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The ecology and harvesting of euphausiids in the Strait of Georgia Heath, William Arthur 1977

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THE ECOLOGY AND HARVESTING OE EUPHAUSIIDS IN THE STRAIT OF GEORGIA WILLIAM ARTHUR HEATH B.Sc.(Hons.), U n i v e r s i t y of B r i t i s h Columbia, 1972 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the F a c u l t y of Graduate Studies (The Department of Zoology and the I n s t i t u t e of Oceanography) We accept t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA December, 1977 (c) W i l l i a m Arthur Heath, 1977 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the regu i rement s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I ag ree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s tudy . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . It i s u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i thout my w r i t t e n p e r m i s s i o n . Department o f Zoology  The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 Date April 10, 1978 i ABSTRACT Po p u l a t i o n s of Euphausia p a c i f i c a Hansen i n the S t r a i t of Georgia r e g i o n which have r e c e n t l y been commercially h a r v e s t e d were s t u d i e d with r e s p e c t to l i f e h i s t o r y , d i s t r i b u t i o n and p o p u l a t i o n dynamics i n order t o examine as p e c t s of the management of the resource. The p o t e n t i a l use of l o c a l e u p h a u s i i d s as a food item f o r f i s h r e a r i n g was a l s o e v a l u a t e d through chemical analyses and f e e d i n g t r i a l s with j u v e n i l e coho salmon. The maximum l i f e span i n l o c a l p o p u l a t i o n s was 19 months f o r males and 22 months f o r females. Spawning, which occurred from May to September, appeared to be c l o s e l y r e l a t e d t o phytoplankton abundance. F i r s t - y e a r growth was maximal i n summer (0.094 mm/day) but slowed i n autumn and h a l t e d i n winter. Growth i n the f o l l o w i n g year showed a s i m i l a r p a t t e r n . Males appeared to grow f a s t e r and experienced s i z e - s e l e c t i v e m o r t a l i t y f o l l o w i n g e a r l y maturity (11-12 mm) , S u r v i v a l i n c r e a s e d with l i f e phase changes between egg (6%/mo) and e a r l y a d u l t s t a g e s (68%/mo) but d e c l i n e d s h a r p l y f o r i n d i v i d u a l s over 18 mm. T o t a l biomass, B, i n each p o p u l a t i o n reached a maximum i n October-November. P r o d u c t i o n by p a c i f i c a , P, i n Saanich I n l e t d u r i n g July-November was 26.8 mgC/ra2/day (P/B = 8.8), which i s s i m i l a r t o t h a t f o r herbivorous copepods, but higher than a p r e v i o u s estimate f o r E._ -p.acifica . J u v e n i l e coho salmon a t 9 C showed mean growth r a t e s of 3.8%/day on f r e e z e - d r i e d e u p h a u s i i d s compared to 3.0%, 2.7% and 3.1%/day on d i e t s of e u p h a u s i i d meal, f r o z e n e u p h a u s i i d s and Oregon Moist P e l l e t , r e s p e c t i v e l y . L o c a l e u p h a u s i i d s have a i i well-balanced' spectrum of amino a c i d s i n t h e i r p r o t e i n s and high c a r o t e n o i d c o n c e n t r a t i o n s (80-219 ya,g/g t i s s u e ) , making them s u i t a b l e f o r use i n a g u a c u l t u r a l feeds. B r i t i s h Columbia's e u p h a u s i i d f i s h e r y harvested about 100 m e t r i c tons d u r i n g e a r l y 1977; the main uses are as an aguarium f i s h food and as a d i e t a r y supplement i n salmon a g u a c u l t u r e . Y i e l d c a l c u l a t i o n s and other management c o n s i d e r a t i o n s have i n d i c a t e d t h a t the optimal h a r v e s t i n g time f o r E± p a c i f i c a i s between October and December r a t h e r than from January to March as suggested by government g u i d e l i n e s on plankton h a r v e s t i n g , a l i m i t e d and c a r e f u l l y monitored e u p h a u s i i d f i s h e r y i n the S t r a i t of Georgia r e g i o n appears t o have p o t e n t i a l value to the new plankton h a r v e s t i n g i n d u s t r y and to managers of a s s o c i a t e d f i s h e r i e s who need f u r t h e r i n f o r m a t i o n on zooplankton p o p u l a t i o n dynamics. TABLE OF CONTENTS Page Ab s t r a c t .................................................. i Table of Contents i i i L i s t o f Ta b l e s v i Lxst of F i g u r e s .••..••........,....... . . . . , . . . . . . . . . . . . . . . v i i i Acknowledgements .......................... ...... .. ...... .. x i i INTRODUCTION 1 CHAPTER 1: BACKGROUND AND METHODS 1«1 X ii^-irocluc "fcion *« • * * « * •«• •«• • •-• • • * • • • •••*§•••••• • Q 1.2 D e s c r i p t i o n of the Study Region .................. 4 1.3 Previous S t u d i e s on E. p a c i f i c a .................. 6 1.4 M a t e r i a l s and Methods ............................ 12 1.41 Sampling Procedures .............................. 13 1.42 Laboratory Procedures ............................ 14 1.421 Length Measurements .............................. 16 1.422 A n a l y s i s of Length-freguency D i s t r i b u t i o n s ....... 17 1.423 Length:weight R e l a t i o n s h i p s 18 1. 424 I d e n t i f i c a t i o n of L i f e H i s t o r y Stages 19 CHAPTER 2: LIFE HISTORY, SIZE STRUCTURE, GROWTH AND MORTALITY 2.1 L i f e H i s t o r y Stages 20 2.2 L a r v a l S u r v i v a l 27 2.3 Po p u l a t i o n S i z e S t r u c t u r e i n Saanich I n l e t ....... 28 2.4 P o p u l a t i o n S i z e S t r u c t u r e i n J e r v i s I n l e t and the S t r a i t Of Georgia ........................... 37 2.5 M o r t a l i t y of J u v e n i l e and Adult E A fiacj.fj.ca 51 i v 2.6 D i s c u s s i o n ....................................... 61 CHAPTER 3: BIOMASS AND PRODUCTION 3.1 Length;weight R e l a t i o n s h i p ,. 74 3.2 Carapace:body Length R e l a t i o n s h i p 76 3.3 Annual and Monthly E. p a c i f i c a Biomass D i s t r i b u t i o n 77 3.4 Production o f E± p_acif i c a .......... 81 3.5 S p a t i a l D i s t r i b u t i o n s of Biomass of Megazooplankton and Phytoplankton i n the S t r a i t of Georgia H@cj x o n * • * • * • • * • * • *••••••*••••*• * • • * * • * • • • * • * • • * * • 3.6 D i s c u s s i o n ....................................... 97 CHAPTER 4: EUPHAUSIIDS AS A FOOD 4.1 I n t r o d u c t i o n 110 4.2 Methods of Chemical A n a l y s i s .....................110 4.3 F i s h Feeding T r i a l s with E u p h a u s i i d P r e p a r a t i o n s . 111 4.31 Methods .....v..;.,.....,.......... 111 # ^  Hss u X • * • « • • * • • • • • • • • • * • • • • • • * • • * • • * « • • • 'tis 4.41 Composition of Euphausiids ....................... 113 4.42 J u v e n i l e Coho Growth on Euphausiid P r e p a r a t i o n s .. 115 4.5 D i s c u s s i o n 118 4.51 Composition of L o c a l Euphausiids .................118 4.52 Coho Growth on Euphausiid D i e t s ..119 CHAPTER 5: ZOOPLANKTON HARVESTING 5.1 I n t r o d u c t i o n ....................... 121 5.2 L i t e r a t u r e Review ................................ 121 5.21 Methods of Plankton Harvesting 125 5.22 Operating C o n d i t i o n s f o r Plankton Harvesting ..... 128 5.23 Examples of Present Micronekton and Zooplankton H a r v e s t i n g ............. .. 132 y 5.231 A n t a r c t i c K r i l l , Euphausia supgrba ............... 132 5.232 North A t l a n t i c Copepods and K r i l l , Calanus f i n m a r c h i c u s and MgganYctiphangs no r v e q i c a 139 5.233 B r i t i s h Columbia's Plankton F i s h e r y , E, p a c i f i c a and Calanus plumchrns ............ 145 CHAPTER 6: NET SELECTIVITY, YIELD AND MANAGEMENT CONSIDERATIONS 6.1 I n t r o d u c t i o n ..................................... 155 6.2 Net S e l e c t i v i t y 155 6.3 F a c t o r s A f f e c t i n q Y i e l d 159 6.4 Other Manaqement C o n s i d e r a t i o n s 166 CHAPTER 7: SUMMARY *7 # 1 Su m iQctir y *••••• • • • «# • •••«• ••*«:•* *«•*•• • • . 167 BIBLIOGRAPHY ........ . ................ 170 APPENDIX A 183 v i LIST OF TABLES Table Page •1. Monthly mean body l e n g t h s by sex f o r E«_ pacJUEica c o h o r t s i n Saanich I n l e t between January 197 4 ana Febuary 1976. .................................. 29 2. Growth c o n s t a n t s f o r von B e r t a l a n f f y equations f i t t e d t o Saanich I n l e t data on mean body l e n g t h by sex, p l o t t e d i n Fig u r e 10. ......................... 35 3. Summary of Saanich I n l e t E. p a c i f i c a growth con s t a n t s f o r von B e r t a l a n f f y equations of Table 2 ac c o r d i n g t o sex and season. ....................... 37 4. Monthly mean body l e n g t h s by sex f o r I A p a c i f i c a c o h o r t s i n J e r v i s I n l e t between A p r i l and December 1975. ..............v................ 38 5. Monthly mean body l e n g t h s by sex f o r E. p a c i f i c a c o h o r t s i n the S t r a i t of Georgia between March 1975 and February 1976 40 6a. Growth c o n s t a n t s f o r von B e r t a l a n f f y equations f i t t e d t o J e r v i s I n l e t data on mean body l e n q t h by sex, p l o t t e d i n F i g u r e 12. ......................... 45 6b. Growth constants f o r von B e r t a l a n f f y equations f i t t e d t o S t r a i t o f Georgia data on mean body l e n g t h by sex, p l o t t e d i n F i g u r e 14. ...................... 45 7. Re s u l t s of Student's t - t e s t s on p a i r e d v a l u e s of von B e r t a l a n f f y c o n s t a n t s f o r sexes w i t h i n Ii. p a c i f i c a c o h o r t s . ....... .... .. . . .. . . . . .. .. ...... 48 8. Values of s e l e c t i v i t y , r , f o r p a c i f i c a sexes from Saanich I n l e t f o r p e r i o d s o f no growth i n 1974 and 1975. .................................. 55 9. Re p r e s e n t a t i v e s u r v i v a l r a t e s f o r stages of I i £a£ifi£a i n the S t r a i t o f Georgia r e g i o n used i n c o n s t r u c t i o n of the h y p o t h e t i c a l s u r v i v a l curves i n F i g u r e 19. ............ 59 10a. Summary of consumption o f euph a u s i i d eggs and l a r v a e by j u v e n i l e f i s h i n Saanich I n l e t d u r i n g A p r i l - J u l y 1968. ..... ........... 66 10b. Summary of p r e d a t i o n by j u v e n i l e f i s h on j u v e n i l e and a d u l t e u p h a u s i i d s i n Saanich I n l e t d u r i n g A p r i l - J u l y 1968. 66 11. Surface (0-10m) temperatures during E. , p a c i f i c a *s main r e p r o d u c t i v e p e r i o d and durin g winter i n s i x re g i o n s o f the North P a c i f i c . ....................,. 72 v i i 12. Summary of r e s u l t s f o r r e g r e s s i o n of body l e n g t h on carapace l e n g t h f o r E. p a c i f i c a from Saanich I n l e t and the S t r a i t o f Georgia. ......................... 77 13. Production e s t i m a t e s and a s s o c i a t e d parameters f o r E A p a c i f i c a p o p u l a t i o n s and co h o r t s d u r i n g June-14. Production:biomass r a t i o s and mean l i f e expectancy f o r E. p a e i f i c a p o p u l a t i o n s and Saanich I n l e t c o h o r t s d u r i n g June-November 1975. ,......................... 84 15. Summary of o b s e r v a t i o n s on t h e 107 kHz sound s c a t t e r i n g l a y e r and cor r e s p o n d i n g MNT e s t i m a t e s of megazooplankfon biomass f o r the October 1975 c r u i s e (75/31). . ................................... 90 16a. Proximate composition o f euphatisiids caught i n Saanich I n l e t , January 1975. ..,;..>......»...... 114 16b. L i p i d and c a r o t e n o i d content of commercial c a t c h e s o f e u p h a u s i i d s from S e c h e l t and Saanich I n l e t s . .... 114 17. amino a c i d c omposition of t h r e e p r e p a r a t i o n s o f eup h a u s i i d s from Saanich I n l e t . , . , . * . . , . . . . . . . . . . . . . 115 18. Comparison of i n i t i a l and f i n a l mean values f o r »et weight and f o r k l e n g t h as w e l l as mean growth r a t e s of d i e t groups i n coho feeding t r i a l s . ....... 116 19. Summary of ANO?a on f i n a l wet weights, f o r k l e n g t h s , and growth r a t e s of the f o u r coho d i e t groups. 117 20. Comparison of means f o r d i e t groups by S c h e f f e ' s l e a s t s i g n i f i c a n t d i f f e r e n c e { LSD ) method. ....... 118 21. Summary of e u p h a u s i i d c a t c h e s by s t a t i s t i c a l area ( F i s h e r i e s Service) and l o c a l i t y f o r 1975-77. ...... 148 22. Beverton-Holt y i e l d parameters f o r f i r s t - and second-year c o h o r t s of E. p a c i f i c a i n Saanich I n l e t d u r i n g 1975. 160 23. L i s t of 1975 c r u i s e s , with dates and d e s t i n a t i o n s . ... 183 v i i i LIST OF FIGURES F i g u r e Page 1. The S t r a i t o f Georgia r e g i o n ......................... 5 2. Euphausiid egg(o) and l a r v a l ( t ) abundances i n Saanich I n l e t d u r i n g June and J u l y 1966, from o b l i q u e M i l l e r hauls(12m-0) 21 3. Euphausiid egg(o), l a r v a l (t) and j u v e n i l e (e) abundances i n Saanich I n l e t from 175m v e r t i c a l hauls during May-July 1968. 22 4. Mean c h l o r o p h y l l - a c o n c e n t r a t i o n i n the upper 20 m of Saanich I n l e t d u r i n g May-July 1968. ........ 23 5. C h l o r o p h y l l - a c o n c e n t r a t i o n s i n the upper 10 m of Saanich I n l e t d u r i n g 1975. 24 6. Frequency of eu p h a u s i i d l a r v a l types encountered in M i l l e r net samples d u r i n g May and June 1975 i n Saanich I n l e t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 7 . . V e r t i c a l d i s t r i b u t i o n of temperature (C) at s t a t i o n Saa-3 duri n g 1974-75. .............................. 26 8. Length frequency d i s t r i b u t i o n s of | A p a c i f i c a from Saanich I n l e t , 1974 30 9. Length frequency d i s t r i b u t i o n s of p a c i f i c a from Saanich I n l e t , Jan. 1975 t o Feb. 1976......... 31 9. (continued). ........,........,,......... •..... ....... 32 10. Mean modal body l e n g t h s and f i t t e d von B e r t a l a n f f y qrowth curves f o r female(a) , male (e) and immature(i) •E. . p a c i f i c a i n Saanich I n l e t durinq 1974-75. ....... 33 11,. .Length frequency d i s t r i b u t i o n s of E^ p a c i f i c a from J e r v i s I n l e t , A p r i l to December 1975 39 12. Mean modal body l e n q t h s and f i t t e d von B e r t a l a n f f y growth curves f o r f e m a l e ( a ) , male (e) and immature (i) JU. E a s l f i s a i n J e r v i s I n l e t d u r i n g 1975. 41 13. Length frequency d i s t r i b u t i o n s of J A p a c i f i c a from the S t r a i t of Georqia, March 1975 to February 1976...................................... 43 14. Mean modal body l e n q t h s and f i t t e d von B e r t a l a n f f y qrowth curves f o r female ( a ) , male (e) and immature(i) E. p a c i f i c a i n the S t r a i t o f Georqia durinq 197 5. ...,77................................. 46 i x F i g u r e Page 15. Mean c h l o r o p h y l l - a c o n c e n t r a t i o n s i n the upper 10 m of J e r v i s I n l e t and the S t r a i t o f Georgia during 1975. ....................................... 47 16. Changes i n sex r a t i o (M : F) with body l e n g t h f o r B. p a e i f i c a p o p u l a t i o n s d u r i n g 1975............ 50 17. Catch curves o f a l l E. p a e i f i c a sampled d u r i n g 1975 by K i l l e r net (HNT) and~by SCOR net i n the S t r a i t of Georgia r e g i o n . 52 18. Examples of s u r v i v a l curves f o r J A j a c i f i c a c o h o r t s . ...... ....................... ...........> .... 57 19. H y p o t h e t i c a l s u r v i v a l curves f o r E. p a e i f i c a i n the S t r a i t o f Georgia r e g i o n . ................... 60 20. Repr e s e n t a t i v e growth curves f o r E. p a e i f i c a from the S t r a i t of Georgia and other r e g i o n s o f the P a c i f i c . 69 21. T o t a l mean biomass and mean biomass by 1 mm s i z e c l a s s e s of E^ p a e i f i c a p o p u l a t i o n s i n the S t r a i t o f Georgia region during 1975................ 78 22. Monthly biomass l e v e l s o f conspicuous s i z e c l a s s e s of p a e i f i c a during 1975 79 23. Monthly changes i n biomass f o r a l l s i z e c l a s s e s (7-23 mm) i n E.. p a e i f i c a p o p u l a t i o n s and i n Saanich I n l e t c o h o r t s d u r i n g 1975. .............................. . 81 24. D i s t r i b u t i o n of wet biomass (g/m3) of megazooplankton ( > 5 ram) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r d u r i n g M a r c h - A p r i l 1975. 85 25. D i s t r i b u t i o n of wet biomass (g/m3) of megazooplankton ( > 5 7m) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r during J u n e - J u l y 1975. , 86 26. D i s t r i b u t i o n of wet biomass (g/m3) of megazooplankton (> 5 mm) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r d u r i n g August-September 1975. 88 27. D i s t r i b u t i o n of wet biomass (g/m3) of megazooplankton (> 5 mm) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r d u r i n g October-November 1975. /. . . 89 28. D i s t r i b u t i o n of megazooplankton biomass(g/m 3) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r i n Saanich I n l e t , J u l y 1975 91 X 29. D i s t r i b u t i o n o f megazooplankton biomass(g/m 3) i n t h e 107 kHz s o u n d s c a t t e r i n g l a y e r i n Saanich I n l e t , August 1975. , .. ...................... 9 3 30. Change i n mean percentage of t o t a l megazooplankton biomass c o n t r i b u t e d by E. p a c i f i c a during 1975 . . . . 94 31. D i s t r i b u t i o n o f c h l o r o p h y l l - a (mg/m3) i n the upper 10 m i n the S t r a i t of Georgia r e g i o n , June-July 1975. .................................... 95 32. D i s t r i b u t i o n of c h l o r o p h y l l - a (mg/m3) i n the upper 10 m, August-September 1975.................. , 96 33. D i s t r i b u t i o n of c h l o r o p h y l l - a {mg/m3) i n the upper 10 m, October-November 1975. ................. 98 34. Freguency d i s t r i b u t i o n s o f wet weight f o r j u v e n i l e coho sampled before and a f t e r f e e d i n g t r i a l s on f o u r d i e t s . ...................................., 116 35..The e f f e c t of f i s h i n g experience on eu p h a u s i i d f i s h i n g s u c c ess, CPE i n S t r a i t of Georgia waters during the 1976 and 1977 seasons. .................. 149 36. Comparison of s i z e compostion of eupha u s i i d c a t c h from SCOH, MNT and IKMT hanls i n Saanich I n l e t , August 1975. 157 37. Comparison o f s i z e composition of euphausiid catch from SCOB and IKMT hauls i n Saanich I n l e t , March 1975. .. 158 38. Comparison of s i z e c omposition of eupha u s i i d c a t c h i n samples from M i l l e r net (MNT) and commercial plankton net tows taken c o n s e c u t i v e l y i n Saanich I n l e t , January 1977. .... .................................. 159 39. Contours o f e g u i l i b r i u m y i e l d / r e c r u i t f o r the s p r i n g 75 co h o r t of E. -.-pacifica-i n a f i s h e r y commencing at time t and ending a t time t=11 m o . ( A p r i l ) . . . . . . . . . . . . . . . . . . . . . 161 40. Contours of e g u i l i b r i u m y i e l d / r e c r u i t f o r the s p r i n g 74 c o h o r t of E A l p a c i f i c a i n a f i s h e r y commmencing at time t and ending at time t=22 mo. ............................ 162 41. R e l a t i o n s h i p s between y i e l d / r e c r u i t and f i s h i n g m o r t a l i t y f o r 3-month f i s h e r i e s beginning i n October and January.................... 164 x i 42. C r u i s e t r a c k s f o r survey c r u i s e s 75/10 (March) and 75/12 ( A p r i l ) . 184 43. C r u i s e t r a c k s f o r survey c r u i s e s 75/21 (June), 75/24 (July) and 75/25 ( J u l y ) . . . . . . . . . . . . . . . . . . . . . . 185 44. C r u i s e t r a c k s f o r survey c r u i s e s 75/27 (August) and 75/29 (September). ............................. 186 45. C r u i s e t r a c k s f o r survey c r u i s e s 75/31 (October) and 75/33 (November) 187 x i i ACKNOWLEDGMENTS Thi s p r o j e c t would not have been p o s s i b l e without the help of many people. I thank ray t h e s i s s u p e r v i s o r . Dr. T.H. Parsons f o r h i s s u g g e s t i o n s , advice and support throughout the study. I am g r a t e f u l t o the many f e l l o w graduate s t u d e n t s , f a c u l t y and t e c h n i c i a n s at the I n s t i t u t e of Oceanography who shared s h i p time and a s s i s t e d i n my work. To the o f f i c e r s and crew of the re s e a r c h v e s s e l s , C.S.S. Ve c t o r , C.N.A.7. Laymore and R.V. Pandora I I , I extend my g r a t i t u d e f o r t h e i r c o - o p e r a t i o n and s e r v i c e s . I a l s o thank the plankton fishermen f o r t h e i r i n t e r e s t i n the p r o j e c t and c o - o p e r a t i o n i n answering the g u e s t i o n a i r e and/or completing b r i d g e l o g s . In a s i m i l a r way, I am g r a t e f u l to the h a r v e s t i n g companies f o r i n f o r m a t i o n on landed c a t c h and access t o commercial samples f o r chemical a n a l y s e s . I thank my wife, V a l e r i e , f o r her generous h e l p i n d r a f t i n g f i g u r e s and ty p i n g much of the manuscript. I am g r a t e f u l t o my r e s e a r c h committee members, Drs. C a r e f o o t , Northcote, Osborn and Walters f o r t h e i r advice and suggestions f o r improving t h e manuscript. I thank Dr. Wilimovsky f o r i n t r o d u c i n g me to the viewpoint o f the f i s h e r y b i o l o g i s t and f o r making a computer program of the Beverton- H o l t model a v a i l a b l e t o me. F i n a l l y , I am g r a t e f u l t o the N a t i o n a l Besearch C o u n c i l of Canada f o r s u p p o r t i n g me through a post-graduate bursary and s c h o l a r s h i p during my work, and f o r r e s e a r c h support through my s u p e r v i s o r ' s grant NBC 67-6689. 1 INTRODUCTION The S t r a i t of Georgia and i t s adjacent i n l e t s maintain p r o d u c t i v e p o p u l a t i o n s o f phyfoplankton and zooplankton (Parsons et a l ^ ,1970) which i n t u r n support a number of s t o c k s of commerical f i s h , such as P a c i f i c h e r r i n g , salmon and v a r i o u s grou n d f i s h (Johnson, 1976). Recently, a commercial f i s h e r y has begun t o e x p l o i t a major zooplankton group, the e u p h a u s i i d s , i n l o c a l i n l e t s . L i m i t e d g u a n t i t a t i v e data have been a v a i l a b l e on the d i s t r i b u t i o n , l i f e h i s t o r y and p o p u l a t i o n dynamics of the euphausiid p o p u l a t i o n s i n B.C. waters. Consequently, the r a t i o n a l management of t h i s marine resource has been hampered. The main goals of t h i s study are t o examine the above asp e c t s of the ecology of Enphausia p a c i f i c a Hansen, th e dominant e u p h a u s i i d s p e c i e s , i n order t o assess the d i s t r i b u t i o n of t h i s zooplankton resource, to i n t e r p r e t the l i f e h i s t o r y i n l o c a l waters, and to estimate p r o d u c t i o n of I i p a c i f i c a i n three subregions of the S t r a i t o f Georgia; and secondly t o d e s c r i b e the r e c e n t development of the f i s h e r y and to examine f a c t o r s a f f e c t i n g the p o t e n t i a l y i e l d . An a u x i l i a r y aim i s to e v a l u a t e the use of e u p h a u s i i d s as a food f o r salmon r e a r i n g . Chapter 1 p r o v i d e s seme background i n f o r m a t i o n on the study area and on the animal s u b j e c t , E._ p a c i f i c a ; a d e s c r i p t i o n o f the methods f o r c o l l e c t i n g and a n a l y s i n g samples of zooplankton and phytoplankton f o l l o w s . Chapter 2 presents r e s u l t s and d i s c u s s i o n c o n c e r n i n g the b a s i c p o p u l a t i o n b i o l o g y of I i , p a c i f i c a i n Saanich I n l e t , J e r v i s I n l e t and the S t r a i t of Georgia; r e s u l t s of the present study 2 are d i s c u s s e d i n r e l a t i o n to p r e v i o u s s t u d i e s on E. p a e i f i c a i n other r e g i o n s of the North P a c i f i c , and where p o s s i b l e , i n r e l a t i o n t o work on other s p e c i e s of euphausiids i n v a r i o u s p a r t s of the world ocean. Chapter 3 extends the a n a l y s i s of growth and m o r t a l i t y t o biomass d i s t r i b u t i o n s through a p p l i c a t i o n of length:weight r e l a t i o n s h i p s . Estimates o f secondary production by • E. . p a e i f i c a i n the subregions of the S t r a i t o f Georgia are compared with previous e s t i m a t e s f o r zooplankton. In a d d i t i o n , the d i s t r i b u t i o n s of biomass f o r megazooplankton and phytoplankton from survey c r u i s e s over the S t r a i t of Georgia r e g i o n d u r i n g 1975 are presented. Chapter 4 examines the q u a l i t i e s of euphausiids which make them a p o t e n t i a l source of p r o t e i n and pigmentation f o r a q u a c u l t u r a l feeds. An experiment i s d e s c r i b e d which compares the qrowth r a t e s of f o u r qroups of j u v e n i l e choho which are f e d t h r e e d i f f e r e n t p r e p a r a t i o n s o f euphausiids and a c o n t r o l d i e t . Chapter 5 l o o k s a t the r e l a t i v e l y new r e s e a r c h i n t o the prospects of zooplankton h a r v e s t i n q . A review of the l i t e r a t u r e i s presented to summarize the present s t a t u s o f t h i s important development i n world f i s h e r i e s . The l o c a l f i s h e r y f o r euphausiids i n B r i t i s h Columbia waters i s d e s c r i b e d i n t h i s c ontext. Chapter 6 examines f a c t o r s which miqht a f f e c t the y i e l d t o the f i s h e r y , such as net s e l e c t i v i t y , time of h a r v e s t i n q and d i s t r i b u t i o n o f h a r v e s t i n q e f f o r t . The f i n d i n q s are d i s c u s s e d i n 3 r e l a t i o n to the r e c e n t l y s t a t e d government g u i d e l i n e s on zooplankton h a r v e s t i n g . Chapter 7 presents a summary of the study and o f f e r s s u ggestions f o r f u r t h e r r e s e a r c h on euphausiid ecology and on zooplankton h a r v e s t i n g . 4 CHAPTER 1: BACKGROUND AND METHODS 1.1 I n t r o d u c t i o n As a p r i n c i p a l aim of t h i s study i s to make a p r a c t i c a l c o n t r i b u t i o n to our knowledge o f the p o p u l a t i o n b i o l o g y of an important zooplankton s p e c i e s i n l o c a l waters, i t i s u s e f u l to begin with a review o f some asp e c t s o f the p h y s i c a l geography and oceanography of the study r e g i o n , and t o summarize the scope of p r e v i o u s s t u d i e s on the b i o l o g y o f E ± . p a e i f i c a • . . 1.2 D e s c r i p t i o n o f t h e Study Region. The S t r a i t of Georgia {Figure 1), between Vancouver I s l a n d and the mainland of Canada and the United S t a t e s , i s about 200 km lo n g , with an average width o f 30 km and an average depth of 156 m. A s s o c i a t e d with the main channel of the s t r a i t are s e v e r a l f j o r d s ( i n l e t s ) , such as Saanich I n l e t on Vancouver I s l a n d , and Burrard I n l e t , Howe Sound and J e r v i s I n l e t on the mainland c o a s t . The waters of the S t r a i t of Georgia exchange with the P a c i f i c Ocean through the S t r a i t o f Juan de Fuca t o the southwest and through Johnstone S t r a i t to the n o r t h . There i s evidence that the shallow approaches to Saanich I n l e t s i g n i f i c a n t l y l i m i t the inward t r a n s p o r t of eu p h a u s i i d p o p u l a t i o n s from the S t r a i t and the P a c i f i c Ocean. The general oceanographic f e a t u r e s of the S t r a i t of Georgia have been d e s c r i b e d by Waldichuck (1 957) and by T u l l y and Dodimead(1957). The oceanography o f Saanich I n l e t was reviewed by Herlinveaux(1962) while Pickard(1961) has d e s c r i b e d oceanographic f e a t u r e s o f s e v e r a l mainland i n l e t s , i n c l u d i n g 5 FIGURE 1. The S t r a i t of Georgia r e g i o n . J e r v i s I n l e t . Lazier<1963) d i s c u s s e d p h y s i c a l processes i n the 6 J e r v i s and S e c h e l t I n l e t systems. The major i n f l u e n c e s on the p h y s i c a l oceanography of the S t r a i t o f Georgia and the adjacent i n l e t s are wind s t r e s s , t i d e s , freshwater r u n - o f f and s u n l i g h t . The annual c y c l e of b i o l o g i c a l production of the s t r a i t i s c l o s e l y a s s o c i a t e d with the seasonal changes i n freshwater r u n - o f f ( a f f e c t i n g s a l i n i t y and l i g h t e x t i n c t i o n i n the s u r f a c e waters) and s o l a r r a d i a t i o n ( a f f e c t i n g water temperature and p h o t o s y n t h e t i c a c t i v i t y of phytoplankton). The p r o d u c t i o n processes of the S t r a i t of Georgia plankton community have been d e s c r i b e d by Parsons and co-workers(1969a,b;1970; LeBrasseur e t a l v ,1969). Euphausia p a e i f i c a i s a temperate North P a c i f i c s p e c i e s which makes up an important p a r t of the zooplankton community of the North P a c i f i c D r i f t between l a t i t u d e s 40 and 50 N; i t s range along the west c o a s t of North America extends from 25 N (southern C a l i f o r n i a ) to 60 N (northern G u l f of Alaska) (Banner, 1949; Brinton,1962). In the S t r a i t of Georgia r e g i o n , E± p a e i f i c a i s u s u a l l y the most abundant e u p h a u s i i d , while other common s p e c i e s i n c l u d e Thysanoessa r a s c h i i x T._, s p i n i f e r a ^ and Tj_ l o n g i p e S i Less f r e q u e n t l y o c c u r r i n g s p e c i e s are Nematoscelis d i f f i c i l i s j , Thysanoessa i n e r m i s and Tessarabr ach i o n o c u l a t u s ( F u l t o n , 1 968) . 1.3 Previous s t u d i e s on E. P a e i f i c a Aspects of the l i f e h i s t o r y o f Euphausia p a e i f i c a have been observed i n a number o f o c e a n i c environments; by Nemoto(1957) and Ponomareva(1963) i n the north temperate r e g i o n of the western P a c i f i c , by Smiles and Pearcy(1971) i n the Oregon 7 o f f s h o r e and i n s h o r e zones, and by Brinton(1976) i n the C a l i f o r n i a Current o f f southern C a l i f o r n i a . The l i f e c y c l e s of two p o p u l a t i o n s of E._ p a c i f i c a i n Puget Sound were determined by H u l s i z e r ( u n p u b l i s h e d manuscript, U n i v e r s i t y o f Washington). The p h y s i o l o g y of JEj_ p a c i f i c a has been i n v e s t i g a t e d by s e v e r a l r e s e a r c h e r s . Lasker and co-workers (Lasker, 1960;1964;1966; Lasker and Theilacker,1965; Jerde and Lasker,1966) have d e s c r i b e d aspects of f e e d i n g , growth, r e s p i r a t i o n , moulting and the carbon budget of specimens i n the l a b o r a t o r y , as w e l l as moulting of specimens observed on board s h i p o f f southern C a l i f o r n i a . Small and c o l l e a g u e s measured e u p h a u s i i d r e s p i r a t i o n a t v a r i o u s temperatures i n the l a b o r a t o r y and estimated energy flow of f i e l d p o p u l a t i o n s o f f Oregon (Small et al.. ,1966; Small,1967). They a l s o c o n s i d e r e d the e f f e c t o f pressure on r e s p i r a t i o n i n these v e r t i c a l l y migrating crustaceans (Small and Hebard,1967; Pearcy and S m a l l , 1968; C h i l d r e s s , 1 9 7 1 ) . With specimens from Saanich I n l e t , Paranjape (1967) s t u d i e d moulting and r e s p i r a t i o n . G i l f i l l a n {1972) compared the r e s p i r a t i o n of E._ p a c i f i c a specimens from o c e a n i c , from mixed o c e a n i c - c o a s t a l and from c o a s t a l waters (Saanich I n l e t ) of B.C. under v a r i o u s experimental combinations of temperature and s a l i n i t y . a c o u s t i c s t u d i e s of the Saanich I n l e t e u p hausiids (as w e l l as other zooplankton and f i s h ) were performed between 1961 and 1970 by Bary and co-workers (Bary, Barraclougb and H e r l i n v e a u x , 1962; Bary,1966a;1966b; Bary and Pieper,1970; Pieper,1971). A b r i e f sketch of the b i o l o g y of E. p a c i f i c a i s presented below. The r e l e v a n c e of s e v e r a l of the above papers w i l l be 8 d e s c r i b e d i n more d e t a i l i n subsequent d i s c u s s i o n s e c t i o n s . I i £acifica i s an omnivorous f i l t e r f e e d er which uses i t mouthparts and t h o r a c i c appendages as a f i l t e r i n q apparatus (Mauchline and F i s h e r , 1969). In oceanic environments, t h i s s p e c i e s has been c o n s i d e r e d to be mainly a predator of s m a l l e r z o o p l a n k t e r s (Ponomareva, 1963). Lasker{1966) has found t h a t i n d i v i d u a l s from waters o f f southern C a l i f o r n i a can maintain themselves on phytoplankton as w e l l as on l i v e c r u s t a c e a n n a u p l i i . Parsons et a l * . (1967) observed t h a t a d u l t B... p a c i f i c a c ould o b t a i n maximal r a t i o n s on suspensions of diatoms from Saanich I n l e t ; p a r t i c l e s as s m a l l as 5u.m i n diameter were eaten. Green masses of phytoplankton c e l l s can o f t e n be observed d u r i n g March to December i n the guts of f r e s h l y cauqht specimens taken from the shallow sound s c a t t e r i n q l a y e r a t n i g h t i n the S t r a i t of Georqia r e g i o n , (personal o b s e r v a t i o n ) . I t appears t h a t during most of the year, phytoplankton i s a major source of food f o r E.. p a c i f i c a i n c o a s t a l and upwelling r e g i o n s , whereas microzooplankton may be more important during the winter and i n oceanic environments (Parsons and LeBrasseur, 1970). The l i f e h i s t o r y of E. p a c i f i c a shows v a r i a t i o n s with l a t i t u d e and environmental c o n d i t i o n s ; the l i f e span ranges from j u s t l e s s than a year i n the p o p u l a t i o n s o f f Oregon (Smiles and Pearcey, 1971) and o f f southern C a l i f o r n i a ( B r i n t o n , 1976) to about two years i n the s u b a r c t i c r e g i o n o f the northwest P a c i f i c (Nemoto, 1957; Ponomareva, 1963). Growth r a t e s are c o r r e s p o n d i n g l y higher i n the southern upwelling r e g i o n s than at hi g h e r l a t i t u d e s . 9 Popu l a t i o n s i n o f f s h o r e r e g i o n s of the P a c i f i c undergo ex t e n s i v e d i e l v e r t i c a l m i g r a t i o n s ; i n daytime most a d u l t l i £acifica are sampled from depths below 200m ( B r i n t o n , 1962) while at ni g h t most specimens are taken i n the upper 50m. The range of v e r t i c a l m i g r a t i o n can be much l e s s i n c o a s t a l waters; Bary and coworkers (e.g. Bary and P i e p e r , 1970) found that I i R a c i f i c a g e n e r a l l y forms a d i s t i n c t sound s c a t t e r i n g l a y e r a t 55-90m du r i n g the day but ascends t o the upper 30m at n i g h t . The presence of o x y g e n - d e f i c i e n t waters below about 100m i n Saanich I n l e t l i m i t s the day depth of the eup h a u s i i d s and most other migrating zooplankton. Q u a n t i t a t i v e measurements of high freguency sound b a c k s c a t t e r i n g by the l a y e r were d i r e c t l y r e l a t e d to the dry biomass o f euphausiids i n the l a y e r i n most months of the year ( P i e p e r , 1971) . Studies on the p o p u l a t i o n b i o l o g y of a group of organisms can c l e a r l y be most r e a d i l y i n t e r p r e t e d i f the i n d i v i d u a l s c o n s t i t u t e a d i s t i n c t p o p u l a t i o n which can be sampled a t i n t e r v a l s . , The observed changes i n p o p u l a t i o n parameters are then due to processes w i t h i n the p o p u l a t i o n r a t h e r than t o replacement of the former popul a t i o n by a newly a r r i v e d assemblage. &s a study area, a semi-enclosed sea r e g i o n such as the S t r a i t of Georgia has obvious advantages over an open area of sea. S e v e r a l l i n e s o f evidence support the c o n t e n t i o n t h a t , w i t h i n the S t r a i t of Georgia r e g i o n , the Saanich I n l e t p o p u l a t i o n o f E.. p a c i f i c a at l e a s t i s l i k e l y to be d i s t i n c t from neighbouring o c e a n i c p o p u l a t i o n s . . F o r example, d i f f e r e n c e s i n p h y s i o l o g i c a l responses between J V p a c i f i c a taken from Saanich I n l e t and from P a c i f i c Ocean p o p u l a t i o n s have i n d i c a t e d t h a t the 10 Saanich I n l e t p o p u l a t i o n has developed t o l e r a n c e s to environmental c o n d i t i o n s which are d i s t i n c t from those p r e f e r r e d by o c e a n i c p o p u l a t i o n s . For example, Boden and Kampa(1965) found that specimens of E. .-paeifica from Saanich I n l e t are more s e n s i t i v e t o green l i g h t than to blue i n c o n t r a s t t o i n d i v i u a l s from the San Diego Trough r e g i o n . E._ p a e i f i c a from Saanich I n l e t have adapted t o environmental l i g h t i n g which i s greener i n c o l o u r and s i g n i f i c a n t l y b r i g h t e r i n i n t e n s i t y than that experienced at day depth (below about 250m) by the C a l i f o r n i a p o p u l a t i o n . The mechanism of a d a p t a t i o n was thought t o be the s t o r i n g of more a s t a x a n t h i n i n the eyes to a c t as a s c r e e n i n g pigment. R e s p i r a t o r y r a t e s can be used t o i n d i c a t e response t o environmental s t r e s s ; i n d i v i d u a l s of a zooplankton s p e c i e s which are w e l l adapted t o a p a r t i c u l a r s e t of c o n d i t i o n s g e n e r a l l y have higher r a t e s of r e s p i r a t i o n than those which are s t r e s s e d by the same c o n d i t i o n s (e.g. G i l f i l l a n , 1972). He found t h a t specimens of E. ..-paeifica from Saanich I n l e t could t o l e r a t e higher temperatures and lower s a l i n i t i e s than i n d i v i d u a l s from Juan de Fuca S t r a i t (mixed o c e a n i c - c o a s t a l water) and from the P a c i f i c west of the Queen C h a r l o t t e I s l a n d s (oceanic water). The r e s p i r a t o r y r a t e s of the i n d i v i d u a l s from o c e a n i c and from mixed o c e a n i c - c o a s t a l waters were s i g n i f i c a n t l y reduced a t 15 C and f o r s a l i n i t i e s below 27%o, whereas the r e s p i r a t i o n of Saanich I n l e t specimens was not reduced s i g n i f i c a n t l y f o r s a l i n i t i e s between 34 and 24 %o and temperatures from 5 to 15 C i n summer. The above d i f f e r e n c e s i n t h e p h y s i o l o g i c a l r e a c t i o n s of 11 JLL p a e i f i c a i n d i v i d u a l s from Saanich I n l e t and from more oce a n i c r e g i o n s suggest that there i s r e l a t i v e l y l i t t l e exchange between these p o p u l a t i o n s of E.. p a e i f i c a . The oceanographic f e a t u r e s of Saanich I n l e t and i t s approaches (Herlinveaux, 1962) provide a p l a u s i b l e mechanism f o r the r e s t r i c t i o n o f admixing of P a c i f i c p o p u l a t i o n elements to the Saanich I n l e t p o p u l a t i o n of I i p a e i f i c a . Saanich I n l e t has a r e l a t i v e l y weak e s t u a r i n e f l u s h i n g a c t i o n because most of the freshwater r u n - o f f e n t e r s the i n l e t from the approaches r a t h e r than from the head of the i n l e t as i s u s u a l i n most B r i t i s h Columbia i n l e t s ( P i c k a r d , 1961). There i s , however, a t i d a l l y a s s i s t e d s u r f a c e outflow from the lower reaches of the i n l e t through S a t e l l i t e Channel i n t o Haro S t r a i t where the water a t a given s u b s u r f a c e depth i s always more dense than at t h e same depth i n Saanich I n l e t ( H e r l i n v e a u x , 1962). A compensating s u b s u r f a c e i n f l o w of water, t o provide the sea water necessary f o r entrainment, tends to f l u s h the waters above the s i l l depth (75m) i n the i n l e t . T h i s weak e s t u a r i n e c i r c u l a t i o n has l i t t l e e f f e c t on the waters i n the deep b a s i n (234m maximum) . Only when the waters i n Haro S t r a i t above the s i l l depth become more dense than the waters below the s i l l i n the i n l e t w i l l s i g n i f i c a n t i n t r u s i o n of seawater occur i n the Saanich I n l e t b a s i n ; t h i s i n f l o w might b r i n g with i t e u p h a u s i i d s and other z o o p l a n k t e r s from o u t s i d e waters and might t r a n s p o r t Saanich I n l e t e u p h a u s i i d s outwards with the d i s p l a c e d r e s i d e n t water. Such an event c o u l d occur s e v e r a l times i n r a p i d 12 s u c c e s s i o n or not at a l l f o r s e v e r a l y e a r s , depending on the occurence o f s u f f i c i e n t l y dense o u t s i d e water i n Haro S t r a i t . In order f o r a l a r g e i n p u t of euphausiids from o u t s i d e waters to occur, though, the immigrants would l i k e l y have t o be present at depths from about 60 t o 80m i n Haro S t r a i t d u r i n g the i n t r u s i o n . T h i s d i s t r i b u t i o n u s u a l l y occurs o n l y f o r a s h o r t time twice a day when the euphausiids migrate v e r t i c a l l y between the s u r f a c e and deeper daytime depths. Conseguently s i g n i f i c a n t immigration of I»_ p a c i f i c a p o p u l a t i o n elements from o u t s i d e waters has a r e l a t i v e l y low p r o b a b i l i t y . Some Saanich I n l e t l i p a c i f i c a are l i k e l y swept from the i n l e t with the s u r f a c e outflow at n i g h t as smal l numbers of !•. p a c i f i c a are o c c a s i o n a l l y caught i n S a t e l l i t e Channel. F u r t h e r evidence from o b s e r v a t i o n s on the composition of plankton samples from Saanich I n l e t and i t s approaches w i l l be presented i n Chapter 3. In summary, i t seems l i k e l y t h a t the euphausiids i n Saanich I n l e t form a d i s t i n c t breeding p o p u l a t i o n with only l i m i t e d exchange with p o p u l a t i o n s i n adjacent waters. 1.4 M a t e r i a l s and Methods In order to f o l l o w the l i f e h i s t o r y and p o p u l a t i o n dynamics o f I i p a c i f i c a , a t o t a l o f 26 c r u i s e s were taken d u r i n g 1974-76, i n c l u d i n g 10 i n Saanich I n l e t during 1974, and 15 durin g 1975 t o Saanich I n l e t , J e r v i s I n l e t , Knight I n l e t and the S t r a i t of Georgia. appendix A c o n t a i n s a l i s t o f the 1975 c r u i s e s , g i v i n g the c r u i s e numbers, dates and d e s t i n a t i o n s as w e l l as c h a r t s with the survey c r u i s e t r a c k s i n d i c a t e d . 13 1.41 Sampling Procedures. The f i e l d sampling procedures were adopted to sample the h o r i z o n t a l d i s t r i b u t i o n and the l i f e stages of e u p h a u s i i d s d u r i n g the survey c r u i s e s . To reduce net avoidance by the eup h a u s i i d s , sampling was done i n the hours o f darkness as much as p o s s i b l e ; dark n e t t i n g m a t e r i a l s were a l s o used ( C l u t t e r and Anraku, 1968) . Most daytime zooplankton samples were c o l l e c t e d by v e r t i c a l haul with a. SCOP, net of 57 era diameter and 0. 350 mm Nitex n e t t i n g (HP -2, 1968) . Hauls i n Saanich I n l e t were g e n e r a l l y from 150-0m while those i n the S t r a i t of Georgia and J e r v i s I n l e t were from 200m to the s u r f a c e . The net was lowered at 60 m/min and r a i s e d at 30 m/min. H o r i z o n t a l d i s t r i b u t i o n o f the euphausiids was sampled a f t e r dark by t r a n s e c t s with standard M i l l e r nets(11.3 cm diameter, 0.350 mm N i t e x ; M i l l e r , 1 9 6 1 ) . These samplers were towed at 6 or 8 knots (3 o r 4 m/sec) i n the s o u n d s c a t t e r i n g l a y e r as recorded by 107 and 200 khz Boss F i n e l i n e echosounders. Sampling depths a t n i g h t were g e n e r a l l y l e s s than 25 m; sampling depth was estimated by the wire angle method. Volume of water f i l t e r e d was estimated from the d i s t a n c e towed and the area of the net mouth, assuming 100% f i l t e r i n g e f f i c i e n c y f o r the M i l l e r net and 94% f o r the SCOB net (HP -2, 1968). C l o g g i n g by phytoplankton was r a r e . Experimental h a r v e s t i n g was done with a modified 6-foot I s a a c s - K i d d midwater t r a w l ( IKMT ) . T h i s net (Isaacs and Kidd, 1953; Banse and Semon, 1963) has an e f f e c t i v e mouth area of 2.9 m2. The mesh ap e r t u r e s were changed t o 8 mm f o r the f r o n t 3 m s e c t i o n and 5 mm f o r the remainder of the net and codend. A 45 14 cm nylon z i p p e r at the end o f t h e codend f a c i l i t a t e d removal of the catch. The IKMT was towed duri n g darkness at 2 knots (1 m/sec) at depths e s t i m a t e d to be w i t h i n the s o u n d s c a t t e r i n g l a y e r . The TKMT catch was randomly subsampled f o r about 25 g of m a t e r i a l f o r l e n g t h frequency a n a l y s i s . Each subsample was preserved i n n e u t r a l 5% f o r m a l i n . The remainder o f the c a t c h was placed i n p l a s t i c bags and f r o z e n f o r use i n f i s h r e a r i n g experiments and f o r chemical a n a l y s e s , Water samples f o r c h l o r o p h y l l - a measurements were c o l l e c t e d i n 7 - l i t r e Van Dorn and 5 - l i t r e N i s k i n b o t t l e s from depths of 0, 2, 5, and o f t e n 10 m. A d d i t i o n a l samples from g r e a t e r depths were f r e g u e n t l y taken, e s p e c i a l l y i n Saanich I n l e t . A n a l y s i s was acco r d i n g to S t r i c k l a n d and Parsons(1972) by s p e c t r o p h o t o m e t r y or f l u o r o m e t r i c methods. V e r t i c a l temperature p r o f i l e s i n saanich I n l e t were measured during 1974 and 1975 by expendable bathythermograph (XBT), by i n s i t u s a l i n o m e t e r (Beckman p o r t a b l e , RS5-2), and by a thermistor-equipped temperature and depth probe which was desiqned and b u i l t a t DBC. 1.42 Laboratory Procedures. The zooplankton samples were analysed i n the f o l l o w i n q manner. SCOR and M i l l e r net samples were preserved immediately i n 5% n e u t r a l f o r m a l i n i n seawater. Wet weiqht measurements were made on 190 M i l l e r net samples, while s i z e frequency a n a l y s i s was performed on 190 samples from the SCOR and M i l l e r nets. Samples with more than about 200 euphausiids were subsampled with a modified Folsom plankton s p l i t t e r which y i e l d e d a l i q u o t s 15 of s i z e 1/2 n , where n i s the number of s u c c e s s i v e s p l i t t i n g o p e r a t i o n s . In such cases, the wet weights were determined on one of the f i r s t subsamples. To check on the c o n s i s t e n c y of t h i s method, o c c a s i o n a l l y two subsamples were weighed. No s i g n i f i c a n t b i a s was d e t e c t e d . Height d e t e r m i n a t i o n s were made a f t e r the sample (or subsample) was wet-sieved through 5 mm mesh n e t t i n g , which was s i m i l a r to the m a t e r i a l i n the IKMT codend. The p l a n k t e r s r e t a i n e d on t h i s mesh were o f t e n mainly a d u l t and j u v e n i l e e u p h a u s i i d s , although s i g n i f i c a n t numbers of amphipods, chaetognaths, l a r g e copepods, and o c c a s i o n a l l y g a l a t h e i d l a r v a e occurred i n t h i s f r a c t i o n . As E A p a e i f i c a alone g e n e r a l l y made up 30-90% of the megazooplankton biomass, the 5 mm s i z e f r a c t i o n was c o n s i d e r e d as an approximate index of euphausiid abundance f o r biomass surveys. The f i l t r a t e from the i n i t i a l s i e v i n g was r e - s t r a i n e d with a 0.35 mm s i e v e to c o l l e c t the zooplankton r e s i d u e , which was c h i e f l y copepods, although e u p h a u s i i d l a r v a l stages predominated at c e r t a i n times. Each s i z e f r a c t i o n was b l o t t e d on paper towels u n t i l no moisture was v i s i b l y t r a n s f e r r e d ( a b o u t 15 minutes). Het weights were determined on a M e t t l e r balance, t o the nearest 0.001 g, and s t a n d a r d i z e d as grams per c u b i c metre of water f i l t e r e d . For 81 of the wet-weighed samples, dry weights f o r each f r a c t i o n were determined; the samples were d r i e d i n an oven a t 60 C f o r 24 h and c o o l e d i n a d e s i c c a t o r p r i o r to weighing on a M e t t l e r balance. ; The c o n v e r s i o n f a c t o r from f o r m a l i n wet weight to f r e s h wet 16 weight was determined by wet weighing two p r e v i o u s l y f r o z e n samples from Saanich I n l e t , then p r e s e r v i n g them i n 5% n e u t r a l f o r m a l i n f o r about f o u r months before re-weighing. The f o l l o w i n g weight c o n v e r s i o n f a c t o r s were e s t a b l i s h e d : S i z e f r a c t i o n Conversion f a c t o r * SAD_. 5 mm Dry wt = 16.9 * 1.15% o f wet wt 0.35 mm Dry wt = 17.0 +2.22% of wet wt Formalin wt = 94.2 ± 1.20% Fresh wt Biomass c h a r t s o f the 5 mm f r a c t i o n o f the M i l l e r net zooplankton were prepared f o r the f o l l o w i n g p e r i o d s from wet biomass v a l u e s and 107 khz echosounding t r a n s e c t r e c o r d i n g s : P e r i o d C r u i s e s Region Mar.-Apr. 75/10/,75/12 S t r a i t of Georgia; Saanich, J e r v i s June - J u l y 75/21,75/24 S t r a i t of Georgia, Saanich, J e r v i s J u l y 75/25 Saanich I n l e t August 75/27 Saanich I n l e t Aug.-Sept. 75/27,75/29 S t r a i t of Georgia, Saanich, J e r v i s Oct.-Nov. 75/31,75/33 S t r a i t of Georgia, Saanich, J e r v i s 1.421 Length Measurements. A l i g u o t s of 100 to 200 euphausiid specimens were i d e n t i f i e d t o s p e c i e s a c c o r d i n g to F u l t o n (1968). J u v e n i l e and a d u l t specimens were measured by means of a b i n o c u l a r microscope and s c a l e to the nearest 0.5 mm. For s t a t i s t i c a l a n a l y s i s , they were grouped i n 1 ram s i z e i n t e r v a l s . E A p a c i f i c a body l e n g t h was measured from the t i p of the r o s t r a l p l a t e t o the t i p of the t e l s o n . For Saanich I n l e t , g e n e r a l l y animals from t h r e e or more v e r t i c a l h a ul samples from each month were measured. A d d i t i o n a l samples from M i l l e r net and IKMT hauls were measured t o examine net s e l e c t i v i t y through comparison o f s i z e d i s t r i b u t i o n s . For 17 the S t r a i t o f Georgia and J e r v i s I n l e t , l e n g t h measurements were mainly f o r M i l l e r net samples, although s e v e r a l IKMT, commercial net and SCOR samples were examined f o r comparison, Adult e u p h a u s i i d s were sexed; the presence or absence of attached spermatophores was a l s o noted. As an a d d i t i o n a l index of body s i z e , carapace l e n g t h was measured to the nearest 0.1 mm from behind the eye to the p o s t e r i o r margin of the carapace. Representative samples with a wide range i n body l e n g t h were analysed f o r the months of January, J u l y and August 1975, and February 1976. L a r v a l samples from May and June 1975 were a l s o measured f o r both body l e n g t h and carapace l e n g t h . L i n e a r r e g r e s s i o n o f body l e n g t h on carapace l e n g t h were computed f o r both sexes of a d u l t s and f o r f u r c i l i a l a r v a e . 1.422 A n a l y s i s of Length-freguency D i s t r i b u t i o n s . To estimate the age and growth r a t e s of e u p h a u s i i d s , the technique of s i z e frequency a n a l y s i s was used; t h i s method has the advantages t h a t i t can be a p p l i e d t o animals l a c k i n g permanent hard p a r t s , such as crustaceans which qrow by s u c c e s s i v e moults, and i t can be a p p l i e d t o l a r g e sample s i z e s . I t i s , though, s e n s i t i v e to t h e p r o p e r t i e s of the sampling qear and technique of c o l l e c t i n g samples which may b i a s the s i z e d i s t r i b u t i o n s obtained. As the e u p h a u s i i d l e n g t h d i s t r i b u t i o n s o f t e n comprised two or more modes, the polymodal a n a l y s i s w i t h p r o b a b i l i t y paper sugqested by Hardinq(1949) and a m p l i f i e d by Cassie(1950,1954) was employed. I n i t i a l data r e d u c t i o n i n v o l v e d p o o l i n q of each 18 month's samples f o r a given r e g i o n a f t e r i n s p e c t i o n of i n d i v i d u a l samples f o r s i g n i f i c a n t v a r i a t i o n among modal len g t h s . Histogram p l o t s and cumulative percentages i n the 1 mm s i z e groups were computed by a BMDP program, P5D {Dixon,1975). The cumulative percentages were p l o t t e d on p r o b a b i l i t y paper which transforms a normally d i s t r i b u t e d curve i n t o a s t r a i g h t l i n e ; d e v i a t i o n s from n o r m a l i t y cause the l i n e to bend. Mean modal l e n g t h s and t h e i r standard d e v i a t i o n s f o r polymodal d i s t r i b u t i o n s were determined from the p l o t s ( C a s s i e , 1954) by i d e n t i f y i n g i n f l e c t i o n p o i n t s and t r a n s f o r m i n g each mode i n t o a separate normal d i s t r i b u t i o n . Euphausiid growth r a t e s f o r each sex and age group were c a l c u l a t e d from the mean modal lengths. von B e r t a l a n f f y growth equations were f i t t e d to t h e growth data f o r each sex w i t h i n cohorts. 1.423 Length-weight R e l a t i o n s h i p s . Length-weight determinations on f o r m a l i n - p r e s e r v e d e u p h a u s i i d samples from Saanich I n l e t , S t r a i t of G e o r g i a , and J e r v i s I n l e t were made f o r the March - A p r i l p e r i o d . For each 1 mm increment of body l e n q t h , up to 25 specimens were i n d i v i d u a l l y wet-weighed t o the nearest 0.0001 g on a M e t t l e r balance. Linear r e g r e s s i o n s o f ln(W) on ln{L) were computed on pooled data f o r each sex. 1.424 I d e n t i f i c a t i o n o f L i f e H i s t o r y Stages. During development, euphausiids progress through a s e r i e s of l a r v a l stages which are separated by numerous moults to permit growth. Boden's(1950) d e s c r i p t i o n o f the E._ p a e i f i c a p o s t - n a u p l i a r stages was used t o d i s t i n g u i s h the three stages of c a l y p t o p e s and seven stages of f u r c i l i a i n samples of l a r v a e from Saanich I n l e t . Other r e f e r e n c e s c o n s u l t e d were Einarsson(1945), Macdonald (1 928) and Mauchline (1965) t o check f o r the presence of l a r v a e o f Thysanoessa r a s c h i i ., 20 CHAPTER 2:. LIFE HISTORY, SIZE STRUCTURE, GROWTH AND MORTALITY 2.1 L i f e H i s t o r y Stages Although s m a l l numbers o f euphausiid eggs and l a r v a l stages are observed d u r i n g l a t e A p r i l i n Saanich I n l e t , the main spawning p e r i o d i s from e a r l y May u n t i l the middle of J u l y (Figures 2 and 3; data from Stephens et a l . . ,1967 and Fu l t o n e t ajU ,1969). As can be seen i n the combined p l o t s o f egg abundance and c h l o r o p h y l l - a c o n c e n t r a t i o n f o r 196 8, the pulses i n spawning a c t i v i t y c o i n c i d e c l o s e l y with the p e r i o d s of h i g h e r phytoplankton abundance during Hay and June (Figure 4 ) . A s i m i l a r r e l a t i o n between the appearance o f a high biomass of eu p h a u s i i d eggs and a p e r i o d of high c h l o r o p h y l l - a c o n c e n t r a t i o n s was noted by Parsons et a l . (1967) i n Saanich I n l e t d u r i n g June 1966. The tr e n d i n phytoplankton d e n s i t i e s was s i m i l a r i n 1975 (Figure 5) although o b s e r v a t i o n s were taken l e s s f r e g u e n t l y than i n the 1968 study by F u l t o n e t al.. (1969). A second p e r i o d of l e s s i n t e n s i v e spawning occurs i n l a t e August-September, as shown by l a r v a l recruitment i n September 1974 and October 1975 and by the presence of spermatophores at t a c h e d t o over 40% of the 19 to 23 mm female euphausiids i n samples from l a t e August 1975. The f r e e - f l o a t i n g e u p h a u s i i d eggs, about 400 u^m i n diameter, hatch as n a u p l i i before growing and moulting through one metanauplius, t h r e e c a l y p t o p i s and seven f u r c i l i a stages (Boden,1950). The number of moults r e g u i r e d t o pass from one f u r c i l i a i n s t a r to the next i s h i g h l y v a r i a b l e and dependent on 2 1 5 0 0 0 | . i FIGURE 2. Euphausiid egq(o) and l a r v a l ( t ) abundances i n Saanich I n l e t d u r i n g June and J u l y 1966, from o b l i q u e M i l l e r hauls (12m-0). Data from Stephens et a l . . (MS, 1967). temperature (R. Ross, p e r s o n a l communication). Consequently, there are up to about 20 d i f f e r e n t i n s t a r s o r l a r v a l types w i t h i n the f u r c i l i a s e r i e s , as shown by the deqree of development of pleopods, s e t a e and t e r m i n a l s p i n e s . Thus, Boden(1950) encountered 18 types amonq 500 f u r c i l i a l a r v a e i n samples from southern C a l i f o r n i a waters taken d u r i n q s p r i n q and summer. The frequency d i s t r i b u t i o n of l a r v a l types had seven 22 lOOOr ll ' 4 I • t 1 ) 1 1 1 1 " 1 * • \ 1 I - ' • Ir 1 • 1 • 1 1 1 ' MAY JUNE I JULY FIGURE 3. Euphausiid egg(o), l a r v a l (t) and j u v e n i l e le) abundances i n Saanich I n l e t from 175m v e r t i c a l h a u l s during May to J u l y , 1968. Data from F u l t o n et a l ^ (MS, 1969). modes which Boden regarded as the a c t u a l stages of that part of the l i f e h i s t o r y , f o l l o w i n g F r a s e r ' s ( l 9 3 6 ) s u g g e s t i o n . To check on l o c a l e u p h a u s i i d developmental s t a g e s , 576 euphausiid l a r v a e , i n c l u d i n g 357 f u r c i l i a , were examined from o b l i q u e M i l l e r tows (15 m to surface) taken at weekly i n t e r v a l s i n daytime during May and June, 1975 i n Saanich I n l e t . F i g u r e 6 gi v e s the frequency d i s t r i b u t i o n f o r a l l staqes from egg to s i x t h f u r c i l i a staqe, i n c l u d i n g 19 of the 20 f u r c i l i a types s c h e m a t i c a l l y d e p i c t e d . 23 ! 1968 j FIGURE H. Hean c h l o r o p h y l l - a c o n c e n t r a t i o n i n the upper 20 m and euphausiid egg abundance from v e r t i c a l hauls (150 m - 0) i n Saanich I n l e t . Data from F u l t o n e t a l . . (1969). Curves f i t t e d by eye. There i s general agreement with Boden's r e s u l t s on the p o s i t i o n s of the dominant modes. D i f f e r e n c e s i n c l u d e two a d d i t i o n a l f u r c i l i a types (no. 5 and 6) and a broadening of the t h i r d f u r c i l i a stage (F3) mode to i n c l u d e type no. 11. Stages F4 through F7 are l i k e l y underrepresented due to a l a r g e r extent of 24 FIGURE 5. C h l o r o p h y l l - a c o n c e n t r a t i o n s i n the upper 10 m of Saanich I n l e t d u r i n g 1975. Mean ± S.p. f o r a l l s t a t i o n s sampled. v e r t i c a l m i g r a t i o n from the s u r f a c e l a y e r by the o l d e r f u r c i l i a (Mauchline and Fisher,1969). The f a c t t h a t l a r g e r numbers of l a r v a e are observed i n the F3 stage i s an i n d i c a t i o n t h a t the l a r v a e moult s e v e r a l times during t h i s stage (Boden,1950). Ross(personal communication) has experimental support f o r t h i s c o n c l u s i o n from o b s e r v a t i o n s on 1000h 500 100 50 10 3 o FURCILIA LARVAL TYPES 1 1 1 I T S 7 I .1 I I t .1 .1 ' \ \ \ 1 1 1 . 1 V V V 3 7 3 7 3 7 Z3, 7 2ND A N T E N N A L E N D O P O D U N S E G M E N T E D Z3 7 " J 7 8 r-r X \ V V 9 C j i i i 12 3 7 1 7 x x x x x 3 7 W x S r 1 7 2ND /'7 13 9 ^ 14 .15 3 6 a 5 3 ^ j r r . . 3 4 A N T E N N A L / ]8 1 1 1 I . E N D O P O D \ >TT."X v» 3 3 S E G M E N T E D \ » 1 x' X 1 X 1 X 1 \2o a 3 2 -?Tx^= 3 1 IV 11—I. I I I I I I E N MCICIICIII 1 I i i i i i i i • i i t V I 2 3 4 5 6 7 8 9 10 1112 13 14 15 1617 1819 20 FURCILIA LARVAL TYPES 25 FIGURE 6. Frequency o f e u p h a u s i i d l a r v a l t y p e s encountered i n M i l l e r net samples d u r i n q May and June 1975 i n Saanich I n l e t . a b b r e v i a t i o n s used are E=egg, N=nauplius, M=metanauplius, CI throuqh C I I I r e f e r to c a l y p t o p e s stages, and TS=number of t e l s o n s p i n e s . Roman numerals I throuqh VI r e f e r t o f u r c i l i a staqes F1 t o F6. the moulting of l a b o r a t o r y - r a i s e d f». p a c i f i c a l a r v a e . F i e l d e stimates o f developmental time to the F3 stage (about 4.5 mm i n body length) were made from data c o l l e c t e d by Stephens e t al., ,1967 ( F i g 2 ) . assuming that l a r g e f l u c t u a t i o n s i n e u p h a u s i i d egg abundance are t r a n s m i t t e d through the l a r v a l s t ages, the developmental time from egg t o F3 can estimated by the d u r a t i o n between corresponding peaks i n egg and F3 l a r v a l 2 6 a b u n d a n c e . In t h i s manner f o u r g r o u p s o f F3 l a r v a e (numbered c n F i g 2) were e s t i m a t e d t o have a d e v e l o p m e n t a l t i m e o f 2 7 . 3 ± 1.5 d a y s (Mean ± S . D . . ) . , D u r i n g t h i s p e r i o d t h e a v e r a g e t e m p e r a t u r e i n t h e u p p e r 30 m o f S a a n i c h I n l e t was be tween 10 and 11 C ( compare F i g u r e 7 f o r 1 9 7 U - 7 5 ) . The above e s t i m a t e i s i n t e r m e d i a t e be tween l a b o r a t o r y e s t i m a t e s o f d e v e l o p m e n t a l t i m e s t o F3 a t 12 and 8 C ( B o s s , p e r s o n a l c o m m u n i c a t i o n ) , b u t i t i s h i g h e r t h a n t h e e s t i m a t e o f 20 d a y s by P e a s e (1968) f o r t h e same p e r i o d i n Saanich I n l e t . However, h i s use of a t h r e e - p o i n t running mean f o r egg and l a r v a l abundances may have b l u r r e d the r e c o g n i t i o n of l a r v a l c o h o r t s and thus the d u r a t i o n of the stages. 2.2 L a r v a l S u r v i v a l Estimates of the r a t e s of s u r v i v a l from egg to l a r v a l stages l e s s than 4.5 mm ( n a u p l i i , c a l y p t o p e s and f u r c i l i a F1-F3) and from l a r v a l t o j u v e n i l e stage (4.6-8 mm) were made from data (eg. F i g 3) presented by Fulton et al.. (1969) . L o g a r i t h m i c p l o t s of abundance f o r corresponding egg, l a r v a l and j u v e n i l e peaks from 175 and 20 m v e r t i c a l h aul samples y i e l d e d the f o l l o w i n g s u r v i v a l (S=N2/M1) and instantaneous (Sicker,1958) m o r t a l i t y (Z=-lnS) values (Mean ± S.D.,), where N2 i s the abundance a t time t2 and N1 i s the abundance a t time t 1 : Egg to Larvae (< 4.5 mm) S = 0.057 ± 0.015 2 = 2.90 ± 0.28 Larvae to J u v e n i l e (4.6-8 mm) S = 0.42 ± 0.17 Z = 0.93 ± 0.41 Egg to J u v e n i l e S = 0.022 ± 0.0083 Z = 3.87 ± 0.39 M o r t a l i t y i s high f o r the e a r l y l a r v a l s t a g e s as only about 5.7% of the eggs s u r v i v e to be f u r c i l i a ; s u r v i v a l r i s e s to about 40% i n the t r a n s i t i o n from f u r c i l i a t o j u v e n i l e . O v e r a l l s u r v i v a l from egg to j u v e n i l e i s only about 2.2%. 2.3 P o p u l a t i o n S i z e S t r u c t u r e i n Saanich I n l e t Changes i n the s i z e (age) s t r u c t u r e of the e u p h a u s i i d 2 8 p o p u l a t i o n i n S a a n i c h I n l e t were f o l l o w e d d u r i n g 1974 , 1975 and i n t o 1976 { F ig 8 and 9 ; T a b l e 1 ) . Dp t o f o u r modes p r o g r e s s e d t h r o u g h t h e l e n g t h f r e q u e n c y {L-F) d i s t r i b u t i o n s d u r i n g e a c h y e a r . R e s o l u t i o n o f t h e 1975 modes i s b e t t e r due t o i n c r e a s e d s a m p l i n g e f f o r t and c o n s e q u e n t l y l a r q e r s a m p l e s i z e s . T h e f o l l o w i n g d i s c u s s i o n w i l l c o n c e n t r a t e on t h e 1975-76 d a t a . 29 TABLE 1. M o n t h l y mean b o d y l e n g t h s by s e x f o r e u p h a u s i i d c o h o r t s i n S a a n i c h I n l e t be tween J a n u a r y 1974 and F e b r u a r y 1 9 7 6 . M o A Sex S p r i n g , 73 F a l l 23 S p r i n c j 74 f a l l 24 1974 Mean ± S . D . Mean + S A D . Mean + Mean A J a n . F 11 . 9 ± 0 .97 F e b . M 1 2 . 0 i 0 . 94 F 12.1 ± 0 .96 Mar . M 12 .1 ± 0. 90 F 12 .4 ± 1. 00 A p r , M 1 1 . 5 + 0 . 8 3 F 1 1 . 7 ± 1.08 May. M 1 3 . 5 ± 1.40 2.0 + 0 . 7 5 Aug . M 1 7 . 7 ± 0 . 7 0 F 2 0 . 0 ± 0.51 1 4 . 8 ± 1.80 8.5 ± 0 .58 Sep . M 1 8 . 5 ± 0 .68 1 6 . 0 ± 0 . 7 0 F 2 0 . 1 ± 1.02 16 . 1 ± 0 . 7 3 1 3 . 1 ± 0 . 6 5 7 .5 i : 1 . 2 9 1975 S p r i n g 75 J a n . M 1 8 . 3 ± 0 . 3 2 1 4 . 9 ± 1.21 F 1 8 . 8 ± 1.0 2 15 .2 ± 1.13 F e b . M 1 3 . 9 ± 1. 13 8 .3 + 0.51 F 1 3 . 9 ± 1.13 8. 3 ± 0.51 Mar. M 14 . 1 + 1.08 1 0 . 7 ± 1.96 F 1 7 . 9 ± 0 .54 1 4 . 2 ± 1.67 8 . 7 ± 1. 10 A p r . M 1 4 . 7 ± 0.94 1 2 . 5 ± 1.00 F 16 . 1 ± 0 .83 May. M 16 . 2 ± 1.00 F 3 .0 ± 1.02 1 9 . 7 ± 0 . 8 8 1 7 . 0 + 0 . 7 5 J u l . M 1 8 . 7 ± 0.91 F 1 0 . 7 ± 2 .04 2 0 . 2 ± 0 .8 3 1 4 . 7 + 1.83 F a l l 25 Aug . M 1 9 . 3 ± 0 . 9 7 15 . 8 ± 0 .70 F 1 2 . 5 + 1.94 2 0 . 2 + 1.26 1 5 . 4 + 0 .67 O c t . M 1 9 . 1 ± 0.9 1 16. 1 ± 0 . 7 8 F 4. 3 ± 1.05 2 0 . 2 ± 1.08 1 5 . 8 ± 1.13 Nov. M 14. 4 + 0 . 7 0 1 9 . 3 ± 0 62 16 0 ± 1 10 F 12. 5 ± 1.67 2 0 . 0 ± 0 . 5 0 1 6 . 0 + 0 .70 1976 F e b . M 1 2 . 3 ± 0 .75 18. 2 ± 0 .94 F 13. 6 ± 1. 59 8 . 4 x 0 . 7 3 1 8 . 2 ± 0.78 M 14. 8 ± 0. 89 I n 1 9 7 5 , two g r o u p s o f r e c r u i t s , t h e s p r i n g and f a l l c o h o r t s , e n t e r e d t h e a d u l t p o p u l a t i o n . Of t h e s e , t h e s p r i n g mode was most s i g n i f i c a n t c o n t r i b u t o r t o t h e F e b r u a r y 1976 p o p u l a t i o n . T h i s c o h o r t ( c u r v e s I and J , F i g u r e 10) grew r a p i d l y f r om a b o u t 3 mm i n May t o 9-12 mm i n J u l y . The L-F FIGURE 8. Length frequency d i s t r i b u t i o n s of E t p a c i f i c a from Saanich I n l e t , 1974. The monthly samples were c o l l e c t e d by v e r t i c a l hauls with a SCOR net(100m - 0 ) . diagrams(Figures 9ft and B) f o r v e r t i c a l ana h o r i z o n t a l sampling show very s t r o n g recruitment i n t o t h i s cohort f o r J u l y ana August. Growth slowed as maturation proceeded and food supply d e c l i n e d d u r i n g the f a l l . The petasma on males became ev i d e n t at a body length of about 14 mm; up to t h i s time members o f the c o h o r t were grouped as immatures. By November, the modal range was 11-15 mm. L i t t l e change i n body length had occurred by 31 1000 soot-lOOf-.10 4000 1000 50 Or-50 \ z IO1 J A N 75 FEB 75 MAR 75 10 JUL 75 A U G 75 1 I 5 10 15 20 25 BODY LENGTH mm '^ 1 APR 75 OCT 75 FIGUBE 9. Length frequency d i s t r i b u t i o n s of 1^ M c i f i c a from Saanich I n l e t , Jan. 1975 to Feb. 1976. S e c t i o n A samples were taken by SC0R v e r t i c a l haul(150m - 0 ) ; S e c t i o n B i s f o r h o r i z o n t a l sampling at night i n the upper 25 m with M i l l e r nets. February 1976; the s p r i n g mode then comprised about 90% of the sampled p o p u l a t i o n . The f a l l c o h o r t, which appeared as 3-5 ram l a r v a e i n October, had reached 7-9 mm by February but accounted f o r only BODY LENGTH mm FIGURE 9 (continued) . 3% of the sampled p o p u l a t i o n . Members of the s p r i n g cohort mature over w i n t e r and appear to spawn f o r the f i r s t time i n the f o l l o w i n g s p r i n g , a c c o r d i n g to o b s e r v a t i o n s o f spermatophores attached to females of t h i s group. Females with a t t a c h e d spermatophores have r i p e eggs(Brinton,1976). Females (19 t o 21 mm) from the o l d e r f a l l t r 1 r - 1 1 • i • i 1 — — i • i i 1 1 1 i i i I 22 FIGUBE 10. Mean body l e n g t h s and f i t t e d von B e r t a l a n f f y growth curves f o r f e m a l e ( a ) , male{e) and immature{i) E A p a e i f i c a c o h o r t s i n Saanich I n l e t during 1974-75. L e t t e r s A-J r e f e r t o the curves l i s t e d i n Table 2. cohort a l s o spawn i n the s p r i n g . The f a l l cohort disappears from the p o p u l a t i o n by J u l y , about 22 months a f t e r i t s o r i g i n . The spring c o h o r t , however, contin u e s to grow i n mean body s i z e . In l a t e August and September, females {now 19-22 mm) apparently spawn f o r the * 5 ; i i i i i i i I 1 o hi o i J F I976 34 second time. In t u r n , t h i s mode disappears from the p o p u l a t i o n by January, about 19 t o 20 months a f t e r i t s f i r s t appearance. l i t h i n a given c o h o r t of e u p h a u s i i d s , the i n f e r r e d growth r a t e s of the females g e n e r a l l y d i f f e r from those of the males. Each mode in the l e n g t h frequency d i s t r i b u t i o n s presented i s t h e r e f o r e the composite of modes f o r each sex. To show the d i f f e r e n c e s i n the i n f e r r e d growth r a t e s f o r the two sexes, p l o t s of mean body l e n g t h s from Table 1 are given i n F i g u r e 10. For the growing season from March to about November, E. p a e i f i c a growth i n l e n g t h i s w e l l d e s c r i b e d by the von B e r t a l a n f f y (1938) growth equation: where Lo© i s the asymptotic l e n g t h , K i s the c o n s t a n t determining the r a t e of change i n qrowth, and t i s the h y p o t h e t i c a l "age" when len g t h i s zero(Bicker,1958;Gulland,1969). The values o f these c o n s t a n t s f o r the curves i n F i g u r e 10, as w e l l as the c o r r e l a t i o n c o e f f i c i e n t , r , have been t a b u l a t e d ( T a b l e 2) . (The f i t t i n g of the growth curves i n v o l v e d f i r s t p l o t t i n g the growth increment (1^ - l , ) / ( t 2 - t ( ) where 1, , 1^ are the mean body l e n g t h s at times t ( , t ^ , a g a i n s t the average length f o r the p e r i o d , 0.5(1, * 1^). The i n t e r c e p t on the l e n g t h a x i s of t h i s p l o t i s an estimate of L a 0 ( G u l l a n d , 1969) . Next, In ( L ^ - 1^) was c a l c u l a t e d and p l o t t e d a g a i n s t the estimated age, t , i n months. The s l o p e of the r e l a t i o n i s -K and the Y - i n t e r c e p t i s lnLtf + Kt , from which t 0 i s estimated ( B i c k e r , 1958). The c o r r e l a t i o n c o e f f i c i e n t , r , i n Table 2 i n d i c a t e s the goodness of 35 f i t f o r the l a t t e r p l o t s . TABLE 2. Growth co n s t a n t s f o r von B e r t a l a n f f y equations f i t t e d t o Saanich I n l e t data on mean body l e n q t h by sex and c o h o r t p l o t t e d i n F i g u r e 10. Curve Mode K ^ 0 r A F Sp73 0.744 20.3 10.62 0.99 B H Sp73 0.236 21.1 8.11 0.999 C F Fa73 0.276 20.1 7.68 1.0 D Sp74 0.377 15.7 0.11 0.999 E F Sp74 0. 451 21. 3 9.20 0.980 F N Sp74 0.287 21.1 7.70 0.99 G F Fa74 0.545 16.1 1.46 0.983 H M Fa74 0. 455 16.3 4.70 0.983 I F Sp75 0.400 13.4 -.40 0.986 J n Sp75 0.354 15.3 -.51 0.982 In Saanich I n l e t , the i n f e r r e d growth r a t e s of second-year female E t p a c i f i c a a r e u s u a l l y higher than those of males i n the same c o h o r t . Nemoto's (1957) data f o r Ej. p a c i f i c a from the western North P a c i f i c a l s o suggest t h a t a d u l t males are s m a l l e r than females of the same age. T h i s may appear to be t r u e f o r the sampled p o p u l a t i o n , but there i s evidence which suggests t h a t the true growth r a t e o f males i s g r e a t e r than t h a t of females f o l l o w i n g onset of maturation, at about 11 mm (Brinton,1S76). The f a s t e r growth i n males, though, i s apparently coupled with higher m o r t a l i t y (compare B i c k e r , 1969) . Consequently, the observed or i n f e r r e d qrowth r a t e i s a c t u a l l y the t r u e qrowth ra t e l e s s the c o n t r i b u t i o n of the f a s t e r qrowinq i n d i v i d u a l s which have d i e d i n the i n t e r v a l . I t f o l l o w s t h a t the i n f e r r e d qrowth r a t e s a re underestimates of the t r u e qrowth r a t e s f o r both sexes; the deqree of underestimation, thouqh, i s l i k e l y h iqher i n males. 36 S u p p o r t f o r t h e h y p o t h e s i s t h a t ma le E. p a c i f i c a have h i g h e r g r o w t h r a t e s t h a n f e m a l e s i s e v i d e n t i n c u r v e s H and J i n F i g u r e 1 0 . C u r v e J (male) ha s a h i g h e r s l o p e t h a n c u r v e I f r o m a b o u t 11 t o 14 mm, r e s u l t i n g i n a d i f f e r e n c e o f o v e r 1 mm i n s i z e be tween s e x e s by F e b r u a r y . C u r v e s H and G show how s u c h a l e a d i n a p p a r e n t g r o w t h c a n be g r a d u a l l y e r o d e d i n t h e s e c o n d s e a s o n . I n M a r c h , when t h e m a l e s i n t h i s c o h o r t w e r e , on t h e a v e r a g e , a b o u t 2 mm l o n g e r , t h e s e x r a t i o (M : F) was 0 . 7 1 . By November , when t h e mean body l e n g t h s were e g u a l , t h e r a t i o was 0 . 2 1 , i n d i c a t i n g a much h i g h e r p r o p o r t i o n o f t h e ma l e s had d i e d . F u r t h e r e v i d e n c e o f t h i s t y p e w i l l be p r e s e n t e d f o r t h e c o m b i n e d S a a n i c h I n l e t , J e r v i s I n l e t and S t r a i t o f G e o r g i a p o p u l a t i o n s . Summary s t a t i s t i c s f o r t h e g rowth c o n s t a n t s o f T a b l e 2 a r e p r e s e n t e d be low ( T a b l e 3 ) . They a l s o g i v e l i m i t e d s u p p o r t t o a h i g h e r ma le g r o w t h r a t e . T h e 10 c u r v e s d e s c r i b e d f a l l i n t o f o u r c a t e g o r i e s a c c o r d i n g t o s e x and number o f g r o w i n g s e a s o n s t h e c o h o r t h a s e x p e r i e n c e d . T h e a s y m p t o t i c l e n g t h , L^, w i l l o f t e n c h a r a c t e r i s e t h e number o f g r o w i n g s e a s o n s s i n c e E x p a c i f i c a r e a c h e s 13 t o 17 mm i n i t s f i r s t f u l l g r o w i n g s e a s o n , and 20 t o 22 mm d u r i n g i t s s e c o n d s e a s o n . The a s y m p t o t i c l e n g t h s f o r ma l e s t e n d e d t o be h i g h e r t h a n f o r f e m a l e s i n b o t h s e a s o n g r o u p s , p o s s i b l y i n d i c a t i n g a h i g h e r g r o w t h p o t e n t i a l w i t h i n a g i v e n s e a s o n . The d i f f e r e n c e i s n o t s i g n i f i c a n t a t t h e 95% l e v e l , t h o u g h , when t h e v a l u e s a r e c o m p a r e d w i t h S t u d e n t ' s t - t e s t . 37 TABLE 3. Summary of Saanich I n l e t E. p a e i f i c a qrowth c o n s t a n t s f o r von B e r t a l a n f f y equations of Table 2 a c c o r d i n q t o sex and season. Mean ± S.D. Sex^Season K i ^ i l l l t o Jmol F.1 .44 + .09 15.1 ± 1.46 -.15 ± .36 F.2 .49 ± . 24 20. 6 ± 0.64 9.2 ± 1.5 F.1 6 2 .47 ± . 16 M. 1 .41 ± .07 15.8 ± 0.71 2.1 ± 3.7 M.2 .26 ± .0 1 21.1 ± 0. 6.8 ± 1.9 M. 1 5 2 .33 ± . 10 2.4 P o p u l a t i o n S i z e S t r u c t u r e i n J e r v i s I n l e t and the S t r a i t of Georqia. S i m i l a r s t u d i e s on the chanqes i n s i z e s t r u c t u r e of E y p a e i f i c a p o p u l a t i o n s i n J e r v i s I n l e t and the S t r a i t of Georqia provide f u r t h e r i n f o r m a t i o n on the l i f e c y c l e of E. p a e i f i c a i n B r i t i s h Columbia c o a s t a l waters. L-F histoqrams f o r J e r v i s I n l e t are presented i n F i q u r e 11, with the correspondinq mean body le n q t h s by sex and cohort appearinq i n Tabl e 4; qrowth curves c o n s t r u c t e d from these data are presented i n F i q u r e 12. In c o n t r a s t to the Saanich I n l e t p o p u l a t i o n , the J e r v i s I n l e t s i z e s t r u c t u r e becomes h i q h l y complex durinq the p e r i o d from June t o November due to the recruitment of f o u r j u v e n i l e c o h o r t s whose development was t r a c e d by l e n g t h frequency a n a l y s i s . 38 TABLE 4. Monthly mean body l e n g t h s by sex f o r E. p a c i f i c a c o h o r t s i n J e r v i s I n l e t between A p r i l and December 1975. Mo.Sex Spr i n g 74 Summer 74 Spring 75 Sum.A 15 Mean ± S.D. Mean ± S.D. Mean ± S. D. Mean ± S.D. Apr. M 18.5 ± 0.71 13.6 ± 1. 88 F 18.7 ± 0.70 14.0 + 2. 26 Jan. M 20. 3 ± 1.08 17. 1 ± 0. 91 I/F 20.6 ± 0.67 18. 5 ± 0. 65 9.3 + 1. 88 J u l . M 20.0 ± 1.22 17.2 + 1. 42 I/F 20. 3 ± 1.34 17.4 + 1.08 12.0 ± 0. 81 7.0 ± Sept.M 20.0 ± 0.70 17.5 + 0.70 I/F 20.9 ± 0.86 17.0 + 0. 27 14.5 + 0.78 11.4 ± Sum.B I 7.8 ± 0. 41 Oct. M 20.0 ± 0.63 17. 1 ± 0.91 I/F 10.7 ± 0.81 19.5 ± 1.34 16.4 + 1. 10 13.0 ± Nov. M 20. 1 ± 0. 54 17.4 ± 0.67 I/F 11.7 ± 1.61 19. 3 ± 1.53 16. 1 + 1.51 F a l l I 7.0 ± 1.10 Dec. M 12. 0 + 0.70 20.0 ± 0. 58 16.2 ± •1. 40 16.2 ± I/F 11.8 ± 1.64 19.8 ± 1. 91 15.2 ± 1.59 15.2 ± 1.37 1, 45 0.62 1.40 1.59 The S t r a i t of Georgia p o p u l a t i o n of E^ p a c i f i c a i s a l s o more complex than the Saanich I n l e t p o p u l a t i o n , but i s s i m i l a r to t h a t o f J e r v i s I n l e t except i n d e t a i l . Length frequency d i s t r i b u t i o n s f o r S t r a i t o f Georqia are qiven i n F i q u r e 13; r e s u l t s o f L-F a n a l y s i s are shown i n Table 5 and are p l o t t e d with the d e r i v e d qrowth curves i n F i q u r e 14. As i n J e r v i s I n l e t , the S t r a i t of Georqia p o p u l a t i o n i n c r e a s e d durinq June to October with the recruitment of f o u r new c o h o r t s . BODY LENGTH mm FIGURE 11. l e n g t h frequency d i s t r i b u t i o n s of E._ p a c i f i c a from J e r v i s I n l e t , A p r i l to December 1975. Samples were taken by h o r i z o n t a l hauls with M i l l e r nets. 40 TABLE 5. Monthly mean body l e n g t h s by sex f o r F/, p a e i f i c a c o h o r t s i n the S t r a i t o f Georgia between March 1975 and February 1976. , Mo.Sex Spring 74 Summer 74 Spring 75 Summer 75 1975 Mean ± S.D. Mean ± S. D. Mean ± S. D. Mean ± S. D. Mar.M 15.3 + 1. 37 11.9 + 1.02 F 16.0 + 2.12 11.7 ± 1. 02 Jun. M 17,6 ± 0.59 15.4 ± 0. 48 I/F 20. 2 ± 1.08 17.8 ± 0. 83 8.0 ± 0. 71 Jul.M 18.9 ± 0.73 I/F 20. 3 ± 0.70 10.0 t 0. 50 A 6.6 + 0.66 Sra73F 23. 0 ± 0.71 Aug. M 19.0 ± 0.78 16.7 ± 2. 04 I/F 20.4 0.94 16.0 ± 1. 02 12.0 ± 1. 34 A 8.9 ± 1. 24 Sept.M 19.6 ± 1.02 16.3 ± 0. 91 I/F 21.0 ± 0.97 16.3 ± 1. 37 13.2 ± 1. 53 B 5.9 ± 0.94 Oct. M 20.0 ± 0.70 18. 1 ± 0. 91 I/F 21. 1 i: 1.29 17. 1 ± 1. 08 A 12.3 ± 1.59 Fa 5.5 3.20 Nov.M 20. 1 + 0.75 17.7 ± 1. 00 17.7 t 1. 00 Fa 7.7 + 0.81 I/F 20. 3 ± 0.94 16.8 + 1.08 16.9 ± 1. 08 B 10.9 ± 1.08 1976 Feb.M 14.8 ± 1. 10 11.7 ± 1. 29 F 16.2 ± 1. 37 12.6 + 1.21 Although l a r v a e l e s s than 4-5 mm were not r o u t i n e l y counted i n the J e r v i s I n l e t and S t r a i t of Georgia samples, the recruitment of j u v e n i l e s i n t o the sampled p o p u l a t i o n s d u r i n g the summer (Figure 11 and 13) suggests heavier spawning a c t i v i t y from June to August i n these areas compared to Saanich I n l e t where s i g n i f i c a n t spawning was c o n f i n e d t o May and September. In J e r v i s I n l e t , h e a v i e s t r e c r u i t m e n t appeared t o o r i g i n a t e from May and June, with s m a l l e r c o h o r t s s t a r t i n g i n J u l y and September-October (Figure 12). In the S t r a i t of Geo r g i a , the str o n g e s t j u v e n i l e c o h o r t s appeared i n J u l y and October (Figure 13); heavy spawning i n June and September i s i n d i c a t e d . The suggested p e r i o d s of i n t e n s e spawning appear t o c o i n c i d e i n t i m i n g with the per i o d s of higher phytcplankton 41 24 FIGURE 12. Mean modal body l e n g t h s and f i t t e d von B e r t a l a n f f y growth curves f o r female (a), male(e) and immature(i) p a e i f i c a i n J e r v i s I n l e t during 1975. abundance i n J e r v i s I n l e t and the S t r a i t of Georgia as determined by c h l o r o p h y l l - a c o n c e n t r a t i o n ( F i g u r e 15), but t h i s i n f e r e n c e i s more t e n t a t i v e than f o r Saanich I n l e t due to a lower frequency of sampling and a l a c k of data on egg abundance f o r these areas. N e v e r t h e l e s s , t h e J e r v i s I n l e t c o h o r t from June appears to match with the high l e v e l of c h l o r o p h y l l - a i n June, 42 while the S t r a i t of Georgia cohorts from June and September l i k e l y were spawned d u r i n g the phytoplankton blooms i n these months. Follow i n g r a p i d growth to t h e e a r l y a d u l t stage (11 t o 15 mm) where gonad development r e q u i r e s a l a r g e r p o r t i o n of a s s i m i l a t e d energy, the new S t r a i t of Georgia and J e r v i s I n l e t c o h o r t s merged or " p i l e d up" (Brinton,1976) with o l d e r c o h o r t s which were s t i l l i n the 15 to 18 mm s i z e range. The str o n g recruitment i n t o an o l d e r mode tends t o lower the mean body l e n g t h o f the assemblage. Rn example of " p i l i n g up" occu r r e d i n the 16 t o 18 mm male and female modes i n November f o r the S t r a i t of Georgia when the s p r i n g c o h o r t (curves G5 and G6) reached that s i z e range (Figure 14). By February the e a r l y summer cohort (curves G7 and G8) had e v i d e n t l y j o i n e d t h a t group as w e l l . The corresponding mean body l e n g t h s of the modes f o r both sexes dropped, l i k e l y due t o the combined e f f e c t o f re c r u i t m e n t and s e l e c t i v e m o r t a l i t y o f l a r g e r i n d i v i d u a l s . At the same time, the l a t e summer and f a l l cohorts (curves G9,10 and 11) a p p a r e n t l y merged t o form a second modal group between 10 and 13 mm. In the J e r v i s I n l e t p o p u l a t i o n two cases of " p i l i n g up" developed d u r i n g 1975 (F i g u r e 12). In the f i r s t , the 19-22 mm mode (spawned i n s p r i n g 1974) was j o i n e d i n September and October by the younger a d u l t s ( c u r v e s 1 and 2, l i k e l y spawned i n l a t e summer 1974). The second example i n v o l v e s merging of the s p r i n g mode (curves 3 and 4) with the e a r l y summer c o h o r t (curves 5 and 6) . In the S t r a i t of Georgia and J e r v i s I n l e t data, the process of " p i l i n g up" reduces the number of r e c o g n i z a b l e modes i n the E. p _ a c i f i c a p o p u l a t i o n to 2 or 3 du r i n g the l a t e f a l l and 43 10000}-50001-1000 soo 100 •50 E o MAR 75 J U N 75 "5 l O 15 2 0 10 B O D Y L E N G T H mm JUL 75 10000 50001-1000*-500 5 10 15 2 0 BODY LENGTH m m FIGURE 13. Length frequency d i s t r i b u t i o n s of E. p a c i f i c a from the S t r a i t of Georqia, March 1975 to February 1976. Samples were c o l l e c t e d by M i l l e r net h o r i z o n t a l tows. w i n t e r , from the 5 or 6 c o h o r t s observed during summer and e a r l y f a l l . As a r e s u l t the o v e r a l l s i z e s t r u c t u r e o f the e u p h a u s i i d p o p u l a t i o n s i n these areas appears s i m i l a r t o the E. p a e i f i c a p o p u l a t i o n i n Saanich I n l e t although r e l a t i v e r ecruitment i n t o the composite modes may vary between areas. Further comparisons of the growth of males and females w i t h i n E. p a e i f i c a c o h o r t s can be made with the S t r a i t of Georgia and J e r v i s I n l e t p o p u l a t i o n data. Table 6a,h presents the growth c o n s t a n t s f o r the von B e r f a l a n f f y equations f i t t e d t o t he data recorded i n Tables 4 and 5 and p l o t t e d i n F i g u r e s 12 and 14. 45 TABLE 6 a . G rowth c o n s t a n t s f o r von B e r t a l a n f f y e q u a t i o n s f i t t e d t o J e r v i s I n l e t d a t a on mean body l e n q t h by s e x , p l o t t e d i n F i q u r e 12 . C u r v e Mode K t — o r 1 F Sum74 0 . 4 8 8 19 .8 8 .74 0 . 9 9 4 2 H Sum74 0 . 3 2 5 2 0 . 9 8 .42 0 . 9 9 5 3 B S p r 7 5 0. 434 1 8 . 8 0 . 4 9 0 . 9 9 3 4 F Sp r75 0 . 2 6 7 2 1 . 0 - . 1 8 0 . 9 9 8 5 H Sum A75 0 . 2 2 4 2 1 . 4 - . 2 8 0 . 9 9 9 6 F SumA75 0 .360 17 .2 0 . 0 3 0 . 9 9 9 7 M SuraB75 1.023 12 .2 0 .74 0. 999 8 F SumB75 1 .045 12 .0 0 .64 0 . 9 8 TABLE 6 b . G rowth c o n s t a n t s f o r t o S t r a i t o f G e o r q i a d a t a p l o t t e d i n F i q u r e 14 . C u r v e Mode K G1 F Sp r74 0 . 4 8 4 G2 M Sp r74 0 . 2 2 0 G3 M Fa 74 0 . 2 9 8 G4 F F a 74 0 .198 G5 M S p r 7 5 0 . 2 9 5 G6 F Sp r75 3 .352 G7 F SumA75 0 . 2 2 8 G8 M SumA75 0 . 2 8 0 G9 F SumB75 0 . 8 2 0 G10 M SumB75 0 . 4 7 0 G1 1 M F a 75 0 . 3 3 8 v o n B e r t a l a n f f y e q u a t i o n s f i t t e d mean body l e n q t h by r 2 1 . 4 2 1 . 5 8 .42 5 .65 0 . 9 9 3 0 . 9 9 2 19.1 1 9 . 3 4 . 9 3 3 .39 0 . 983 0. 993 21 .2 1 8 . 7 0 . 7 8 0 . 7 3 0 . 986 0 . 98 18 .9 1 6 . 3 - . 3 9 0 .50 0 . 9 9 8 0 . 9 9 4 1 2 . 7 1 2 . 2 1 3 . 7 0 . 8 8 - . 4 0 0.51 0 . 996 0 . 9 6 3 0 . 999 As i n t h e S a a n i c h I n l e t d a t a , q r o w t h c u r v e s o f J e r v i s I n l e t c o h o r t s i n t h e i r f i r s t y e a r { c u r v e s 3 , 5 and 7 i n F i q u r e 12) show somewhat f a s t e r q r o w t h a f t e r 11-12 mm body l e n q t h f o r m a l e s c o m p a r e d t o t h e c o r r e s p o n d i n g f e m a l e s . F o r t h e f i r s t - y e a r S t r a i t o f G e o r g i a c o h o r t s { F i g u r e 1 4 ) , m a l e s have h i g h e r i n f e r r e d 46 FIGDBE 14. Mean modal body l e n g t h s and f i t t e d von B e r t a l a n f f y growth curves f o r f e m a l e ( a ) , male (e) and immature(i) I i p a e i f i c a i n the S t r a i t of Georgia during 1975. growth i n curves G3 and G5 than for t h e i r female c o u n t e r p a r t s . Females i n curves G7 and G9, though, a p p a r e n t l y outgrow the corresponding males. The gap i n sampling between November and February makes t h i s i n f e r e n c e more t e n t a t i v e as d i f f e r e n t i a l m o r t a l i t y may a l s o be a f a c t o r over t h i s p e r i o d . An i n t e r e s t i n g o b s e r v a t i o n from the l i s t of Lv> values i n Table 6a,b i s t h a t the asymptotic l e n g t h s o f the s p r i n g and e a r l y summer c o h o r t s i n J e r v i s I n l e t and the S t r a i t of Georgia are c l o s e t o those of the second year a d u l t s , suggesting that growth t o f i n a l a d u l t s i z e might have been completed i n a l i f e span of 11 to 12 months i f food a v a i l a b i l i t y and water temperature had not d e c l i n e d i n the l a t e f a l l and winter. T h i s r a t e of growth i s i n l i n e with o b s e r v a t i o n s of E x p a e i f i c a p o p u l a t i o n s o f f the c o a s t of Oregon (Smiles and Pearcy,1971) and o f f southern C a l i f o r n i a ( B r i n t o n , 1 9 7 6 ) . Ml 12h 10 £ oi2 x JERVIS INLET » STRAIT of GEORGIA _ J _ JUN JUL AUG SEPT OCT NOV DEC 1975 FIGDBE 15. Mean c h l o r o p h y l l - a c o n c e n t r a t i o n s i n the upper 10 m of J e r v i s I n l e t and the S t r a i t of Georgia d u r i n g 1975. Bars i n d i c a t e one standard d e v i a t i o n . The tendency f o r the males' growth curves to have higher 48 asymptotic l e n g t h s was examined f o r the S t r a i t of Georgia, J e r v i s I n l e t and Saanich I n l e t c o h o r t s ; p a i r e d Student's t - t e s t s comparing male and female values of K i n f i r s t and second growing seasons showed t h a t the d i f f e r e n c e between sexes was s i g n i f i c a n t a t the 95% l e v e l (t = 2.21, P < .05) i n the second season, but not i n the f i r s t growing season. S i m i l a r s t a t i s t i c a l t e s t s on p a i r e d male and female v a l u e s f o r L«>and t G r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e at the 95% p r o b a b i l i t y l e v e l i n these co n s t a n t s between male and female components of E x p a e i f i c a c o h o r t s . The r e s u l t s of Student's t - t e s t s are l i s t e d below (Table 7). In c o n c l u s i o n , the i n f e r r e d growth of E, p a e i f i c a i n the sampled p o p u l a t i o n s expressed as von B e r t a l a n f f y equations v a r i e s s i g n i f i c a n t l y between sexes w i t h i n c o h o r t s i n t h e i r second growing season., TABLE 7. R e s u l t s of Student's t - t e s t s on p a i r e d v a l u e s of von B e r t a l a n f f y c o n s t a n t s f o r sexes w i t h i n E A p a e i f i c a c o h o r t s . Season Constant i f = n-1 t l x i S L t i £ a l c A L Probj. 1 K 6 1. 94 0.93 0.20 2 K 5 2.02 2.21 < .05 1 L C O 6 1.94 0.53 0.30 2 L co 5 2.02 1.37 0. 15 1 to 6 1.94 0.10 0. 45 2 to 5 2.02 1.86 < .10 The evidence f o r s e l e c t i v e m o r t a l i t y of f a s t e r growing males should be c o n s i d e r e d i n connection with growth r a t e s . The change i n sex r a t i o (M : F) f o r the s i z e range from e a r l y maturity when the sexes are f i r s t d i s c e r n i b l e (11-12 mm) u n t i l the c ohort disappears from the sampled p o p u l a t i o n i s an index o f the r e l a t i v e amount o f time spent at the v a r i o u s s i z e increments. S i g n i f i c a n t d e v i a t i o n s from the expected 1 : 1 r a t i o are l i k e l y due to d i f f e r e n c e s i n the r a t e o f development up to f u l l a d u l t s i z e and to d i f f e r e n c e s i n m o r t a l i t y (or c a t c h a b i l i t y ) , F i g u r e 16 shows t h e change i n sex r a t i o with i n c r e a s i n g body s i z e f o r a l l measured E«. p a c i f i c a from Saanich I n l e t , J e r v i s I n l e t and S t r a i t of Georgia samples taken d u r i n g 1975-76. On the average, females are a p p a r e n t l y more abundant except at about 12 mm and at 18-19 mm. According to a c h i - s g u a r e t e s t , t h e mean r a t i o a t 12 mm (0.85) i s not s i g n i f i c a n t l y d i f f e r e n t from 1.0 (X* = 2.29, P < 0.05). S i m i l a r l y , the mean sex r a t i o s at 18 and 19 mm do not d e v i a t e s i g n i f i c a n t l y from 1 (X 2 = 1.34, P < 0.05 and X* = 3.51, P < 0.05, f o r 18 and 19 mm r e s p e c t i v e l y ) . Note, however, t h a t the M : F r a t i o of 1.29 at 19 mm f o r the S t r a i t of Georgia p o p u l a t i o n i s s i g n i f i c a n t l y g r e a t e r than 1 (X 2 = 5.00, P < .05). A l l of the mean r a t i o s below about 0.80 are s i g n i f i c a n t l y d i f f e r e n t from 1 (X* =4.10, P < 0.05). The high H:F r a t i o at 14 mm f o r the S t r a i t of Georgia p o p u l a t i o n was l a r g e l y due to a high p r o p o r t i o n of males a t 14-15 mm i n e a r l y s p r i n g when the m a j o r i t y of females were a t 11-13 mm. The v a r i a t i o n i n sex r a t i o may be i n t e r p r e t e d i n the f o l l o w i n g manner. As secondary sexual c h a r a c t e r i s t i c s such as the petasma on males are beginning t o be expressed at about 10-11 mm body l e n g t h , the apparent sex r a t i o i s s i g n i f i c a n t l y l e s s than 1 u n t i l the l a t e maturing males are d i s c e r n i b l e (about 12-14 mm). At e a r l y maturity the males seem t o grow f a s t e r i n l e n g t h than the females which must use more energy f o r gonad development and egg p r o d u c t i o n . Consequently the males graduate to the l a r g e r s i z e increments at an e a r l i e r age, r e s u l t i n g i n 50 • MEAN o JERVIS INLET v SAANICH INLET o 3 0 O STRAIT of GEORGIA BODY LENGTH mm FIGURE 16. Changes i n sex r a t i o (M : F) with body l e n g t h f o r JLL p a c i f i c a p o p u l a t i o n s d u r i n g 1975. the s i g n i f i c a n t l y lower sex r a t i o i n the range from 13-17 mm. Except i n J e r v i s I n l e t where male m o r t a l i t y was ap p a r e n t l y very high a f t e r 17 mm, the males have t h e i r h i g h e s t r e l a t i v e abundance at 18 to 19 mm which suggests t h a t they reach t h i s s i z e range sooner and/or spend a g r e a t e r p o r t i o n of t h e i r l i f e s p a n at t h i s s i z e than do the females. At s i z e s over 19 mm the male m o r t a l i t y r a t e was a p p a r e n t l y very high as few s u r v i v e d 51 to reach 21 mm. Some females, though, p e r s i s t e d u n t i l about 22-24 mm, probably l i v i n g 1-2 months longer than t h e i r male c o u n t e r p a r t s . There are other p o s s i b l e causes f o r some of the v a r i a t i o n i n sex r a t i o , such as d i f f e r e n c e s i n c a t c h a b i l i t y with s i z e and sex but as most of the sampling was by high speed (3-4 m/sec) M i l l e r net h a u l s , c a t c h a b i l i t i e s are l i k e l y o f l e s s s i g n i f i c a n c e than d i f f e r e n c e s i n growth r a t e and m o r t a l i t y . 2.5 M o r t a l i t y of J u v e n i l e and Adult E. p a e i f i c a . Catch curves i n F i g u r e 17 show the average L-F d i s t r i b u t i o n s during 1975 f o r E^ . p a c i f i c a taken by SCOH net v e r t i c a l hauls i n Saanich I n l e t and by M i l l e r nets i n a l l three study areas. There i s g e n e r a l l y good agreement i n the shapes of the curves f o r the two methods of capture; the d i f f e r e n c e s i n d e n s i t y are p r i m a r i l y due to the v e r t i c a l s t r a t i f i c a t i o n of E. p a e i f i c a . That i s , the SCOfi d e n s i t i e s r e p r e s e n t the average c o n c e n t r a t i o n i n the 0-150 m water column while the M i l l e r net determinations from the sound s c a t t e r i n g l a y e r of e u p h a u s i i d s more c l o s e l y r e p r e s e n t l o c a l c o n c e n t r a t i o n s near the s u r f a c e a t n i g h t . The presence o f a shoulder r a t h e r than a peak f o r the 19-21 mm females taken by SCOP, net suggests t h a t the sampled abundance o f these l a r g e r amimals was underestimated due to net avoidance. The problem of net s e l e c t i v i t y w i l l be d i s c u s s e d l a t e r . The poly modal nature of the average c a t c h curves suggests that d i f f e r e n t p e r i o d s of time are spent i n the v a r i o u s s i z e 52 BODY LENGTH mm FIGURE 17, Catch curves of a l l E A p a c i f i c a sampled dur i n g 1975 by M i l l e r net (MNT) and by ~SCOR n e t " i n the S t r a i t of Georgia r e g i o n . increments, more i n the modes and l e s s where numbers are d e c l i n i n g r a p i d l y . a r i s i n g l e f t - h a n d limb o f a c a t c h curve i n d i c a t e s r e c r u i t m e n t i n t o the mode exceeds m o r t a l i t y over that s i z e range (cf R i c k e r , 1958) w h i l e a descending right-hand limb i n d i c a t e s graduation from the mode and/or m o r t a l i t y . The steep negative slope over the f i n a l s i z e increments i s l i k e l y due to high m o r t a l i t y f o r the 20-24 mm members of the M i l l e r net sample p o p u l a t i o n ; net avoidance probably c o n t r i b u t e s t o the change i n s l o p e f o r the 18-22 mm range i n the SCOB net sample p o p u l a t i o n . Comparison of male and female M i l l e r net catch curves by u s i n g the above i n t e r p r e t a t i o n s o f changing s l o p e s suggests t h a t male E.. p a c i f i c a tend to spend l e s s time i n the 12-15 mm range but accumulate i n the 16-19 mm range e a r l i e r ; females accumulate i n the 14-16 mm mode before g r a d u a t i n g to the 19-21 mm mode. Support f o r t h i s c o n t e n t i o n i s seen i n curves 5 and 6 of F i g u r e 12 and curves G5 and G6 i n F i g u r e 14., The male E.. p a c i f i c a having approached t h e i r f u l l a d u l t s i z e e a r l i e r , experience a high r a t e of s i z e - s e l e c t i v e m o r t a l i t y from a younger age than the females i n the same cohort. Conseguently the males a p p a r e n t l y d i e at a s m a l l e r maximum s i z e than the females which l i v e somewhat longer. T h i s seguence of events i s c o n s i s t e n t with the i n t e r p r e t a t i o n of the sex r a t i o s presented e a r l i e r . The f a c t o r of s i z e - s e l e c t i v e m o r t a l i t y has been invoked s e v e r a l times above. Evidence i n E.. p a c i f i c a , f o r t h i s phenomenon, which i s common t o most f i s h p o p u l a t i o n s a t some stage of t h e i r l i f e (Bicker,1969) i s c l e a r e s t i n the winter months when no s i g n i f i c a n t growth occurs. As Jones (1958, i n Bicker,1969) has shown, i n a y e a r - c l a s s o f animals which i s not growing and which has a normal length d i s t r i b u t i o n w i t h i n which the i n s t antaneous m o r t a l i t y r a t e , Z, i s a p o s i t i v e l i n e a r f u n c t i o n of l e n g t h , the average s i z e of animals i n the year-c l a s s d e c l i n e s with time, but the length frequency d i s t r i b u t i o n i n the y e a r - c l a s s remains normal and t h e standard d e v i a t i o n does not change. B i c k e r (1969) has proposed an index of i n t e n s i t y o f s e l e c t i o n ( r ) or s e l e c t i v i t y index d e f i n e d as : r = 1. 349as = 1.349d/s where d = decrease i n mean l e n g t h i n one time i n t e r v a l ; a = the d i f f e r e n c e i n ins t a n t a n e o u s m o r t a l i t y r a t e during t h i s i n t e r v a l , between animals t h a t d i f f e r i n s i z e by one u n i t o f l e n g t h ; s = standard d e v i a t i o n i n length. T h i s s e l e c t i v i t y index i s egual t o the d i f f e r e n c e i n average instantaneous m o r t a l i t y r a t e between the s m a l l e r h a l f and the l a r g e r h a l f of the age-group. The best examples of apparent s i z e - s e l e c t i v e m o r t a l i t y i n the present study a r e from the Saanich I n l e t p o p u l a t i o n d u r i n g the e a r l y months of 1974 and 1975 (Figure 10) where a gen e r a l d e c l i n e i n mean body l e n g t h i s observed between January and A p r i l before s i g n i f i c a n t growth i n le n g t h resumes. To c a l c u l a t e values o f the s e l e c t i v i t y index, r , f o r E,. p a e i f i c a sexes i n Saanich I n l e t mean body l e n g t h s from February and A p r i l 1974 and January and Harch, 1975 were chosen i n p a i r e d examples of approximately normal length frequency d i s t r i b u t i o n s with s i m i l a r standard d e v i a t i o n s ( c f F i q u r e s 8 and 9). The r e s u l t s of the c a l c u l a t i o n s of r have been recorded i n Table 8. 55 TABLE 8. Values of s e l e c t i v i t y index, r , f o r E. p a c i f i c a sexes from Saanich I n l e t f o r p e r i o d s of no qrowth i n 1974 and 1975. Date Sex Mean ± d (rom/roo. 1 20Feb.74 M 12.0 + 0. 94 3 Apr.74 M 11.5 ± 0.83 0. 36 0.53 0.44 20Feb.74 F 12.1 ± 0. 96 3Apr.7U F 11.7 + 1.08 0. 29 0.38 0.28 20Jan.75 M 14.9 ± 1. 21 24Mar.75 M 14.1 ± 1.08 0.39 0.45 0.29 20Jan.75 F 15.2 ± 1. 13 24Mar.75 F 14.2 ± 1.37 0.48 0. 56 0.25 The above v a l u e s of r show no s i q n i f i c a n t d i f f e r e n c e by sex (t = 0.15, P > 0.40); they i n d i c a t e t h a t d u r i n q the winter months of each year the l a r q e r h a l f of the c o h o r t experienced an averaqe m o r t a l i t y r a t e that was q r e a t e r by about 0.5 than that which a f f e c t e d the s h o r t e r h a l f o f t h e cohort. I f the assumption of a l i n e a r i n c r e a s e i n instantaneous m o r t a l i t y r a t e with l e n q t h i s a t a l l r e a l i s t i c f o r a d u l t euphausiids, then the hiqher growth r a t e s of male E. p a c i f i c a would r e a d i l y account f o r the observed hiqher m o r t a l i t y o f males and consequently the low averaqe M . F sex r a t i o . S u r v i v a l of E.. p a c i f i c a c o h o r t s was estimated from l o q a r i t h r a i c p l o t s of the month-to-month p o p u l a t i o n d e n s i t i e s i n the r e s p e c t i v e c o h o r t s (eq. F i q u r e 18). In Saanich I n l e t the s p r i n q 1975 cohort had an averaqe s u r v i v a l of 76%/mo between J u l y and February, a c c o r d i n q t o l i n e a r r e g r e s s i o n of monthly abundances from SCOR v e r t i c a l h a u l s (Fiqure 18,A). Fo l l o w i n q the p e r i o d of r a p i d qrowth i n J u l y and Auqust, when s u r v i v a l of j u v e n i l e s and immature a d u l t s (7-12 mm) was only about 41%/mo (Z = .89), t h e i r percent s u r v i v o r s h i p i n c r e a s e d t o 56%/mo between august and October, then to about 68%/mo f o r the p e r i o d of e a r l y maturity between October and February. From M i l l e r net estimates of abundance, j u v e n i l e (7-12 mm) s u r v i v a l i n Saanich I n l e t was 35%/mo between J u l y and August. S u r v i v a l of 14-18 mm males was about 55%/mo durin g June and J u l y i n J e r v i s I n l e t . For the Saanich I n l e t s p r i n g 1974 cohort, m o r t a l i t y of the two sexes c o u l d be d i s t i n g u i s h e d d u r i n g 1975. The mean s u r v i v a l of 19-22 mm females between J u l y and August from M i l l e r and SCOB net abundances was 57.4 + 5.1%/mo (Z=.559 ± .101). The average s u r v i v a l f o r J u l y t o February from r e g r e s s i o n of SCOB abundances was about 65Vmo (F i g u r e 18,B). By February, o n l y the 19 mm component of t h i s mode was s t i l l sampled by the SCOB net. In c o n t r a s t , mature females o f 18-24 mm were taken by M i l l e r nets i n the S t r a i t of Georgia and J e r v i s I n l e t d u r i n g the f a l l ; r e p r e s e n t a t i v e segments of s u r v i v a l c u r ves f o r these c o h o r t s are given i n F i g u r e 18, D and E. S u r v i v a l of the o l d e r females was 50%/mo (Z = .692) between J u l y and October i n the S t r a i t of Georgia and 45.7 ± 2.7%/mo (Z = .783 ± .059) between June and December i n J e r v i s I n l e t , Male s u r v i v a l i n Saanich I n l e t was lower than f o r females but the d i s p a r i t y between estimates from the two methods of capture was g r e a t e r . The estimate of s u r v i v a l of 17-21 mm males from M i l l e r net abundances was 25%/mo (Z = 1.386) between J u l y and August c r u i s e s , but the SCOB net abundances y i e l d e d a f a i r l y steady s u r v i v a l r a t e of 62%/mo (Z = .476) f o r t h i s c o h o r t 57 between J u l y and February (Figure 18, C). The corresponding male mode i n Saanich I n l e t had a s u r v i v a l r a t e of 21.5 ± 5.5%/mo (Z = 1. 555 ± .559) between June and December (Figure 18, G). The E S T I M A T E D A G E months FIGDBE 18. Examples of s u r v i v a l curves f o r E A p a e i f i c a c o h o r t s . Age of c o h o r t s determined as (12Y • estimated age increment) where y=0 f o r f i r s t year c o h o r t s and y= 1 f o r second year c o h o r t s . s u r v i v a l of s i m i l a r males i n the S t r a i t o f Georgia was about 3251/mo (Z = 1.15) between J u l y and October (Figure 18, F) . I t appears that the SCOR net hauls underrepresented the abundance of the 21-23 mm male and female E. p a e i f i c a l e a d i n g t o underestimations of the m o r t a l i t y of the modes as a whole, as 58 the catch curves i n F i g u r e 17 a l s o i n d i c a t e . The e s t i m a t e s of j u v e n i l e and e a r l y a d u l t s u r v i v a l by SCOH and M i l l e r net d e n s i t i e s seem to agree reasonably w e l l . Net avoidance l i k e l y becomes a s i g n i f i c a n t f a c t o r i n r e p r e s e n t a t i v e sampling of e u p h a u s i i d s over about 18 mm with v e r t i c a l l y hauled nets. Brinton(1976) noted a s i m i l a r r a p i d d e c l i n e i n abundance o f E. p a e i f i c a over 18 mm taken by v e r t i c a l l y hauled CalCOFI nets; the p o s s i b i l i t y of net avoidance by l a r g e i n d i v i d u a l s was a l s o suggested. To summarize the r e s u l t s on s u r v i v a l o f E,. p a e i f i c a i n the S t r a i t o f Georgia r e g i o n , h y p o t h e t i c a l s u r v i v a l curves are presented i n F i g u r e 19; the s u r v i v a l r a t e s expressed i n c l u d e those f o r e g g - t o - l a r v a e and l a r v a e - t o - j u v e n i l e estimated from data s u p p l i e d by Fulton e t a l . . (1969). The curves f o l l o w the s u r v i v a l of males and females of an E. p a c i f j c a c o h o r t which begins as 10 7 eggs i n e a r l y May. The r a t e s used i n c o n s t r u c t i o n of the curve are c i t e d i n Table 9. 59 TABLE 9. Rep r e s e n t a t i v e s u r v i v a l r a t e s f o r stages of E A p a c i f i c a i n the S t r a i t of Georgia r e g i o n used i n c o n s t r u c t i o n of the h y p o t h e t i c a l s u r v i v a l curves i n F i g u r e 19. Stage S i z e Age S u r v i v a l M o r t a l i t y Numbers (mm) (mo) r a t e %/mo Z= - l n (s) s u r v i v i n g 1.0 x 107 Egg .40 0 5.7 ± 1.5 2.86 ± .28 L a r v a l 1-4.5 1 42.0 ± 1.7 .86 8 ± .41 N to F3 1.34 x 105 F u r c i l i a 4. 6-8 2.7 40.8 ± 5.6 .897 ± .14 F3 t o J 4. 08 x 10* J u v e n i l e 8-12 4 56. 3 .574 1.72 x 10* Small 12-14 5. 5 67.8 . 389 a d u l t 2.99 x 103 Medium 14-18 10 F 67.8 ,389 a d u l t F 4.28 x 10« M 55.5 .588 M 1.58 x 102 Large 18-24 15 F 57.4 ± 2.9 .559 ± . 10 a d u l t F 8.00 x 102 M 32. 3 1.13 M 5.32 18 F 43. , . 825 F 1. 54 x 10i M 31.7 1. 15 M 0.53 20 L i n e a r r e g r e s s i o n of the n a t u r a l l o g a r i t h m of s u r v i v i n g p o p u l a t i o n on age y i e l d s t h e f o l l o w i n g mean l i f e - s p a n s u r v i v a l r a t e s from 4.6 mm l a r v a e i n the h y p o t h e t i c a l E.. p a c i f i c a c o h o r t ; 60.7%/mo (Z = ,500) f o r females and 51.3I/mo (Z = .668) f o r males. A f t e r 20 months the males have d e c l i n e d to i n s i g n i f i c a n t numbers, but the females p e r s i s t f o r about three more months befo r e r e a c h i n g v i r t u a l e l i m i n a t i o n . The l i f e - s p a n s o f the h y p o t h e t i c a l c o h o r t agree c l o s e l y with the es t i m a t e s from l e n g t h freguency d i s t r i b u t i o n a n a l y s i s which were presented e a r l i e r . 500000 lOOOOOf-60 4 6 8 IO 12 14 16 18 20 22 24 26 t (age) months FIGURE 19. H y p o t h e t i c a l s u r v i v a l curves f o r E^. fiacltica i n the S t r a i t of Georgia r e g i o n . For e x p l a n a t i o n see t e x t . Symbols i n d i c a t e immatures (i) , females (a) and males(e). 61 2.6 D i s c u s s i o n . In the S t r a i t of Georgia r e g i o n , spawning and subsequent s t r o n g recruitment of E. p a e i f i c a l a r v a e appears t o be a s s o c i a t e d with high phytoplankton abundance. Spawning occurred i n a l l three study areas d u r i n g May and/or June when high c h l o r o p h y l l - a l e v e l s were present. The s p r i n g c o h o r t s provided the s t r o n g e s t r e c r u i t m e n t i n Saanich and J e r v i s I n l e t s , while the S t r a i t o f Georgia p o p u l a t i o n was a l s o b o l s t e r e d by a s u c c e s s f u l f a l l c o h o r t which b e n e f i t t e d from a phytoplankton bloom i n September and warm weather i n t o November. Parsons et a l . . (1967) a l s o noted the c o i n c i d e n c e o f a high biomass of e u p h a u s i i d eggs with a diatom bloom i n Saanich I n l e t d u r i n g 1966 as mentioned e a r l i e r . Brinton{1976) has presented evidence t h a t h e a v i e s t E^ g a c i f i c a spawning a c t i v i t y o f f southern C a l i f o r n i a c o i n c i d e s with s p r i n g - e a r l y summer upwelling along t h a t c o a s t . During the main up w e l l i n g p e r i o d , A p r i l t o September, p u l s e s of eu p h a u s i i d l a r v a l r e c r u i t m e n t were observed i n the n u t r i e n t - e n r i c h e d s u r f a c e waters i n nearshore areas o f f southern C a l i f o r n i a . Likewise, o f f Oregon most e u p h a u s i i d l a r v a e were encountered i n nearshore u p w e l l i n g areas c h a r a c t e r i z e d by lower s u r f a c e temperatures and high primary p r o d u c t i v i t y (Smiles and Pearcy,1971). In c o n t r a s t to the year-round r e c r u i t m e n t of l a r v a e o f f Oregon and southern C a l i f o r n i a , i n the S t r a i t of Georgia r e g i o n J i p a e i f i c a l a r v a e are r e c r u i t e d only i n the p e r i o d from May t o October. The s p r i n g and e a r l y summer c o h o r t s are g e n e r a l l y most s u c c e s s f u l , but f a l l cohorts may a l s o c o n t r i b u t e s i g n i f i c a n t l y 62 to the a d u l t p o p u l a t i o n . In the southern p o p u l a t i o n s , the c o h o r t s with h i g h e s t s u r v i v a l are g e n e r a l l y produced i n the l a t t e r h a l f of the year; June to December o f f southern C a l i f o r n i a (Brinton,1976) and October to December o f f Oregon (Smiles and Pearcy,1971). Growth of E i p a c i f i c a c o h o r t s i n the S t r a i t of Georgia p o p u l a t i o n s i n f e r r e d from l e n g t h frequency d i s t r i b u t i o n s i s w e l l d e s c r i b e d by the von Bertalanffy(1938) eguation which has f u r t h e r a p p l i c a t i o n i n y i e l d e s t i m a t i o n by the method of Beverton and Holt(1957)., F o l l o w i n g r a p i d growth d u r i n g the s p r i n g and summer, growth slows i n the f a l l u n t i l body l e n g t h reaches a w i n t e r maximum. As growth may slow down i n e a r l y adulthood, two or more c o h o r t s may a t t a i n n e a r l y the same winter body s i z e , r e s u l t i n g i n " p i l i n g - u p " of groups of d i f f e r e n t - a g e d a d o l e s c e n t s i n t o one mode. In the f o l l o w i n g s p r i n g , s u r v i v o r s resume growth toward t h e i r maximum a d u l t s i z e . O f f southern C a l i f o r n i a , E.. p a c i f i c a commonly reaches f u l l a d u l t s i z e w i t h i n one year, but during p e r i o d s of lower food a v a i l a b i l i t y " p i l i n g -up" of a d o l e s c e n t euphausiids a l s o o c c u r s ( B r i n t o n , 1 9 7 6 ) . D i f f e r e n t i a l growth of sexes a f t e r adolescence (11-12 ram) i s i n d i c a t e d by s e v e r a l d i r e c t and i n d i r e c t types o f evidence. F i r s t , i n f e r r e d growth r a t e s near the end of the growing season appeared to be h i g h e r f o r E t p a c i f i c a males than f o r females i n s e v e r a l c o h o r t s of f i r s t - y e a r a d u l t s i n the three p o p u l a t i o n s s t u d i e d . The d i f f e r e n c e s i n f i r s t season growth were not s u f f i c i e n t t o d i s t i n g u i s h the von B e r t a l a n f f y c o n s t a n t s of the growth equations f o r the two sexes. Secondly, the von 63 B e r t a l a n f f y c o n s t a n t , K, f o r the second season of growth d i d vary s i g n i f i c a n t l y between sexes, i n d i c a t i n g d i f f e r e n t r a t e s of completion of the growth p a t t e r n . T h i r d l y , changes i n the sex r a t i o with i n c r e a s i n g body l e n g t h (Figure 16) and c a t c h curves (Figure 17) suggest t h a t males advance i n t o the 16-19 mm s i z e range before females and conseguently experience a higher s i z e -s e l e c t i v e m o r t a l i t y than the slower growing females. Males r a r e l y exceeded 22 mm due to high m o r t a l i t y (Z = 1.13) i n the over 18 mm s i z e range. Females, though, experienced lower m o r t a l i t y r a t e s (Z = .559 ± .10) as l a r g e a d u l t s ; they appeared to have o u t l i v e d the l a r g e males by 2-3 months and some achieved body l e n g t h s of 23-24 mm. Since E. p a e i f i c a females tend t o remain l o n g e r i n the 14-16 mm and 19-21 mm c l a s s e s than males, they have o f t e n been c o n s i d e r e d as the l a r g e r sex; males of the same ages, though, have ap p a r e n t l y matured e a r l i e r and have reached the s i z e where i n c r e a s e d m o r t a l i t y occurs (over 18 mm) b e f o r e the females. I f t h i s i s indeed the case, then the males of 16-18 mm i n the catch curves (Figure 17) are contemporaries o f the 14-16 mm females; the dwindling number of > 19 mm males correspond i n age with the 18-20 mm females. That slower growing females appear i n c r e a s i n g l y abundant r e l a t i v e to males at s u c c e s s i v e increments of body l e n g t h was r e c o g n i z e d by Brinton(1976) as a p o s s i b l e e x p l a n t i o n f o r the b i a s of the sex r a t i o i n favour of females i n the E i p a e i f i c a p o p u l a t i o n o f f southern C a l i f o r n i a . Nemoto(1975) and other authors have g e n e r a l l y considered t h a t a d u l t males of I*. p a e i f i c a tend to be s m a l l e r than females of the same age, as i s thought t o be the case with Meganjctiphanes n o r v e g i c a (eg. Mauchline,1960) . Other workers have not d i f f e r e n t i a t e d between sexes i n t h e i r s t u d i e s of s i z e s t r u c t u r e and growth o f euphausiids (eg. Smiles and Pearcy,1971; Matthews,1973) . At l e a s t i n E± p a c i f i c a p o p u l a t i o n s , the evidence f o r d i f f e r e n t i a l growth and m o r t a l i t y m e r i t s s e p a r a t e treatment o f the sexes. M o r t a l i t y r a t e s based on abundance estimates from SCOP, and M i l l e r net hauls are c o n s i s t e n t with each other f o r s i z e s up t o 18 mm, Euphausiids over t h i s s i z e appear t o be under-represented i n the SCOR samples, r e s u l t i n g i n a b i a s to m o r t a l i t y r a t e s , e s p e c i a l l y f o r males. From the M i l l e r net estimates and SCOR net m o r t a l i t y e s t i m a t e s f o r e u p h a u s i i d s under 18 mm, the f o l l o w i n g p a t t e r n i n E.. p a c i f i c a s u r v i v a l i s suggested. S u r v i v a l r a t e s tend to i n c r e a s e by about 10-15 % with changes from l a r v a l phase (4.6-8 mm) to j u v e n i l e (8-12 mm) and from j u v e n i l e to small a d u l t (12-14 mm). A f t e r e a r l y m a turity, f a s t e r growth o f males l e a d s to a high e r s i z e - s e l e c t i v e m o r t a l i t y of males. S u r v i v a l of females d e c l i n e s as they reach f i n a l s e x u a l maturation i n the 18-24 mm range. Large males r a p i d l y disappear from the sampled p o p u l a t i o n a f t e r 19-20 mm. For the E. p a c i f i c a p o p u l a t i o n o f f southern C a l i f o r n i a , Brinton(1976) observed that a f t e r the l a r v a l phase, mean s u r v i v a l dropped by about 4%/mo with l i f e h i s t o r y phase changes whereas i n a h y p o t h e t i c a l age-frequency d i s t r i b u t i o n c o n s t r u c t e d t o mimic observed length-biomass d i s t r i b u t i o n s the mean s u r v i v a l i n c r e a s e d by 11-12S/mo at phase changes up to e a r l y adulthood (13 mm). Brinton(1976) a t t r i b u t e d the d i f f e r e n c e between observed and d e r i v e d s u r v i v a l r a t e s t o uneveness i n r e a l growth 65 r a t e s . The changes i n s u r v i v a l with l i f e h i s t o r y phases may be i n par t due to s i z e - s e l e c t i v e m o r t a l i t y . Sicker(1969) p o i n t s out th a t as the l a r g e r i n d i v i d u a l s i n a cohort disappear more r a p i d l y than the s m a l l ones, the o v e r a l l average m o r t a l i t y r a t e of the s u r v i v o r s w i l l decrease with time, i f no other f a c t o r s have a l a r g e r e f f e c t on m o r t a l i t y r a t e . In a d d i t i o n t o the e f f e c t s of s i z e - s e l e c t i v e m o r t a l i t y , changes i n behaviour pa t t e r n s between l i f e - p h a s e s (and thus s u c c e p t i b i l i t y t o predation) are l i k e l y i n v o l v e d . Although a sampling program to examine p r e d a t i o n on E. p a c j f i c a was not undertaken i n t h i s study, some i n f o r m a t i o n about predation on eup h a u s i i d s by l a r v a l and j u v e n i l e f i s h i n Saanich I n l e t i s a v a i l a b l e from a data r e p o r t by Barraclough e t al^_ , (1968). The r e s u l t s f o r consumption of euph a u s i i d eggs and l a r v a l stages are presented i n Tab l e 10a while p r e d a t i o n on j u v e n i l e and a d u l t e u p h a u s i i d s i s summarized i n Table 10b. 66 TABLE 10a, Summary o f consumption of e u p h a u s i i d eggs and l a r v a e by j u v e n i l e f i s h i n Saanich I n l e t during A p r i l - July,1S68. (data are from Barraclough e t a l . ,1968), F i s h Number Mean (mm) Mean no. o f each stage eaten. f o r k l e n g t h Eggs F u r c i l i a Others 0_. gorbuscha 304 90. 2 739.9 40. 1 p7 keta ~ 220 88. 1 171.0 45. 6 0. nerka 83 113.7 43 6.1 85. 2 G. a c u l e a t u s 118 77. 8 194.3 8. 5 £ i p a 1 1 a s i i 22 104. 2 166.6 0. 3 0._ k i s u t c h 5 127. 6 9.8 0. 2 Ejj. mordax 5 100.2 32.0 P l e u r o n e c t i d a e 3 16.3 7.7 Sebastodes sp^ 6 10.3 1.0 0.3 l i s i g n a t u s 7 20. 2.3 As. hexagterus 3 20. 6.0 lis. a l e u t e n s i s 3 20.7 20.7 H. s t e l l e r i 3 55. 17.0 TABLE 10 b. Summary o f p r e d a t i o n by j u v e n i l e f i s h on j u v e n i l e and a d u l t e u p h a u s i i d s i n Saanich i n l e t d u r i n g A p r i l - J u l y 1968. (data from Barraclough e t al,, 1968) . F i s h Number Mean(mm) Mean no. of size(mm) eaten f o r k l e n q t h 5.1-8. 8. 1-15. > 15. s. g a i f d n e r i i 50 175.0 19.4 0.36 Oi k i s u t c h 63 141. 3 7. 2 0.02 Oi keta 84 92.3 0.02 2. 4 0.06 G7 a c u l e a t u s 56 73.9 0.02 2.7 0.04 o. gorbuscha 43 97.0 1.8 1.5 0. 12 o. nerka 22 101. 1 2. 3 c. p a l l a s i i 3 128.7 14.7 I i productus 2 154.0 14. 5 S i s t e l l e r i 4 62. 3 2.0 The young f i s h with e u p h a u s i i d s i n t h e i r stomach consumed about 10 times more euph a u s i i d e g g s / f i s h than f u r c i l i a and other l a r v a l stages. J u v e n i l e salmon, (Oncorhynchus s p p ^ i i t h r e e s p i n e s t i c k l e b a c k , G a s t e r o s t e u s a c u l e a t u s ; P a c i f i c h e r r i n g , Clupea p a l l a s i i ^ and the anchovy, E n g r a u l i s mordax x had the highest average consumption o f the e a r l y e uphausiid stages among the f i s h taken i n the two-boat t r a w l . P r e d a t i o n by j u v e n i l e f i s h on j u v e n i l e and a d u l t e u p h a u s i i d s , predominantly I i p a e i f i c a , was h e a v i e s t i n the 8.1-15 mm s i z e range. J u v e n i l e s t e e l h e a d t r o u t , Salmo g a i r d n e r i i , and salmon, pneorhynchus s p p i X and G._ a c c u l e a t u s were the most f r e g u e n t l y caught consumers of the j u v e n i l e and a d u l t e u p h a u s i i d s . Although few were taken i n the t r a w l c a t c h e s , young h e r r i n g and P a c i f i c hake, M e r l u c c i u s productus. appear t o be important p r e d a t o r s o f young euphausiids. Barraclough and Herlinveaux(1965 MS) r e p o r t e d the presence of l a r g e q u a n t i t i e s of j u v e n i l e d o q f i s h , Squalus s u c k l e y i , hake and h e r r i n q which appeared to be f o l l o w i n q a s o u n d s c a t t e r i n q l a y e r i n Saanich I n l e t which contained i n v e r t e b r a t e zooplankton. Stomach co n t e n t s of the j u v e n i l e and a d u l t d o q f i s h , hake, whitinq, r o c k f i s h and some h e r r i n q c o n t a i n e d s e v e r a l s p e c i e s o f zooplankton; I i p a e i f i c a was the predominant s p e c i e s eaten. Other predators of eu p h a u s i i d s i n the S t r a i t of Georgia r e g i o n i n c l u d e c a r n i v o r o u s z o o p l a n k t e r s , notably t h e ctenophore, f l e g r p b r a c h i a p i l e u s x which becomes h i g h l y abundant i n summer and f a l l and i s capable o f c a p t u r i n g many e u p h a u s i i d l a r v a e each day (W. Greve, p e r s o n a l communication) . Presumably the change from l i v i n g near the s u r f a c e as l a r v a e to migrating t o g r e a t e r depths f o r the d a y l i g h t hours as j u v e n i l e s and a d u l t s helps to reduce p r e d a t i o n by s u r f a c e - d w e l l i n g enemies and those which r e l y on v i s u a l d e t e c t i o n o f prey. The increased m o b i l i t y of the l a r g e r e u p h a u s i i d s may a l s o help i n escaping from c e r t a i n p r e d a t o r s . Working a g a i n s t improved s u r v i v a l of l a r g e r e uphausiids are t h e i r l a r g e r t a r g e t s i z e s and dense aggregations which pr e d a t o r s can d e t e c t , a c o u s t i c a l l y i n the case of baleen 68 whales (eg. Beamish and M i t c h e l l , 1971) and l i k e l y i n other ways by hake, h e r r i n g and oth e r f i s h e s . The l i f e span of E A p a e i f i c a p o p u l a t i o n s i n the S t r a i t o f Georgia r e g i o n i s longer than t h a t d e s c r i b e d f o r p o p u l a t i o n s i n more s o u t h e r l y r e g i o n s of the eastern North P a c i f i c Ocean. The l i f e - s p a n of cohort s i n the present study was between 19 and 22 months, with females l i v i n g about 2 or 3 months longer than males. In c o n t r a s t , E. p a e i f i c a from Oregon, southern C a l i f o r n i a and Puget Sound had l i f e - s p a n s of about one year or l e s s (Smiles and Pearcy,1971; Brinton,1976; Hulsizer,MS). The d i f f e r e n c e i n l i f e - s p a n between the S t r a i t o f Georgia p o p u l a t i o n s and t h e i r southern c o u n t e r p a r t s can probably be a t t r i b u t e d to the low a v a i l a b i l i t y of food, e s p e c i a l l y phytoplankton, i n the S t r a i t of Georgia during l a t e f a l l and winter and t o lower water temperatures compared to the southern r e g i o n s . Whereas growth i n le n g t h appears t o h a l t during winter i n the S t r a i t of Georgia p o p u l a t i o n , i t co n t i n u e s at a reduced r a t e d u r i n g winter o f f Oregon and southern C a l i f o r n i a , where water temperatures are more uniform and phytoplankton i s more abundant than i n the S t r a i t o f Georgia. F i g u r e 20 compares the g e n e r a l i z e d growth curves f o r E. p a e i f i c a from f o u r other r e g i o n s of the North P a c i f i c with curve D-E of the 1974 s p r i n g cohort from Saanich I n l e t presented i n F i g u r e 10. Although the average l i f e - s p a n growth f o r c o h o r t s i n the S t r a i t of Georgia r e g i o n i s only about 0.038 mm/day compared to 0.065 mm/day f o r E. p a e i f i c a o f f Oregon and southern C a l i f o r n i a (Smiles and Pearcy,1971; Brinton,1976), the maximum r a t e s f o r j u v e n i l e growth are s i m i l a r f o r these r e g i o n s ; Saanich I n l e t j u v e n i l e s averaged 0.094 mm/day between 69 NORTHWEST. PACIFIC 1 (NEMOTO) t -OREGON 4 6 8 10 MONTHS FIGURE 20. Re p r e s e n t a t i v e growth curves f o r E t fiacifica from the S t r a i t of Georgia and other r e g i o n s of the P a c i f i c . ( A f t e r B r i n t o n , 1976; Smiles and Pearcey, 1971). May and August while Oregon j u v e n i l e s i n c r e a s e d by 0.095 mm/day (Smiles and Pearcy, 1971). B r i n t o n (1976) and H u l s i z e r have a l s o reported maximum growth r a t e s o f about 0.095 mm/day i n f i e l d p o p u l a t i o n s d u r i n g the s p r i n g and summer. These f i e l d e s t i m a t e s of the maximum growth r a t e exceed Lasker* s (1966) l a b o r a t o r y estimate of maximum growth i n j u v e n i l e E^ p a c i f i c . a (C.038 mm/day). The average growth r a t e of E x p a e i f i c a i n the S t r a i t of Georgia r e g i o n appeared to be higher and the l i f e span s h o r t e r 70 than f o r E A p a c i f i c a p o p u l a t i o n s i n t h e northwestern P a c i f i c . Nemoto(1957) c o n s i d e r e d that E. p a c i f i c a o f f Japan and south of the A l e u t i a n I s l a n d s reached a l e n g t h o f 17-18 mm i n t h e i r f i r s t year as d i d the s p r i n g c o h o r t s i n the S t r a i t of Georgia and J e r v i s I n l e t . F o l l o w i n g spawning, members of Neinoto's p o p u l a t i o n s may l i v e f o r another year, a t t a i n i n g 22 mm a f t e r 2 y e a r s . E t p a c i f i c a i n the S t r a i t of Georgia region grew more r a p i d l y i n t h e i r second season than Nemoto's and g e n e r a l l y disappeared from the sampled p o p u l a t i o n before the end of two years. Ponomareva(1963) i n f e r r e d t h a t E A p a c i f i c a l i v e up to 2 years i n the Sea o f Okhotsk on the b a s i s of bimodal l e n g t h frequency d i s t r i b u t i o n s of winter and s p r i n g c o l l e c t i o n s . The winter mode at 8 mm was c o n s i d e r e d t o have hatched d u r i n g the p r e v i o u s summer while the 14-15 mm mode was thought to be s t a r t i n g i t s second year. The s p r i n g modes were a t 12-13 mm (1 year old) and 19 mm (2 year o l d ) . Growth of other e u p h a u s i i d s p e c i e s has been summarized by Smiles and Pearcy(1971). S e v e r a l e u p h a u s i i d s p e c i e s with l i f e spans of 2 or more years have been found to reach a body l e n g t h of about 22 mm i n t h e i r f i r s t year, growing o n l y slowly or not at a l l d u r i n g the winter then a t t a i n i n g t h e i r f i n a l s i z e i n the succeeding growing season. Examples from r e g i o n s of the North A t l a n t i c are Meqanyctiphanes noryegica ( E i n a r s s o n , 1945; Mauchline,1960; Matthews,1973; and Berkes,1976), Thysanoessa r a s e h i i (Mauchline,1966) and Xiisanopoda a c u t i f r o n s (Einarsson,1945). Euphausia superba , the A n t a r c t i c k r i l l , a l s o grows to about 22 mm i n i t s f i r s t year(Ruud,1932; Bargmann,1945; Marr, 1962) . 71 Few authors have attempted to d e s c r i b e the growth of euphausiids by mathematical e x p r e s s i o n s . Matthews (1973) found that f o r Meganyctiphanes no r y e g i c a the growth i n carapace l e n g t h f o r combined sexes was w e l l d e s c r i b e d by the combination of two e m p i r i c a l e x p r e s s i o n s , one a p p l y i n g t o A p r i l t o October of the f i r s t year and the second f o r November of the f i r s t year onwards. Growth d i d not cease, but was r e t a r d e d f o r about f o u r months i n winter. "Negative" mean growth was observed i n each February, p o s s i b l y i n d i c a t i n g t h a t t h e e f f e c t o f s i z e - s e l e c t i v e m o r t a l i t y exceeded growth at that time of year. Jorgensen and Matthews(1975) developed a g e n e r a l growth eguation to d e s c r i b e the growth of s i x e u p h a u s i i d s p e c i e s , i n c l u d i n g Meganyctiphanes noryegica and Thysanoessa r a s c h i i ; t h e i r eguation i s a m o d i f i c a t i o n of the a u t o c a t a l y t i c model: dL/dt = k l ( L m - L) / L m where L i s the carapace l e n g t h and L„, i s the asymptotic value of L. V a r i a b i l i t y i n the r a t e s of development, growth and s e x u a l m a t u r i t y between g e o g r a p h i c a l l y separated p o p u l a t i o n s of the same euphausiid s p e c i e s has been widely acknowledged (eg. Einarssori,1945; Nemoto, 1957; Ponomareva,1963; Mauchline and Fisher,1969; Matthews,1973). Regional d i f f e r e n c e s i n food a v a i l a b i l i t y and temperature are c o n s i d e r e d to be the p r i n c i p a l causes f o r such v a r i a b i l i t y ( M a u c h l i n e and F i s h e r , 1 9 6 9 ) . D i f f e r e n c e s i n s e a s o n a l a v a i l a b i l i t y of phytoplankton were c i t e d e a r l i e r i n comparing E A p a e i f i c a p o p u l a t i o n s i n the S t r a i t of Georgia with those o f f Oregon and southern C a l i f o r n i a . Brinton(1976} has summarized the s u r f a c e water temperatures d u r i n g E._ p a c i f i c a f s main r e p r o d u c t i v e season and during winter i n f i v e areas of the North P a c i f i c where the l i f e h i s t o r y of t h i s s p e c i e s has been i n v e s t i g a t e d . In Table 11 mean temperatures f o r 0-10 m from Saanich I n l e t ( H e r l i n v e a u x , 1 9 6 2 ) f o r the corresponding p e r i o d s have been added t o the v a l u e s guoted by B r i n t o n (Sverdrup et a l . ,1942; Anonymous,1963). TABLE 11. Surface {0-10 m) temperatures during E^. p a c i f i c a »s main r e p r o d u c t i v e p e r i o d and d u r i n g winter i n s i x r e g i o n s of the North P a c i f i c . l e g i o n Spawning time Winter Sea o f Okhotsk O f f Kamchatka South of A l e u t i a n s S t r a i t o f Georgia O f f Oregon Off southern C a l i f o r n i a 10-13C{Aug.) 0C(Feb.) 9-11C (Aug. ) 0- lC(Feb.) 10-12C(Aug.) 2-4C(Feb.) 9~13C(May) 6- 8C{Feb.) 10-14C(Sept.) 9-11C(Feb.) 10-18C(June) 12-15C(Feb.) Although E p a c i f i c a i s apparently not l i m i t e d i n d i s t r i b u t i o n by low winter temperatures, the s u i t a b l e range f o r re p r o d u c t i o n i s much narrower, about 9-16C. In the northwestern P a c i f i c , Ej. p a c i f i c a does not begin to spawn u n t i l June a f t e r the phytoplankton bloom i s almost f i n i s h e d , much l a t e r than the other common eupha u s i i d s p e c i e s of that region(Ponomareva,1963). The main r e p r o d u c t i v e a c t i v i t y i s i n August at 9-13C, the highest temperatures of the year. In Saanich I n l e t , phytoplankton abundance i s o f t e n high i n A p r i l , but the main E. p a c i f i c a spawning a c t i v i t y g e n e r a l l y begins i n e a r l y May when s u r f a c e temperatures are j u s t i n t o the range from 9-13C (compare F i g u r e 7). Besides a s u i t a b l e range of temperature, a p e r i o d of c o n d i t i o n i n g of spawning a d u l t s on phytoplankton may a l s o be necessary as suggested by Ponomareva{1963). Off Oregon and southern C a l i f o r n i a t h e r e i s l i t t l e change between winter and summer temperatures which are lowered by u p w e l l i n g of c o o l subsurface water. Spawning happens i n a l l months of the year i n those r e g i o n s although u s u a l l y i t occurs i n p e r i o d i c p u l s e s . F a r t h e r south o f f mainland Mexico high temperatures and low oxygen c o n c e n t r a t i o n s appear to l i m i t the range of E A p a c i f i c a ( B r i n t o n , 1976) . CHAPTER 3: BIOKASS AND PRODOCTION 74 3.1 Length:Weight R e l a t i o n s h i p . To convert l e n g t h - f r e g u ency data i n t o the corresponding weight or biomass d i s t r i b u t i o n s , a f u n c t i o n a l r e l a t i o n s h i p between l e n g t h and weight i s necessary. Bicker(1973) has shown that the a p p r o p r i a t e form of l i n e a r r e g r e s s i o n i s the geometric mean (GH) r e g r e s s i o n i n a l l s i t u a t i o n s where the v a r i a b i l i t y i s mainly in h e r e n t i n the m a t e r i a l ( l i t t l e v a r i a b i l i t y due t o e r r o r s of measurement) and where open-ended d i s t r i b u t i o n s are concerned ( d i s t r i b u t i o n s or o b s e r v a t i o n s are of uniform d e n s i t y and of i n d e f i n i t e e x t e n t ) . The more widely-used p r e d i c t i v e l i n e a r r e g r e s s i o n s u s u a l l y under-estimate the value of the exponent i n the l e n g t h : weight r e l a t i o n s h i p and the value of the r e g r e s s i o n c o e f f i c i e n t i n morphometric r e g r e s s i o n s (eg. carapace versus body l e n g t h ) . L e t t i n g the e g u a t i o n of the f u n c t i o n a l r e g r e s s i o n l i n e be Y = u + vX, one c a l c u l a t e s the s l o p e of the l i n e as v = ± f <k {Y - Y ) 2 / ^ ( X - X ) 2 io.* ( T e i s s i e r , 1 9 4 8 ) . T h i s l i n e minimizes the sum of the products of the v e r t i c a l and h o r i z o n t a l d i s t a n c e o f each poin t from the l i n e . A l t e r n a t i v e l y , the s l o p e , v, can be found as v = ± (sy/sx) = ± (b/r) = ± (b/d) °s where sy and sx are the standard d e v i a t i o n s of Y and X r e s p e c t i v e l y ; b i s r e g r e s s i o n c o e f f i c i e n t of the p r e d i c t i v e r e g r e s s i o n of Y on X and r i s the c o r r e l a t i o n c o e f f i c i e n t between X and Y while d i s t h e r e g r e s s i o n c o e f f i c i e n t of the p r e d i c t i v e r e g r e s s i o n o f X on Y (Bicker,1973). Thus v i s the geometric mean of the p r e d i c t i v e r e g r e s s i o n of Y on X and the r e c i p r o c a l of the p r e d i c t i v e r e g r e s s i o n of X on Y. The s i g n of v i s the same as t h a t o f b,d and r . R i c k e r ( l 9 7 3 ) and c o l l e a g u e s recommend the f o l l o w i n g symmetrical c o n f i d e n c e l i m i t s f o r the GM r e g r e s s i o n : v ± t f v* {1-r«)/(N-2) ] 0-5 where N i s the sample s i z e and t i s the Student m u l t i p l i e r f o r the given c o n f i d e n c e l e v e l with N-2 degrees of freedom. , The computed le n g t h : weight r e g r e s s i o n s of the form; InW = l n a • B (InL), were based on length-weight measurements on specimens between 10 and 21 mm body l e n g t h , c o l l e c t e d i n March and A p r i l , 1975. For male p a e i f i c a , t h e GM r e g r e s s i o n was: InW = -4. 86 «-2.98(lnL) ; N = 376. The male L ; W exponent, v and i t s 95% c o n f i d e n c e l i m i t s were c a l c u l a t e d as 2.98 ± 0.059. In comparison, the p r e d i c t i v e r e g r e s s i o n of W on L was: InW = -4.71 • 2 . 9 0 ( l n L ) ; r = 0. 973. For the female E. p a e i f i c a , the GM r e g r e s s i o n was: InW = -5.01 + 3.03 (InL); H = 443. The comparable p r e d i c t i v e r e g r e s s i o n was: InW = -4.70 + 2.92 (InL) ; r - 0.961. Thus, the female L : W exponent, v, and i t s 95% c o n f i d e n c e l i m i t s were found t o be 3.03 ± 0.066. As there i s c o n s i d e r a b l e o v e r l a p of the male and female confidence l i m i t s t here does not appear to be a s i g n i f i c a n t d i f f e r e n c e between L : W exponents f o r the two sexes; both exponents are very c l o s e to 3.0. 76 3.2 Carapace:Body Length R e l a t i o n s h i p Another s i t u a t i o n i n work on euphausiids and other crustaceans where a f u n c t i o n a l r e g r e s s i o n i s best used i s the r e l a t i o n between carapace l e n g t h and body l e n g t h (eg. Smiles and Pearcy,1971; Matthews,1973). At times i t may be necessary or more convenient to measure carapace l e n g t h r a t h e r than t o t a l l e n g t h (eg. when the t e l s o n or rostrum i s damaged or when a specimen i s bent and cannot be s t r a i g h t e n e d properly) . In order to p r e d i c t the corresponding body le n q t h f o r a given carapace l e n g t h , the o r d i n a r y p r e d i c t i v e r e g r e s s i o n has been commonly used; in these s i t u a t i o n s the r e g r e s s i o n c o e f f i c i e n t tends t o in c r e a s e as the range o f a v a i l a b l e l e n g t h s i n c r e a s e s ( P i c k e r , 1 9 7 3 ) . For such r o u t i n e length c o n v e r s i o n s the GM r e g r e s s i o n has no sy s t e m a t i c b i a s r e l a t e d to the range of lengths i n c l u d e d i n the sample; i t i s t h e r e f o r e recommended f o r c o n v e r t i n g from one l e n g t h measurement to another(Ricker,1973). Carapace : t o t a l l ength comparisons were made on f o r m a l i n preserved male and female p a c i f i c a a d u l t s from Saanich I n l e t and the S t r a i t of Georgia, c o l l e c t e d i n J u l y 1975 and February 1976, F u r t h e r comparisons were made on f u r c i l i a l a r v a e (F1 to F5) from Saanich I n l e t i n May 1975. The r e s u l t s of the GM and p r e d i c t i v e (AM) r e g r e s s i o n a n a l y s i s are presented i n Table 12. 77 TABLE 12. Summary of r e s u l t s f o r r e g r e s s i o n of body l e n g t h on carapace l e n g t h s f o r Ej_ p a c i f i c a from Saanich I n l e t and the S t r a i t of Georgia. Stage Sample Type of I n t e r c e p t Regression 95% C.L. Size Regression C o e f f i c i e n t or r F u r c i l i a 28 GM -0.72 4.18 4.18 ± 0.39 AM -0.54 4.01 r = 0.96 Male 45 GM 0.59 3.38 3. 38 ± 0.19 AM 0.93 3.30 r = 0.975 Female 170 GM 0.88 3.35 3. 35 ± .083 AM 1. 11 3.29 r = 0.981 There i s a notable change i n body p r o p o r t i o n s between the f u r c i l i a p e r i o d and the a d u l t c o n d i t i o n . As a d u l t s , the two sexes do not d i f f e r s i g n i f i c a n t l y with r e s p e c t t o the carapace : t o t a l l e n g t h r e l a t i o n ; there i s a wide o v e r l a p i n the 95% c o n f i d e n c e l i m i t s f o r the r e g r e s s i o n c o e f f i c i e n t s . 3.3 Annual and Monthly Ej. p a c i f i c a Biomass D i s t r i b u t i o n s The mean annual biomass per mm of body le n g t h shows f a i r l y c o n s i s t e n t d i s t r i b u t i o n s during 1975 i n the t h r e e study areas ( F i g u r e 21), L o c a l maxima i n the d i s t r i b u t i o n s g e n e r a l l y occur at 11 mm, 16-17 mm and 19-20 mm body le n g t h . These peaks correspond t o the begin n i n g of the a d u l t phase, the e a r l y part of the main r e p r o d u c t i v e phase and the f u l l y mature r e p r o d u c t i v e phase, r e s p e c t i v e l y . In these p e r i o d s , growth i n body l e n g t h slows probably because energy reguirements f o r r e p r o d u c t i v e processes are higher then. In the S t r a i t of Georgia, the 19-20 mode c o n t r i b u t e s more to t o t a l biomass than do the 16-17 mm s i z e s ; the l a t t e r s i z e s are the major c o n t r i b u t o r s i n J e r v i s I n l e t and Saanich I n l e t . FIGURE 21. T o t a l mean biomass and mean biomass by 1 mm s i z e c l a s s e s of E^ p a e i f i c a p o p u l a t i o n s i n the S t r a i t o f Georgia r e g i o n d u r i n g 1975. The value of mean biomass f o r a l l s i z e c l a s s e s was more than twice as hig h i n J e r v i s I n l e t than i n the S t r a i t of Georgia on the b a s i s of M i l l e r net (MNT) estimates. The Saanich I n l e t value i s lower as the SCOR estimates are from a 150 m water column. For the prominent 11,16 and 19 ram s i z e c l a s s e s , the monthly values o f biomass are p l o t t e d i n Figure 22 A and B. For the combined MNT biomass estimates from the S t r a i t of Georgia and J e r v i s I n l e t , the changes f o r a l l t h r e e s i z e c l a s s e s a r e u s u a l l y i n phase. There i s a general d e c l i n e i n biomass of these s i z e s 79 E O O o \ o> Oiool UJ 1 !< o A. MNT BIOMASS JERVIS INLET STRAIT of GEORGIA O I9mm -I 1 1 I l _ _1 ' ' B. SCOR BIOMASS SAANICH INLET 0-—O I6r -I I l _ I F M A M I I A S O N O 197S FIGURE 22. Monthly biomass l e v e l s of conspicuous s i z e c l a s s e s o f E. p a e i f i c a during 1975. during A p r i l t o J u l y as the overwintered a d u l t s dwindle i n numbers or grow out o f . these c l a s s e s . From about J u l y to October, r e c r u i t m e n t i n t o these major s i z e c l a s s e s expands, l e a d i n g t o r a p i d r i s e s i n t h e i r biomass. A f t e r October, biomass 80 at these body l e n g t h s a g a i n d e c l i n e s . The above p a t t e r n appears to be i n response to the r a p i d growth of a d u l t s and s t r o n g r e c r u i t m e n t of j u v e n i l e s throughout t h e summer i n the S t r a i t of Georgia and J e r v i s I n l e t . The trends i n the biomass of the t h r e e prominent s i z e c l a s s e s i n Saanich I n l e t were more complex as changes were o f t e n out of phase. A f t e r d e c l i n i n g s h a r p l y i n January to March, the 19 mm s i z e c l a s s s t e a d i l y i n c r e a s e d i n biomass d u r i n g A p r i l t o October. The 16 mm c l a s s tended t o drop i n biomass from January to J u l y , then rose r a p i d l y t o a high i n October as the new s p r i n g c o h o r t was s t r o n g l y r e c r u i t e d from August t o October. On the other hand, the 11 mm c l a s s d i s p l a y e d c y c l e s of r e c r u i t m e n t and d e c l i n e at s h o r t e r i n t e r v a l s ; recruitment from the s p r i n g c o h o r t rose s h a r p l y from May to J u l y , then dropped as the young a d u l t s advanced i n t o l a r g e r s i z e c l a s s e s d u r i n g August. In the autumn, recr u i t m e n t from the f a l l c ohort again swelled the biomass of the 11 mm s i z e c l a s s . Monthly changes i n the t o t a l p a c i f i c a biomass i n the t h r e e areas show s i m i l a r i t i e s to the trends i n the 16 and 19 mm s i z e c l a s s e s (Figure 23). Changes i n the biomass of two important c o h o r t s i n the Saanich I n l e t p o p u l a t i o n are a l s o given. E v i d e n t l y , the p e r i o d of s i g n i f i c a n t i n c r e a s e i n biomass of the I i . p a c i f i c a p o p u l a t i o n s of the S t r a i t of Georgia r e g i o n i s from about June to November. Conseguently, t h i s p e r i o d was chosen f o r e s t i m a t i o n of production by each o f the E. p a c i f i c a p o p u l a t i o n s as w e l l as the p r o d u c t i o n of the major c o h o r t s i n the Saanich I n l e t p o p u l a t i o n . 81 1 0 0 0 100] SOf-5 ° 10i JERVIS TOTAL ^.STRAIT OF . . • •••-.GEORGIA TOTAL J.-SPRING 74 .SAANICH - l — - — i 1 1 1 ' • • M M 1 J 1975 J L FIGUBE 23. Monthly changes i n biomass f o r a l l s i z e c l a s s e s (7-23 mm) i n E. p a c i f i c a p o p u l a t i o n s and i n Saanich I n l e t c o h o r t s during 1975. 3.4 Production of E,. p a c i f i c a P roduction i s d e f i n e d here as the t o t a l amount of biomass e l a b o r a t e d i n a group of organisms i n a given p e r i o d of time, i n c l u d i n g t h a t due to organisms which died during the p e r i o d (cf. Ivlev,1945; Chapman, 1968) . The method of c a l c u l a t i o n which was used (LeBlond and Parsons,1977) assumes e x p o n e n t i a l r a t e s of m o r t a l i t y and of growth i n biomass. The a p p r o p r i a t e e x p r e s s i o n f o r production i n a g i v e n p e r i o d i s : P = (1 + Z/G)AB where Z i s the in s t a n t a n e o u s m o r t a l i t y r a t e and G i s the 82 observed r a t e o f i n c r e a s e i n biomass,B, between times t and t , such t h a t B(t) = B ( t 0 ) exp (G f t - t 0 ] ). For each p o p u l a t i o n or cohort d u r i n g the p e r i o d s i n d i c a t e d , the r a t e of i n c r e a s e i n biomass, G, was determined by p l o t t i n g l n [ B ( t ) / B ( t ) 3 a g a i n s t t i m e , t , f o r each observed biomass i n the p e r i o d . The sl o p e of the r e s u l t i n g l i n e i s the r a t e o f i n c r e a s e i n biomass,G. Corresponding values of the m o r t a l i t y r a t e , 2, were c a l c u l a t e d as d e s c r i b e d e a r l i e r . The change i n biomass, B, was computed as the d i f f e r e n c e between the f i n a l and i n i t i a l biomass o b s e r v a t i o n s i n the p e r i o d . Values of these parameters and the r e s u l t i n g production e s t i m a t e s are presented i n Table 13.,For the Saanich I n l e t cohorts and t o t a l p o p u l a t i o n , p r o d u c t i o n estimates from SCOB v e r t i c a l h a u l s were a l s o expressed i n u n i t s of carbon produced under a sguare meter of water per day (mgC/mz/day) f o r comparison with other p u b l i s h e d values. The f a c t o r of 0.05 was used t o convert grams wet weight t o grams body carbon (cf. Mullin,1969; C r i s p , 1 9 7 5 ) . As the S t r a i t of Georgia and J e r v i s I n l e t biomass es t i m a t e s were from h o r i z o n t a l h a u l s over a l i m i t e d v e r t i c a l range, i t was not p r a c t i c a l t o convert from u n i t s of volume to u n i t s of s u r f a c e area. 83 TABLE 13. Pr o d u c t i o n e s t i m a t e s and a s s o c i a t e d parameters f o r I i p a e i f i c a p o p u l a t i o n s and c o h o r t s d u r i n g 1975., P o p u l a t i o n or Cohort P e r i o d lday_sjL /mo G /mo B P P g/103 m3 q/10 3 m3/da mgC/m*/da S t r a i t of Georgia Jun-N (143) . 576 .268 24 2.3 5.34 J e r v i s I n l e t Jun-N (143) . 693 .541 1364. 21.8 Saanich I . T o t a l J u l - N (105) . 564 .442 175.6 3.81 26.8 Sp 75 Cohort J u l - N (105) .586 .477 162.8 3.45 24.4 Sp 74 Cohort J u l - 0 (77) .559 .334 24.6 0.85 6.0 Production per 1000 in 3 was higher i n J e r v i s I n l e t which had a higher s t a n d i n g stock than the S t r a i t of Georgia. For such comparisons, , production per u n i t average biomass, P/B, i s more u s e f u l than the production e s t i m a t e s alone. Table 14 presents a summary of production : biomass r a t i o s and mean l i f e expectancy i n t h i s p e r i o d (1/Z) , assuming e x p o n e n t i a l m o r t a l i t y and von B e r t a l a n f f y growth models ( c f . ,Alien,1971) , f o r the E.. p a e i f i c a p o p u l a t i o n s and cohorts analysed above. There i s s i m i l a r i t y i n the v a l u e s of P/B f o r the va r i o u s p o p u l a t i o n s and c o h o r t s , d e s p i t e the d i f f e r e n c e s i n average biomass. During t h i s p r o d u c t i o n p e r i o d , E.. p a e i f i c a apparently has a s l i g h t l y l o n g e r l i f e expectancy i n Saanich I n l e t and the S t r a i t o f Georgia than i n J e r v i s I n l e t . 84 TABLE 14. Production : biomass r a t i o s and mean l i f e expectancy f o r E. p a c i f i c a p o p u l a t i o n s and Saanich I n l e t c o h o r t s d u r i n g 19757" P o p u l a t i o n L i f e P B P/B P/B or Cohort Expectancy a/103 m3/da q/10 3 m3 da - * y r ~ S t r a i t of 1.7 mo 5.34 228 .023 8.4 Georgia J e r v i s 1.4 21.8 837 . 026 9.5 I n l e t Saanich I, 1.8 3.81 157 . 024 8.8 T o t a l Sp 75 1.7 3.45 123 .028 10.3 Sp 74 1.8 0.85 35 .025 9,0 3.5 S p a t i a l D i s t r i b u t i o n s of Biomass of Megazooplankton and Phytoplankton i n the S t r a i t of Georgia Region Biomass c h a r t s o f the 5 mm s i z e f r a c t i o n from M i l l e r net samples taken d u r i n g the zooplankton survey c r u i s e s i n 1975 are presented as Figures 24 to 27. Although megazooplankton are g e n e r a l l y considered to i n c l u d e zooplankton over 2 mm (Parsons and Takahashi, 1973), the > 5 mm f r a c t i o n here r e p r e s e n t s the n e t t a b l e megazooplankton f o r commercial plankton nets c u r r e n t l y used i n B. C. The d i s t r i b u t i o n i n the M a r c h - A p r i l p e r i o d (Figure 24) shows areas o f high biomass (over 2 g/m3) i n the S t r a i t of Georgia o f f Nanaimo, o f f the northwest end of Texada I s l a n d and i n J e r v i s I n l e t . As o n l y daytime sampling was done o f f the mouth of the Fraser R i v e r , the n i g h t t i m e d i s t r i b u t i o n of megazooplankton there i s u n c e r t a i n f o r the e a r l y s p r i n g . During J u n e - J u l y , l e v e l s of the l a r g e zooplankton were g e n e r a l l y lower, e s p e c i a l l y i n J e r v i s I n l e t and in the northern s e c t i o n of the S t r a i t of Georgia (Figure 25) . Areas of moderate 85 FIGURE 24. D i s t r i b u t i o n o f wet biomass {g/m3| of megazooplankton ( > 5 mm) i n the 107 kHz sound s c a t t e r i n g l a y e r during H a r c h - A p r i l 1975. FIGURE 25. D i s t r i b u t i o n o f wet biomass (q/m3) of meqazooplankton { > 5 mm) i n the 107 kHz sound s c a t t e r i n q l a y e r d u r i n q June-July 1975. 87 biomass (1-2 g/m3) and pockets o f higher c o n c e n t r a t i o n s (2-4 g/m3) were observed i n the southern h a l f of the S t r a i t of Georgia and i n Saanich I n l e t ( J u l y ) . The d i s t r i b u t i o n of biomass i n Saanich I n l e t w i l l be c o n s i d e r e d i n more d e t a i l l a t e r . For the August- September p e r i o d , the survey c r u i s e s were spaced by o n l y two weeks so s t a t i o n coverage i n v o l v e d l i t t l e o v e r l a p . Biomass was higher than f o r the p r e v i o u s p e r i o d i n the northern s e c t i o n of the S t r a i t of Georgia and i n J e r v i s I n l e t (Figure 26). The area of the S t r a i t o f Georgia south of Nanaimo was only r e p r e s e n t e d by daytime sampling. High biomass l e v e l s were observed i n Saanich I n l e t but much lower c o n c e n t r a t i o n s of l a r g e z o o p l a n k t e r s were found i n the Haro S t r a i t and Swanson Channel approaches to Saanich I n l e t . Over 80% of the megazooplankton biomass i n the l a t t e r areas was c o n t r i b u t e d by the mysid, Pseudomma truncatum, r a t h e r than e u p h a u s i i d s . In the October-November survey p e r i o d , biomass d e n s i t i e s of over 2 g/m3 were widespread i n J e r v i s I n l e t and o f f the mouth of the F r a s e r River i n the S t r a i t o f Georgia ( F i g u r e 27). A l a r g e area of the S t r a i t of Georgia from Malaspina S t r a i t to Nanaimo had c o n c e n t r a t i o n s of 1-2 g/m3, according to estimates from net sampling and from continuous echosounding r e c o r d s . Table 15 presents an example of echosounding o b s e r v a t i o n s and corresponding biomass estimates which were taken on each survey c r u i s e . 88 FIGURE 26. D i s t r i b u t i o n o f wet biomass (g/m3) of megazooplankton {> 5 mm) i n the 107 kHz sound s c a t t e r i n g l a y e r d u r i n q August-September 1975. 89 E IGUBE 2 7 . D i s t r i b u t i o n o f wet b i o m a s s (g/m 3) o f m e g a z o o p l a n k t o n (> 5 mm) i n the 107 kHz s o u n d s c a t t e r i n g l a y e r d u r i n g O c t o b e r - N o v e m b e r 1975 . 90 TABLE 15. Summary of o b s e r v a t i o n s on the 107 kHz sound s c a t t e r i n g l a y e r and corres p o n d i n g MNT estimates of megazooplankton biomass f o r the October 1975 c r u i s e (75/31). Time S t a t i o n Biomass Layer Remarks on l a y e r d e n s i t y PDST depthiml Oct. 6 1857 Je-4 13. 40 0-40 Very heavy l a y e r ; d i f f u s e from 40-70 m., 1925 Je-3.5 2.28 0-40 Heavy l a y e r with darker patches w i t h i n . 2000 Je-3 0. 60 0-30 Moderate l a y e r . 2127 Je-2 2.4 2 0-30 Heavy l a y e r . 2158 Je-1.5 5.06 0-40 Very heavy, e s p e c i a l l y i n the top 10 m. 2230 Je-1 4.90 0-40 As above. „ 2335 3508 1.37 0-40 Heavy with darker Oct. 7 patches w i t h i n . 0104 2500 1.00 0-30 Moderately heavy. 0200 2254 1.23 0-30 Heavy i n l a y e r , d i f f u s e from 30-60 m., 0335 1748 1.05 0-35 Moderately heavy with darker patches w i t h i n . 0515 1230 1.39 0-30 Heavy between s t a t i o n s , esp. top 10m; d i f f u s e 30-60m 0610 1036 - 0-20 Moderate, d i f f u s e t o 50m. 0740 09 35 0.20 0-20 Light-moderate 1822 Saa-4.7 - 30-110 pre-dusk; heavy l a y e r forming. 1900 Sat4424 0. 03 0-50 L i g h t ; s c a t t e r e d patches 1950 Swa4417 0.04 0-40 L i g h t ; s c a t t e r i d patches 2215 5723 2. 15 0-30 Heavy, esp. Upper 10m. 2230 5926 1.31 0-30 Heavy, esp, upper 15m. 2305 0326 0.56 0-30 Moderate; d i f f u s e 30-80m 2345 0331 - 0-30 Heavy; esp. Near s u r f a c e 0025 0430 1.04 0-35 Moderately heavy, esp. near s u r f a c e . 0120 0635 0.07 0-30 L i g h t ; d i f f u s e to 70m. The composition and d e n s i t y of the megazooplankton i n the approaches t o Saanich I n l e t again d i f f e r e d d u r i n g October-November from t h a t i n the i n l e t proper. I n t e n s i v e sampling o f the euphausiid sound s c a t t e r i n g l a y e r was performed i n Saanich I n l e t i n J u l y and August 1975 ( F i g u r e s 28 and 29). The M i l l e r net h a u l s and IKMT tows are i n d i c a t e d by 91 FIGURE 28. D i s t r i b u t i o n o f megazooplankton wet biomass (q/m3) i n the 107 kHz sound s c a t t e r i n q l a y e r i n Saanich I n l e t , J u l y 1975. s o l i d arrows and dashed arrows, r e s p e c t i v e l y . In J u l y , high d e n s i t i e s , aided by s t r o n g r e c r u i t m e n t of the s p r i n g 1975 co h o r t °f Si. £§.£ifi£a » were observed, e s p e c i a l l y o f f Bamberton and i n Sg u a l l y Reach (Figure 28). Co n c e n t r a t i o n s were l i g h t e r (1-2 g/m3) toward the mouth of the i n l e t . In August, the p a t t e r n o f biomass was a l t e r e d from the previous s u r v e y ( F i g u r e 29)..A pocket of high c o n c e n t r a t i o n (4-8 g/m3) was found near the s i l l o f the i n l e t while lower d e n s i t i e s (1-2 g/m3) extended almost as f a r as Bamberton. F a r t h e r up i n l e t the biomass d e n s i t i e s i n c r e a s e d t o 2-4 g/m3., The s p r i n g 1975 cohort of E. p a e i f i c a was t h e major component of the sound s c a t t e r i n g l a y e r cf zooplankton ( c f . F i g u r e 30). The percentage of the t o t a l megazooplankton biomass c o n t r i b u t e d by E A p a e i f i c a tended to i n c r e a s e d u r i n g the summer and f a l l , r e a c h i n g 90% i n HNT samples from November i n Saanich I n l e t and J e r v i s I n l e t ( F i g u r e 30) . , In c o n j u n c t i o n with the zooplankton sampling, c h l o r o p h y l l - a determinations were made a t survey s t a t i o n s d u r i n g June t o November. Charts of c h l o r o p h y l l - a d i s t r i b u t i o n a re presented as F i g u r e s 31 to 33 to i n d i c a t e the gen e r a l a v a i l a b i l i t y of phytoplankton f o r g r a z i n g by zooplankton such as JL. p a e i f i c a l a r v a e and a d u l t s . During June-July, t h e r e were high s t a n d i n g crops of phytoplankton (4-8 mg Chl-a/m 3 and over) i n J e r v i s I n l e t and on the outer p a r t s of the F r a s e r R i v e r plume (Figure 31). The gr a d i e n t of c h l o r o p h y l l - a i n the plume region i s n o t i c a b l e as a 93 / 2 3 ° 3 o ' W U G C N D . - _ oo» coNtom - I C O " CONTOW • SlAHON • MOOHDUnr 1MXON FIGURE 29, D i s t r i b u t i o n cf megazooplankton wet biomass (g/m3) i n the 107 kHz sound scattering layer i n Saanich I n l e t , August 1975. 94 FIGURE 30. Change i n mean percentage o f t o t a l megazooplankton biomass c o n t r i b u t e d by E. p a e i f i c a d u r i n g 1975 c r u i s e s . s e r i e s o f l e n s e s focussed on the mouth of the main channel o f the r i v e r . In Saanich I n l e t g e n e r a l l y high c h l o r o p h y l l - a l e v e l s {4-8 mg/m3) were a l s o observed. In the n o r t h e r n h a l f of the S t r a i t o f Georg i a , phytoplankton biomass tended t o be lower {2-4 mg/m3 and l e s s ) . During August-September phytoplankton standing c r o p s were lower than i n the pre v i o u s p e r i o d i n a l l areas except i n the F r a s e r R i v e r plume, and west of Texada I s l a n d i n September. In the l a t t e r a rea, c h l o r o p h y l l - a c o n c e n t r a t i o n s r o s e t o 4-8 mg/m3 or higher (Figure 32) . FIGURE 31. D i s t r i b u t i o n o f c h l o r o p h y l l - a (ag/m3) i n the upper 10 m i n the S t r a i t of Georgia r e g i o n , J u n e - J u l y 1975. 97 By October-Hoveinber (Figure 33) phytoplankton biomass was d e c l i n i n g i n the r e g i o n o f t h e F r a s e r B i v e r plume, but was higher i n Saanich I n l e t (2-4 mg/m3) and i n the c e n t r a l p a r t of the S t r a i t of Georgia (4-8 mg Chl-a/m 3) . 3.6 D i s c u s s i o n Previous p u b l i s h e d r e s u l t s on l e n g t h : weight r e l a t i o n s h i p s f o r e u p h a u s i i d s have been reviewed by Mauchline and F i s h e r ( 1 9 6 9 ) ; a s i n g l e r e g r e s s i o n l i n e was f i t t e d t o combined data f o r s e v e r a l e u p h a u s i i d s p e c i e s , i n c l u d i n g E. p a e i f i c a . The r e g r e s s i o n e g u a t i o n and the c o e f f i c i e n t of r e g r e s s i o n were not s t a t e d . I n s p e c t i o n o f the p l o t t e d data i n d i c a t e d that the r e s u l t s from the S t r a i t of Georgia r e g i o n were w i t h i n the range of values shown f o r c o r r e s p o n d i n g body l e n g t h s . F u l t o n (1968 MS) presented a l e n g t h :wet weight r e l a t i o n s h i p of e u p h a u s i i d s from Saanich I n l e t c o l l e c t e d d u r i n g June-July 1966. The measure of body le n g t h used by F u l t o n was the l e n g t h from the eye s t a l k t o the t i p of the t e l s o n , which d i f f e r s from the measure of body l e n g t h used i n the present study by the l e n g t h of the r o s t r a l p l a t e , about 0.5 mm i n mature E. p a e i f i c a , but somewhat more i n s p e c i e s such as Thysanoessa r a s c h i i which has a l o n g e r rostrum than E_. p a e i f i c a . . The need f o r f u r t h e r i n v e s t i g a t i o n of l e n g t h : weight r e l a t i o n s h i p s i n e u p h a u s i i d s i s i n d i c a t e d by evidence of v a r i a t i o n a c c o r d i n g t o stage of development and with season, F u l t o n ' s (1968) r e s u l t s suggested t h a t the r e l a t i o n s h i p may be d i f f e r e n t f o r specimens below about 10 mm i n length than f o r 98 FIGURE 33. D i s t r i b u t i o n o f c h l o r o p h y l l - a (mq/m 3) i n t h e u p p e r 10 m, O c t o b e r - N o v e m b e r 1975 . 99 i n d i v i d u a l s o v e r t h a t s i z e . I n a d d i t i o n , M a u c h l i n e a n d F i s h e r ( 1 9 6 9 ) h a v e p o i n t e d o u t t h a t d e t a i l e d k n o w l e d q e o f t h e s t a t e s o f s e x u a l m a t u r i t y o f i n d i v i d u a l s m u s t b e k n o w n i n o r d e r t o c o m p a r e t h e l e n q t h : w e i q h t r e l a t i o n s h i p s o f e u p h a u s i i d s i n d i f f e r e n t s e a a r e a s a n d a t d i f f e r e n t s e a s o n s ; s u c h s t u d i e s h a v e n o t y e t b e e n p e r f o r m e d . A s t h e L:W e x p o n e n t f o r b o t h s e x e s o f Et p a c i f i c a i n t h e S t r a i t o f G e o r q i a r e q i o n w a s c l o s e t o 3.0 a n d q r o w t h i n b o d y l e n q t h was w e l l d e s c r i b e d b y t h e v o n B e r t a l a n f f y e q u a t i o n , t h e B e v e r t o n a n d H o l t ( 1 9 5 7 ) y i e l d m o d e l may be a p p l i e d t o e x p l o i t e d p o p u l a t i o n s o f Ej_ p a c i f i c a w i t h o u t v i o l a t i n g t h e s e b a s i c a s s u m p t i o n s o f t h e m o d e l . A p p l i c a t i o n s o f t h e m o d e l a r e c o n s i d e r e d i n C h a p t e r 6. T h e r e g r e s s i o n s o f b o d y l e n g t h o n c a r a p a c e l e n g t h f o r f u r c i l i a a n d a d u l t s i n d i c a t e t h a t t h e r a t e o f i n c r e a s e i n b o d y l e n g t h c h a n g e s w i t h r e s p e c t t o c a r a p a c e l e n g t h b e t w e e n t h e f u r c i l i a p e r i o d ( u p t o a b o u t 6.5 mm) a n d a d u l t h o o d . A p p l i c a t i o n o f t h e a d u l t r e g r e s s i o n e q u a t i o n s t o l a r v a e o f l e s s t h a n 5mm l e a d s t o s i g n i f i c a n t o v e r e s t i m a t i o n o f b o d y l e n q t h f r o m c a r a p a c e l e n g t h m e a s u r e m e n t s f o r JEj_ p a c i f i c a . I f t h e i n c r e a s e i n c a r a p a c e l e n g t h i s t o b e u s e d t o i n d i c a t e g r o w t h i n b o d y l e n g t h t h r o u g h o u t t h e f u r c i l i a a n d a d u l t p h a s e s t h e n s e p a r a t e r e g r e s s i o n e q u a t i o n s a r e a d v i s e d f o r e a c h p h a s e . W i t h i n t h e a d u l t p h a s e f o r E._ p a c i f i c a r e q r e s s i o n s f o r m a l e a n d f e m a l e s e x e s q i v e s i m i l a r r e s u l t s , e s p e c i a l l y when m e a s u r e m e n t s a r e q r o u p e d i n 1 mm i n c r e m e n t s o f b o d y l e n q t h . S m i l e s a n d P e a r c e y ( 1 9 7 1 ) r e p o r t e d a p r e d i c t i v e (AM) 100 r e g r e s s i o n equation f o r c o n v e r s i o n from carapace l e n q t h to t o t a l l e n q t h (from the p o s t e r i o r o f the eye to the t i p o f the t e l s o n ) f o r Ji. p a e i f i c a o f f Oreqon. The equation f o r grouped sexes was Y = 2.54X + 0.66 where Y=total lenqth and X=carapace le n q t h . The ranqe of s i z e s i n c l u d e d i n the r e g r e s s i o n c a l c u l a t i o n was not s t a t e d ; nor was the r e q r e s s i o n c o e f f i c i e n t . Carapace l e n q t h has o f t e n been used as an index of qrowth f o r s t u d i e s on l a r g e r e u p h a u s i i d s p e c i e s such as Megan yetiphanes norvegica and other s p e c i e s i n the North A t l a n t i c (eq. Mauchline, 1960; Matthews, 1973; Jorqensen and Matthews, 1975). Mauchline (1960) found t h a t the r a t i o of t o t a l l e n q t h t o carapace le n q t h i n Meganyctiphanes noryegica v a r i e d from 4.0 3 t o 4,8 7 i n immature males and from 3.87 to 4.58 i n immature females. In s e x u a l l y mature animals with r i p e qonads, the ranqe of these r a t i o s was 4.12 to 4.91 i n males and 3.86 to 4.33 i n females. Por c o n v e r t i n q carapace measurements t o t o t a l l e n g t h , Mauchline(1960) used mean f a c t o r s ; carapace l e n g t h s of immature males were m u l t i p l i e d by 4.33, of mature males by 4.27. For females, the c o n v e r s i o n f a c t o r s were 4.27 f o r immatures and 4.05 f o r mature specimens. For the same s p e c i e s from Norwegian waters, Matthews (1973) c a l c u l a t e d a r e g r e s s i o n l i n e f o r combined sexes and a wide range o f s i z e s as f o l l o w s : T o t a l l e n g t h = 3.18 (carapace length) + 2.41. From the v a r i a t i o n i n the form of the r e p o r t e d r e l a t i o n s h i p s of carapace l e n g t h to t o t a l body length w i t h i n s p e c i e s and between study areas, i t i s apparent t h a t f u r t h e r 101 a t t e n t i o n should be pa i d to s t a n d a r d i z a t i o n o f methods of l e n q t h measurement and s t a t i s t i c a l treatment o f the r e s u l t s f o r g r e a t e r ease of comparison. The annual d i s t r i b u t i o n of biomass by s i z e c l a s s f o r E. p a c i f i c a r e v e a l e d t h r e e prominent groups, at 11mm, 16-17mm and at 19-20mm, d u r i n g 1975 i n the S t r a i t of Georgia r e g i o n . These s i z e s corresponded t o the onset of sexual maturation, the e a r l y p e r i o d o f r e p r o d u c t i o n , and the f i n a l p e r i o d of peak r e p r o d u c t i o n , r e s p e c t i v e l y . These s i z e s were g e n e r a l l y reached toward the end of the growing season, a c c o r d i n g t o the time of o r i g i n of the c o h o r t , and were maintained u n t i l the s p r i n g bloom. By that time the winter breeding p e r i o d was over and growth had resumed. Brinton(1976) found that E. p a c i f i c a o f f southern C a l i f o r n i a had c o n s i s t e n t peaks i n the annual s i z e d i s t r i b u t i o n of biomass a t 3-4mra, 7mm, 10-12mm and a t 15mm during 1953 to 1956. In two of these y e a r s , 1954 and 1956, biomass peaks a l s o developed at 17 and 18mm, r e s p e c t i v e l y . Brinton(1976) considered that the peak at 3-4mm was due to the c o n s i s t e n t abundance o f l a r v a e i n the e a r l y f u r c i l i a phase ( l i k e l y F3; c f Boden, 1950). The 7mm peak corresponded with the t r a n s i t i o n from l a r v a l to j u v e n i l e phase while the peaks at l a r g e r s i z e s l i k e l y corresponded with the r e p r o d u c t i v e p e r i o d s r e f e r r e d t o i n r e l a t i o n t o the S t r a i t of Georgia p o p u l a t i o n s . The biomass peaks at s i z e s below 11mm were not observed i n the S t r a i t o f Georgia p o p u l a t i o n s as these stages were only present f o r a s h o r t p e r i o d of the year r a t h e r than at a l l times of the year as i n southern 102 C a l i f o r n i a waters. T o t a l biomass of B. p a e i f i c a p o p u l a t i o n s i n the S t r a i t of Georgia r e g i o n g e n e r a l l y peaked i n October to November, at the end of the growing season; the s p r i n g c o h o r t s had by t h i s p e r i o d reached s i z e s of 13-17mm. The r a p i d r i s e i n biomass from June t o November appeared t o be the r e s u l t of r a p i d growth r a t e s and improving s u r v i v a l i n t h i s i n t e r v a l . A f t e r October, the d e c l i n e i n growth r a t e s and i n c r e a s e d m o r t a l i t y of second-year a d u l t s l e d t o a drop i n t o t a l biomass i n J e r v i s I n l e t . Such a p a t t e r n would a l s o be expected f o r the Saanich I n l e t and the S t r a i t of Georgia p o p u l a t i o n s i f they had been monitored i n December. The second-year Saanich I n l e t c o h o r t had d e c l i n e d s i g n i f i c a n t l y between October and November c r u i s e s ( F i g u r e 23). Off southern C a l i f o r n i a , where the l a t e summer and f a l l c o h o r t s of E A p a e i f i c a are t h e most s u c c e s s f u l ones, major peaks i n t o t a l E.. p a e i f i c a biomass were noted i n t h e f a l l and w i n t e r ( B r i n t o n , 1976); the c o h o r t s of a d o l e s c e n t s then had body l e n g t h s of 8-12mm. T h i s r e g u l a r b u i l d - u p of biomass at the j u v e n i l e - a d u l t t r a n s i t i o n may r e p r e s e n t a s t a g i n g p e r i o d to promote s i z e u n i f o r m i t y i n the p o p u l a t i o n and hence higher breeding e f f i c i e n c y i n the e a r l y s p r i n g (Br i n t o n , 1976). In the S t r a i t of Georgia r e g i o n , the seasonal d e c l i n e s i n phytoplankton abundance and water temperatures, through t h e i r impacts on growth r a t e s , l e a d to g r e a t e r s i z e u n i f o r m i t y , as evidenced by the " p i l i n g - u p " of s e v e r a l c o h o r t s i n the l a t e f a l l and winter. Production of l o c a l E. p a e i f i c a p o p u l a t i o n s was examined f o r comparison with p r e v i o u s estimates due t o Lasker(1966) , 103 based on l a b o r a t o r y s t u d i e s of E t p a e i f i c a growth and on f i e l d data from the l i t e r a t u r e ( e g . Ponomareva, 1963). From Lasker's l a b o r a t o r y estimate t h a t 5% of the carbon i n the biomass o f E. p a e i f i c a i s needed to maintain the growth, r e s p i r a t i o n and moulting of the p o p u l a t i o n each day, and from the l i t e r a t u r e e stimate of 110 mgC/m2 f o r the l i v e biomass of E. p a e i f i c a over i t s range i n the P a c i f i c Ocean, a va l u e of 5.5 mgC/m2/day was obtained f o r d a i l y i n g e s t i o n by t h e p o p u l a t i o n . I t was f u r t h e r estimated from L a s k e r ' s carbon budget f o r E8_ p a e i f i c a t h a t about 16% of the i n g e s t e d carbon i s used f o r growth and egg pr o d u c t i o n ( M u l l i n , 1969). On t h i s b a s i s , the mean r a t e of pr o d u c t i o n of the n a t u r a l p o p u l a t i o n i n the North P a c i f i c would be about 0.9 mgC/mVday or 0.48% of net primary production (from M c A l l i s t e r e t a l , 1960). The value of P/B estimated f o r E. p a e i f i c a i s thus about 3.0 /year ( C r i s p , 1975). T h i s estimate does not i n c l u d e allowance f o r pr o d u c t i o n by animals l o s t through m o r t a l i t y . A f u r t h e r source o f e r r o r i n t h i s estimate i s that growth r a t e s and r e s p i r a t o r y r a t e s of l a b o r a t o r y specimens of a l i m i t e d s i z e range were assumed to be a p p l i c a b l e t o d i v e r s e n a t u r a l p o p u l a t i o n s . In a d d i t i o n , the annual net primary production would be lower than t h e summer r a t e used i n one v e r s i o n of t h i s e s t i m a t e . The present study o f f e r e d an op p o r t u n i t y to estimate the pro d u c t i o n of more w e l l - d e f i n e d c o a s t a l p o p u l a t i o n s o f E. p a e i f i c a based on o b s e r v a t i o n s on r a t e s of m o r t a l i t y and i n c r e a s e i n biomass. The values of production estimated f o r JL. j9JJcifica i n the S t r a i t of Georgia r e g i o n a re much higher than the one based on Lasker's(1966) carbon budget. The l o c a l 104 p o p u l a t i o n s had a mean P/B r a t i o of 8.9 ± 0.56 which was h i g h e r than Lasker*s by about three times. Much of the d i f f e r e n c e can l i k e l y be a t t r i b u t e d to the higher growth r a t e s observed i n the l o c a l p o p u l a t i o n s compared t o Lasker*s l a b o r a t o r y animals. In a d d i t i o n , the c o n t r i b u t i o n due to i n d i v i d u a l s l o s t throuqh m o r t a l i t y i s i n c l u d e d i n the present e s t i m a t e s . Mullin(1969) has reviewed much o f the zooplankton p r o d u c t i o n l i t e r a t u r e up t o 1968. P r o d u c t i o n values f o r s i n q l e copepod s p e c i e s were found to ranqe from about 0.2 t o 77 mqC/n>2/day while P/B v a r i e d from 0.002 to 0.50 /day. The va l u e s of p roduction (26.8 mqC/mz/da) and P/B (0.0 24/da) f o r E, p a c i f i c a i n Saanich I n l e t a re thus w i t h i n the ranqe of valu e s reported f o r her b i v o r o u s copepods, but hiqher than the estimate f o r E x p a c i f i c a i n the Sorth P a c i f i c due to Lasker(1966). Observations at n i q h t on the d i s t r i b u t i o n of biomass of meqazooplankton i n the S t r a i t o f Georqia r e q i o n r e v e a l e d l a r q e -s c a l e p a t c h i n e s s i n the hiqh frequency sound s c a t t e r i n q l a y e r . As the l e n q t h of M i l l e r net tows was u s u a l l y one n a u t i c a l mile (10 minutes at 3m/sec), s c a l e s o f patchiness below t h i s l i m i t would not be d e t e c t a b l e by net samplinq. Continuous r e c o r d i n q d u r i n q c r u i s e t r a n s e c t s with a 107 kHz echosounder, thouqh, o f t e n d e t e c t e d patches with diameters l e s s than a mile w i t h i n the s c a t t e r i n q l a y e r ( c f . Table 15). Pieper (1971) has di s c u s s e d p a t c h i n e s s w i t h i n the sound s c a t t e r i n q l a y e r of euphausiids i n Saanich I n l e t . The survey c r u i s e s i n d i c a t e d the presence of s e v e r a l areas of hiqh abundance o f megazooplankton, e u p h a u s i i d s i n p a r t i c u l a r . 105 These i n c l u d e Saanich I n l e t , J e r v i s I n l e t ( e s p e c i a l l y down i n l e t from J e - 5 ) , and i n the S t r a i t of Georgia the f o l l o w i n g a r e a s : west of Texada I s l a n d ; north of Nanaimo i n the c e n t r a l part of the S t r a i t ; and i n the v i c i n i t y of the Fraser River plume. The areas of high abundance i n the S t r a i t o f Georgia tended to s h i f t i n l o c a t i o n between c r u s i e s much more than the megazooplankton p o p u l a t i o n s w i t h i n the i n l e t s . Data on the d i s t r i b u t i o n of e u p h a u s i i d catches from the S t r a i t of Georgia plankton f i s h e r y which w i l l be presented i n Chapter 5 a l s o i n d i c a t e high c o n c e n t r a t i o n s of euphausiids occur i n S e c h e l t I n l e t , i n the C r o f t o n area of S t u a r t Channel, and o c c a s i o n a l l y toward the mouth of Howe Sound (see F i g u r e 1) . E a r l i e r studies(1965-1967) on the d i s t r i b u t i o n of zooplankton i n the s u r f a c e waters of the S t r a i t of Georgia have been r e p o r t e d by Stephens et a L , MS{1969) and by Parsons et a l . . (1970); however, t h e i r data were from daytime M i l l e r net tows which would not have sampled the v e r t i c a l l y m i g r a t i n g megazooplankton of t h e h i g h freguency sound s c a t t e r i n g l a y e r . Biomass estimates from v e r t i c a l hauls(400m-0) i n the c e n t r a l S t r a i t ( S t a t i o n 1748 of the present study) d u r i n g 1966-1968 showed an annual maximum during October to about December (Stephens e t al.. . MS, 1969) s i m i l a r to t h a t observed f o r Ej_ p a c i f i c a p o p u l a t i o n s i n the present study. For the G u l f of St. Lawrence est u a r y , Berkes(1973; 1976) and Sameoto (1976) have r e p o r t e d on the d i s t r i b u t i o n of the e u p h a u s i i d s , Meganyctiphanes noryegica , Thysanoessa r a s c h i i . T ^ i n e r m i s and T A l o n g i c a u d a t a (Berkes, o n l y ) . Sameoto(1976) 106 used a 120 kHz echo sounder to r e c o r d the d i s t r i b u t i o n of sound s c a t t e r i n g l a y e r s which were comprised l a r g e l y of the f i r s t t h r e e e u p h a u s i i d s p e c i e s mentioned above. He found a c o n s i s t e n t r e l a t i o n s h i p between i n t e n s i t y of b a c k s c a t t e r i n g and the d e n s i t y of numbers and biomass of euphausiids from c o n c u r r e n t l y c o l l e c t e d plankton samples. In a d d i t i o n , d u r i n g flay or June c r u i s e s on three s u c c e s s i v e years (1972-74) s i g n i f i c a n t c o r r e l a t i o n s between the d e n s i t y of the sound s c a t t e r i n g l a y e r s and the amount o f c h l o r o p h y l l - a i n the s u r f a c e waters were noted. In summary, p o p u l a t i o n s o f E± J B S c i f i c a i n the S t r a i t of Georgia r e g i o n were observed to reach maximum biomass i n October to November, f o l l o w i n g the p e r i o d of high p r o d u c t i o n i n summer. During June-October, p a e i f i c a c o n t r i b u t e d an i n c r e a s i n g p r o p o r t i o n of the t o t a l megazooplankton biomass i n the sound s c a t t e r i n g l a y e r s of the study areas. The survey c r u i s e s i n d i c a t e d t h a t s i z a b l e s t o c k s o f megazooplankton (e.g. about 100,000 metric tons d u r i n g October-November 1975) are present i n the shallow s c a t t e r i n g l a y e r s o f the S t r a i t o f Georgia region a t n i g h t . To conclude the d i s c u s s i o n on the p o p u l a t i o n b i o l o g y of E. p a e i f i c a , I w i l l c o n s i d e r a problem which i s c e n t r a l to p o p u l a t i o n b i o l o g y , e s p e c i a l l y to that of e x p l o i t e d p o p u l a t i o n s : the r e l a t i o n s h i p between the s i z e of the parent stock and that of the f o l l o w i n g g e n e r a t i o n (e.g. L a r k i n , 1973). The g u e s t i c n i s very d i f f i c u l t t o r e s o l v e e m p i r i c a l l y f o r n a t u r a l p o p u l a t i o n s s i n c e a wide range of s i z e s of a d u l t and f i l i a l s t o c k s should i d e a l l y be observed and the e f f e c t o f environmental v a r i a b i l i t y 107 on r e p r o d u c t i o n and r e c r u i t m e n t taken i n t o account. Consequently, a favoured approach of f i s h e r y b i o l o g i s t s has been to c o n s t r u c t models f o r stock and recruitment based on simple assumptions about the a c t i o n of d e n s i t y dependent mechanisms such as p r e d a t i o n , growth r a t e s and f e c u n d i t y . The model o f Ricker(1954;1958) f o r example, assumes: "t h a t the average abundance of the p r e d a t o r s (durinq the time of t h e i r contact with the prey) v a r i e s from year t o year, as some constant f r a c t i o n of the i n i t i a l abundance o f prey ( f i s h eqqs or l a r v a e , e t c . , at whatever staqe compensation beqins) , but t h a t the p r e d a t o r s have a minimum abundance which i s s u s t a i n e d by t h e i r other foods. " ks t h e predators can be more than one s p e c i e s and i n c l u d e parents of the eqqs or l a r v a e i n question, then i f a qiven s p e c i e s of predator "becomes s a t i a t e d a t some d e n s i t y of prey and ceases t o f u n c t i o n as a c o n t r o l , t h at merely s h i f t s a p a r t of the compensatory mechanism to some other predator or aqent which can f u n c t i o n at the hiqher d e n s i t y . " From these assumptions, the mathematical d e r i v a t i o n proceeds to the f o l l o w i n q r e l a t i o n (Ricker, 1958), i n which the p a r e n t a l and f i l i a l s t o c k s are expressed i n terms of t h e i r e q u i l i b r i u m replacement v a l u e s : Z = 8-exp £ a (1-W) 1 where Z i s the r a t i o of f i l i a l abundance to replacement abundance, W i s the r a t i o of p a r e n t a l abundance t o replacement abundance, and "a" i s the r a t i o of p a r e n t a l abundance at replacement to p a r e n t a l abundance a s s o c i a t e d with maximum r e p r o d u c t i o n . From c o n s i d e r a t i o n o f a t h e o r e t i c a l s i t u a t i o n i n which 108 c o m p e t i t i o n f o r food l i m i t s growth r a t e , Beverton and Holt(1957) d e r i v e d the same e x p r e s s i o n . As slower growth r a t e i s l i n k e d with higher r a t e s of p r e d a t i o n on the e a r l y st a g e s of the prey, then d e n s i t y dependent r e g u l a t i o n i s accomplished. The present study was not c a r r i e d out over a s u f f i c i e n t l y long p e r i o d t o monitor a wide range of p a r e n t a l and f i l i a l stock d e n s i t i e s necessary to apply t h e e m p i r i c a l approach to the stock recruitment q u e s t i o n f o r E. p a c i f i c a . However, a model such as des c r i b e d above can p r o v i d e a p r e l i m i n a r y view which c o u l d be c r i t i c a l l y examined throuqh f u r t h e r f i e l d s t u d i e s . The q u e s t i o n s of p a r t i c u l a r i n t e r e s t here a r e (a) what i s the minimum a d u l t stock necessary t o produce a replacement stock of mature progeny? ( c f . S i c k e r , 1958) and thus (b) how much highe r c o u l d the t o t a l m o r t a l i t y ( n a t u r a l and f i s h i n g ) be without lowering the stock's production? The a d u l t stock i n s i t u a t i o n (a) would possess the maximum p o s s i b l e r e p r o d u c t i o n r a t e i n order t o generate a replacement cohort. T h e r e f o r e we are i n t e r e s t e d i n the r e l a t i o n between maximum r e p r o d u c t i o n and simple replacement r e p r o d u c t i o n . From R i c k e r ' s equation, the r a t i o of maximum r e p r o d u c t i o n t o replacement r e p r o d u c t i o n i s : Z m= 1/a • exp(a - 1) where Z ^ i s the r a t i o of maximum f i l i a l abundance to replacement f i l i a l abundance. In order to ev a l u a t e t h i s e x p r e s s i o n one needs i n f o r m a t i o n on e i t h e r the a d u l t or f i l i a l r e l a t i v e abundances under maximum and replacement c o n d i t i o n s . In the absence of h a r v e s t i n g , the Saanich I n l e t p o p u l a t i o n of eup h a u s i i d s f o r 109 i n s t a n c e , has l i k e l y been r e p r o d u c i n g at replacement l e v e l s as the r e i s no evidence over the period from 19 61-77 o f high v a r i a b i l i t y i n the annual biomass l e v e l s o f e u p h a u s i i d s i n t h a t i n l e t {cf. Bary et a l ^ ,1962; Bary and Pieper,1970). I f high h a r v e s t i n g m o r t a l i t y (or adverse environmental c o n d i t i o n s ) were to s i g n i f i c a n t l y reduce the a d u l t spawning st o c k , then the subseguent l e v e l of r e c r u i t m e n t could i n d i c a t e the nature of d e n s i t y dependent r e l a t i o n s h i p . I f the shape of the stock recruitment curve i s obta i n e d , then the maximum e g u i l i b r i u m c a t c h and l i m i t i n g e g u i l i b r i u m r a t e of e x p l o i t a t i o n (Bicker,1958) can be c a l c u l a t e d . Although i t would be premature to determine a r e l i a b l e s t o c k r e c r u i t m e n t r e l a t i o n from present i n f o r m a t i o n , i t appears t h a t the maximum r e p r o d u c t i o n of Ej_ p _ a c i f i c a i n Saanich I n l e t could e a s i l y be s e v e r a l times the replacement r e p r o d u c t i o n s i n c e the spawning season i s p r o t r a c t e d (May-September) and females p o s s i b l y spawn s e v e r a l times per season ( B r i n t o n , 1976). Under c o n d i t i o n s of lower d e n s i t y of a d u l t spawners, more of the r e p r o d u c t i v e p o t e n t i a l might be r e a l i z e d and replacement s t i l l achieved. T h i s p o s s i b i l i t y should be examined more thoroughly by monitoring harvested p o p u l a t i o n s over a p e r i o d of years. 110 CHAPTER 4: EUPHAUSIIDS AS A FOOD 4.1 I n t r o d u c t i o n I f h a r v e s t i n g of zooplankton i s t o develop i n importance commercially then f u r t h e r i n f o r m a t i o n on the composition and p o t e n t i a l uses of the products must be obtained. At the same time, data on the c h e m i c a l composition of z o o p l a n k t e r s and on the growth response o f experimental animals to the zooplankton p r e p a r a t i o n s can be u s e f u l i n a s s e s s i n g the r o l e of the z o o p l a n k t e r s i n the marine food web. Although l i v e zooplankton have been g e n e r a l l y r e c o g n i z e d as a s u p e r i o r food f o r f i s h , e s s e n t i a l l y negative r e s u l t s obtained by B r e t t (1971) on the value of frozen marine zooplankton as a d i e t f o r young salmonids have i n d i c a t e d that a r e a p p r a i s a l of the use of marine crustaceans such as E.. p a c i f i c a as food f o r r e a r i n g young f i s h i s needed. Analyses on the composition of l o c a l euphausiids and a growth experiment with j u v e n i l e coho are d e s c r i b e d below. 4.2 Methods f o r Chemical Analyses Eu p h a u s i i d samples were su b j e c t e d to the f o l l o w i n g chemical a n a l y s e s : proximate a n a l y s i s ( c r u d e p r o t e i n , crude l i p i d , f i b r e , ash), c a r o t e n o i d d e t e r m i n a t i o n , and amino a c i d a n a l y s i s . The proximate a n a l y s i s of a January 1975 sample from Saanich I n l e t was k i n d l y s u p p l i e d by A. Barnes o f the F i s h e r i e s Research Board of Canada, Vancouver Labora t o r y . F u r t h e r f r o z e n samples were p e r s o n a l l y analysed f o r l i p i d and c a r o t e n o i d content. The amino a c i d analyses were performed under c o n t r a c t by Dr. J . SheIford 111 at the Department of animal S c i e n c e , UBC . For the proximate a n a l y s i s , % p r o t e i n was found by the K j e l d a h l d e t e r m i n a t i o n of n i t r o g e n as d e s c r i b e d by Steyermark(1961) . L i p i d was e x t r a c t e d i n c h l o r o f o r m : methanol (1:2 by volume). Ash was determined by twice combusting the sample i n a muffle f u r n a c e at 525 C. D e t a i l s of these procedures and of the crude f i b r e d e t e r m i n a t i o n are given i n the a s s o c i a t i o n of O f f i c i a l A g r i c u l t u r a l Chemists(1960) manual o f a n a l y s i s . L i p i d and c a r o t e n o i d were determined i n our l a b o r a t o r y a c c o r d i n g to Herring(1972). The amino a c i d analyses on f r e e z e - d r i e d , f r o z e n and steam-d r i e d e u p h a u s i i d s were performed f o l l o w i n g h y d r o l y s i s f o r 24 h i n 6 N HCl, according to Spackman et a l . (1958). T h i s method does not g i v e q u a n t i t a t i v e recovery of c y s t e i n e , methionine or tryptophan. 4.3 F i s h Feeding T r i a l s with Euphausiid P r e p a r a t i o n s 4.31 Methods J u v e n i l e coho salmon { Oncqrhynchus kisutch), were obtained from C a p i l a n o Hatchery, Department of the Environment. I n i t i a l l y a l l of the f i s h were kept i n one tank f o r one week to i n t r o d u c e the d i e t s . P r i o r to the f e e d i n g t r i a l s , the 548 f i s h were separated i n t o e q u a l groups i n f o u r i d e n t i c a l f i b r e g l a s s tanks. I n i t i a l f o r k l e n g t h and wet weight was estimated by sampling 26 f i s h from each tank. The f o u r f i s h d i e t s i n c l u d e d t h r e e e u p h a u s i i d p r e p a r a t i o n s 112 and a c o n t r o l d i e t of Oregon moist p e l l e t (OMP) Formula No. 2 (Halver, 1972), prepared commercially by Moore-Clarke Company, LaConnor, Washington. The e u p h a u s i i d p r e p a r a t i o n s were (1) minced f r o z e n , (2) f r e e z e - d r i e d and (3) a ' f i s h meal processed' moist p e l l e t . The l a t t e r d i e t was prepared with a f i s h meal p i l o t p l a n t at P a c i f i c Environmental I n s t i t u t e , West Vancouver. T h i s equipment, b u i l t by t h e Chemical Research O r g a n i z a t i o n , E s b j e r g , Denmark, i s b a s i c a l l y a worm-drive press and a steamheated dryer-cooker. The press p a r t i a l l y separates the l i q u i d and s o l i d p a r t s of the raw m a t e r i a l . The u n i t then cooks and d r i e s the s o l i d f r a c t i o n . To make the e u p h a u s i i d meal, f r o z e n e u p h a u s i i d s c o l l e c t e d from Saanich I n l e t i n January and February 1975 were used as the raw m a t e r i a l . A f t e r p r e s s i n g and cooking the d r i e d product was moistened by adding one p a r t l i g u i d e x t r a c t from the press t o three p a r t s by weight of the d r i e d f r a c t i o n . The mixture was p e l l e t t e d with a L a b o r a t o r y P e l l e t M i l l ( C a l i f o r n i a P e l l e t M i l l Co., San F r a n c i s c o , C a l i f . ) To s t a n d a r d i z e the p a r t i c l e s i z e of t h e d i e t s , the f r e e z e -d r i e d and p e l l e t e d e u p h a u s i i d meals and the OMP meal were passed through a No. 16 O.S. Standard S i e v e with 1.19 mm meshes and r e t a i n e d on a No. 30 s i e v e (0.595 mm). The f r o z e n e u p h a u s i i d s were minced i n t o p i e c e s about 1-2 mm l o n g . The f i x e d d a i l y r a t i o n s of a l l d i e t s (30% of i n i t i a l body weight per day, 14 to 17% of f i n a l body weight per day on an e g u i v a l e n t dry weight basis) were set i n excess of expected growth reguirements. A f t e r two days of no f e e d i n g , the f e e d i n g t r i a l c ontinued f o r 21 days with once d a i l y f e e d i n g s between 113 1030 and 1430 PDT. The f o u r experimental groups were maintained i n f o u r f i b r e g l a s s tanks (200 1) i n the outdoor c o u r t y a r d of the B i o l o g i c a l S c i e n c e s B u i l d i n g at OBC. The f l u s h i n g r a t e i n the freshwater tanks with bottom i n l e t s and s u r f a c e o u t l e t s was adjusted t o maintain oxygen s a t u r a t i o n and r e l a t i v e l y uniform temperature (mean 9 C, range 8-10.5 C ) . a n a l y s i s o f v a r i a n c e on d a i l y s u r f a c e temperature readings r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e between the tank means at the 1% s i g n i f i c a n c e l e v e l . P r i o r to the end of the experiment the f i s h were st a r v e d f o r 24 h to c l e a r t h e i r guts. A l l of the f i s h were k i l l e d then d i r e c t l y measured and wet weighed f o r comparison of treatments f o r growth i n l e n g t h and weight. 4.4 R e s u l t s 4.41 Composition of Euphausiids The proximate composition of l o c a l e u p h a u s i i d s , based on a n a l y s i s o f a c a t c h from Saanich I n l e t , i s shown i n Table 16a. L a t e r a n a lyses of l i p i d and c a r o t e n o i d content (Table 16b) r e v e a l e d marked v a r i a t i o n s (6.6 t o 19.6% l i p i d , 80 to 219 ug c a r o t e n o i d / g t i s s u e ) with date of c o l l e c t i o n and l o c a t i o n . P o s s i b l e sources of t h i s v a r i a t i o n w i l l be d i s c u s s e d . 114 TABLE 16a. Proximate composition of e u p h a u s i i d s caught i n Saanich I n l e t , January 1975. Dry weight b a s i s . Component % P r o t e i n 69.1 L i p i d s 17.3 Ash 11.1 Crude F i b r e 2.5 TABLE 16b. L i p i d and c a r o t e n o i d content of commercial ca t c h e s e u p h a u s i i d s from S e c h e l t and Saanich I n l e t . Dry weight b a s i s . I n l e t Date L i p i d X l l Carptenoid (flq/q) 219. 94. 80. S e c h e l t 18- 31/Jan/77 19. 6 S e c h e l t 16- 28Feb/77 13. 1 S e c h e l t 01- 11/Mar/76 11. 0 S e c h e l t 20- 31/Mar/76 9. 0 Saanich 16- 23/Feb/76 6. 6 The amino a c i d compositions of the p r o t e i n of three p r e p a r a t i o n s of e u p h a u s i i d s , used i n the f e e d i n g t r i a l s with j u v e n i l e coho salmon, are given i n Table 17. TABLE 17. Amino a c i d composition o f t h r e e p r e p a r a t i o n s of euphausiids from Saanich I n l e t i n January and February 1975. L a b e l s are e x p l a i n e d i n the t e x t . P r e p a r a t i o n FDE EM FZE DryMatter % 91.6 74.5 17.0 ASiS2 Acid mg aa/mq sample x VOQ Jdry, wt basis) Alanine 3.34 2.40 3.94 A r q i n i n e 3. 58 2.62 2.91 A s p a r t i c A c i d 5. 93 2.98 6. 52 Glutamic A c i d 7. 16 5.35 4. 17 G l y c i n e 3.91 2.59 4.68 H i s t i d i n e 1. 24 .68 1.46 I s o l e u c i n e 2.59 2.01 3.08 Leucine 4. 21 3. 17 4.67 L y s i n e 3. 33 2.34 5.03 Methionine 1.76 •1. 40 2.07 P h e n y l a l a n i n e 2. 87 1.85 3.30 P r o l i n e 2. 10 1.31 2.07 S e r i n e 2.31 . 58 2.59 Threonine 2.70 .91 2.98 T y r o s i n e 2. 33 1.46 2.36 V a l i n e 2. 66 2.03 3.11 4.42 J u v e n i l e Coho Growth on Euphausiid P r e p a r a t i o n s 115 The r e s u l t s of the growth experiment to t e s t the e f f e c t i v e n e s s of t h r e e e u p h a u s i i d p r e p a r a t i o n s compared to OMP are summarized i n Table 18. Frequency d i s t r i b u t i o n s i n Fi g u r e 34 i l l u s t r a t e the changes i n wet weiqht between the i n i t i a l and f i n a l samples f o r each treatment. Althouqh the f i n a l mean wet weiqht o f the OMP qroup was m a r q i n a l l y hiqher, the f r e e z e - d r i e d e u p h a u s i i d ( FDE ) qroup had the hi q h e s t mean qrowth r a t e a t 3.8% wet body wt/day, compared t o 3.1% f o r the OHP qroup, 3.0% f o r the e u p h a u s i i d meal ( EM ) qroup and 2.8% f o r the f r o z e n e u p h a u s i i d ( F Z E ) qroup. Within qroup v a r i a t i o n i n qrowth r a t e s was hiqh, e s p e c i a l l y i n the FZE and EM qroups, where the standard d e v i a t i o n s exceeded the mean qrowth r a t e s . TABLE 18. Comparison of i n i t i a l and f i n a l mean values f o r wet weiqht and f o r k l e n q t h as w e l l as mean qrowth r a t e s of d i e t qroups i n coho f e e d i n q t r i a l . Mean Euphausiid P r e p a r a t i o n s C o n t r o l js_. dj, i_ Frozen F r e e z e - d r i e d Meal OMP I n i t i a l 276.0 297.3 329.9 349.2 wet weiqht (8.6) (7.5) (5.4) (8.0) F i n a l 532.3 684.0 643.6 692.6 wet weiqht (52.7) (46.8) (47.6) (48.9) (mg) I n i t i a l 3. 16 3.21 3.24 3.24 f o r k l e n q t h (.06) (. 04) (.02) (.04) (cm) F i n a l 3.65 3.87 3.73 3.87 f o r k l e n q t h (.16) (.13) (.12) (.13) (cm) Growth r a t e 2.67 3. 76 2.95 3.05 (%body wt/ (5. 53) (2.94) (3.08) (2.80) day) S t a t i s t i c a l s i q n i f i c a n c e o f the r e s u l t s was assessed by one-way c l a s s i f i c a t i o n a n a l y s i s of vari a n c e { ANOVA ) (Sokal and 116 BEFORE AFTER 2 0 15 10 5 0| 20 15 10 5 0 20 15 10 5 .2 .3 .4 .5 A. FROZEN' B. FREEZE-DRIED *-n r - i n C. MEAL D. OMP .6 .2 .3 .4 .5 .6 .7 .8 .9 10 1.1 1.2 WET WEIGHT (g ) FIGOEE 34. Frequency d i s t r i b u t i o n s of wet weiqht for juvenile coho sampled before and afte r feeding t r i a l s on four diets: a. Frozen euphausiids, B. Freeze-dried euphausiids. C. Euphausiid meal, D, OMP , Rohlf, 1969) and by Scheffe*s(1959) least s i g n i f i c a n t difference ( LSD ) procedure. The ANOVa tests (Table 19) established that there were highly s i g n i f i c a n t (P< 0.01) differences between treatments for f i n a l mean wet weights and forklengths as well as growth rates. 117 TABLE 19. Summary of ANOVA on f i n a l wet weights and f o r k l e n g t h s ; growth r a t e s of the f o u r coho d i e t groups. Source of V a r i a t i o n df SS MS I F i n a l wet weight treatment 3 1.81 .603 11.27** w i t h i n treatment 440 23.55 .0535 F i n a l f o r k l e n g t h treatment 3 3.94 1.31 8.95** w i t h i n treatment 440 64.52 .147 Growth r a t e treatment 3 71.6 3 23. 88 6.01** w i t h i n treatment 440 1746. 3.97 ** P<.01 By the LSD procedure f o r comparing means, (Table 20) i t was found t h a t the mean wet weight of the FZE group was s i g n i f i c a n t l y lower (P<0.01) than the other means. The mean f o r k l e n g t h s of the FDE and OMP groups were a l s o s i g n i f i c a n t l y higher than those of the FZE and EM groups. F i n a l l y , the mean growth r a t e of the FDE group was higher (P<.05) than f o r the other d i e t groups. TABLE 20. Comparison of means f o r d i e t s by S c h e f f e ' s l e a s t s i g n i f i c a n t d i f f e r e n c e ( LSD ) method. Means Frozen Meal C o n t r o l Freeze-dry LSD FZE EM OMP " FDE~ ~ (prob) Wet Wt 532.3** 643.6 692.6 684w0 104.4 (mg) (.01) Fo r k l e n g t h 3.65** 3.73* 3.87 3.87 . 14 (.05) (cm) .16 (.01) Growth Rate 2.67 2.95 3.05 3.76* .706 (.05) {% body wt . 85 (. 01) per day) *P<.05 **P<.01 Note t h a t LSD i s the s m a l l e s t s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e between compared means and can be c a l c u l a t e d as df x F(cr) x standard e r r o r of the d i f f e r e n c e between the compared means (Scheffe,1959; Sokal and Rohlf,1969). 118 4.5 D i s c u s s i o n 4.51 Composition of S t r a i t of Georgia Euphausiids Due e s p e c i a l l y t o the q u a n t i t y and high q u a l i t y of t h e i r p r o t e i n s , euphausiids are l i k e l y to be an e x c e l l e n t c o n s t i t u e n t f o r the d i e t s of qrowinq animals. C e r t a i n l y a qood example i s the r a p i d qrowth of baleen whales which feed almost e n t i r e l y upon euphausiids i n the Southern Ocean and i n the North P a c i f i c Ocean (Nemoto, 1957; 1959; 1968) . The r e s u l t s presented f o r % p r o t e i n agree with v a l u e s d e r i v e d from Lasker's (1966) data on E A p a c i f i c a body n i t r o g e n . C o n v e r t i n g h i s K j e l d a h l n i t r o q e n values to % p r o t e i n by m u l t i p l y i n g by 6.25 y i e l d s a mean of 71.9% f o r f i v e d e t e r m i n a t i o n s , with a ranqe from 65 t o 81.21. V a r i a t i o n of l i p i d c o n t e n t with time of year was noted, with values i n euphausiids from Sechelt and Saanich I n l e t s d e c l i n i n g markedly d u r i n q l a t e winter. F i s h e r e t a l . ,(1954) observed s i m i l a r trends i n the f a t content of Meganyetiphanes noryegica and Thysanoessa r a s e h i i from Loch Fyne, S c o t l a n d . The d e p l e t i o n o f l i p i d r e s e r v e s appears t o be a s s o c i a t e d with use f o r body maintenance dur i n g winter and, i n some females, f o r egg prod u c t i o n p r i o r to spawning i n l a t e March and A p r i l . The c a r o t e n o i d s , predominantly a s t a x a n t h i n and i t s e s t e r s ( F i s h e r et aJU , 1955) a l s o appear to d e c l i n e as the l i p i d content drops. Although the present data must be regarded as p r e l i m i n a r y , they i n d i c a t e t h a t euphausiids i n the S t r a i t of Georgia r e g i o n are s i m i l a r i n c a r o t e n o i d c o n c e n t r a t i o n t o the 119 p e l a g i c red c r a b , Pleuroncodes p i a n i p e s , from the G u l f o f C a l i f o r n i a which has r e c e n t l y been suggested as an a g u a c u l t u r a l feed i n g r e d i e n t to enhance pigmentation of pen-reared salmonids (Wilkie,1972: S p i n e l l i et a l A ,1974). Wilkie(1972) obtained tissue(mean 93) i n a s t a x a n t h i n u n i t s . The amino a c i d compositions of the three p r e p a r a t i o n s of E. j O a c i f i c a from Saanich I n l e t show t h a t the p r o t e i n s have a f a v o u r a b l e balance o f e s s e n t i a l amino a c i d s f o r use as a d i e t a r y p r o t e i n . Levels of the important amino a c i d s and % recovery were higher f o r the f r o z e n and f r e e z e - d r i e d p r e p a r a t i o n s than f o r the e u p h a u s i i d meal, i n d i c a t i n g t h a t s i g n i f i c a n t l o s s of p r o t e i n l i k e l y o ccurred d u r i n g the p r e s s i n g stage of meal p r o c e s s i n g . 4.52 Coho Growth on E u p h a u s i i d D i e t s Eor the s h o r t term o f t h e experiment, the e u p h a u s i i d based d i e t s compared f a v o u r a b l y with the OMP d i e t . Although there was no s i g n i f i c a n t d i f f e r e n c e between mean growth r a t e s of the OMP group and the f r o z e n { FZE ) and meal { EM ) groups, the f r e e z e -dry { FDE ) group had a s i g n i f i c a n t l y higher growth r a t e than the others. The s u p e r i o r i t y of the f r e e z e - d r i e d d i e t over the f r o z e n d i e t was c l e a r l y not a r e s u l t of more f a v o u r a b l e amino a c i d composition; more l i k e l y the d i f f e r e n c e was i n the a v a i l a b i l i t y of the d a i l y r a t i o n to the f i s h . Thus, the f r e e z e -d r i e d meal f l o a t e d at t h e s u r f a c e w i t h i n range o f the s u r f a c e f e e d i n g coho while the minced f r o z e n euphausiids tended to cause c l o u d i n e s s due to l e a c h i n g and t o s i n k t o the bottom i f not consumed w i t h i n seconds. With the f r o z e n e u p h a u s i i d s , the more t o t a l pigment y i e l d s of 8 3 t o 99 of whole animal 120 a q g r e s s i v e f i s h were ab l e t o feed w e l l , but the t i m i d ones d i d p o o r l y ; with the other meals, d i s t r i b u t i o n was more even as the sm a l l p e l l e t s d i d not s i n k so r a p i d l y as the f r o z e n b i t s . The growth r a t e s obtained i n t h i s experiment are comparable to values r e p o r t e d f o r j u v e n i l e salmon of c l o s e l y r e l a t e d s p e c i e s , e s p e c i a l l y when the e f f e c t o f water temperature on growth r a t e i s con s i d e r e d . LeBrasseur(1969) f e d j u v e n i l e chum salmon, Oncorhynchus k e t a T on l i v e zooplankton, i n c l u d i n g e u p h a u s i i d s , i n tanks a t 14-16 C. F i s h on excess d i e t s i n c r e a s e d i n weight a t 5.4% per day, but at c o n s i d e r a b l y warmer ambient temperatures than i n the present experiment. K o e l l e r and Parsons(1977) observed a growth r a t e o f 4% per day f o r j u v e n i l e chum salmon f e e d i n g p r i m a r i l y on l i v e Calanus plumchrus a t 10 t o 13.5 C i n a f u l l - s c a l e C o n t r o l l e d Experimental Ecosystem(1700 m3 ). I n c o n t r a s t , Brett(1971) found that j u v e n i l e sockeye salmon, Oncorhynchus n e r k a x at 15 C gained only 1.5% per day on f r o z e n Cala£fi§ PiiJSSllESs whereas those f e d d i e t s based on f i s h meal i n c r e a s e d at up to 2 . 8% per day on f i x e d r a t i o n s o f 6% dry body weight per day. The present f i n d i n g s are c o n t r a r y t o B r e t t ' s c o n t e n t i o n t h a t c r u s t a c e a n foods are i n f e r i o r to f i s h meal based foods. In meal forms which reduce s i n k i n g and l e a c h i n g l o s s e s , c r u s t a c e a n foods can be e q u a l l y o r more e f f e c t i v e i n promoting r a p i d growth i n young salmonids. 121 CHAPTER 5: ZOOPLANKTON HARVESTING 5.1 I n t r o d u c t i o n , The h a r v e s t i n g of zooplankton and micronekton i s an important r e c e n t development i n world f i s h e r i e s ; i t a l s o r e p r e s e n t s a s i g n i f i c a n t area of i n t e r a c t i o n f o r oceanographic and f i s h e r y s c i e n c e s . To i n d i c a t e the present s t a t u s of t h i s area of a c t i v e r e s e a r c h and technology, a review of the l i t e r a t u r e i s presented, 5.2 L i t e r a t u r e Review what are the prospects and advangages of h a r v e s t i n g seafood from lower t r o p h i c l e v e l s than those of most present commercial f i s h e s ? T h i s q u e s t i o n may be addressed i n r e l a t i o n to mankind's food requirements and the p o t e n t i a l f o r i n c r e a s i n g food p r o d u c t i o n from the sea. The average person r e q u i r e s 35-40 qrams of h i q h - q u a l i t y p r o t e i n each day f o r an adequate d i e t (FAG and WHO, 1973); thus the present annual f i s h p r o d u c t i o n of 70 m i l l i o n metric tons can f u r n i s h about 24% of the p r o t e i n requirements of the world's 4 b i l l i o n people. Ricker(1969b) estimated that p r o d u c t i o n of food from the sea can probably be i n c r e a s e d to about 150-160 m i l l i o n m e tric tons per year of f i s h ; 20% o f t h i s t o t a l i s usable h i q h - q u a l i t y p r o t e i n . Suppose t h i s s i q n i f i c a n t i n c r e a s e could be achieved by 2000 A.D. The p r o j e c t e d world p o p u l a t i o n then would be about 5,9 b i l l i o n , based o p t i m i s t i c a l l y on a d e c l i n e i n f e r t i l i t y t o a net replacement of 1,0 by 2000 A,D.(Frejka,1973). Seafood c o u l d p r o v i d e about 35% of the 122 world's minimal p r o t e i n needs i n t h i s s i t u a t i o n , but only about 3% of i t ' s b i o l o g i c a l energy requirements (based on 3000 kcal/day and a p o p u l a t i o n of 6 b i l l i o n ) . Landings of 150 m i l l i o n tons by 2000 ft.D, would r e p r e s e n t an i n c r e a s e of 37% i n f i s h p r o t e i n per c a p i t a , assuming a pop u l a t i o n of about 6 b i l l i o n (Bicker,1969b). The s e a , then, can be expected to grew i n importance as a source of mankind's p r o t e i n provided t h a t l a n d i n g s i n c r e a s e r o u g h l y i n p r o p o r t i o n to p o p u l a t i o n up to two or t h r e e times the present l e v e l s . Many of the world's major e x i s t i n g f i s h e r i e s f o r f i n f i s h e s are nearing or are at the maximum s u s t a i n a b l e h a r v e s t l e v e l (Gulland,1971). From where then i s the bulk of the a n t i c i p a t e d i n c r e a s e i n seafood p r o d u c t i o n to come? The most promising u n d e r u t i l i z e d s t o c k s can be r e a d i l y grouped as the micronekton and megazooplankton. Micronekton can be considered as p e l a g i c organisms w i t h i n the range 2-10 cm (WP-4,1968) which have s u f f i c i e n t m o t i l i t y t o maintain t h e i r p o s i t i o n and to move ag a i n s t l o c a l c u r r e n t s . T h i s group i n c l u d e s l a r g e decapods (eg. S e r g e s t i i d s , and other Penaeids), small a d u l t f i s h (myctophids or l a n t e r n f i s h ) , s m a l l cephalopods and l a r g e e u p h a u s i i d s . Megazooplankton i n c l u d e zooplankton over 2 mm (Parsons and Takahashi,1973), such as l a r g e copepods and s m a l l e u p h a u s i i d s , whose d i s t r i b u t i o n i s i n f l u e n c e d s t r o n g l y by ocean c u r r e n t s . With the advent of the 200 mile economic zones, n a t i o n s f a c i n g c u r t a i l m e n t of f i s h i n g grounds f o r t h e i r d i s t a n t water f l e e t s (eg. Japan, and the S o v i e t Onion) are developing the technology f o r h a r v e s t i n g such u n d e r u t i l i z e d s t o c k s as the 123 A n t a r c t i c k r i l l , Euphausia superba , and the widespread oceanic s t o c k s of rayctophids. Such prominent f i s h i n g n a t i o n s as Norway and Japan have a l r e a d y developed nearshore f i s h e r i e s f o r micronekton and megazooplankton (eg. Komaki,1957; 1974; 0mori,1969; Wiborg,1966; 1976). From the standpoint of e c o l o g i c a l e f f i c i e n c y i t makes good sense to h a r v e s t from as low a t r o p h i c l e v e l as i s p r a c t i c a l . E c o l o g i c a l e f f i c i e n c y , d e f i n e d as the r a t i o of the amount o f energy e x t r a c t e d from a t r o p h i c l e v e l to the amount of energy s u p p l i e d t o t h a t t r o p h i c l e v e l , i s a concept which has been used i n e s t i m a t i n g the production of v a r i o u s t r o p h i c l e v e l s of an ecosystem (eg. Schaefer, 1965) . In t h i s sense pr o d u c t i o n (P) can be d e f i n e d as: P = BE* where B i s the annual change i n biomass at the primary t r o p h i c l e v e l , E i s the e c o l o g i c a l e f f i c i e n c y and n i s the number o f t r o p h i c l e v e l s . T y p i c a l l y , values of E i n the oceans range between 5% ( f o r a c t i v e p e l a g i c c a r n i v o r e s such as salmcn or tuna) and about 30% (eg. a p l a n k t o n i c h e r b i v o r e ) . C l e a r l y , the fewer the number of t r o p h i c l e v e l s between the primary l e v e l and the harvested t r o p h i c l e v e l , the g r e a t e r i s the production a v a i l a b l e f o r h a r v e s t , and t h e more e f f i c i e n t i s the food c h a i n from phytoplankton t o man o v e r a l l . On the other hand, p r a c t i c a l c o n s i d e r a t i o n s which enter the h a r v e s t i n g process, such as r e l a t i v e c o s t s of h a r v e s t i n g a t d i f f e r e n t t r o p h i c l e v e l s and u l t i m a t e uses of the catches, can decrease the o v e r a l l t r a n s f e r e f f i c i e n c y . 124 The f i r s t s e r i o u s s c i e n t i f i c d i s c u s s i o n s on the prospects of plankton h a r v e s t i n g sere i n i t i a t e d by Clarke(1939), Hardy(1941), Ruud{1932) and Juday (1943). Clarke(1939) concluded t h a t " i f the marketing of plankton on a commercial s c a l e i s t o become a p r a c t i c a l r e a l i t y , e i t h e r areas of g r e a t l y i n c r e a s e d r i c h n e s s (greater than 0. 1 g dry wt/m3 ) must be l o c a t e d or some method must be found f o r making the above r a t e of p r o c u r i n g plankton economically f e a s i b l e " . However, he a l s o mentioned t h a t "there might be some p o s s i b i l i t y o f o p e r a t i n g economically a f i l t e r i n g p l a n t i n the t i d a l flow between s u i t a b l y l o c a t e d i s l a n d s or i n the entrance o f an e s t u a r y " . Hardy (1941) enla r g e d upon the p o s s i b l e use of t i d a l c u r r e n t s i n plankton h a r v e s t i n g . He d e s c r i b e d the s u i t a b i l i t y o f areas such as the west co a s t of S c o t l a n d f o r t e s t i n g the use of l a r g e nets moored from anchor c h a i n s so t h a t they might swinq as the t i d a l c u r r e n t s change d i r e c t i o n . Hardy f u r t h e r remarked that "perhaps i n time i t would be economically f e a s i b l e t o employ s p e c i a l s h i p s to h a r v e s t the s t i l l r i c h e r plankton of the p o l a r seas". Despite two years of survey work, the i d e a of a plankton f i s h e r y i n Scotland was s h e l v e d as c o n c e n t r a t i o n s were inadeguate f o r economical h a r v e s t i n g (Hardy, 1956). Jackson(1954) contended t h a t e n g i n e e r i n g and economic drawbacks were more f o r m i d a b l e o b s t a c l e s to a p l a n k t o n f i s h e r y than were the t e c h n i c a l problems of e x t r a c t i n g p l a n k t o n from the sea. His r e p o r t dampened i n t e r e s t i n commercial plankton h a r v e s t i n g f o r s e v e r a l years. 125 5.21 Methods of Plankton H a r v e s t i n g Before r e t u r n i n g t o Jackson's arguments, i t i s worthwhile to examine some of the suggested methods of plankton h a r v e s t i n g . The most common method of c a t c h i n g plankton i s by towed net or t r a w l . Plankton net designs range from the f a m i l i a r c o n i c a l nets to o t t e r t r a w l s and beam t r a w l s . I n a l l cases the c y c l e of o p e r a t i o n i n v o l v e s streaming the net at the s u r f a c e , lowering i t t o f i s h i n g depth by paying out the warp (towing l i n e ) , towing at depth to f i l t e r the c a t c h , h a u l i n g i n the warp, and r e t r i e v i n g the c a t c h from the codend. For s m a l l e r n e t s , the e n t i r e u n i t i s l i f t e d , r i n s e d and emptied. For l a r g e r nets (5 m or more i n length) i t may be more p r a c t i c a l to leave the body of the net submerged unless a s u i t a b l e crane, d a v i t o r drum i s a v a i l a b l e f o r h a u l i n g the e n t i r e net aboard. I f only the codend i s t c be hauled, then a t h r o t t l i n g l i n e i s f i t t e d around the c o l l a r of the codend. T h i s l i n e can be r e t r i e v e d and hauled by hand or winch to r a i s e the c a t c h on deck. A l t e r n a t i v e l y , when catches are so l a r g e as to s t r a i n the net seams, a l i f t net of h e a v i e r webbing may be p u l l e d over the codend and r a i s e d by winch. There are s e r i o u s drawbacks to the t r a w l method. During towing, f i l t e r i n g e f f i c i e n c y of the net may drop d r a s t i c a l l y due t o c l o g g i n g o f meshes. A shortened towing peri o d might reduce the degree of c l o g g i n g , but t h i s a c t i o n makes h a u l i n g and c l e a r i n g of the net more fre q u e n t . Consequently, unproductive h a n d l i n q time i n c r e a s e s i n r e l a t i o n t o f i l t e r i n q time. Since c o n d i t i o n s a f f e c t i n q f i l t e r i n q r a t e are o f t e n h i q h l y v a r i a b l e , choosinq the optimum l e n q t h of tow i s a s u b s t a n t i a l problem. A p o s s i b l e s o l u t i o n i s t o monitor f i l t r a t i o n e f f i c i e n c y 126 with a telemetered flow meter. When f i l t r a t i o n e f f i c i e n c y f a l l s too low, the net i s hauled. a major advantage o f t r a w l i n g i s the m o b i l i t y of the h a r v e s t i n g u n i t ; t h i s permits the l o c a t i o n and e x p l o i t a t i o n of plankton patches over a l a r g e area of o p e r a t i o n . S e l e c t i o n of the best f i s h i n g depth f o r day or n i g h t o p e r a t i o n i s a l s o p o s s i b l e . In a d d i t i o n , net avoidance by l a r g e z o o p l a n k t e r s and micronekton (eg euphausiids and s e r g e s t i d shrimps) i s reduced when l a r g e t r a w l s are used. A m o d i f i c a t i o n of the t r a w l method i s the beam-trawl pumping system. The t r a w l f i l t e r s the c a t c h which i s c o n t i n u o u s l y withdrawn from the codend by a pump or l i f t system. A water s e p a r a t o r onboard removes the c a t c h from the water e f f l u e n t f o r p r o c e s s i n g . The c a p a c i t y of a pumping system i s l i m i t e d by the maximum economical pumping r a t e . For example, i n a system having a net opening of 20m2 and a towing speed 0.5 m/sec, the maximum f i l t r a t i o n r a t e i n the net would be 10 m 3/sec (10» 1/sec). However, even with a s u c t i o n pipe diameter of 30 cm, the pumping r a t e i s l i k e l y t o be l e s s than 250 1/sec (about 4000 gal/min). Consequently the pumping c a p a c i t y i s l e s s than 2.5% of the f i l t e r i n g c a p a c i t y of the net. The flow p a t t e r n i n the net would l i k e l y be very s i m i l a r to the c o n v e n t i o n a l l y towed net; c l o g g i n g would probably c o n t i n u e t o be a problem. Other disadvantages are the d i f f i c u l t y of manipulation and the danger o f permanently damaging the s u c t i o n pipe by k i n k i n g . another method of plankton h a r v e s t i n g , suggested by Hardy (1941), i s the s t a t i o n a r y swing net. For use i n areas with 127 stro n g t i d a l c u r r e n t s and abundant zooplankton, t h i s method has the advantage of s e l f - o r i e n t a t i o n to c u r r e n t s and low o p e r a t i o n a l l a b o u r . One fisherman i n a smal l v e s s e l can tend 10 to 15 anchored swing nets (Wiborg, 1976). The only d u t i e s i n v o l v e d are checking and emptying the net at r e g u l a r i n t e r v a l s , u s u a l l y each morning. To reduce c l o g g i n g the nets can be i n v e r t e d a f t e r emptying. a l s o , a c o a r s e r n e t t i n g can be s t r e t c h e d a c r o s s the net mouth t o reduce the occurrence of u n d e s i r a b l e l a r g e r p l a n k t e r s , such as medusae and ctenophores, i n the c a t c h . Shortcomings of the swing net method are i t s r e l a t i v e i m m o b i l i t y and the high v a r i a b i l i t y i n i t s d a i l y c a t c h . Over longer p e r i o d s , (weeks or months) marine f o u l i n g organisms ( b a r n a c l e s , mussels, etc) must be counteracted. The purse s e i n i n g method can be h i g h l y e f f e c t i v e f o r h a r v e s t i n g zooplankton and micronekton which swarm near the s u r f a c e during c e r t a i n stages of t h e i r l i f e h i s t o r y (eg e u p h a u s i i d s ) . However, t h i s method i s i m p r a c t i c a l when the p o p u l a t i o n s are d i s p e r s e d or i n deep subsurface l a y e r s . another method f o r h a r v e s t i n g n a t u r a l l y o c c u r r i n g or a r t i f i c i a l l y induced swarms i s by hand-operated or mechanical di p net. The eguipment i s i n e x p e n s i v e , but the c a t c h r a t e i s g e n e r a l l y lower than f o r purse s e i n i n g or t r a w l i n g . In the absence of swarms, d i p n e t t i n g i s i m p r a c t i c a l . Shropshire(1944) devised and experimented with a system of r o t a t i n g screens and spray n o z z l e s t o f i l t e r and c o l l e c t plankton from seawater on a continuous b a s i s . Although h i s apparatus overcomes t h e problem o f c l o g g i n g , i t has other r e s t r i c t i o n s . The screen drum must remain p a r t i a l l y emerged from 128 the water f l o w i n g i n t o i t i n order to permit e f f e c t i v e back washing by the spray j e t s . Thus, the drum must be f i x e d a t the water s u r f a c e , where plankton c o n c e n t r a t i o n s are o f t e n lower than a t subsurface l e v e l s . For continuous o p e r a t i o n at sea, S h r o p s h i r e ' s d e v i c e would r e q u i r e a conveyor to remove p l a c k t o n from the drum to a p r o c e s s i n g u n i t . An o b s t a c l e t o economic h a r v e s t i n g by t h i s method i s t h a t t h e r e are few l o c a l i t i e s where t h e r e i s enough plankton on a r e q u l a r b a s i s to j u s t i f y the continuous o p e r a t i o n of a machine designed t o h a r v e s t from a f i x e d p o s i t i o n by usinq t i d a l flow. In a d d i t i o n , the c a p i t a l c o s t of the u n i t compared with the r e l a t i v e l y low h a r v e s t i n q r a t e would l i k e l y produce a low r e t u r n on investment. In summary, there are s e v e r a l e f f e c t i v e methods of plankton h a r v e s t i n g ; the c h o i c e f o r a p a r t i c u l a r l o c a l i t y w i l l depend on the d i s t r i b u t i o n and behaviour of the t a r g e t s p e c i e s , on the o p e r a t i n g c o n d i t i o n s , and on the f i n a n c i a l r e s o u r c e s a v a i l a b l e . 5.22 Operating C o n d i t i o n s f o r Plankton H a r v e s t i n g Returning to the Jackson Report, a number of o p e r a t i n g c o n d i t i o n s which Jackson(1954) c o n s i d e r e d to be o b s t a c l e s to economic h a r v e s t i n g are d i s c u s s e d below. F i r s t , he argured t h a t plankton p o p u l a t i o n d e n s i t i e s f l u c t u a t e widely with time, place and depth (Harvey, 1950; Hardy and Paton,1947; R i l e y and Gorgy,1948)., F u r t h e r , without knowledge of the mechanisms i n f l u e n c i n g plankton p o p u l a t i o n s i t i s i m p o s s i b l e t o p r e d i c t t h e i r magnitudes or d e n s i t i e s i n a given region, (Note t h a t d u r i n g t h a t p e r i o d e l e c t r o n i c d e v i c e s f o r d e t e c t i n g l a y e r s or swarms of plankton were u n a v a i l a b l e ) . 129 Consequently, s e a r c h i n g time to l o c a t e hiqh c o n c e n t r a t i o n s of plankton would he e x c e s s i v e l y hiqh f o r economic h a r v e s t i n q . Since 1954, hiqh frequency sonar and echosounders (100 khz and greater) have been i n t r o d u c e d which are capable of d e t e c t i n g zooplankton, such as e u p h a u s i i d s (Beamish, 1969; Bary and Pieper,1970) and copepods (Barraclough et ajL. , 1969). Plankton surveys employing these instruments have q r e a t l y i n c r e a s e d our knowledqe of zooplankton and micronekton d i s t r i b u t i o n s and t h e i r v e r t i c a l m i g r a t i n g behaviour (Bary and P i e p e r , 1970; 0mori,l969). During s c i e n t i f i c sampling and h a r v e s t i n g o p e r a t i o n s , high frequency sounders are i n v a l u a b l e f o r l o c a t i n g s ubsurface plankton o r micronekton l a y e r s and f o r determining the best depth f o r towinq nets. Today, the processes c o n t r o l l i n q plankton production are b e t t e r understood than p r e v i o u s l y , althouqh the mathematical models developed so f a r (eq Steele,1974; Patten,1968) are not yet d i r e c t l y a p p l i c a b l e t o q u a n t i t a t i v e p r e d i c t i o n o f plankton abundance i n r e a l time and space. Despite t h i s , i n c e r t a i n r e q i o n s i t i s p o s s i b l e t o p r e d i c t q u i t e r e l i a b l y the occurrence o f dense aqqreqations of zooplankton and micronekton. For example, Koraaki {1967) has de s c r i b e d the seasonal s u r f a c e swarminq of Euphausia p a c i f i c a a l o nq the Sea of Japan and P a c i f i c c o a s t a l r e q i o n s of Japan i n r e l a t i o n to s u r f a c e water temperature. Off t h e west coast of Norway, Calanus f i n m a r c h i c u s o f t e n swarms near the s u r f a c e i n afte r n o o n and eveninq durinq s p r i n q and summer (fl i b o r q , 1976). A second, more s e r i o u s problem a c c o r d i n q t o Jackson(1954) i s t h a t the averaqe d e n s i t y of plankton p o p u l a t i o n s i s very low. Thus Clarke(1939) suqqested a maximum averaqe d e n s i t y of 0.1 130 g/m3 dry weight while Cashing {in Jackson,1954) c o n s i d e r e d 0,05 g/m3 dry weight to be a " r i c h " c o n c e n t r a t i o n . In h i s c a l c u l a t i o n s , Jackson used a va l u e o f 0.1 g/m3 f o r mobile h a r v e s t e r s and 0.01 g/m3 f o r s t a t i o n a r y h a r v e s t e r s i n t i d a l e s t u a r i e s . The above f i g u r e s a re too c o n s e r v a t i v e a c c o r d i n g to r e c e n t surveys of e x t e n s i v e marine r e g i o n s . Barraclough et al._ (1969) detected copepod c o n c e n t r a t i o n s o f about 1.5 g/m3 wet weight (0.3 g/m3 dry weight) by 200 khz echosounder and net sampling d u r i n g t r a n s e c t s of the s u b a r c t i c P a c i f i c Ocean i n s p r i n g . These r e s u l t s supported Klumov's (1961) c o n t e n t i o n that dense seasonal c o n c e n t r a t i o n s of zooplankton a re present over e x t e n s i v e areas as i n d i c a t e d by the food reguirements of p l a n k t i v o r o u s f i n whales. In B. C. c o a s t a l i n l e t s , e u p h a u s i i d c o n c e n t r a t i o n s o f about 2.5 g/m3 dry weight have been recorded (Pieper, i n Parsons,1972). Along the west coa s t o f Norway, Calanus c o n c e n t r a t i o n s as high as 6 t o 24 kg/m3 wet weight have o f t e n been observed i n s u r f a c e patches dur i n g s p r i n g and summer (Wiborg,1976). In the Southern Ocean, Euphausia superba c o n c e n t r a t i o n s of 10 t o 16 kg/m 3 wet weight have been r e p o r t e d (Burukovskiy, 1967; S a s a k i et al.. ,1968). Thus, on a s e a s o n a l b a s i s a t l e a s t , t h e r e are o f t e n e x t e n s i v e r e g i o n s i n which the plankton or micronekton c o n c e n t r a t i o n s are much higher than the "average" f i g u r e of 0.1 g/m3 dry weight used by C l a r k e (19 39) and Jackson(1954). Economic h a r v e s t i n g depends on the prompt l o c a t i o n and e x p l o i t a t i o n of such dense a g g r e g a t i o n s or patches r a t h e r than "average" c o n c e n t r a t i o n s . Another problem c i t e d by Jackson{1954) i s the v a r i a t i o n i n 131 zooplankton c a t c h composition and the mixing of phytoplankton and zooplankton i n the c a t c h . However, i n p r a c t i c e , d u r i n g a given harvest season the catch composition i n an area i s o f t e n very c o n s i s t e n t s i n c e mesh s i z e s and towing speed tend to s e l e c t f o r a s i n g l e s p e c i e s or c l o s e l y r e l a t e d s p e c i e s of r e l a t i v e l y uniform s i z e range. I n t h e S t r a i t of Georgia r e g i o n , commercial zooplankton catches d u r i n g t h e f a l l and winter months are comprised almost e n t i r e l y of Euphausia p a e i f i c a and other e u p h a u s i i d s p e c i e s (personal o b s e r v a t i o n ) . In Norway, the commercial zooplankton c a t c h along the coast i n s p r i n g and e a r l y summer i s almost e n t i r e l y of Calanus f i n m a r c h i c u s (Wiborg, 1976). Further o f f the Norway c o a s t , euphausiids are sometimes caught with C a l a n u s x e s p e c i a l l y near the s u r f a c e a t n i g h t . During summer months, though, medusae, ctenophores and diatoms can hinder h a r v e s t i n g o p e r a t i o n s along the c o a s t by c l o g g i n g nets or s p o i l i n g the c a t c h . Jackson (1954) a l s o s t a t e d t h a t c o n d i t i o n s such as bad weather and seasons o f low p l a n k t o n d e n s i t i e s may d i s r u p t the c o n t i n u i t y of plankton h a r v e s t i n g . Poor sea c o n d i t i o n s , though, are d e t r i m e n t a l to most types o f f i s h i n g o p e r a t i o n s . Seasonal v a r i a t i o n i n abundance a l s o a f f e c t s many c o n v e n t i o n a l f i s h e r i e s as w e l l as p o t e n t i a l plankton f i s h e r i e s . To reduce the adverse e f f e c t s of weather, i n r e g i o n s such as Norway and B. C , where plankton h a r v e s t i n g has commenced, the p r o t e c t e d waters of f j o r d s or i n l e t s have been f i s h e d i n w i n t e r , with o p e r a t i o n s moving to more exposed waters d u r i n g the calmer months of s p r i n g and summer. Jackson's f i n a l o b j e c t i o n t o plankton h a r v e s t i n g was t h a t 132 "not a l l forms of plankton are p a l a t a b l e or even n u t r i t i o u s , and some are t o x i c , p r e s e n t i n g very s e r i o u s problems i n bulk h a r v e s t i n g when we have i n s u f f i c i e n t knowledge of the composition of the community". He has assumed t h a t l a r g e s c a l e h a r v e s t i n g would i n v o l v e u n s e l e c t i v e f i l t r a t i o n of a l l t y p e s of plankton from sea water. On the c o n t r a r y , plankton h a r v e s t i n g gear can be h i g h l y s e l e c t i v e through a p p r o p r i a t e c h o i c e of mesh s i z e s , as i n c o n v e n t i o n a l f i s h e r i e s . 5.23 Examples of Present Micronekton and Zooplankton H a r v e s t i n g Operations. 5.231 A n t a r c t i c k r i l l , Euphausia superba T h i s euphausiid s p e c i e s l i v e s i n a l l s e c t o r s of the Southern Ocean, the f r i g i d waters surrounding A n t a r c t i c a and bounded t o the north by the A n t a r c t i c convergence zone; i t does not l i v e i n temperate seas. Except during the summer months from November t o l a t e March, the k r i l l spend most of t h e i r l i v e s a t 0 C beneath the i c e or a t the perimeter of the packice (Marr,1962; Shevtsov and Makarov, 1969). In open water during summer, t h e i r h o r i z o n t a l d i s t r i b u t i o n i s a s s o c i a t e d with the c o l d waters of the East Rind and Weddell D r i f t s ( M a r r , 1 9 6 2 ) . Surface swarms with d e n s i t i e s as high as 10-16 kg/m 3(Burukovskiy,1969) have been l o c a t e d a c o u s t i c a l l y and v i s u a l l y i n d a y l i g h t and a l s o a t n i g h t when t h e i r bioluminescence i s s u f f i c i e n t l y i n t e n s e (Ivanov, 1969; 1970) . The swarms are mobile aggregations of k r i l l , of one age group u s u a l l y . The diameters of swarms range from s e v e r a l meters t o s e v e r a l tens of meters. ,. Large areas s p o t t e d 133 with thousands of s m a l l e r swarms, known as " f e e d f i e l d s " are o f great i n t e r e s t commercially(Burukovskiy,1967). The r e g i o n which shows best promise f o r a commercial f i s h e r y , a c c o r d i n g to the S o v i e t s , i s the A t l a n t i c s e c t o r of the S c o t i a Sea and the area around t h e A n t a r c t i c P e n i n s u l a (Shevtsov and Makarov,1969; Ivanov,1970). Adult k r i l l (42-60 mm) tend t o swarm i n the v i c i n i t y of i s l a n d c h a i n s i n the S c o t i a Sea (Shevtsov e t al., , 1969) while more j u v e n i l e s (20-36 mm) are taken i n catches from oc e a n i c swarms(Ivanov,1970) . The formation of the swarms appears to be a s s o c i a t e d with areas of convergence, back eddies of c u r r e n t s and the c e n t r e s of c y c l o n i c g y r a l s (Buud, 1932). S o v i e t and Japanese s c i e n t i s t s ( A v i l o v et a l . ,1969; Bogdanov et al.. ,1969; E l i z a r o v , 1 9 7 1 ; S a s a k i e t a l . ,1968) b e l i e v e t h a t swarms are o f t e n found i n the v i c i n i t y of p e r s i s t e n t g y r a l s i n the covergence zones of the West Wind and Weddel D r i f t s , o f t e n near i s l a n d s and sea mounts which a l t e r the flow of these c u r r e n t s . Ivanov(1970) r e l a t e s r e s u l t s f o r and a g a i n s t the above g e n e r a l i z a t i o n s ; f u r t h e r r e s e a r c h i n t o the e f f e c t s of oceanographic c o n d i t i o n s on k r i l l swarming i s needed b e f o r e r e l i a b l e p r e d i c t i o n s can be made. The v e r t i c a l d i s t r i b u t i o n of Euphausia superba v a r i e s a c c o r d i n g t o d a i l y and s e a s o n a l c y c l e s which are dependent on l i f e h i s t o r y stage. A b r i e f d e s c r i p t i o n o f the k r i l l ' s l i f e h i s t o r y f o l l o w s . Two thousand to 10,000 k r i l l eggs per a d u l t female (Bargmann 1945; Nemoto,1968) are spawned during e a r l y summer i n 134 s h e l f and oce a n i c waters. They s i n k while developing i n t o the f i r s t n a u p l i u s which hatches a t depths of 100 0 m or more. During ascent t o the s u r f a c e the l a r v a e progress through the second n a u p l i u s , metanauplius and t h r e e c a l y p t o p i s stages. By the f u r c i l i a I stage, the l a r v a e are i n the upper 100 m where fe e d i n g on phytoplankton proceeds. They spend the l a t e f u r c i l i a stages (> 20 mm) mostly i n the upper 40 m. Growth i s r a p i d d u r i n g the summer as a body l e n g t h of about 22 mm i s reached i n the f i r s t year(Ruud,1932; Bargmann,1945). According t o Marr(1962) the k r i l l mature i n t o the sep a r a t e sexes as two year o l d s . Ivanov(1970) contends t h a t maturation takes three y e a r s , with breeding o c c u r r i n g i n the f o u r t h year. In the summer the v e r t i c a l d i s t r i b u t i o n s of j u v e n i l e s and a d u l t s are r e l a t e d to the th e r m o c l i n e . Age s t r a t i f i c a t i o n with depth i s observed when s u r f a c e swarming i s not present; the j u v e n i l e s are most abundant i n the p h y t o p l a n k t o n - r i c h waters above the 40 m t h e r m o c l i n e , while a d u l t s g e n e r a l l y predominate below 40 m (Shevtsov et al.. ,1969). The S o v i e t s have found t h a t the k r i l l are h a r v e s t a b l e from the time they begin t o swarm a t the s u r f a c e as l a t e j u v e n i l e s (about 30 mm). Shevtsov et a l . . (1969) suggest t h a t a d u l t k r i l l of 42-60 mm, which w i l l d i e before the next summer, should be e x p l o i t e d during the f i r s t h a l f o f the summer, while the j u v e n i l e s which are completing summer f e e d i n g and growth should be f i s h e d at the end of the summer. The Japanese have considered a l l stages over 20 mm to be h a r v e s t a b l e ( S a s a k i e t a l . , 1968). U n t i l r e c e n t l y the f i s h e r y f o r A n t a r c t i c k r i l l has been 135 e x p e r i m e n t a l , i n v o l v i n g a s m a l l number o f s h i p s from the S o v i e t Onion, Japan, and West Germany. S o v i e t research on k r i l l began i n the southern summer of 1961-62. E a r l y attempts at h a r v e s t i n g were by modified f i s h t r a w l s and f i s h pump u n i t s (Burukovskiy, 1967) . In 1964-65 aboard the t r a w l e r "Muksun" a c a t c h of 70 tons was processed i n t o 11 tons of k r i l l meal by a f i s h meal process. The product was t e s t e d with success as a l i v e s t o c k feed i n g r e d i e n t . The f o l l o w i n g summer the r e s e a r c h v e s s e l "Akademik K n i p o v i c h " accompanied by two s m a l l e r t r a w l e r s c a r r i e d out e x p l o r a t o r y h a r v e s t i n g i n the area of the South Shetlands and i n the S c o t i a Sea(Shevtsov and Makarov,1969). For the 1968 season, Ivanov(1970) r e p o r t e d a c a t c h o f 136 tons from a 10-day t r i a l f i s h e r y which used a " k r i l l t r a w l with codend mesh s i z e of 6 mm", although t h i s t r a w l c o u l d f i s h at d i f f e r e n t depths, most of the c a t c h was from the upper 10 m. Catch r a t e s averaged about 2 tons per hour, with a maximum r a t e of 7 t/h. More r e c e n t l y , the S o v i e t s have developed a mid-water o t t e r -t r a w l f o r k r i l l which has y i e l d e d 10-12 t/h (Lyubiraova e t a.l± ,1973). The annual S o v i e t c a t c h of k r i l l has not been r e p o r t e d i n the FAO Yearbook o f F i s h e r y S t a t i s t i c s , but there are u n o f f i c i a l r e p o r t s t h a t about 20,000 tons was caught i n 1974 { SCAR/SCOP., 1977) . The S o v i e t c a t c h i s processed i n t o a p r o t e i n paste f o r human consumption by p r e s s i n g the k r i l l , cooking the e x t r a c t e d f l u i d s and s e p a r a t i n g the coagulated paste, which i s then packed i n t r a y s and deep f r o z e n . Food products d e r i v e d from the k r i l l paste i n c l u d e "shrimp b u t t e r " and a melted cheese, as w e l l as ready-to-eat i n g r e d i e n t s f o r s a l a d s , s t u f f e d eggs and s t u f f e d 136 f i s h . . apparently the k r i l l paste has been accepted on the S o v i e t market, but t h e r e are p r i c e problems(Lyubimova e t al.. , 1973; C. Atkinson, p e r s o n a l communication). Japan has s e r i o u s l y i n v e s t i g a t e d the p o t e n t i a l of an A n t a r c t i c k r i l l f i s h e r y s i n c e 1964-65 when the "Omitaka Haru" of the Tokyo U n i v e r s i t y of F i s h e r i e s made a c r u i s e t o the D ' O r v i l l e and Foss Sea a r e a s ( S a s a k i et al.. ,1968) , They i n i t i a l l y experimented with a sguare net, with and without a f i s h pump attached t o the codend; a purse s e i n e was a l s o t e s t e d . The pumping and s e i n i n g technigues were co n s i d e r e d promising, but f u r t h e r inprovements were r e g u i r e d f o r commercial a p p l i c a t i o n . Ozawa et a]U (1968) r e p o r t e d o b s e r v a t i o n s on fiuphausia superba patches d u r i n g the 1964-65 c r u i s e . Comparatively frequent occurrences of k r i l l swarms were noted i n the area bounded by 61 S t o the n o r t h , the p a c k i c e to the south and between the meridians of 130 E and 150 E. In 1973, 59 tons of k r i l l , which was deep-frozen f o r s t o r a g e , was taken i n an i n e f f i c i e n t midwater t r a w l . Koyama et al(1974) developed a more e f f i c i e n t surface-midwater o t t e r t r a w l f o r k r i l l . The Japanese k r i l l c a t c h was reported as 643 tons i n 1974 and 1000 tons i n 1975 (FAO,1975;1976). Re c e n t l y , two l a r g e f i s h i n g c o r p o r a t i o n s i n Japan have announced t h e i r commitment to the development of a commercial f i s h e r y f o r A n t a r c t i c k r i l l ( F i s h i n g News I n t e r n a t i o n a l , 1 9 7 6 ) . In Japan, f r o z e n whole k r i l l has found a ready market f o r d i r e c t use i n t r a d i t i o n a l ways a p p l i e d to s i m i l a r s m a l l Crustacea. Research on d i v e r s i f i c a t i o n of product use i s a l s o 137 under way (PAG B u l l e t i n , 1974). West Germany entered the A n t a r c t i c k r i l l f i s h e r y i n the 1975 southern summer when the r e s e a r c h s h i p "Walther Herwig" landed 250 tons of k r i l l . German food t e c h n o l o g i s t s have s u c c e s s f u l l y developed sauces, soups and a sandwich paste from the k r i l l which they c l a i m t a s t e s very s i m i l a r t o c r a b ( F i s h i n g News I n t e r n a t i o n a l , 1 9 7 7 ) . Other products from the k r i l l i n c l u d e a " f i s h s t i c k " i n which packets of k r i l l , with c h i t i n removed, are pressed t o g e t h e r ( T . Parsons, personal communication). The g i a n t of the pet f i s h food i n d u s t r y , TetraWerke, has r e c e n t l y s t a r t e d t o market a new product, T e t r a K r i l l F l a k e s , which l i s t s whole f r e s h f r o z e n k r i l l and Calanus among i t s i n g r e d i e n t s . The p o t e n t a l production of t h e A n t a r c t i c k r i l l has not been measured d i r e c t l y but e s t i m a t e s have been p u b l i s h e d which r e l y on e s t i m a t i o n s o f the amount consumed by baleen whales and other k r i l l - e a t i n g animals (Peguegnat, 1958; Klumov, 196 1}. The s t a n d i n g s t o c k of k r i l l a c c o r d i n g to these sources i s between 800 m i l l i o n and 5000 m i l l i o n m e t r i c tons. Numerous e s t i m a t i o n s of the p r o d u c t i o n and biomass of the A n t a r c t i c k r i l l have been made (eg. McQuillan, 1962; Shevtsov,1963; Jonsgard and Ruud,1964; Mackintosh,1966; 1970; Lyubimova e t a l . . , 1973; Omura, 1973; F i s c h e r , 1974; Tomo and Marschoff,1974; Bverson, 1976) . Most estimates p l a c e the annual h a r v e s t a b l e y i e l d between 100 and 150 m i l l i o n t o n s , based on a v a r i e t y of approaches. These methods i n c l u d e t a l l y i n g the estimated annual consumption by past and present p o p u l a t i o n s of baleen whales and by other k r i l l p r e d a t o r s , e s t i m a t i o n of the 138 p r o p o r t i o n of primary p r o d u c t i o n i n c o r p o r a t e d i n t o k r i l l , and e x t r a p o l a t i o n from c a t c h r a t e s of k r i l l i n plankton h a u l s . Although the r e s u l t s are i n d i r e c t and very approximate est i m a t e s , i t appears t h a t EuEhausia sugerba has a p o t e n t i a l y i e l d of the same order of s i z e by weight as that of a l l the p r e s e n t l y e x p l o i t e d f i s h stocks combined (Burukovskiy,1967). There are c o n s i d e r a b l e d i f f i c u l t i e s f a c i n g a major h a r v e s t i n g o p e r a t i o n . The g r e a t B r i t i s h A n t a r c t i c oceanographer, J.W. S. Barr(1962), has e l o q u e n t l y s t a t e d the n a t u r a l r e s t r i c t i o n s on whaling and oceanographic o p e r a t i o n s i n the A n t a r c t i c r e g i o n , which would a l s o apply t o a l a r g e s c a l e k r i l l f i s h e r y : M A vast area of the A n t a r c t i c Ocean, i n v o l v i n g much of the r i c h e s t of the whaling qrounds, has f o r s i x v i t a l months, from June t o November, never been v i s i t e d by our v e s s e l s , nor i n the nature of t h i n q s i s i t ever l i k e l y to be. Indeed s i n c e the hiqhest l a t i t u d e s can only be a t t a i n e d i n January, Pebruary and March, i t i s c l e a r t h a t much of t h e r e q i o n south o f the 65th p a r a l l e l , and probably everywhere south of the A n t a r c t i c c i r c l e , an enormous c o a s t a l b e l t t h a t w i l l be demonstrated l a t e r t o be of major importance to the whalinq i n d u s t r y , i s v i r t u a l l y c l o s e d to n a v i q a t i o n f o r a l l but 3 months of the y e a r — a n a c c i d e n t of qeoqraphy t h a t w i l l always present a problem to A n t a r c t i c oceanoqraphers." Thus l a r q e s c a l e h a r v e s t i n q would be l i m i t e d t o the short southern summer season which i n c l u d e s bad weather too. Sasaki e t l l i (1968) have poi n t e d out ways f o r s h i p s t o a v o i d e x c e s s i v e l y rouqh seas caused by s h i f t i n q low pressure areas and so continue to h a r v e s t k r i l l . Of p a r t i c u l a r importance, thouqh, w i l l be the a b i l i t y to d e t e c t and/or p r e d i c t where and when the swarminq o f k r i l l i s l i k e l y to occur, as only a s m a l l f r a c t i o n of the k r i l l p o p u l a t i o n seems t o occur i n dense aqqregations a t one time. 139 T h i s behaviour a c t s as a n a t u r a l b u f f e r a g a i n s t the c o l l a p s e of the food pyramid i n which the k r i l l are a keystone. Making allowance f o r such c o n s i d e r a t i o n s , the p r o j e c t e d annual y i e l d of k r i l l t o man's h a r v e s t i s s t i l l i n the order of s e v e r a l tens o f m i l l i o n s of tons(PAG B u l l e t i n , 1 9 7 4 ) . In a n t i c i p a t i o n of the development of a major i n t e r n a t i o n a l f i s h e r y f o r the A n t a r c t i c k r i l l , an i n t e r n a t i o n a l convention t o d r a f t r e g u l a t i o n s f o r the new f i s h e r y i s being arranged by the 13 A n t a r c t i c t r e a t y nations(Anonymous,1977a). The n a t i o n s i n t e r e s t e d i n e x p l o i t a t i o n o f the k r i l l , i n c l u d i n g the U.S.S.R. , Japan, the United S t a t e s , West Germany, the U.K., Norway and A u s t r a l i a , have planned a prepara t o r y meeting i n Canberra f o r e a r l y 1978 t o draw up a d r a f t regime and to decide what a d d i t i o n a l n a t i o n s and i n t e r n a t i o n a l o r g a n i z a t i o n s w i l l be i n v i t e d t o p a r t i c i p a t e i n the convention conference. T h i s marks the f i r s t time i n t e r n a t i o n a l c o n t r o l s w i l l be placed on a f i s h e r y before the s p e c i e s i s n e a r i n g o v e r e x p l o i t a t i o n . 5.232 North A t l a n t i c copepods and k r i l l , Calanus f i n m a r c h i c u s and MeganYgtiphanes no r v e g i c a , Since about 1960, a s m a l l - s c a l e , experimental f i s h e r y f o r copepods has been developing i n f j o r d s of western Norway(Wiborg,1976). The p r i n c i p a l s p e c i e s taken i s Calanus f i n m a r c h i c u s which g e n e r a l l y has two gen e r a t i o n s per year i n Norwegian waters (Wiborg, 1954) . In c o a s t a l and s h e l f waters of western Norway, the o v e r w i n t e r i n g Calanus , as copepodite stage V, migrate to the s u r f a c e i n l a t e February; they soon mature as 140 a d u l t s and breed. Progeny from the March spawning reach copepodite stage V i n l a t e A p r i l or May, a t which time t h e r e i s o f t e n a maximum i n the biomass of plankton(Wiborg,1976). Along the c o a s t of northern Norway, the s p r i n g maximum i n plankton biomass may develop l a t e r i n May or i n e a r l y June. Although the second generation o f Calanus peaks i n biomass i n July-August, t h e r e i s o f t e n contamination of the h a r v e s t a b l e stock by medusae, cl a d o c e r a n s and other n e r i t i c p l a n k t e r s , e s p e c i a l l y i n the f j o r d s and c l o s e to the coast (Wiborg, 1976). The copepcdite stage V i n d i v i d u a l s from the l a t e summer c o h o r t overwinter i n deeper water before s t a r t i n g t h e c y c l e anew i n the f o l l o w i n g s p r i n g . The copepod f i s h e r y i s based upon the e x p l o i t a t i o n of s m a l l but dense aggregations of Calanus f i n m a r c h i c u s x O f f western Norway, Wiborg has observed l o c a l c o n c e n t r a t i o n s of 3-25 g/m3 and swarms with d e n s i t i e s of 6-15 kg/m3. The swarms are v i s i b l e as red c l o u d s , 1-3 m long and 0.5-1 m i n diameter, at the s u r f a c e or j u s t below i t . F l o c k s of s e a b i r d s and s h o a l s of f i s h o f t e n congregate i n f j o r d s and bays c o n t a i n i n g such swarms, which are most o f t e n observed d u r i n g the a f t e r n o o n and evening. During t h i s time, Calanus migrates to the s u r f a c e t o feed on phytoplankton, and i s c a r r i e d i n t o the i n l e t s by t i d a l currents(Wiborg,1976). Many types of nets have been t r i e d i n the copepod f i s h e r y , i n c l u d i n g c o n i c a l plankton nets, o t t e r t r a w l s , beam t r a w l s and nets using the parachute p r i n c i p l e ; the beam t r a w l i s most widely used at p r e s e n t (Wiborg, 1976), A t y p i c a l t r a w l has a m r e c t a n g u l a r mouth, 4 m wide by 3 m h i g h . The n e t t i n g i s a woven nylon f a b r i c produced commercially f o r making c u r t a i n s ; i t has meshes o f 0.5 x 0,8 mm and a p o r o s i t y o f about 0.5, although the s t r e n g t h of t h i s m a t e r i a l i s s u f f i c i e n t f o r s t a t i o n a r y swing ne t s , i t r e q u i r e s f u r t h e r support and p r o t e c t i o n from a coarse outer l a y e r of n e t t i n g i n towed t r a w l s . To prevent u n d e s i r a b l e l a r g e r organisms such as medusae from s p o i l i n g the c a t c h the net mouth i s o f t e n p r o t e c t e d by a b a r r i e r net with about 30 mm meshes. The shape of the t r a w l i s e i t h e r tapered from mouth to codend, or c y l i n d r i c a l f o r the f r o n t 7 m and c o n i c a l f o r the 10 m codend s e c t i o n . The beam t r a w l with attached b r i d l e i s towed on a s i n g l e warp 120-150 m long. The top and bottom s i d e s of the net are attached to s t e e l pipes as i n the s t a t i o n a r y nets. The bottom pipe i s b a l l a s t e d with lead i n the towed t r a w l ; depth of t r a w l i n g i s adjusted by changing the l e n g t h s of rope between the top bar and two s u r f a c e buoys, one at e i t h e r end of the bar. The u s u a l depths of towing are from 5 t o 25 m i n d a y l i g h t and 10 m to the s u r f a c e a f t e r dusk. As most of the boats i n the f i s h e r y l a c k f r e e z e r s , the d u r a t i o n o f towing i s prolonged, sometimes up t o 6-10 hours. The r a t i o n a l e i s t h a t the Calanus w i l l remain a l i v e l o n g e r and t h e r e f o r e f r e s h e r i n the net than i f s t o r e d without f r e e z i n g onboard the boat. A f t e r towing i s completed the c a t c h i s drained and f r o z e n a t shore f a c i l i t i e s . The above procedure appears to be a compromise to accommodate the s m a l l s i z e of the v e s s e l s i n the f i s h e r y a t the s a c r i f i c e of h a r v e s t i n g e f f i c i e n c y and product g u a l i t y . Long 142 hauls a re o f t e n plagued by c l o g g i n g o f meshes which reduces f i l t e r i n g e f f i c i e n c y . As the r e s u l t s of the hauls are not monitored f o r l o n g p e r i o d s , adjustments of the path of towing or depth of towing to improve t h e c a t c h r a t e may be overlooked. More s e r i o u s l y , the q u a l i t y of a l a r g e c a t c h may s u f f e r under the prolonqed pressure o f towinq and aqain while the c a t c h i s landed; as copepods a r e r i c h i n l i q u i d storaqe l i p i d s , they are e a s i l y ruptured by e x c e s s i v e pressure and handlinq. As i n any f i s h e r y , the l o c a t i o n of h a r v e s t a b l e c o n c e n t r a t i o n s i s the key to s u c c e s s f u l catches. V i s u a l s i q n s of s u r f a c e swarms i n c l u d e f l o c k i n q o f s e a b i r d s , the presence o f whales or basking sharks and d i r e c t s i q h t i n q s of the "red f e e d " . Hiqh frequency echosounders can detec t and r e c o r d d i s t i n c t i v e t r a c e s of subsurface zooplankton. C o n f i r m a t i o n o f such plankton l a y e r s can be made by h a u l i n q a s m a l l plankton net throuqh the a p p r o p r i a t e depth ranqe. The volume of a sample can be measured i n a c a l i b r a t e d c y l i n d e r with f i n e n e t t i n q over the bottom end. Reasonable c a t c h e s u s u a l l y r e s u l t from c o n c e n t r a t i o n s of 1-3 ml/m3 or more{Wiborq,1976). The s t a t i o n a r y n e t s , as suqqested by Hardy(1941), are u s u a l l y anchored i n sounds or between i s l a n d s where moderate t i d a l c u r r e n t s flow. A swinq net i s moored t o an anchor buoy by means of a b r i d l e and i s supported by two other buoys att a c h e d to the top bar o f the net's mouth; a s m a l l e r buoy i s t i e d t o the t h r o t t l i n g - l i n e on the codend. The net i s u s u a l l y s e t near the s u r f a c e and allowed t o o r i e n t a q a i n s t the t i d a l c u r r e n t s . Such nets are o f t e n tended by fishermen who a l s o p a r t i c i p a t e i n the 143 gape net f i s h e r y f o r salmon. One man i n a s m a l l boat (7.6-10.7 m v e s s e l s are used) can tend up t o 10-15 anchored swing nets. During the h e i g h t o f the plankton season, the swing nets are emptied i n the morning and sometimes a l s o i n the evenings. In s l a c k p e r i o d s the nets are l e f t open. To empty the s t a t i o n a r y net the codend i s hauled by the heaving l i n e and l i f t e d aboard by hand u n l e s s the c a t c h i s l a r g e . I n t h a t case a l i f t net of hea v i e r mesh i s p u l l e d over the codend and a winch i s used i f necessary. The c a t c h i s emptied i n t o a d r a i n i n g box before i t i s packaged i n p l a s t i c bags and taken t o a shore f r e e z i n g p l a n t . The s i z e o f catches from the swing nets v a r i e s a great d e a l . A few days of good catches are of t e n f o l l o w e d by long p e r i o d s without any c a t c h . When plankton i s abundant, catches o f up t o 400 kg per net per ni g h t have been recorded. The Calanus f i s h e r y i s p r i m a r i l y along the coast from Bergen t o Trondheim (60-64N) although s u c c e s s f u l t r i a l s were a l s o made i n the L o f o t e n area of northern Norway. The copepod season u s u a l l y begins at the end o f A p r i l and extends to l a t e June. Unfavourable c o n d i t i o n s can be caused by n o r t h e r l y winds which tend t o d r i v e s u r f a c e waters o f f s h o r e , c a r r y i n g the plankton c o n c e n t r a t i o n s away from the c o a s t . A l s o the heavy recr u i t m e n t of c l a d o c e r a n s and l a r v a e o f b e n t h i c i n v e r t e b r a t e s i n t o the n e t t a b l e p l a n k t o n may sometimes reduce the g u a l i t y o f the Calanus c a t c h i n f j o r d s and i s l a n d areas. Medusae and ctenophores such as B o l i n o p s i s infundibulum may o c c a s i o n a l l y become very abundant; they may c l o g towed nets but can be excluded from the cat c h o f swing nets by a b a r r i e r net placed a t 144 the mouth. At the same time a few k i l o m e t r e s o f f s h o r e , o u t s i d e the f j o r d water but s t i l l i n the c o a s t a l c u r r e n t , the zooplankton may c o n s i s t almost e n t i r e l y of Calanus f i n m a r c h i c u s (Wiborg, 1976) . During r e c e n t years up to 1975, the annual Norwegian catch O I Calanus was about 50 m e t r i c tons, mostly from s t a t i o n a r y n e ts. An experimental f i s h e r y with towed nets was planned f o r 1975 with the aim of l a n d i n g about 80 metric tons. The annual p r o d u c t i o n of zooplankton along the Norwegian co a s t i s estimated t o be of the order of 10-100 m i l l i o n tons. I t i s a n t i c i p a t e d that the y i e l d o f the Calanus f i s h e r y might be c o n s i d e r a b l y i n c r e a s e d , pending the d e t a i l e d study of swarming and other c o n c e n t r a t i o n s of plankton(Wiborg,1976). The main use o f Calanus i n Norway has been as a source of a s t a x a n t h i n i n salmonid r e a r i n g t o give the f i s h f l e s h the d e s i r e d red c o l o u r . Raw Calanus c o n t a i n s up t o 85 mg a s t a x a n t h i n /kg (0tne,1974) and as much as 918 mg/kg o f o i l ( F i s h e r e t a l x ,1952). The present p r i c e of Calanus (about Norwegian kr. 2-3/kg) i s too high f o r i t t o be used as a major d i e t a r y item i n aguaculture, although some f i s h farmers c a t c h Calanus themselves f o r l a t e r use. Experiments are underway to develop products from copepods f o r human consumption. The problems encountered are s i m i l a r t o those f o r k r i l l as the proximate composition of these z o o p l a n k t e r s i s very s i m i l a r . Because of the p a t t e r n o f d i s t r i b u t i o n and the r e l a t i v e l y 145 sho r t f i s h i n g season, no o v e r f i s h i n g of the copepod plankton i s p r e s e n t l y f o r e s e e n , even at c o n s i d e r a b l y h i g h e r l e v e l s of e x p l o i t a t i o n . In some Norwegian f j o r d s , k r i l l are f i s h e d commercially du r i n g February to A p r i l by means of l i g h t l u r e s and d i p nets. Meganyetiphanes n o r y e g i c a i s the p r i n c i p a l s p e c i e s although Thysanpessa i n e r m i s a l s o c o n t r i b u t e s . In 196 6 and subseguent years the annual c a t c h has been about 3000 kg which i s used mainly f o r c u l t u r e of rainbow trout(Wiborg,1966; J. Matthews, p e r s o n a l communication). 5.233 B r i t i s h Columbia ,s plankton f i s h e r y , E A p a e i f i c a and Calanus plumchrus . I n t e r e s t i n plankton h a r v e s t i n g along the P a c i f i c c o a s t of Canada was f i r s t s t i m u l a t e d by s c i e n t i s t s at the Nanaimo B i o l o g i c a l S t a t i o n . Parsons (1972) has d e s c r i b e d catches of the copepod, Calanus plumchrus , i n the v i c i n i t y of the F r a s e r B i v e r estuary. Experimental h a r v e s t i n g of t h i s copepod and E A p a e i f i c a was c a r r i e d out i n c o n j u n c t i o n with s e v e r a l commercial fishermen. The c a t c h was s o l d as a f i s h food to the Vancouver P u b l i c Aquarium and was a l s o t r i e d a t government f i s h h a t c h e r i e s ( P a r s o n s , 1 9 7 2 ) . For s e v e r a l years a f t e r the i n i t i a l experiments i n 1970 only a few fishermen were i n v o l v e d i n the f i s h e r y ; the annual c a t c h was l e s s than 10 tons of E^ p a e i f i c a . (The copepod f i s h e r y was not developed any f u r t h e r ) . Operating from a small boat, the f i r s t Canadian commercial plankton fishermen used a 10 146 m long sguare net (about 2 m x 2 m i n the mouth) which was equipped with s u r f a c e f l o a t s , b r i d l e and h o r i z o n t a l bars much as d e s c r i b e d f o r the towed nets i n the Norweqian copepod f i s h e r y . The mesh of the e u p h a u s i i d net was 6 mm k n o t l e s s nylon while the codend c o n s i s t e d of a p l a s t i c bucket which screwed onto a threaded s e c t i o n of p l a s t i c p i p e on the cone of the net. The net was towed on a p o l y e s t e r warp about 100 m i n lenqth and was r e t r i e v e d by hand. A f t e r d r a i n i n q , the c a t c h was f r o z e n onboard i n p l a s t i c baqs. In December 1974 experimental hauls were made with a modified Isaacs-Kidd midwater t r a w l aboard a 54-ton f i s h i n q v e s s e l equipped with winches and f r e e z e r . The IKMT desiqn proved to be more v e r s a t i l e f o r s e l e c t i n q depth of f i s h i n q than the net with s u r f a c e f l o a t s and e a s i e r f o r emptyinq the c a t c h throuqh i t s z i p p e r e d codend. F u r t h e r m o d i f i c a t i o n s i n t r o d u c e d to s c a l e the qear f o r commercial use i n c l u d e d e n l a r q i n q the f i l t e r i n q area by combininq two square-mouthed (3.7 m x 3.7 m) nets alonq a common s i d e ; the r e s u l t i n q "bonqo" IKMT had a mouth area of about 26 m2. The nets were att a c h e d to a s i n q l e l a r q e depressor vane and v i a the wire-rope b r i d l e to a s i n q l e towinq warp. The bonqo nets c o u l d be r a i s e d with a 12 m s t e e l boom so that they c l e a r e d the boat's deck, a l l o w i n q the c a t c h t o be dumped i n a d r a i n i n q box. The r e s u l t i n g arranqement kept net handlinq time reasonably s h o r t , but d i d tend t o s t r a i n the nets when catches of over 200 kq were l i f t e d i n each net. The hiqh aspect of the r i q q i n q when the nets were hauled i s not a handicap i n the s h e l t e r e d waters of the S t r a i t of Georgia r e g i o n , but would p o s s i b l y present h a n d l i n g problems i n rough seas or i n a hiqh 147 wind. The v e s s e l d e s c r i b e d above has been used i n , e u p h a u s i i d h a r v e s t i n g i n Saanich I n l e t and i n the C r o f t o n area (Stuart Channel and Sansum Narrows). During January-March 1975 appproximately 40 metric tons were caught i n Saanich I n l e t ; i n 1976 the v e s s e l ' s t o t a l f o r a comparable period was about 45 tons . During 1976, f i v e other v e s s e l s j o i n e d the euphausiid f i s h e r y ; a l l were eguipped with IKMT t r a w l s g e n e r a l l y about 13 rn2 i n mouth area. The a d d i t i o n a l c a t c h from Saanich I n l e t i n 1976 was about 6.7 tons f o r a t o t a l of 51.7 ton s . Other l o c a l i t i e s where E. p a c i f i c a was harvested d u r i n g 1976 were Howe Sound (2.5 t o n s ) , J e r v i s I n l e t (4,4 t o n s ) , and S e c h e l t I n l e t (10.6 t o n s ) . The h a r v e s t i n g season from January t o A p r i l 1977 saw s h i f t i n g p a t t e r n s o f f i s h i n g e f f o r t . The boat with bongo IKMT nets moved o p e r a t i o n s t o the C r o f t o n area where 68 tons were landed i n 45 days f i s h i n g . Another v e s s e l a l s o harvested f o r 9 days i n the C r o f t o n area, c a t c h i n g 8,8 tons. T o t a l c a t c h from the C r o f t o n area was t h e r e f o r e about 76.8 tons i n e a r l y 1977, Meanwhile i n Saanich I n l e t two other boats landed about 9 tons of E x E a c i f i c a i n 1977, A d d i t i o n a l s m a l l c a t c h e s were recorded f o r Malaspina S t r a i t (1 ton) and Howe Sound (0,2 t o n ) . The c a t c h from S e c h e l t I n l e t rose to 17.4 tons i n 1977. T o t a l e u p h a u s i i d l a n d i n g s from a l l areas i n the S t r a i t of Georgia r e g i o n i n e a r l y 1977 were about 104 tons. The breakdown of catch by area i s summarised i n Table 21. 148 TABLE 21, Summary of eu p h a u s i i d c a t c h e s by s t a t i s t i c a l area ( F i s h e r i e s and Marine Service) and l o c a l i t y f o r 1975-77. Year S t a t i s t i c a l L o c a l i t y C a tch areas J J L tons 1975 18 Saanich I n l e t 40.0 1976 18 Saanich I n l e t 51.7 16 S e c h e l t I n l e t 10.6 16 J e r v i s I n l e t 4.4 28 Howe Sound 2.5 A l l T o t a l 69.2 1977 17 C r o f t o n 76.8 18 Saanich I n l e t 9.0 16 S e c h e l t I n l e t 17.4 16 Malaspina S t r a i t 1.0 28 Howe Sound 0.2 A l l T o t a l 104. 4 The B r i t i s h Columbia e u p h a u s i i d f i s h e r y i s c a r r i e d out a t ni g h t when the e u p h a u s i i d s have migrated c l o s e to the s u r f a c e . Heavy patches of t h e s e z o o p l a n k t e r s can be detected by h i g h -freguency echosounders or sonar. With p r a c t i c e , i t i s p o s s i b l e to t e l l whether a given showing on the echosounder w i l l y i e l d reasonable catches. T e s t samples taken with a smal l high speed plankton sampler such as the M i l l e r net are a l s o u s e f u l to judge commercial c o n c e n t r a t i o n s . The e f f e c t of experience on h a r v e s t i n g success i s c l e a r l y e v i d e n t i n Fig u r e 35 which shows the p a t t e r n of i n d i v i d u a l boats* c a t c h per u n i t e f f o r t (CPE) with c o n t i n u i n g plankton f i s h i n g a c t i v i t y over the f i r s t season or two i n the f i s h e r y . With the exce p t i o n of the curve on the l e f t , each p o i n t on the curves r e p r e s e n t s the average CPE f o r a t r i p ; the corres p o n d i n g number of days f i s h e d i s cumulative from date o f en t r y i n t o the f i s h e r y . Values of CPE i n the f i r s t curve are based on d a i l y c a t c h e s from a v e s s e l using a 3.7 x 3.7 m o t t e r t r a w l ; a b r i d g e l o g o f d a i l y catch had been maintained by 149 0 10 20 30 40 50 60 70 DAYS FISHED FIGUBE 35. The e f f e c t of f i s h i n g experience on e u p h a u s i i d f i s h i n g success, CPE i n S t r a i t o f Georgia waters dur i n g the 1976 and 1977 seasons. the crew who were on t h e i r f i r s t plankton t r i p . The general trend i n CPE i n c l u d e s a sharp r i s e during the f i r s t one or two t r i p s . During subseguent t r i p s i n the same season a plateau i n CPE developed f o r two v e s s e l s . One boat reached a second and higher p l a t e a u d u r i n g i t s second season, as CPE i s q u i t e dependent on f i s h i n g experience these p a t t e r n s c o u l d be d e s c r i b e d as " l e a r n i n g " curves. A l s o , the t h r e s h o l d CPE f o r a new fisherman t o stay i n the f i s h e r y appears to be about 100 kg/day. One fisherman q u i t when h i s f i r s t t r i p y i e l d e d l e s s than t h i s while a second q u i t a f t e r a p a r t i c u l a r l y d i s a p p o i n t i n q 150 t r i p even though on t h e average he had managed only m a r g i n a l l y b e t t e r f o r over a season. Jackson(1954) estimated the c o s t of h a r v e s t i n g a dry ten of plankton based on assumed c o n c e n t r a t i o n s of plankton (0.1 g dry wt/m 3), h a r v e s t i n g hours per season, f i l t e r i n g e f f i c i e n c y of nets and so on; h i s l o w e s t e s t i m a t e was 1800 pound s t e r l i n g . The present market p r i c e f o r f r o z e n e u p h a u s i i d s i n B r i t i s h Columbia i s e q u i v a l e n t t o about $3530 per dry ton {2000 l b . ) , based cn a 0.17 wet to dry weight c o n v e r s i o n f a c t o r . What i s the c o s t to the plankton fisherman f o r producing the e g u i v a l e n t of a dry ton {ie. 11,800 lb.) of f r o z e n euphausiids? To estimate the c o s t s of e u p h a u s i i d h a r v e s t i n g a g u e s t i o n a i r e was c i r c u l a t e d t o s e v e r a l euphausiid fishermen a f t e r the 1976 season. {The g u e s t i o n a i r e form i s a v a i l a b l e from the author upon reguest.) Only two completed g u e s t i o n a i r e s were r e c e i v e d . Although t h i s sample s i z e i s s m a l l , the boats of the fisherman who r e p l i e d are considered to be r e p r e s e n t a t i v e of the multi-purpose v e s s e l s p r e s e n t l y engaged i n the f i s h e r y . Both v e s s e l s are p r i m a r i l y used as salmon t r o l l e r s and are eguipped with f r e e z e r s f o r on-board p r o c e s s i n g of the c a t c h . ( I t s h o u l d be noted that f r e e z i n g c a p a c i t y tends t o be the l i m i t i n g f a c t o r f o r the maximum d a i l y c a t c h as the e u p h a u s i i d s must be promptly f r o z e n l e s t they s p o i l . ) The major eguipment expenses t o gear up f o r the f i s h e r y are f o r the net, a high-freguency sounder (100 khz or more), and p o s s i b l y a h y d r a u l i c winch or drum i f the v e s s e l was not p r e v i o u s l y so equipped. Operating expenses i n c l u d e f u e l and l u b r i c a t i n g o i l and p l a s t i c bags i f used; crew shares are another major item. By p r o r a t i n g the i n i t i a l eguipment c o s t s 151 over the f i r s t year, the f o l l o w i n g c o s t s per dry ton were estimated: One v e s s e l f i s h e d 19 days p l u s 3 days t r a v e l l i n g ; c a t c h 1.6 "dry" t ons. Operating e x p e n s e s ( f u e l / o i l , e t c ) a t $32.50/day $610, Crew shares 596. Equipment costs($3200,prorated) 2000. T o t a l $3206. Therefore t h i s boat made a p r o f i t of about $324 per "dry" ton a f t e r payinq o f f the net, winch, warp and echosounder w i t h i n the f i r s t year. Of course t h i s equipment i n subsequent years c o u l d be used to har v e s t euphausiids at a p r o f i t l e v e l of about $230 0 per dry to n , not i n c l u d i n g d e p r e c i a t i o n c o s t s . The other v e s s e l f i s h e d 5 9 days p l u s 10 days t r a v e l l i n g ; c a t c h 4,6 "dry" tons. Operating e x p e n s e s ( f u e l / o i l , e t c ) a t $ 1 9 . 0 0 / d a y $285. Crew shares(25% gross) 887, Equipment costs{$705,prorated) 153. T o t a l $1325. T h i s v e s s e l made a f i r s t year p r o f i t of about $2205 per "dry" t on ($412 per wet metric t o n ) ; equipment c o s t s were lower as the fisherman made h i s own net and the boat was alre a d y equipped with a winch and sonar. Takinq i n t o account d e v a l u a t i o n of the pound s t e r l i n q from i t s l e v e l i n the e a r l y 1950's, and the i n f l a t i o n of p r i c e s i n the i n t e r v e n i n q y e a r s , i t i s apparent t h a t Jackson's c o s t a n a l y s i s s e r i o u s l y o v e r estimates the c o s t of h a r v e s t i n q zooplankton such as eu p h a u s i i d s i n B r i t i s h Columbia waters and l i k e l y the c o s t of h a r v e s t i n q copepods and k r i l l i n Norweqian waters. E u p h a u s i i d h a r v e s t i n q i n the S t r a i t o f Georqia r e q i o n can be q u i t e p r o f i t a b l e f o r multi-purpose f i s h i n q v e s s e l s , e s p e c i a l l y because the h a r v e s t i n q season comes a f t e r the summer salmon f i s h e r y and before the s p r i n q P a c i f i c h e r r i n q f i s h e r y . Zooplankton h a r v e s t i n q , then, can act as a u s e f u l form of 152 employment f o r a l i m i t e d number o f fishermen d u r i n q t h e i r g e n e r a l l y slow time of the year. In a d d i t i o n , t h e r e i s a new and growinq manufacturing i n d u s t r y f o r p r o c e s s i n g the plankton i n t o v a r i o u s products f o r export and domestic markets. De s p i t e the promising beginnings of t h i s new B r i t i s h Columbia f i s h e r y and i n d u s t r y , the f u t u r e i s u n c e r t a i n . Recently, Mr. B,ft. C r o u t e r , D i r e c t o r o f the F i e l d O p e r a t i o n s , D i r e c t o r a t e of the F i s h e r i e s S e r v i c e , has i s s u e d management g u i d e l i n e s "to meet the t h r e a t of o v e r f i s h i n g the resource"(Anonymous,1977b). A f t e r b r i e f l y d e s c r i b i n g methods f o r h a r v e s t i n g e u p h a u s i i d s , the statement c o n t i n u e s as f o l l o w s : "Zooplankton form the b a s i c food resources f o r many marine f i s h e s , and a plankton f i s h e r y c o u l d reduce t h e i r food supply u n l e s s c a r e f u l l y c o n t r o l l e d . A c c o r d i n g l y , the g u i d e l i n e s f o r t h i s f i s h e r y take i n t o c o n s i d e r a t i o n t h i s important c o n s t r a i n t . C u r r ent s c i e n t i f i c knowledge i n d i c a t e s t h a t a f i s h e r y i n o f f s h o r e waters c o u l d have l i t t l e e f f e c t due to the vast plankton r e s o u r c e a v a i l a b l e . However, i n the S t r a i t of Georgia, zooplankton abundance i s s m a l l e r and a l a r g e f i s h e r y w i l l not be permitted. The g u i d e l i n e s and management c o n t r o l f o r the zooplankton f i s h e r y are as f o l l o w s . To enable t h i s developing i n d u s t r y to design f i s h i n g eguipment and processing technology i n p r o t e c t e d waters, a f i s h e r y of not more than 500 tons a n n u a l l y w i l l be allowed i n the S t r a i t of Georgia u n t i l 1980. T h i s amount i s l e s s than one-tenth of one per cent of the annual food requirements of a l l f i s h e s i n the S t r a i t of Georqia, a c c o r d i n q to s c i e n t i s t s . The f i s h e r y i n Georqia S t r a i t (sic) i s a l s o l i m i t e d t o the winter months on l y (January t o March a n n u a l l y ) , to minimize the p o s s i b i l i t y of c a t c h i n q l a r v a l f i s h o r s h e l l f i s h which are found i n the summer months. Zooplankton are a l s o near the end of t h e i r l i f e c y l c e i n the winter months when they w i l l be allowed to be f i s h e d . A f t e r 1980, there w i l l be a moratorium on plankton f i s h i n q i n the G u l f of Georqia ( s i c ) . I t i s 153 a n t i c i p a t e d t h a t t h e i n d u s t r y w i l l have developed t o the stage where they w i l l be ab l e to f i s h i n the ou t s i d e waters by t h a t time. F u r t h e r p o l i c y development f o r the a n t i c i p a t e d f i s h e r y o u t s i d e the S t r a i t o f Georgia w i l l be developed i n the f u t u r e as i n f o r m a t i o n from on-going s t u d i e s becomes a v a i l a b l e . " In Chapter 6, the announced g u i d e l i n e s to c o n t r o l plankton h a r v e s t i n g i n the S t r a i t of Georgia w i l l be compared with c o n c l u s i o n s obtained from a p p l i c a t i o n o f the Beverton-Holt y i e l d model t o c o h o r t s of E. p a c i f i c a . The apparent reasoning behind the g u i d e l i n e s w i l l a l s o be d i s c u s s e d . At t h i s p o i n t , however, some of the advantages o f a c o n t i n u i n g but c l o s e l y monitored f i s h e r y f o r euphausiids i n the S t r a i t of Georgia w i l l be mentioned. At present, the f i s h e r y i n v o l v e s s e v e r a l m u l t i -purpose v e s s e l s which otherwise would be i d l e f o r much of the winter. In g e n e r a l , these boats would not be s u i t a b l e f o r an o f f s h o r e plankton f i s h e r y i n winter due to rough sea c o n d i t i o n s . One only has to look to t h e poor s a f e t y r e c o r d of the s p r i n g f i s h e r y f o r P a c i f i c h e r r i n g o f f the west coa s t of Vancouver I s l a n d t o a p p r e c i a t e the d i f f i c u l t i e s o f o p e r a t i n g i n that area f o r extended p e r i o d s i n winter. For the eupha u s i i d h a r v e s t i n g / p r o c e s s i n g i n d u s t r y to r e l y e n t i r e l y on st o c k s i n the " o u t s i d e " waters would l i k e l y r e q u i r e s p e c i a l l y designed and c o n s t r u c t e d v e s s e l s to operate under harsh sea c o n d i t i o n s {unless other s h e l t e r e d waters were a v a i l a b l e f o r h a r v e s t i n g i n the ''outside" a r e a s ) . An o f f s h o r e e u p h a u s i i d f i s h e r y i n summer would have t o compete with c o n v e n t i a l f i s h e r i e s f o r m u l t i -purpose v e s s e l s . Conseguently, heavy c a p i t a l investment by fishermen and /or the p r o c e s s i n g i n d u s t r y would l i k e l y be r e q u i r e d f o r new v e s s e l c o n s t r u c t i o n when t h e r e are a l r e a d y 15U s u i t a b l e v e s s e l s f o r a l i m i t e d " i n s h o r e " e u p h a u s i i d f i s h e r y . That i s not to say t h a t an o f f s h o r e e u p h a u s i i d f i s h e r y i s not f e a s i b l e , but t h a t the f e a s i b i l i t y has yet to be e s t a b l i s h e d . A f u r t h e r advantage to a c o n t i n u i n g i n s h o r e e u p h a u s i i d f i s h e r y i s t h a t i t o f f e r s an o p p o r t u n i t y to monitor the response of q u i t e w e l l - d e f i n e d p o p u l a t i o n s t o h a r v e s t i n g and n a t u r a l m o r t a l i t i e s . The approach of a d a p t i v e c o n t r o l of the f i s h e r y (eg. Walters and H i l b o r n , 1976) c o u l d p r o v i d e v a l u a b l e i n f o r m a t i o n f o r management of the " o u t s i d e " water s t o c k s as w e l l . The c a r r y i n g c a p a c i t y of such zooplankton p o p u l a t i o n s f o r i n c r e a s e d p o p u l a t i o n s of commercial f i s h s p e c i e s might a l s o be assessed i n t h i s s i t u a t i o n . Such a program would r e g u i r e c l o s e s c r u t i n y , though, as a c r a s h i n e u p h a u s i i d p o p u l a t i o n s w i t h i n the S t r a i t of Georgia area could be d i s a s t r o u s to salmon and h e r r i n g production i n the southern B.C. waters. 155 CHAPTER 6: NET SELECTIVITY, YIELD AND MANAGEMENT CONSIDERATIONS 6.1 I n t r o d u c t i o n A l l members of a sampled or harvested p o p u l a t i o n are g e n e r a l l y not e q u a l l y s u s c e p t i b l e to capture by a qiven qear, due to p h y s i c a l p r o p e r t i e s o f the qear and/or t c morpholoqical or b e h a v i o u r a l d i f f e r e n c e s w i t h i n the p o p u l a t i o n . Consequently, i n f o r m a t i o n on the s e l e c t i v i t y of the v a r i o u s equipment i n use i s important t o the e s t i m a t i o n of p o p u l a t i o n parameters and t o the manaqement of a f i s h e r y . 6.2 Net S e l e c t i v i t y Although no attempt was made here to separate the e f f e c t s of b e h a v i o u r a l and mechanical s e l e c t i o n processes or to raeaure s e l e c t i v i t y throuqh experimental designs(eg. Pope et aJL. , , 1975), the r e l a t i v e s e l e c t i v i t y o f t h e d i f f e r e n t qear types used was assessed by comparing the compositions of catches taken under s i m i l a r c o n d i t i o n s . S e l e c t i v i t y here r e f e r s t o l e n g t h s e l e c t i o n as body l e n g t h was the measure of s i z e used. Conversions to weight and age are p o s s i b l e with r e l a t i o n s h i p s d e s c r i b e d e a r l i e r . In Chapter 2, r e f e r e n c e was made t o net s e l e c t i v i t y when comparing c a t c h curves f o r MNT and SCOR nets ( F i g u r e 17}. I t appeared t h a t , although s i m i l a r mesh s i z e s were used i n the n e t s , the numbers of l a r g e r E t i p a c i f i c a (over 19 mm) were under-represented i n the SCOR samples. Avoidance of the v e r t i c a l l y hauled net by the more mobile euphausiids was suggested as a 156 p o s s i b l e cause. On Saanich I n l e t c r u i s e s i n J u l y and august 1975, e x t e n s i v e sampling with M i l l e r n e ts and SCOR nets r e s u l t e d i n s i m i l a r l y shaped length freguency d i s t r i b u t i o n s f o r both nets i n each month (F i g u r e 9A, B) . The l a r g e r euphausiids did not appear t o be under-represented i n the SCOR catches. However, i n October-February samples from Saanich I n l e t , l a r g e e u p h a u s i i d s (over 19 mm) were s c a r c e i n comparison with samples from J e r v i s I n l e t and the S t r a i t o f Georgia ( c f . F i g u r e s 11 and 13). Thus an a l t e r n a t i v e reason f o r the d i f f e r e n c e s i n the average c a t c h curves f o r the n e t s may be the lower a v a i l a b i l i t y of l a r g e r e uphausiids i n Saanich I n l e t d u r i n g the f a l l and winter months, due to m o r t a l i t y o r oth e r causes. Percentage compositions by s i z e c l a s s f o r MNT, SCOR and IKMT euph a u s i i d samples c o l l e c t e d at Saanich I n l e t s t a t i o n SAa-2 on august 21, 1975 are shown i n F i g u r e 36. There i s g e n e r a l agreement i n the p o s i t i o n of the maximum a t 14-15 mm, but more v a r i a t i o n i n r e p r e s e n t a t i o n a t the t a i l s of the l e n g t h d i s t r i b u t i o n s . The SCOR net sample i n c l u d e d specimens from 9 to 22 mm; a second mode at 18-22 mm was a l s o present. The MNT sample i n c l u d e d 8-21 mm i n d i v u d u a l s , but showed only a shoulder at 18-19 mm and a s i n g l e specimen at 21 mm as evidence of a second mode. In c o n t r a s t , the IKMT d i s t r i b u t i o n ranged from 12 to 21 mm. Only a shoulder at 17-19 mm and a s i n g l e i n d i v i d u a l a t 21 mm i n d i c a t e d t h a t a second mode might be present i n the p o p u l a t i o n . S e l e c t i v i t y of the IKMT i s more n o t i c e a b l e at s m a l l e r modal 157 S A A 2 AUGUST 1975 BODY LENGTH mm FIGURE 36. Comparison of s i z e composition of euph a u s i i d c a t c h from SCOR (•), MNT (v) and IKMT (•) hauls i n Saanich I n l e t , august 1975. s i z e s , a comparison o f the s i z e composition of e u p h a u s i i d s from SCOR and IKMT samples from March 1975 i s given i n F i g u r e 37. The SCOR d i s t r i b u t i o n shows a s m a l l mode at 8 mm, a l a r g e r mode at 13 mm and a low shoulder at 16-19mm. The IKMT d i s t r i b u t i o n shows a high degree of s e l e c t i v i t y f o r the 14-15 mm e u p h a u s i i d s ; i n d i v i d u a l s of 13 mm body l e n g t h and l e s s are g r e a t l y under-represented. A f i n a l example i n F i g u r e 38 compares the c a t c h composition of c o n s e c u t i v e tows by MNT and by a commercial t r a w l with s i m i l a r mesh s i z e as the codend of the IKMT used i n t h i s study { ca. 5 mm). The MHT d i s t r i b u t i o n i n d i c a t e s a mode at 12 mm while the d i s t r i b u t i o n f o r the commercial net has a maximum at 14mm. Again, s e l e c t i o n by t h i s type o f t r a w l at body l e n g t h s over 13 mm i s apparent. 158 u O V 40 30 20 10 .c. SAA 4.7 MARCH 1975 V /•• \ m \ 10 II 12 13 14 15 BODY LENGTH mm Vi 17 18 19 20 FIGURE 37, Comparison of s i z e composition of eu p h a u s i i d c a t c h from SCOR («) and IKMT (•) hauls i n Saanich I n l e t , March 1975. In summary, the SCOR and MNT nets give g u i t e c o n s i s t e n t s i z e d i s t r i b u t i o n s f o r contemporary samples from the same l o c a l i t y . In c o n t r a s t , the IKMT and commercial t r a w l s s e l e c t e u p h a u s i i d s with body l e n g t h s over about 13-14 mm. For the s p r i n g c o h o r t s of E t p a e i f i c a t h i s corresponds t o an age of recruitment t o the f i s h e r y o f about 5 months (cf. F i g u r e s 10,12 and 14) which i s reached by l a t e September to e a r l y October. 6.3 F a c t o r s A f f e c t i n g Y i e l d of the Euphausiid F i s h e r y The y i e l d or c a t c h i n weight of the euph a u s i i d f i s h e r y w i l l depend on s e v e r a l f a c t o r s , i n c l u d i n g f i s h i n g e f f o r t , time o f h a r v e s t i n g , mesh s i z e , and c h a r a c t e r i s t i c s of the harvested c o h o r t s (eg. growth r a t e , n a t u r a l m o r t a l i t y r a t e and maximum s i z e d u r i n g the h a r v e s t a b l e l i f e s p a n ) . I t has been shown t h a t 159 FIGURE 38. Comparison of s i z e composition of e u p h a u s i i d c a t c h from M i l l e r net (MNT) and commercial plankton net tows taken c o n s e c u t i v e l y i n Saanich I n l e t , January 1977. growth i n each year f o r E^ p a c i f i c a c o h o r t s can be d e s c r i b e d by von B e r t a l a n f f y growth c u r v e s and t h a t the l e n g t h : weight exponents are n e a r l y 3.0 f o r both sexes. In a d d i t i o n , n a t u r a l m o r t a l i t y i s f a i r l y constant from e a r l y maturity (ca. 12 mm) u n t i l l a t e adulthood (over 18 mm). Conseguently the assumptions of the model of Beverton and Holt(1957) appear to be s a t i s f i e d . The f o l l o w i n g a n a l y s i s examines t h e y i e l d o f Ei3L p a c i f i c a c o h o r t s from Saanich I n l e t by using the e g u i l i b r i u m approach of Beverton and Holt(1957) and by using t h e o p t i m a l dynamics approach of C l a r k et §JLA (1973). The parameters of the Beverton-Holt model f o r f i r s t - and 160 second-year p a e i f i c a c o h o r t s observed i n 1975 are given i n Table 22. Values of were c a l c u l a t e d from the c o r r e s p o n d i n g Lao v a l u e s obtained i n Chapter 2. In terms of w eight ? the von B e r t a l a n f f y eguation i s : w(t) = l a [ 1 - e x p { - K ( t - t 0 ) ) ] where w(t) i s the body weight at time t , and i s the asymptotic weight. K and t 0 are the same as f o r the von B e r t a l a n f f y equation f o r growth i n l e n q t h . I n T a b l e 22, the aqe of r e c r u i t m e n t , t r , was estimated from the body le n q t h of f u l l r e c r u i t m e n t i n t o the mid-water t r a w l f i s h e r y ( 1 3 - 1 4 mm). Age of e x i t from the f i s h e r y , T E , was taken as t h e c o h o r t age at the end of f i s h i n g i n A p r i l . The two c o h o r t s were examined as i f they were d i f f e r e n t s t o c k s , due to the l a r q e d i f f e r e n c e i n growth parameters between the f i r s t and second qrowinq seasons. TABLE 22. Beverton-Holt y i e l d model parameters f o r f i r s t - and second-year E^ p a e i f i c a c o h o r t s i n Saanich I n l e t d u r i n q 1975. Parameter S p r i n q 74 S p r i n q 75 ¥^ (mq) 73.4 26.2 K 0.45 0.35 t a (mo) 9.2 -0.5 t r (mo) 16. 5. T E (mo) 22. 11. n (min) 0.50 0.35 H (max) 0.80 0.70 The e f f e c t s of v a r y i n g the age at f i r s t c a p t u r e , t c , and the f i s h i n g m o r t a l i t y , F, on the e q u i l i b r i u m y i e l d / r e c r u i t f o r each cohor t are shown i n the y i e l d contours of F i q u r e 39 and 40. For both c o h o r t s , y i e l d / r e c r u i t r i s e s much f a s t e r f o r a 161 FIGOBE 39. Contours of e g u i l i b r i u m y i e l d / r e c r u i t f o r the s p r i n g 75 cohort of E._ p a c i f i c a i n a f i s h e r y commencing a t time t= 11 mo. ( A p r i l ) . I n part A, M - 0.35 while i n part B, M = 0.70; K =0.35 throughout. 162 FIGOEE 40. Contours o f e g u i l i b r i u m 74 cohort of JU p a c i f i c a i n time t=22 mo. In pa r t A, M = = 0.80; K = 0.4 5 throughout. y i e l d / r e c r u i t f o r the s p r i n g a f i s h e r y commencing a t 0.50 while i n part B, I! given i n c r e a s e i n f i s h i n g m o r t a l i t y i f h a r v e s t i n g begins when 163 the c o h o r t s are f i r s t a v a i l a b l e t o the t r a w l f i s h e r y . Given t h a t the h a r v e s t i n g season always f i n i s h e s at the end of March, the y i e l d / r e c r u i t of the s p r i n g 75 cohort (at a n a t u r a l m o r t a l i t y o f 0.35 and a f i s h i n g m o r t a l i t y of 0.20) i n c r e a s e s by 50 to 30% f o r each month e a r l i e r t h a t t h e season s t a r t s between January and the preceeding September; the cor r e s p o n d i n g i n c r e a s e s i n season l e n g t h a re only 33 t o 17%. For the s p r i n g 74 c o h o r t , the y i e l d / R (at M=0.50 and F=0.20) i n c r e a s e s by 88 to 60% f o r each month added between January and September. At higher r a t e s of n a t u r a l m o r t a l i t y , the percentage i n c r e a s e s i n y i e l d / r e c r u i t are s i g n i f i c a n t l y h i g h e r . Thus the advantage of commencing h a r v e s t i n g e a r l i e r when the c o h o r t s are n u m e r i c a l l y s t r o n g e r but s i m i l a r i n body s i z e are l i k e l y t o be s u b s t a n t i a l , a c c o r d i n g to the e q u i l i b r i u m y i e l d approach. F i g u r e 41 shows t h a t i f t h e len g t h o f the h a r v e s t i n q season i s maintained a t t h r e e months, there i s a l s o much hiqher y i e l d / r e c r u i t f o r a given f i s h i n g m o r t a l i t y i f the season runs from October t o the end of December(t c = 5; t e = 8) as opposed t o January-March ( t c =8;t g = 11). The optimal dynamics approach o f C l a r k e t a l A - (1973) seeks to o p t i m i z e the body s i z e of the harvested animals under d i f f e r e n t l e v e l s of t i m e - d i s c o u n t i n g , "\ . If one assumes t h a t ^=0 ( i e . z e r o d i s c o u n t rate) f o r the e u p h a u s i i d f i s h e r y , then the time of optimal h a r v e s t i s at the time o f maximum biomass f o r the co h o r t (Clark et a l . , 1973). The optimal h a r v e s t s t r a t e g y a c c o r d i n g t o t h e i r F i s h e r Rule i s to apply the maximum p o s s i b l e f i s h i n g e f f o r t , Fmax, f o r a s h o r t period a t the time of maximum 164 12 .1 .2 .3 .4 .5 .6 .7 F FIGDBE 41. R e l a t i o n s h i p s between y i e l d / r e c r u i t and f i s h i n g m o r t a l i t y f o r 3-month f i s h e r i e s beginning i n October and January, r e s p e c t i v e l y . biomass i n order to q u i c k l y reduce the p o p u l a t i o n to a l e v e l where biomass, B = c/p (here c i s the c o s t of a u n i t f i s h i n g e f f o r t and p i s the p r i c e per u n i t weight o f h a r v e s t p r o d u c t ) . I d e a l l y one miqht expect that t h i s remaining p o p u l a t i o n would be s u f f i c i e n t to qenerate a new cohort o f s i m i l a r maximum biomass or l a r g e r than t h a t of the parent g e n e r a t i o n . From the a n a l y s i s o f C l a r k et a l . . (1973) the o p t i m a l age of harvest f o r the Beverton-Holt model i s given by: t ^ = t D + 1/K [ l n ( 1 + 3K/(M +*)) ] 165 HhenA=0, the o p t i m a l age i s the age of maximum biomass. For the s p r i n g 75 cohort of E A p a c i f i c a , t^=3.5 mo when M=0.35. This corresponds t o about e a r l y September f o r a co h o r t which began i n mid-Hay; at t h i s time the mean body l e n g t h i n the cohort would be about 13 mm, which i s near the s i z e of f u l l r e c r u i t m e n t i n t o the mid-water t r a w l f i s h e r y . T h e r e f o r e , the c o n c l u s i o n s from the e g u i l i b r i u m and from the op t i m a l dynamics approach are i n c l o s e agreement r e g a r d i n g time of h a r v e s t . Commencement of h a r v e s t i n g i n l a t e September or e a r l y October i s suggested f o r optimal e x p l o i t a t i o n by the f i s h e r y . Other f a c t o r s a f f e c t i n g h a r v e s t i n g p o l i c y are d i s c u s s e d below. 6.4 Other Management C o n s i d e r a t i o n s As pointed out by t h e government g u i d e l i n e s quoted i n Chapter 5, an u n r e s t r i c t e d plankton f i s h e r y c o u l d reduce t h e food supply of many marine f i s h e s , notably P a c i f i c salmon and h e r r i n g . A c e n t r a l problem, then, i s to determine a c c e p t a b l e l e v e l s o f plankton h a r v e s t i n g e f f o r t which would maintain s t o c k s which can regenerate themselves each year. T h i s q u e s t i o n r e q u i r e s more a t t e n t i o n from f i e l d s t u d i e s and a p p l i c a t i o n of recruitment models such as d i s c u s s e d i n Chapter 3. The l e v e l of h a r v e s t i n q c u r r e n t l y permitted (500 tons annually) i s l i k e l y t o have a n e g l i g i b l e e f f e c t on S t r a i t of Georgia euphausiid p o p u l a t i o n s i f the c a t c h i s d i s t r i b u t e d over s e v e r a l l o c a l i t i e s as i t has been r e c e n t l y . Most u s e f u l i n f o r m a t i o n on the response o f the euphausiid p o p u l a t i o n s to h a r v e s t i n g could be obtained i f the h a r v e s t i n g e f f o r t were s t a b i l i s e d f o r c e r t a i n c l o s e l y monitored p o p u l a t i o n s t o allow 166 then t o approach e q u i l i b r i u m . The stock r e c r u i t m e n t r e l a t i o n s h i p would be more r e a d i l y s t u d i e d under these c o n d t i o n s . The choice of the best time of year f o r plankton h a r v e s t i n q o b v i o u s l y depends on the p r i o r i t i e s of manaqement, whether i t be t o minimize the impact on f i s h p r e d a t o r s or t o opt i m i z e the body s i z e of the harvested zooplankton. With r e s p e c t t o minimizinq impact on l a r v a e o f f i s h or s h e l l f i s h , plankton h a r v e s t i n q should be r e s t r i c t e d from s p r i n q and summer months i n nursery areas, but h a r v e s t i n q i n the f a l l and winter months i s not i n c o n f l i c t with t h i s r e s t r a i n t . Consequently, the p e r i o d from October t o l a t e March i s c o n s i d e r e d here to be s u i t a b l e f o r a l i m i t e d e u p h a u s i i d f i s h e r y i n the S t r a i t o f Georqia, with the opt i m a l time of h a r v e s t i n q beinq e a r l y i n t h i s p e r i o d . 167 CHS PTES 7: SUMMARY 7.1 Summary The l i f e h i s t o r y , d i s t r i b u t i o n and p o p u l a t i o n dynamics of Euphausia p a e i f i c a Hansen i n the S t r a i t of Georgia r e g i o n were s t u d i e d during 1974-76. Zooplankton samples, c o l l e c t e d by high speed M i l l e r nets, I s a a c s - K i d d mid-water t r a w l and by SCOR net v e r t i c a l hauls were examined f o r eu p h a u s i i d s p e c i e s and t o t a l biomass. Length frequency a n a l y s i s of E A p a e i f i c a specimens was used t o i d e n t i f y c o h o r t s and to c a l c u l a t e i n f e r r e d growth r a t e s i n p o p u l a t i o n s from Saanich I n l e t , J e r v i s I n l e t and the S t r a i t of Georgia. The p o t e n t i a l use of l o c a l euphausiids as a food f o r f i s h r e a r i n g was e v a l u a t e d through chemical analyses on samples and throuqh f e e d i n g t r i a l s with j u v e n i l e coho salmon. B r i t i s h Columbia's r e c e n t f i s h e r y f o r euphausiids was de s c r i b e d i n r e l a t i o n t o zooplankton and micronekton f i s h e r i e s i n other p a r t s o f the world. F a c t o r s a f f e c t i n g y i e l d , such as net s e l e c t i v i t y and time of h a r v e s t , have been c o n s i d e r e d i n comparison with government g u i d e l i n e s f o r plankton h a r v e s t i n g . The maximum l i f e span of E,. p a e i f i c a i n the S t r a i t o f Georgia r e g i o n was found t o be about 19 months f o r males and up to 22 months f o r females. Spawning i n Saanich I n l e t was mainly d u r i n g May-June and to a l e s s e r extent i n August-September. In J e r v i s I n l e t and the S t r a i t of Georgia, s e v e r a l c o h o r t s of l a r v a e were produced d u r i n g May-September. Spawning a c t i v i t y appeared to be c l o s e l y r e l a t e d to phytoplankton abundance. Growth of co h o r t s was w e l l d e s c r i b e d by von B e r t a l a n f f y 168 growth equations; qrowth of s p r i n q c o h o r t s was r a p i d (0.094 mm/day) duri n q summer but slowed durinq autumn at body l e n q t h s of 15-17 mm and stopped i n win t e r . Second-year qrowth showed a s i m i l a r p a t t e r n . D i f f e r e n t i a l qrowth and m o r t a l i t y of sexes was apparent; males had h i q h e r qrowth r a t e s and experienced s i z e -s e l e c t i v e m o r t a l i t y f o l l o w i n q e a r l y maturity(11-12 mm). Females appeared to qrow slower i n l e n q t h at peak r e p r o d u c t i v e s i z e s { 1 4 -16 mm and 19-21 mm). S u r v i v a l was lowest between eqq and e a r l y l a r v a l staqes(6%/mo) but i n c r e a s e d to about 40%/mo f o r l a t e l a r v a l staqes(4.6 t o 8mm), Subsequently s u r v i v a l r a t e i n c r e a s e d by 10-15%/mo with l i f e phase chanqes [ l a t e l a r v a l to j u v e n i l e (8-12 mm) and j u v e n i l e to smal l adult(12-14 mm) J . S u r v i v a l of l a r q e males and females (over 18mm) d e c l i n e d s h a r p l y . The lenqth:weiqht exponent f o r both sexes over 10 mm body l e n q t h was n e a r l y 3,0. Durinq 1975, peaks i n the annual d i s t r i b u t i o n of biomass by s i z e c l a s s occurred at 11, 16-17 and 19-20 mm body l e n q t h . T o t a l biomass, B, i n each p o p u l a t i o n reached a maximum i n October-November. E. p a c i f i c a p r o d u c t i o n , P, i n Saanich I n l e t d u r i n q July-November was 26,8 mqC/m2/day; the correspondinq value o f P/B was 8,8# which i s s i m i l a r to values r e p o r t e d f o r herbivorous copepods but hiqher than a previous estimate of E. p a c i f i c a . Dense, shallow sound s c a t t e r i n q l a y e r s of meqazooplankton (> 5mm) were recorded a f t e r dusk at 107 kHz i n Saanich and J e r v i s I n l e t s and i n par t s of the S t r a i t of Georqia, e s p e c i a l l y d u r i n q f a l l and winter. The wet biomass i n such l a y e r s was q e n e r a l l y over 2 q/m3. 169 J u v e n i l e coho salmon at 9 C showed mean growth r a t e s of 3.8%/day on f r e e z e - d r i e d e u p h a u s i i d s compared to 3.0%, 2.7% and 3.1%/day on d i e t s of e u p h a u s i i d meal, f r o z e n e u p h a u s i i d s and Oregon Moist P e l l e t , r e s p e c t i v e l y . L o c a l e u p h a u s i i d s have a well-balanced spectrum of amino a c i d s i n t h e i r p r o t e i n s and high c a r o t e n o i d c o n c e n t r a t i o n s (80-219 ^»g/g t i s s u e ) , making them s u i t a b l e f o r use i n a g u a c u l t u r a l feeds. B r i t i s h Columbia's e u p h a u s i i d f i s h e r y harvested about 100 metric tons during e a r l y 1977; the main uses are as an aguarium f i s h food and as a d i e t a r y supplement i n salmon aguaculture. 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P h y s i o l . 42B: 731-734. WP- 2 (Working Party No. 2) 1968. Smaller mesoplankton. Report of Working P a r t y No. 2. In : Zooplankton sampling. Monographs on Oceanographic Methodology 2. UNESCO, P a r i s p. 153-59. WP- 4 (Working P a r t y No. 4) 1 968. Micronekton. Report of Working Party No. 4 In: Zooplankton Sampling. Monographs on Oceanographic Methodology 2. UNESCO, P a r i s p.164-167. 183 APPENDIX A Table 23. L i s t o f 1975 c r u i s e s , with dates and d e s t i n a t i o n s . Date C r u i s e No.. D e s t i n a t i o n 20,21 Jan. 75/3 Saanich I n l e t 17,18 Feb. 75/5 Saanich I n l e t 17-20 Mar. 75/10 Knight I n l e t , S t r a i t o f Georgia 24,25 Mar. 75/11 Saanich I n l e t , Howe Sound 1-4 Apr. 75/12 S t r a i t o f Georgia, J e r v i s I n l e t 27,2 8 Apr. 75/13 Saanich I n l e t 12,13 May 75/15 Saanich I n l e t 16-20 Jun 75/21 S t r a i t of Georgia, J e r v i s I n l e t 16-18 J u l y 75/24 S t r a i t o f Georgia, J e r v i s I n l e t 21-22 J u l y 75/25 Saanich I n l e t 19-22 Aug. 75/27 S t r a i t o f Georgia, Saanich I n l e t 3,4 Sept. 75/29 S t r a i t of Georgia, J e r v i s I n l e t 6-8 Oct. 75/31 J e r v i s I n l e t , S t r a i t of Georgia, Saanich I n l e t 3-5 Nov. 75/33 J e r v i s I n l e t , S t r a i t o f Georgia, Saanich I n l e t 1-4 Dec. 75/34 J e r v i s I n l e t 184 FIGURE 44. C r u i s e t r a c k s f o r survey c r u i s e s 75/27 " (August) and 75/29 {September) . FIGURE 45. C r u i s e t r a c k s f o r survey c r u i s e s 75/31 (October) and 75/33 (November). 

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