any d e c r e a s e prey:predator in  s t o c k was v a r i e d b u t  The m o d e l ' s p r e v i o u s r e s u l t s  growth  suggested  i n m o r t a l i t y due t o an i n c r e a s e i n t h e  ratio,, may be more t h a n  o f f s e t by t h e i n c r e a s e  p r e d a t i o n m o r t a l i t y due t o d e n s i t y r e l a t e d  fry  into  one week.  t h e abundance o f t h e e n h a n c e d kept r e l a t i v e l y  f r ymigration  decreases i n  rate.  The  wild  p i n k and chum f r y a r e assumed  to begin  their  m i g r a t i o n on M a r c h 1, t o i n c r e a s e i n mean s i z e o v e r t h e duration of their migration into temperature rate.  and d e n s i t y  The i n i t i a l  constant million  (model 2) r e l a t e d  abundance o f w i l d  p i n k and chum s t o c k s i s pink  complete r e s u l t s  i n figures  Figures migration  of this  experiment  are graphically  2$ t o 2'.8.  2[4 t o 287 show t h e r e s u l t s ,  s t a r t i n g dates,  o f changing  both  f o r four  o f enhancement p i n k  p i n k abundance.  Regardless  on t h e e s t i m a t e o f  the e n t i r e  of their  range o f enhanced  initial  s i z e o r any  reduction  i n g r o w t h r a t e due t o d e n s i t y - r e l a t e d  are  t o o b i g t o e a t when t h e coho s m o l t s  still  Nevertheless,  increasing  improve t h e i r  survival  estuary  i n the season.  later  In f i g u r e  16 March) , t h e i n i t i a l  f r y h a s no e f f e c t  e n h a n c e d f r y m o r t a l i t y (0%) o v e r  separate  t h e abundance and  f r y s i z e o f . t h e enhanced p i n k p o p u l a t i o n .  2!4 (enhancement m i g r a t i o n b e g i n n i n g  estuary.  f r y and 34.5  chum f r y ) .  displayed  size  r e d u c t i o n s i n growth  f o r e a c h s i m u l a t i o n (195.5 m i l l i o n  The  initial  t h e e s t u a r y , and t o e x p e r i e n c e  their  chances i f they  effects,  reach the  initial  size  may  have t o e n t e r t h e  F o r example, i n f i g u r e  25  they  FIGURE  Effect and  24 . ?  on I n d i c a t o r s o f C h a n g i n g Mean Abundance  o f Enhancement  (Migration Begins  The  combined e f f e c t  both  the i n i t i a l  their  initial  enhancement are  the estuary  M a r c h 1.  Fry  mean s i z e  abundance.  pink  The  constant  Mortality pink")  and  Wild  abundance  34.5, and  pink  "wild" pink  pink  2) .  f r y and  f r y migration  of wild  2 million,  and  f r y begin  pink,  chum to  begins  chum a n d  respectively).  g r o w t h r a t e i s a f f e c t e d by t e m p e r a t u r e and  f(*model  changing  and a d u l t r e t u r n o f  Enhancement  on M a r c h 16.  (195.5,  March)  o f t h e enhancement  ("enhanced  initial  Fry  t h e i n d i c a t o r s shown o f  calculated separately.  enter  is  on  16  Pink  Size  density  coho  Enhanced pink fry  %  mortality  enhanced pink fry mortality  Enhanced pink adult return  enhanced pink adult return  (xlO )  (xlO ) 6  24 T  %  6  oo  18  00  18  -80S  • 14  10  12 •00  •80-3  00  Wild chum fry mortality (xlO ) 6  %  wild chum fry mortality  24  -+%  Wild chum odult return  return  (xlO ) 6  I 3-1  36 -120  18 J-  wild chum odult 38 39  34  13-5  - II-S  40  • no  12  32  41 -10-5  • 30  -i Wild pink fry mortality (xlO ) 6  24  140  %  wild pink fry mortality  -4 (xlO )  —  wild pink adult return  -34  76  •18  -.36  I8|  •74  • 144  12  r  140  38  •20  -40  -72  - 42 •70  136  3-35  "  6  t  •148  %  Wild pink odult return  3-55  3-75  3-35  3-55  3-75  -22  - 44  3-35  3-55  1  3-75  3-35  Mean size (cm) of enhanced pink f r y - - e n t e r March 16  3-55  3-75  121  FIGURE 25.  E f f e c t on I n d i c a t o r s o f Changing Mean S i z e and Abundance of Enhancement Pink F r y (Migration Begins 1 A p r i l )  The combined e f f e c t on the i n d i c a t o r s shown o f changing both the i n i t i a l mean s i z e o f the enhancement pink f r y and t h e i r i n i t i a l abundance. enhancement pink  M o r t a l i t y and a d u l t r e t u r n o f  ("enhanced pink") and " w i l d " pink and chum  are c a l c u l a t e d s e p a r a t e l y .  Enhancement pink f r y begin t o  enter the e s t u a r y on A p r i l 1. March 1.  The i n i t i a l  i s constant Fry  W i l d f r y m i g r a t i o n begins  abundance o f w i l d pink, chum and coho  (195.5, 34.5, and 2 m i l l i o n ,  respectively).  growth r a t e i s a f f e c t e d by temperature  (model 2 ) .  and d e n s i t y  Enhanced pink fry mortality  %  (xlO ) 24TI4  O O O 0~ O  a o  c  enhanced pink fry  Enhanced pink adult return  mortality  6  T63  10  49  35  21  24-  %  enhanced pink adult  (xlO )  return T I 360;  7  Wild chum adult return Wild chum fry mortality (xlO )  %  6  wild chum fry mortality  %  wild chum adult  (xlO )  return  6  4L  122  I8t  13-6  12 +  140  39.  o  T3 C 3 JD O  42  — Wild pink fry mortality  c: CL  c  xa:  %  wild pink fry mortality  Wild pink adult  %  (xlO )  (xlO )  36 .  T  I  wild pink adult return  6  6  24  return  19  18.  18 +  cr .  Lul  12 + 23,  3-35  3-35  3-5 5  3-75  3-35  Mean size (cm) of enhanced pink f r y - - e n t e r  3 55  April I  375  3 35  3-55  3-75 ro ro  FIGURE 2'6.  E f f e c t on I n d i c a t o r s . o f Changing Mean S i z e and Abundance o f Enhancement Pink F r y ( M i g r a t i o n Begins 15 A p r i l )  The combined e f f e c t on the i n d i c a t o r s shown o f changing both the i n i t i a l mean s i z e o f the enhancement pink f r y and their i n i t i a l  abundance.  enhancement pink  M o r t a l i t y and a d u l t r e t u r n o f  ("enhanced pink") and " w i l d " pink and chum  are c a l c u l a t e d s e p a r a t e l y . enter the e s t u a r y on A f r i l March 1.  The i n i t i a l  i s constant Fry  Enhancement pink f r y begin t o 15.  W i l d f r y m i g r a t i o n begins  abundance o f w i l d pink, chum and coho  (195.5, 34.5, and 2 m i l l i o n ,  respectively).  growth r a t e i s a f f e c t e d by temperature  (model 2 ) .  and d e n s i t y  Enhanced pink fry mortality  %  (xlO )  enhanced pink fry mortality  6  %  Enhanced pink adult return  enhanced pink adult return  (xlO ) 3  24 r • 22 -18  18  less  to  b o o o~ o o  a> o c a -o c jQ O  98 8  -14  than  12 + -II  —  -7  1  1—  1 e  %  wild chum fry mortality  %  24  wild chum adult return  4 |  _  T  - 14-Z  181  •10-4  12  • 30-o  •29-3  -f-  -I  %  (xlO ) 6  1  Wild pink adult return  wild pink adult return  6  44  •45  "23  "46  -133  3-75  %  (xlO )  134  3-55  -t-  1  135  12 +  3-35  -I  70  136  "42  •-  wild pink fry mortality  24  18 +  --  1 4-4  101  Wild pink fry mortality  a sz c UJ  Wild chum odult return  Wild chum fry mortality (xlO )  -t-  T3 <D O C  1%  98-9  -68  3-35  3-55  3-75  •24  47.  335  3-55  3-75  3-35  Mean size (cm) of enhanced pink f r y - - e n t e r April 15  3-55  3-75 ro  FIGURE  Effect and  2B.  on I n d i c a t o r s o f C h a n g i n g Mean Abundance  o f Enhancement  (Migration Begins  The  combined e f f e c t  both  the i n i t i a l  their  initial  enhancement are  M a r c h 1. is Fry  abundance.  Mortality  ("enhanced  the estuary The  constant  initial  growth r a t e  (model 2 ) .  o n May  (195.5,  May)  o f t h e enhancement  calculated separately.  enter  Fry  on t h e i n d i c a t o r s shown o f  mean s i z e  pink  1  Pink  Size  pink")  Wild  and  "wild" pink  pink  f r y and  2 million,  and  f r y begin  f r y migration  abundance o f w i l d  34.5, and  pink  and a d u l t r e t u r n o f  Enhancement  1.  changing  pink,  to  begins  chum a n d  respectively).  i s a f f e c t e d by t e m p e r a t u r e and  chum  density  coho  Enhanced pink fry mortality  % enhanced pink fry  (xlO )  mortality  6  D  H  3 35  1  3-55  Enhanced pink adult return  1  3-75  H  3 35  1  355  %  enhanced pink odult  (xlO )  return  3  1  3-75  J  3-35  1  355  1  3-75  4  3 35  Mean size (cm) of enhanced pink fry — e n t e r May I  1  3 55  1  3-75  ro  FIGURE 28.  Effect and  Date o f E n t r y  The  combined  the  initial  initial pink  o n I n d i c a t o r s o f C h a n g i n g Mean  effect mean  date of.entry  f r yentry  March!. Figure figures of  into  o f Enhancement P i n k F r y  on t h e i n d i c a t o r s  size  shown on c h a n g i n g  o f t h e enhancement p i n k into  estuary  the estuary. lagged  29 w a s c r e a t e d  from  Start  information  both  f r y and t h e i r o f enhanced  ( i n# o f days)  2 5 t o 28 f o r a n e n h a n c e d p i n k  18 m i l l i o n .  Size  from  taken  f r yi n i t i a l  1  from  abundance  Enhanced pink fry mortality UIO ) 6  61 r  %  enhanced pink fry  Enhonced pink adult return  mortality  %  (xlO )  return  6  I  T  Mean size (cm) of enhanced pink fry  enhanced pink adult  T  mortality fry 2t]l  of  3.7 5 cm the  size  to greater  enhanced  to  already due  than  f r y migrate  prey  item  i n short to  overlap  the  of  continued  at  a  supply.  prey  and  estuarine  late  timing,  enhanced  abundance  If  the  prey  a l l coho  between  size, date (18  not  figure in  They a c t  as fry  of  these  refugia,  are fry  total  and  the  These  invalidate and  an  wild  smolts.  survival  the  migration  mortality  than  76%)  increases. depresses  The the  the  increased  are  vulnerable  the  enhanced pink  the  are  increase  resulting density-related of  an  i m p a c t on  fry mortality o f 67  and  28  and  the  and  mortality  entire  entering  early increases  than  f r y i n the  run  of w i l d  length  of  in figures the  estuary  the  returns percent,  wild  in wild  fry, time  almost to  the  respectively,  they  to  2%  later  in  25  i n the  the  the  f r y growth  f r y already  fry  estuary  i n t o t a l f r y abundance and reduction  7 0%  enhancement p i n k  f r y and  However,  chum f r y  for  fry.  estuary  from l e s s  t o t a l density of  to predation.  Thus the  pink  increased  the  between  enhancement p i n k  f r y enter  number o f  stocks  of  abundance o f  growth r a t e of  increasing  of m i g r a t i o n  to wild  greater  as  relationship  million)  fry mortality  level  of  u n r e a l i s t i c , do  pink  Wild  no  for  increase  spatial distributions  wild  less  f o r the  In  total annihilation  enhancement p i n k  2'fy,  in figure  has  t h a n 7%  f r y 3.3 5 cm.  for survival.  2 8 i l l u s t r a t e s the  fry initial  constant  season.  less  etc. Figure  thereby  from  t i m e when v u l n e r a b l e  residence  relationship  to  too  predator  demonstrated  (e.g.  for  model's assumptions of  although  as  63%  The  assumptions,  a  f r y ranges  improve t h e i r chances  alternative  is  enhanced pink  rate  estuary.  pre-enhancement in figure  27>.  This  130 pattern  of 1.  results The  occurs  for three  overall patern  changes date, time  the  of  time  the  wild  i n the  fry.  As  wild  f r y remain  number o f w i l d any  of  enhanced  given  left  predator. took  56  density 6.3  cm  the  i n the  of  overlaps for  is  figure  reflected length  estuary, and  with  and  in  vulnerable  With  the  later introduction  f r y , more o f  the  wild  the For  estuary  another  cm  outgrown  pink  the  cohort,  u n d e r one  set  8 0 days to reach  i t  of  only  set of density c o n d i t i o n s .  t h i s example r e l a t e s s p e c i f i c a l l y  model experiment d i s c u s s e d prey:predator  from  57.5:1 t o  this  information  Nevertheless,  f r y have  already  f o r one  8.1  c o n d i t i o n s and under  or  example,  days to reach  (where t h e  entry  length  f r y , i n the  fry available  time.  (Unfortunately  previously  r a t i o was  increased  230:1) b e c a u s e I d i d n o t  the  for  extreme because  less  e x t r e m e and  record  thespresentieTxpeEiments.  effects  less  the  are  comparable,  density increase  distributed  differently  although is over  season.)  Since  a l l of  the  enhanced  f r y can  outgrow t h e i r coho p r e d a t o r s the  the  estuary  estuary  fry  discussed  growth r a t e of w i l d  either  2.  enhanced  t o t a l abundance and  the  at  the  the  t h i s changing density pattern  in  to  f r y d e n s i t y i n the  to  t h e i r presence  that of 2%,  of  i n response  their  reasons:  estuary,  they  are  now  no  before  subject to  longer they  reach  predation  131 mortality fry  t o some e x t e n t  wild in  pink  pink  from p r e d a t i o n .  The i n c r e a s e d  predation initial  by the r i g h t  at migration,  possible  size  late  o f enhancement p i n k f r y  i n t h e season does n o t reduce  relative  size  their  due  combination  2.4  t o 9.5 p e r c e n t  a n d 1.8  subsequent decreases compensated due  i n w i l d pink  Nevertheless,  success  i fthis  alone.  I t i s doubtful, given  "real"  system,  w i l d pink  attributed said  were based  stock.  t o 8.4 p e r c e n t ,  f o r by t h e i n c r e a s e  returns).  f r y populations  The  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 :  i n total  adult  salmon  ( 0 . 8 t o 2.9 m i l l i o n the p r o j e c t would  on t h e s u r v i v a l  i s :  return  increase i n  be j u d g e d  o f enhanced  the natural v a r i a b i l i t y  t o t h e enhancement p r o j e c t . result  increases  respectively.  I t hardly  Creating  a  fish of the  shown i n T a b l e  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  this  i s the  I n t h e example  i f decreases o f the magnitude  how i m p o r t a n t  The  however,  a n d chum  time.  t i m i n g and  experiment.  experiments,  over  f r y survival,  a n d chum f r y m o r t a l i t y  t o t h e enhancement p r o j e c t  adult  in  of migration  impact on w i l d p i n k  11, w i l d pink  increases  i n enhanced  by t h i s  o f these  to  t o w i l d f r ybecause the  t o t h e presence o f t h e enhanced  shown i n T a b l e  vulnerability  of wild f r yalso  i s confirmed  result  negative  constant  (24 m i l l i o n ) o f e n h a n c e m e n t  Thus t h e p o t e n t i a l i n c r e a s e  most important  f r o m 77.6%  salmon.  substantially  size  F o r example,  f r ym o r t a l i t y i s reduced  abundance  migrating  achieved  a n d chum  f i g u r e 24 t o 7 0 % i n f i g u r e 2 6 , f o r a  initial  3.  and thus b u f f e r w i l d p i n k  11  o r even  needs t o be  conditions  which  132  TABLE 11. One example p r e d i c t e d by the model o f the n e g a t i v e e f f e c t enhancement pink p o p u l a t i o n s may have on w i l d pink and chum p o p u l a t i o n s . . Enhanced f i s h March 16 - March 22. at  migration.  migrate  R e s u l t s were independent  Both temperature  of size  and d e n s i t y (model 2)  were assumed t o a f f e c t f r y growth r a t e .  Wild pink  and chum f r y i n c r e a s e i n i n i t i a l mean s i z e over  time.  The i n i t i a l w i l d prey:predator r a t i o i s 115:1.  Wild  fry  m i g r a t i o n begins March 1.  Number o f f r y 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 a d u l t r e t u r n s a r e much higher than observed  i n the ' r e a l ' system.  message o f the experiment  actually  N e v e r t h e l e s s the b a s i c  is still  valid.  cont'd.  T A B L E 11, P a g e  2. Enhanced Pink  Stock  ( millions  0.0  Abundance )  6.0  12.0  18.0  24.0  131.0  135.6  140.2  144.9  149.5  67.1  69.5  71.9  74.3  76.6  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  # Pink  48.2  44.6  41.0  37.3  33.7  24.7  22.9  21.0  19.1  17.3  14.8  14.4  14.0  13.6  13.1  43.0  31.9  40.7  39.4  37.9  0.0  4.8  9.6  14.4  19.2  0.0  0.8  1.6  2.3  ;.2v9  # Pink  f r yeaten  1  % Pink # Chum  f r y eaten  adult return  1  % Pink # Chum  f r yeaten  1  adult 1  adult  % Chum a d u l t  return return return  # Enhanced pink  2  adult  return  . 3 T o t a l n e t increase i n fish returns  "Wild"  pink  a n d chum  populations.  Control Total  net increase  i n fish  r e t u r n minus t h e decrease return, stock).  returns i nwild  as compared t o t h e c o n t r o l  equals pink  enhanced  a n d chum  (i.e.,  no  pink  adult  enhancement  134 i n c r e a s e the l i k e l i h o o d of s u r v i v a l of enhancement stocks may r e s u l t i n a decrease i n the s u r v i v a l of n a t u r a l stocks and could l e a d to t h e i r e v e n t u a l d e s t r u c t i o n .  4.  Examination  of Data found i n the L i t e r a t u r e  The r e s u l t s of experimentation with the model suggest that: 1.  the presence of pink f r y i n the e s t u a r y may b u f f e r chum f r y from p r e d a t i o n , or  2.  the presence o f pink f r y i n the e s t u a r y may r e s u l t i n d e n s i t y - r e l a t e d r e d u c t i o n s i n chum growth r a t e / w i t h a subsequent  increase i n  p r e d a t i o n mortality.; because small f r y a r e s u b j e c t to p r e d a t i o n f o r a longer p e r i o d of triime and more of them are r e q u i r e d t o s a t i a t e the predator.. I looked f o r evidence i n the l i t e r a t u r e t o support e i t h e r 1 or 2.  F r a s e r R i v e r pink f r y are produced i n  s i g n i f i c a n t numbers o n l y d u r i n g odd brood years and thus c r e a t e a " n a t u r a l " experiment.  I encountered  a number o f  problems-,! ho.wewe'2t,erwh?env r-».a'fe'fc'emp^edirtr6:i.use>t&£s> -ver, f  whs-  ap.p.r.oachui t o use th.-.s .approach: 1.  E s t i m a t e s of f r y p r o d u c t i o n and s u r v i v a l a r e v i r t u a l l y n o n - e x i s t e n t , i n the l i t e r a t u r e or cover such a l i m i t e d time span they are o f l i t t l e use.  2.  There seems t o be no c o o r d i n a t i o n or c o n s i s t e n t method o f data g a t h e r i n g or r e p o r t i n g by the  agencies of  responsible f o rthe d i f f e r e n t  salmon  attempt  found  necessary  3.  R i v e r , a n d no  i s made t o s y n t h e s i z e t h e d a t a  Consequently,  over  i n the Fraser  species  i t was d i f f i c u l t  data  f o rboth  a sufficiently  The two t o f i v e  pink  long  year  life  to obtain the  a n d chum  time  gathered.  salmon  span.  history  c y c l e o f chum  salmon makes a n a l y s i s d i f f i c u l t . 4.  Fry-to-adult mortality period it  estimates  o f e s t u a r i n e and oceanic  has g e n e r a l l y been accepted  include the life.  Although  t h a t ocean'mortality  ratesi areymchtlowerrthanjes^^ 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 e s t i m a t e s c o v e r cthecegg a n d ' p a r t o f t h e f r e s h w a t e r f r y s t a g e s o f l i f e . 5.  Estimates original any  survival  example,  adults,  reduce evident  a 5% v e r s u s  of fry-to-adult  Thus,  fry-to-  survival.  number o f r e t u r n i n g of egg-to-fry  i n a 100% i n c r e a s e i n t h e  a n a l y s i s should  survival.  o n l y be c o n s i d e r e d  suggestive  investigation.  postulated that i fthe presence  from  on t h e  o f e r r o r s made  a 10% e s t i m a t e  estimate  the survival  of  of egg-to-fry  a constant  results  f u t u r e avenues o f I  on estimates  estimates  given  depend  of egg-to-fry survival.  survival  Thus t h e f o l l o w i n g  survival  may b e a n a r t i f a c t  the original  For  of  estimates  c o n c l u s i o n s based  adult in  of fry-to-adult  r a t e o f chum  f r y , then  of pink this  a comparison o f even and odd brood  f r ywere t o  would year  be estimates  136 of  chum s u r v i v a l .  (This assumes t h a t the o n l y d i f f e r e n c e  between odd- and even-year brood years i s the presence or absence o f pink f r y . ) I  first  looked a t freshwater e g g - t o - f r y chum s u r v i v a l  because what happens a t t h i s l i f e a n a l y s i s o f the marine l i f e the  stage.  stage i s important t o the Pink and chum salmon share  same major spawning areas i n the F r a s e r R i v e r below Hope  and migrate to sea a t about the same time. of  coho a r e a l s o found i n these a r e a s .  by F r a s e r  Major c o n c e n t r a t i o n s  Using data p r o v i d e d  (1976) f o r brood years 1964 to 1974, I found t h a t  mean chum e g g - t o - f r y s u r v i v a l was lower d u r i n g even, brood years than d u r i n g odd, pink brood years 16.25%). (arc  non-pink  .(11.64%yversus  Although the d i f f e r e n c e was not s i g n i f i c a n t  s i n square r o o t transform of data, t-test,p'> 0005) , i t  suggests t h a t chum f r y may be b u f f e r e d from p r e d a t i o n by the presence o f pink f r y . contention:  F i g u r e 29 seems to support t h i s  chum m o r t a l i t y d u r i n g the e g g - t o - f r y l i f e  stage  appears t o be depensatory although the r e l a t i o n s h i p between t o t a l egg abundance and chum e g g - t o - f r y s u r v i v a l was not significant  (t-test,p>0.05). The p o t e n t i a l b e n e f i t o f  i n c r e a s i n g the abundance o f f r y m i g r a t i n g downstream a t any one •time iirayybe)<masked<<teQ S p m e h ^ ^ t e M e f c ^ ^ ^ e ^ S c O l r ^ i ^ h j ^ S^f  11  d e p o s i t i o n due to non-predator m o r t a l i t y on the spawning grounds  (such as egg s u f f o c a t i o n or egg displacement by l a t e  spawners). The r e v e r s e s i t u a t i o n was t r u e f o r chum f r y - t o - a d u l t survival.  Using a combination o f data taken from Palmer  and F r a s e r  (1976) f o r brood years 1961 t o 1970, I found t h a t  mean chum f r y - t o - a d u l t s u r v i v a l was higher d u r i n g even,  (197 2)  non-pink  FIGURE 29.  R e l a t i o n Between % Chum  Egg-to-Fry  S u r v i v a l and T o t a l Pink and Chum Egg D e p o s i t i o n  R e l a t i o n between percent e g g - t o - f r y s u r v i v a l o f F r a s e r River chum salmon and the estimated  t o t a l egg d e p o s i t i o n o f  F r a s e r R i v e r pink and chum salmon (brood years 1964 to 1974). F r a s e r R i v e r pink f r y a r e produced o n l y d u r i n g odd brood years.  Brood years a r e i n d i c a t e d f o r each data p o i n t .  Source o f data:  Fraser  (1976).  24 .67  r = 0-484 pr005  2CH  >  16-J  CO  12  I  '71  • 70  O  I 8A  •4—  CP CP CD  >68  e  3 SZ  O  4-\  T 4  8  12  16  20  24  28 8 3  Estimated pink and chum abundance in eggs (xlO )  00  139 brood years than d u r i n g odd, pink brood years Again the d i f f e r e n c e i s not s i g n i f i c a n t  (1.54% versus 0.91%).  (are s i n square r o o t  t r a n s f o r m o f d a t a , t - t e s t , p > 0.05) but i t does suggest  that  the presence o f pink salmon may have a n e g a t i v e e f f e c t on chum s u r v i v a l a f t e r they l e a v e the r i v e r .  A l t e r n a t i v e l y , perhaps i f  the abundance o f pink and chum f r y were i n c r e a s e d even more, the percent m o r t a l i t y would decrease due t o predator s a t u r a t i o n (assuming  t h e r e was not a concomitant  i n c r e a s e i n m o r t a l i t y due t o  other sources such as d i s e a s e ) . F i g u r e 3 0 suggests t h a t chum f r y - t o - a d u l t s u r v i v a l may be r e l a t e d more t o the t o t a l abundance o f pink and chum f r y i n the e s t u a r y than t o t h e presence o r absence o f pink f r y per se.  There  was no r e l a t i o n s h i p between chum f r y - t o - a d u l t s u r v i v a l and chum f r y abundance alone over the range o f chum abundances examined. Thus the i n c r e a s e i n t o t a l f r y abundance d u r i n g pink years may have a net n e g a t i v e e f f e c t on the s u r v i v a l o f chum salmon. Any  i n c r e a s e i n s u r v i v a l due t o pink b u f f e r i n g d u r i n g the e a r l y  e g g - t o - f r y stage may be more than compensated f o r by the i n c r e a s e in mortality occurring later.  Whether the i n c r e a s e i n m o r t a l i t y  occurs i n the e s t u a r y o r d u r i n g a l a t e r p e r i o d o f l i f e can not be determined  from these d a t a .  lower average  A l t e r n a t i v e l y , t h i s change from a  even brood year chum e g g - t o - f r y s u r v i v a l i n a  higher average  even brood year chum f r y - t o - a d u l t s u r v i v a l  (com-  pared t o odd brood years) c o u l d be due t o measurement e r r o r i n the estimates o f e g g - t o - f r y s u r v i v a l  ( i . e . , #5, p. 135)! F u r t h e r -  more, even without measurement e r r o r , i t i s very d i f f i c u l t t o o b t a i n "evidence o f s i g n i f i c a n t e f f e c t s " from a s h o r t s e r i e s o f observations  (see d i s c u s s i o n i n R i c k e r , 1975).  Thus the  140  FIGURE 3®.  R e l a t i o n Between % Chum F r y - t o - A d u l t S u r v i v a l and T o t a l Pink and Chum F r y Abundance  R e l a t i o n between percent  fry-to-adult survival of Fraser  R i v e r chum salmon and the t o t a l abundance o f F r a s e r R i v e r and chum f r y (brood years 1964 t o 1970).  F r a s e r River  salmon a r e produced o n l y d u r i n g odd brood y e a r s . are i n d i c a t e d f o r each data p o i n t . (1976) .  Brood  Source o f data:  pink  pink years  Fraser  3  H  ••68 • 65  IH70^*66  •69 167  1  1  100  1  1  200  1  1  300  1  1  400  Estimated pink and chum fry abundance (xlO )  142 suggestions as t o what might be o c c u r r i n g d u r i n g  each l i f e - s t a g e  are s p e c u l a t i v e and r e q u i r e f u r t h e r i n v e s t i g a t i o n . I f the decrease i n chum s u r v i v a l i s a d i r e c t r e s u l t o f d e n s i t y dependent decreases i n growth r a t e e i t h e r i n the estuary or l a t e r i n l i f e ,  then one might expect t o be able t o observe  a t l e a s t one o f the f o l l o w i n g : 1.  A decrease i n the mean s i z e o f chum salmon produced from high d e n s i t y brood years and a subsequent decrease i n the p r o p o r t i o n o f age three a d u l t r e t u r n s .  (This assumes t h a t age  of r e t u r n i s r e l a t e d t o s i z e o r growth r a t e as Foerster  (.1968) suggests i t i s f o r sockeye.)  Thus, the mean s i z e o f chum which do r e t u r n as t h r e e year o l d s 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 s i z e a t r e t u r n and  an i n c r e a s e , r a t h e r than a decrease, i n mean  s i z e a t r e t u r n due t o the i n c r e a s e d  susceptibility  and m o r t a l i t y o f s m a l l - s i z e d chum d u r i n g d e n s i t y brood y e a r s .  T h i s s e l e c t i o n by  high predators  of slower-growing f i s h c o u l d a l s o l e a d t o a decrease i n mean age a t r e t u r n , i f the assumption made i n #1 i s true.  I t should  be noted, however, t h a t e x p e r i -  ments conducted by Jones (1958) and R i c k e r (both c i t e d by R i c k e r ,  (1969)  1975) suggest t h a t any change  i n the shape o f the s i z e d i s t r i b u t i o n o r the v a r i a b i l i t y o f the frequency d i s t r i b u t i o n due t o even q u i t e severe n o n - l i n e a r  size-selective mortality  143 i s l i k e l y t o be "too l i t t l e practice 3.  t o be d e t e c t a b l e i n  (Ricker, 1975)."  An o v e r a l l i n c r e a s e i n mean s i z e of chum salmon produced d u r i n g high d e n s i t y brood years  because  the increase' i n m o r t a l i t y may a c t u a l l y r e s u l t i n improved growth o f the chum which s u r v i v e . I found t h a t the mean l e n g t h o f age t h r e e , male chum salmon was s i g n i f i c a n t l y l a r g e r f o r chum produced d u r i n g odd brood (73.8  cm versus  70.7 cm; t - t e s t , p < 0.02).  The d i f f e r e n c e i n  mean l e n g t h between odd and even brood year, age three chum salmon was not s i g n i f i c a n t t - t e s t , p > 0.05).  years  (68.8 cm versus  female  67.3, r e s p e c t i v e l y ;  For age f o u r chum salmon the d i f f e r e n c e s i n  mean l e n g t h , between odd and even brood year f i s h , were a l s o insignificant.  T h i s i s due, perhaps t o the p o s s i b l e masking  e f f e c t o f one e x t r a year o f growth. data taken from Palmer  (The a n a l y s i s was done on  $1972) f o r brood years  1957 t o 1966.)  Thus, although t h e r e may be a r e a l i n c r e a s e i n the mean s i z e o f age  three chum salmon produced from odd brood years, the reason  for  t h i s i n c r e a s e i s not apparent. There were i n s u f f i c i e n t data t o a s c e r t a i n i f there was  a r e l a t i o n s h i p between the p r o p o r t i o n o f chum r e t u r n i n g a t age  three and t h e i r s i z e .  There d i d not appear t o be any  r e l a t i o n s h i p between the p r o p o r t i o n o f chum r e t u r n i n g a t age three and chum f r y - t o - a d u l t s u r v i v a l f o r brood years  1961 t o 1970.  (These data were taken from Anderson  (197 2) and  Fraser  (1976).  (1976), Palmer  143a Although  f i g u r e 31 suggests an i n t r i g u i n g  relationship  between the p r o p o r t i o n o f chum r e t u r n i n g a t age three and the t o t a l abundance o f pink and chum f r y , I can not e x p l a i n i t based  on the i n f o r m a t i o n a v a i l a b l e f o r those y e a r s . Godfrey  (1959) looked a t the average  annual weight o f  pink salmon i n B r i t i s h Columbia and southeastern A l a s k a and found t h a t pink salmon from the even-year c y c l e  (like Fraser  R i v e r male chum salmon) were c o n s i s t e n t l y s m a l l e r than o f the odd-year c y c l e .  Furthermore,  those  d u r i n g t h i s time p e r i o d  i n both B r i t i s h Columbia and southeastern A l a s k a , odd-year c y c l e pink salmon were more abundant than the even-year c y c l e which suggested  that i n t r a s p e c i f i c competition f o r a v a i l a b l e  food was not a f a c t o r i n the decreased fish  (Godfrey, 1959).  of average  s i z e o f even-year c y c l e  The s i m i l a r i t y i n the t r e n d  (1944-1958)  s i z e among f i v e d i s t i n c t g e o g r a p h i c a l areas,  extending from southern B r i t i s h Columbia  t o southeastern  A l a s k a , suggests t h a t " a t l e a s t d u r i n g t h a t phase o f t h e i r ocean r e s i d e n c e which i s most important  i n determining  their  f i n a l s i z e , the s e v e r a l s t o c k s o f B r i t i s h Columbia pink salmon have l i v e d and f e d e i t h e r i n the same ocean area, o r i n adjacent areas s i m i l a r l y a f f e c t e d by v a r i a t i o n s i n oceanographic conditions  (Godfrey, 1959)."  S i z e d i f f e r e n c e s , however, can occur without limitation.  food  Brown (1957) found t h a t "when groups o f f i s h e s o f  144  FIGURE 31. R e l a t i o n Between Age Three Chum Returns and T o t a l Pink and Chum F r y Abundance  R e l a t i o n between the p r o p o r t i o n o f F r a s e r R i v e r chum r e t u r n i n g a t age three and the t o t a l abundance o f F r a s e r R i v e r pink and chum f r y (brood years 1964 t o 1971).  F r a s e r R i v e r pink  f r y are produced o n l y d u r i n g odd brood y e a r s . are i n d i c a t e d f o r each data p o i n t .  Percent age three chum  r e t u r n f o r 1971 i s based on incomplete not y e t r e t u r n e d ) . a f t e r spending  data  (5 y e a r s o l d s had  Age three chum salmon r e t u r n to spawn  two years a t sea.  (1976) and F r a s e r  Brood, years  (1976).  Source o f data:  Anderson  Q  Chum adult return percentage age three ro  o  CD O  O J_  _L_  o  • cn o o  CD  CD  cn cn  ro  o o  _ *  o  O =r = -h  O  o  o o  cn  ^  146 one  s p e c i e s are kept together, i t commonly happens t h a t the  d i s p e r s i o n i n s i z e between the l a r g e s t and i n c r e a s e s as they grow l a r g e r . "  smallest i n d i v i d u a l s  Furthermore, B l a x t e r  (1965),  studying the f e e d i n g and ecology of h e r r i n g l a r v a e , found t h a t "at the end of a p e r i o d of two hatching  to three months a f t e r  the l a r g e s t l a r v a i n a tank  o f the s h o r t e s t , although  may  be twice the  length  abundant food has been o f f e r e d and  the l a r v a e came from the same parents."  They both suggest  t h a t t h i s i n c r e a s e i n s i z e v a r i a b i l i t y i s due e f f e c t s — l a r g e r f i s h being more a g g r e s s i v e and the f e e d i n g response of s m a l l e r f i s h .  The  to " s i z e - h i e r a r c h y " there by  inhibiting  g r e a t e r abundance,  hence i n c r e a s e d e s t u a r i n e d e n s i t y , of odd-year c y c l e pinks accentuate  this  Martin  may  effect.  (1966) found t h a t s i z e d i f f e r e n c e s w i t h i n a  p o p u l a t i o n of pink salmon from A l a s k a c o u l d r e s u l t from d i f f e r e n c e s i n t i m i n g of m i g r a t i o n  (food supply c o n t r o l l e d ) .  He found t h a t e a r l y migrants not o n l y were s i g n i f i c a n t l y i n s i z e by the time l a t e migrants entered retained this r e l a t i v e size difference.  greater  the e s t u a r i n e s but a l s o If survival i s positively  r e l a t e d to s i z e , any negative e f f e c t s on growth caused by g r e a t e r abundance of odd-year c y c l e pinks may decreased  be masked by  the the  s u r v i v a l of small f i s h . T h i s i s very l i k e l y i f M a r t i n ' s  (.1966) o b s e r v a t i o n s  are c o r r e c t and  i f l a t e migrants are more  a f f e c t e d than e a r l y migrants by the i n c r e a s e i n abundance: r e l a t i v e l y more e a r l y migrants would c o n t r i b u t e to the r e t u r n of a d u l t pink  salmon.  final  147 Thus the salmon c o u l d also  be  cited  by  that  correlated  with  that this  the  variance  in  There that  North  could  valid  to  the  for a  (Royce, e t  total  pink  index  high  i f total than  North odd  negatively (r=-0.516)  proportion  Thus the  trend  of  difference  s a l m o n may  competition  for  be food  rather  interpretation is  American catch a  abundance,  s a l m o n catovh  This  1968,  American  Oncorhynchus d e n s i t y  se.  years;  a l . ,  North  of  even-year c y c l e pink  of  of  temporal  s a l m o n was  significant  size  Oncorhynchus  Using  interference or  years  of and  an  It is  reduced  spatial  as  pink  intraspecific  species  American  salmon d e n s i t y per  only  tends  t o be  that appears  greater  likely  from  3%.  figure  Alternatively, River pink  average weight of differences catch  and  species  ocean d u r i n g  even years  Fraser  five  Pacific.  account  than  ( F - t e s t , p<.025, f i g u r e 32).  in part,  the  combined e f f e c t s .  i s evidence the  North  odd-year c y c l e  i s causing  average weight of total  the  rather  of Oncorhynchus  w e i g h t between odd-  than pink  in  i n the  the  and  due,  these  interspecific  fish.  (1952-1972)  found  of  of  America have o v e r l a p p i n g  distributions catch  result  L a r k i n , 1975)  from North  mean s i z e  f o r a v a i l a b l e food  even-year c y c l e  in  the  possible that  competition  I  higher  and  spurious.  could  odd-year c y c l e pinks  the  correlation  (Fraser River fish  salmon, produced d u r i n g  the  with  especially i f only  pink  of  t h a t the  was  total  due  to  North  salmon tend  (Godfrey,  shows t h a t mean s i z e  correlated  argue,  salmon were c o n s i d e r e d ,  even f o r odd-year c y c l e however,  one  1959).)  adult pink  same b r o o d  (r=0.795, F - t e s t , p < 0 . 0 1 ) ;  year, with  and are fish  increased genetic  American t o be Figure age  large, 33,  three  chum  positively from  odd-brood  148  FIGURE  32.  R e l a t i o n Between Average A d u l t Pink Salmon Weight and T o t a l North American  Catch  ( i n pieces) of Oncorhynchus Salmon  R e l a t i o n between B r i t i s h Columbia average pink a d u l t weight , and abundance of North American Oncorhynchus c a t c h years 1952  to 1972).  F r a s e r R i v e r pink salmon are only  present i n the c a t c h d u r i n g odd c a t c h y e a r s . data:  INPFC (1976, unpublished  Statistics.  (catch  Source o f  manuscript) and B.C.  Catch  FIGURE 33.  R e l a t i o n Between A d u l t Pink Salmon Weight and Length of Age Three A d u l t Chum Salmon  R e l a t i o n between B r i t i s h Columbia average pink a d u l t weight and average l e n g t h o f age three F r a s e r R i v e r chum salmon (brood y e a r s 1957 to 1966). females.  and  F r a s e r R i v e r pink salmon are produced and caught  only d u r i n g odd y e a r s . data p o i n t .  Brood years are i n d i c a t e d f o r each  Age three chum salmon r e t u r n t o spawn a f t e r  spending two years a t sea. and B.C.  Data i n c l u d e both males  Catch S t a t i s t i c s .  Source o f d a t a :  Palmer  (1972)  1  CD  1  r=0-795 pkOOl 5 7 . 61  5-J  cn  k_ —  CD >  62*  D  r-  C  CD  5  3 '  T  < 58  62  T  ~r~ 66  70  T  T  74  Age three chum average length ( c m )  78  152 years being  larger, i n general.  between even- and odd-year result by  suggests that pink  similar  Fraser  River  of Fraser  pink  second year  increment  first age  year  a t s e a may chum  of  during  l a r g e l y determine  odd- and  the data  suggest  the evidence  ocean year i s as i t i s f o r during  the ultimate  interaction  that  inter-species interactions  a t sea.  between  however,  depth.  t o examine  F o r example,  and t h e i r  s u r v i v a l may p r o v e t o b e v e r y enhancement p r o p o s a l s .  or  negative  i s really  Determining  species  of  data  of the problem.  i f ocean growth  year  even-year pink  this  size of  i s w e a k diiie t o t h e p a u c i t y  raised i n greater  might determine first  first  I f the length  c o m p a r i s o n o f odd- and even-year c y c l e , age t h r e e  their  chum,  t h e chum's  then conditions  might prove worthwhile,  the issues  with  o f subsequent years,  and t h e complexity  It  cohabit  respectively.  1969),  affected  history  and age t h r e e  the f i r s t  this  salmon.  occurring,  available  pink  chum o n l y  life,  (Foerster,  Although are  River  l a r g e r than that  salmon  three  Due t o t h e l i f e  f o r chum s a l m o n d u r i n g  appreciably sockeye  a n d chum s a l m o n a r e b e i n g  River  of marine  the difference i n size  chum i s a l s o g e n e t i c ,  salmon p o t e n t i a l l y  even-year c y c l e Fraser or  cycle  factors a t sea.  characteristics  Unless  chum  scales  d i f f e r e n t during  e f f e c t s on growth and i n view of  F o r example, would River  a  t h e p o s s i b l e avenues o f  important  run to the Fraser  some  future  r e s t o r a t i o n o f an  have a n e t b e n e f i c i a l  e f f e c t o n t h e s u r v i v a l a n d g r o w t h o f chum  salmon?  153  CHAPTER I V .  The  purpose  complexity of  their  that  of analysis  simulation  doing this. used  areas needing positions  further  the density  of water  but also  the predator.  rate  of different  positions to  I was  also  phase  I was  o f p r e y and "effective  The  theoretical  assumptions column  of  tool  data  able to  identify  the  relative  column  predator per u n i t volume" effect  of water on  prey  determine volume searched  encounter  regarding  their  s h o u l d be  s t u d i e d . a n d compared  the model  to identify to relate  to the paucity  d e s c r i b e many o f t h e b i o l o g i c a l  relative  rate.  t o change and  i n t h e m o d e l due  clearly  F o r example,  of encounter  a b l e t o use  verbal  a useful  t o p r o p o s a l s f o r enhancement, even  weaknesses to  thesis  the i n i t i a l  the model,  which were most s e n s i t i v e results  this  m o d e l l i n g c a n be  the  studies  the  etc.] usual  predator i n the water  i n the water  laboratory  As  research.  o f p r e y and  not only  by  hypotheses,  From j u s t to build  "make e x p l i c i t  t h e more a b b r e v i a t e d c h a r a c t e r  (Quinton, 1977)."  demonstrates,  synthesis  i s to  i s h i d d e n by  [ie.assertions,  formulation  for  GENERAL D I S C U S S I O N  though of data  processes.  the  parameters  these there  are  available  Furthermore,  154  the p o t e n t i a l e x i s t s f o r u s i n g t h i s model to a s s i s t managers i n making d e c i s i o n s r e g a r d i n g proposals.  f u t u r e enhancement  Enhancement managers have been given the  mandate to i n c r e a s e the abundance o f salmonid (Johnson, 1976).  stocks  The r e s u l t s of the s e n s i t i v i t y a n a l y s i s  and model enhancement experiments c o u l d be used t o suggest a l t e r n a t i v e ways o f a c h i e v i n g the "best" between c o n f l i c t i n g o b j e c t i v e s .  compromise  For example, while the  manager may be given the e x p l i c i t o b j e c t i v e t o i n c r e a s e the abundance of salmonid s t o c k s , he u s u a l l y must a l s o consider (ie.  l e s s - d e f i n e d but very r e a l  "implicit"  objectives  maximize d o l l a r r e t u r n on investment c o s t s of f r y  production;  minimize any p o s s i b l e negative  e f f e c t s on  wild stocks).  While he may o n l y be able to manipulate  t o some extent  such parameters as enhanced f r y abundance,  initial  s i z e , t i m i n g and d u r a t i o n of m i g r a t i o n , he needs  some method f o r e v a l u a t i n g the r e s u l t s of such  manipulations.  The model r e s u l t s showed t h a t : 1.  Increasing i n i t i a l  s i z e and m i g r a t i n g  early i n  the season may i n c r e a s e the likel'ihoodi.of pink. . and 2.  chum f r y s u r v i v i n g e s t u a r i n e coho p r e d a t i o n .  I n c r e a s i n g the abundance o f f r y e n t e r i n g the estuary may s u b s t a n t i a l l y i n c r e a s e f r y s u r v i v a l i f the prey:predator  ratio also  increases  155  sufficiently 3.  ( i e . reach p r e d a t o r s a t u r a t i o n ) .  S u s c e p t i b i l i t y to p r e d a t i o n 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 o f the prey species  ( i e . growth rate) and second on the  r e l a t i v e p r o p o r t i o n o f t h a t s p e c i e s i n the prey population. 4.  Wild populations  o f pink and chum may be n e g a t i v e l y  a f f e c t e d by d e c i s i o n s r e g a r d i n g the enhancement stock  ( i e . the p o s s i b l e negative  impact a t  critical  times d u r i n g the season o f i n c r e a s e d f r y d e n s i t y on w i l d f r y growth r a t e s ) . 5.  Decisions fry  i n s u r i n g the maximization o f t o t a l  s u r v i v a l d u r i n g the e s t u a r i n e stage o f l i f e  may c o n f l i c t with the i m p l i c i t o b j e c t i v e t o maximize d o l l a r r e t u r n on investment c o s t s o f fry  production  ( i e . not only the r e l a t i v e number  and weight of pink and chum a d u l t r e t u r n s are important 6.  but a l s o t h e i r r e l a t i v e market v a l u e ) .  Parameters beyond the c o n t r o l o f managers  (such  as t i m i n g o f w i l d coho m i g r a t i o n , the e f f e c t of temperature on growth rate) can g r e a t l y a f f e c t the predictions of f r y s u r v i v a l during t h i s  life  stage. Using the model t o analyse  these r e s u l t s i n r e l a t i o n t o  156  management o b j e c t i v e s c o u l d r e s u l t i n s p e c i f i c enhancement proposals etc.)  ( i e . what s p e c i e s to enhance, how  that  many to produce,  would take advantage o f the l i m i t e d a b i l i t y  the manager to manipulate c e r t a i n parameters.  The  problem w i l l be measuring the "success" of these Any  system or method of "monitoring  f o r hazard  (ie any negative e f f e c t s enhancement stocks may w i l d stocks) may  be completely  of  major  manipulations.  effects have on  i n c a p a b l e 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 n a t u r a l , but u n p r e d i c t a b l e , fluctuations  ( C l a r k , 1978)."  be c o n s i d e r e d a reason  Nevertheless  t h i s should  not  f o r not t a k i n g the r i s k to enhance.  I t only means t h a t any e v a l u a t i o n of a p r o p o s a l to enhance should be e v a l u a t e d with due inescapable s i t u a t i o n .  c o n s i d e r a t i o n given to t h i s  A d d i t i o n a l r e s e a r c h i s needed to  determine more e f f e c t i v e methods of monitoring of  the system ( i e .  i d e a l l y one  the " s t a t e "  should be a b l e to d i s t i n g u i s h  enhanced s t o c k s from w i l d stocks so t h a t separate growth and s u r v i v a l r a t e s , at the v a r i o u s stages of l i f e , determined).  c o u l d be  157  LITERATURE Allen,  CITED  Brian. 1974. E a r l y marine l i f e h i s t o r y of B i g Q u a l i c u m R i v e r chum s a l m o n . In: Proceedings of the 1 9 7 4 N.E. P a c i f i c p i n k a n d c h u m s a l m o n workshop. D.R. H a r d i n g , ed. 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 salmon 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. Tech. Rept. S e r . PAC/T-76-6. Environment Canada. F i s h e r i e s and 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 p p . Aro,  K.V. a n d M.P. Shepard. 1967. Salmon o f the N o r t h P a c i f i c OSean. P a r t IV. Spawning p o p u l a t i o n s of N o r t h P a c i f i c Salmon. 5. P a c i f i c Salmon i n Canada. I n t . N o r t h P a c i f i c F i s h . Commission B u l l . 23. pp. 225-327.  B a i l e y , J a c k E . , B r u c e L . W i n g a n d 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 abundance and f e e d i n g h a b i t s o f f r y o f p i n k salmon, Oncorhynchus.keta, i n T r a i t o r s Cove, 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 the a r e a . Fishery Bulletin. V o l . 73. #4. pp. 846-861. B a i l e y , Mike. 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 the 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 and a r t i f i c i a l l y p r o d u c e d chum and 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 system. In: 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 a n d c h u m s a l m o n w o r k s h o p . D.R. Harding, ed. pp. 121-132. B a k s h t a n s k y , E.L. 1964. E f f e c t on p r e d a t o r s on t h e young 'of O n c o r h y n c h u s g o r b u s c h a ( W a l b . ) a n d O n c o r h y n c h u s k e t a (walb.) i n t h e W h i t e and B a r e n t s Sea. US D e p t . o f Comm. O f f . o f T e c h n i c a l S e r v i c e s J o i n t P u b l n s . R e s e a r c h Service. J . of • Fisheries'- Research T r a n s l a t i o n S e r i e s . V o l . 38. #12. B a r r a c l o u g h , W.E. 1967a. Number, s i z e and f o o d o f l a r v a l and j u v e n i l e f i s h c a u g h t w i t h a two b o a t s u r f a c e t r a w l i n t h e S t r a i t o f G e o r g i a A p r i l 25-29, 1966. Data Record. F i s h e r i e s R e s e a r c h Bd. o f Canada. Manuscript Report Series. No. 922. B a r r a c l o u g h , W.E. 19E$b. Number, s i z e and f o o d o f l a r v a l and j u v e n i l e f i s h c a u g h t w i t h an I s a a c s - K i d d t r a w l i n the s u r f a c e w a t e r s o f the S t r a i t o f G e o r g i a A p r i l 25-29, 1966. Data Record. F i s h e r i e s R e s e a r c h Bd. o f Canada. Manuscript Report Series. No. 926.  158  B a r r a c l o u g h , W.E. 1967c. Number, s i z e c o m p o s i t i o n and f o o d o f l a r v a l and j u v e n i l e f i s h c a u g h t w i t h a two-boat s u r f a c e t r a w l i n t h e S t r a i t o f G e o r g i a J u n e 6-8, 1966. Data Record. F i s h e r i e s R e s e a r c h Bd. o f Canada. Manuscript Report Series. No. 928. 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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. 1042-1052. 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 sunfishes: e x p e r i m e n t a l evidence and s i g n i f i c a n c e . Science. V o l . 191. pp. 404-406. W i c k e t t , W. P e r c y . Length and weight s t u d i e s o f coho a t Chef Creek. Abstract. Unpublished. Fisheries 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  Prey  Types  found  I  i n Salmon  Stomachs  Number 1.  C l e v e l a n d i a i o s (Arrow-Goby)  2.  Clupea  3.  Sebastodes  ±4.  pallasii  (Pacific  sp. l a r v a e  Merluccius productus  (Pacific  Thaleichthys pacificus  6.  Leuroglossus  7.  Gobiidae  8.  Ammodytes h e x a p t e r u s  9.  Lyopsetta  stilbius  289 42  hake)  32  (Eulachon) (Northern  670  smooth  tongue)  (Gobies)  exilis  (Pacific  sandlance)  40  (Slender sole)  Gasterosteus  aculeatus  11.  Stichaiidae  12.  Ophiodon elongatus  13.  Theragra  14.  Unidentified  (Threespine  1 stickleback)  (Pricklebacks)  Barraclough,  23  (Whiting or Pollock)  larvae  1967  6 17  and B a r r a c l o u g h  Tows done i n A p r i l ,  3 7  (Lingcod)  chalcogrammus fish  55 1  10.  1967.  herring)  (Rockfish larvae)  5.  Source:  2  and F u l t o n ,  June and  July.  APPENDIX I I  Range o f  Parameter Cruising predator  velocity  of  1 body length/second body lengths/second 0.2 ( v e r y t u r b i d ) (clear)  Turbidity (reactive  Values  distance)  -  - 5 1.0  Area o f dispersion  15,319 h e c t a r e s (approximate area o f f o r e s h o r e , marsh & slough) - 45,957 h e c t a r e s  Hours spent s e a r c h i n g and h a n d l i n g  4 hours  Proportion eaten o f those encountered  see  figure  13  Density - growth functions  see  figure  6  rate  initial  size  S t a r t o f p i n k a n d chum fry migration Number o f d a y s c o h o entry lagged behind pink and chum f r y e n t r y i n t o the estuary Average pink rate  hours  0.044 - 0 . 0 8 5 o f body w e i g h t  Maximum p r e y s i z e predator can ingest Coho s m o l t  - 20  9.5 cm,  March  0.-50  predator's  1 1 . 0 cm  1, M a r c h  15  days  f r y growth 6.1%,  6.4%,  9.0% p e r d a y  D u r a t i o n o f coho m i g r a t i o n into the estuary  during early l i f e 16 - 48 d a y s  Non-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 the estuary  0 . 0 0 0 2 - 0.02 r a t e p e r day  P i n k a n d chum f r y s i z e a t seaward m i g r a t i o n from the estuary  4.0  - 9.0  cm  i n estuary  instantaneous  Range o f V a l u e s  Parameter P i n k and chum f r y a l s o allowed t o migrate t o sea i f growth r a t e dropped below a p r e - s e t value  1%,  2%,  3% p e r day  T o t a l abundance o f p i n k . and chum f r y  40 - 520 m i l l i o n  T o t a l abundance o f coho smolts  2-4  million  I n i t i a l s i z e o f enhanced pink f r y  3.35  - 3.75 cm  Number o f days enhanced p i n k f r y lagged behind " w i l d " p i n k and chum f r y entry into estuary  16 - 61 days  Abundance o f enhanced p i n k fry  6 - 24 m i l l i o n  P e r c e n t chum f r y o f t o t a l p i n k and chum f r y p o p u l a t i o n  5% - 100%  Average chum f r y growth r a t e  6.4% p e r day d u r i n g e a r ] l i f e i n estuary  I n i t i a l s i z e of pink f r y  3.35  - 3.55  cm  I n i t i a l s i z e o f chum f r y  3.68  - 3.88  cm  Non-coho n a t u r a l m o r t a l i t y to coho s m o l t s i n e s t u a r y  0.00043 i n s t a n t a n e o u s r a t e p e r day  Coho smolt m i g r a t i o n  about A p r i l 2 3  begins  P i n k f r y m i g r a t i o n ends  about May 2 5  Chum f r y m i g r a t i o n ends  about May 22  APPENDIX I I I  Generalized  Logic  Initialize Migrate  o f Model  variables  into  estuary  Grow Calculate baseline mortality for a l l species C a l c u l a t e number o f p i n k and chum f r y e a t e n b y c o h o s m o l t s Are Are  a l l p i n k & chum f r y e a t e n ? a l l p i n k & chum f r y t o o b i g to eat? 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 assuming b a s e l i n e m o r t a l i t y rate during time a t sea. Calculate  and p r i n t  statistics  Reset parameters and begin a new s i m u l a t i o n ? NO Stop  

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