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UBC Theses and Dissertations

Observations on the predation by squawfish (Ptychocheilus oregonense) on sockeye salmon (Oncorhynchus… Steigenberger, Lance W. 1972

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O B S E R V A T I O N S O N T H E P R E D A T I O N B Y S Q U A W F I S H ( P t y c h o c h e i l u s o r e g o n e n s e ) O N S O C K E Y E S A L M O N ( O n c o r h y n c h u s n e r k a ) , W I T H P A R T I C U L A R R E F E R E N C E T O C U L T US L A K E , B R I T I S H C O L U M B I A . by L a n c e W . S t e i g e n b e r g e r B . S c , U n i v e r s i t y of B r i t i s h C o l u m b i a , 1966 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n the D e p a r t m e n t i of Z o o l o g y W e 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 s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A A p r i l , 1972 In presenting t h i s thesis In p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. L a n c e W. S t e i g e n b e r g e r Department of Zoology The University of B r i t i s h Columbia Vancouver 8, Canada Date 20 A p r i l 1972 A B S T R A C T This study was aimed at providing information that could be used to estimate the predation effect of squawfish on sockeye salmon. I n i t i a l studies at G r i f f e n Lake revealed that the percentage of the population acting as preda-tors, and the average stomach volume, increased with increasing size in non-spawning squawfish. Squawfish in G r i f f e n Lake appeared to be most active at night. F o r the most part, a force fed volume (2.0 ± .1 gms) was digested by a l l sizes of squawfish i n less than 24 hours. Furthe r studies at Cultus Lake i n the laboratory revealed that the rate of digestion was dependent on temperature, volume of food, and size of f i s h . A t 6°C a lag p r i o r to digestion commencing was observed and digestion was not complete for the medium volume in less than 52 hours. On an average the medium fed volume was digested in less than 24 hours for temperatures greater than 15°C. Medium volume corresponded to approximately twice the smallest volumes recorded in stomach contents in the f i e l d . A l i f e span of ten years for males and 14 years for females with no di f f e r e n t i a l i n the growth rate was determined f r o m the banding patterns and sections of pharyngeal teeth. Consumption rates and p e r i o d i c i t y of feeding and activity were within the l i m i t s of data f r o m G r i f f e n Lake. Laboratory calculated routine metabolic rate was approximately twice the the o r e t i c a l rate for pooled species. A tagging experiment at Cultus Lake revealed a population of approxi-mately 20, 000 squawfish greater than 720 cm that, on an average, grew l e s s than 0.36 c m during the winter. Growth during the summer was assessed to be i n the f o r m of weight increase of body tissue and gametes. Trap catches and temperature preference experiments indicated that squawfish are found within p a r t i c u l a r temperature regimes in different phases of the year. Within Cultus Lake, distance did not prevent squawfish aggrega-i i i tion on concentrations of sockeye smolts. There was increased consumption of smolts during smolt migration from the lake. In the field a significant difference in rate of digestion for different sizes of squawfish could not be demonstrated; however, there was a difference in the volume voluntarily consumed. With these findings and other theoretical information, it is possible to determine quantitatively the predation effect of a squawfish population on sockeye. Having established a population estimate, an estimate of annual mortality (55.2 per cent per year), and the temperature specific phases (early smolt phase, peak smolt phase, spawning phase, summer phase, f a l l phase, winter phase), two methods for the assessment of the predation effect were possible. Fi r s t , knowing proportion of the size classes acting as predators, the numbers and frequency distribution of squawfish remaining within any phase, the duration and temperature characteristics of the phase, the effect of tem-perature on the rate of digestion, and the volumes that can be digested in 24 hours, it was possible to get an accumulated volume consumed for the popu-lation. For the 20, 000 squawfish greater than 20 cm fork length in Cultus Lake, this represents an approximate consumption of 1.4 million sockeye smolt equivalents. The second estimate of consumption was based on the energy require-ments converted to consumption rates using conversion coefficients for the same population. The energy requirements to complete spawning, growth and mean metabolism were summed, then converted to a consumption volume for the population. The findings revealed that approximately 2.8 million sockeye equivalents are required. iv TABLE OF CONTENTS P a g e TITLE PAGE i ABSTRACT ii TABLE OF CONTENTS... iv LIST OF FIGURES vii LIST OF PLATES.... xi LIST OF TABLES xii LIST OF APPENDICES xvi ACKNOWLEDGMENTS xviii i : INTRODUCTION. 1 I I . OBSERVATIONS AND EXPERIMENTS 5 A. Stomach content analyses of Griffen Lake squawfish 5 1 . Methods. 5 2 . Results 5 B. Digestion experiment with Griffen Lake squawfish. 1 2 1 . Methods 1 2 2 . Results 1 2 C. Trap catches as an index of activity in Griffen Lake 1 4 1 . Methods 1 4 2 . Results 1 6 D. Consumption rates of eggs and prey in Griffen Lake 1 9 1 . Methods 1 9 2 . Results 1 9 E. Digestion experiments with Cultus Lake squawfish 1 9 1 . Methods 1 9 2 . Results 2 7 F. The determination of age of squawfish by sectioning and banding patterns of pharyngeal teeth. 2 8 V Page 1. Methods 28 2. Results 32 G. Laboratory temperature preference experiment at Cultus Lake... 36 1. Methods 36 2. Results 39 H. L i m i t e d information on the voluntary short t e r m consumption rates of squawfish at Cultus Lake 41 1. Methods 41 2. Results ,., 41 I. Laboratory feeding p e r i o d i c i t y experiment at Cultus Lake .41 1. Methods.. 41 2. Results 43 J. Determination of squawfish winter growth rates f r o m tagging. 44 1. Methods..... 44 2. Results 44 K. F i e l d conducted experiments on activity and p e r i o d i c i t y of feeding (Cultus Lake, 1969) • 46 1. Methods 46 2. Results ,„-.. 46 L. Population census and migration of squawfish. w i t h i n Cultus Lake. - 5 0 M. F i e l d conducted digestion experiments 55 1. Methods 55 2. Results ..... 55 N. The available seasonal trap catch data f r o m G r i f f e n and Cultus lakes and the temperature patterns i n Cultus JLake 58 O. The use of gillnet data to study the effect of sgijuawfish on smolt migration and f r y emergence ...... 58 P. Reproductive condition and the potential egg dleposition of squawfish f r o m Cultus Lake 61 Q. Determination of the basal metabolic rate of siquawfish 66 1. Methods 66 2. Results.... 67 R. Length-weight relationship 67 vi Page III. SYNTHESIS 69 A. Population distribution by age and season. 69 B. The effect of temperature on the rate of digestion ?0 C. An estimate of squawfish predation based on consumption 7 5 1. Early smolt migration volumes 75 2. Peak smolt migration volumes 76 3. Spawning volumes 76 4. Summer volumes 77 5. Fall volumes 77 6. Winter volumes 78 7. Recapitulation 78 D. An estimate of squawfish predation based on caloric  requirements 84 1. Energy for metabolism and growth 84 2. Energy for spawning 86 3. Recapitulation.... 88 IV. CONCLUDING REMARKS 94 LITERATURE CITED 97 APPENDICES 99 v i i ' . . L I S T O F F I G U R E S F i g u r e P a g e 1 The p e r c e n t a g e o c c u r r e n c e of v a r i o u s food i t e m s i n the s t o m a c h s of 874 s q u a w f i s h c o l l e c t e d f r o m G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) 6 2 The per cent f r e q u e n c y d i s t r i b u t i o n of f o r k l e n g t h s (cm) of the s a m p l e of s q u a w f i s h d i s s e c t e d at G r i f f e n L a k e ( J u l y -S eptember, 1967) . 7 3 The per cent f r e q u e n c y of f o r k lengths (cm) of f i s h w i t h empty s t o m a c h s i n the s a m p l e of 377 s q u a w f i s h d i s s e c t e d at G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) 7 4 The per cent f r e q u e n c y of f o r k lengths (cm) of s q u a w f i s h w i t h food i n t h e i r s t o m a c h s p r e s e n t i n the s a m p l e of 497 s q u a w f i s h d i s s e c t e d at G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) 7 5 The per cent f r e q u e n c y of f o r k lengths (cm) of s q u a w f i s h c o n t a i n i n g f i s h and i n s e c t s as s t o m a c h contents. T h e r e i s a s h i f t i n food i t e m s , f r o m i n s e c t s to f i s h , w i t h i n c r e a s i n g s i z e ( G r i f f e n L a k e , J u l y - S e p t e m b e r , 1967) 6 P l o t of the l o g (average v o l u m e (gms) ) + 1 vs f o r k l e n g t h of those f i s h (non-spawning) d i s s e c t e d at G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) w h i c h c o n t a i n f i s h i n the s t o m a c h contents. ( F o r c a l c u l a t i o n s , sp.gr. = 1.) 9 7 P l o t of the p r o p o r t i o n of the s a m p l e c o n s u m i n g f i s h v s f o r k . l e n g t h (cm) of those f i s h (non-spawning) d i s s e c t e d at G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) w h i c h c o n t a i n f i s h i n the s t o m a c h contents 9 8 P l o t of the p o r p o r t i o n of the s a m p l e c o n s u m i n g f i s h v s f o r k l e n g t h (cm) of those f i s h (spawning) d i s s e c t e d at G r i f f e n L a k e ( J u l y - S e p t e m b e r , 1967) w h i c h c o n t a i n f i s h i n the s t o m a c h contents 9 9 The d i f f e r e n c e i n the a v e r a g e v o l u m e of f i s h i n the s t o m a c h (gms) at d i f f e r e n t t i m e s of the day i n s q u a w f i s h d i s s e c t e d at G r i f f e n L a k e (p=.05) 1 0 10 The p e r cent o c c u r r e n c e of f i s h i n the s t o m a c h at d i f f e r e n t t i m e s of the day ( f r o m s q u a w f i s h d i s s e c t e d at G r i f f e n L a k e , J u l y - S e p t e m b e r , 1967) 10 v i i i F i g u r e Page, 11 The per cent occurrence of insects in the stomach at different times of the day (from squawfish dissected at G r i f f e n Lake, July-September, 1967) i 0 12 The rate of digestion of squawfish fed 2.0 gms of redside shiner (Richardsonius balteatus) (Griffen Lake, 1967). The log (weight fed (gms) ) + 1 i s plotted against the time after feeding in hours *^a 13 Trap catch (July 26-28, 1967, and August 2-5, 1967) depicting the daily v a r i a t i o n i n the number of squawfish captured at different times of the day ^ 14 P e r i o d i c i t y of activity (mathematically deduced f r o m trap catch) of squawfish f r o m G r i f f e n Lake (1967) 18 15 The linear r e g r e s s i o n of the age (years) in male squawfish (determined by sectioning the left pharyngeal teeth) vs the fork length (cm) 34 16 The linear r e g r e s s i o n of the age (years) of female squawfish (determined by sectioning the left pharyngeal teeth) vs the fork length (cm) 34 17 The line a r r e g r e s s i o n of the age (years) of male squawfish (determined by the banding pattern of the right pharyngeal teeth) vs the fork length (cm) 34 18 The linear r e g r e s s i o n of the age (years) of female squawfish (determined by the banding pattern of the right pharyngeal teeth) vs the fork length (cm) 34 19 The line a r r e g r e s s i o n of the age (years) of male squawfish (determined by the rule of majority) vs the fork length (cm) 35 20 The linear r e g r e s s i o n of the age (years) of female squawfish (determined by the rule of majority) vs the fork length (cm) 3 5 21 Temperature preference tank 38 22 Laboratory calculated p e r i o d i c i t y of feeding of squawfish on hatchery trout (Cultus Lake, 1968) 45 ix Figure Page 23 Illustration of the zoning, trap location and gillnet positions at Cultus Lake (Spring, 1969) 4 7 24 The three-hour interval trap catch of squawfish from Cultus Lake 48 2 5 The average stomach volume (gms) of squawfish caught at different times of the day (three-hour intervals) 48 26 Smolt migration curve for sockeye smolts (Oncorhynchus nerka) from Cultus Lake (Spring, 1969) 49 27 Fry emergence curve for sockeye fry (Oncorhynchus nerka) from Cultus Lake (Spring, 1969) '. 4 9 28 ' Population mortality of Cultus Lake squawfish as determined by the plot of the age of the fish vs the log of the number of fish 5 3 29 Cultus Lake field conducted digestion experiment. Plot of the log (average volume (gms) ) + 1 vs the fork length (cm) for the sample of squawfish considered to be at initial feeding or time zero 56 30 The calculated daily trap catch between trap checks at Cultus Lake (Fall 1968 and Spring 1969) 59 31 The average seasonal change in temperature for depths less than 10 meters (0, 5, 10 meter temperature values are pooled) (Ricker, 1937) 60 32 The average seasonal change in temperature for depths greater than 10 meters (15, 20, 25, 30, 35, 40 meter temperature values are pooled) (Ricker, 1937) 60 33 Plot of the weight (gms) of the ovaries of spawning squawfish vs the age (years) 65 34 Length-weight relation. Plot of the weight (gms) of a sample of squawfish vs the fork length (cm) 68 3 5 Length-weight relation. Plot of the log (weight (gms)) of a sample of squawfish vs log (fork length (cm) ) 68 Figure Page 36 Length-weight relation. Plot of the weight (gms) of a sample of squawfish vs age (years) 37 Length-weight relation. Plot of the log (weight (gms) ) of a sample of squawfish vs log (age (years) ) xi LIST OF P L A T E S Plate Page 1 The stomach pump 13 2 Cultus Lake digestion experiment tanks 23 3 Shore lead l i v e trap 1 0 2 x i i LIST OF T A B L E S T A B L E Page I • The consumption, average volume and per cent occurrence of various food items recorded i n the stomachs of squaw-f i s h dissected at G r i f f e n Lake (July-September, 1967) 11 II Summary of the trap catch data collected at G r i f f e n Lake August 20-2 5, 1967 16 III Deduced number of squawfish taken at various time periods at Griffen Lake 17 IV Short t e r m voluntary consumption rate of eggs (Oncorhynchus  nerka) by s m a l l squawfish 20 V Short t e r m voluntary consumption rates of prey (Richardsonius balteatus) by squawfish at G r i f f e n Lake 21 VI Format presentation of Cultus Lake digestion experiments (each replicate included f i s h fed on each of three volumes of food) 2 5 VII Determined weights of food fed to squawfish i n Cultus Lake Laboratory digestion experiments 26 VIII Intercepts (a) for rates of digestion experiments at different temperatures (in each case the intercept i s the log ((weight at time zero (grams)) + 1) 29 IX Slopes (b) for the rates of digestion experiments at different temperatures (in each case the slope is the r e g r e s s i o n log ((weight (grams) of food in the stomach) + 1) against time (hours) 30 X Slopes (b^) of the lines between the known intercept at i n i t i a l feeding and the log ((weight (grams) of food i n stomach) + 1) at the time of the f i r s t observation (x^) 31 XI Age determination of squawfish by the sectioning and banding of pharyngeal teeth 33 XII Number of squawfish in various temperature zones of Cultus Lake temperature preference experiment 40 x i i i T A B L E Page XIII Weight (grams) of frozen hatchery trout eaten by squawfish (various fork lengths) i n the voluntary short t e r m feeding experiment (Cultus Lake, 1968) 42 XIV Laboratory p e r i o d i c i t y of feeding of squawfish on trout at Cultus Lake 43 XV The number, average volume, proportion consuming sockeye smolts, and/or fry, and the average number of smolts per squawfish for a l l the squawfish dissected the day p r i o r to and during the 3-hour i n t e r v a l activity and p e r i o d i c i t y of feeding experiment 51 X V I Comparison of the slopes (b) and intercepts (a) of the laboratory and f i e l d digestion data (temperature approxi-mately I0°C) (from plots of log (weight (grams)) + 1 vs time (hours)) 57 XVII Consumption of sockeye smolts by squawfish as determined by a unit effort of gillnet on the smolt migration pathway of Cultus lake 62 XVIII Consumption of sockeye f r y as determined by a unit effort of gillnet on the f r y emergence area of ( L i n d e l l Beach) Cultus Lake 63 X I X Number of eggs in squawfish (spawning and non-spawning) of various fork lengths (cm) (Cultus Lake, A p r i l - J u n e , 1969) 64 X X The seasonal phases used i n calculation of consumption of f i s h by squawfish i n Cultus Lake 70 X X I Ages, number and frequency dis t r i b u t i o n of potential predators remaining in Cultus Lake during mid phase of any phase of the year 7 2 XXII Summary of the pooled routine percentage decrease i n the stomach volume/hour for squawfish of various sizes fed a range (low, medium and high) of volumes of food at different laboratory temperatures. The time lag p r i o r to digestion commencing is also included in the table f o r laboratory ex-periments (Tables IX and X). The f i e l d conducted decrease i n stomach volume per hour i s summarized f r o m Table XVI... 73 x i v T A B L E Page XXIII The rates of digestion for the different phases of the year. The rates were either determined by the routine rate of digestion and the predominant temperature within each phase (Figure 31), or were elevated as indicated by the slopes of r e g r e s s i o n lines hi and b f r o m the laboratory and f i e l d conducted digestion experiment completed at Cultus Lake. The adjusted rate i s the rate that should p r e v a i l as suggested by the lake temperature 74 X X I V Time required (hours) to reduce stomach volumes by 80 per cent of i n i t i a l volume (calculations based on R i c k e r (1958), Appendix V, and the adjusted rates of digestion, Table XXIII) 74 X X V P r o p o r t i o n of predators within each phase observed or assumed to contain f i s h or f i s h products i n the stomach contents 80 X X V I The average volumes (grams) of food (observed or c a l c u -lated) found i n the stomachs of predators during each phase of the year 81 X X V I I The calculated daily ration for various ages of squawfish for any phase of the year for temperatures found i n Cultus Lake 82 XXVIII Calculated consumption of prey (grams) by the population of squawfish present i n Cultus Lake for a l l phases of the year based on the number in the age classes, the propor-tions observed or calculated to contain food, and the amount of food i n the stomach that can be digested per day (daily ration) when exposed to the pr e v a i l i n g phase temperature 83 X X I X Routine c a l o r i c requirements and routine metabolic rate of squawfish of different ages, lengths or weights (except for spawning fish) 85 X X X Table of factors (q) for adjusting values of metabolism to 20°C on the basis of the "normal curve" ( f r o m Winberg, 1956) 87 X X X I The average temperature of the different in Cultus Lake , ases evident 87 XV T A B L E Page X X X I I The weight, growth and spawning contribution (grams), and the energy equivalents (Kcalories) for the various ages of squawfish i n Cultus Lake 89 XXXIII Mean metabolic rate (calories per day) of various ages when exposed to the average phase temperature for the different phases evident in Cultus Lake 90 X X X I V Theoretical mean metabolic rate (Kcalories) for the population of squawfish present in Cultus Lake for the different phases and temperatures of the year 92 X X X V Energy requirements (Kcalories) necessary for growth and reproduction (based on the increase in weight (grams) and conversion coefficients for growth (1 K c a l o r i e / g r a m wet weight) and reproduction (1.3 K c a l o r i e s / g r a m wet weight)) 93 xvi LIST OF A P P E N D I C E S Appendix Page I Explanatory notes of G r i f f e n Lake, B r i t i s h Columbia 99 II Explanatory notes of Cultus Lake, B r i t i s h Columbia 100 III Explanatory notes of the shore lead l i v e trap used at G r i f f e n Lake and Cultus Lake, B r i t i s h Columbia 101 IV The trap catch data of squawfish f r o m G r i f f e n Lake (1967) 104 V Laboratory temperature preference data f r o m Cultus Lake (1968) . 106 VI Laboratory feeding pe r i o d i c i t y data f r o m Cultus Lake 107 VII Winter growth rate data of squawfish f r o m Cultus Lake (1968) 108 VIII Trap catch data of squawfish f r o m Cultus Lake ( F a l l , 1968) .... 110 IX Trap catch data of squawfish f r o m Cultus Lake (Spring, 1969) i l l X Cultus Lake smolt migration (Spring, 1 9 6 9 ) — • 112 XI Catches of f r y and other common species seined during f r y emergence at Cultus Lake (Spring, 1969) H 3 XII . Sample size and the method of capture of the sample used i n the Petersen Mark-Recapture estimate of the Cultus Lake squawfish population 114 XIII A n a l y s i s of covariance of the slopes and intercepts of the rates of digestion f r o m the Cultus Lake f i e l d digestion data 115 XIV Total weight of the ovaries (grams) for squawfish of various fork lengths (cm) samples f r o m Cultus Lake :-, (Spring, 1969) • 1 1 6 x v i i Appendix Page X V Calculation of dissolved oxygen levels f r o m duplicate water samples (Winkler method), expressed as m i l l i g r a m s / l i t e r and m i l l i l i t e r s / l i t e r X V I Calculation of oxygen consumption and metabolic rate expressed as m i l l i g r a m s 0 ?/kg/hr and Kcal/gm/day 118 x v i i i A C K N O W L E D G M E N T S Quality i n the future should be the a i m of a l l graduate students when completing r e s e a r c h projects. Quantity, I've discovered, leads to communi-cation and assistance f r o m many helpful people. I should li k e to thank personally each and every one who assisted and made this thesis possible. I should li k e to thank P e t e r R o w s e l l and B r i a n Wong, who were w i l l i n g and devoted r e s e a r c h assistants at G r i f f e n and Cultus lakes. Both Dr. J i m Bryan and A r t Tautz provided assistance, constructive c r i t i c i s m , helpful suggestions, and enthusiasm during different phases of the research. A t initiation, George Stringer, Regional D i r e c t o r of the F i s h and W i l d l i f e B ranch at Kamloops, B.C., devoted two days to inspecting and selecting G r i f f e n Lake as the r e s e a r c h site f r o m more than one hundred lakes i n the M e r r i t t , Revelstoke and Kamloops d i s t r i c t s . L l o y d Royal of the International P a c i f i c Salmon F i s h e r i e s Com-mi s s i o n in New Westminster, gave p e r m i s s i o n to esta b l i s h a r e s e a r c h labora-tory at Cultus Lake. At Cultus Lake, J. S e r v i z i , and especially Dr. E. Brannon, provided man years (Bob Land), equipment and knowledge for the colle c t i o n of valuable f i e l d data (sockeye fry, sockeye smolts, gillnetting and tagging). In addition, the Commanders of the Canadian A r m e d F o r c e s Base Chilliwack, B.C., (Colonel R.W. Potts and Colonel R.M. Black) gave m i l i t a r y assistance and p e r m i s s i o n to esta b l i s h a r e s e a r c h site and equipment storage area within the bounds of the Task Force and Rafting A r e a of Cultus Lake. Another of the people who made this thesis possible i s Mr. Roy Hamilton of the P a c i f i c Power and Light at Portland, Oregon. He provided many useful suggestions and the shore lead live trap for the capture of an adequate supply of squawfish with the least amount of effort. To my committee (Dr. P. A. L a r k i n , supervisor; Dr. H. Nordan and xix Dr. T. G. Northcote) I will always be grateful — to Dr. Northcote for his sug-gestions in the field at Griffen Lake and in the final preparation of the thesis; to Dr. Nordan for his continued support throughout my undergraduate and graduate studies; and to Dr. Larkin for his faith in my ability, his critical evaluation and his enthusiasm, even in times of discouragement, which enabled the completion of the research. His patient assessment of the manu-script enabled the completion of the thesis. I wish also to thank Dolores Lauriente, for the computer analysis of the data and graphing of many of the results; Helen Hahn for the typing of the manuscript; Peter Ellickson for his assistance in setting up the research area; and Mr. W. W. Coward for his advice and administrative assistance. Thanks are also due to the National Research Council of Canada and the University of Br i t i s h Columbia for funding the project. 1 I. INTRODUCTION This study was designed to collect f i e l d and laboratory information that would be useful i n a general model to evaluate the order of magnitude of pre-dation on salmon by a squawfish population. The e a r l i e s t published informa-tion on food habits of squawfish in B r i t i s h Columbia was that of Clemens and Munro (1938) who reported on less than fi f t y f i s h and afford no data which can be incorporated into a model. R i c k e r (1941) provided detailed information on the "consumption of sockeye by predaceous fish, mainly squawfish, in Cultus Lake, B r i t i s h Columbia." His information is qualitatively valuable, but the samples were f r o m gillnets set for various periods of time. Hence, various degrees of digestion had occurred, and the data has l i m i t e d quantitative value. Additionally, stomach contents were recorded for only some sizes of squawfish. M ore recently, Thompson (1961) examined stomach contents of squawfish of the lower 180 m i l e s of the Columbia R i v e r . Valuable informa-tion on the yearly dietary change of the squawfish was obtained but hatchery releases of salmon were involved as food, and a subjective scoring method of analysis makes the data useless for quantitative assessment of predation. Ideally, what i s required i s information which enables estimation of quantities of f i s h consumed over a long period, which i n turn r e q u i r e s knowledge of the quantities eaten by d i f f e r e n t - s i z e d f i s h and the rates of digestion at different temperatures. In a crude way this has already been attempted. R i c k e r (1941) considered the rate of consumption and number of squawfish i n a population to estimate quantities consumed i n a year, and hence the possible significance of squawfish as predators on salmon. He concluded that, at least i n Cultus Lake, squawfish were substantial predators of sockeye. Thompson (1961) concluded that salmon made up such a s m a l l proportion of the diet (approximately 3.5 per cent) as to suggest that squawfish were insignificant as predators. F o r •• both of these studies, the rate at which food i s digested by squawfish was un-known, so that the conclusions based on quantities found i n stomachs are under-estimates of unknown degree. It i s to this question that this study was 2 chiefly addressed. The rates of consumption, the rates of digestion, the effect of volume of food, and the effect of temperature, must a l l be con-sidered in the formulation of a model for estimating total consumption of an individual. Other important factors such as activity, p e r i o d i c i t y of feeding, growth rates, l i f e span, and reproductive potential, are additional factors which affect the f i n a l formulation of a model of population consumption. The f i e l d work was c a r r i e d out on two lakes i n B r i t i s h Columbia. F i e l d work began on Griffen Lake (Appendix I) near Revelstoke in June, 1967, and was terminated in early September. The remainder of the data were col-lected at Cultus Lake (Appendix II) near C h i l l i w a c k i n the late summer and f a l l of 1968, and the spring of 1969. A shore lead l i v e trap (Appendix III) provided an adequate source of predators and prey f o r f i e l d and laboratory investigation. The investigation of squawfish completed at G r i f f e n Lake provided i n i t i a l information on stomach contents (Section A), digestion rates (Section B), activity (Section C), and consumption rates by squawfish of salmon eggs and various prey (Section D). A t Cultus Lake, the colle c t i o n of data was more intensive. In the late summer of 1968, a detailed set of digestion experiments was completed (Section E). Age determinations and l i f e expectancy of a sample of squaw-f i s h were attempted by sectioning of pharyngeal teeth (Section F). In the f a l l , l i m i t e d laboratory experiments enabled a b r i e f look at temperature preference (Section G), consumption rates (Section H), and p e r i o d i c i t y of feeding (Section I). In addition, a l i m i t e d number of f i s h were tagged and released to deter-mine winter growth rates (Section J). In the spring of 1969. Cultus Lake was a r b i t r a r i l y zoned, the l i v e trap was placed in the lake and designated gillnet sites were fixed. The trap pro-vided f i s h for tagging and future growth rate determinations as we l l as the 3 means (aided by gillnets) of studying activity and pe r i o d i c i t y of feeding (Section K), population census and migration within the lake (Section L), and a supply of (approximately 700) squawfish for a f i e l d conducted digestion experiment (voluntary consumed prey, temperature approximately 12°C) (Section M). Since the trap i s a shore lead l i v e trap, the available seasonal trap catch data (June, 1967 to May, 1969) provides a means of investigating the length of time spent on the shoal area of the lake. This, i n turn, can be related to temperature (Section N). Each year the International P a c i f i c Salmon F i s h e r i e s Commission i n s t a l l s a fence to census smolt migration f r o m Cultus Lake. In the spring of 1969» an additional experiment was conducted to determine sockeye salmon f r y emergence curves (E. Brannon, unpublished data) on the major sockeye spawning grounds ( L i n d e l l Beach). A joint g i l l n e t and trapping pro-cedure adjacent to the outlet and in close p r o x i m i t y to the emergence study area was completed in an attempt to assess squawfish predation on these two phases of the sockeye l i f e cycle. Additional netting was c a r r i e d out at other locations on the lake (Appendix III). Thus, the re l a t i v e catch per unit effort, and the stomach contents of netted f i s h (aided by trap catch data), were used to provide additional infor-mation on activity, p e r i o d i c i t y of feeding, and degree of predation of squaw-f i s h on smolts and prey at different times of mig r a t i o n and emergence (Section O). Moreover, comparisons of f i s h i n varying reproductive condition (spawning versus non-spawning) emphasize the importance of considering reproductive condition while assessing squawfish predation. The potential egg deposition of squawfish was also attempted by taking ovary weights and sample counts (Section P). F i n a l l y , during the course of the collection of f i e l d data, a laboratory experiment was completed to. determine the routine r e s p i r a t o r y metabolism of squawfish (acclim. 9-12°C, post-absorptive) (Section Q). 4 These various investigations provide a suitable background for attempting two estimates of the total consumption of prey by a population of squawfish in a lake in a year. The f i r s t estimate is based on what the squawfish are observed to eat; the second on what they would probably be required to eat to maintain themselves, to be active, to grow, and to reproduce. 5 II. OBSERVATIONS AND E X P E R I M E N T S A. Stomach content analyses of G r i f f e n Lake squawfish 1. Methods • ' A large sample of G r i f f e n Lake squawfish, f r o m the l i v e trap, (Appendix III), was analyzed for stomach contents. The items i n the stomachs were designated as f i s h products (identifiable or non-identifiable fish), insects, plants, molluscs, d e t r i t a l m a t e r i a l , and non-identifiable. The total volume of the stomach contents was measured by water displacement. A trace amount of any item was recorded as a 0.25 m l displacement. The total displacement, food items, presence of i n t e s t i n a l products (presence or absence of food), the average percentage digestion of f i s h products in the stomach, fork length, reproductive condition, and sex of each dissected f i s h was recorded. 2. Results F i s h occurred i n approximately 37 per cent of the squawfish stomachs (Figure 1). Clemens and Munro (1934) reported 56.5 per cent occurrence of fi s h , and Thompson (1958) reported seven per cent. Obviously, such large v a r i a b i l i t y deserves investigation. The most l i k e l y explanation i s the d i f -ference i n the length frequency distribution of the squawfish samples because size affects the selection of p a r t i c u l a r food items. Other var i a b l e s are the col l e c t i o n times, p a r t i c u l a r l y i n r e l a t i o n to the length of time the f i s h may be i n a gillnet, and the reproductive condition of the f i s h (spawning f i s h do not eat). F i g u r e s 2, 3, and 4 give the percentage frequency of squawfish of different lengths for the sample dissected, for the empty fish, and for the f i s h with food in the stomach. Squawfish less than approximately 13.5 cm are not predators on f i s h . There i s a shift in food items taken, f r o m insects to fish, as the size of the squawfish increases (Figure 5). The average per-The percentage occurrence of various food items in the stomachs of 874 squawfish collected from Griffen Lake (July-Septemb 1967). PER CENT OCCURRENCE OF FOOD ITEMS IN STOMACH O O o H m 2 CO X to m o —i > z o rn —i 3 § > ? CD O r- m m 2 T o o CD Z o z m "0 o JL. no o Oi o _ l _ _ L _ O _L ro F I G U R E 2. The per cent frequency dis t r i b u t i o n of fork lengths (cm) of the sample of squawfish dissected at Gr i f f e n Lake (July-September, 1967). F I G U R E 3. The per cent frequency of fork lengths (cm) of f i s h with empty stomachs in the sample of 377 squawfish dissected at G r i f f e n Lake (July-September, 1967). F I G U R E 4. The per cent frequency of fork lengths (cm) of squawfish with food in their stomachs present i n the sample of 497 squawfish dissected at G r i f f e n Lake (July-September, 1967). F I G U R E 5. The per cent frequency of fork lengths (cm) of squawfish containing f i s h and insects as stomach contents. There is a shift i n food items, f r o m insects to fish , with increasing size (Griffen Lake, July-September, 1967). PERCENT FREQUENCY B t» a a car PERCENT FREQUENCY 8 K M O m m z . (fi PERCENT FREOLENCY u 8 tn H O 2 8 centage occurrence of food items i s thus dependent on the length frequency di s t r i b u t i o n of the sample. F i g u r e s 6 and 7 show that for non-spawning squawfish both average volume and proportion of squawfish consuming prey increases with increasing size. A t G r i f f e n Lake 85 spawning squawfish were examined. F o r these f i s h only presence or absence of food i n the stomachs was recorded, but i n most cases only a trace amount was present. The proportion of spawning f i s h con-suming prey decreased with increasing size of predator (Figure 8), although the trend i s not s t a t i s t i c a l l y significant. There was also a difference i n average volume of f i s h and frequency of occurrence of f i s h and insects in the stomachs at different times of the day (Figures 9. 10, and 11). The greatest percentage occurrence of f i s h i n the stomachs is at 0 900 hours and, of insects, at 0 500 hours. Probably, feeding of squawfish between 0 500 and 0 900 increases the percentage occurrence of f i s h i n the stomach, and this causes the apparent decrease i n occurrence of insects. F o r the most part, throughout the remainder of the day the per-centage occurrence of f i s h i s constant. A significant difference i n the average volume at different times of the day could not be detected (p = .05) (Figure 9). The re s u l t s are weak because of s m a l l sample sizes at 2100 and 0100. In summary, the stomach content analysis shows that frequency d i s -t r i b u t i o n of sample size, c o l l e c t i o n time, and the reproductive condition of the f i s h are va r i a b l e s that influence proportions, volumes and frequency of occurrence of food items for different sized squawfish. The consumption, average volume and per cent occurrence of various food i s shown in Table I. F I G U R E 6. P l o t of the log (average volume (gms) ) + 1 vs fork length of those f i s h (non-spawning) dissected at Gr i f f e n Lake (July-September, 1967) which contain f i s h i n the stomach contents. (For calculations, sp. gr. = 1). F I G U R E 7. P l o t of the proportion of the sample consuming f i s h vs fork length (cm) of those f i s h (non-spawning) dissected at G r i f f e n Lake (July-September, 1967) which contain f i s h i n the stomach contents. F I G U R E 8. P l o t of the proportion of the sample consuming f i s h vs fork length (cm) of those f i s h (spawning) dissected at G r i f f e n Lake (July-September, 1967) which contain f i s h i n the stomach contents. LOG ({AVERAGE VOLLNE (GMS? * 1) F I G U R E 9. The difference i n the average volume of f i s h i n the stomach (gms) at different times of the day in squawfish dissected at Gr i f f e n Lake (p = .05). F I G U R E 10. The per cent occurrence of f i s h in the stomach at different times of the day (from squawfish dissected at G r i f f e n Lake, July-September, 1967). F I G U R E 11. The per cent occurrence of insects in the stomach at different times of the day (from squawfish d i s -sected at G r i f f e n Lake, July-September, 1967). o T A B L E I. The consumption, average volume and per cent occurrence of various food items recorded i n the stomachs of squawfish dissected at G r i f f e n Lake (July-September, 1967). Number of f i s h consuming food items at different times . Food items 0 900 1300 2100 0100 0 500 F i s h 269 34 4 4 17 Insect 39 11 0 2 28 Plant 7 1 0 1 D e t r i t a l 8 3 2 0 2 Non-identifiable m a t e r i a l 5 1 . 4 Combination of food items 39 7 1 8 Empty f i s h 239 78 13 8 39 Total examined 606 134 19 16 99 Average vol. f i s h 3.47 + .41 2.32 + 1.45 3.06 + 6.39 7.25 + 9.01 1.29 + 1.13 % occurrence f i s h 44.39% 25.37% 21.05% 25.00% 17.17% % occurrence insect 6.44% 8.20% 0.00 12.50% 28.28% 12 B. Digestion experiment with G r i f f e n Lake squawfish 1. Methods A p r e l i m i n a r y set of digestion experiments was completed at G r i f f e n Lake. The experimental f i s h were held for 72 hours in 3/4 inch mesh tanks (6 ft x 8 ft x 6 ft deep). P r i o r to feeding and stomach pumping, the experi-mental f i s h were anaesthetized with tricane methane-sulphonate (Sandox. M.S. 222) at a dilution of 1 i n 15,000. While under the effect of M.S. 222, squawfish were force-fed a redside shiner (Richardsonius balteatus) of 2.0 Hr .1 gr. The r e s i d u a l contents were then pumped out at 6, 12, 18 or 24 hours after feeding. The stomach pump (modification of Seaburg, 1957, Plate 1) consisted of a p r e s s u r i z e d water supply, foot-controlled release valve, rubber tubing, and copper i n s e r t s (approximately 4 mm to 20 mm in diameter with a 2 mm water inset duct) mounted on quart se a l e r s . Pumping was by an inflow of water through the water ins e r t duct. The food i n the stomach was flushed into the l a r g e r stomach i n s e r t . The outflow was c o l -lected i n a quart sealer. The samples were f i l t e r e d through sections of permascreen (1 mm squares). P a r t i c u l a t e matter not collected was assumed to be digested but not absorbed. A f t e r f i l t e r i n g , the collected food was damp dr i e d and weighed to a r l gm accuracy. 2. Results A total of 164 squawfish, average fork length 24 + .55 cm (min. 19.4 and max. 38.3 cm) were force-fed 2.0 + .1 gm of redside shiner. The average environmental temperature fluctuated between 17°Cto 20°C. The data suggest, and i t seems reasonable to assume, that the rate of digestion i s best described by a linear r e g r e s s i o n of log weight off food remaining on time (hours) (Figure 12). 1 The fitted line seems adequate and the i n t e r -cept (1.13) is a good estimate of the log of the i n i t i a l weight fed plus 1 (1.10). In F i g u r e 12 the y axis is log (weight of food i n grams) plus 1. This avoids negative values and i s a convenience for computer plotting. P L A T E 1. The s t o m a c h p u m p . F I G U R E 12. The rate of digestion of squawfish fed 2.0 gms of redside shiner (Richardsonius balteatus) (Griffen Lake, 1967). The log (weight fed (gms) ) + 1 i s plotted against the time after f e e d i n g r i n hours. 13a F I G 12 GRIFFEN - DIG- EXPT- ALL SIZE F I S H FED 2 - 0 0 GJ^. Y = 0-113BE 01 + -0-41JE5E-01X N = 1£4 TrE PROBABILITY CF THE SLXPE BEING ZERO IS 0-0000 RSO = 0-340302 LIRRELAFTCN LDU-r IdENT R = 0-SB32S9 + TIME (HOURS) 14 Digestion is three-quarters accomplished i n 18 hours and v i r t u a l l y complete 2 i n 24 hours. However, the value of r i s only .340 202 and the data obviously lack p r e c i s i o n . Some reasons for the large v a r i a b i l i t y are: (1) the unknown effect of anaesthetic M.S. 222; (2) the v a r i a t i o n i n the lengths of the squaw-fis h ; (3) temperature effects; and (4) the effect of volume on the rate of digestion for different sized f i s h may be variable. C. Trap catches as an index of activity i n G r i f f e n Lake 1. Methods P e r i o d i c trap checks revealed a large v a r i a t i o n i n catch at different times of the day (Appendix IV). On two occasions (July 26-28, 1967, and August 2-5, 1967) the trap was emptied at various times (Figure 13). A signific a n t l y l a r g e r number of f i s h were trapped during darkness. To further pinpoint the period of greatest catches, a special pattern for l i f t i n g the trap was designed. The experiment entailed recording the number of f i s h caught at predetermined time i n t e r v a l s for s i x consecutive days. The inte r v a l s for recording the number i n the trap, designated as captial l e t t e r s , and four hour time intervals i n the day (smal l let t e r s ) , may be represented as follows: Time 0100 0500 0900 1300 1700 2100 0100 0500 Interval , u i I J I . t ^ i 1 a . l b l c l d l e l f 1 a l i n day S e t ^ g ! B — — - 1 D -1 A - 1 -i n t e r v a l 1 E 1 1 --C ---1 1 _ F 1 I G 1 F I G U R E 13. Trap catch (July 26-28, 1967, and August 2-5, 1967) depicting the daily v a r i a t i o n i n the number of squawfish captured at different times of the day. NUMBER OF SQUAWFISH • TRAPPED The sequence of the intervals over the s i x day period was: Day 1 0100--- B D 1700 A --0900--- 1 ... 1_. 0100--- . . ? . 2 . . . --0900--- . . R z . . . .---1700----...A 2.. 0100--- . „ ? . 3 . . . --0900--- ----2100 -0500---~9-i — . --2100--- . . . q 2 . . . 0500--- --1700---0100--- . .?.«.--- 0900 Day 6 This arrangement partitions the most active periods of the day into overlapping 4-hour time periods, and permits a deduction of the activity pattern f r o m the trap catch data f r o m August 20-25, 1967 (Table II). T A B L E II. Summary of the trap catch data collected at Gr i f f e n Lake August 20-25, 1967. 0100 0 500 a b T I M E 0900 1300 1700 c d e 2100 f 0100 0 500 a Day 1 : 3 3 ^ ) : 3(D A) : 132(A X) • 2 84(B 2) 5(D 2) : 74(A 2) • 3 58(B 3) : 26(F 1) • 67(C X) : 4 2 7 ( 0 ^ • 18(C 2) : 5 • 21 (E x) . : 40 (A 3) • 6 : 37(B 4) 2. Results The solution for the determination of activity for the 4-hour time 17 periods proceeds on the premise that a l l f i r s t deductions are used to pro-vide average values before proceeding to second and further deductions; i.e., f r o m Table II three estimates of e are available: F^-D^; - ^ j - - ^ ' ^ 1~^1' and these are, respectively, 23, 21, and 6, with a mean e" - 17. S i m i l a r l y , three estimates of b are available: E -D ; E -D ; G - F ; and these are, J. J. J. £< J. J. respectively, 18, 16, and 1, with a mean b - 12. F r o m b - 12 there are four estimates of a available f r o m subtracting b f r o m each of the four B values, and these are, respectively, 33, 84, 58 and 37, for a mean a of .41. F r o m e three estimates of f are available, subtracting e~ f r o m each of the A values and the estimates of f are res p e c t i v e l y 115, 57, and 23, for a mean f of 65. F i n a l l y , f r o m E-b and F-e~ we can deduce (c+d) as 9 and 9, and these values averaged with D and D (3 and 5) yie l d (c + d) = 7. Thus, the activity of f i s h at different times can be summarized as follows: T A B L E III. Deduced number of squawfish taken at various time periods at Gri f f e n Lake. Time P e r i o d A c t i v i t y Index a = 0100 - 0500 41. b = 0500 - 0900 12 c + d = 0900 - 1700 7 e = 1700 - 2100 17 1 = 2100 - 0100 65 Averages deduced f r o m Table II F i g u r e 14 depicts the mathematically deduced a c t i v i t y index. It shows that the greatest number of f i s h were captured between 2100 and 0100 (65), and the second greatest number were captured between 0100 and 0500. It is to be noted, then, that if food consumption i s related to activity, i t is neces-F I G U R E 14. P e r i o d i c i t y of activity (mathematically deduced f r o m trap catch) of squawfish f r o m G r i f f e n Lake (1967). T 19 sary to consider the time lag and possible digestion that could have occurred when assessing stomach contents collected f r o m an overnight set. D. Consumption rates of eggs and prey in G r i f f e n Lake 1. Methods A l i m i t e d amount of data was collected f r o m August 23 to September 4, 1967, on the voluntary feeding of captive squawfish. The average daily con-sumption rates of redside shiners and kokanee eggs (('Oncorhynchus nerka Walbaum) were determined for six squawfish (environmental temperature fluctuating f r o m 18° to 20°C). A voluntary feeding; response required approximately ten days to establish if the f i s h were presented kokanee eggs. A 20 to 30 day conditioning period was required f o r squawfish fed shiners. 2. Results The l i m i t e d information obtained i s summarised in Tables IV and V. A squawfish 10.6 cm (fork length) can consume between 2.0 and 5.0 eggs per day, and l i k e w i s e a l a r g e r f i s h (14.8 cm fork length^ can consume between 4 and 10 eggs per day. S i m i l a r l y , the consumption ©if prey by s t i l l l a r g e r squawfish shows significantly different (p = .0 5) d a i l y consumption rates for the three f i s h ranging f r o m 16.7 to 26.7 c m fork length. E. Digestion experiments with Cultus Lake squawffish 1. Methods ' To determine the effect of temperature, volunme and size of f i s h on the rate of digestion, five digestion experiments were completed at Cultus Lake. The basic plan was to feed a known volume of food and to s a c r i f i c e f i s h after an i n t e r v a l of time and measure the quantity of food s t i l l remaining in the stomach. Squawfish were taken in a trap s i m i l a r to that used on G r i f f e n Lake, T A B L E IV. Short t e r m voluntary consumption rate of eggs (Oncorhynchus nerka) by s m a l l squawfish. Feeding Number of eggs consumed by — Date Interval Squawfish 1 Squawfish 2 Squawfish 3 (1967) (hours) (f . l . 14.8 cm) (f. l . 12.2 cm) (f . l . 10.6 cm) August 23 24 33 26 24 August 26 24 0 0 0 August 27 24 8 4 7 August 28 24 14 2 4 August 30 48 41 0 14 August 31 24 20 0* 15 September 1 24 4 1 September 2 24 13 5 September 4 24 13 2 Number of days 20 20 Da i l y consumption 7.295 3.523 Variance 42.804 10.842 Standard Deviation 6.542 3.293 Standard E r r o r 1.463 0.718 5% - Upper L i m i t 10.356 5.023 Lower L i m i t 4.233 2.025 •fungus infection; removed f r o m experiment f . l . = fork length T A B L E V. Short t e r m voluntary consumption rates of prey (Richardsonius balteatus) by squawfish at G r i f f e n Lake. Weight in Grams of P r e y Eaten By Feeding Squawfish 4 Squawfish 5 Squawfish 6 Date Interval (fork length 26.7 cm) (fork length 22.1 cm) (fork length 16.7 cm) (1967) (hours) Weight No. Consumed Weight No. Consumed Weight No. Consumed August 23 24 4.5 2 1.7 ! 0.0 0 August 26 72 8.7 5 1.6 1 0.0 0 August 29 72 8.3 4 4.3 1.6 1 August 30 24 7.6 4 1.7 1 1.5 1 August 31 24 9.3 5 1.7 1 0.0 0 September 1 24 3.8 2 1.6 1 0.0 0 September 2 24 1.8 1 2.0 1 0.0 0 September 4 48 3.8 2 0.0 0 0.0 0 Number of day s 13 13 13 13 13 13 Da i l y Consumption 3.615 1.923 1.114 0.615 0.237 -Variance 5.638 1.472 0.483 0.146 0.196 -Standard Deviation 2.374 1.213 0.695 0.382 0.443 -Standard E r r o r 0.658 0.336 0.193 0.106 0.123 -5% - Upper L i m i t 5.0 50 2.656 1.535 0.846 0.50.6 -Lower L i m i t 2.180 1.189 0.694 0.385 -0.030 ! 22 were graded for size, and held i n a laboratory holding channel where they were fed (Richardsonius balteatus) ad l i b . The channel temperature was o o between 11 C and 13 C. The experimental tanks, 5/8 inch plywood, were 2 ft x 8 ft x 16 in deep (Plate 2). Each was divided into eight s m a l l e r sections by permascreen d i v i d e r s . A n elevated headbox with mixing chamber was used to provide o o water f r o m 4 C to 25 C by mixing in various quantities of deep lake water (4°C), shallow lake water (approximately 12°C to 15°C), and boiler r oom water. F i v e individual digestion experiments were required to investigate o o temperatures f r o m approximately 4 C to 2 5 C. F o r each experiment the f i s h were placed in covered "digestion tanks" the evening p r i o r to an i n i t i a l feeding. The following morning they were force fed a redside shiner approximately comparable i n weight to the hatchery trout to be fed late r i n the experiment. This procedure standardized the time since last feeding, decreased regurgitation, conditioned the f i s h to the experimental tanks, and accustomed the f i s h to force feeding. Seventy-two hours later the f i s h were force fed a determined weight of hatchery trout. The f i s h to be dissected were transported to the laboratory and the int e r n a l temperature was recorded by a telethermometer. A few seconds later the stomach contents were removed and placed on sections of perma-screen (1 mm squares). The samples were washed to remove mucous and particulate matter (<lmm) assumed to be digested but not absorbed. The remaining f i s h products were damp dried, tagged, placed i n p l a s t i c bags, and quickly frozen. Once solidly frozen, the samples were weighed to the nearest one hundredth of a gram. F o r each fish, standard length, fork length, total length, sex, weight and distance f r o m the nose to the p y l o r i c sphincter were recorded. Moreover, scales and selected pharyngeal teeth were collected for possible age determination. The two loops of the int e s -tine below the ph l o r i c sphincter were each a r b i t r a r i l y divided into upper and lower segments. It was hoped that by- recording the position of intestinal f i s h products i n some of the experiments the rate of passage of the stomach contents through the intestine could also be determined. It was o r i g i n a l l y intended that a l l size categories of f i s h in the popula-tion would be examined; however, dif f i c u l t y was i n c u r r e d i n obtaining the extreme sizes i n adequate numbers. Thus, the number of repl i c a t e s and the number of size categories i n each experiment were manipulated according to the supply of squawfish. Each digestion experiment included three volume categories or feeding levels (see below). These volume categories were comparable to the average stomach volume of f i s h dissected at Gr i f f e n Lake. It also became evident that the predetermined d i s s e c t i o n i n t e r v a l s (6, 12, 18 and 24 hours after feeding) were too far apart at temperatures greater than o 16 C. F o r this reason, as the temperature in c r e a s e d there was an increase in the number of dissection intervals, a decrease i n the o v e r a l l time to termination, and a decrease i n the time i n t e r v a l between dissection i n t e r v a l s . The format of the five digestion experiments i s easiest to v i s u a l i z e in table f o r m (see Table VI). In summary, each digestion experiment included a low, medium and high volume category or feeding l e v e l . The sizes of squawfish used, the number of time intervals, the time to termination, and the time between dissections, was v a r i e d with changing temperature. A t G r i f f e n Lake the feeding administered was 2.0 + .1 gms. A more r e a l i s t i c approach for the Cultus Lake experiments was to feed a weight of food related to f i s h size. Three a r b i t r a r y levels of feeding (low (2 grs)„ medium (4 grs), and high (8 grs) ) were f i r s t established for a f i s h of 32.5 c m fork length. This set of weights of food spans the average weight in the stomachs of squawfish (average fork length 32.5 cm) dissected at G r i f f e n Lake. 25 TABLE VI. Format presentation of Cultus Lake digestion experiments (each replicate included f i s h fed on each of three volumes of food). Experiment , Temperature Size Number Dis s e c t i o n Number Range (°C) Categories* Replicates Time Intervals (Hour s) 4 6 8 10 12 1 4 18 24 1 4° - 6°C l b 2 X X X X 2 2 X X X X 3 2 X X X X 4 2 X X X X 5 2 X X X X 6 2 X X X X 2 8° - 10°C 2 2 X X X X 3 4 X X X X 4 4 . X X X X 3 15° - 16°C 2 2 X X X X 3 4 X X X X 4 4 X X X X 4 24° - 25°C 3 4-5 X X X X X 5 19° - 21°C 3 4 X X X X X X Size Category- l a = Fork.length 10,0 - 14.9 c m l b = 15.0 - 19.9 . 2 = 20.0 - 24.9 3 = 25.0 - 29.9 4 = 30.0 - 34.9 5 - 35.0 - 39.9 6 '= 40.00 T A B L E VII. Determined weights of food fed to squawfish in Cultus Lake laboratory digestion experiments. Size Feeding Weight fed Category Length (cm) Levels (grams) l a 12.5 Low .556 Medium 1.11 High 2.23 l b 17.5 Low .87 Medium 1.17 High 3.46 2 22.5 Low 1.22 Medium 2.39 High 4.79 3 27.5 Low 1.60 Medium 3.19 High 6.39 4 32,5 Low 2.00 Medium 4.00 High 8.00 5 37.5 Low 2.42 Medium 4.84 High 9.68 6 42.5 Low 2.86 Medium 5.73 • High 11.44 It i s widely accepted that the weight of ration eaten per unit of time is proportional to the weight of the f i s h r a i s e d to the 2/3 power; i.e., dR/dt = k W m (Ursin, 1967). F r o m this relation, for t=l we may write: log^R = l°§ek + m lo& Substituting 2.00 for R, and 0.67 for m, and dealing i n unit weight for a 32.5 cm fish, log 200 = log k + .67 log 1 and log k = 0.693. e e e Since weight of f i s h is proportional to the cube of length, the ra t i o of two weights is equal to the ratio of the cubes of the lengths. Accordingly, the ra t i o n for a 12.5 cm f i s h is given by 3 l o g e R = 0.693 + 0.67 log (jf^f) f r o m which l o g e R = -1.2276 and R = 0.293. This quantity seemed too s m a l l in r e l a t i o n to even the s m a l l e r volumes of food i n stomachs of 12.5 cm f i s n . F o r the experiments the value of m was r e v i s e d to 0.444, f r o m which R = 0.556 gms for the ra t i o n for 12.5 c m f i s h at the low l e v e l of feeding. This value was doubled for the medium l e v e l of feeding and quadrupled for the high l e v e l of feeding. S i m i l a r values were calculated for the other size categories of squawfish and are l i s t e d i n Table VII. 2. Results The r e s u l t s of the Cultus Lake digestion experiments are presented as plots of the log ((weight of food) (grams) + 1) against time (hours). The inter cepts and slopes of the rates of digestion at 6°, 10°, 15°, 20° and 24°C are summarized in Tables VIII and IX. A discrepancy is apparent when com-paring the calculated r e g r e s s i o n line intercepts with the intercepts for the known log ((initial amount fed) (gms) + 1) F o r example, at 6°C, i n a l l cases except size 2 squawfish fed the low and medium volumes, the intercept of the r e g r e s s i o n line i s slightly greater than the known value. It would seem that digestion occurs at the rate indicated by the slopes of the r e g r e s s i o n lines, but only after an i n i t i a l lag period, possibly related to hydration. At 6°C this hydration period is close to six hours. A t a somewhate higher temperature (9°C) a s i m i l a r phenomenon is v i s i b l e . In the case of the medium and large volume fed, there i s an apparent lag period of approxi-mately six hours. In the smallest volumes fed to size 2, 3 and 4 fi s h , the calculated r e g r e s s i o n line intercepts the Y axis below the log ((initial fed intercept value) + 1). This would suggest that the rate of digestion between the i n i t i a l feeding and the time of the f i r s t observation (X^) is faster than subsequently. This feature, apparent i n graphs (although not presented), is even more apparent at the higher temperatures. Digestion i s thus a complicated event and rates of digestion vary i n re l a t i o n to the volume of food i n the stomach (Table IX). A t the lowest temperature (6°C) a lag period of approximately six hours is evident. A t a higher temperature (9°C) there i s a lag period for medium and l a r g e r volumes, but the smallest volume digests at a rate greater than indicated by the slope of the r e g r e s s i o n line beyond the f i r s t observation of a residue. A t s t i l l higher temperatures the slope (b^) between i n i t i a l feeding and the f i r s t observation (X^) becomes very marked. The lag periods and the slopes of these lines for the various experiments are given in Table X. F. The determination of age of squawfish by sectioning and  banding patterns of pharyngeal teeth 1. Methods L i f e expectancy is an important ingredient i n assessing the total T A B L E VIII. Intercepts (a) f o r r a t e s of digestion experiments at different temperatures (in each case the intercept i s the log ((weight at time z e r o (grams)) + 1). L o g (Amount Fed) + 1 Te m p e r a t u r e 6"C Te m p e r a t u r e 1 0 ° C Temperature 1 5 ° C Temperature 2 0 ° C Temperature 2 4 ° C F o r k L e n g t h Volume F e d Intercept Volume Pooled Intercept Volume Pooled Intercept Volume Pooled Intercept Volume Pooled Volume Intercept P o o led 15.0 - 19.9 (size lb) L o w M e d i u m High .626 1.004 1.495 .696 1.363 1.559 1.164 20.0 - 24.9 (size 2) L o w M e d i u m High .798 1.224 1.756 .776 1.140 1.658 1.339 .647 1.612 2.028 1.369 .125 .950 1.802 1.078 25.0 - 29.9 (size 3) Low M e d i u m High .956 1.433 2.000 1.155 1.428 2.043 1.495 .720 1.641 2.043 1.332 .251 .885 1.865 .995 .326 1.164 2.008 1.103 .365 1.046 .949 1.499 30.0 - 34.9 (size 4) Low M e d i u m High 1.099 1.609 2.197 1.198 . 1.773 2.270 1.748 .975 1.598 2.374 1.444 .381 1.301 1.905 1.193 35.0 - 39.9 (size 5) Low Medium High 1.230 1.765 2.368 1.617 1.837 2.540 1.998 >40.0 (size 6) Low M e d i u m High 1.351 1.907 2.521 1.656 2.440 2.487 2.354 Siz e s pooled L o w M e d i u m High 1.151 1.660 2.108 .807 1.611 2.114 .291 1.057 1.859 .326 1.164 2.008 .365 1.046 1.499 S i z e s and volumes pooled 1.668 1.375 1.089 TABLE DC. Slopes (b) for the rates of digestion experiments at different temperatures (in each case the slope is the regression log ( (weight (grams) of food in the stomach) + 1) against time (hours). Log Temperature 6°C Temperature ;0°C Temperature 15°C Temperature 20°C Temperature 24°C Fork Length Volu me Fed (Amount Fed)+ 1 Slope Volume Pooled Slope Volume Pooled Slope Volume Pooled Volume Slope Pooled Volume Slope Pooled 15.0 - 19.9 Low Medium High .626 1.004 1.495 -.0110 -.0421 -.0086 -.0168 20.0 - 24.9 Low Medium High .798 1.224 1.756 -.0138 +.0012 +.0038 -.0197 -.0257 -.0626 -.0 501 -.0455 -.0059 -.0438 -.0829 -.0504 25.0 - 29.9 Low Medium High .956 1.433 2.000 -.0327 -.0181 -.0206 -.0222 -.0252 -.0558 -.0254 -.0279 -.0104 -.0395 -.0752 -.0409 -.0263 -.0875 -.0799 -.0139 -.0331 -.0909 -.0813 -.1268 30.0 - 34.9 Low Medium High 1.099 1.609 2.197 -.0262 -.0286 -.0164 -.0238 -.0318 -.0359 -.0467 -.0279 -.0176 -.0559 -.0812 -.0 515 35.0 - 39.9 Low Medium High 1.230 1.765 2.368 -.0497 -.0293 -.0374 -.0388 > 40.0- Low Medium High 1.351 1.907 2.521 -.0488 -.0652 -.0521 -.0576 Sizes pooled Low Medium High -.0287 -.0289 -.0175 -.0279 -.0485 -.0348 -.0130 -.0466 -.0781 -.0263 -.0875 -.0139 -.0331 -.0909 -.1268 Sizes and volumes pooled -.0288 -.0307 -.0469 TABLE X. Slopes (bj) of the lines between the known intercept at initial feeding and the log ( (weight (grams) of food in stomach) + 1) at the time of the first observation ( x j ) Fork Length Volume Fed Log (Amount Fed)+ 1 Temperature 6°C Lag x Slope bl Temperature 10° C Lag x Slope \ Temperature 15°C Lag x Slope 1 b' 1 15.0 - 19.9 Low .626 6 6 0. (9ize lb) Medium 1.004 6 6 0. High 1.495 6 6 0. 20.0 - 24.9 Low .798 6 6 • 0. 0 6 -0.0 50 0 6 -0.113 (size 2) Medium 1.224 6 6 0. 6 6 0.00 0 6 -0.087 High 1.756 6 6 0. 6 6 0.00 0 6 -0.000 25.0 - 29.9 Low .956 6 6 0. 0 6 -0.059 0 6 -0.126 (size 3) Medium 1.433 6 6 0. 6 6 0.00 0 6 -0.122 High 2.000 6 6 0. 6 6 0.00 0 6 -0.100 30.0 - 34.9 Low 1.099 6 6 0. 0 6 -0.049 0 6 -0.133 (size 4) Medium 1.609 6 6 0. 6 . 6 0.00 0 6 -0.102 High 2.197 6 6 0. 6 6 0.00 0 6 -0.125 35.0 - 39.9 Low 1.230 6 6 0. (size 5) Medium 1.765 6 6 0. High 2.368 6 . 6 0. > 40.0 Low 1.351 6 6 0. Medium 1.907 6 6 0. High 2.521 6 6 0. Temperature 20°C Lag x Slope b. Temperature 24°C Lag 1 Slope bl 0 4 -0.184 0 4 -0.176 0 4 -0.158 0 4 -0.183 0 4 -0.000 0 4 -0.2 50 32 effect of predation by a squawfish population. Clemens (1939). using scale readings, aged squawfish f r o m Okanagan and Woods lakes. The v a l i d i t y of such a technique seems questionable because attempts to age f i s h f r o m scales f r o m G r i f f e n and Cultus lakes were unsuccessful. Opercular bones (LeCren, 1947) are equally enigmatic. Sectioning of f i n rays and vertebrae (Bilton, 1968) also failed to provide unequivocal r e s u l t s . Otoliths were di f f i c u l t to collect, cup shaped and d i f f i c u l t to age by means of surface structure examination (Wiellemann Smith, 1968). It was f i n a l l y decided to attempt to age squawfish f r o m sections of pharyngeal teeth. A selected group of teeth, usually four f r o m each size category, and sex was taken f r o m the Cultus Lake digestion experiment f i s h . The left teeth were sectioned and the right dried to provide a comparison of the sections with externally v i s i b l e banding patterns. The sections were cut on a B r o n w i l l thin section machine using a 4 i n diamond cutting wheel and 320 g r i t at 5500 rpm. The sections (250 microns) were mounted in paramount and read using a Bausch and Lomb dissecting scope. The data are summarized i n Table XI. Four readings of the light and dark banding were made of sections of each left tooth, and two readings of v i s i b l e banding patterns of each right tooth. 2. Results F i g u r e s 15, 16, 17 and 18 show graphically the estimated ages i n r e l a t i o n to fork length of male and female squawfish by the two above methods. In Figures 19 to 20 the age determination of squawfish f r o m Cultus Lake i s by "rule of majority"; i.e., pooling the banding and sectioning estimate of age and assigning the age that appears most frequently. S u r p r i s i n g l y , growth i n length appears to be a lin e a r function of age. Some consideration must also be given to the fact that the r e g r e s s i o n line i n t e r s e c t s the X axis between 10 and 15 cm fork length, implying either that growth i s very much more rap i d i n the f i r s t year than subsequently, or that the method of ageing under-estimates the age of young f i s h . Cartwright (1956), i n a comparison of TABLE XI. Age determination of squawfish by the sec tioning and banding of pharyngeal teeth. Male Squawfish Female Squawfish Length Range Fork Length Ag e Age Fork Length Age Age Category- (cm) (cm) (secti oning) (banding) (cm) (sectioning) (banding) lb 15.0 - 19.9 15.7 3 3 2 2 17.3 2 2 2 2 1 16.8 3 2 2 2 2 3 18.7 3 3 2 2 3 3 16.0 2 2 2 2 2 1 18.1 2 2 3 3 2 16.6 3 3 3 3 2 4 18.3 3 3 5 4 2 3 J 18.2 3 . 2 2 2 3 3 2 20.0 - 24.9 19.9 3 3 3 3 2 2 19.8 3 2 2 2 2 3 19.9 3 2 2 2 2 2 19.8 2 2 2 2 4 4 19.8 3 2 2 2 4 4 20.0 3 2 3 3 2 2 19.7 4 , 3 2 3 3 3 3 25.0 - 29.9 24.5 2 2 2 3 4 5 24.9 3 3 4 4 4 5 24.5 2 3 2 2 4 5 24.9 2 2 3 2 3 24.9 3 2 4 4 4 4 25.0 • 3 2 2 2 4 3 4 30.0 - 34.9 30.2 6 5 6 6 6 7 30.3 5 4 5 . 4 6 7 30.0 6 5 6 7 6 6 30.0 12 11 11 11 12 12 30.0 6 6 5 5 7 7 30.5 4 3 3 3 5 6 30.5 8 8 7 7 7 6 30.0 4 4 3 3 7 6 5 35.0 - 39.9 35.7 8 7 7 7 8 8 35.2 5 5 5 5 5 5 36.2 12 11 11 10 10 10 35.1 10 10 9 1° 11 11 36.2 10 9 9 8 9 10 . : 6 40.0 - 44.9 39.8 11 10 10 10 10 12 30.0 11 10 10 10 10 10 39.5 11 11 11 11 11 11 40.7 10 10 9 9 8 7 40.9 11 10 9 9- 10 9 39.0 14 14 15 13 1.4 12 7 45.0 - 49.9 43.0 9 9 9 8 8 46.0 17 16 17 17 14 14 45.5 11 11 11 10 10 11 44.5 14 14 13 14 13 13 43.2 12 12 12 12 50.0 11 12 13 13 12 12 F I G U R E 15. The linear regression of the age (years) in male squawfish (determined by sectioning the left pharyngeal teeth) vs the fork length (cm). F I G U R E 16. The linear regression of the age (years) of female squawfish (determined by sectioning the left pharyngeal teeth) vs the fork length (cm). F I G U R E 17. The linear regression of the age (years) of male squawfish (determined by the banding pattern of the right pharyngeal teeth) vs the fork length (cm). F I G U R E 18. The linear regression of the age (years) of female squawfish (determined by the banding pattern of the right pharyngeal teeth) vs the fork length (cm). F I G U R E 19. The linea r r e g r e s s i o n of the age (years) of male squawfish (determined by the rule of majority) vs the fork length (cm). F I G U R E 20. The linear r e g r e s s i o n of the age (years) of female squawfish (determined by the r u l e of majority) vs the fork length (cm). FIG 19 n i Tl FT AGE DETER'N BY THE RULE C F MAJORITY YCM). =-0-4213E 01 + 0-349SE OOX NCM)= IB RSQ =0-B753 CORRELATION COEFFICIENT R= 0-935E FORK LENGTH (CM) FIG 20 m Tl R AGE DETER'N BY THE RULE DF MAJORITY YtF) =-0-5320E 01 > 0-3B41E OOX NCF)=30 RSQ =0-77B2 CORRELATTDN LUJ-HCIENT R= O-BBS FORK LENGTH (CM) Ul growth rates f r o m scales of squawfish f r o m Okanagan, Shumway and Shuswap lakes, assigns an age of 3 years to squawfish between 9.0 and 14.9 cm and, i n addition, puts an upper l i m i t of 11 years of age on 50.0 c m f i s h . He also states that, "It i s clear that f i s h growing normally or rapidly w i l l show a distinct annulus in their f i r s t year, while slow growing animals w i l l show no check at a l l or possibly only a slight one very near the focus of the scale." According to the present data, an age of one year is assigned to f i s h that Cartwright would have said were 3 years of age. Thus, the age of a Cultus Lake male squawfish of the maximum fork length of 40.0 c m would be 10; the age of a female of a maximum fork length of approximately 50.0 cm is 14 years. F r o m the slopes of the r e g r e s s i o n lines, i t would appear that d i f f e r e n t i a l growth of male and female squawfish does not occur, but female lifespan i s greater than that of males. G. Laboratory temperature preference experiment at Cultus Lake Temperature affects the rates of digestion of squawfish. Seasonal temperature regimes undoubtedly provide a range of available temperature and, accordingly, i t i s important to have understanding of some aspects of temperature preference to accurately assess predation by squawfish. 1. Methods A laboratory temperature preference experiment was c a r r i e d out at Cultus Lake (limited experimentation) f r o m November 26 to 30, 1968. The experimental temperature preference tank was made of 5/8 in plywood and was 4 f t x 8 f t x l 6 i n deep. The tank was longitudinally divided (2 in. insulated 5/8 in. plywood walls) into three sections (A, B and C). A notch 18 in. long x 6 in.deep was removed (bottom of the tank) f r o m one end of the two insulated d i v i d e r s . A t the opposite end of the tank, water of different temperatures and regulated flow was admitted. Temperature regulation was controlled by mixing deep lake water (4°C), shallow lake 37 water (11 -15 C), and boiler r o o m water. Outflow and water depth (notched ends) was regulated by three 2 in.elbows and standpipes cent r a l l y located behind each temperature section. The elbows were threaded into the ends of the tank approximately 1 in.off the bottom. E s s e n t i a l l y , the backflow of the heavier, colder water would be reduced by this procedure. Individual gates (with overhead connections) with permascreen openings separated the area anterior to the notches. An overhead pulley f a c i l i t a t e d simultaneous opening of a l l three gates a short distance f r o m the tank (Figure 21). In r e f e r r i n g to Appendix V, remember that the tank was divided into three sections separated by insulated walls. The coldest, intermediate and hottest temperatures were designated as sections A, B, and C. The area anterior to the notches was designated as the experimental zone. The area posterior to the gates was a r b i t r a r i l y called the mix. E a c h of the experimental zones (anterior to the gates) was divided into head (inflow of water), center and foot (outflow of water). Temperatures were recorded by a telethermometer (6 in.below the surface). Water depth approximated 14 i n . This was later modified (due to stratification) to top (surface) and bottom temperatures in the foot region of the highest temperature (section C). Thus, in Appendix V the recording sites within each experimental zone (A, B and C) are designated as head, center, foot (top or bottom) and mix (area posterior to the experimental zone). The temperature and the number of f i s h i n each re c o r d i n g site and/or the mix (considered for the f u l l distance across the tank) is presented i n Appendix V. On November 26, 1968, at approximately 0900, ten f i s h were placed i n the mix of the temperature preference tank. Approximately one hour later the gates were opened. F i s h positions and temperature recordings were c a r r i e d out until after 1100 on November 27, 1968. A t this time eight additional f i s h were placed in the tank. One hour l a t e r the f i s h were released f r o m the mix and temperature recordings and f i s h locations were observed until November 30, 1968. Thus, for a period of five days a group 39 of ten (increased to 18 on the second day) squawfish (acclim. to 11 C) were presented with three temperature ranges (approximately 6° to 8°C, 10°-14°C, and 20° to 24°C). 2. Results A total of 121 squawfish could be assigned to a specific temperature they had selected (Table X I and Appendix V). Of the 22 f i s h recorded in the coldest water, none had selected a temperature 8°C. A l l 22 squaw-f i s h were found in water temperatures between 8.0° - 9.5°C. A total of 61 were observed i n temperatures of 9.6° to 11°0. Another 25 squawfish were observed at temperatures between 11.1°C and 16°C. Only 13 f i s h could be s p e c i f i c a l l y assigned to temperatures greater than 16.1°C. The remaining 30 f i s h were within a temperature range which may have been as high as 25°C; however, this i s possibly high because occasional temperature readings at depths in the highest temperature revealed s t r a t i f i c a t i o n and average temperatures w e l l below 25°C. It therefore seems more l i k e l y that these f i s h (for the most part f i s h recorded at temperatures >16.1°C) were selecting lower temperatures than was indicated by the temperature recorded. F r o m this experiment, it would seem reasonable to assume that when the surface temperature of the lake reaches 11°C, squawfish are l i k e l y to spend only l i m i t e d time i n water below 9.6°C. While completing the digestion experiments, i t was observed that at a temperature below 10.5°C squawfish appear "docile". (J. D. M c P h a i l , pers. comm., also noted this.) A t such times as the lake temperature approaches 11°C, squawfish in the f i e l d ( A p r i l to November) do not appear in this docile state. It i s therefore reasonable to assume that squawfish inhabit water temperatures in the warmer months of the year greater than 10.5°C. This information is important i n specifying the minimum tempera-ture at which f i s h spend the summer months. This w i l l affect estimates of the routine metabolism and the rates of digestion. 40 T A B L E XII. Number of squawfish in various temperature zones of Cultus Lake temperature preference experiment. Temperature Ranges (°C) T r i a l 6.0-9.5 9.6-11.0 11.1-14.0 14.1-16.0 >16.1 Va r i a b l e Temperatures in variable 1 0 0 0 3 0 7 15 - 25.8 2 0 0 0 0 0 10 8.1 - 12.5 3 0 4 4 0 2 0 -4 0 4 0 0. 1 13 8.4 - 22.7 5 13 3 0 0 1 0 -6 0 3 4 9 2 0 -7 0 11 0 2 4 0 -8 3 10 1 2 1 0 -9 3 13 0 0 1 0 -10 3 13 0 0 1 0 -22 61 9 16 13 30 41 H. L i m i t e d information on the voluntary short t e r m consumption  rates of squawfish at Cultus Lake. 1. Methods This experiment was completed at the same time as the temperature preference experiment. The f i s h were held i n digestion tanks (four groups of five each) and presented frozen hatchery trout. One hour late r the weight of food consumed was recorded. A summary of this data i s given i n Table XIII. 2. Results This experiment, although limit e d , i s of some value when related to the approximate basal metabolic rate. The f i s h (mean fork length 28.5 + I. 0 cm) consume an average of 1.91 + .70 gms of prey per day. Assume the energy content of the food (fish flesh) i s equal to 1 Keal/gm wet weight (Winberg, 1956). The squawfish consumed on an average 1.91 + .70 K c a l per day. The average weight of the squawfish was 225.0 gms. F r o m the basal metabolic rates of .00826 .00158 Kcal/gm/day (see section Q), a f i s h of approximately 225.0 gm should consume between .00668 and .00983 Kcal/gm/day. This represents for f i s h averaging 225.0 gms, between 1.4 to 2.2 Kcal/day. The basal requirements based on prey consumption l i e between 1.22 to 2.61 Kcal/day. It therefore seems that the daily consump-tion rates conform approximately to expectation and that oxygen consump-tion could be used for estimating maintenance requirement in model formu-lation. I. L a b oratory feeding p e r i o d i c i t y experiment at Cultus Lake 1. Methods A feeding pe r i o d i c i t y experiment was set up on October 30, 1968. An enclosuf-e of 3/8 in. mesh webbing, 16 ft x 16 ft, and of depth varying f r o m T A B L E XIII. Weight (grams) of frozen hatchery trout eaten by squawfish (various fork lengths) i n the voluntary short t e r m feeding experiment (Cultus Lake, 1968). F-ork length (cm) November 26 November 27 November 28 November 29 Average con-sumption (gm/day) 31.0 3.34 3.34 3.53 3.53 3.44 27.7 2.23 3.34 3.53 3.53 3.41 30.8 3.34 1.11 2.42 0.00 1.72 26.9 3.34 3.34 , 3.53 1.22 2.86 27.2 1.11 2.23 3.53 0.00 1.72 27. 6 0.00 2.23 2.42 2.42 1.77 30.2 0.00 3.34 1.11 0.00 .86 28.1 1.11 1.11 0.00 1.22 .86 28.6 0.00 1.11 2.42 3.64 1.79 29.2 2.23 1.11 2.42 3.64 2.37 28.2 0.00 1.11 0.00 0.00 .28 6 ft to 14 ft, was located i n the lake. Twenty squawfish (4 between 20.0 and 24.9 cm; 11 between 25.0 to 29.9 cm; and 5 between 30.0 to 34.9 cm (fork length)) were placed in the net. One hundred hatchery trout (approximate fork length 2.0 to 4.0 cm) were placed i n the net at 0900 on October 31, 1968. A t designated time intervals (usually 6 hours) the trout remaining were counted, removed and replaced by another 100 trout. Six days later (November 6, 1968) the experiment was terminated. A t this time the squawfish appeared to be i n very poor condition (weak and with fungus in-fection). 2. Results The re s u l t s of the p e r i o d i c i t y experiment are located i n Appendix V and summarized in Table XIV. T A B L E XIV. Laboratory p e r i o d i c i t y of feeding of squawfish on trout at Cultus Lake Consumption / 20 Consumption/ squaw-Time P e r i o d Time Interval squawfish f i s h / t i m e i n t e r v a l a 0900 - 1500 5.8 .29 trout b 1500 - 2100 6.8 .34 trout c 2100 - 0300 3.5 .28 trout d 0300 - 0900 4.6 .23 trout Average daily consumption/squawfish = 1.14 trout/day In some cases the number of f i s h remaining was greater than 100 (Appendix VI). These positive values ( > 100) o c c u r r e d after mid-night sampling. It therefore became necessary to average the consumption rates for the positive value and the value immediately preceding the positive value for the specific number of time intervals that the two values span. It then became possible to calculate the o v e r a l l average values for a, b, c, d (time category a equals time i n t e r v a l between 0900 and 1500, b equals 44 1500 and 2100, c equals 2100 and 0300, and d equals 0300 and 0900). The re s u l t s do not demonstrate a significant difference in the number of f i s h consumed at different times of the day (Figure 22). However, it i s possible that the total energy provided by the l i m i t e d number of hatchery trout (approximately 2 gms each) was inadequate for maintaining the 20 squawfish. Each squawfish on an average consumed 1.14 trout per day and this would probably be a minimum estimate of the i r daily requirements. J . Determination of squawfish winter growth rates f r o m tagging 1. Methods Approximately 100 squawfish were tagged (Petersen tags) and released i n Cultus Lake ( M i l i t a r y rafting area) on the four days October 1, 6, 15, and November 30, 1968. The standard length, fork length, total length, and sex of each f i s h was recorded. The recovery location, date of recovery, fork length and the i n i t i a l data are summarized i n Appendix VII. 2. Results A total of 16 squawfish released i n the f a l l of 1968 were recovered i n the spring of 1969. F r o m October, 1968, to approximately A p r i l , 1969. the increase i n fork length was only .23 _+ .13 cm (mean f o r k length of the sample approximately 30.0 cm). F r o m the equations for growth in F i g u r e s 19 and 20, the annual incre-ments i n length for males and females r e s p e c t i v e l y are 2.87 and 2.62 cm, so that the winter increments are negligible. It i s even possible that this t r i v i a l increase i n length i s co r r e l a t e d with a corresponding decrease i n body weight. It i s then possible to postu-late that there i s essentially no energy input and perhaps even a loss during the winter. Accordingly, it i s probably v a l i d to r e l a t e energy requirements F I G U R E 22. Laboratory calculated p e r i o d i c i t y of feeding of squawfish on hatchery trout (Cultus Lake, 1968). 46 for growth to the increase i n weight only over the summer growing season. K. F i e l d conducted experiments on activity and p e r i o d i c i t y of  feeding (Cultus Lake, 1969) 1. Methods In the spring of 1969 the trap and a number of g i l l n e t s were set i n Cultus Lake. The "zone" areas of the lake and the trap and gillnet loca-tions are shown i n Fig u r e 23. The detailed trap net catches are given in Appendix VIII a n d Appendix IX. On three occasions ( A p r i l 25, May 1 and 9» 1969) the trap was checked at three hour i n t e r v a l s . The catches by period and the stomach contents of the f i s h presumably re f l e c t activity and feeding habits. Since the trap was stationed near the outlet, the data more rea d i l y applies to the consumption of smolts by squawfish. 2. Results By comparing the catches in the trap i n various three-hour periods (Figure 24), it can be seen that the greatest number of squawfish are caught between 2400 and 0600. The average volume of food i n the stomachs at th times (Figure 25) i s also the largest. However, significant differences i n volume cannot be demonstrated, reflecting the wide range of weight of food in the stomachs. Comparing the trap catch of different weeks (Figure 24) with the curve describing smolt migration (Figure 26 and Appendix X), the trap catch increases concurrently with the daily migration of smolts f r o m the lake. It seems reasonable to conclude that squawfish are aggregating on the pathway of smolts and the greatest activity and feeding on smolts i s at night. Smolt migration takes place at the same time as fry emergence (Figure 27 and Appendix XI) and, since there seems to be an aggregation of squawfish near F I G U R E 23. I l l u s t r a t i o n of the zoning, trap location and gil l n e t positions at Cultus Lake (Spring, 1969). F I G U R E 23 Scale: 3/4 mile = 1 inch where A = Outlet B = L i n d e l l Beach C = Dept. National Defence Rafting A r e a Li = Outlet G i l l n e t (smolt migration) M = Rafting A r e a G i l l n e t (smolt migration) N.O = L i n d e l l Beach Gillnets ( F r y emergence) X = Trap Location (1) Appendix II Y = Trap Location (2) Appendix II 1,2,3,4 = Zoning A r e a s of Cultus Lake F I G U R E 24. The three-hour i n t e r v a l trap catch of squawfish f r o m Cultus Lake. F I G U R E 25. The average stomach volume (gms) of squawfish caught at different times of the day (three-hour in t e r v a l s ) . WEIGHT CONSUMED (GRAMS) § NUMBER OF SQUAWFISH TRAPPED to » o i o » S B X * i i i * ' F I G U R E 26. Smolt migration curve for sockeye smolts (Oncorhynchus nerka) f r o m Cultus Lake (Spring, 1969). F I G U R E 27. F r y emergence curve for sockeye fry (Oncorhynchus  nerka) f r o m Cultus Lake (Spring, 1969). MARCH APRIL MAT JUNE 50 the outlet, predation i s probably low on f r y which are l a r g e l y at the oppo-site end of the lake. Gi l l n e t data support this observation. P r i o r to commencing the three-hour p e r i o d i c i t y observations, a l l the f i s h f r o m the previous day were removed and dissected. The number of f i s h taken and the average volumes of stomach contents of these squawfish were greater than those i n the experiment (Table XV). Frequent removals apparently disturb the squawfish i n the v i c i n i t y of the trap. The re s u l t s f r o m the three-hour catches thus probably underestimate squawfish numbers and rates of predation. F o r most observations, the average number of smolts consumed per squawfish during the p e r i o d i c i t y experiments was be-tween 2.22 and 2.62 smolts (volume 8.72 to 13.72 gms), but for the catches before the experiments the range was f r o m 0.39 smolts/predator at the beginning, and .0068 smolts/predator at the end, to 24.8 smolts/predator at the peak of the smolt migration. The average number of smolts in squaw-f i s h taken before experiments tended to follow the pattern of the smolt migration (Table X V and F i g u r e 25). Thus, the p e r i o d i c i t y experiments suggest that activity and consumption are related and most l i k e l y occur to the greatest degree during darkness. In addition, a minimum of at least two smolts per squawfish is consumed during the slow phase of smolt migration ( A p r i l 18 to 24). Approximately 35 per cent of the f i s h examined contained sockeye during the slow phase of migration. F r o m A p r i l 25 to May 19 (peak of migration), 85 per cent of the squawfish examined contained an average of 8 sockeye per squawfish. Li. Population census and migration of squawfish within Cultus Lake The number of squawfish present in Cultus Lake was estimated by the P e t e r s e n mark-recapture method. In the f a l l of 1968, 103 f i s h (1 dead recovery, October 15, Appendix VII) were tagged and released. In the spring a sample of 2992 squawfish recovered 16 previously tagged (Appendix XII). F r o m this a f i r s t approximation of population size of squawfish i s T A B L E XV. The number, average volume, proportion consuming sockeye smolts, and/or fry, and the average number of smolts per squawfish for a l l the squawfish dissected the day p r i o r to and during the 3-hour interval activity and periodicity of feeding experiment. Pr o p o r t i o n con- Average volume Number Average Di s s e c t e d Total suming sockeye (grams) of number of smolts Date (1969) Squawfish catch smolts f r y smolts f r y smolts per squawfish A p r i l 24 trap dissection 18 .33 0.00 2.68 0.00 7 .39 A p r i l 25 experimental 5 .40 0.00 13.72 0.00 13 2.60 May 1 trap d i s s e c t i o n 34 .97 0.00 29.43 0.00 2 52 7.65 May 2 exper imental 18 .78 0.00 8.72 0.00 40 2.22 May 4 trap d i s s e c t i o n 5 1.00 0.00 97.00 0.00 124 24.8 May 9 trap dissection 41 .97 0.00 37.58 0.00 335 8.27 May 10 experimental 32 .7 5 0.00 10.68 0.00 84 2.62 May 20 trap d i s s e c t i o n 47 .04 0.00 .22 0.00 3 .0068 where Experimental = f i s h dissected at 3-hour intervals; Trap dissection = the day's catch of squawfish p r i o r to commencing the experiment. 52 19. 074. With the assumption of a P o i s s o n distribution, the 95 per cent confidence l i m i t s on this estimate are approximately 19.074 + 9.450, or 10,624 to 28,524. Because e r r o r s i n this type of calculation are more l i k e l y to be i n the d i r e c t i o n of causing an overestimate, this may be con-sidered to be a maximum estimate of population s i z e . R i c k e r (1941) suggests a population of approximately 10,000 squawfish. There i s quite a difference i n these estimates, but the author feels the estimate of approxi-mately 20,000 is the better. The gillnetting m o r t a l i t y of Ricker's squawfish (those tagged and released) i s unknown. In addition, his recaptures are biased by gillnet selectivity and the unit effort.of net nights of fishing. The f i s h trap i s also selective (as indicated by the graph of population mortality, (Figure 28). If one accepts the mortality as being correct, then even the estimate of 20,000 may be low. The 104 f i s h tagged and released in the f a l l of 19.68 had fork lengths of 15.5 to 36.4 cm. Only nine of the marked f i s h were less than 20 cm and none of these were recaptured. One could say that the experimenter was only effectively tagging and releasing squawfish that theore t i c a l l y were a l l potential predators (over 20 cm). More corr e c t l y , then, the estimate of 20,000 should r e f e r to the squawfish that are over 20 cm and known to be predators. This would increase the estimate of the total population of squawfish i n the lake. Thus, it i s d i f f i c u l t to accept Ricker's estimate as accurate for model calculations. M i g r a t i o n within the lake can be assessed by two separate methods. F i r s t , since a l l the squawfish were tagged and released at the army base site, the recovery of f i s h in different areas of the lake should give an i n d i -cation of d i s p e r s a l . Of the 16 f i s h recovered, nine were recaptured at the spring trap site. Three squawfish each were captured in gillnets at the army base (rafting area gillnet) and L i n d e l l Beach. One squawfish was captured in the outlet gillnet. E s s e n t i a l l y , then, d i s p e r s a l to other parts of the lake takes place but an aggregation near the outlet in the spring is apparent. FIGURE 28. Population mortality of Cultus Lake squawfish as determined by the plot of the age of the fish vs the log of the number of fish. F IG28 QJLTUS'LAKE - AGE VS LEG (NUvEER OF FISH) Y = 0-H17E 02 + -Q'BCfSEE COX N = 7 THE PROBABILITY CF THE SU3FE EONS ZERO IS 0-0000 RSQ = 0-281211 O332ELATI0N I33SFFILTENT R = 0-S905S1 12 . i ; 0 S 10 IS AGE (YEARS) 54 In the spring tagging program approximately 1200 squawfish were tagged and released into the four zones of the lake. A total of 407, 105, 152, and 559 squawfish were released respectively i n zones 1, 2, 3, and 4. Over the period May 1 to June 3, 1969 (not including the tag releases of June 3), 13.1 per cent (45 of 341), 12.4 per cent (13 of 105), 32.1 per cent (17 of 53), and 10.6 per cent (54 of 508) of the releases f r o m zones 1, 2, 3, and 4, respectively, were recaptured at the trap in zone 3. There i s not an apparent difference in the percentage of f i s h captured f r o m zones 1, 2, and 4, but r e c o v e r i e s f r o m zone 3 were at three times as great a rate. The distance between the trap and zone 4 i s short in r e l a t i o n to the distance between the trap and zones 1 and 2 (Figure 23). It seems that movement f r o m zones 1, 2 and 4 to the outlet is substantial and that the various di f -ferences i n distance involved are not a significant factor i n movement. The whole population of squawfish could w e l l be involved i n active predation at the outlet. The increase in the percentage of recaptures of squawfish f r o m zone 3 (32.1 per cent) suggests that the trap l i e s on the major migration pathway of smolts ( s i m i l a r suggestions were reported by R i c k e r , 1941). The best estimate of consumption and periodicity of feeding of squawfish on smolts should be f r o m f i s h sampled i n zone 3. The remainder of the population i n different areas of the lake presumably r e f l e c t s consumption in other areas of the lake. In conclusion, the population of predaceous squawfish within the lake i s estimated at 20,000, aggregation on the smolt migration pathway apparently occurs and d i s p e r s a l f r o m other zones of the lake to the outlet i s substantial. F i n a l l y , distance i n a lake the size of Cultus does not seem to be a factor influencing the degree to which squawfish can aggregate at smolt concentra-tions. 55 M. F i e l d conducted digestion experiments 1. Methods In the spring of 1969. concurrent with gillnetting, p e r i o d i c i t y t r i a l s and tagging, a f i e l d digestion experiment was completed. The l i v e trap provided, after two days (1200 May 1 to 1000 May 2, 1969) of fishing, approxi-mately 700 f i s h which were divided into five groups (suspended in the lake i n 3/4 in mesh tanks (6 ft x 8 ft x 6 ft deep) ). A f t e r sorting, one group of f i s h was k i l l e d and preserved to establish the average quantity of food i n the stomachs at time of capture. A f t e r 6, 12, 18 and 24 hours, additional groups were preserved i n 10 per cent formaldehyde. 2. Results In the analysis, the squawfish were divided into one centimeter groups f r o m 24.6 cm to 34.5 cm. The average volumes at time zero show that there i s an increase i n volume with increase in size of f i s h (Figure 29). In Table X V I the intercepts and slopes of the f i e l d digestion squawfish (voluntary con-sumed food) are compared to the slopes and intercepts of laboratory force-fed squawfish (temperatures comparable). A n a l y s i s of covariance for f i e l d digestion experiment showed that there is no significant difference i n the rates of digestion for different size f i s h ; however, the intercepts are signi-ficantly different (Appendix XIII). Moreover, the slopes and intercepts of the f i e l d digestion experiment f a l l within the l i m i t s set by the low and high feeding levels of the laboratory conducted digestion experiments. In most cases the intercepts and slopes for the f i e l d experiment approximate the laboratory medium feeding l e v e l . This i s to be expected as the laboratory medium lev e l was established f r o m the average volume versus fork length of squawfish dissected at G r i f f e n Lake. FIGURE 29 . Cultus Lake field conducted digestion experiment. Plot of the log (average volume (gms) ) + 1 vs the fork length (cm) for the sample of squawfish con-sidered to be at initial feeding or time zero. FIG 29 Q J L T T J S L A K E - S T D d - C E N T - AVE- VOL- VS- FTJFK L E N G T H Y = -O-S^S: 01 •»• 0-1541E OOX N = 10 THE PRLBAaiLXTY CF THE SLLFE EEIM5 ZERO TS 0-0002 RSQ = 0-B47573 LLfcJ-r 1L1ENT R = G 4 ; ; • ~ 5 + 0 1 M I I I I I'l ! I I I I 1 I I I I i I I I I I I I I | | | I | | | -10 15 B O S S 30 35 4 0 4 5 FORK LENGTH (CM) TABLE XVI. Comparison of the slopes (b) and intercepts (a) of the laboratory and field digestion data (temperature approximately 10°C) (from plots of log (weight (grams)) + 1 vs time (hours) ). CULTUS LAKE LABORATORY RESULTS CULTUS LAKE FIELD RESULTS Fed all vols. Fed low vols. Fed med. vols. Fed hig h vols. Fork length a b a b a b a b Fork length a b 20.0 - 24.9 1.369 -.0455 .647 -.0257 1.612 -.0626 2.028 -.0501 24.6 -25.5 1.165 -.0427 25.0 - 29.9 1.332 -.0279 .720 -.0252 1.641 -.0558 2.043 -.0254 25.6 -26.5 1.206 -.0309 26.6 -27.5 1.169 -.0395 27.6 -28.5 1.159 -.0405 28.6 -29.5 1.251 -.0340 30^ 0 - 34.9 1.444 -.0279 .975 -.0318 1.598 -.0359 2.374 -.0467 29.6 -30.5 1.624 -.0 524 30.6 -31.5 1.715 -.0519 31.6 -32.5. 1.858 -.0369 32.6 -33.5 1.982 -.0 549 33.6 -34.5 . 2.296 -.0643 Sizes and volume pooled (laboratory data) 1.375 .0307 58 N. The available seasonal trap catch data f r o m G r i f f e n and  Cultus lakes and the temperature patterns in Cultus Lake F r o m the trap catch data i t is possible to determine the length of time squawfish spend on the shoal of the lake. Since the trap fishes approxi-mately 30 feet deep, i t r e flects activity within a c e r t a i n depth and tempera-ture regime. Reference to F i g u r e 30 (where the squawfish population i s considered absent when the daily trap catch is less than five f i s h per trap day) shows that the squawfish migrate f r o m the shoal area in mid-October and reappear on the f i r s t of May. This agrees with data suggested by R i c k e r (1941). The trap catch would presumably r e m a i n high during the summer as indicated by G r i f f e n Lake data (Appendix IV). The f i s h in the shoal area would thus be exposed to temperatures within 30 feet of the sur-face. The seasonal changes i n temperature in Cultus Lake over three years (1934, 1935 and 1.936) were given by R i c k e r (1937). Pooling the temperature estimates (taken at 5 m depths) above and below 10 m yields the r e s u l t s in F i g u r e s 31 and 32. Below 10 m the mean temperature never reaches 11°C, but above 10 m the mean temperature is. greater than 11°C f r o m ea r l y May until the end of October. A c c l i m a t i o n to an increase i n temperature i s 20 times faster than the acclimation to a corresponding decrease in tempera-ture (Winberg, 1956). Therefore, i n the f a l l (mid-October to mid-December) and in the spring ( A p r i l 1 to May 1), when the squawfish are not on the shoal area of the lake, they are most l i k e l y exposed to the temperatures of the lake above 10 m. By mid-December the lake i s essentially uniform in tempera-ture and the squawfish are exposed to the temperatures of the lake below 10 m (mid-December to A p r i l 1). O. The use of gillnet data to study the effect of squawfish on smolt  migration and f r y emergence To assess squawfish predation on sockeye smolts and fry, two gillnets, F I G U R E 30. The calculated daily trap catch between trap checks at Cultus Lake ( F a l l 1968 and Spring 1969). 59 / F I G U R E 31. F I G U R E 32. The average seasonal change in temperature for depths less than 10 meters (0, 5, 10 meter tem-perature values are pooled) (Ricker, 1937). The average seasonal change in temperature for depths greater than 10 meters (15, 20, 25, 30, 3 5, 40 meter temperature values are pooled) (Ricker, 1937). TEMPERATURE C * A CD O R X 0> S O 61 one of 1-7/8 i n . m e s h and the o ther of 3-5/8 i n . m e s h w e r e f i s h e d f r o m A p r i l 4 to J u n e 10, 1969 ( T a b l e s X V I I and X V I I I ) o n the s m o l t m i g r a t i o n p a t h w a y and the f r y e m e r g e n c e a r e a . C o m p a r i n g t h e g i l l n e t d a t a and the s m o l t m i g r a t i o n ( T a b l e X V and F i g u r e 26) c u r v e , i t c a n be o b s e r v e d that the g r e a t e s t n u m b e r of s m o l t s p e r s q u a w f i s h s t o m a c h ( a p p r o x i m a t e l y two) o c c u r at the peak of s m o l t m i g r a t i o n . S i m i l a r l y , the p o i n t of m a x i m u m c o n s u m p t i o n of f r y ( T a b l e X V I I I ) i s c l o s e to the p e a k of f r y e m e r g e n c e ( F i g u r e 27). B o t h the a v e r a g e n u m b e r and v o l u m e of f r y a n d s m o l t s a p p e a r l o w ( T a b l e X V I I ) and t h i s d a t a p e r h a p s u n d e r e s t i m a t e s the p o t e n t i a l c o n s u m p -t i o n r a t e s . T h e e f f e c t s of s u c h f a c t o r s as r e g u r g i t a t i o n l o s s e s , the t i m e b e t w e e n c a p t u r e and l i f t i n g of the net , a n d the a s s o c i a t e d d i g e s t i o n a r e u n k n o w n . A d d i t i o n a l l y , the g i l l n e t s a r e h i g h l y s e l e c t i v e . N u m e r o u s s c u l -p i n s a n d o n l y a f e w of the s m a l l e r s q u a w f i s h c o n t a i n e d e m e r g i n g f r y , and t h u s t h e r e i s a l i m i t e d s i g n i f i c a n c e to s t o m a c h c o n t e n t s b a s e d o n g i l l n e t s e l e c t e d s i z e s . The a v e r a g e v o l u m e i s s m a l l ( u s u a l l y 2.25 g m s ) a n d i s , f o r the s e v e r a l r e a s o n s g i v e n , a d u b i o u s v a l u e as a n e s t i m a t e of i n t e n s i t y of p r e d a t i o n . A l t h o u g h the d a t a i s r e p o r t e d , i t s s i g n i f i c a n c e and the v a l u e i t p r o v i d e s to a f i n a l m o d e l f o r m u l a t i o n i s q u e s t i o n a b l e . . P . R e p r o d u c t i v e c o n d i t i o n and the p o t e n t i a l egg d e p o s i t i o n  of s q u a w f i s h f r o m C u l t u s L a k e S p a w n i n g i s a n i m p o r t a n t event i n the l i f e c y c l e of f i s h , and the r e p r o -d u c t i v e c o n d i t i o n m a y a f f e c t the d e g r e e of p r e d a t i o n . F o r t h i s r e a s o n , the r e p r o d u c t i o n ( n o n - s p a w n i n g , d e v e l o p i n g or spawning!) of e a c h s q u a w f i s h w a s r e c o r d e d . In a d d i t i o n , the p o t e n t i a l egg d e p o s i t i o n t o the p o p u l a t i o n w a s c a l c u l a t e d f r o m t o t a l o v a r y w e i g h t s a n d c o u n t s of s a i m p l e s f r o m the o v a r i e s ( T a b l e X I X ) . F r o m the s a m p l e of f e m a l e s c o l l e c t e d ! at C u l t u s L a k e the a v e r a g e w e i g h t of o v a r i e s f o r s p a w n i n g f i s h ( s i z e n e t c o n s i d e r e d ) w a s 66.26 + 22.03 g m s . T h i s w e i g h t r e p r e s e n t s b e t w e e n 16,7^(6 and 30,423 e g g s . O v a r y w e i g h t i n c r e a s e s w i t h f o r k l e n g t h of the s q u a w f i s h ( F i g u r e 33 a n d A p p e n d i x X I V ) . If t h e r e i s an e q u i v a l e n c e i n e n e r g y l o s s f o r eggs and s p e r m TABLE XVII. Consumption of sockeye smolts by squawfish as determined by a unit effort of gillnet on the smolt migration pathway of Cultus Lake. Date (1969) Time Total catch Proportion with sockeye Average volume (mis) Number of smolts Number of fry Average number of smolts per fish smolts fry smolts fry April 22 0600 13 .077 0. 0.50 0.00 1 0 .078 April 29 0600 8 .375 0. 0.65 0.00 4 0 .50 May 5 0100 5 .20 0. 1.75 0.00 3 0 .60 May 5 0500 18 .11 0. 0.34 0.00 2 0 .11 May 13 0200 1 1.00 0. 3.69 0.00 2 0 2.00 May 19 0200 34 0.00 • . 0. 0.00 0.00 0 0 0.00 May 19 0500 35 0.00 0. 0.00 0.00 0 0 0.00 May 26 0100 30 0.00 0. 0.00 0.00 0 0 0.00 May 26 0600 25 0.00 0. 0.00 0.00 0 0 0.00 June 3 0200 28 0.00 0. 0.00 0.00 0 0 0.00 June 3 0500 20 0.00 0. 0.00 0.00 0 0 0.00 June 10 2430 16 .063 0. 1.05 0.00 0 0 .063 June 10 0430 43 .023 0. .00 5 0.00 0 1 .00 5 June 15 0930 28 0.00 0. 0.00 0.00 0 0 0.00 TABLE XVIII. Consumption of sockeye fry as determined by a unit effort of gillnet on the fry emergence area of (Lindell Beach) Cultus Lake. Date (1969) Time Total catch Proportion with sockeye smolts fry Average volume (mis) smolts fry Number of smolts Number of fry Average Number of smolts or fry per fish smolts fry April 4 0 900 3 0. 0. 0.00 0.00 0 0 April 14 0 500 18 0.0 55 0.055 4.25 0.25 1 1 0.0 55 0.055 April 22 0 500 20 0.10 0.00 1.87 0. 2 , 0 0.10 0.00 April 29 0600 22 0.045 0.045 0.12 0.20 1 1 0.12 0.09 May 5 2445 14 .072 0.20 0.11 0.11 1 22 0.072 1.57 May 5 0600 25 .080 0.24 0.24 0.07 3 12 0.12 0.41 May 13 2425 17 0.00 0.17 0.00 0.02 0 3 0.00 0.018 May 13 0100 19 0.00 • 0.16 0.00 0.051 0 7 0.00 0.037 May 13 0 500 26 0.00 0.115 0.00 0.056 0 8 0.00 0.326 May 19 2430 5 0.00 0.00 0.00 0.00 o 0 0.00 0.00 May 19 0630 13 0.00 0.00 0.00 0.00 . 0 0 0.00 0.00 May 26 2410 5 0.00 0.00 0.00 0.00 0 0 0.00 0.00 May 26 0 500 4 .25 0.00 1.19 0.00 2 0 0.50 0.00 June 3 2430 7 0.00 0.00 0.00 0.00 0 0 0.00 0.00 June 3 0600 8 0.00 0.00 0.00 0.00 0 0 0.00 0.00 June 10 0100 3 0.00 0.00 0.00 0.00 0 0 0.00 0.00 June 10 0 500 11 0.00 0.00 0.00 0.00 0 0 0.00 0.00 T A B L E XIX. Number of eggs i n squawfish (spawning and non-spawning) of various fork lengths (cm) (Cultus Lake, A p r i l - J u n e 1969). • ' Weight of Weight of Number of Number of Sample Reproductive sample ovaries eggs per eggs per Number Condition (grams) (grams) sample fi s h F o r k length 2 spawning 3.0 41.81 912 12, 710 35.2 3 spawning 3.0 51.94 1, 042 18, 040 34.5 4 spawning 3.0 53.70 1, 30 5 23, 360 31.2 5 spawning 3.0 42.43 1, 067 15, 091 32.4 6 spawning 3.0 36.19 2, 041 24,621 31.0 8 spawning 3.0 47.28 1, 175 18, 518 29.1 11 spawning 3.0 89.60 873 26, 074 36.1 12 spawning 3.0 87.22 885 25, 730 37.5 13 spawning 3.0 120.60 1,016 40, 843 40.5 15 spawning 3.0 144.60 971 46, 80 2 49.0 16 spawning 3.0 46.35 1, 335 20, 626 31.3 17 spawning 3.0 30.43 1, 075 10, 904 29.0 Average 23, 610 34.7 5 per cent lower l i m i t 16, 796 31.1 5 per cent upper l i m i t 30,423 38.3 1 non-spawning 1.0 4.95 too s m a l l no estimate 31.8 7 non-spawning 1.0 8.94 706 6, 312 29.9 9 non-spawning 1.0 11.40 1, 079 12, 301 31.0 10 non-spawning 1.0 10.26 647 6, 638 33.8 14 non-spawning 1.0 9.27 979 9, 075 31.3 Average 8, 582 5 per cent lower l i m i t 4, 183 28.9 5 per cent upper l i m i t 12, 980 34.1 F I G U R E 33. P l o t of the weight (gms) of the ovaries spawning squawfish vs the age (years). FIG 3 3 QJLTLB LAKE-WEIGHT OF OVARIES (GM) VS AGE (YEARS) Y = -0-4535E OB + 0.1541E 02X N = 49 THE PFcOBABILITY OF THE SLOPE BEING ZERO IS 0-0000 RSQ = 0-759757 UJif^ ELATTOSI OJEr-rlCIENT R = 0-B773E3 200 5 lO AGE (YEARS) 66 and this loss of gametes is equivalent for a l l sizes of spawning f i s h and to energy stored in one gram of fish, the energy expenditure on reproduction can be calculated for a population. It appears, and i s supported by Cart-wright (1956), that squawfish spawn each year. Assuming that the energy equivalents for eggs (trout and kokanee) average 1.30 K c a l of energy per g r a m of wet weight of tissue (Sandercock, 1969), the energy required by the total population i s r e a d i l y calculated. This information can be used in model formulation. Q. Determination of the basal metabolic rate of squawfish 1. Methods In the spring of 1968, a laboratory experiment on G r i f f e n Lake squaw-f i s h (acclimatized to 9° to 12°C) was completed to calculate the basal meta-bolic rate. Numerous works relating oxygen consumption to metabolic rate have been reported for a number of species of f i s h . F o r example, Brett (1962), stated that i t should be the aim to relate energy and work performed to efficiency of production. Hoar (1966) and Brett (1962) pointed out that oxygen debt, activity, carbon dioxide, temperatures, starvation, a c c l i m a -tion and season were important factors influencing metabolic rate. The determination of squawfish basal metabolism is an obvious f i r s t step in estimating food consumption. Oxygen consumption was measured on two squawfish, one 252 gms and the other 234 gms. The f i s h were housed i n air t i g h t containers of known oxygen saturation. After designated time intervals, duplicate water samples were titrated (the t i t r a t i o n value averaged) to determine dissolved oxygen levels by the Winkler method. Replicates of each f i s h were completed. The calculation of metabolic rate was as described by Hoar and Hickman (1967), and K l e i b e r (1961). 67 2. Results The data reported i n Appendix X V and Appendix XVI give the basal metabolic rates with 95 per cent confidence intervals as 108.54 _+ 20.89 mgm O /kg/hr, or .00826 + .00158 Kcal/gm/day for temperatures close to 10°C. The value of 108.54 + 20.89 mgm 0 2/kg/hr i s f a i r l y close to those of Beamish (1964) of 80.8 and 79.3 mgm/kg/hr for Salmo trutta and Sal mo fontinalis at 10°C. It therefore seems reasonable to use the figure of .00826 + .00158 Kcal/gm/day (based on two fish, 252.0 and 234.0 gms) to establish a maintenance requirement for individuals of a population. Winberg (1956, Table XIX) gives an energy requirement of .0115 Kcal/day (temperature 20°C) as a pooled estimate for a l l f r e s h water f i s h (weight = 300 gms). The value of .00826 + .00158 Kcal/gm/day at 10°C corresponds to a value at 20°C of .0228 + .00425 Kcal/gm/day (Table XXX), which i s almost twice Winberg's figure. This is possibly due to excessive activity. Winberg (1956, p. 110) states that " i t was found that basal metabolism com-posed about 60 per cent of routine metabolism." Assuming that my re s u l t s are perhaps more righ t l y reflecting routine metabolism, an adjustment using Winberg's 60 per cent figure gives a BMR of 67.9 mg/kg/hr, or .005016 + .000944 Kcal/gm/day. It i s this routine metabolism value which r e p r e -sents the best estimate for squawfish metabolism on which the model w i l l be fundamentally structured. R. Length-weight relationship F i g u r e s 34 and 3 5 depict weight in rel a t i o n to fork length in arithmetic and log plots. Conversion of the fork length to age provides a means of establishing a weight for any f i s h of given age (Figures 36 and 37). A l l of these figures were constructed f r o m a large sample of squawfish collected at Cultus Lake. F I G U R E 34. Length-weight relation. P l o t of the weight (gms) of a sample of squawfish vs the fork length (cm). F I G U R E 35. Length-weight relation. P l o t of the log (weight (gms))of a sample of squawfish vs log (fork length (cm)). F I G U R E 36. Length-weight relation. P l o t of the weight (gms) of a sample of squawfish vs age (years). F I G U R E 37. Length-weight relation. P l o t of the log (weight (gms)) of a sample of squawfish vs log (age (years) ). WEIGHT (GM) WEIGHT (GM) CO 69 III. SYNTHESIS The foregoing provides information which can be used to synthesize an estimate of total annual consumption of f i s h as food by a squawfish population. The synthesis could be applied to any population but, in the following, the Cultus Lake squawfish population i s used for i l l u s t r a t i o n . Two ways of estimating total f i s h consumption are presented. F i r s t , it i s possible to estimate preda-tion f r o m what is observed to be present in the stomachs of squawfish. This method requires knowledge of volumes of food eaten, frequency of eating for various sizes of f i s h at various temperatures and times of the year. Second, it is possible to estimate predation by calculation of energy requirements essential for routine and active metabolism, growth and reproduction. Both methods require as an i n i t i a l step an estimate of the numbers of f i s h of various ages and sizes in the population. A. Population distribution by age and season The estimated population of squawfish of age 3 and over i n Cultus Lake may be taken as 20,000. The calculated numbers of various ages with a natural m o r t a l i t y of 55.2 per cent per year (based on F i g u r e 28; l i s t e d in column two of Table XXI). Squawfish less than 20 c m are also predators, and most age 2 f i s h (average length 18-19 cm) should be included as part of the predator population. Assuming that the rate of m o r t a l i t y i s the same for age 2 to 3 as at older ages, it is possible to estimate the number of predators at age 2, and this i s included in Table XXI. The intensity of food consumption and the rate of digestion are, of course, seasonablly variable, and the numbers of f i s h of any age changes during the year. The year was divided into s i x seasonal phases or time i n t e r v a l s . F o r Cultus Lake (Table XX) and for each phase the abundance of squawfish was calculated for the mid-point; i.e., N t . N o ( - 8 0 3 / 3 6 5 ) t _ 70 where N^ = the number of f i s h of any pa r t i c u l a r age at the mid-point of a phase; = the number of f i s h of any pa r t i c u l a r age at the beginning of the "early smolt pha^se"; t = the number of days f r o m the beginning of the year to halfway through the phase for which the population estimate i s being calculated. T A B L E XX. The seasonal phases used in calculation of consumption of f i s h by squawfish in Cultus Lake. Approximate dates of Phase beginning and ending No. of days 1. E a r l y smolt migration A p r i l 1 8 - A p r i l 24 7 2. Peak smolt migration A p r i l 25-May 19 25 3. Spawning May 20 - June 30 41 4. Summer July 1 -September 30 92 5. F a l l October 1-November 30 61 6. Winter December 1 - A p r i l 17 139 B. The effect of temperature on the rate of digestion F r o m the digestion experiments the slopes b^ and b can be used to calculate the percentage decrease i n volume of food/hour during digestion in the laboratory. This would essentially be the routine rate of digestion. F r o m Tables IX and X the rate of digestion averages 3 per cent per hour (based on pooled volumes fed and pooled sizes of fisJb.). A more r e a l i s t i c approach would be to compare the laboratory rates of digestion with the f i e l d conducted digestion experiment (Table XVI). l a t h e f i e l d , the slopes approximate .05 and this i s approximately a 5 per cent decrease in volume/ hour as compared to a 3 per cent decrease per hour i n laboratory e x p e r i -ments at the same temperature. At higher temperatures the rates of digestion would be greater than those indicated by the laboratory values. 71 F o r f i s h in the laboratory at summer temperatures of between 15 C and 20 C, the rate of digestion was calculated to be 5 per cent per hour. This rate i s the same as for the f i e l d conducted digestion experiment at a lower tempera-ture of 11°-12°C. It therefore does not seem unreasonable to increase the estimated rates of digestion in the f i e l d for the higher temperatures. F o r temperatures near to 15°C, a 7 per cent decrease in. volume per hour w i l l be used. At temperatures that are s t i l l higher and approach the summer maxi-mum (near 19°C), a 10 per cent per hour rate of digestion w i l l be used in the calculations. This is suggested and is evident in the laboratory conducted o o experiments at 15 C and 20 C. A t these higher temperatures the rates of digestion were described by two separate lines having slopes b^ and b (Table IX and Table X). The percentage decrease per hour i s substantially higher shortly after feeding (Table XXII). The estimates of rates of digestion are to be u t i l i z e d i n two different ways. F i r s t , the volumes found in the stomachs are to be adjusted to ref l e c t the digestion that had occurred since the f i s h were caught (say in a gillnet). Second, the rates of digestion are to be converted to estimates of amounts of food consumed per 24 hours. F o r the summer and f a l l phases of the year, the rates of digestion used in the calculations of the daily r a t i o n (amount of digestion that can occur i n 24 hours) are w e l l below twice the routine rate that Winberg (1956) suggests as a normal maintenance metabolic rate. The active metabolism is s t i l l greater than the maintenance level, and therefore the adjusted estimates i n Table XXIII tend to minimize the rate of digestion. Winberg (1956) estimates that the maximum digestible energy i s approximately 80 per cent of the daily ration. In the present calculations it is assumed that sockeye smolts and f r y are 100 per cent digestible. Nevertheless, i n the calculation of the daily ration the time for the volume to decrease by 80 per cent (Table XXIV) (when exposed to the temperature during a seasonal phase and thus a specific rate of digestion) is considered an T A B L E XXI. Ages, number and frequency distributiun of potential predators remaining in Cultus Lake during mid phase of any phase of the year. Calcul ated E a r l y smolt Peak smolt Spawning Summer F a l l Winter Age Di s t r i b u t i o n phase phase phase phase phase phase 1 2 24, 459 24, 271 23,431 21,791 ' 18, 825 15, 909 12, 767 3 11, 006 10, 873 10, 497 9, 762 8, 434 7, 127 5, 720 4 4, 955 ' 4, 871 4, 703 4, 374 3, 778 3, 193 2, 562 5 2, 223 2, 182 2, 107 1, 959 1,693 1, 430 1, 148 6 1, 000 978 944 878 758 641 514 7 450 438 423 393 340 287 230 8 202 196 189 176 152 129 103 9 92 88 85 79 68 58 46 10 41 39 38 35 31 26 21 11 19 18 17 16 - 14 12 9 12 8 8 8 7 6 5 4 13 4 4 4 3 3 2 2 1^ T A B L E XXII. Summary of the pooled routine percentage decrease in the stomach volume/hour for squawfish of various sizes fed a range (low, medium and high) of volumes of food at different laboratory temperatures. The time lag p r i o r to digestion commencing is also included i n the table for laboratory experiments (Tables IX and X). The f i e l d conducted decrease i n stomach volume per hour is summarized f r o m Table XVI. Temperature Time lag (hrs) Percentage decrease in volume i n per cent per hour based on the slope b^, pooled volumes (Table X) Percentage decrease i n per cent per hour on the slope b (Table IX) Percentage decrease i n per cent per hour based on a pooled estimate of slopes b, f r o m the f i e l d conducted digestion ex-6 6 0%/hour for six hours 3%/hour 1° 6 1%/hour for six hours 3%/hour 5%/hour 15 0 10%/hour for six hours 5%/hour • 20 0 15%/hour for four hours 8%/hour 24 0 20%/hour for four hours 8%/hour —0 OJ T A B L E XXIII. The rates of digestion for the different phases of the year. The rates were either determined by the routine rate of digestion and the predominant temperature within each phase (Figure 31), or were elevated as indicated by the slopes of reg r e s s i o n lines bi^ and b f r o m the laboratory and f i e l d conducted digestion experiment completed at Cultus Lake. The adjusted rate i s the rate that should p r e v a i l as suggested by the lake temperature. Routine rate of Adjusted rate of Phase digestion digestion E a r l y smolt migration phase 3 % per hour 3% per hour Peak smolt migration phase 3 % per hour 5% per hour** Spawning phase 3 % per hour 5% per hour** Summer phase 5% per hour 1 0 % per hour F a l l phase 5% per hour 7% per hour Winter phase 3 % per hour 3% per hour ** f i e l d conducted digestion experiment data T A B L E XXIV. Time required (hours) to reduce stomach volumes by 80 per cent of i n i t i a l volume (calculations based on R i c k e r (1958), Appendix V, and the adjusted rates of digestion, Table XXIII). Seasonal Phase Time required to reduce volume by 8 0 % E a r l y smolt migration 53 hours Peak smolt migration 32 hours Spawning 32 hours Summer 16 hours F a l l 23 hours Winter 53 hours 75 adequate base on which to calculate the amount of digestion that can occur in 2 4 hours. The procedure of calculation of food consumed in 2 4 hours is thus as follows: 1. The observed weight of stomach contents is converted into a weight eaten from consideration of the probable time between feeding and capture (t), and the ambient temperature for the season of the year (T). Thus, if the observed weight of food is Fj., then the weight eaten by given by R T i t e x • where Rrp is the routine rate of digestion at the ambient temperature as given in Table XXIII. 2. The quantity Fjr; is then converted into an estimate of food consumed in 2 4 hours (F-Q) using the relation F D = FE ("F^~ ) ^ T 8 0 where TgQ is the time required to digest 8 0 per cent of the food in the stomach (Table XXIV). 3. By substitution, in the above two equations, we have as the daily ration F° = C^ ^ 8 0 C. A n estimate of squawfish predation based on consumption 1. E a r l y smolt migration volumes During the early phase of smolt migration approximately 33 per cent of the squawfish contained food, and they contained an average of 0 . 3 9 smolts or 2.68 grams of food. The time lag between feeding and dissection was 76 estimated as eight hours. A t a digestion rate of three per cent per hour, the volume i n the stomach represents 78 per cent of what was eaten. The ad-justed food volume is thus 3.44 grams of food. This volume is for squaw-f i s h of an average length of between 28 and 29 cm and age of s i x years. Volumes for other ages (Table XXV I ) were scaled to be in proportion to 3.44 grams, as indicated by the r e l a t i v e volumes observed for the f i s h of various ages during the peak smolt migration. 2. Peak smolt migration volumes During the peak of migration, 85 per cent of the squawfish contained fi s h , and they contained an average of 8 smolts or an average volume of 33.0 grams. Just p r i o r to the peak of smolt migration the f i e l d conducted digestion experiment was completed (Table XV I , F i g u r e 29). Ninety-five per cent contained, f i s h in their stomachs, and this figure was used in calcu-lations (Table X X V ) . This experiment enabled estimation of the average volume of food at dissection for various ages of f i s h . The time lag between feeding and dissection was 12 hours, the rate of digestion was 5 per cent per hour, so the volumes present represented 58 per cent of what was present 12 hours previously. It is possible that the volume estimates i n Table X X V I may be underestimates because there was also f i e l d evidence of f r y consumption, and f r y may be digested more rapidly (see Table XVII I ) . 3. Spawning volumes The average volume in the spawning phase was calculated f r o m G r i f f e n Lake data. In most cases only a trace amount (0.25 mis) was recorded in the stomachs of dissected fish. This compared with s i m i l a r observations at Cultus Lake. The proportion of spawning f i s h of various ages consuming prey was based on conversion of fork lengths to age (Figure 8). The spawning volumes were adjusted for an eight hour lag period between feeding 77 activity and dissection. The volumes were compensated for a routine rate of digestion of 5 per cent per hour. The adjusted volume then became 0.36 gms per f i s h at a temperature of approximately 11°-12°C (Table X X V I ) . 4. Summer volumes The proportion of f i s h feeding and the average volume was based on a large number of predators dissected at Gr i f f e n Lake. The average volume for each age is based on conversions f r o m fork lengths. In Gr i f f e n Lake the squawfish were found to be most active between 0100 - 0500. Most of the dissections were c a r r i e d out between 0900 - 1000. This i s an eight hour delay f r o m the mean of the most active feeding times to dissections. During the summer phase the lake temperature fluctuated over a range of 15°-20°C. The adjustment for volume was based on laboratory routine rates of diges-tion of 5 per cent per hour, which minimizes the adjusted volume and thus the postulated effect of squawfish as predators. The adjusted volumes for each size of squawfish are l i s t e d i n Table XXVI. 5. F a l l volumes While completing the p e r i o d i c i t y of feeding experiment (Table XIV) and the laboratory short t e r m voluntary consumption experiment (Table XIII), averages of 1.91 and 2.28 gms per day (range 20-35 cm; age 3-8) were respectively recorded for squawfish i n each of the experiments at ambient lake temperatures. The average adjusted summer volume for predators i n this length range was 5.97 gms per day (an average based on Table X X V I ) . Using this figure, the f a l l volume i s only 35 per cent of the recorded summer adjusted volumes, and this figure was used to scale summer food volumes to reasonable estimates of f a l l consumption (Table X X V I ) . It was assumed that the proportion of squawfish consuming prey was the same as the summer proportion. 7 8 6. Winter volumes Ricker ( 1 9 4 1 ) during the winter phase (Table I ) has two estimates based on dissections (January-April) for the winters of 1 9 3 2 - 3 3 and 1 9 3 6 - 3 7 . For the winter of 1 9 3 2 - 3 3 an average volume of 0 . 3 4 gms per predator was recorded and 4 7 per cent of the fish examined (length range 1 0 - 4 0 cm) contained sockeye. During January-April of 1 9 3 6 - 3 7 for pooled sizes of squawfish, 3 2 per cent contained 1 . 3 6 gms. These proportions of squawfish acting as predators are within the range and closely approximate the proportion obtained for Griffen Lake summer fish. There does, however, seem to be a potential error in the average volume estimates. It is difficult to believe that this is accountable strictly by sampling, and is more likely explained by differences in the sizes of squawfish examined and differences in abundance of smolts in the lake. For the present calculations a volume of 0 . 5 gms was assigned to squawfish six years of age (which is an average of . 0 1 gms greater than the lowest estimate of Ricker ( 1 9 4 1 , Table V I , p. 3 0 5 ) for squawfish (range 2 0 0 - 2 9 9 mm) in the winter of 1 9 3 2 - 3 3 ) . This estimate is also 0 . 4 9 gms smaller than the average volume found in the stomach of predators didssected during the winter phase of 1 9 3 6 - 3 7 for squawfish in the length range of 2 0 0 - 2 9 9 mm). The corresponding volumes for the various ages were obtained by scaling in accordance with the volumes during the fall phase (Table X X V I ) . 7 . Recapitulation P r i o r to summarizing all of the volumes for the different phases of the year, it is important to bear in mind the following points. ( 1 ) The summer volumes and proportions were determined at Griffen Lake. ( 2 ) The spawning volumes and proportions were calculated at Griffen Lake. 79 (3) The phases were based on observations of squawfish at Cultus Lake. (4) The early, peak, f a l l and winter volumes were the r e s u l t of observa-tions and calculations at Cultus Lake. (5) The average rates of digestion were determined at Cultus Lake. (6) The early and peak volumes, and the summer and spawning volumes were adjusted to compensate for the lag between time of feeding and dissection for a rate of digestion appropriate to the ambient tempera-ture within a seasonal phase. E a r l y smolt migration volume was scaled f r o m values for squawfish of age s i x years, in r e l a t i o n to the volumes found i n the stomach of f i s h of the same age during the peak phase. (7) The f a l l volume was adjusted to 35 per cent of the summer adjusted volumes. (8) The winter volume was assessed to be slightly l a r g e r than a trace (.25 gms) amount, and a 0.5 gm volume was specified for predators age six. This volume was then scaled up or down in a relationship s i m i l a r to the f a l l volumes. (9) The daily ration was based on the amount of digestion that could occur in 24 hours at the stipulated rate of digestion for the different phases of the year. It is now possible to summarize i n three tables the proportion of the population consuming prey (Table XXV), the average volumes (Table XXVI), and the calculated daily rations for each phase of the year (Table XXVII) for the population of squawfish present i n Cultus Lake. F r o m these tables a f i r s t estimate of the predation of squawfish consumption on sockeye salmon can be calculated. Table XXVIII gives the total yearly consumption in grams for the population of squawfish present in Cultus Lake. The estimate was based on the number in the age classes, the proportion observed or calculated to con-tain food, and the amount of food in the stomach that could be digested per day (daily ration) when exposed to the prevailing phase temperature. T A B L E XXV. P r o p o r t i o n of predators within each phase observed or assumed to contain f i s h or f i s h products i n the stomach contents. E a r l y smolt Peak smolt Summer, F a l l and F o r k lengths migration migration Spawning Winter Age (cm) phase phase phase phases 1 - 17 .25 2 18 - 19 .33 .95 .42 .33 3 20 - 22 .33 .95 .41 .39 4 23 - 35 .33 .95 .39 .43 5 26 - 27 .33 .95 .38 .47 6 2 8 - 2 9 .33 .95 .36 .50 7 30 - 32 .33 .95 .35 .53 8 3 3 - 3 5 .33 .95 .33 • .60 9 36 - 38 .33 .95 .31 .65 10 3 9 - 4 0 .33 .95 .30 .69 11 41 - 43 .33 .95 .28 .73 12 4 4 - 4 5 .33 .95 .27 .77 13 over 45 .33 .95 .26 .80 CO o T A B L E X X V I . The average volumes (grams) of food (observed or calculated) found i n the stomachs of predators during each phase of the year. E a r l y smolt Peak smolt A S e . .. F o r k lengths migration volume migration volume Spawning volume Summer volume F a l l volume Winter volume 1 —17 c m 1.71 . .60 .16 2 18 - 19 c m .137 .323 .36 2.71 .95 .25 3 20 - 22 cm .584 1.38 .36 3.71 1.30 .34 4 23 - 25 cm 1.35 3.19 .36 4.36 1.52 .41 5 . 26 - 27 cm 2.31 5.43 .36 5.29 1.85 .43 6 28 - 29 cm 3.44 8.07 .36 6.14 2.15 .50 7 30 - 32 cm 5.43 12.75 .36 7.29 2.55 ..59 8 33 - 35 cm 9.04 21.22 .36 9.00 3.15 .73 9 36 - 38 cm 14.79 34.72 .36 11.00 3.85 .89 10 39 - 40 cm 20.39 47.87 .36 12.93 4.53 • 1.04 11 41 - 43 cm 32.39 76.04 .36 15.21 5.32 1.22 12 44 - 45 cm 47.87 . 112.37 .36 17.86 6.25 1.43 13 over 45 cm 72.65 170.55 .36 18.63 6.52 1.49 T A B L E XXVII. The calculated daily ration for various ages of squawfish for any phase of the year for temperatures found i n Cultus Lake. Age F o r k lengths E a r l y smolt phase daily r a t i o n Peak smolt phase daily ration Spawning phase., daily ration Summer phase daily r a t i o n F a l l phase daily ration Winter phase daily ration 1 —17 cm 2.56 .626 .072 2 18 - 19 c m .062 .242 .27 . 4.07 • 990 .113 3 20 - 22 cm .264 1.04 .27 5.57 1.36 .154 4 23 - 25 c m .611 2.39 .27 6.54 1.59 .186 5 26 - 27 c m 1.0 5 4.07 .27 7.93 1.93 .195 6 28 - 29 c m 1.56 6.05 .27 9.21 2.24 .226 7 30 - 32 c m 2.46 9.56 .27 10.94 2.66 .267 8 33 - 35 cm 4.09 15.92 •27 13.50 3.29 .330 9 36 - 38 c m 6.70 26.04 .27 16.50 4.02 .403 10 39 - 40 cm 9.23 35.90 .27 19.40 4.73 .471 11 41- - 43 cm 14.67 57.03 .27 22.82 5.55 .552 12 44 - 45 c m 31.68 84.28 .27 26.79 6.52 .648 13 over 45 cm 32.90 127.90 .27 27.95 6.80 .675 T A B L E XXVIII. Calculated consumption of prey (grams) by the population of squawfish present i n Cultus Lake for a l l phases of the year based on the number i n the age classes, the proportions observed or calculated to contain food, and the amount of food in the stomach that can be digested per day (daily ration) when exposed to the pr e v a i l i n g phase temperature. E a r l y smolt Peak smolt Spawning Summer F a l l Winter Age phase phase phase phase phase phase 1 2 3476.00 134, 669.67 101, 315.08 3 6630.79 259, 275.90 44, 306.79 4 6874.98 266, 954.04 18, 883.87 5 5292.44 203, 667.89 8, 240.72 6 3524.32 135, 641.00 3, 499.00 7 2488.99 96, 042.15 1, 522.67 8 1851.79 71, 460.90 642.94 9 1361.98 52, 568.25 271.10 10 831.53 32, 399.75 116.24 11 609.98 23, 025.86 49.59 12 585.45 16, 013.20 . 20.92 13 304.00 12, 150.00 8.63 2, 326, 114.89 317, 045.69 66, 175.32 1, 685, 548.39 230, 589.80 47, 752.50 977, 453.22 133, 166.30 28, 482.32 580,518.19 79, 126.33 14, 624.77 321, 134.28 43, 793.12 8, 073.40 181, 367.70 24, 681.39 4, 524.07 113, 270.40 15, 533.40 2, 824.77 67, 095.60 9, 244.79 1, 674.90 38, 176.87 5, 176.23 948.65 21, 456.28 2, 965.70 504.10 11, 386.82 1, 531.22 277.42 6, 171.36 663.68 150.12 Total grams consumed = 8, 837, 400.05 Sockeye equivalents (total/6 gms) = 1, 472, 900 84 The total consumption for a l l phases of the year was 8,837,400 gms. Assuming that, on an average a smolt represents 6 gms,. this estimate for the population represents 1,472,900 smolt equivalents of consumption over the course of a year. A n estimate of squawfish predation based on c a l o r i c requirements It is also possible to estimate squawfish food consumption by considera-tion of energy requirements for routine and active metabolism, growth and reproduction. This energy requirement then can be converted to an e s t i -mate of consumption of prey by using a conversion coefficient of 1 K c a l / gm/wet weight of body tissue, or 1.3Kcal/gm/wet weight of eggs. It i s assumed that males of age 2 (physiologically the same age as a 4 year old female) contribute the same percentage of their body weight to spawning, and the energy loss i s calculated for production of either eggs and sperm (Figure 32) (both sexes appear to spawn each year). 1. Energy for metabolism and growth Winberg (1956, Table 19) shows that the routine metabolism for a l l 0 8 fishes can be closely approximated by the general equation Q = 0.3W ' . The log of calories/gm/day plotted against the log of body weight (gms) for a large range of f i s h (temperature 20°C), enables an estimate of the c a l o r i c requirements for metabolism of squawfish of various weights. This value can then be related to the age classes present. In Qaltus Lake the c a l o r i c requirement for growth was related to the mean summer weight (Table XXIX). The energy i n the rat i o n i s only 80 per cent "p h y s i o l o g i c a l l y u s e f u l " (Winberg, 1956, p. 157) so that the food intake for routine metabolism must be 1.25 times the c a l o r i c requirement. Metabolic rate over the course of a year is also affected by the tem-perature. The routine rate of metabolism was calculated in the laboratory (Appendix XVI) but only on two f i s h , and the value at 20°C was approximately T A B L E XXIX. Routine c a l o r i c requirements and routine metabolic rate of squawfish of different ages, lengths or weights (exceptfor spawning fish). Routine * Routine Weight requirements metabolic rate Age (year s) F o r k length (cm) (gms) (midsummer weight) (calories/gm/day) at 20 C * (calories/day) at 20°C* 1 -17 cm 26 21.54 560.04 2 18 - 19 70 15.33 1,073.10 3 20 - 22 116 13.33 1, 546.28 4 2.3 - 25 168 12.55 2, 108.40 5 26 - 27 245 11.70 2, 866.50 6 28 - 29 314 11.36 3, 567.04 7 30 - 32 403 10.91 4,396.73 8 33 - 35 483 10.49 5, 066.67 9 36 - 38 572 10.18 5, 822.96 10 39 - 40 665 9.78 6, 503.70 11 41 - 43 7 54 9.58 7, 223.32 12 44 - 45 8 54 9.30 7, 942.20 13 over 45 992 9.12 9,047.04 The rate w i l l be increased for males and females during the spawning season. •tt-From Winberg, 1956 86 twice that suggested by Winberg (1956); Therefore, the routine rates for model formulation were calculated f r o m Winberg's data (Table XXIX).' A c c o r d i n g to Winberg, at lower temperatures the metabolic requirements are decreased. Winberg gives a table to f a c i l i t a t e the adjustments of c a l o r i c requirements or metabolic rates to various temperatures (Table X X X ) . When it is necessary to change c a l o r i c requirements to values other than at 20°C the factors are used as d i v i s o r s . This then makes i t possible to convert routine rates at 20°C (as i n Table XXIX) to those for the p r e v a i l i n g phase temperatures within the lake. The prevailing temperatures used for each phase within Cultus Lake were the averages of the temperatures determined at two week in t e r v a l s , for either the surface (depths less than 10 m), or at depths greater than 10 m (determined at 5 m intervals) (Figure 31 and F i g u r e 32 f r o m R i c k e r , 1937). F o r the most part, squawfish are exposed to the deep water temperature only during the winter. The temperatures for adjustment of the routine meta-bolic rate for each phase of the year are given in Table XXXI. 2. Energy for spawning F i e l d observations indicated that male squawfish spawn f i r s t at a length of 18-19 cm (age 2). Females r a r e l y spawned at less than 24 cm (age 4). . It i s assumed that since males of age 2 are at a physi o l o g i c a l l y s i m i l a r stage of reproduction as age 4 females, the male expenditure on reproduction at age 2 and older (maximum li f e span 10 yrs) would be the same percentage of their body weight as females two years older. F o r older squawfish, this assumption i m p l i e s almost equal expenditure on spawning by both sexes. The conversion coefficient f r o m grams to energy for gametes was that used by Sandercock (1969) for eggs of trout and kokanee -- 1.3 K c a l / T A B L E XXX. Table of factors (q) for adjusting values of metabolism to 20°C on the basis of the "normal curve" (from Winberg, 1956). T° q T° q T° q T° q T° q 5 5.19 10 2.67 15 1.57 20 1.00 25 0.659 6 4.55 11 2.40 16 1.43 21 0 . 9 2 0 26 0.609 7 3.98 12 2.16 17 1.31 22 0.847 27 0.563 8 3.48 13 1.94 18 1.20 23 0.779 28 0.520 9 3.05 14 1.74 19 1,09 24 0.717 29 0.481 30 0.444 20-T where q = Q^Q 10 T A B L E X X X I . The average temperature of the different phases evident in Cultus Lake. Phase Dates Average phase temperature E a r l y smolt migration phase A p r i l 18 - A p r i l 24 9 C Peak smolt migration phase A p r i l 25 - May 19 10°C Spawning phase May 20 - June 30 14°C Summer phase July 1 - September 30 18°C F a l l phase October 1 - November 30 11°C Winter phase December 1 - A p r i l 17 5°C 88 gm wet weight of tissue. Energy requirements for reproduction are sum-ma r i z e d i n Table XXXII. Over the course of a year metabolism does not r e m a i n constant at the routine rate (Table XXIX). Winberg (1956) states (p. 117) that in the "majority of cases under natural conditions the mean metabolic rate is about twice as high as the le v e l of routine metabolism." Mean metabolic rate (calories/day or Kcalories/day) for the various ages of squawfish exposed to the average phase temperature were therefore calculated on this basis (Table XXXIII). Since the mean metabolic rate is related to weight i n grams, and since eggs and sperm are shed p r i o r to the mid-summer weight, it i s essential for the spawning phase at least to add half the weight of the shed gametes to the mean summer weight i n the determination of the mean metabolic rate during the spawning phase. 3. Recapitulation The estimate of the food consumption of squawfish as determined by metabolism, growth and reproduction, i s an expansion of Winberg's equation. Energy of the ration = 1.25 (energy of metabolism + energy of weight increase). A l l the energy requirements for a l l ages, numbers and phases of the year for the mean metabolism, growth and reproduction are summed. This value multiplied by 1.25 gives a summed energy consumption, and this can easily be related to the consumption of prey by the c a l o r i c value of one g r a m wet weight of tissue. In the calculations: (1) the mean metabolic rate is twice the theoretically-determined rate for a l l s izes of fish; (2) the metabolic rate is affected by temperature according to Winberg's table of factors (q); T A B L E X X X I I . The. weight, growth and spawning contribution (grams), and the energy equivalents (Kcalories) for the various ages of squawfish in Cultus Lake. Age Mid-summer weight Growth Energy for growth (Kcalories) Spawning weight - eggs Energy for eggs (Kcalories) Spawning weight -sperm. Energy for sperm (Kcalories) 1 26 44 44 2 70 46 46 7.0 9.1 3 116 52 52 15.0 19.5 4 168 77 77 16.0 20.8 25.0 32.5 5 245 69 69 32.0 41.6 38.0 49.4 6 314 89 89 47.0 61.1 51.0 66.3 7 40 3 80 80. 63.0 81.9 65.0 84.5 8 483 89 89 78.0 101.4 79.0 102.7 9 572 93 93 93.0 120.9 94.0 122.2 10 667 89 89 109.0 141.7 109.0 140.7 11 7 54 100 100 124.0 161.2 12 , 8 5 4 138 138 140.0 182.0 13 992 155.0 201.5 TABLE XXXIII.Mean metabolic rate (calories per day) of various ages when exposed to the average phase temperature for the different phases evident in Cultus Lake. Age Mean metabolic rate at 20°C Early smolt phase at 9°C Peak smolt phase at 10°C Spawning (Males) phase at 14°C (Females) Summer phase at 18°C • Fall phase at 11°C Winter phase at 5°C 1 1,120.08 367.24 419.51 b43.72 643.72 933.40 466.70 215.82 2 2, 146.20 703.67 803.82 1, 295.12 1, 233.45 1, 788.50 894.25 413.53 3 3,092.56 1, 013.95 1, 158.26 1, 892.25 1,777.33 2, 577.13 1, 288.57 595.87 4 4, 216.80 1, 382.56 1, 579-33 2, 603.76 2, 538.85 3, 514.00 1, 757.00 812.49 5 5, 733.00 1, 879.67 2, 147.19 3, 550.34 3,510.00 4, 777.50 2, 388.75 1, 104.62 6 . 7, 134.08 2, 339.04 2, 671.94 4, 433.01 4,406.90 5, 945.06 2, 972.53 1, 374.58 7 8, 793.46 2, 883.10 3, 293.43 5, 461.27 5,448.73 7, 327.88 3, 663.94 1, 694.31 S 10, 133.14 S, 322.41 1, 79S.E6 6, 300.03 6, 294.00 8, 444.45 4, 222.23 1. 952.47 9 11, 645.92 3,818.33 4, 361.77 7, 243.01 7,237.16 9, 704.93 4, 852.47 2, 243.92 10 13, 007.40 4, 264.72 4, 871.69 8, 088.17 8, 088.17 10, 839.50 5, 419.75 2, 506.24 11 14, 446.40 4,736.60 5,410.73 9.007.40 12, 038.87 6. 019.43 2. 783.55 12 15, 884.40 5, 208.00 5, 949.21 9. 834.48 13, 237.00 6,618.50 3.060.58 13 18,094.08 5, 932.48 6, 776.81 * 11,200.82 15. 078.40 7, 539.20 3, 486.34 O 91 (3) the average exposure temperature within each seasonal phase was determined by averaging the temperatures (two-week interva l s ; R i c k e r , 1937) of the shallow or deep lake; (4) growth as indicated by increase in weight was determined f r o m a large sample of mid-summer non-spawning fish; . (5) the contribution to spawning (another f o r m of shed growth) was c a l -culated f r o m egg production; (6) theoretical c a l o r i c equivalents for growth and reproduction were used to convert weights to ca l o r i e s which i n turn were related to consump-tion of prey; (7) mean weight of the f i s h during spawning phase was adjusted by one-half the weight of the contribution to gametes i n the calculation of the mean metabolic rate. In addition, the age at which spawning com-mences and the death of the males at age 10, was also considered in the energy contribution during spawning. (8) The metabolic requirement for the population was based on the weight, number, distribution and c a l o r i c requirements (calories/gm/day) for the f i s h remaining during any phase of the year. Tables X X X I V and X X X V contain the calculations for the theoretical mean metabolic rate and the energy requirements for.growth and reproduc-tion. Summation of the requirements for metabolism, reproduction, and growth gives a total c a l o r i c requirement of 18,836,045 K c a l o r i e s . The energy of the ration must be 1.25 times this amount, or 23,545,081 K c a l o r i e s . Cummin and Wuycheck (1971) gave a gram c a l o r i c value of 1 .369 K c a l o r i e s / gm wet weight for smolt sockeye salmon. Assuming an average weight of 6 gms/sockeye, the total c a l o r i c value of 23,545,081 to sockeye equivalents. This value represents 2,866,457 sockeye smolt equivalents of consumption by the squawfish population in Cultus Lake. T A B L E XXXIV. The o r e t i c a l mean metabolic rate (Kcalories) for the population of squawfish present i n Cultus Lake for the different phases and temperatures of the year. E a r l y smolt Peak smolt Spawning phase Summer F a l l Winter Age • jjhase phase Males Females phase phase phase 1 2 119, 551.42 470, 857.66 578, 523.63 550, 957.95 3, 097, 503.15 867, 824.02 73.3, 855.71 3 77, 172.75 303, 956.38 378, 678.96 355, 681.06 1, 999, 667.33 560, 201.94 473, 764.32 4 47, 141.15 185, 689.72 233, 471.35 227, 651.06 1, 221, 382.06 342, 216.16 289, 342.31 5 28, 710.08 113, 103.23 142, 652.66 141, 031.80 744, 124.29 208, 370.66 176, 626.42 6 16, 013.07 63, 057.78 79, 971.50 79, 500.47 414, 584.70 116, 228.89 98, 208.24 7 8, 839.58 34, 828.02 43, 886.77 43, 785.99 229, 216.09 64, 144.60 54, 167.09 8 4, 558.35 17, 932.60 22, 988.80 22, 966.80 118, 087.19 33, 224.73 27, 953.51 9 2, 352.09 9, 268.76 11, 878.54 11, 868.94 60, 714.04 17, 168.04 14, 347.62 10 1, 164.27 4, 628.11 5, 637.45 5, 637.45 30, 914.25 8, 595.72 7, 315.71 11 596.81 2,299.56 5, 908.85 15, 506.06 4, 406.22 3, 482.22 12 291.65 1, 189.84 2, 822.49 6, 754.82 2, 018.64 1, 701.68 13 166.11 677.68 1, 377.70 . 4, 161.64 919.78 969.20 Total K c a l o r i e s for mean metabolism = 16, 478, 433.85 Ration (1.25 x energy of metabolism) = 20, 598, 054.81 Total grams consumed (ration/1.369) = 15,046,0 59.0 3 Sockeye smolt equivalents (grams/6 grams/smolt) = 2, 507,676.50 T A B L E XXXV... Energy requirements (Kcalories) necessary for growth and reproduction (based on the increase i n weight (grams) and conversion coefficients for growth (1 K c a l o r i e / g r a m wet weight) and reproduction (1.3 K c a l o r i e s / g r a m wet weight) ).. Spawning phase Summer phase additional requirements additional requirements Age Mal e s - s p e r m Females-eggs Growth 1 2 99, 144.50 865, 950.00 3 95, 179.50 438, 568.00 4 71, 077.50 45, 489.60 290, 906.00 5 48, 412.00 40, 768.00 116, 817.00 6 29, 172.00 26, 884.00 67, 462.00 7 16, 562.00 16, 052.40 27, 200.00 8 9, 140.30 9,024.60 13, 528.00 9 4, 888.00 4, 836.00 6, 324.00 10 2,391.90 2, 408.90 2, 759.00 11 2, 579.20 1, 400.00 -12 1, 274.00 828.00 13 604.50 Total K c a l o r i e s for growth and reproduction Ration (1.25 x energy weight increase) Total grams consumed (ration/1.369) Sockeye smolt equivalents (grams/6 grams/smolt) 2, 357, 630.90 2, 947, 038.58 2, 152, 694.36 358, 782.39 IV. CONCLUDING R E M A R K S The foregoing estimates of the total f i s h consumption by a population of squawfish in a year are remarkably s i m i l a r considering their disparate origins and the many assumptions involved i n their calculations. F o r example, the estimate based on food observed in the stomachs of squawfish and its rate of digestion i s subject to wide e r r o r f r o m extrapolation of amounts observed i n the stomach to amounts ingested. Using minimum rates of digestion, the estimates are indeed low. They are also subject to additional e r r o r f r o m the estimates of the proportion of f i s h which were eating or observed to contain food. Since a l l f i s h found i n the f i e l d grow, then the proportions observed seem to r e f l e c t rapid rates of digestion, consumption of minimum volumes that can be digested quickly or passed out of the stomach or perhaps regurgitation due to the method of capture. The estimate based on c a l o r i c requirements effectively assumes that squawfish digest their food where they are caught in the f i e l d . Thus, if they catch their prey on shoals i n mid-summer, that i s where we catch squawfish we do not account for the p o s s i b i l i t y that squawfish may feed on the shoals and digest at greater depths where temperatures are lower. Likewise, the rev e r s e is true and, since upward acclimation to increased temperatures i s 20 times faster than adaptation to colder temperatures, there may be an additional underestimate of the c a l o r i c requirement, p a r t i c u l a r l y i n the f a l l and spring. Both estimates may significantly underestimate the total impact of predation. An average size of 6 gms was used to convert stomach volumes to sockeye smolt equivalents consumed. Consumption, of course, i s on juvenile sockeye f r o m egg to smolt stages. Because the increments in the sockeye population biomass are positive in the f i r s t year, the loss of 6 gms earl y i n the season im p l i e s a greater loss than the consumption of a smolt of equivalent weight. 95 It is also possible that predation i n some years is much lower or much higher than these estimates indicate. In' some years, squawfish as a popula-tion may f a i l to take enough food to meet their total potential requirements for maintenance, growth and reproduction. A group of unfed squawfish (approximately 12) were maintained at 11°C i n the laboratory for greater than a year and thus i t is possible that a squawfish population could maintain enough stored energy i n the f o r m of adipose tissue, or become " d o c i l e " during the slower years of sockeye production. In other years, squawfish may f l o u r i s h on a surfeit of prey throughout a l l seasons. It seems reasonable to consider the estimate based on rations eaten to be a r e l a t i v e l y low estimate, while that based on c a l o r i c requirements as an estimate of potential predation i n an average year of growth and reproduction. This, of course, i m p l i e s that, given a greater abundance and a v a i l a b i l i t y of prey, squawfish might consume even more than i s indicated by the c a l o r i c estimate because they might grow more (and perhaps have higher survival). Conspicuously, the consumption volumes during sockeye abundance were far below the number of sockeye/predator and the volume/predator found i n the stomachs of many of the individual predators. No consideration was given to "gorging" i n the calculations. The s u r v i v a l is based on an instantaneous mo r t a l i t y rate. Sparsely fed squawfish kept i n an a r t i f i c i a l sockeye spawning channel failed to suffer a m o r t a l i t y as high as used i n this study (55 per cent), and it i s felt that in future calculations an assumption of f a l l or winter mor-tal i t y might be more appropriate. The m e r i t s of control of predators such as squawfish for i n c r e a s i n g production of sockeye salmon have been a matter of anecdotal r e m a r k for many years. The estimates of R i c k e r (1941) indicated that, because of the quantity of prey taken, squawfish removal programs could be profitable. This theme was developed f r o m suggestions established by F o e r s t e r as early as 1925-. This study suggests that the benefits could be even la r g e r than these authors suggest. There remains, of course, the possibility that squawfish control could generate changes in the whole mix of fish species in the lake such as Cultus, with attendant harmful effects on salmon in the long term. This should certainly be explored, and a large-scale long-term field experiment would seem desirable. 97 L I T E R A T U R E CITED Beamish, F.W.H. 1964. R e s p i r a t i o n of fishes with special emphasis on standard oxygen consumption. Can. J. Zool. 42; 161 -17 5 and 355-366. B e l l , G.R. 1964. Anaesthetics for f i s h . F i s h . Res. Bd. Canada B u l l . 148:1-4. Brett, J.R. 1962. Some considerations i n the study of r e s p i r a t o r y meta-b o l i s m i n fish, p a r t i c u l a r l y salmon. J. F i s h . Res. Bd. Canada, 19(6):1025-1038. Brody, S. 1945. Bioenergetics and Growth. Reinhold Publishing Corp., New York. Cartwright, J.W. 1956 Contributions to the l i f e h istory of the northern squawfish (Ptychocheilus oregonense (Richardson)). Unpub. B.A. thesis, Dept. of Zoology, U n i v e r s i t y of B r i t i s h Columbia. Clemens, W.A. 1939. The fishes of Okanagan Lake and nearby waters. F i s h . Res. Bd. Canada B u l l . 56:27-38. Clemens, W.A. and J.A. Munro. 1934. The food of the squawfish. F i s h . Res. Bd. Can. Prog. Rept. P a c , No. 19. pp. 3-4. Cummins, K.W. and J.C. Wuycheck. 1971. C a l o r i c equivalents for investigations i n ecological energetics. Mitt. Internat. Verein. Limnol., No. 18, p. 118. F o e r s t e r , R.E. 1925. Studies in the ecology of the sockeye salmon. Contr. Canad. B i o l . Fish., 11:15-22. Hoar, W. S. 1966. General and Comparative Physiology. P r e n t i c e - H a l l Inc., Englewood C l i f f s , New Jersey. Hoar, W.S. and C P . Hickman, J r . 1.967. A Laboratory Companion for  General and Comparative Physiology. P r e n t i c e - H a l l Inc., Englewood C l i f f s , New Jersey. K l e i b e r , Max. 1961. The F i r e of L i f e . John Wiley & Sons, Inc., New York. LeCren, E.D. 19,47. The determination of the age and growth of the perch (Perca f l u v i a t i l i s ) f r o m the opercular bone. J. Anim. E c o l . l6(2):188-204. 98 R i c k e r , W. E. 1937. P h y s i c a l and chemical c h a r a c t e r i s t i c s of Cultus Lake, B r i t i s h Columbia. J. F i s h . Res. Bd. Canada, 3(4):363-402. . 1941. The consumption of young sockeye salmon by predaceous f i s h . J. F i s h . Res. Bd. Canada, 5(3):293-313. . 1958. Handbook of computations for b i o l o g i c a l s t a t i s t i c s of f i s h populations. F i s h . Res. Bd. Canada B u l l . 119. 300pp. Sandercock, F.K. 1969. Bioenergetics of the rainbow trout (Salmo gairdneri) and the kokanee (Oncorhynchus nerka) populations of M a r i o n Lake, B r i t i s h Columbia. Ph.D. thesis, Department of Zoology, U n i v e r s i t y of B r i t i s h Columbia. Seaburg, K.G. 1957. A stomach sampler for l i v e f i s h . P r o g. F i s h . Cult. 19(3):137-139. Thompson, R.B. . 1958. Food of the squawfish Ptychocheilus oregonensis (Richardson) of the Columbia R i v e r . B u l l . F i s h and Wildl. Serv., U.S. Dept. Interior, No. 157, pp. 33-41. U r s i n , E. 1967. A mathematical model of some aspects of f i s h growth, r e s p i r a t i o n and mortality. J. F i s h . Res. Bd. Canada, 24(11):2355-2453. Wielleman Smith, W.S. 1968. Otolith age reading by means of surface structure examination. J. Cons. perm. int. Explor. Mer. 32(2): 270-277. Winberg, G.G. 1956. Rate of metabolism and food requirements in fishes. (Translated f r o m the Russian). F i s h . Res. Bd. Canada Translation Series No. 194. 99 A P P E N D I X I. Explanatory notes of G r i f f e n Lake, B r i t i s h Columbia. G r i f f e n Lake i s situated 16.Z miles west of Revelstoke, B r i t i s h Columbia, on the Eagle R i v e r system. The lake is the lowest i n a chain of lakes that d r a i n f r o m the east into Shuswap Lake. It i s nested in a steep-sided valley and has a maximum depth of 3 5 feet. Squawfish (Ptychocheilus  pregonense Richardson) and red sided shiners (Richardsonius balteatus Richardson) dominate the complex of f i s h inhabiting the lake. The location of the shore lead l i v e trap i s designated as (1) on the sounding and scale r e p r o -duction of the lake. Shore line elevation 1498.0, May 13, 1954 Scale: 1/4 mile = 1 inch Prom: Dept. Northern A f f a i r s and National Resources, Water Resources Divi s i o n , P l a n No. 2096. 100 A P P E N D I X II. Explanatory notes of Cultus Lake, B r i t i s h Columbia. Cultus Lake is situated 76 miles east of Vancouver, B r i t i s h Columbia, in the western Cascade mountains. It i s connected by Sweltzer Creek and the Vedder R i v e r to the F r a s e r R i v e r system. R i c k e r (1937) reported the detailed p hysical and chemical properties of the lake. Cultus Lake in peak years supports an adult sockeye population of approximately 35,000 f i s h . In addition, the lake supports a large population of squawfish (Ptychocheilus oregonense Richardson), red side shiners (Richardsonius  balteatus Richardson) and sticklebacks (Gasterosteus aculeatus Linnaeus). The trap locations on the reproduction of Cultus Lake are designated as stations (1) and (2) (Figure 23). The trap was i n operation at station (1) f r o m September 15 to December 15, 1967, and f r o m August 12 to December 1, 1968. The trap was relocated to station (2) f r o m A p r i l 23 to May 26, 1969. 101 A P P E N D I X III. Explanatory notes of the shore lead l i v e trap used at G r i f f e n Lake and Cultus Lake, B r i t i s h Columbia. An adequate supply of f i s h for experimental use was obtained by means of a shore lead l i v e trap (Plate 3). The plate depicts the trap in operation on G r i f f e n Lake. The trap is composed of four sections of mesh net, six floats and associated catwalk. The sections of the trap are: (1) shore lead; (2) heart; (3) pot; and (4) s p i l l e r . The shore lead (section 1) i s a 3/4 in . stretched mesh net (approxi-mately 32 ft in depth) which can be adjusted in length. Adequate numbers of f i s h were obtained with a shore lead approximately 125 ft in length. The lowest point i n section 1 is usually attached to shore unless the trap i s fishing off shore regions of the lake,. In this case, the lowest section of the lead i s weighted and buoyed. The lead (corked and leaded) acts as a v e r t i c a l obstruc-tion to the movement of f i s h . F i s h encountering such an obstacle i n s t i n c t i v e l y move to deeper water. The offshore end of the lead usually attaches to the heart (section 2; 3/8 i n . stretched mesh). The attachment of the lead to the innermost section of the wings of the heart forms a funnel. F i s h enter the heart through two recessed slotted openings (approximately 6 in. x 25 ft deep; one opening on each side of the lead). The heart i s maintained in the proper fishing position by the corks and lead lines (vertical fishing position), the s t a b i l i z e r (2 in. x 4 i n . x 24 ft in length — to maintain the openings into the heart), and the two rope connectors (separate and connect the pocketed ends of the heart to shore). The heart has a maximum depth of approximately 32 ft and a depth of 16 ft adjacent to the pot (section 3; 3/8 i n . stretched mesh). The hearts, wings and bottom converge upon a funnelly-recessed slotted opening (18 in . x 12 ft i n depth) into the pot. F i s h in the heart search the bottom and outside walls f o r the recessed opening into the pot. 102 P L A T E 3. Shore lead l i v e trap. 103 Once inside the pot (approximately 16 ft x 16 ft x 16 ft), the f i s h undergo another searching response and enter the s p i l l e r (section 4; 3/8 in. stretched mesh), approximately 16 ft x 16 ft x 16 ft) by means of another recessed funnel opening (decreases f r o m 5 ft in diameter to 8 in. i n diameter). The pot and the s p i l l e r are supported by s i x plywood floats (2 ft x 8 ft x 16 in. i n depth). A catwalk of 2 in. x 12 in. x 18 ft and 22 ft) planks connect and support the pot and s p i l l e r . A number of weights f r o m each float to various positions i n the lake sta b i l i z e the trap in the c o r r e c t fishing position. The v e r t i c a l position of the pot and s p i l l e r i s maintained by a s m a l l weight in each corner. Removal and checking of the f i s h in the trap i s accomplished simply by l i f t i n g the pot and s p i l l e r weights, loosening off the s p i l l e r funnel (main-tained i n an extended position by ropes to the catwalk), and l i f t i n g the 3/8 in. mesh net off the s p i l l e r . F i s h caught i n such a trap range in size f r o m 0.5 gms to 4500 gms (approximately 9 pounds). 104 APPENDIX IV. The trap catch data of squawfish from Griffen Lake (1967). Date Time Trap Catch Daily Total Fishing Time (hrs) June 29 1700 139 139 153.0 July 5 1700 176 176 144.0 10 1300 No Tally 13 1430 124 124 73.5 14 2130 No Tally 15 1030 45 23.0 15 2130 19 64 11.0 16 1230 0 0 15.0 17 1230 _ 27 27 24.0 20 1000 22 1000 23 1500 24 1000 172 172 165.5 26 0 500 4 56 43.0 26 1300 10 8.0 26 2100 14 180 8.0 27 0530 158 8.5 27 1300 16 8.0 27 2100 7 181 8.0 28 0500 227 8.0 28 1300 8 8.0 28 2100 9 244 8.0 29 1930 287 22.5 29 2100 98 385 .1.5 30 0100 33 4.0 30 0900 32 8.0 30 1900 8 73 10.0 31 1300 227 30.0 31 2100 16 243 8.0 Aug. 1 0900 127 12.0 1 1300 7 134 4.0 2 0900 157 20.0 2 1300 7 4.0 2 2100 10 174 8.0 3 0900 127 12.0 3 1300 8 4. 4.0 3 2100 4 139 8.0 4 0900 135 12.0 4 1300 23 4.0 4 2100 7 165 8.0 5 0900 136 12.0 5 1300 0 136 4.0 6 0900 92 20.0 6 1300 1 93 4.0 7 0915 70 70 20.0 8 0920 119 119 24.0 9 0915 98 98 24.0 105 APPENDIX IV. continued Date Time Trap Catch Daily Total Fishing Time (hrs) 10 0910 77 77 24 .0 11 0900 116 116 24 .0 12 0910 112 112 24.0 13 0915 84 84 24.0 14 0915 64 24.0 2115 10 74 12.0 15 0920 84 84 12.0 16 1300 40 40 28.0 17 1320 94 94 24 .5 18 0515 72 72 16.0 19 0100 - 34 20.0 0900 40 8.0 1700 4 78 8.0 20 0100 69 8.0 0900 33 8.0 1700 3 105 8.0 21 0100 132 8.0 0900 84 8.0 1700 5 221 8.0 22 ' 0100 74 8.0 0900 58 8.0 2100 26 158 12.0 23 0 500 67 8.0 2100 27 94 16.0 24 0 500 18 8.0 1700 21 39 12.0 25 0920 77 77 16.0 26 1020 97 97 25.0 27 0930 74 23 .0 1930 5 79 10.0 28 0930 62 62 14.0 29 0 9 2 5 72 72 24 .0 30 0900 94 94 23 .5 31 0915 96 96 24.0 1 0 9 1 5 92 92 24 .0 2 0930 82 82 48 .0 4 1100 92 92 50.0 106 A P P E N D I X V. L a b o r a t o r y temperature p r e f e r e n c e data f r o m Cultus L a k e . (1968) T e m p e r a t u r e (° C) of Number of f i s h at T o t a l r e c o r d i n g sites i n ex- each temperature with- Number Date T i m e Recording p e r i m e n t a l zone in e x p e r i m e n t a l zones of f i s h i n (1968) (hrs) Site A B C A B C E x p e r i m e n t November 26 1200 Head 7.1 14.1 27.0 3 Center F o o t - Top 7.0 11.5 26.2 M i x 15.2 21.9 25.8 7 10 1700 Head 6.9 11.5 26.7 Center Foot - Top 7.2 11.2 26.4 M i x 8.1 8.8 12.5 10 10 2100 Head 1 Center Foot - Top 1 Mix 2 4 2 10 November 27 1100 Head 7.8 10.8 24.6 Center 2 Foot - Top " 7.8 10.3 25.0 Mix 8.0 10.1 12.2 4 4 10 2000 Head 7.4 10.7 24.2 1 Center 1 1 Foot - Top 7.2 9.9 24.1 2 M i x 8.4 20.1 22.7 13 18 2300 Head 6.8 10.2 25.2 3 1 Center Foot - Top 6.7 9.8 24.1 - Bottom 11.0 1 M i x 8.0 7.3 9.3 4 4 5 . 18 November 28 0930 Head 6.4 10.0 22.6 1 Center 2 2 Foot - Top 9.0 9.4 22.0 - Bottom 10.0 M i x 12.3 15.5 15.5 4 7 2 18 November 29 1330 Head 7.7 10.2 23.4 10 1 Center Foot - Top 7.7 9.5 23.0 - Bottom 11.0 Mix . 10.2 16.0 18.0 1 2 3 17 1630 Head 7.0 10.5 21.8 5 Center 4 1 Foot - Top 6.9 9.7 21.0 1 - Bottom 9.0 Mix 8.1 15.7 12.0 3 2 1 17 2130 Head 7.8 11.0 23.0 6 Center 2 Foot - Top 7.5 9.6 22.2 - Bottom 10.0 5 1 Mix 8.0 19.2 19.5 ' 3 17 November 30 Head 7.0 10.0 24.1 6 Center 4 1 Foot - Top 6.9 9.5 23.0 - Bottom 9.2 Mix 7.0 9.8 9.5 3 3 17 A P P E N D I X VI. Laboratory feeding p e r i o d i c i t y data f r o m Cultus Lake. Time Number of Date Time F i s h F i s h Interval of f i s h Time (1968) Jhrs) Remaining Added (hrs) consumed Category Average October 31 0 900 100 1500 86 100 6 -14 a -14.0 2100 82 100 6 -18 b -18.0 November 1 0300 94 100 6 - 6 c - 6.0 0900 87 100 6 -13 d -13.0 1500 93 100 6 - 7 a - 7.0 2100 87 100 6 -13 " b -13.0 November 2 0300 77 100 6 -23* c - 5.5* 0 900 112 100 6 +12* d - 5.5* 1500 98 100 6 - 2 a - 2.0 2100 87 100 6 -13* b - 3.0* November 3 0 300 * c - 3.0* 0 900 104 100 12 + 4* d - 3.0 * 1500 98 100 6 - 2 a - 2.0 2100 99 100 6 - 1 b - 1.0 N o v e m b e r 4 0 300 * c - 2.5* 0900 95 ' 100 . 1 2 - 5* d - 2.5 1500 91 100 6 - 9 a - 9.0 2100 79 100 6 -21* b - 4.0 * November 5 0300 * c - 4.0 * 0 900 113 100 12 +13* d - 4.0 * 1500 99 100 6 - 1 a - 1.0 2100 98 100 6 - 2 b - 2.0 November 6 0300 c 0900 100 100 12 - 0 d - 0.0 T O T A L -121 * Averaged data 108 APPENDIX VII. Winter growth rate data of squawfish from Cultus Lake (1968). Standard F o r k T o t a l F o r k Tagging Tag Length Length Length R e c o v e r y R e c o v e r y L e n g t h G r o w t h Date Number (cm) (cm) (cm) Sex T i m e L o c a t i o n (cm) (cm) October 1 59-825 October 7 59-826 59-827 59-828 59-829 59-830 59-831 59-832 59-833 59-834 59-835 59-836 59-837 59-838 59-839 59-840 59-841 59-842 59-844 59-845 59-846 59-847 59-848 59-849 59-850 59-851 .59-852 59-853 59-854 59-855 59-856 59-857 59-858 59-859 59-860 59-861 59-862 59-863 59-864 59-865 59-866 59-867 59-868 59-869 59-870 59-871 59-872 59-873 59-874 59-875 59-876 59-877 59-878 59-879 59-880 59-681 31.0 34.1 37.6 M 23.8 27.2 30.5 M 27.9 32.5 35.9 M 15.0 17.2 19.4 F 24.2 27.7 31.8 F 24.7 27.5 30.3 M 24.8 28.1 30.6 M 29.5 33.5 37.4 M 27.4 31.4 34.0 M 17.8 20.6 22.6 F 26.7 30.6 33.8 M 17.2 19.7 21.7 F 23.1 26.4 29.2 M 24.2 27.3 30.5 M 15.4 17.3 19.0 F ; 14.7 17.1 18.5 F 25.7 _ 29.6 31.9 M 28.6 32.4 35.8 M 24.6 28.8 30.8 M 27.6 32.3 35.2 M 25.4 29.1 32.2 M 29.2 33.0 36.5 F 30.3 34.6 37.8 F 29.8 33.4 36.9 F 23.6 27.0 29.9 M 13.6 15.5 17.0 F 26.0 29.6 32.6 M 26.7 29.7 33.1 M 23.3 26.7 28.9 M 17.6 20.1 22.5 F 26.0 29.7 32.2 M' 15.6 18.1 19.4 F 25.7 29.3 M 28.5 32.0 35.3 F 25.6 29.5 32.4 F 25.1 28.6 31.7 M 26.1 29.9 32.4 M 26.0 30.3 33.1 F 25.3 28.8 31.1 M 23.4 26.7 29.4 M 26.2 29.9 33.0 M 25.7 28.9 32.0 M 27.7 31.8 35.2 M 24.9 27.5 30.3 M 24.7 28.0 31.4 M 25.1 28.6 31.6 M 25.8 29.4 32.0 M 23.2 26.7 29.4 M 16.0 18.4 21.2 F 16.8 19.2 21.4 F 18.1 20.1 22.0 • F 24.5 28.1 31.0 F 26.1 30.6 33.8 M 25.4 28.9 32.4 F 25.7 29.7 M 22/4/69 A r m y 10/6/69 Outlet 12/5/69 T r a p 32.7 0.2 28.1 0.0 31.4 0.0 20/5/69 L i n d e l l 12/5/69 T r a p 15/9/68 Fence 29.7 0.1 29.0 -0.1 Dead r e c o v e r y 3/6/69 T r a p (2) 12/5/69 T r a p (2) 10/6/69 A r m y 27.2 0.5 28.1 0.1 27.0 0.3 3/6/69 T r a p (2) 29.8 0.1 109 APPENDIX VII. Continued Tagging Date Tag Number Standard Length (cm) F o r k Length (cm) To t a l Length (cm) Sex R e c o v e r y T i m e R e c o v e r y L o c a t i o n F o r k L e n g t h G r o w t h (cm) (cm) 59-882 23.8 27.6 30.4 M 59-883 25.5 29.2 31.8 M 59-884 25.5 29.5 32.7 M 13/5/69 L i n d e l l 29.8 0.3 59-885 26.2 29.4 32.3 M 22/4/69 L i n d e l l 29.9 0.5 59-886 25.6 28.9 31.5 M ' 59-887 28.0 31.7 35.0 F 59-888 26.6 31.1 33.0 F 59-889 23.1 26.4 29.2 M 59-890 23.9 27.6 31.3 F * 59-891 25.5 28.9 32.2 M 59-892 27.2 31.1 34.1 M 59-893 26.6 30.6 33.4 F October 15 59-894 31.9 36.3 39.7 F 14/5/69 T r a p (2) R e l e a s e A r e a (4) 59-895 25.6 28.4 31.2 M 59-896 23.8 26.2 M 59-897 27.6 31.0 33.8 M 59-898 24.9 27.7 F 59-899 27.4 30.2 33.1 M 59-900 27.6 30.8 33.7 M 59-901 24.3 26.9 29.4 . M 59-902 27.4 30.2 33.3 F 59-903 23.4 26.4 29.2 M 59-904 24.5 27.1 30.2 M 59-90 5 27.1 30.2 33.1 M 14/5/69 T r a p (2) R e l e a s e A r e a ( 1 ) 59-906 25.6 28.4 M 59-907 24.9 27.6 30.3 M 59-908 24.3 27.2 30.1 M 59-909 25.0 28.1 31.1 M 8/5/69 T r a p (2) R e l e a s e A r e a (2) 59-910 23.9 26.8 29.6 M 59-911 26.2 29.2 32.1 M 59-912 26.2 28.9 M 59-913 25.7 28.2 31.1 M 59-914 30.0 33.2 36.2 F 59-915 24.4 27.2 M 59-916 27.3 30.7 33.1 F -59-917 27.2 30.8 34.1 F 59-918 29.2 32.3 F 59-919 30.1 33.3 37.6 F 59-920 24.6 27.0 29.7 F 5/5/69 A r m y 27.0 0.0 59-921 26.2 29.4 32.3 F 59-922 23.4 26.5 29.0 M 59-923 30.8 34.5 38.0 F 59-924 25.6 28.4 31.3 M 59-925 25.2 28.1 31.1 M 10/6/69 T r a p (2) 28.9 0.8 59-926 25.3 28.2 M 59-927 26.1 29.0 32.2 U 59-928 25.1 28.2 31.0 M 59-929 18.1 20.0 22.1 M 59-930 34.4 38.1 41.6 F A P P E N D I X VIII. Trap catch data of squawfish f r o m Cultus Lake ( F a l l , 1968). Date Time Hours (1968) (hrs) Trap Catch D a i l y Total F i s h i n g Time August 8 *Trap Installed 11 1200 68 240 25 1200 370 336 26 1200 177 . 24 September 16 1200 208 504 24 1200 84 192 October 1 1200 44 148 3 1200 59 48 7 1200 22 96 15 1200 1 192 .21 1200 • - 8 - - - • - 144 30 1200 16 216 November 12 1200 3 288 19 1200 4 168 28 1200 8 *Trap Removed 216 A P P E N D I X IX. Trap catch data of squawfish f r o m Cultus Lake (Spring, 1969). Date Squawfish Squawfish Squawfish P e r i o d i c i t y F i e l d D i s s e c t i o n Total (1969) released tagged dissected experiment Experiment A p r i l May June 20 *Trap Installed 24 18 18 25 1 1 26 4 4 28 11 11 30 23 23 1 23 34 0 57 2 18 18 4 5 5 5 53 53 6 63 63 7 160 160 8 26 26 9 41 41 1.0 32 32 12 784 784 14 319 319 15 244, 244 20 260 47 307 27 70 70 3 16 208 224 276 1200 145 55 784 2460 Gillnet Dissection 493 Gillnet Tagging 23 Petersen Tag Recoveries 16 2992 112 A P P E N D I X X. Cultus Lake smolt migration (Spring, 1969). Cumulative Relative Date Y e a r l i n g s 2 year olds total Smolt Size P r i o r to A p r i l 1 5 13 9 22 A p r i l 15 23 11 56 16 4 2 • 62 17 7 3 72 18 13 3 88 19 7 5 100 20 40 5 145 21 241 25 411 22 228 25 674 23 641 41 1, 356 53 f i s h / c m 24 505 42 1.903 25 813 110 2, 826 26 458 95 3,379 27 342 127 3, 848 28 4, 996 165 9, 009 60 f i s h / c m 29 12, 530 380 21. 919 62 f i s h / c m 30 11, 663 79 33, 661 65 f i s h / c m May 1 15, 760 322 49, 743 67 f i s h / c m 2 48, 488 8 52 99.083 65 f i s h / c m 3 167, 828 1627 268,538 70 f i s h / c m 4 180, 450 0 448, 988 75 f i s h / c m 5 252, 0 50 0 701, 038 82 f i s h / c m 6 276,085 0 977,123 82 f i s h / c m 7 190, 600 0 1, 167, 723 89 f i s h / c m 8 83, 255 \ 333 1,251.311 86 f i s h / c m 9 61, 315 245 1,312,871 86 f i s h / c m 10 175, 093 347 1,488,311 89 f i s h / c m 11 138, 092 88 1, 626, 491 93 f i s h / c m 12 105, 431 169 1, 732, 091 94 f i s h / c m 13 119, 300 0 1.851, 291 98 f i s h / c m 14 116, 7 57 163 1, 968, 211 102 f i s h / c m 15 120, 970 0 2, 086. 171 104 f i s h / c m 16 74, 460 0 2, 161, 141 111 f i s h / c m 17 20, 833 107 2, 180, 781 111 f i s h / c m 18 39, 630 80 2, 220, 491 106 f i s h / c m A P P E N D I X XI. Catches of fry and other common species seined during f r y emergence at Cultus Lake (Spring, 1969). F R Y COMMON SPECIES D A T E Sockeye Chum Coho Sculpins Squawfish Sticklebacks Suckers M a r c h 31 10 A p r i l 8 14 18 21 25 28 5 7 50 112 184 634 0 0 3 11 0 2 2 0 0 0 0 0 12 3 6 83 60 66 5 4 0 0 3 0 0 1 0 6 0 8 0 0 0 0 0 0 May 1 5 9 13 16 23 25 29 400 54 220 57 121 92 139 45 2 0 4 0 0 0 0 0 0 0 0 7 8 12 10 3 57 45 42 . 30 90 118 97 77 0 0 0 3 0 0 5 0 T 6 11 9 0 42 35 20 0 0 0 0 0 0 0 0 June 2 6 20 40 0 0 2 0 0 53 2 0 21 14 0 0 A P P E N D I X XII. Sample size and the method of capture of the sample used i n the Petersen Mark-Recapture estimate of the Cultus Lake squawfish population. Number of Squawfish 1. P e t e r s e n Tag Recoveries 16 2. P e r i o d i c i t y Experiments 55 3. Trap Catch Dissections 145 4. Gi l l n e t Dissections ( (37 tags) (530-37) ) 493 5. Spring Tagging. Number released lone 1 407 2 105 3 152 4 559 6. F i e l d Conducted Digestion Experiment (663 + 121) 784 7. Additional Releases (June 3, 1969) 16 (May 20, 1969) approx. 260 T O T A L 2992 APPENDIX XIII. Analysis of covariance of the slopes and intercepts of the rates of digestion from the Cultus Lake field digestion data. Deviations from regression Fork * a * * - R eS- Mean Length f . £r Coef£> f £ y 3 . (£xy)2/2xa Square 1 24.6 - 25.5 12 753.00 - 33.18 4.08 -.0427 11 2.71 .2463 2 25.6 - 26.5 28 1464.43 - 44.94 14.36 -.0307 27 12.99 .4811 3 . 26.6 - 27.5 42 2489.14 - 98.35 28.42 -.0395 41 24.54 .5985 4 27.6-28.5 82 5997.52 -243.08 58.11 -.0404 81 48.26 .5958 5 28.6 - 29.5 106 5855.44 -199.05 88.62 -.0340 105 81.85 .7795 6 29.6 - 30.5 117 7067.08 -370.51 118.04 +.0524 116 98.62 .8502 7 30.6 - 31.5 96 6434.63 -334.27 101.99 +.0519 95 84.63 .8908 8 31.6 - 32.5' 81 5723.56 -211.28 84.76 +.0369 80 76.97 .9621 9 32.6 - 33.5 50 3618.00 -198.52 59.01 +.0549 49 48.11 .9818 10 , 33.6 - 34.5 45 2692.80 -173.15 55.60 +.0643 44 44.47 ' 1.0107 Within 649 523.15 .8061 Reg. Coefficient 1 9 3.60 .40 Common 659 42095.60 -1905.33 612.99 -.0453 658 526.75 .8005 Adj. Means 9 45.98 5.108 Total 668 43159.37 -2050.52 670.15 667 572.73 .8587 F test slopes = M.S. Reg. Coeff. = 0.40 — 0.8061 = 0.49 d.f. = 9: 649; p = .0 5 = 1.88 M.S. within F test intercepts = M.S. Adj. Means = 5.108 - 0.8005. = 6.6 d.f. = 9; 658; p = .05 = 1.88 M.S. Common 116 A P P E N D I X XIV. Total weight of the ovaries (grams) for squawfish of various fork lengths (cm) samples f r o m Cultus Lake . (Spring, 1.969) F o r k Weight of Fork• * Weight of Length ovaries Length ovaries (cm) (gms) (cm) (gms) 29.4 44.19 37.7 81.14 28.4 38.20 37.4 87.74 29-0 26.92 39.9 104.34 28.8 24.64 37.2 103.68 30.0 23.18 35.2 54.86 28.1 41.21 35.8 100.54 29.6 28.12 36.1 89.60 29.0 30.43 35.1 82.69 29.1 30.61 36.1 63.68 29.1 47.28 38.1 94.89 30.0 39.65 37.5 87.22 28.9 43.26 36.9 94.80 31.8 40.43 35.2 41.81 35.0 83.14 49.0 144.60 30.7 50.12 48.0 128.10 32.0 77.52 40.5 120.60 30.4 55.16 40.8 98.80 32.8 58.16 31.3 46.35 33.0 70.00 30.6 34.76 33.5 40.26 31.0 36.19 32.6 55.80 32.5 • 58.40 30.9 54.38 30.7 45.66 34.5 51.94 31.0 59.44 31.2 53.70 32.4 42.43 33.2 41.86 APPENDIX XV. Calculation of dissolved oxygen levels from duplicate water samples (Winkler method), expressed as milligrams/liter and milliliters/liter. Fish Average mg Os/ Average mg Os / Change Volume Expt. Change Weight titer liter titer liter mg Oa / Hg O Duration ml 0 2 / (gms) before before after after liter (liters) (min) liter 252 8.20 7.75 7.90 8.00 8.00 8.00 13.12 12.40 12.64 12.80 12.80 12.80 3.75 5.95 4.0 5 4.00 5.45 5.40 6.00 9.52 6.48 6.40 8.72 8.64 7.12 3.20 6.16 6.40 4.08 4.16 4.862 4.862 4.862 4.862 4.862 4.862 60 60 60 60 60 60 4.979 2.238 4.308 4.475 2.853 2.909 234 8.25 8.10 8.05 7.85 7.75 8.05 13.20 12.96 12.88 12.56 12.40 12.88 4.65 5.60 5.50 6.25 5.90 6.05 7.44 8.96 8.80 10.00 9.44 9.68 5.76 4.00 4.08 2.56 2.96 3.20 4.855 4.855 4.855 4.855 4.855 4.855 40 40 40 40 40 40 4.028 2.797 2.853 1.790 2.070 2.238 APPENDIX XVI. Calculation of oxygen consumption and metabolic rate expressed as milligrams Oa /kg/hr and Kcal/gm/day. ' Fish Weight 0 2 Consumption Oa Consumption Metabolic Rate Metabolic Rate (gms) (mg 03) (ml Oa) (mg 03/kg/hr) (Kcal/gm/ day) 252 34.617 23.323 137.369 .010106 15.558 10.881 61.738 .004715 29.950 20.945 118.849 .009076 31.117 21.757 123.480 .009428 19.837 13.871 78.718 .006010 20.226 14.143 80.261 .006129 100.069 .007577 234 27.965 19.556 179.263 . .013689 19.420 13.579 124.487 .009505 19.808 - 13.851 126.974 .- : .009695 12.429 8.690 79.673 .006083 14.370 10.0 50 92.115 .007035 15.536 10.865 99.590 .007605 Average 108.54 .00826 Variance 1074.47 .00001 S.D. 32.77 .00248 S.E. 9.46 .00072 5% Lower Limit 87.72 .00668 5% Upper Limit 129.37 .00983 

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