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Mussel culture in British Columbia : the influence of salmon farms on mussel growth and biochemical… Taylor, Barbara Elan 1990

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MUSSEL CULTURE IN BRITISH COLUMBIA: THE  INFLUENCE OF SALMON FARMS ON MUSSEL GROWTH AND BIOCHEMICAL COMPOSITION by BARBARA ELAN TAYLOR B.Sc,  University of B r i t i s h  Columbia  THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE  REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in  THE  FACULTY OF GRADUATE STUDIES (ZOOLOGY)  We accept  t h i s as conforming  to the required  THE  UNIVERSITY OF BRITISH COLUMBIA July  (c)  standard  1990  Barbara Elan Taylor,  1990  In  presenting  degree  this  thesis  in  partial  fulfilment  at the University  of  British Columbia,  freely available for reference and study. copying  of  department  this or  thesis by  for scholarly  his  publication of this thesis permission.  Department of The University o r Vancouver, Canada  DE-6  (2/88)  or  her  of  the  requirements  I agree  for  an  advanced  that the Library shall make it  I further agree that permission for extensive  purposes  may be  representatives.  It  for financial gain shall not  is  granted  by the head  understood  that  be allowed without  of  my  copying  or  my written  ii ABSTRACT To r e a l i s e t h e p o t e n t i a l f o r mussel c u l t u r e i n B r i t i s h Columbia, m a r i c u l t u r e r e s e a r c h must i d e n t i f y  specific  environments and s u i t a b l e l o c a t i o n s which promote maximum growth i n mussels.  The present  study  i n v e s t i g a t e s the p o s s i b l e  advantages, through n u t r i t i o n a l enrichment, o f salmon farms as s i t e s f o r mussel c u l t u r e . Mussels were c u l t u r e d at d i f f e r e n t d i s t a n c e s around two salmon farms on t h e east coast o f Vancouver I s l a n d and Genoa Bay). index,  Three parameters o f mussel growth:  carbohydrate  content,  (Departure Bay condition  and crude p r o t e i n content  were  monitored at 3-6 wk i n t e r v a l s from September 1988 t o August 1989. Distinct  seasonal d i f f e r e n c e s i n growth were observed, but  d i s t a n c e from t h e farm d i d not s u b s t a n t i a l l y i n f l u e n c e mussel growth.  A d u l t m o r t a l i t y and l a r v a l settlement  were s i m i l a r l y  unaffected. Contrary  t o p r e d i c t i o n , t h e farms d i d not i n c r e a s e  a v a i l a b l e food f o r mussels.  Measures o f seston and c h l o r o p h y l l  c o n c e n t r a t i o n , made c o n c u r r e n t l y with the mussel c o l l e c t i o n s , i n d i c a t e d that neither a d i r e c t c o n t r i b u t i o n of n u t r i e n t s i n the form o f feed and f i s h faeces, nor an i n d i r e c t c o n t r i b u t i o n o f waste ammonia t o augment phytoplankton  production,  occurred.  T h i s was d e s p i t e c u r r e n t s f l o w i n g , at l e a s t p a r t o f t h e time, i n such a d i r e c t i o n as t o t r a n s p o r t p o t e n t i a l n u t r i e n t s from t h e farms t o t h e mussels.  iii TABLE OF CONTENTS Abstract Table o f Contents  i i i i i  L i s t o f Tables  iv  L i s t of Figures  v  Acknowledgements  vi  Introduction  1  M a t e r i a l s and Methods S i t e s and C u l t u r e Technique Mussel Sampling Data C o l l e c t i o n 1. S h e l l Length 2. C o n d i t i o n Index 3. Carbohydrate 4. Crude P r o t e i n 5. Spat D e n s i t y 6. C h l o r o p h y l l and Seston 7. C u r r e n t s 8. S t a t i s t i c a l Analyses  10 10 18 19 19 20 22 22 23 24 26 26  R e s u l t s and D i s c u s s i o n 1. C o n d i t i o n Index 2. Carbohydrate 3. Crude P r o t e i n 4. Spat D e n s i t y 5. C h l o r o p h y l l 6. Seston 7. C u r r e n t s  28 28 42 48 52 52 55 61  General D i s c u s s i o n  66  References C i t e d  87  iv LIST OF TABLES 1.  Energy r e s e r v e s and energy budgets o f mussels c u l t u r e d i n Departure Bay and Genoa Bay  85  V  LIST OF FIGURES 1.  L o c a t i o n o f study s i t e s at Departure Bay and Genoa Bay and l o c a t i o n of source mussels i n Indian Arm and Okeover I n l e t 12  2.  Site-diagrams of Departure Bay and Genoa Bay showing the array o f s t a t i o n s at the salmon farms  14  3.  L o n g - l i n e system f o r c u l t u r e of mussels w i t h i n p r o t e c t i v e cages  17  4.  Monthly f l u c t u a t i o n s i n c o n d i t i o n i n d i c e s o f mussels c u l t u r e d i n Departure Bay and Genoa Bay  30  5.  Monthly f l u c t u a t i o n s i n dry s h e l l weights o f mussels c u l t u r e d i n Departure Bay and Genoa Bay  35  6.  Monthly f l u c t u a t i o n s i n dry t i s s u e weights o f mussels c u l t u r e d i n Departure Bay and Genoa Bay  37  7.  Monthly f l u c t u a t i o n s i n carbohydrate contents of mussels c u l t u r e d i n Departure Bay and Genoa Bay  44  8.  Monthly f l u c t u a t i o n s i n crude p r o t e i n contents o f mussels c u l t u r e d i n Departure Bay and Genoa Bay  50  9.  Monthly f l u c t u a t i o n s i n c h l o r o p h y l l at Departure Bay and Genoa Bay  54  suspended  concentrations  10. Monthly f l u c t u a t i o n s i n seston c o n c e n t r a t i o n s at Departure Bay and Genoa Bay  57  11. F l u c t u a t i o n i n t i d a l h e i g h t and seston c o n c e n t r a t i o n i n Departure Bay  60  12. C u r r e n t - f l o w d i r e c t i o n i n Departure Bay and Genoa Bay  63,64  vi ACKNOWLEDGEMENTS My f i r s t words of thanks are t o my s u p e r v i s o r Dr. Thomas C a r e f o o t f o r h i s advice, help, and moral support d u r i n g the course of the study. I am a l s o indebted t o Dr. Glen Jamieson, S h e l l f i s h S e c t i o n Head, and h i s s t a f f at the P a c i f i c B i o l o g i c a l S t a t i o n e s p e c i a l l y Wayne H a r l i n g , Steve Head, Dwight Heritage, Anton P h i l l i p s , and Dr. Ian Whyte, f o r the l o g i s t i c a l support they p r o v i d e d as w e l l as the i n v a l u a b l e experience they l e n t t o the p r o j e c t . I would a l s o l i k e t o thank my other committee members, Dr. Bruce Owen and Dr. Timothy Parsons f o r t h e i r input to t h i s project. Greg Mullen deserves s p e c i a l c r e d i t f o r h i s h e l p i n producing the f i g u r e s . F i n a l l y I would l i k e t o c r e d i t some s p e c i a l people who l e n t moral support i n darker moments, who b r i g h t e n e d monotonous times, and who were c o n s i s t e n t l y t h e r e t o l e n d a hand: M i c h e l e Cook, Norma Ginther, Sabine Kalwa, S t i r l i n g T a y l o r , and Gavin St. M i c h a e l . T h i s work was supported through o p e r a t i n g g r a n t s from Science C o u n c i l of B r i t i s h Columbia (G.R.E.A.T. Award) and NSERC t o Dr. T.H. C a r e f o o t , and by o p e r a t i n g funds of the S h e l l f i s h S e c t i o n of the P a c i f i c B i o l o g i c a l S t a t i o n , Department of F i s h e r i e s and Oceans at Nanaimo.  1  INTRODUCTION Culture centuries edulis  o f mussels  ( B a r d a c h e t al., 1912),  has dominated  cosmopolitan species abundant  i s endemic  culture  this potential,  mussels.  specific  to British  mariculture  investigation.  on f i s h - f a r m  without f i s h  the p o s s i b l e  Nutritional  floats  farms.  advantages,  c u l t u r i n g mussels  r e s e a r c h must  location Wallace  growth  assessment  be e x p l a i n e d description  rate,  f o r mussels  and/or  condition  accretion  i n detail  later.  relative  o f how n u t r i t i o n a l  s t a t u s might  emanating  or i n d i r e c t l y  some s t o r a g e .  investigates  farms.  c l o s e t o salmon  i n energy s t o r a g e index.  The l a t t e r  t o mussel  size  i s an  and w i l l  i s a brief  i n m u s s e l s w i t h an e x p l a n a t i o n be e n h a n c e d  by f o o d  f r o m a salmon  materials  farm.  (Gabbott, 1983).  In  Mytilus  gland i s the site- of glycogen synthesis The m a n t l e ,  of those  a r e c o n s i d e r e d t h e primary energy  storage products o f mussels the d i g e s t i v e  reported  enrichment, o f  growing  The f o l l o w i n g  o f energy metabolism  G l y c o g e n and p r o t e i n  f o r mussel  The p r e s e n t s t u d y  through n u t r i t i o n a l  enhancement  directly  potential  f o c u s on  (1980)  i n c l o s e p r o x i m i t y t o salmon  of tissue  A  grew a t t w i c e t h e r a t e  f a r m s c o u l d be m a n i f e s t e d as an i n c r e a s e products,  and i s o f t e n  e n v i r o n m e n t s w h i c h p r o m o t e maximum g r o w t h o f  c u l t u r e which warrant  from s i t e s  zones.  This  i n B r i t i s h Columbia but, t o  Salmon f a r m s a r e a p o t e n t i a l  t h a t mussels  Columbia  seven  Mytilus  of these bivalves.  and s h a l l o w s u b t i d a l  f o r mussel  identifying  and t h e e d i b l e mussel  the world harvest  in intertidal  thus e x i s t s realise  f o r f o o d has e x t e n d e d o v e r t h e p a s t  however,  i s t h e main s i t e  edulis  as w e l l as of glycogen  2 storage,  specifically  amounts o f t h i s  i t s vesicular  carbohydrate  s t o r e d as g r a n u l e s  as  (Thompson e t al.,  secondary  equal  energy  (Gabbott, 1974).  1983)  and  the  importance  edulis,  in essential  as  Mytilus  products cycle.  and  their  Bayne,  t h a t a l l have  source.  (Hawkins,  D a r e and  Edwards,  al.,  1979;  Zurburg  e t al.,  al.,  1980;  Hawkins and  1975;  1979;  Bayne,  follows a  Zandee,  i n the t i m i n g of the  populations  (Emmett,  The  1984;  seasonal cycle  storage products  e t al.,  1980;  Emmett e t al., Europe.  The  Zandee e t  1987)  with  characteristics  s t u d i e s have b e e n Columbia, w i t h  c y c l e being noted  Emmett e t al,  of accumulation  i s closely  composititon  et  in British  differences  seasonal  Pieters  i n these  edulis  1985).  Widdows, 1978;  of  a p p l i e d t o M.  M.  and  and  generally  in  Gabbott  most work b e i n g done i n B r i t a i n mussel e n e r g e t i c s i d e n t i f i e d  Slow  1972;  Pieters  1985;  example,  storage  S t u d i e s o f s e a s o n a l changes i n b i o c h e m i c a l  1973;  For  p r o t e i n s because  o f energy  subsequent e x p e n d i t u r e  (de Zwaan and  regarded  are r e c y c l e d f o r  components  the accumulation  m u s s e l s a r e numerous  digestive  i s known t o e x i s t  degradation products  edulis  i n the  mantle's  a feeding structure.  tissues  maintenance of e s s e n t i a l p r o t e i n  In  of the  mobilised before g i l l  of the g i l l  and p r o t e i n  Protein i s also  i t is unlikely  c a p a c i t y t o be m o b i l i s e d as an e n e r g y  protein turnover  of  1983) .  store large  A l l body p r o t e i n s c a n be  r e s e r v e s , but  muscle p r o t e i n s are l i k e l y of  (Gabbott,  w h i c h can  i n the adipogranular c e l l s  connective t i s s u e matrix gland  cells  for  only  local  1987).  and  l i n k e d to the  expenditure  annual  of  energy  gametogenic  3 cycle  (Bayne, 1973; Gabbott and Bayne, 1973; Thompson et al.,  1974).  In B r i t i s h and European p o p u l a t i o n s the demand f o r  m e t a b o l i c energy decreases i n summer as mussels s w i t c h from the energy-demanding  gametogenesis  reproductive i n a c t i v i t y Widdows  of winter/spring to a period of  (Widdows and Bayne, 1971; Bayne, 1973) .  (1973) and Thompson and Bayne (1974) have confirmed t h i s  decrease i n metabolism i n mussels d u r i n g summer by showing evidence o f decreased oxygen uptake by mussels i n t h i s season as compared w i t h w i n t e r .  A l s o , at t h i s time, food i s r e a d i l y  a v a i l a b l e i n the form o f abundant  phytoplankton.  Therefore,  energy s t o r e s such as glycogen and p r o t e i n s are accumulated d u r i n g summer, and t h e r e i s a concomitant r i s e i n c o n d i t i o n index.  At t h i s time, glycogen r e s e r v e s are accumulated i n both  mantle and non-mantle t i s s u e s , w i t h h i g h e s t l e v e l s b e i n g p r e s e n t i n the d i g e s t i v e g l a n d and mantle Gabbott and Bayne, 1973; Emmett,  (de Zwaan and Zandee, 1972; 1984).  P r o t e i n s a l s o accumulate d u r i n g summer through p r o c e s s e s o f t i s s u e growth and granule storage (Bayne, 1973; Dare and Edwards, 1975; P i e t e r s et al., 1979; Emmett, 1984), w i t h the m a j o r i t y o f accumulation b e i n g through growth o f non-mantle t i s s u e s 1983).  (Gabbott,  An i n c r e a s e i n c o n d i t i o n index a t t h i s time r e f l e c t s  i n c r e a s e i n body mass r e l a t i v e t o s h e l l  size.  F o l l o w i n g summer's r e l a t i v e l y low m e t a b o l i c a c t i v i t y , m e t a b o l i c r a t e g r a d u a l l y i n c r e a s e s over autumn and w i n t e r due t o h i g h energy demands o f gametogenesis Bayne, 1973).  (Widdows and Bayne, 1971;  The m a j o r i t y o f s t o r e d glycogen i s used up i n  4 early winter.  As t h i s  and v i t e l l o g e n e s i s  depletion  i s synchronous w i t h oogenesis  i t i s generally believed that  during winter  glycogen energy r e s e r v e s are p r e f e r e n t i a l l y  allocated  garnetogenesis  1982).  protein  ( G a b b o t t , 1975;  stored  gametogenesis Since  as g r a n u l e s i n t h e m a n t l e at t h i s time  food l e v e l s  i n t h e non-mantle 1975).  (Hawkins,  i s met  tissues  1985).  ( G a b b o t t and Bayne,  The m u s c l e s ,  ( Z u r b u r g e t al.,  conclusive  i s used t o support  1978;  a d d u c t o r s and  foot,  Zandee e t al.,  evidence f o r a switch  (1973).  1973;  Dare  show a  and greater  d u r i n g w i n t e r months t h a n do o t h e r 1980).  The  most  from c a r b o h y d r a t e m e t a b o l i s m i n  summer t o d e p e n d e n c e on p r o t e i n m e t a b o l i s m Bayne  required  u s i n g energy r e s e r v e s o f p r o t e i n s  decrease i n percentage p r o t e i n organs  Similarly,  a r e low d u r i n g w i n t e r , t h e e n e r g y  for high metabolic rate  Edwards,  Bayne e t al.,  to  This author reports  i n w i n t e r comes  from  seasonal differences i n  n i t r o g e n e x c r e t i o n whereby w i n t e r m u s s e l s u n d e r t e m p e r a t u r e nutritive  stress excrete  extensive protein Columbia  large  amounts o f ammonia,  indicating  deamination.  Mussel p o p u l a t i o n s  in British  appear a l s o t o e x h i b i t  f o r energy metabolism. d u r i n g w i n t e r months Emmett  and  Lowered  a w i n t e r d e p e n d e n c e on levels  of t o t a l  body  (December t o F e b r u a r y ) h a v e b e e n  (1984) f o r m u s s e l s  growing  i n D e p a r t u r e Bay  proteins  protein reported  by  and B a m f i e l d  Inlet.  Thus,  i n w i n t e r , s o m a t i c growth  and s o m a t i c t i s s u e s may maintenance  i n Mytilus  edulis  i s minimal  e v e n be m o b i l i s e d t o s u p p l y e n e r g y f o r  and g a m e t o g e n e s i s .  This decline  i s evident  i n lower  5  condition 1973;  indices  reported  Emmett e t al.,  for this  1987),  season  and r e s u l t s  m u s s e l meat f r o m c o m m e r c i a l c u l t u r e some B.C.  ( G a b b o t t and  i n a lower y i e l d  spawning  susceptibility  o f mussels t o post-spawning m o r t a l i t y .  (1978), H e r i t a g e  i s low and t h i s may  (1989) .  f o r B.C.  (1983), Emmett e t al.  Insufficient  Indeed, w i n t e r f o o d q u a n t i t y  identified  as l i m i t i n g  factors  both sides of the A t l a n t i c Rosenberg  (1987), and  and Loo,  farms r e p r e s e n t  mussels,  Ocean  First,  potential  s o l u b l e waste  have  ( I n c z e and L u t z ,  a potential  f o r constant  1980;  p o s t - s p a w n i n g months.  mussels.  Salmon  farms  nutritional  of the  salmon  contribution.  o r g a n i c w a s t e made up o f unconsumed f i s h  and c o n t a i n i n g p r o t e i n s ,  carbohydrates, l i p i d s ,  represents a direct  as  s e r v e as a n i t r o g e n  T h i s r e p r e s e n t s an i n d i r e c t  for  because  s u c h as ammonium and u r e a a r e e x c r e t e d  farm.  c a r o t e n o i d pigments,  Wallace,  enrichment inputs t o the environment.  f o r blooms o f p h y t o p l a n k t o n i n t h e v i c i n t y  and f a e c e s ,  on  food supply to  source  particulate  been  o f mussels c u l t u r e d  t h e b y - p r o d u c t s o f m e t a b o l i s m and t h e s e may  Second,  may  1983).  even i n t h e c r i t i c a l  p r o v i d e two  Quayle  in British  and q u a l i t y  f o r growth  high  Jamieson  Mussel-salmon p o l y c u l t u r e warrants i n v e s t i g a t i o n salmon  A  m u s s e l s by  f o r mussel c u l t u r e  Columbia.  1980;  increase  food i n the post-spawning p e r i o d  t h e r e f o r e be a p r i m e o b s t a c l e  In  o f energy r e s e r v e s at the  time of s p r i n g  reported  of  operations during winter.  mussel p o p u l a t i o n s the l e v e l  summer m o r t a l i t y has b e e n  Bayne,  nutritional  meal and  contribution  6 E x c r e t e d ammonium a n d u r e a c a n b e u s e d phytoplankton (M Carthy c  and are, i n f a c t ,  e t al., 1 9 7 7 ) .  o x i d i s e d by b l u e - g r e e n  minimal  nitrogen  Lee, 1980).  i s the primary  Codispoti,  limiting nutrient  1989),  an i n f l u x  of nitrogen  i t follows that  f o ralgal production i n 1971; E p p l e y  salmon f a r m i n g  p r o d u c t i o n and t h u s  Since  e t al.,  should  increase the p r i n c i p a l  o f food f o r mussels.  Particulate  o r g a n i c m a t e r i a l s . f r o m f i s h meal a n d f a e c e s  provide basic protein, Carbohydrates  carbohydrate,, and l i p i d  (Crosby  and R e i d ,  Mussels  can even u t i l i s e  enhancer,  Some l i p i d s ,  and s o l u b l e  carbohydrates  and p r o t e i n ,  and faeces break  Thus, t h e s e n u t r i e n t s have a r e d u c e d those obtained are r e a d i l y o f t h e type  utilised.  and T r i d e r ,  are l i k e l y  down i n s e a w a t e r .  availability  t o mussels, but  A l l bivalves  commonly u s e d  c o n t a i n i n g a high percentage (Castell  f e e d as a  b u t one w h i c h i s n o t d i g e s t e d b y s a l m o n .  as t h e food p e l l e t s  converting o i l s  cellulose  1971), a m a t e r i a l o f t e n a d d e d t o f i s h  palatability  glycogen  nutrients.  and p r o t e i n s from p a r t i c u l a t e waste a r e r e a d i l y  consumed a n d d i g e s t e d .  to  i s probably  I t i s , therefore, reasonably  (Ryther and Dunstan,  augment p h y t o p l a n k t o n  those  before  forms t o t h e s u r r o u n d i n g s e a w a t e r .  the marine environment  lost  (this n i t r i f i c a t i o n  a salmon f a r m w o u l d g e n e r a t e  several different  source  and n i t r a t e s  b e c a u s e C y a n o p h y c e a e make up a v e r y l i m i t e d p a r t o f t h e  certain that  1979;  forms o f n i t r o g e n  t h e s e compounds may be  algae into n i t r i t e s  marine phytoplankton;  in  their preferred  Alternatively,  b e i n g t a k e n up b y p h y t o p l a n k t o n  d i r e c t l y by  i n fish  are capable of feeds  o f e s s e n t i a l w3 f a t t y  1974),  and mussels  (e.g., acids)  possess  a  7 typical  complement o f enzymes f o r d i g e s t i n g  carbohydrates  and  proteins. Antibiotics  and c a r o t e n o i d p i g m e n t s a r e l e s s e r  o f salmon m e a l s , b u t may  p r o v i d e an i m p o r t a n t  c o n t r i b u t i o n t o mussels. enhance al.  flesh  (1988)  e t al.  R e c e n t s t u d i e s by H e r t z b e r g e t  (1989) have  c a r o t e n o i d compounds f r o m t h e t i s s u e s including  some v a r i e t i e s  a capacity  curtailing effect  edulis,  and have  on m u s s e l s . shell  growth i n mussels  t o be h i g h l y v a r i a b l e  on l a r v a l  and o f t e n  by  i s known o f t h e i r  T h e r e a r e , however, r e p o r t s  of a n t i b i o t i c s  indicated  o f c a r o t e n o i d s by m u s s e l s .  t h e growth o f pathogens, but l i t t l e  the e f f e c t s  of  antibiotics  (Dey and B o l t o n ,  1978), b u t  g r o w t h and s u r v i v a l  contradictory  ( l e Pennec  appear and  1977).  The amount and c o m p o s i t i o n varies  of Mytilus  19-20  a r e added t o improve t h e h e a l t h o f salmon  causing rapid  Prieur,  isolated  u s e d i n salmon d i e t s ,  for interconversion  Antibiotics  nutritional  C a r o t e n o i d p i g m e n t s a r e added t o  c o l o u r o f salmon.  and P a r t a l i  constituents  o f f o o d wastage  d e p e n d i n g upon f e e d c o m p o s i t i o n  practices  employed by  estimate that  farm o p e r a t o r s .  i n salmon  and f e e d management B r a a t e n e t al.  20% o f f o o d goes u n e a t e n by c a g e - r e a r e d figures  culture  Furthermore,  digestibility  suggest t h a t  26% o f f o o d e a t e n by salmon ends up as  (1983) salmon.  f r o m Gowen and B r a d b u r y  (1987)  faeces.  Thus, t h e r e  i s s u b s t a n t i a l p a r t i c u l a t e waste  from salmon  (equivalent  t o a b o u t 40% o f a l l f e e d g i v e n ) ,  the bulk o f which i s  organic  compounds o f n i t r o g e n  and c a r b o n .  These c o u l d  be  farms  8 directly  u t i l i s e d b y many o r g a n i s m s ,  the v i c i n i t y  o f t h e farm.  i n c l u d i n g mussels  However, t h e e f f e c t s  living in  of this  form o f  enrichment a r e l i m i t e d by t h e range o f d i s p e r s a l .  Most f o o d -  wastage p a r t i c l e s ,  b e i n g more d e n s e  sink  immediate  o f t h e farm.  vicinity  reviewing the ecological that  impact  Gowen a n d B r a d b u r y  the majority  a r o u n d t h e salmon  influx  Gowen a n d B r a d b u r y consumed by salmon  abundance i n t h e v i c i n i t y  and n i t r a t e  i s excreted.  o f salmon  t h e y e a r , and p o s s i b l y mm).  o p e r a t i o n s and would  farms.  growers.  mussel-salmon  polyculture  This  gain  and r e p r o d u c t i o n ) throughout  o f mussel  size  (50-75  culture  costs with obvious b e n e f i t  study i n v e s t i g a t e d the p o t e n t i a l o f  in British  mussel  Columbia  growth.  and a n a l y s e s o f c o n d i t i o n  and c r u d e p r o t e i n  f a r m s t h e y may  i n a h i g h e r "scope f o r  reduce p r o d u c t i o n  o f enhanced  a considerable  phytoplankton q u a l i t y or  the productivity  t o commercial  were s t u d i e d ,  f o r growth  68-86% o f t h e  d e c r e a s e d t i m e t o r e a c h market  T h i s c o u l d enhance  perspective  Thus,  a r e c u l t u r e d c l o s e t o salmon  (energy a v a i l a b l e  are soluble i n  (1987) e s t i m a t e t h a t  a continuous food supply, r e s u l t i n g growth"  immediately  s i n c e ammonium, u r e a , a n d o f  o f n i t r o g e n e x i s t s t o enhance  I f mussels  settle  i s about  enrichment through m e t a b o l i c by-products  oxidation products, n i t r i t e  nitrogen  f o r feed debris  of particles  s h o u l d be more w i d e l y d i s p e r s e d  seawater.  (1987),  farm.  In comparison,  their  i n the  o f salmonid farming, reported  t h e maximum r a n g e o f d i s p e r s a l  120 m, b u t t h a t  than seawater,  content i n mussels  from t h e  Two s a l m o n - f a r m  sites  index, glycogen content,  suspended  at different  9 distances seston  f r o m t h e f a r m s , a s w e l l as m e a s u r e s o f c h l o r o p h y l l and  concentration  possible  enhancement.  at these  same d i s t a n c e s , were u s e d t o  assess  10  METHODS AND  MATERIALS  S i t e s and C u l t u r e Technique Mussels  (Mytilus  edulis)  on t h e e a s t  coast  the P a c i f i c  Biological  (Fig.  1).  o f Vancouver  salmon  p o l y c u l t u r e was  direct  comparison  hoped t h a t i n mussel  Station,  An i d e n t i c a l  environment  were c u l t u r e d  was  Island,  one i n D e p a r t u r e Bay  of the p o t e n t i a l  out a t each s i t e ,  i n t e n d e d because  u s e o f two s i t e s w o u l d  practicality  farms.  a l t h o u g h no  However,  travelled  em's -'- ( i n t h e p e r i o d m o n i t o r e d ) .  f r o m 2.1 °C i n F e b r u a r y t o 18.5 °C i n A u g u s t ;  ranged  from  d e p t h was  i n F e b r u a r y t o 32.0 %  10-15 m i n t h e v i c i n i t y  averaged  1.5 c i r r s  salinity  d a t a were n o t t a k e n a t t h i s  s i t e s mussels  - 1  2).  possible,  site.  s t a t i o n was  t h e m u s s e l s were i s o l a t e d  s u b j e c t e d t o markedly s t a t i o n s were s i t e d  different  I n Genoa Bay,  Temperature  At both  were d e p l o y e d a t f o u r s t a t i o n s :  The c o n t r o l  salinities  o f t h e farm and c u r r e n t s  ( i n the period monitored).  75 m f r o m t h e p e r i m e t e r o f t h e farm, (Fig.  i n May.  at a  Temperatures  -  ranged  water  variation  A t t h e D e p a r t u r e Bay  20-25 m deep and t h e c u r r e n t  19.0 %  i t was  i n f o r m a t i o n on t h e  o f p o l y c u l t u r e w i t h salmon.  mean s p e e d o f 2.7  o f mussel-  indicate between-site  a n d p r o v i d e more  f a r m t h e w a t e r was  near  of differences i n  a n d o p e r a t i o n a t t h e salmon  culture  farms  a n d t h e o t h e r i n Genoa Bay  investigation carried  a t two salmon  3 m,  salmon-farm 15 m,  and a t a c o n t r o l  located  and  such t h a t ,  and  station as much as  from t h e farm b u t not  environmental conditions.  along a west-east axis  The  i n D e p a r t u r e Bay a n d a  11  F i g u r e 1. L o c a t i o n o f s t u d y s i t e s a t D e p a r t u r e Bay and Genoa Bay on t h e e a s t c o a s t o f V a n c o u v e r I s l a n d , and l o c a t i o n o f s o u r c e m u s s e l s i n I n d i a n Arm. and O k e o v e r I n l e t .  13  F i g u r e 2. S i t e - d i a g r a m s o f a) D e p a r t u r e Bay and b) Genoa Bay s h o w i n g t h e a r r a y o f s t a t i o n s 3 m, 15 m, and 75 m f r o m t h e farm, and a c o n t r o l s t a t i o n p h y s i c a l l y s e p a r a t e d f r o m t h e f a r m .  14  15 south-north axis  i n Genoa Bay.  due t o t h e t o p o g r a p h i c a l Four groups station  T h i s d i f f e r e n c e was  features  o f t h e two  The c a g e s were c l o s e d  m d i a m e t e r ) o f v e x a r mesh  (2 cm).  Suspended  e l i m i n a t e b e n t h i c p r e d a t o r s (e.g.,  to  food.  sites.  o f m u s s e l s were hung i n s e p a r a t e c a g e s a t e a c h  at each s i t e .  enhance growth  obligatory  s i n c e the mussels  In B r i t i s h  Columbia  cylinders culture  (0.8 X  i s known t o  c r a b s and s t a r f i s h )  and  are afforded continuous access  use o f p r o t e c t i v e e n c l o s u r e s i s  a l s o n e c e s s a r y t o e x c l u d e p e l a g i c p r e d a t o r s s u c h as p i l e (when t h e m u s s e l s  are small;  (when t h e m u s s e l s  are l a r g e r ) .  e . g . , < 14 mm),  be l o s t  parallel  By c u l t u r i n g  a t 2 m,  initial  was  s e t out  juvenile  farm.  To t h i s  s t a g e i n June  "collectors"  c o l l e c t o r s were 3-m  on t h e c a g e s a n d sponges,  reduced.  i n t e n t was t o u s e m u s s e l  a r o u n d e a c h salmon  traditional  fouling  bryozoans, mussels,  a n d o t h e r o r g a n i s m s was  at the e a r l y  The  might  and w i t h i t s c e n t r e a p p r o x i m a t e l y 2 m b e n e a t h t h e  (Fig. 3).  tunicates  bay  E a c h cage  o f an a n c h o r e d l o n g - l i n e  m u s s e l s by a l g a e , b a r n a c l e s ,  The  a cage  t o t h e p e r i m e t e r o f t h e farm a t t h e a p p r o p r i a t e  distance, surface  ducks  replicated  and t o p r o v i d e back-up i n t h e event t h a t  from t h e f l o a t s  perch  a measure o f i n t r a - s t a t i o n  t o s t o r m s , b o a t s , o r i n o t h e r ways.  suspended  and s c o t e r  Cage t r e a t m e n t was  four times at each s t a t i o n t o o b t a i n variability  0.4  spat  collected  from t h e  end, m u s s e l s were o b t a i n e d  1988 by s u s p e n d i n g  from t h e f l o a t s  o f t h e salmon  l e n g t h s o f w e l l - w e a t h e r e d , 2-cm  p o l y p r o p y l e n e rope which had been c o i l e d  farms. diameter  and w e i g h t e d s u c h  that  16  F i g u r e 3 . L o n g - l i n e system f o r c u l t u r e o f mussels suspended w i t h i n p r o t e c t i v e cages. T h i s s y s t e m was u s e d a t a l l s t a t i o n s a t both s i t e s . -  17  18 t h e y hung i n t h e t o p 0.5 m o f t h e w a t e r where s e t t l e m e n t i s heaviest  (Chipperfield,  1953).  However, t h e s e m u s s e l  consumed b y p r e d a t o r s a t b o t h s i t e s them i n p r o t e c t i v e  Fig.  1).  f r o m two s i t e s  The m u s s e l s u l t i m a t e l y  The l o s t  a n i m a l s were  on t h e m a i n l a n d c o a s t ( s e e  cultured  i n Genoa Bay came f r o m  I n d i a n Arm, a n d t h e s e were c o l l e c t e d by t h e same method above.  were  b e f o r e t h e need t o e n c l o s e  c a g e s was r e c o g n i z e d .  r e p l a c e d w i t h mussels  spat  I n September 1988, 16 o f t h e s e c o l l e c t o r s  with  described attached  m u s s e l s were e n c l o s e d i n t h e c a g e s a n d d e p l o y e d a t t h e Genoa Bay site.  The D e p a r t u r e Bay m u s s e l s were r e p l a c e d  w i t h a n i m a l s p u r c h a s e d from a commercial These mussels had s e t t l e d stripped  during  from t h e l o n g - l i n e s  summer  were c o i l e d  inside  D e p a r t u r e Bay.  grower  i n Okeover  Inlet.  1988, a n d h a d b e e n  o f an o y s t e r  l e n g t h s o f n e t t u b i n g known a s " s o c k s " .  i n O c t o b e r 1988  farm and p l a c e d  i n 3-m  Sixteen o f these socks  cages and d e p l o y e d a t t h e s t a t i o n s i n  Thus,  t h e mussel  b o t h i n s o u r c e and i n attachment  stocks  a t t h e two s i t e s  differed  substrate w i t h i n the cages.  Mussel Sampling S a m p l i n g o f e x p e r i m e n t a l a n i m a l s b e g a n when t h e m u s s e l s deployed a t each s i t e  (September  1988 i n Genoa Bay and O c t o b e r  1988 i n D e p a r t u r e B a y ) , a n d c o n t i n u e d a t 3-6 wk i n t e r v a l s August of  1989.  The more f r e q u e n t  1989 when m u s s e l  growth  were  sampling occurred  i n t h e summer  was a n t i c i p a t e d t o be most  Samples were a l w a y s t a k e n d u r i n g d a y t i m e  low t i d e .  until  active.  At each  s a m p l i n g t i m e , a p p r o x i m a t e l y 15 cm o f r o p e o r s o c k were removed f r o m t h e s t o c k w i t h i n e a c h cage  ( f o r some samples  later  i nthe  19 study  i t became n e c e s s a r y t o u s e m u s s e l s w h i c h h a d m i g r a t e d t o  t h e s i d e s o r bottoms healthy, sampled  firmly  o f t h e c a g e s , b u t t h e s e a p p e a r e d t o be  a t t a c h e d , and o f a s i z e  comparable  f r o m o t h e r c a g e s a t t h e same s t a t i o n ) .  h a n d l e d as g e n t l y  and as q u i c k l y  minimise s t r e s s .  At sampling times the mussel  of water  min  growth  f o r 2-10  h a d t o be  as p o s s i b l e  d e p e n d i n g upon w h e t h e r  removed f r o m t h e c a g e s .  m u s s e l s were t a k e n t o t h e l a b o r a t o r y  to  ones  A l l mussels  during  were  sampling t o  cages remained  or not  Following  out  fouling sampling the  and k e p t f r o z e n a t -40  °C  u n t i l analysed.  Data C o l l e c t i o n F o u r g r o w t h p a r a m e t e r s were m o n i t o r e d i n t h e mussels:  1)  shell  content,  and  length,  2)  condition  cultured  i n d e x , 3) c a r b o h y d r a t e  4) c r u d e p r o t e i n c o n t e n t .  1. S h e l l Length Shell likely  length  (maximum a n t e r i o - p o s t e r i o r  of v a r i a b i l i t y , i n the a l l o m e t r i c  b e t w e e n l e n g t h and o t h e r s h e l l a q u i c k o v e r v i e w o f growth  the  dimensions.  among m u s s e l s  15-cm  samples  t a k e n from each cage.  relationships  However, i t p r o v i d e d  i n any g i v e n  as a c o n v e n i e n t means t o g e t s t a n d a r d i s e d  mussels  was  a l e s s u s e f u l measure o f t o t a l body s i z e t h a n o t h e r  measures because  well  dimension)  The  sample  subsamples  shell  o b t a i n e d f r o m e a c h cage were m e a s u r e d u s i n g  as  from  lengths of a l l electronic  calipers.  A l e n g t h - f r e q u e n c y h i s t o g r a m g e n e r a t e d from t h e s e d a t a  identified  t h e modal l e n g t h - c l a s s  o f t h e sample;  mussels  of  this  l e n g t h - c l a s s were t h e n u s e d f o r f u r t h e r w i t h measuring  shell  lengths,  seasonal pattern  shell  Moribund  because: b)  of mortality  mussels  and whether  o r n o t m o r t a l i t y was  range o f a g i v e n  sample.  c e n s u s e s were, however, n o t c o m p l e t e l y a c c u r a t e  a) breakdown a n d l o s s  identification  frozen  and dead  l e n g t h s measured t o determine b o t h  evenly d i s t r i b u t e d throughout the s i z e The m o r t a l i t y  Concurrent  a s e m i q u a n t i t a t i v e measure o f  m o r t a l i t y was t a k e n f o r e a c h sample. were c o u n t e d , a n d t h e i r  analyses.  o f empty s h e l l s was r a p i d , a n d  o f dead b u t n o t y e t d e c a y i n g mussels  s t a t e was d i f f i c u l t .  These  i n the  f a c t o r s may have c a u s e d an  underestimation of mortality. 2. C o n d i t i o n  Index  Condition tissue  i n d e x was u s e d t o r e l a t e  i n t h e mussels, t h u s i n d i c a t i n g t h e i r market  apparent h e a l t h .  C O N D I T I O N  The  Condition  I N D E X  =  D R Y  T I S S U E  comparison  W T  ( D R Y  S H E L L  q u a l i t y and  _  (100)  1  a n d Chen  (1987), i n a  o f v a r i o u s methods u s e d t o a s s e s s c o n d i t i o n  Condition  o f modal l e n g t h  from t h e samples  and s i t e .  The s h e l l  aluminum w e i g h i n g p a n s . f o u l i n g growths  stable  and e a s i l y  index, measured  i n d e x was a s s e s s e d f o r e a c h o f 10 m u s s e l s t a k e n f r o m e a c h cage a t e a c h  and t i s s u e  s e p a r a t e d and d r i e d t o c o n s t a n t weight  all  W T )  Davenport  f o u n d i t t o be a c c u r a t e a n d t o employ parameters.  to living  i n d e x was a s s e s s e d a s :  above was c h o s e n b e c a u s e  station  amount o f s h e l l  Prior  o f each mussel  were  a t 90 °C i n p r e - w e i g h e d  t o drying,  s h e l l s were s t r i p p e d o f  (e.g., b y s s u s t h r e a d s , b a r n a c l e s , and  bryzoans) T h i s was  and a l l b y s s u s t h r e a d s were removed f r o m t h e body. done f o r t h e s a k e o f c o n s i s t e n c y b e c a u s e  inadvertently Because  removed f r o m some m u s s e l s m u s s e l s were f r o z e n  f o o d remnants  regularly  t i s s u e weight. t h e magnitude length  of t h i s  f r o m 26-59 mm  individual  food  400  error  were s u s p e n d e d  t o c o n s t a n t weight  T h e s e m u s s e l s were t h e n  t h e m u s s e l s was  filter  a t 60 ° C .  edulis  The  papers  guts.  The  a t 5-15  °C:  o f 7 6%  placed  f a e c e s were  (Whatman GF/C)  dry weight  and  Results  showed t h a t  of faeces  (mean o f r e p o r t e d v a l u e s  Widdows and Bayne,  1971;  Vahl,  o f gut c o n t e n t s t o i t s d r y t i s s u e gut c o n t e n t s a c c o u n t e d f o r o n l y  of the dry t i s s u e weight encompasses t h e s i z e course of the study).  of the t o t a l  f a e c a l weight t h i s would  c o n t e n t s t o 8.2%  of  weight. S.D.%  (which  a n a l y s e d over the  T h i s does not a c c o u n t f o r t h e however, e v e n  1973).  5 + 4  f o r the range o f animals used  r a n g e o f most m u s s e l s  components o f t h e f a e c e s ,  dried  o f gut c o n t e n t s i n  E a c h a n i m a l ' s t i s s u e s were a l s o d r i e d t o a l l o w c o m p a r i s o n e s t i m a t e d dry weight  site  and k e p t w i t h o u t  t h e n e s t i m a t e d from t h e measured weight  u s i n g an a b s o r p t i o n e f f i c i e n c y f o r M.  ranging i n  n e a r t h e D e p a r t u r e Bay  ml b e a k e r s i n t h e l a b o r a t o r y  onto pre-weighed  as  undertaken t o assess  Twenty m u s s e l s  f o r 18 h r t o a l l o w them t o v o i d t h e i r  filtered  s a m p l i n g , some  i n t h e g u t and were i n c l u d e d  source.  f o r 24 h r s .  sampling.  immediately a f t e r  A s e p a r a t e i n v e s t i g a t i o n was  and a l l o w e d t o f e e d in  remained  during  t h r e a d s were  soluble  i f t h e s e amounted t o  only  of the dry t i s s u e weight.  25%  i n c r e a s e t h e gut Thus,  inclusion  of  gut c o n t e n t s i n the dry t i s s u e weights o f mussels p r o b a b l y represented only a small error  source throughout the course of  22  the  experiment,  non-tissue  and no  c o r r e c t i o n was  a p p l i e d t o account  for this  weight.  3. Carbohydrate Carbohydrate,  predominantly glycogen, i s the primary  s t o r a g e compound i n m u s s e l s previously, indication  of metabolic state 1974).  t i s s u e weight length-class  widely  as  noted  any  influence  (Gabbott  and  from t h e i d e n t i f i e d  stations  cage  a t t h e 3-m  at each  site.  (closest to It  was  o f t h e s a l m o n f a r m on m u s s e l  For carbohydrate analysis  dry  modal  r e s e r v e w o u l d be most e v i d e n t i n a c o m p a r i s o n  each mussel  growth of these  the t i s s u e s  of  ( w i t h b y s s u s t h r e a d s removed) were h o m o g e n i z e d w i t h a  Brinkman P o l y t r o n Carbohydrate  triplicate  and,  a s s e s s e d as p e r c e n t a g e  from each  control  spaced s t a t i o n s .  o f Dubois  was  i n e a c h o f 10 m u s s e l s  salmon farm) and  energy  in- b i v a l v e s  Carbohydrate  o f t h e samples  expected that or  1976)  a measure o f c a r b o h y d r a t e c o n t e n t i s a good  Stephenson,  the  (Gabbott,  energy  tissue grinder  c o n t e n t was  e t al.  (1956).  f o r each  and t h e n l y o p h i l i s e d .  measured u s i n g the p h e n o l - s u l f u r i c The  colourimetric  a s s a y was  test  done i n  mussel.  4. Crude P r o t e i n Measurement o f c r u d e p r o t e i n  content afforded  of b i o a c c u m u l a t i o n o f the mussel's product.  The  l y o p h i l i s e d mussel  c a r b o h y d r a t e a n a l y s i s was (thus,  o n l y mussels  secondary  energy  an  assessment  storage  t i s s u e remaining a f t e r  used t o determine  f r o m t h e 3 m and  control  crude p r o t e i n s t a t i o n s at  content each  s i t e were a n a l y s e d ) . crude p r o t e i n  To have s u f f i c i e n t  analysis,  c a g e were c o m b i n e d .  the t i s s u e s  Each  lyophilised tissue for  o f a l l 10 m u s s e l s  c o m b i n e d sample was  duplicate using a modified selenium-catalyst (Williams,  1984).  sampled  per  analysed i n Kjeldahl  N i t r o g e n i n t h e t i s s u e was  method  converted to  ammonium s u l f a t e by w e t - a c i d d i g e s t i o n u s i n g a m i x t u r e o f H 2 0 , 2  H2SO4, and  a LiSC^/Se  more r e s i s t a n t reacted  r e a d a t 660  %  which  organic molecules.  aided i n decomposition  solution to y i e l d  C R U D E  and  P R O T E I N  =  %  a  The  was  sodium  a green c o l o u r r e a c t i o n which  urn i n a T e c h n i c o n A u t o a n a l y s e r I I .  o f t h e t i s s u e was  of  Ammonia i n t h e a c i d d i g e s t  i n series with salacylate/nitroprusside  hypochlorite  content  catalyst  was  nitrogen  c o n v e r t e d t o crude p r o t e i n  content  by:  (6.25)  N I T R O G E N  and e x p r e s s e d as p e r c e n t a g e d r y t i s s u e  weight.  5. S p a t D e n s i t y Settlement  o f mussel  measure o f salmon-farm s p a t were s t r i p p e d polypropylene structure  rope.  spat at each  i n f l u e n c e on m u s s e l  f r o m 5-cm These  o f the mussel  than being s p e c i f i c a l l y  r o p e s were p a r t  at each  farm-site.  station  mussels  I n May  of the  1989  support  and t h e s a l m o n f a r m s ,  and  further  diameter  designed c o l l e c t o r s .  were t a k e n a t e a c h  u s e d as a  vitality.  l e n g t h s o f 2-cm  long-lines  samples  The  s i t e was  Three  rather  replicate  from w i t h i n a salmon  i n t h e s e samples  d e n s i t y d a t a compared w i t h r e s p e c t t o d i s t a n c e  pen  were c o u n t e d  from t h e  farm.  and  24 6. C h l o r o p h y l l a n d S e s t o n C o n c u r r e n t w i t h e a c h 3-6 wk m u s s e l samples  6 seawater  o f 0.5 L were t a k e n a t e a c h s t a t i o n u s i n g a Van Dorn  sampling b o t t l e . surface, samples  sample,  The s a m p l e s  were t a k e n f r o m 2 m b e l o w t h e  t h e same d e p t h a t w h i c h t h e m u s s e l s were c u l t u r e d . were u s e d t o d e t e r m i n e c h l o r o p h y l l  c o n c e n t r a t i o n s a t each s t a t i o n Chlorophyll  at both  the  technique included:  at  -15 °C i n g l a s s v i a l s  up t o 6 wk, extraction  and s e s t o n  sites.  a n a l y s e s were p e r f o r m e d i n t r i p l i c a t e  t e c h n i q u e a d a p t e d f r o m P a r s o n s e t al.  (1984).  containing  o f t h e pigments  silica  available  Modifications to  g e l as a d e s i c c a n t f o r f o r acetone-  by s o n i c a t i n g t h e s a m p l e s ,  Admittedly,  i s n o t a p r e c i s e measure o f t h e amount  to f i l t e r  carbon v a r i e s  feeders since the r a t i o  of food  of chlorophyll to  c o n s i d e r a b l y w i t h t h e t y p e and n u t r i t i o n a l  phytoplankton. phytoplankton  and  concentrations using a Perkin-Elmer  S p e c t r o p h o t o m e t e r w i t h a p a t h l e n g t h o f 1 cm. chlorophyll  using a  1) s t o r i n g p h y t o p l a n k t o n - b e a r i n g f i l t e r s  2) s h o r t e n i n g t h e t i m e r e q u i r e d  3) m e a s u r i n g p i g m e n t  Generally,  state of  however, t h e d r y w e i g h t o f  i s c o n s i d e r e d t o be an o r d e r o f m a g n i t u d e  than t h e weight  greater  of chlorophyll.  Determinations of t o t a l  seston concentration  (total  s u s p e n d e d p a r t i c u l a t e m a t t e r ) were a l s o done i n t r i p l i c a t e a t e c h n i q u e adapted from S t r i c k l a n d S e a w a t e r samples  These  and P a r s o n s  using  (1972).  were p a s s e d t h r o u g h a 120 urn s c r e e n a n d t h e n  25 v a c u u m - f i l t e r e d onto pre-weighed m i l l i p o r e porosity.  The c o m b i n a t i o n o f p o r e s i z e  e x c l u d e d z o o p l a n k t o n and l a r g e (although there bacteria).  Thus,  filters  weight  within the size  of the f i l t e r s  was e l i m i n a t e d b y i n c l u d i n g  (wetted w i t h d i s t i l l e d  and l i k e l y  (inorganic p a r t i c l e s , size,  inedible  contrast,  included  f o r mussels).  possibly bacteria To o b t a i n  suspended p a r t i c l e s some n o n - f o o d i t e m s  Therefore,  concentrations  seston  likely  food.  under-  i n addition t o the phytoplankton. estimate of the contribution t o  c o n c e n t r a t i o n made b y salmon meal, were t a k e n f r o m t h e 3-m These  p h y t o p l a n k t o n was s c a r c e . above.  t h e measured  f o o d b e c a u s e m u s s e l s c a n f e e d on d e t r i t u s a n d  a more d e t a i l e d  2 h r s f o r 24 h r s .  in a  o v e r - e s t i m a t e d a v a i l a b l e mussel  the chlorophyll  estimated available  as  water and d r i e d ) w i t h each  a n d o r g a n i c p a r t i c l e s w h i c h were, b y v i r t u e  c o n c e n t r a t i o n presumably  samples  3-5  group.  s e a w a t e r sample  seston  range f o r f e e d i n g  Change i n w e i g h t due t o  Seston c o n s i s t e d o f the t o t a l  In  m u s s e l s c a n f e e d on  a s were some p o s s i b l e n o n - f o o d i t e m s .  o f s e s t o n measured.  blank f i l t e r s  of  bacteria  were d r i e d t o c o n s t a n t w e i g h t a t 60 °C a n d t h e d r y  hygroscopicity  sample  seston, but retained  a l lparticles  o f 0.22 urn  i n s c r e e n and f i l t e r  i s some d e b a t e a s t o w h e t h e r  by m u s s e l s were measured, The  filters  station  a series  a t D e p a r t u r e Bay e v e r y  s a m p l e s were c o l l e c t e d Chlorophyll  o f water  i n November when  and s e s t o n were  measured  26  7.  Currents F o r a salmon farm t o c o n t r i b u t e n u t r i e n t s d i r e c t l y t o  p o l y c u l t u r e d mussels, p a s t t h e salmon farm were m o n i t o r e d  t h e w a t e r c u r r e n t w o u l d have t o f l o w and then t o t h e mussels.  a t t h e two s a l m o n - f a r m s i t e s  Current  July,  and August  4-5 d a f t e r  meter a t t h e Departure  Bay f a r m  The model 135 m e t e r r e c o r d e d c o n t i n u o u s l y f o r  e a c h d e p l o y m e n t , whereas t h e AANDERAA m e t e r made  recordings every  15 m i n t h r o u g h o u t  i t s deployment.  m e t e r s were s i t e d between t h e s a l m o n f a r m lines.  (February,  1989) a n d an AANDERAA  temperature/salinity/current (March-June 1 9 8 9 ) .  patterns  u s i n g an I n t e r o c e a n  Systems M o d e l 135 c u r r e n t m e t e r a t t h e Genoa Bay f a r m April,  The model 135 m e t e r was k e p t  The c u r r e n t  and t h e mussel  a t 2 m depth  (in accordance  with t h e pre-emptive  programme b e i n g c o n d u c t e d  8. S t a t i s t i c a l  needs o f a s c a l l o p  by t h e P a c i f i c  Biological  a t 10 m culture  Station).  Analyses  Growth d a t a ,  except  w i t h 3-way A n a l y s e s  Station.  crude  protein  of Variance  M o d e l s p r o g r a m o f SAS  c a g e s were p o o l e d  content,  were  analysed  (ANOVA) u s i n g t h e G e n e r a l  Linear  ( S t a t i s i c a l A n a l y s i s System) a t t h e P a c i f i c Crude p r o t e i n  two-way ANOVA w i t h cage t r e a t m e n t f o r protein  c o n t e n t was a n a l y s e d w i t h a omitted  analysis.  f o r each growth parameter a t each farm. were u s e d  long-  ( t h e same a s  m u s s e l c u l t u r e ) w h i l e t h e AANDERAA m e t e r was i n s t a l l e d  Biological  first  s i n c e samples  from t h e  A s e p a r a t e ANOVA was r u n Arcsine transformed  f o r t h e g r o w t h p a r a m e t e r s w h i c h were m e a s u r e d a s  data  percentages  (i.e.,  c o n d i t i o n index,  crude p r o t e i n c o n t e n t ) .  No  statistical  between m u s s e l s grown a t t h e environmental  different  blooms),  and  freshwater  sites  run-off,  owing  as w e l l as number, s i z e ,  Chlorophyll  and  package but  with  seston  and  and  Genoa  flushing  (e.g.,  d a t a were a n a l y s e d  the  feed type,  species of  at  UBC.  seston  and  Bay  rate,  feeding  fish).  using the  same  SAS  2-way ANOVA s. 1  A m u l t i p l e r e g r e s s i o n a n a l y s i s of dry t i s s u e weight, s h e l l weight,  and  to  owing t o d i f f e r e n c e s between  c u l t u r e programmes a t e a c h s a l m o n f a r m regime,  content,  c o m p a r i s o n s were made  d i f f e r e n c e s between D e p a r t u r e Bay  (e.g., water temperature, phytoplankton  carbohydrate  shell  l e n g t h was  done u s i n g t h e MIDAS programme  S i m p l e one-way ANOVAs f o r s p a t s e r i e s were done u s i n g t h e  dry  UBC  d e n s i t y and  Genlin  f o r the  programme.  24-hr  28  RESULTS AND DISCUSSION 1. C o n d i t i o n  Index  Condition pattern  at both s i t e s .  condition stations not  i n d e x was s i m i l a r i n m a g n i t u d e a n d s e a s o n a l  indices  Fig.4 illustrates  i n mussels c u l t u r e d  f o r both s i t e s .  been d e p i c t e d ;  Individual  rather,  monthly  fluctuation of  a t each o f the four c a g e s a t e a c h s t a t i o n have  t h e c a g e d a t a were c o m b i n e d  s t a t i o n b e c a u s e t h e r e were no s i g n i f i c a n t d i f f e r e n c e s mussels c u l t u r e d  i n s e p a r a t e cages a t t h e s t a t i o n s  D e p a r t u r e Bay F Q Q ( 2 ) , 3 , 1 2 7 4 #  F  0 .05 (2),3,1428  significantly  latter  index  2.1, p=0.20).  influenced  (ANOVA:  influence  F Q  #  Q  5  at the control  TMCT).  condition  Condition  =  1  i n d i c e s were n o t  from t h e salmon farm i n *  ( l ) , 3 , 1274  0  =  /  P=0.39) b u t were i n 2 7  * '  t o that  7  P<0.001).  i twill  station  (22.3 + 9.9  (23.7+10.0  (p<0.05, Tukey M u l t i p l e  be s e e n t h a t  SD%)  Comparison on  other parameters o f mussel n o r was s u r v i v a l .  Mortality  rates  were s i m i l a r a t a l l s t a t i o n s w i t h i n  Virtually  no m o r t a l i t i e s were r e c o r d e d b e f o r e  t h i s time, m o r t a l i t y  Mussels  condition  Despite the s i g n i f i c a n t distance-effect  index,  However,  hypothesized.  l o w e r t h a n a t b o t h 15 m  g r o w t h were n o t s i m i l a r l y i n f l u e n c e d ,  after  (ANOVA:  s t a t i o n h a d t h e l o w e s t mean  (22.7 + 9.1 SD%)  between  ' P=0-62; Genoa Bay  (20.3 + 9.4 SD%), b u t t h o s e a t t h e 3-m  75 m  Test:  2  by d i s t a n c e  was c o n t r a r y  SD%) were s i g n i f i c a n t l y and  >  #  D e p a r t u r e Bay  cultured  1  (ANOVA: F Q Q 5 ( l ) , 3 , 1 4 2 8  Genoa Bay  the  =  =  5  f o r each  a  site.  June 1989 and,  counts rose r a p i d l y ,  reaching  almost  29  -  F i g u r e 4. M o n t h l y f l u c t u a t i o n s i n c o n d i t i o n i n d i c e s o f m u s s e l s c u l t u r e d i n a) D e p a r t u r e Bay a n d b) Genoa Bay a t d i f f e r e n t - d i s t a n c e s f r o m s a l m o n f a r m s (3 m, 15 m, 75 m, a n d c o n t r o l s t a t i o n s ) d u r i n g 1988-89. D a t a a r e e x p r e s s e d as means + SD, combining v a l u e s f o r a l l mussels a t a g i v e n s t a t i o n s i n c e cages c o m p r i s e d an homogenous s e t . N = 40 f o r a l l p o i n t s e x c e p t as i n d i c a t e d (*), where N = 30 due t o l o s s o f a c a g e .  CONDITION INDEX (DRY TISSUE WEIGHT [DRY SHELL WEIGHT]" X 100) -1  CONDITION INDEX (DRY TISSUE WEIGHT [DRY SHELL WEIGHT]  -  1  X 100)  50%  o f mussels  August  significant,  F  e.g.,  month-station - '  1 4  i n Genoa Bay  p<0.001).  =  4  ' '  M o n t h - s t a t i o n e f f e c t s may  of the s t a t i o n s  d i f f e r e n c e s which  since  t h i s may  were more p r o n o u n c e d  example, a t D e p a r t u r e Bay,  F  t h e 3 m and  Bay  o.05(2),27,  (ANOVA: D e p a r t u r e  P<0.001; Genoa Bay  0  highly  F(). 05 ( 2 ) , 27, 1428  (ANOVA: Genoa Bay  p=0.01), m o n t h - s t a t i o n - c a g e  positioning  i t , t h e 75 m s t a t i o n was  less the  mussel  Fo.05(2),80,1428 have r e s u l t e d  w o u l d be most p r o n o u n c e d  75 m s t a t i o n s a t Genoa bay  the  control  summer, any  An  shadowed  influence  exposure  to  being heaviest  and t o t h e g r e a t e s t  Station position  led  to  differences  i n summer.  and t h e n e c e s s i t y  o f t h e two  i n current  on  15  m, than  i n the  g r o w t h w o u l d have  15 m,  features  of  sunlight  b e e n e x p e r i e n c e d p r i m a r i l y by t h e 3 m,  Topographical  was  were s i t e d c l o s e r t o a m a r i n a  e f f e c t o f b o a t p o l l u t i o n on m u s s e l  d e t e r m i n e d by t o p o g r a p h y  For  15 m s t a t i o n s were s i t e d  S i m i l a r l y , t h e 3 m,  With boat t r a f f i c  degree  station  i n c e r t a i n months.  a differential  and  station.  =  s i t e d on t h e s o u t h s i d e  i n summer.  =  from  have g e n e r a t e d  t h e most s u n l i g h t .  g r o w t h g e n e r a t e d by  1428  f u r t h e r o f f t h e n o r t h s h o r e and  shadowed, w h i l e t h e c o n t r o l was i s l a n d and r e c e i v e d  =  Bay  c l o s e t o t h e n o r t h s h o r e o f an i s l a n d and were u s u a l l y by  by  station-cage  were  (ANOVA: D e p a r t u r e  P<0.001; Genoa Bay  6  p<0.001), month-cage  0.05(2),71,1274  4.5,  40%  and month-cage a t D e p a r t u r e Bay,  0.05(2),24,1274 =  3.6,  and  i n t e r a c t i v e e f f e c t s , with the exception of  at both s i t e s ,  14.0,  i n D e p a r t u r e Bay  1989.  All  F  sampled  and  75 m,  to avoid  mussels, was  boat  traffic.  study s i t e s almost c e r t a i n l y  flow  ( s p e e d and d i r e c t i o n )  between  32 stations.  For  proximity flow  instance,  to the  at the  15  m,  control flow for  75  use  and  was  not.  one  rock  wall  of  A difference i n current  flow  among  evidenced  I t was  remained f i x e d  and  two  l o n g - l i n e may  with  (positioned resulting  i n February  This  3  1989,  m,  but  current  to the  interaction  M u s s e l s i n c a g e s on  have had  access  because they on  to a greater  were i n  only  one  filtering  water  "filterings i d e whereas  on  both  competition  c h a n g e s i n g r o w t h p a r a m e t e r s due  sides  and  any  to decrease  in  food  flow  slower  drive  ( p e r h a p s i n summer when t h e r e was o r when t h e  (barnacles, bryozoans, sponges,  and  caprellids,  attempt t o minimise the  and  of the  t h u s may  station-cage interaction  by  macrophytes,  fouling  e f f e c t s may at d i f f e r e n t  of  fouling  on  the  have somewhat h i n d e r e d  have a d v e r s e l y  growth  1989).  removed a t e a c h s a m p l i n g t i m e i n  effects  mesh may  was  encrusting  t u n i c a t e s s e t t l e d most h e a v i l y i n M a y - J u l y  W h i l e a l l f o u l i n g g r o w t h was  occlusion  l e s s wind t o  c a g e s were more o c c l u d e d  mussel  a d i f f e r e n c e i n the  stations.  an  cages,  a f f e c t e d mussel growth.  reflect  of  the  w o u l d have b e e n most p r o n o u n c e d a t t i m e s when c u r r e n t  currents)  the  salmon f a r m i n D e p a r t u r e  a competing p o p u l a t i o n  1 m away).  t h a t the  c u r r e n t m e t e r s were a v a i l a b l e  a mussel p o p u l a t i o n  i n n e r c a g e s had  fact  the  p o s s i b l e to monitor  at the  flow.  t h e r e f o r e more f o o d ,  competition"  the  have b e e n due  regard to current  of the  by  not  s i n c e o n l y two  Month-cage e f f e c t s may  outside  difference in  caused a d i f f e r e n c e i n current  s t a t i o n s were i c e d - o v e r  s t a t i o n was  cages w i t h  the  m  at each s t a t i o n  Bay.  flow  slower.  i n Genoa Bay  and  likely  the  s t a t i o n s s i n c e c u r r e n t near the  i s l a n d w o u l d be stations  island  a t D e p a r t u r e Bay  feeding  Monthmonth-cage  Owing t o p a t c h i n e s s  of  33 fouling  growth,  s t a t i o n s may  filtering  competition  organisms  settled  in late  would  on m u s s e l  have been  r o p e s and  a c a g e may  growth.  a t t i m e s o f low  identified  protein  f o r mussels  by  (see  i n D e p a r t u r e Bay  parameters,  are the  apply to  s u c h as d r y  ( F i g . 4a) autumn 1988  resulted  mussels  crude  P<0.001).  4  a significant  of s h e l l  =  #  8- /  i n February  showed  significant  F Q Q 5 ( 2 ) , 8,1274  and w i n t e r 1989  ( F i g . 6).  ( F i g . 5a)  2 1  exhibited  from growth  constant  =  f r o m an e x t r e m e  (36%) t o a low  remained  i n d i c e s were h i g h l y  F Q . 0 5 ( 2 ) , 9, 1428  index d e c l i n e d  D e p a r t u r e Bay  These  flow  interactive  (ANOVA: D e p a r t u r e Bay  TMCT). C o n d i t i o n  body t i s s u e  growth.  c a r b o h y d r a t e c o n t e n t , and  i n condition  at both s i t e s  actually  f o r the  filtering  i n d e x , and t h e y l i k e l y  weight,  during  decline  month-  later).  changes  i n October  The  would  o r when w a t e r  f o r the s i g n i f i c a n t  to-month d e c l i n e  stations  of mussels.  fouling  on o t h e r g r o w t h  269.9, p<0.001; Genoa Bay Mussels  cage  and t h e s e c h a n g e s  food concentration  impeded  dry s h e l l  content  Monthly  competition  h a v e b e e n most p r o n o u n c e d  for condition  effects  t i s s u e weight,  fouling  an i m p o r t a n t  have e x p e r i e n c e d g r e a t e r  most p r o b a b l e e x p l a n a t i o n s  interactive  a l s o have been  efficiency  i n t e r a c t i o n would  t h r o u g h t h e c a g e s was  effects  Filtering  o r were c o l l e c t e d ,  c a g e s w h i c h may  competition  summer when  Mussel d e n s i t y w i t h i n each  have a f f e c t e d t h e f i l t e r i n g  inside  and  e v e r - c h a n g i n g as m u s s e l s moved, s l o u g h e d o f f  socks, died,  station-cage  spring  and grew on t h e c a g e s .  between mussels w i t h i n influence  have e x h i b i t e d d i f f e r e n c e s i n  month-  (p<0.05,  high  for a l l  (15%).  This  ( F i g . 5) w h i l e  S h e l l weight significant  of the  34  F i g u r e 5. M o n t h l y f l u c t u a t i o n s i n d r y s h e l l w e i g h t s o f m u s s e l s c u l t u r e d i n a) D e p a r t u r e Bay a n d b) Genoa Bay a t d i f f e r e n t d i s t a n c e s a r o u n d s a l m o n f a r m s (3 m, 15 m, 75 m a n d c o n t r o l s t a t i o n s ) d u r i n g 1988-89. D a t a a r e e x p r e s s e d as means + SD, combining v a l u e s f o r a l l mussels sampled a t a g i v e n s t a t i o n s i n c e c a g e s c o m p r i s e d an homogenous s e t . N = 40 f o r a l l p o i n t s e x c e p t as i n d i c a t e d (*), where N = 30 due t o l o s s o f a c a g e .  DRY SHELL WEIGHT (mg)  36  F i g u r e 6. M o n t h l y f l u c t u a t i o n s i n d r y t i s s u e w e i g h t s o f m u s s e l s c u l t u r e d i n a) D e p a r t u r e Bay and b) Genoa Bay a t d i f f e r e n t d i s t a n c e s f r o m s a l m o n f a r m s (3 m, 15 m, 75 m and c o n t r o l s t a t i o n s ) d u r i n g 1988-89. D a t a a r e e x p r e s s e d as means + SD, combining v a l u e s f o r a l l mussels sampled a t a g i v e n s t a t i o n s i n c e c a g e s c o m p r i s e d an homogenous s e t . N = 40 f o r a l l p o i n t s e x c e p t as i n d i c a t e d (*), where N = 30 due t o l o s s o f a c a g e .  37  1500  T  H  '  1  s  0  N  1 0  1  1  1  1  1  1  1  1  J  F  M  A  M  J  J  A  MONTH  o  O O  1500 T  A  —  A  D  —  D  3 m O 15 m 75 m Control  1  38 seasonal  fluctuations  (ANOVA: F g 0 5 (2), 8, 1274  w i t h month-to-month s i g n i f i c a n c e  f o r the  p<0.001) b e f o r e  same p e r i o d increasing  (p<0.05, TMCT). February-April  s h e l l weight had t i s s u e weight s h e l l weight significant thus and  (ANOVA:  F  as  ( F i g . 6a)  significantly  shell  later  increased significantly,  again remained c o n s t a n t .  decrease  =  3  7  8  * ' 7  in spring  1989  slightly  from  (even  though  p<0.05 TMCT) and  dry  From F e b r u a r y - A p r i l  t o t i s s u e weight,  i n c o n d i t i o n index.  1989  but without  C o n d i t i o n index  only coarsely responsive to r e l a t i v e  changes i n s h e l l  a  was weight  t i s s u e w e i g h t d u r i n g t h e s e p e r i o d s , s u g g e s t i n g t h a t i t may  less useful  as an  usage might  imply.  Condition sharply  i n the  indicator  indices  of mussel h e a l t h than  1989,  shell  growth  ( F i g . 5a;  F o l l o w i n g peak s p r i n g / s u m m e r c o n d i t i o n i n d i c e s 15-m  stations,  control,  25%;  and  30%  and  i n July  34%,  respectively;  f o r 75 m,  once a g a i n d i s p l a y e d s i g n i f i c a n t extending  t o t h e end  of the  indices  for a l l sites  August,  s h e l l weight  (12%)  growth  Fig.  6a;  p<0.05, TMCT). ( i n May  for  3-m  i n June f o r  a l l treatment  groups  1989,  The  greatest d e c l i n e at a l l  and  l o w e s t mean c o n d i t i o n  were r e c o r d e d  ( F i g . 5a)  rose  month-to-month d e c l i n e s  study.  s t a t i o n s occurred July-August  30%)  Bay  as t i s s u e  i n c r e a s e i n dry t i s s u e weight,  p<0.05, TMCT) o u t p a c e d  be  i t s common  of mussels c u l t u r e d i n Departure  spring, during April-May  (seen as a s i g n i f i c a n t  and  remained  remained constant  growth slowed  increased relative  winter  o . 05 (2), 8, 1274  C o n d i t i o n index then 1989  2403.9, p<0.001),  d u r i n g autumn and  (p<0.05, TMCT), w h i l e d r y t i s s u e w e i g h t constant  =  #  was  still  i n August. increasing  During  May-  significantly  (p<0.05, TMCT), w h i l e d r y t i s s u e w e i g h t constant August  i n May-July  and t h e n dropped  1989 (p<0.05, TMCT).  a wasting period  i n summer  Thus,  ( F i g . 6a) f i r s t  significantly  a l s o t h a t m o r t a l i t y had  r e a c h e d a l m o s t 50% b y A u g u s t ) .  Some o f t h e w e i g h t  summer  due t o s p a w n i n g .  filled  m a n t l e s were o b s e r v e d i n m u s s e l s  After The  seasonal pattern  cultured  i n Genoa Bay  described October April  June t h e m a j o r i t y  T h i c k gamete-  indices  f o r t h o s e i n D e p a r t u r e Bay.  only  slightly  Initially, increase,  in  (ANOVA: F  0 >  Q 5 (2), 9,1426  =  4 9 2  * ' 7  o.05(2),9,1425  1989 t h e r e was a s i g n i f i c a n t  month r i s e  i n condition  in  F  Dry s h e l l weight  ( F i g . 5a) a l s o  o v e r t h e s e months b u t p e a k e d  August  1989.  condition  index  =  month-toand b o t h  increased  i n July.  Condition  f r o m 40.1 + 13.3 SD% t o 21.8 + 8.2  at t h i s  level  I t was i n t e r e s t i n g (22.9 + 9 . 9  was  2641.3,  i n d e x and d r y t i s s u e weight,  and remained  o f 41.0 +  P<0.001) w h i l e s h e l l w e i g h t  In A p r i l - J u n e  SD% i n J u l y ,  September-  ( F i g . 5b) r e m a i n i n g c o n s t a n t  p<0.001).  i n d i c e s dropped d r a m a t i c a l l y  that  1989, a n d  (ANOVA:  significantly  from  (for a l l stations)  significantly  i n June.  gametes.  (p<0.05,  increasing  peaked  this  b u t from O c t o b e r -  8.8 SD% i n O c t o b e r 1988, t o 14.4 + 3.5 SD% i n A p r i l from d r y t i s s u e weight  June,  f o r mussels  month-to-month d e c l i n e  T h i s d e c l i n e was f r o m a mean  resulted  until  condition until  ( F i g . 4b) d e v i a t e d  1988, t h e r e was a s i g n i f i c a n t  TMCT).  i n early  o f mussels had shed t h e i r  of condition  t h e r e was a s i g n i f i c a n t  loss  at both s i t e s  i n d i c a t i n g t h a t m u s s e l s were i n s p a w n i n g time.  i n July-  D e p a r t u r e Bay m u s s e l s e n t e r e d  (recall  (May-June) may have b e e n  held  until  t h e end o f sampling  t o note t h a t  SD%), d e s p i t e  about  t h e August a 40% d e c r e a s e i n  number, was (14.4  significantly  + 3.5  SD%)  h i g h e r t h a n t h e extreme  when m o r t a l i t y was  virtually  nil.  r a i s e s the question of usefulness of condition of  market  quality  The m e r i t tissue to shell  size  product  i n bivalves  i n d i c e s which  and w h i c h  shell  size:  has been  dry s h e l l  raised  study) or s h e l l weight,  weight  as t o w h e t h e r  station  R e g r e s s i o n : F(). 05 (2), 3,198 d e s c r i b e d by t h e m u l t i p l e  -1.165+0 .250  Considering dry s h e l l apparent that predictor 3.6,  size may  be  question this  tissue and  randomly  A regression  of the  (ANOVA o f M u l t i p l e best  regression equation:  (LOG SHELL WT) +0 .186  and s h e l l  weight  length separately,  i t is  i s t h e s l i g h t l y more a c c u r a t e (dry s h e l l  0  c o u l d be  (LOG SHELL LENGTH)  reliably  weight t Q ^ ( ) , l , 1 9 8 2  =  2  - ' 7  P  =  0-009).  u s e d t o e s t i m a t e body  and g i v e n t h e e a s e o f measurement,  preferable.  measures  (Davenport  f r o m 20 m u s s e l s  significant  of  (as u s e d i n  c o r r e l a t e with dry  l e n g t h t . 0 5 (2j1,198  e i t h e r parameter  The  442.6, p<0.001) and was  =  o f dry t i s s u e weight  i n mussels  weight  i n Genoa Bay. highly  o f two  length.  used f o r mussels  weight  dry s h e l l  p<0.001; s h e l l  Thus,  dry s h e l l  D a t a were c o l l e c t e d  l o g - t r a n s f o r m e d v a l u e s was  used t o assess  and e i t h e r  and s h e l l  length i s a better  s e l e c t e d a t t h e 3-m  LOG TISS WT =  i n d e x as a measure  c a n be a s s e s s e d by t h e d e g r e e  s i n c e b o t h have b e e n  Chen, 1 9 8 7 ) .  This again  compare amount o f body  are popularly  c o r r e l a t i o n between d r y t i s s u e w e i g h t of  April  and a p p a r e n t h e a l t h o f m u s s e l s .  of condition  quality  low o f  shell  length  =  The was  coefficient  high  (r  tissue will  of determination f o r the m u l t i p l e  = 0.82)/  2  be  suggesting that  seasonal fluctuations  apparent  d u r i n g the study,  shell of  is likely  being unreliable  The  i n condition  indicate that  dry t i s s u e weight  length  based  t o be  f o r comparisons  cage  on d r y t i s s u e  this  notion of seasonal inconsistency.  D e p a r t u r e Bay  F  o . 0 5 (2),24,1274  0.05(2),27/1426  F  D e p a r t u r e Bay  F  Q #  =  1 0  '  =  3  3  F  F  0 . 0 5 (2), 9, 1274  =  3  «6/  3.2,  =  0 5 (2),24,1274  interaction  =  F  0 . 0 5 ( 2 ) , 9,1274  F  0 . 0 5 ( 2 ) , 24,1274  F  0 . 0 5 (2), 71, 1274  =  was  4  -6/  o f month, s t a t i o n , at both s i t e s  ,  2  /  ~  2  ' ' 4  /  « ' 4  P  «00)  p<0.001; Genoa  Other  weight: Bay  interactive  on t h e s e two  dry t i s s u e weight  weight:  Bay  P<0.001; Genoa  effects growth  was  also interaction  p=0.01) b u t n o t month-cage P  = 1  -°°) °  r  s t a t i o n - c a g e (ANOVA:  Contrastingly,  the station-cage  I n Genoa Bay,  i n f l u e n c e d by  (ANOVA:  (ANOVA:  and m o n t h - s t a t i o n - c a g e  P=0.16) d i d n o t .  significantly  and  supports  i n f l u e n c e d dry s h e l l weight  = 1  point  I n a l l c a s e s t h e month-  p=0.03) b u t month-cage  ^•^  =  1  p=0.12).  significantly  t i s s u e weight  0  or  seasons.  i n f l u e n c e d by t h e m o n t h - s t a t i o n - c a g e  (ANOVA: o . 0 5 ( 2 ) , 7 1 , 1274 0 #  3  of influence  I n D e p a r t u r e Bay,  significantly  (ANOVA: F  =  P < 0 . 0 0 1 ) .  showed a d i s p a r a t e d e g r e e parameters.  to the  P<0.001; ANOVA f o r d r y s h e l l  l f  became  (ANOVA f o r d r y t i s s u e  21•6/  =  Q 5 (2),24/1274  0.05(2),27/1425  F  significant  size.  dry s h e l l weight  influenced,  and d r y s h e l l w e i g h t  i n t e r a c t i o n was  shell  the accuracy of  between  effects  of  index, which  on e i t h e r  seasonally  nature of i n t e r a c t i v e  station  amount  r e f l e c t e d w i t h r e a s o n a b l e a c c u r a c y / by  However/  predicting  year-round/  regression  (ANOVA: dry  month-station-cage  42  (ANOVA: F  Q  m  05(2), 80,1426  F  0 . 0 5 ( 2 ) < 2 7 , 1 4 2 6  F  0 . 0 5 ( 2 ) , 9 , 1 4 2 6  significantly (ANOVA: F o . 0 5  =  /  2  ( 2 ) , 9 , 1 4 2 5  F  0 . 0 5  ( 2 ) , 2 7 , 1 4 2 5  p=0.03)  3 . 4 ,  p = 0 . 1 4 ) .  5 . 4 ,  =  Dry s h e l l  =  *  2  '  8  weight,  however,  (ANOVA:  T i s s u e and s h e l l  p = 0 . 7 8 ) .  or at least  (see e x p l a n a t i o n s f o r c o n d i t i o n  to different  index).  e x h i b i t e d temporal  was  interaction  b u t n o t month-cage  as a f f e c t e d by t h e i n t e r a c t i o n s  to shell  (ANOVA:  a n d s t a t i o n - c a g e (ANOVA:  P = 0 « 0 3 )  p = 0 . 0 1 ) ,  2 . 2 ,  =  differently,  of t i s s u e  a n d month-cage  P = 0 . 0 0 4 )  b u t n o t s t a t i o n - c a g e (ANOVA:  3 - 4 ,  ( 2 ) , 8 0 , 1 4 2 5  0 . 0 5  availability  «  3  i n f l u e n c e d by t h e m o n t h - s t a t i o n - c a g e  F  responded  =  =  growth  degrees,  o f time  t o food  and l o c a t i o n  Thus, t h e r e l a t i o n s h i p  and s p a t i a l  inconsistencies.  2 . Carbohydrate Total  c a r b o h y d r a t e c o n t e n t , as a p e r c e n t a g e  weight,  was s i m i l a r  mussels  at both  shown b e c a u s e cage  means  Genoa Bay  F  i n magnitude and s e a s o n a l p a t t e r n  sites  d i f f e r e n c e s were i n d i c a t e d  (ANOVA: D e p a r t u r e Bay F ( 2 ) , 3 , 7 0 9  =  2 . 2 ,  f l u c t u a t i o n s were a g a i n h i g h l y 0 . 0 5  2 2 9 . 1 ,  (2) , 8, 6 2 4  =  P < 0 . 0 0 1 ) .  2 1 2 . 0 ,  sites-,  s a l m o n f a r m h a d , on a v e r a g e ,  ^  0  5  ^ ) , 3 , 6 2 4  P = 0 . 1 2 ;  Carbohydrate  content  as c o n d i t i o n  Genoa Bay mussels  carbohydrate than those a t the c o n t r o l  =  index, and monthly  (ANOVA: D e p a r t u r e Bay F Q  #  Q5 ( 2 ) , 9 , 7 0 9  cultured  significantly  among  2 . 4 ,  significant  p < 0 . 0 0 1 ;  At both  Q  p = 0 . 1 8 ) .  f o l l o w e d t h e same s e a s o n a l t r e n d  F  i nthe  ( F i g . 7 ) . A g a i n o n l y s t a t i o n means a r e  no s i g n i f i c a n t  o.05  of dry tissue  3  =  m from t h e  higher percent  station  (ANOVA:  Departure  F i g u r e 7. M o n t h l y f l u c t u a t i o n s i n c a r b o h y d r a t e as p e r c e n t a g e s d r y t i s s u e w e i g h t o f m u s s e l s c u l t u r e d i n a) D e p a r t u r e Bay a n d b) Genoa Bay d u r i n g 1988-89. A c o m p a r i s o n i s made b e t w e e n mussels c u l t u r e d 3 m from t h e farm'and a t t h e c o n t r o l s t a t i o n . D a t a a r e e x p r e s s e d as means + SD, c o m b i n i n g v a l u e s f o r a l l m u s s e l s s a m p l e d a t a g i v e n s t a t i o n s i n c e c a g e s c o m p r i s e d an homogenous s e t . N = 40 f o r a l l p o i n t s e x c e p t as i n d i c a t e (*), where N = 30 due t o l o s s o f a c a g e .  CARBOHYDRATE CONTENT (% DRY TISSUE WEIGHT)  CARBOHYDRATE CONTENT (% DRY TISSUE WEIGHT)  45 B  a  v  F  0 . 0 5 ( 1 ) , 1 , 624  39.7,  p<0.001).  = 43.2,  However, d e s p i t e t h i s ,  whether d i f f e r e n c e s i n f l u e n c e d mussel differed SD%  by  a t 3-m  Genoa Bay control was  growth. 3%  v e r s u s 12.3 + 5.9  station.  important  in  + 6.7  t o mussel  SD%  at the c o n t r o l 12.6  greater store  a l l months, Bay  14.7  station;  + 5.6  SD%  +  at  the  of carbohydrate  T h i s was  not  a t t h e 3-m  the case.  energy  content w i t h i n mussel  stations  Also,  groups  was  and would  note t h a t  high the  8.8  and  production, then greater v i t a l i t y  o f the mussels  =  significantly  Departure  d u r i n g summer when m o r t a l i t y was  carbohydrate  5 ( 1 ) , 1,709  i t i s questionable  sites:  at 3 m versus  If this  have been e x p e c t e d . sites,  Q # 0  Means, w h i c h i n c l u d e at both  SD%  hence lower m o r t a l i t y  both  F  i n mean p e r c e n t c a r b o h y d r a t e  l e s s than  14.1  p<0.001; Genoa Bay  at  variation  much h i g h e r  than  during winter.  Increased carbohydrate relative sites.  t o those at the c o n t r o l I n B.C.  phytoplankton  waters,  i t may  be  summer t h e  salmon farm  that  (i.e.,  o f h i g h energy  sufficient  content o f mussels  during times  interactive  The  effect  p<0.001; Genoa Bay  significance  of the  (ANOVA: D e p a r t u r e f  Q Q5(2),9,709 #  =  8  ,  Bay 4  /  F  at  both  low f o r mussels.  food l e v e l s  of  to  grown c l o s e t o  of higher natural  a significant  1989  nutrients  the  food concentration  d u r i n g a u t u m n a l p h y t o p l a n k t o n blooms) t h i s  nutrition.  of  requirements  d u r i n g t h e low n a t u r a l  c o n t r i b u t i o n d i d not generate mussel  grown a t 3 m  o c c u r r e d May-August  contributed  enhance t h e c a r b o h y d r a t e but t h a t  o f mussels  summer i s n o r m a l l y a t i m e  l e v e l s but  Therefore,  farm,  levels  minimal  contribution  to  month-station  o . 0 5 ( 2 ) , 8, 624  P<0'001) was  =  likely  due  to  the  3-m  increased  station  interactive  F  c o n t e n t was effects  0.05(2),27,709  Departure  content  as compared t o t h o s e  Carbohydrate  F  carbohydrate  Bay  =  5  ,  also  4  P  /  < 0  3.6,  «0°1), =  Bay.  on  likely  content  have been p o s t u l a t e d  from  significant  1989, and  carbohydrate 3-m  the  farm.  through  + 1.4  station  SD%  at the  levels i n May,  12.5  i n condition  ( F i g . 7a)  percent  study  i n September  index,  demonstrated  and  content  control  winter  1988.  e x t r e m e lows o f 3.9  21.2  station.  + 6.1  levels  SD%  rapidly  After  In  of t o t a l carbohydrate  resembled  carbohydrate  that  SD%  declined  reached  from  at  a  at  in  + 3.8  SD%  i n August  the  the  station  14.5  in  3-m  1989  SD%  levels  o f mussels  of  February  April  to  station  similar  exhibited  + 1.5  declined  at the control  and  since  i n percent  control  1988  as  regardless  stations  (p<0.05, TMCT) d e c l i n e early  a  at the  ( F i g . 7b)  Again,  3-m  control  SD%  effects  same phenomena  and  + 5.2  Bay.  the  + 9.6  monthly p a t t e r n  Genoa Bay  from  nor  interactive  o f 26.4  and  (ANOVA:  Bay  rebounded t o highs  at  in  The  reached  Following this,  The  Bay  autumn and  June. 3-m  significant  result  the  for station-cage,  o f change i n c a r b o h y d r a t e  carbohydrate  3.8  not  by  inter-related.  month-to-month  carbohydrate  P<0.001; Genoa  6  the  (ANOVA:  * '  The  are  i n Departure  seasonal pattern distance  4  at  station.  month-station-cage  for differences  t h e s e growth parameters  Mussels  control  and  p=0.01), b u t  month-cage i n D e p a r t u r e carbohydrate  cultured  s i g n i f i c a n t l y influenced  t  =  at the  o f month-cage i n Genoa Bay  FQ Q5(2),23,624  0.05(2),27,709  o f mussels  of  1989.  mussels  Departure start  e x t r e m e lows o f 3.2  of  + 0.9  the SD%  at  3-m  and  2.9  + 0.6  SD%  Thus, t h e d e c l i n e was  (17.8  low, + 2.9  station). initial  a t 3 m,  level  a high level  both stations  mussels  3 m  control  group  a  v  from t h e  i n October  1989  p>0.20) and  t h e r e was  i t was  outpaced  sites  been the r e s u l t  no  at the  a l l mussels  secondary  to  TMCT) a t t h e end low b u t ,  the presumably  1988.  content d e c l i n e d  a t 3 m,  and  11.6  at  + 2.1  SD%  carbohydrate  the percent carbohydrate  significantly  higher than  tg 05(2),78  =  p<0.01).  P>0.50; Genoa Bay:  4  t . 5<2).78 0  control, counterparts.  sites  o f the study i n August  as a l r e a d y n o t e d ,  =  ' ' 2  at the  unlikely  3-m  higher  almost  that  t o have  to carbohydrate (p<0.05  than d u r i n g the  m o r t a l i t y was  1  This suggests  s i t e was  significantly  (Departure  0  Second, t h e mean p e r c e n t was  the  However, i n  i n s p r i n g t h a t mussels  at each  of  #  o f a d i f f e r e n c e which e x i s t e d p r i o r  at both  the  control  d i f f e r e n c e between s t a t i o n s  experimental manipulation.  time  following  i n summer  ( D e p a r t u r e Bay:  only l a t e r their  as  1989.  t h e d i f f e r e n c e between s t a t i o n s  of  SD%  tQ.05(2),78 =2.8,  4  stations  SD%  juveniles  + 2.5  f a r m was  to.05(2),78 = °- '  ;  +.5.1  peak, c a r b o h y d r a t e  at both  p<0.001; Genoa Bay:  B  Bay,  r e c o r d e d i n September w h i c h  i n the  i n August  First,  1989.  i n Genoa Bay  f u r t h e r p o i n t s c a n be made w i t h r e s p e c t t o  contents.  February  15.4  r e a c h i n g 13.5  the c o n t r o l , Two  i n Departure  in April  c o n t e n t r e b o u n d e d and p e a k e d i n June and  F o l l o w i n g t h e J u n e 1989  at  As  T h i s summer h i g h , however, was  carbohydrate  reflected  Bay.  carbohydrate SD%  station  s l i g h t l y more p r o t r a c t e d  compared w i t h D e p a r t u r e spring  at the c o n t r o l  50%  springhigher.  48 Thus, in  the mussels  were d y i n g d e s p i t e  e x c e s s o f 15%  3. C r u d e  of t h e i r  body  crude p r o t e i n  to condition  i n d e x and p e r c e n t c a r b o h y d r a t e ,  c o n t e n t showed a l e s s p r o n o u n c e d  from t h e f o u r cages  analysis,  distance  There  from t h e salmon  o.06(1),1,80  =  were s i g n i f i c a n t F  at each  0 . 0 5 ( 2 ) , 8,70  p<0.001).  =  The  at both s i t e s  I*  4 8  '  F  o . 0 5 ( 1 ) , 1, 70  p=0.23).  8.3,  p=0.003; Genoa Bay  FQ.Q5(2),9,140  interaction  results  postulated condition  f o r growth  parameters  crude p r o t e i n  stations.  ( F i g . 6a)  declining  7  0  #  0  5  0  however,  Bay  ( 2 )  ,  9 /  8  =  0  also  Q 5 (2),8,122  * '  either  =  P<0.001).  27.1,  significant 6  ,  8  /  This  f r o m t h e same phenomena as h a v e i n general  i n D e p a r t u r e Bay  a l m o s t c o n s t a n t a t 48%  a t t h e two weight  =  at  (see s e c t i o n  been  on  index).  Percent remained  F  o f m o n t h - s t a t i o n was 0 #  of  differences,  (ANOVA: D e p a r t u r e  F  sample  P=0.97; Genoa  Monthly  (ANOVA: D e p a r t u r e Bay  likely  influence  =  p<0.001; Genoa Bay  interaction  Since  a n a l y s e s on e a c h  f a r m on p e r c e n t c r u d e p r o t e i n  at both s i t e s 1 2  (Fig. 8).  s t a t i o n were p o o l e d f o r  a p p e a r s t o h a v e b e e n no  (ANOVA: D e p a r t u r e Bay F  seasonal v a r i a t i o n  between s i t e s  o n l y mean v a l u e s f o r r e p l i c a t e  are presented.  Bay  store  weight.  and t h e s e a s o n a l p a t t e r n d i f f e r e d  site  an e n e r g y  Protein  In c o n t r a s t  mussels  containing  was  ( F i g . 7a).  Recall also  c a r b o h y d r a t e t o gametes.  f r o m autumn 1988  that  during t h i s  c o n s t a n t , but  This  significant  ( F i g . 8a)  to spring  time dry  carbohydrate  seems i n d i c a t i v e A  mussels  1989  tissue  was  of a conversion of  decline  i n p e r c e n t crude  49  F i g u r e 8. M o n t h l y f l u c t u a t i o n s i n c r u d e p r o t e i n as p e r c e n t a g e s o f d r y t i s s u e w e i g h t o f m u s s e l s c u l t u r e d i n a) D e p a r t u r e Bay and b) Genoa Bay d u r i n g 1988-89. A c o m p a r i s o n i s made between m u s s e l s c u l t u r e d 3 m f r o m t h e salmon f a r m and a t t h e c o n t r o l station. D a t a a r e e x p r e s s e d as means + SD. N = 4, w i t h e a c h v a l u e r e p r e s e n t i n g a n a l y s i s on t h e combined t i s s u e s o f 10 m u s s e l s (where i n d i c a t e d , *, N = 3 due t o l o s s o f a c a g e ) .  100 90 80 70 60 o. 2  50  Ul 52 o v-  40  O Q  30 20 10 0 N  +F + M  M  MONTH  o-  •O 3 m  •• Control  100 90 80  .1 g  u  lxl 0 3  01 O  £2  I>OC O  70 60 50 40 30 20 10 0  + +0 +N +D + +F S J  4-  H  M  M  MONTH  h  J  protein  o c c u r r e d May-July  1989 (p<0.05  protein  c o n t e n t r e a c h e d a low o f 36.0 + 2.7 S D % i n J u l y 1989.  T h i s may have b e e n a r e f l e c t i o n w a s t i n g as mussel significant TMCT).  rise  TMCT), s u c h t h a t  /  o f gamete r e l e a s e  condition declined.  By A u g u s t  This apparent  late  summer i n c r e a s e  loss of non-protein tissues  have a l r e a d y b e e n  crude p r o t e i n  counterparts.  t h e r e was a  i n crude  protein  on t h e r e l a t i v e l y  such as c a r b o h y d r a t e ,  e x h i b i t e d even  l e s s monthly  which  variation i n  ( F i g . 8b) t h a n t h e i r D e p a r t u r e Bay  However, t h e r e was a s i g n i f i c a n t  means f o r m u s s e l s  a s some  noted.  Genoa Bay m u s s e l s percent  as w e l l  i n c r u d e p r o t e i n t o 54.4 + 2.2 S D % (p<0.05,  c o n t e n t may be m i s l e a d i n g , however, b a s e d greater  crude  at this  site  drop  i n overall  (p<0.05, TMCT), f r o m 51.3 +  5.5 SD% i n September 1988 t o 44.7 + 2.5 SD% i n F e b r u a r y 1989. D u r i n g autumn a n d w i n t e r , a s w i t h m u s s e l s Bay,  d r y t i s s u e weight  carbohydrate dropped carbohydrate energy gametogenesis,  since  remained  significantly  ( F i g . 6b), but p e r c e n t  (Fig. 7b).  i t was n o t f u e l i n g p r o t e i n from t h e body.  e x t r e m e low o f 41.9 + 3.1 SD% i n A u g u s t .  seen  Presumably,  the  s h e d d i n g o f gametes as w e l l  a n a b o l i s m and  After April  r o s e t o 50.8 + 4.9 SD% a n d t h e n d r o p p e d  reflected  i n Departure  r e s e r v e was b e i n g d e p l e t e d a t t h e e x p e n s e o f  m a t e r i a l was n o t b e i n g l o s t protein  steady  cultured  steadily  t o an  T h i s d e c l i n e may have  a s a summertime  i n t h e d e c r e a s e d d r y t i s s u e weight  crude  (Fig.  6b).  wasting  52 4.  Spat D e n s i t y  Spat different the  samples  taken at each  with respect  salmon farm  5.  F  g Q5(l),4,10  in relation  farm d i d not  to distance  FQ.05(l),4,10  2.6,  =  #  significantly  p=0.10).  influence  from  2.9,  =  Thus,  distance  spat settlement.  Chlorophyll  As  w i t h a l l the parameters  considered,  chlorophyll  showed a s i g n i f i c a n t  0 . 0 5 ( 2 ) , 8, 62  was  also  monthly  variation ~  0  9 0  significant F  Q #  Q5(1),3,62  being characterized  15 m < 75 m  and  control,  (statistically  However, s c r u t i n y be  station  largely  due  keeping with t h i s ,  8.9,  at both  f o r s u c h an  water  Genoa  and  1 2  as  .1/  FQ^Q5  stations  F .Q5(2),24,62 Q  interaction  phytoplankton d i s t r i b u t i o n  may  =  Bay  i n January  (ANOVA: D e p a r t u r e Bay 29.5,  <  and  differences  i n May  the month-station i n t e r a c t i o n sites  3 m  TMCT).  station  station  Bay  75 m < 15 m  at the Departure  3.9,  the  Departure  3 m and  farm  (l),3,53 =  p<0.001) w i t h  follows:  t h e 3-m  3-m  (ANOVA:  Bay  homogenous s u b s e t s : p<0.05,  and  ( F i g . 9)  D i s t a n c e from t h e salmon  and Genoa Bay  1989  p<0.001; Genoa Bay  reason  =  to "outliers"  f o r t h e 75-m  significant  <  of the data suggests that  i n February  Genoa Bay  P 0'001/  5  growth a l r e a d y  at both s i t e s  (ANOVA: D e p a r t u r e Bay  differences  may  * '  129.3, p<0.001).  =  p=0.01; Genoa Bay  control  r e l a t e d t o mussel  c o n c e n t r a t i o n i n sampled  F . Q 5 (2),7,53  D e p a r t u r e Bay F  to density  were n o t  (ANOVA: D e p a r t u r e Bay  p=0.08; Genoa Bay from a salmon  site  75-m  1989,  and  1989.  was  at  In  also  F g 0 5 (2),21,53  =  #  p<0.001.  The  i s u n c l e a r ; however, p a t c h i n e s s i n have been a c o n t r i b u t i n g  factor.  53  F i g u r e 9. M o n t h l y f l u c t u a t i o n s i n c h l o r o p h y l l c o n c e n t r a t i o n s a t t h e 3 m, 15 m, 75 m, and c o n t r o l s t a t i o n s a t a) D e p a r t u r e Bay and b) Genoa Bay d u r i n g 1988-89. D a t a a r e e x p r e s s e d as means. N = 3.  CHLOROPHYLL CONCENTRATION (mg/L)  CHLOROPHYLL CONCENTRATION (mg/L)  55  6 . Seston The  c o n c e n t r a t i o n of seston at both  significantly  i n f l u e n c e d by  FQ Q5(1),3,62  (ANOVA: D e p a r t u r e Bay F  0 . 0 5 (1),3,59  month e f f e c t  =  °« »  distance  p<0.001; Genoa Bay  Fq 05(2),7,59  similar  sites.  significant 5.9,  at both  sites  p=0.001; Genoa Bay  chlorophyll  been a  ,  D  F  '  P  o . 0 5 ( 2 ) , 7 , 62  Bay  significant  !87.5,  255.3, p<0.001) w h i c h  =  (ANOVA: D e p a r t u r e Bay  o.05(2),21,59 the reason  =  4  * '  F  was  was  also  o.05(2),21,62  P=0.03).  2  not  f o r s u c h an  As  with  interaction  again, patchiness of seston d i s t r i b u t i o n s  =  may  is  have  factor.  13 m g . L  i n a l l months e x c e p t  - 1  1),  July  4.4  mg.L ),  (overall - 1  Genoa Bay  mean = 5.4  January  mg.L ), - 1  (p<0.05, TMCT).  ( F i g . 10b)  demonstrated  D e p a r t u r e Bay. seston dropped  From 14.4  significantly  t o 18.2  to  mg.L  2.7  mean = 3.0  and A u g u s t  (overall  - 1  mg.L  - 1  a  mg.L  o f h i g h s and  at the s t a r t  statisically  v a r i a b i l i t y but  lows  as n o t e d f o r study,  (p<0.05, TMCT) t o a low  o f 1.5  mg.L  -  month-to-month  i n June b e f o r e s u b s t a n t i a l l y  i n July-August.  -  mean =  of the  - 1  about  seston concentrations i n  g r e a t e r monthly  and t h e n r o s e w i t h a l m o s t  significance about  mg.L  at  (overall  The  t h e same s e a s o n a l d i s t r i b u t i o n  i n January,  were s i m i l a r  and t h e s e e x c e p t e d months c o m p r i s e  homogenous s u b s e t  1  =  a  was  farms  « 3 9 Genoa  however,  S e s t o n c o n c e n t r a t i o n s i n D e p a r t u r e Bay  had  = 0  Month-station interaction  concentration,  u n c l e a r but,  F  t  a t t h e two  1  T h e r e was,  (ANOVA: D e p a r t u r e Bay  ( F i g . 10)  from t h e salmon  #  p=0.53).  7  =  sites  dropping  56  F i g u r e 10. Monthly f l u c t u a t i o n s i n seston c o n c e n t r a t i o n s at the 3 m, 15 m, 75 m, and c o n t r o l s t a t i o n s at a) Departure Bay and b) Genoa Bay d u r i n g 1988-89. Data are expressed as means. N = 3.  SESTON CONCENTRATION (mg/L)  SESTON CONCENTRATION (mg/L)  58 The  24-hr s e s t o n  phytoplankton essentially  was  series,  scarce  z e r o ) , was  carried  an  attempt  t o measure t h e  from the p a r t i c u l a t e o r g a n i c  without  excessive  tidal  and  F  and  seston  i n summer.  The  results  fluctuation  i n seston  p<0.001) and  not  the t i d a l  t h e AANDERAA m e t e r  (see n e x t  of t i d e  through t i d a l l y on  seston  on  seston  can  likely  feeding  during  daylight.  seston  concentration  farm.  The  of the  o v e r a 4-d  and  two.  tidal  both  the  that  period  Therefore,  the  A with  c y c l e showed since  an  any  operated  speed,  an  influence  of  dismissed.  t h u s appears t o have f l u c t u a t e d i n salmon farm which o c c u r r e d  after  several-hour  c e s s a t i o n of  the  feeding  r a t e of water flow  sampling  on mean c u r r e n t  i n the  f e e d was  cnrs  hour - 1  of  evening  away f r o m  s t a t i o n w i t h i n one s p e e d o f 2.7  hourly  lag in decline  e n t i r e volume o f w a t e r i n t o w h i c h t h e  (based  (ANOVA:  feeding  f o l l o w i n g reason.  collected  section)  However, t h e  would have p a s s e d t h e feeding  to effects  w o u l d p r e s u m a b l y have  be  at the  appears incongruous with  11.  However, i t i s l i k e l y  d e r i v e d changes- i n c u r r e n t  Seston concentration tandem w i t h  in Fig.  as  highly significant  c y c l e f o r the  a b s e n c e o f c o r r e l a t i o n between t h e influence  component  complete  seemed t o p a r a l l e l  f l u c t u a t i o n s were r e s p o n d i n g  comparison of c u r r e n t v e l o c i t y  tide  of sampling over a  was  salmon-feeding c y c l e s .  c y l e and  seston  background i n f l u e n c e from p h y t o p l a n k t o n  0 . 0 5 (2),11,23 ~ 10.8,  tidal  was  w a s t e o f salmon c u l t u r e  feeding c y c l e are presented  Daily  i n l a t e November when  (chlorophyll concentration  derived  would e x i s t  out  the added  after  f o r Departure  59  F i g u r e 11. F l u c t u a t i o n i n t i d a l h e i g h t and s e s t o n c o n c e n t r a t i o n as m e a s u r e d 3 m f r o m t h e s a l m o n f a r m i n D e p a r t u r e Bay. Arrows at t h e b o t t o m o f t h e g r a p h r e p r e s e n t (by p o s i t i o n ) f e e d i n g t i m e s a t t h e f a r m and (by s i z e ) t h e r e l a t i v e i n p u t o f f e e d ( t a l l a r r o w s r e p r e s e n t a p p r o x i m a t e l y 50% more f e e d ) / w h i l e h o r i z i n t a l l i n e s a t t h e t o p o f t h e g r a p h i n d i c a t e s t a t i s t i c a l l y homogenous s u b s e t s o f s e s t o n c o n c e n t r a t i o n s (p<0.05/ TMCT).  SESTON CONCENTRATION (mg/L)  TIDAL HEIGHT (m)  o  61 Bay  over t h e monitored  until it  8-10 h a f t e r  s h o u l d be n o t e d  been comprised (i.e., time  a t 1730h.  In t h i s  of a l l particulate  o r g a n i c w a s t e o f salmon  and f a e c e s ) .  Thus, g i v e n a  i t may have r e f l e c t e d t h e p r e s e n c e  diets  i n t u r n , r e f l e c t e d the presence  (Fange a n d  reasonable,  of faeces  steep i n c r e a s e i n seston which o c c u r r e d a f t e r  culture  gut-passage  1979), t h e p r o t r a c t e d d e c l i n e i n s e s t o n was  dawn may have,  regard,  t h a t t h e f a r m ' s s e s t o n c o n t r i b u t i o n w o u l d have  o f 24 h f o r s a l m o n e a t i n g t y p i c a l p e l l e t t e d  since  at  Y e t , s e s t o n d i d n o t r e a c h a low  f e e d i n g had stopped  feed p a r t i c l e s  Grove,  The  period).  i n t h e water. f e e d i n g resumed of particles of  salmon meal i n t h e water.  7. C u r r e n t s D a t a on c u r r e n t d i r e c t i o n Fig.  12.  These pie-diagrams  among t h e f o u r p r i m a r y  at both  farms a r e p r e s e n t e d i n  show t h e a p o r t i o n i n g o f c u r r e n t  and f o u r secondary  flow  compass d i r e c t i o n s .  In  Departure  Bay ( F i g . 1 2 a ) , c u r r e n t d i r e c t i o n was most f r e q u e n t l y  eastward,  with northeastward  direction  o f flow,  flowed  i n a l l months.  most  The f r e q u e n c y  i n t h e s e two d i r e c t i o n s was g r e a t e r t h a n  directions  combined i n A p r i l  predominant eastward flow  b e i n g t h e next  flow,  a n d May.  rather than  (with r e s p e c t t o frequency  current changes.  flow i n Departure B a s i n topography  maintain the eastwardly  frequent a t which c u r r e n t a l l other  The e x i s t e n c e o f s u c h a a counterbalanced  of direction),  suggests  current that  Bay was n o t d i r e c t e d p r i m a r i l y b y t i d a l and w i n d s must have o p e r a t e d t o  flow.  The e a s t w a r d l y  flow,  however,  62  F i g u r e 12. D i a g r a m a t i c p r e s e n t a t i o n o f t h e a p o r t i o n i n g o f c u r r e n t f l o w (as p e r c e n t a g e o f t h e m o n i t o r e d p e r i o d ) t o t h e f o u r p r i m a r y and f o u r s e c o n d a r y compass d i r e c t i o n s a t t h e two f a r m s i t e s . C u r r e n t s i n D e p a r t u r e Bay (a) were m o n i t o r e d c o n t i n u o u s l y f r o m M a r c h - J u n e 1989 w h i l e t h o s e i n Genoa Bay (b) were m o n i t o r e d i n t e r m i t t e n t l y o v e r 4-d p e r i o d s i n e a c h o f F e b r u a r y , A p r i l , J u l y , and A u g u s t 1989. Insets i n d i c a t e the p o s i t i o n i n g of treatment s t a t i o n s (3 m, 15 m, and 75 m) a r o u n d t h e f a r m s : D e p a r t u r e Bay s t a t i o n s e x t e n d e d i n a l i n e 1 0 ° n o r t h o f e a s t ; Genoa Bay s t a t i o n s were i n a l i n e e x t e n d i n g n o r t h f r o m t h e f a r m .  N  NW/^" /  W  "  N  5 /10  7  23 [  33 Sv.  \  r  L  W  6  sw \ ^^  c " ~  ^ \  >\  NE  25  \  36  ^  0.7  \o.03  2 /  5  0.4  s  s  FEBRUARY  APRIL  N 10 /  yv.  2  w 0.7 \  ^ \ N E  NW/^  11  2 9 \  42  E  swV^  SW  s  N  W• 15 m • 3m FARM  NE  BE  s AUGUST  JULY  • 75 m  N  52  W  10y/  2  ^  65  s h o u l d have been b e n e f i c i a l site,  since At  l o n g - l i n e s were s i t e d  Genoa Bay  eastward  t o mussel-salmon p o l y c u l t u r e  ( F i g . 12b),  almost  current also  i n a l l monitoring periods.  period of monitoring, eastwardly w e s t w a r d f l o w f o r 23% p e r i o d s t h e combined c u r r e n t s was  due  f l o w e d most  Also,  Bay  that,  eastward  as i n D e p a r t u r e  were n o t t h e p r i m a r y  current  direction.  ideal  sited  Bay,  directly  tidal  i n f l u e n c i n g the  n o r t h from the  north  It again  c h a n g e s i n Genoa frequency  u n l i k e Departure  and n o r t h e a s t w a r d  f o r mussel-salmon p o l y c u l t u r e ,  almost  a  f l o w seemed t o become  N o t e , however, t h a t  predominance o f eastward not  force  February  During a l l other monitoring  i n c r e a s i n g l y more f r e q u e n t d u r i n g A p r i l - A u g u s t 1989. seems a p p a r e n t  farm.  c o u n t e r b a l a n c e d by  f r e q u e n c y o f e a s t , n o r t h e a s t , and  o v e r 80%.  this  frequently  However, d u r i n g t h e  f l o w was  of the time.  east of the  at  Bay,  f l o w i n Genoa Bay  since  farm.  of  long-lines  the was  were  66  GENERAL DISCUSSION Salmon f a r m i n g i s t h e most e x t e n s i v e British  Columbia.  being active Licensing  I n 1989,  217  (B.C. M i n i s t r y  S t a t i s t i c s March,  Intensive culture  substantial  1990),  (Gowen and B r a d b u r y ,  o f n u t r i e n t s has mussels  Such  However, i n t h e p r e s e n t s t u d y  a l l showed no  comes i n t o  For p a r t i c l e s  consistent  o f mussels  o f enrichment  as  duck  provision  f r o m salmon  of  growth,  c o n t e n t , and  or s u b s t a n t i a l  f r o m a salmon  i n the  farm.  spat  increase  with  Thus,  culture with regard to  question.  t o be e a t e n by m u s s e l s t h e y must be  120  urn d i a ; p a r t i c l e s  The  24-h  seston  form  r a i s e d the issue of p o t e n t i a l p o l y c u l t u r e  decreasing distance availability  a  and  as w e l l  1978).  index, carbohydrate content, p r o t e i n  settlement,  mussels  ( P e a r s o n and R o s e n b e r g ,  and s a l m o n .  condition  generates  1987),  w i t h d o m e s t i c sewage  Report,  a r e known t o p r o v i d e n u t r i e n t s t o o r g a n i s m s  surrounding waters  125  12,385  Annual  i n c o a s t a l waters  f r o m wood p u l p and seaweed p r o c e s s i n g ,  farming, which  with  Fisheries:  and t h e s e p r o d u c e d  o f salmon  amounts o f w a s t e  and  (B.C. Salmon F a r m e r ' s  o f o r g a n i c enrichment comparable effluent  l e a s e s were h e l d ,  of Agriculture  t o n n e s o f c a g e - r e a r e d salmon 1989) .  salmon  form o f a q u a c u l t u r e i n  l a r g e r than t h i s  sampling s e r i e s  are r e j e c t e d  i n D e p a r t u r e Bay  less  (Reid,  indicated  salmon-feeding increased the concentration of p a r t i c l e s range  f o r feeding mussels:  Thus,  addition  1982). that  ( i n the  0.2-120 urn) f r o m 1 t o 4 mg.L-1.  o f farm-generated s e s t o n would  doubled the a v a i l a b l e  than  food f o r mussels.  a p p e a r t o have  However,  seston  concentrations  i n the present  and  an  order  can  be  efficiently  seston  were n e v e r above 20  o f magnitude l e s s than s e s t o n  In t h e p r e s e n t greatly  study  filtered  study,  then,  by  mussels  The  as  low  salmon farms p r o b a b l y  increase  reported production  1979).  c o u l d not  s t u d i e s on  Gowen and  Bradbury  i n seston  through a d d i t i o n of  concentration  present  the  study  associated  with  seems anomalous  e c o l o g i c a l impact  (1987) i n d i c a t e d t h a t  f e e d became o r g a n i c w a s t e i n t h e  o f salmon  40%  diversity  farm, and  to  m.  120  The  (1987) was s p e e d was  of benthic  of the  administered  (1987) showed t h a t  fauna i n the  were a l t e r e d , a l b e i t  and  settlement  l o c a t e d i n a S c o t t i s h sea 4 crrrs  characteristics Genoa Bay,  and  - 1  are with  and  d e p t h was  20  comparable w i t h  for  deposited  f e e d i n g by  generate seston explanation  mussels,  m.  These  those  s a l m o n - f e e d i n g may  be  low  seston  for  up  al.  current  o f D e p a r t u r e Bay The of  study  and of  sediment w i t h i n the  some f a r m s ,  feeding mussels.  apparently  Brown e t  around  site  s a l m o n f a r m was  corroborating that  available to  f o r the  by  most s a l m o n f a r m s i n B.C..  around the  15 m  l o c h where mean  Brown e t a l . (1987) i n d i c a t e d t h a t mean s i z e particles  first  number,  t o a l e s s e r degree,  salmon farm s e l e c t e d f o r study  In  farming,  o f p a r t i c u l a t e o r g a n i c waste s t r o n g l y i n f l u e n c e d s p e c i e s  a fish  to  form o f uneaten p e l l e t s  F u r t h e r m o r e , Brown e t al.  and  have  o f o r g a n i c waste b y . o t h e r salmon farms.  reviewing  biomass,  which  predicted.  salmon-feeding noted i n the  faeces.  concentrations  (Widdows e t al.,  enhanced the mussels' n u t r i t i o n food  mg.L-1,  A  at  range least,  possible  increase  despite  t h a t t h e w a t e r s a m p l e s were t a k e n  3 m  68 outside,  rather than  from w i t h i n ,  o r g a n i c w a s t e s were f i l t e r e d f a r m and, t h u s , n e v e r known pumping r a t e s mussels  t h e farm.  o u t by m u s s e l s  Perhaps  particulate  on t h e n e t s o f t h e  reached the experimental animals.  o f mussels  on t h e n e t - p e n s  (Vahl,  B a s e d on  1973) a n d t h e d e n s i t y o f  o f , f o r example, t h e Genoa Bay f a r m  ( e s t i m a t e d t o b e 2 * c m " ) , t h e e n t i r e volume o f a t y p i c a l  salmon  2  pen  (5.0 m X 5.0 m X 6.0 m) c o u l d t h e o r e t i c a l l y  3 minutes  by t h e mussels  on t h e n e t - p e n s .  w i t h i n a farm i s e n c i r c l e d by a c u r t a i n  be f i l t e r e d  Because each pen  o f n e t and t h e e n t i r e  farm i s e n c i r c l e d by a p r e d a t o r n e t , and depending density  o f mussels  In f a c t ,  p e n s c a n be s i m i l a r and D a n k e r s systems  well  capacity  for filtering  (1988) u r g e t h a t  on some n e t -  mussel  b e d , a n d Dame  s u c h p o p u l a t i o n s be v i e w e d  f o r s u b s t a n t i a l uptake  phytoplankton, o r g a n i c carbon,  as e x c r e t i o n  particulate  t h e p o p u l a t i o n o f mussels  i n density to a typical  responsible  sediments,  upon t h e  on t h e s e , salmon f a r m n e t s may r e p r e s e n t a  screen with substantial o r g a n i c waste.  every  of significant  of  as  suspended  and f i x e d n i t r o g e n ,  as  amounts o f ammonium a n d o r g a n i c  phosphate. Any  influence  o f t h e salmon farm i n terms  c o n c e n t r a t i o n would, seasonal  influences  i n any e v e n t , have b e e n o v e r s h a d o w e d b y on t h i s p a r a m e t e r .  s e s t o n c o n c e n t r a t i o n were s i m i l a r the  of seston  S e a s o n a l changes i n  i n some r e s p e c t s t o t h o s e o f  measured growth and e n e r g y - s t o r a g e p a r a m e t e r s .  summer  lows  i n seston corresponded with d e c l i n i n g  W i n t e r and condition  index  and c a r b o h y d r a t e c o n t e n t i n t h e same s e a s o n  at both  (although i t i s notable that  continued f o r three  these declines  farm-sites  69 months a f t e r  seston  see F i g s . 4-7).  with  i n the mussels. represented  h a d begun t o r i s e  i n spring,  D r y s h e l l w e i g h t , however, i n c r e a s e d o v e r  despite the seston corresponded  concentrations  low. strict  Thus, o n l y t h e summer lows i n s e s t o n fidelity  t o a m e t a b o l i c a l l y poor  Possibly the winter  a concentration  s u s t a i n mussels a t t h i s  winter  "low" i n s e s t o n  state  actually  o f f o o d t h a t was s u f f i c i e n t t o  time o f year,  when m e t a b o l i c  activity  was  low.  Phytoplankton  production,  like  seston,  apparently  augmented b y t h e s a l m o n f a r m s , d e s p i t e an e x p e c t a t i o n w o u l d be b a s e d on n i t r o g e n o u s approximately excreted excretion  as  (Gowen a n d B r a d b u r y , i s ammonium  c  can  (Rychly,  1979), t h e r e  and u r e a  enrichment by t h e farms.  e x c r e t e d b y c u l t u r e d s a l m o n may be o x i d i s e d o r , directly  e t al., 1977; G i l b e r t  1981).  of this,  s h o u l d have b e e n  u t i l i s e d by  phytoplankton  e t al., 1982a; 1 9 8 2 b ) .  a l s o be a b s o r b e d r a p i d l y by m a r i n e p h y t o p l a n k t o n  Goldman,  I t seems c l e a r t h a t  enhance t h e growth p o t e n t i a l a v a i l a b l e t o primary of  Since  1987), a n d t h e m a j o r i t y  f o r phytoplankton  a p r e f e r r e d route,  (M Carthy  that i t  68% o f n i t r o g e n consumed b y f a r m e d s a l m o n i s  ample p o t e n t i a l Ammonium  e x c r e t i o n by salmon.  was n o t  salmon f a r m i n g  o f phytoplankton  producers  Ammonium  ( G i l b e r t and should  by m a k i n g n i t r o g e n  and, t h r o u g h t h i s ,  enhance  growth  mussels.  There a r e s e v e r a l p o s s i b l e ' e x p l a n a t i o n s  f o r lack of  increased chlorophyll concentration despite a nitrogen generated  by t h e salmon farms.  influx  F o r example, Gowen a n d B r a d b u r y  (1987) have s u g g e s t e d not  that primary  p r o d u c t i o n c a n be  lead to increased phytoplankton  q u i c k removal  by  to think that  i n the present  somehow e x c l u d e d utilisation l i m i t e d by  grazers.  from  the v i c i n i t y  t h e r e w o u l d be  phytoplankton  l o n g enough t o c a p i t a l i s e  Alternatively,  other environmental  temperature, nutrients nitrogen  low  light  chlorophyll  carbon).  The  salmon.  The  monthly  corresponded and  energy  declining was  weight  was  fluctuations  only s l i g h t l y  such  levels  study  may  as  be  low  of other required  o r g a n i c compounds  (see F i g . 9)  i n production of  condition  w i t h monthly  i n d e x and  at t h i s  constant.  time  of  suggests by  nitrogenous  i n chlorophyll concentration fluctuations  In Departure  c o n c e n t r a t i o n (November 1988)  noted that  in  salmon f a r m s s i n c e t h e r e w o u l d  reserves of the mussels.  chlorophyll  remain  p o p u l a t i o n s were p r o b a b l y more i n f l u e n c e d  seasonal f l u c t u a t i o n  w a s t e by  not  farm  e x i s t e n c e o f s e a s o n a l changes i n  s e a s o n a l c h a r a c t e r i s t i c s t h a n by have b e e n no  may  be  At  phytoplankton  o r low  c o n c e n t r a t i o n d u r i n g the  that phytoplankton  i s that  despite high  ( s u c h as m i n e r a l s , v i t a m i n s , and and  1983).  characteristics  intensity,  were  on t h e h i g h c o n c e n t r a t i o n s  concentrations of nitrogenous nutrients, l i m i t e d by  reason  s a l m o n may  (Gowen e t al.,  but  of  a priori  possibility  u r e a e x c r e t e d by  i s rapid,  of nitrogenous n u t r i e n t s .  no  study e x p e r i m e n t a l mussels  f l u s h i n g time  s i t e s where f l u s h i n g  c o n c e n t r a t i o n because  such g r a z i n g . Another  o f ammonium and rapid  Yet,  enhanced  carbohydrate  shell  was  Bay  i n growth the  synchronous  content.  g r o w t h o c c u r r e d and  Therefore, despite s c a r c i t y  of  lowest with  However, i t dry  tissue  p h y t o p l a n k t o n i n November/ producing s h e l l  i n autumn 1988  p h y t o p l a n k t o n , b u t t h i s was growth  only s l i g h t condition, winter.  reversed  and e n e r g y  summer f l u c t u a t i o n s  less  to spring  were a p p a r e n t l y u n a f f e c t e d by  condition,  were m e t a b o l i c a l l y  and c o n v e r t i n g c a r b o h y d r a t e .  t h e i r deployment mussels  the mussels  growth,  1989,  in  parameters.  a l l growth Thus,  nutrition factors  1989,  salmon  but here  a t Genoa Bay  feeders,  the e f f e c t . insured  s i m p l y by  The  via liberation  light  importance  of s i t e  on m u s s e l  and D i c k i e ,  1979;  e t al.,  Dickie  1986;  presence  growth  1984;  competing  c l o s e t o salmon  and  be farms.  culture  survival  Widdows e t al.,  by M a l l e t  reduce  of the influence  1987a; 1987b; S w a r b r i c k et  R e c i p r o c a l t r a n s p l a n t s o f mussels  other  of  cannot  t o the success o f mussel  and g e n e t i c s  t o augment  operate to  i n investigations  rise  o f wastes,  o f mussels  cultures  environment  e t al.,  f e e d , may  i n c r e a s e d growth  been r e p e a t e d l y emphasised  Mallet  intensity,  be  chlorophyll  compounds, p r e s e n c e o f  s i t i n g mussel  in  appeared t o  f a r m s have t h e p o t e n t i a l  and t y p e o f salmon  Clearly,  with  i t was  although  with  was  coincidental with a spring  o f p o l y c u l t u r e d mussels  other than nitrogen  there  concentration  reserves,  growth  s u c h as t e m p e r a t u r e ,  nutrients filter  even though  when  I n Genoa Bay  r e l a t e d to phytoplankton fluctuations, r o s e i n May  Bay  r e s e r v e s d i d seem t o c o r r e l a t e  and e n e r g y  concentration  from  Departure  i n summer 1989  of chlorophyll  I n summer, m u s s e l  In g e n e r a l ,  fluctuations i n  i n phytoplankton.  correlation  active,  al.,  e t al.  has of  (Freeman 1984;  1990). (1987b) have  indicated, that This  genotype i s p r i m a r i l y r e s p o n s i b l e  contradicts  reported  that  the  growth r a t e s  environments d i f f e r are  marked and  Therefore, the  are  only the  r e s u l t i s the  slightly,  same:  e f f e c t on  environment Thus, t o  carefully selected.  Trial  culture  and  Genoa Bay  may  mussel source, high,  and  predicted  of  a trial be  since mortality  site,  since  on  mussels, there  may  For  the  still  may  example,  o f m u s s e l and polyculture  be  be  the of  fulfill  logistical  with was  mussel-salmon  advantages t o  for this  provide structural  f o r mussel suspension.  s h o u l d be  Bay  their  n u t r i t i o n a l advantage  two  crops  There from  A primary  parasites  one  coupling  investigated before  implemented.  t r a n s f e r o f p a t h o g e n s and  a  stocks  o t h e r sometimes n e g a t i v e a s p e c t s o f  i s commercially  only  growth.  s a l m o n f a r m s may  salmon c u l t u r e  should  1989).  transplanted  farms d i d not  long-lines  may  a problem a s s o c i a t e d  of the  o f any  mussel-salmon  experiments at Departure  economic advantages t o h a r v e s t i n g  Conversely,  potential  the  r e s u l t s cannot advocate  basis  for deploying  a l s o be  lease.  the  mortality,  influences  from  (Jamieson,  p o t e n t i a l t o augment m u s s e l  polyculture  support  area  i n d i c a t i v e ' of  Although present  pairing.  effort,  or  source of mussels studies  two  production.  p o t e n t i a l growth r a t e  s p e c i f i c mussel source i n a given  in  differences  substantially  and  have  same s t o c k  growth r a t e  reap b e n e f i t  e f f e c t i v e means t o e s t a b l i s h t h e  as  from the  (1984) who  while mortality  both salmon-farm s i t e  Furthermore,  al.  mortality.  p r i n c i p a l determinants of net  of mussels.  polyculture,  et  of mussels  w h e t h e r t h r o u g h an  production  be  r e s u l t s of Dickie  for  concern  such is  between m u s s e l s  and  salmon.  D i s e a s e i s an i m p o r t a n t c o n c e r n i n a l l c u l t u r e  o p e r a t i o n s because spread o f pathogens  i s e n h a n c e d by  d e n s i t y which i s a hallmark o f animal husbandry.  increased  Disease  c o n c e r n s t a k e on new d i m e n s i o n i n p o l y c u l t u r e b e c a u s e t h e s p e c i e s might respond d i f f e r e n t l y differential  t o p o t e n t i a l pathogens.  r e s p o n s e has been n o t e d w i t h b a c t e r i a ,  which a r e p o t e n t i a l l y  edulis  higher concentration than i n e i t h e r  stomach  (Bouvy a n d D e l i l l e ,  may i n c r e a s e t h e r i s k potential  risk  Vibrio  spp.,  h a r m f u l t o salmon a n d known t o be h a r b o u r e d  i n t h e h i n d - g u t s o f m u s s e l s , Mytilus  seawater  Such  1987).  t r a n s m i t t e d t o salmon.  At least  f o r northeast P a c i f i c mussels condition of blood c e l l s  in  or surrounding  Contact w i t h mussel  of Vlfcrio-infeetion  i s the p o s s i b i l i t y  desolationis,  i n salmon.  faeces  Another  f o r m u s s e l d i s e a s e s t o be one d i s e a s e h a s b e e n  identified  ( J a m i e s o n , 1989), a t u m o r o u s  known as h e m i c n e o p l a s i a w h i c h c a n be  f o u n d i n 60% o f p o s t - s p a w n i n g m u s s e l s i n B.C. 70% o f m u s s e l s f r o m P u g e t  (Bower,  Sound  (Elston  et a l . ,  t h e r e h a s b e e n no i n v e s t i g a t i o n  of this  disease with respect t o  salmon.  A contrasting  differential  consideration  (bacterial  kidney disease)  thus p o s s i b l y  reducing r i s k  investigation  of disease risks  potential  and d i g e s t  bacteria  (Evelyn et a l . ,  of infection.  salmon; t h a t i s ,  of parasitic  intestinalis,  a parasitic  digestive tissues,  responsible f o r  unpubl. data),  I n any c a s e , t h o r o u g h  i s necessary t o assess the  c o u p l i n g o f m u s s e l and salmon c u l t u r e .  investigation  As o f y e t  i s the p o t e n t i a l f o r  r e s p o n s e w h i c h may a c t u a l l y b e n e f i t  m u s s e l s may be a b l e t o f i l t e r BKD  1988).  1989) a n d  risks  Thorough  i s also necessary.  copepod,  i s occasionally  Mytilocola  found w i t h i n  a n d u n i d e n t i f i e d p r o t o z o a n s a n d Nematopsis  sp.  74 have b e e n o b s e r v e d i n t h e lumen o f k i d n e y s i n B.C. m u s s e l s . A l t h o u g h Emmett  (1984) r e p o r t e d  that  low f r e q u e n c y  of these p a r a s i t e s tended t o reduce t h e i r populations/ on  there  salmon.  has  have b e e n no s t u d i e s  Bradbury,  1987) a n d m u s s e l c u l t u r e  1985; Dame a n d D a n k e r s ,  extrapolated  that  o f the present  This  that  (about  mussels) d i d n o t g i v e of  inorganic  nutrients  edulis  rise  significant  release  mussel beds. to  ammonia  Thus,  c a n be  160 t o n n e s w e t - w e i g h t o f  t o measurable changes i n c o n c e n t r a t i o n  a n d o x y g e n i n t h e w a t e r mass  Dame a n d D a n k e r s  passing  sometimes d o u b l e d a n d (1988) a l s o  o f ammonium a n d p h o s p h o r u s f r o m since  study.  2 1 - m o n t h - l o n g s t u d y showed  through t h e c u l t u r e , b u t ammonia-nitrogen phosphorus quadrupled.  would  (1985) i n v e s t i g a t i o n o f i n f l u e n c e o f  m u s s e l c u l t u r e on w a t e r q u a l i t y . l o n g - l i n e s o f Mytilus  i n this  In t h i s  t h i s process  type o f p o l y c u l t u r e  from L a r s s o n ' s  e t al., 1982;  s a l m o n c u l t u r e h a s b e e n one  and t h e p o s s i b i l i t y  effects of this  (Galkina  of polyculture.  mussel c u l t u r e formed t h e b a s i s  Reciprocal  ( r e v i e w e d i n Gowen  1988) have b e e n s t u d i e d  t h e c h i e f concern regarding  of eutrophication, favour  B o t h salmon c u l t u r e  but never i n t h e context  context,  on m u s s e l s  i n a q u a c u l t u r e h a s a l s o b e e n shadowed by c o n c e r n s  o f water q u a l i t y e f f e c t s .  regard,  c>f t h e i r p o s s i b l e e f f e c t  investigated.  Interest  Larsson,  e f f e c t on m u s s e l  S i m i l a r l y / t h e e f f e c t o f salmon p a r a s i t e s  n o t been  and  of occurrence  reported natural  s a l m o n a r e known t o b e h i g h l y  sensitive  ( I n t e r n a t i o n a l Programme on C h e m i c a l S a f e t y ,  1986), i t  may b e n e c e s s a r y t o s i t e m u s s e l - s a l m o n p o l y c u l t u r e s  i n areas  with  75 high  flushing  negatively The  rates to prevent  e x t e n s i v e mussel c u l t u r e  i n f l u e n c i n g water q u a l i t y  present  practicality  s t u d y has  p r o v i d e d i n f o r m a t i o n not  of accumulation  p r o d u c t s by B.C.  mussels.  and  c o n d i t i o n between B.C. counterparts.  populations study,  g l y c o g e n was  are accounted  o b t a i n e d measure o f t o t a l  this,  and t h a t  f o r as b l o o d s u g a r s  and m a n t l e and u t i l i s a t i o n  content  i n Mytilus  estimates of t o t a l  of glycogen.  Edwards  (1975),  European success  mussels  In the  (whose l e v e l  i n mussels  represents the  from t h e d i g e s t i v e  was  energy  is  carbohydrates  o f g l u c o s e by body t i s s u e s ) , carbohydrate  present  total  a l l other  thought  reserve.  gland  the  to provide  a  In support  of  (1975) r e p o r t e d t h a t v a l u e s f o r g l y c o g e n  edulis  were i n c l o s e  agreement w i t h  indirect  carbohydrate.  I n E u r o p e a n p o p u l a t i o n s o f M y t i l u s edulis and  and  r e p o r t e d f o r European  of glycogen  assessment o f carbohydrate Dare and Edwards  apparent  to the  storage i n  since practically  b a l a n c e between m o b i l i s a t i o n  useful  important  storage  are  growth,  r e p r e s e n t e d i n t h e measure o f  and  the  o f energy  Since the m a j o r i t y of carbohydrate  s t o r e d as g l y c o g e n ,  on  the  B.C..  r e l a t e s to the c y c l i n g  carbohydrate.  be  d i f f e r e n c e between e n e r g y study  o n l y on  a n d . t h e i r much-studied  operations i n  i n the present  also  of i n t e r e s t  metabolism,  T h e s e d i f f e r e n c e s may  of mussel c u l t u r e A primary  mussels  but  expenditure  Particularly  d i f f e r e n c e s w i t h r e s p e c t t o energy  cultured  f o r salmon.  o f mussel-salmon p o l y c u l t u r e ,  seasonal cycle  from  Pieters  e t al.  (1979),  d e s c r i b e d by  Zurburg  e t al.  Dare (1979),  and  Zandee e t al.  April-June  Emmett  glycogen  t o 30-40% d r y w e i g h t ,  before declining I n B.C.  (1980)/  and  s l o w l y t o an A p r i l  populations, both (1984) and  l a t e winter,  was  lowest  remained at t h i s low  i n the  i n the present  Emmett e t al.  in April,  (1987),  study  rose i n level  f o l l o w i n g year. and  glycogen  those  was  of  again  r o s e s t e e p l y i n s p r i n g r e a c h i n g 15-30% d r y  remained e l e v a t e d through w i t h some s l i g h t  summer, and  lowest  weight,  t h e n began a s t e e p d e c l i n e  c o u n t e r a c t i o n i n October.  Thus, where E u r o p e a n  m u s s e l s a p p a r e n t l y s p e n d 5 months a t 30-40% g l y c o g e n  content  before  during  s l o w l y expending  gametogenesis: al.,  their  store  Bayne e t al.,  content  1987  e x h i b i t e d by  inability  B.C.  onset  as b e g i n n i n g  resulting  e x t r e m e low  mussels i s not  Rather,  i s used  i t may  be  up  indicative  of a lack of  time  study  changing  content.  tissues  (Emmett e t a l . (1987) h a v e a l s o  activity  At t h i s  nor  of  reserves  acquired through  protein  exhausting  carbohydrate  i n maintenance requirements  content without  and  of  R e c a l l t h a t winter mussels i n the present carbohydrate  content  gametogenesis  that a carbohydrate  because the energy  Peek e t  i n December).  t o undergo gametogensis because energy  accumulated  their  of  m e t a b o l i s m d u r i n g autumn and w i n t e r ,  insufficient.  feeding  reported this  e a r l y d e c l i n e and  carbohydrate  1982;  f o r o n l y 3 months b e f o r e r a p i d l y  s t o r e i n A u g u s t , months b e f o r e t h e  The  (likely  m u s s e l s peak a t o n l y 15-30% g l y c o g e n  level  (Emmett e t al.,  not  glycogen  Bayne e t a l . , 1975;  1989), B.C.  maintain t h i s  their  and  an are  reserve i s autumn-winter  gametogenesis.  ( F i g . 7)  depleted  dry t i s s u e weight  t h e y were l i k e l y  producing  gametic  r e p o r t e d gametogenic  i n mussels d u r i n g autumn-winter).  This pattern  or  contrasts with  that  of energy accumulation  f o r European mussels. is  i n v o l v e d i n accumulation  and to  In t h e s e  Zandee,  1972)  and  meet m e t a b o l i c  the  (Gabbott,  this  remaining to the  1975;  during  summer  season  and  (de  (Bayne,  (glycogen  1979;  engage i n g a m e t o g e n e s i s and This s i m i l a r i t y capable  in timing  Zandee e t  ability  spawning p a t t e r n  to a l t e r (Newell  i s not  reproduction  survival.  e t al.,  1982)  edulis  1983;  These a u t h o r s  gametogenesis but as  that  (Lowe e t al.,  i n c r e a s e d age,  B.C.  opportunistic  apparently  1982;  are  By  virtue and  to  synchronise  a  1984;  al.,  Hawkins e t of  al.,  Mytilus  s t r a t e g y where  accumulated t h e n expended i n  f o o d q u a l i t y and  l e d t o a change t o an  quantity,  "opportunistic"  fueled directly  by  nutrient  m u s s e l s , however, seem t o e x h i b i t a more strategy  and  plastic  Newell et  reproductive  were f i r s t  s t r a t e g y where g a m e t o g e n s i s was intake.  i n response  Rodhouse e t al.,  increased  mussels  1975)  r e p o r t e d t h a t most p o p u l a t i o n s  products  al.,  same t i m e .  (Bayne,  i s known t o be  exhibited a "conservative"  energy storage  of  c o n d i t i o n s f o r l a r v a l growth  strategy  i n mussels  Bayne e t al.,  1985).  optimal  Reproductive  characteristic 1982;  with  European  spawning t i m e s .  gametogenic r a t e  and  differences  s u r p r i s i n g s i n c e mussels  e n v i r o n m e n t a l c o n d i t i o n s , mussels can their  and  spawning at about the  o f wide a d j u s t m e n t s i n t h e i r  of t h e i r  B.C.  upon  1973).  protein consituents  P i e t e r s e t al.,  c y c l e s of energy r e s e r v e s ,  Zwaan  i s heavily relied  energy r e s e r v e s  lipid  noted  e n t i r e body  K l u y t m a n s e t a l . , 1 9 8 5 ) . .Thus, d e s p i t e n o t a b l e  seasonal  well  allocation  u s u a l l y the  energy r e s e r v e  demands d u r i n g  converted  gametes  1980; in  are  of glycogen  this  Then, i n a u t u m n - w i n t e r , protein)  mussels,  and  i n t h a t energy  storage  seems t o  be  as  78 synchronous  w i t h gametogenesis  (carbohydrate content  May-June w h i c h i s g e n e r a l l y a t i m e A comparison  o f B.C.  mussels  o f s p a w n i n g f o r B.C. with t h e i r  counterparts with respect to protein most i m p o r t a n t  energy  less difference populations, year 1975;  protein  (40-60%, Thompson et and  mussels  40-54% i n Genoa Bay, b o t h degree similar  al.,  1974;  present  of v a r i a t i o n  cycling  g r o w t h and,  and  this,  content,  increase  i n the  case  i n B.C.  remains  spring  ones.  (April)  In f a c t ,  generally time, al.,  and A u g u s t . Genoa Bay  Regardless  index.  B.C..  Zandee e t al.  B.C.  Bay  and Thus,  content  are  influence  on  seems t o  C o n d i t i o n index,  (1980),  In c o n t r a s t , m u s s e l s had  lowest  condition  location,  than  be  like  are completing 1982;  cultured i n indices  temperate  1989)  of  condition  gametogenesis  Peek e t al.,  i s the  i n a study  in  late  mussels  i n poorest condition during February-April.  Bayne e t al.,  of  1984) .  There  recorded highest  of geographic  European mussels 1975;  an o b v i o u s  i n European mussels  i n July  summer.  Edwards,  content  33-65%, Emmett,  the  high for a longer p e r i o d after i t s  indices  and  Protein  of  (36-54% i n D e p a r t u r e  on c o n d i t i o n  i n t h e D u t c h Wadden Sea,  Bay  shows  In E u r o p e a n  45-75%, Dare and  r e s e r v e s has  mussels  Departure  second  mussels.  a common p a t t e r n i n b o t h E u r o p e and glycogen  1983),  actual value of p r o t e i n  local  o f energy  through  study;  the  over the course  1980).  fluctuations  i n E u r o p e a n and  The  fluctuates  30-52%, Zandee e t al.,  showed s i m i l a r  Gabbott,  f o r carbohydrate.  content  mussels).  European  ( r e p o r t e d t o be  storage product:  than noted  increased i n  At  this  (Bayne e t  as a r e  B.C.  are  ones  (Emmett e t al., 1 9 8 7 ) .  differ  Thus,.to  from t h o s e o f Europe  condition  index:  i n that  one o c c u r r i n g  concurrent w i t h gametogenesis,  summarise, B.C. m u s s e l s  they e x h i b i t  i n early  spring,  two lows i n presumably  and a second i n l a t e  summer,  concurrent with high mortality.  Notwithstanding t h e extended p e r i o d content, poor c o n d i t i o n mussels  i n d e x , and s i m i l a r p r o t e i n  have a f a s t e r g r o w t h  temperate  European  waters.  Genoa Bay r e a c h e d market  rate than t h e i r Mussels  size  cultured  (50 mm)  f a v o u r a b l y w i t h 8-15 months r e q u i r e d and  12-14 months r e q u i r e d  slightly  improves  1980),  i n Spain  i n New E n g l a n d  i n D e p a r t u r e Bay a n d compares  (Korringa,  197 6)  (Incze and L u t z ,  as A t l a n t i c  i n most o f  Canada  (Incze  a n d i s much f a s t e r t h a n t h e "3-6 summer circle  1980),  seasons"  ( W a l l a c e , 1980; T h e i s e n ,  1973).  d i f f e r e n c e s must, t o some e x t e n t , be due t o g e o g r a p h i c  variations  i n seasonal temperature,  food; n o n e t h e l e s s , i t remains in  counterparts i n  on t h e "two summer s e a s o n s " r e q u i r e d  required within the A r c t i c Such  c o n t e n t , B.C.  i n 14 months. T h i s  t h e N o r t h Sea ( W a l l a c e , 1980) a s w e l l and L u t z ,  o f low c a r b o h y d r a t e  terms  o f energy  reserves,  favourably with that harvest  clear that, B.C. m u s s e l  size  and a v a i l a b i l i t y o f  despite culture  i n other areas of the world:  i s one o f t h e s h o r t e s t  Market  salinity,  short-comings compares t h e time t o  anywhere.  f o r c u l t u r e d mussels  i s d e f i n e d by s h e l l  length,  and g r o w t h - r a t e d a t a a r e most o f t e n p r e s e n t e d a s i n c r e a s e i n shell  length over time.  g o v e r n s t h e market  However, s i n c e  quality  o f mussels,  relative  tissue  weight  i t i s i m p o r t a n t t o know  80 the r e l a t i o n s h i p indicated in  o f t h e s e two  and s h e l l  i t i s apparent that  d e f i n e d by d r y t i s s u e w e i g h t  growth  study).  (1982) r e p o r t e d t h a t  Kautsky  preceded s h e l l  growth  and s h e l l  in Baltic  concommitent Genoa Bay  rise  mussels  ( K a u t s k y , 1982;  pertain  on r a t e  only  in shell  s t u d i e d and c u l t u r e d  the point  t i s s u e weight  i s that  i n spring  and  also present sometimes  growth  October-April without a  significant  qualification,  which  remains t h a t ,  based  l e n g t h and t h e c o r r e l a t i o n B.C.  mussels  between  grow f a s t e r  European  and B.C.  mussels  mussels  increase  which  i n dry  summer, and t h e n l o s e t i s s u e i n  autumn and w i n t e r , b u t w i t h o u t s u f f e r i n g t h e h i g h m o r t a l i t y i n B.C.  populations.  dry t i s s u e weight suffering  about  than  i n Europe.  A n o t h e r d i f f e r e n c e between E u r o p e a n relates to culture,  of  Mytilus  without a  Despite this  l e n g t h and d r y t i s s u e w e i g h t ,  mussels  shell  high  and o v e r t h e same p e r i o d  f r o m 28-40 mm  i n autumn-winter,  of increase  growth  f r o m 32-43 mm  i n dry t i s s u e weight,  change i n d r y t i s s u e w e i g h t ) .  shell  of observations  tissue  well-  However, t h i s  ( f o r example,  increased  increased  2  c a n be e q u a l l y  w h i l e t h e p r e s e n t s t u d y showed t h a t  i n D e p a r t u r e Bay  increase  (r =0.82).  Sea p o p u l a t i o n s o f  sometimes p r e c e d e d t i s s u e g r o w t h  may  mussels  length.  in light  of tissue  has  2  rate  uncoupled growth  mussels  (1986)  (r =0.97) i n A t l a n t i c  or s h e l l  c o r r e l a t i o n must be q u a l i f i e d  .  length  as has t h e p r e s e n t s t u d y f o r B.C.  From t h i s  edulis,  Hilbish  a h i g h d e g r e e o f c o r r e l a t i o n between m o n t h l y  dry t i s s u e weight  mussels,  parameters.  seen  Mussels i n the present study i n c r e a s e d i n  i n spring  and b e g a n t o w a s t e  50% m o r t a l i t y by  summer's e n d .  in late  summer,  The m a g n i t u d e  of  81 tissue but  l o s s was  similar  high mortality  i n b o t h European  seems s p e c i f i c t o t h e P a c i f i c  represents a serious obstacle respect  to tissue  t h a t Af. edulis of  loss  t i s s u e weight Bay m u s s e l s a 29% of  loss  regularly  of tissue.  i n s p r i n g and c a r r i e s d u r i n g spawning 1953).  body t i s s u e s  since  low and m e t a b o l i s m  loss  Bayne e t al.,  loss  loss) 25%  English  r e c o v e r e d from a lost  68%  43% o f t h e i r  w h i l e Genoa  in  to mobilisation  spans  Mussels  a 3-4  "fasting" necessitates  mortality  non-  wk  (increased temperature  period  s u c h as t h a t  i s at a  i n summer  m u s s e l s : Widdows and Bayne, 1980).  cease  mobilisation  Therefore,  f o r growth"  a s t a t e w h i c h c o n t i n u e s t h r o u g h summer and imposes  of  maintenance  t h r o u g h t o autumn.  I n c z e and L u t z ,  from  represents the emission  i t o c c u r s when c a r b o h y d r a t e r e s e r v e  i s high  dry  becomes n e c e s s a r y d u r i n g  e n t e r a p e r i o d o f n e g a t i v e "scope  possibly study.  1978;  first  which u s u a l l y  This  induces metabolic s t r e s s  spawning,  i n the  (50% m o r t a l i t y ) ,  Some o f t h i s  Such m o b i l i s a t i o n  (Chipperfield,  likely  30-50%  showed a l m o s t as p o o r a r e c o v e r y (40% m o r t a l i t y )  metabolism.  of  reported  s u r v i v e d 78%  r e p r o d u c t i v e t i s s u e t o meet e n e r g y demands o f  filtration  With  r e c o v e r y from a  D e p a r t u r e Bay m u s s e l s  gametes, b u t a n o t h e r p o r t i o n must owe  spawning  and  region.  survived  individual  and r e c o v e r e d p o o r l y  northeast  (1982)  f o r 3 - y r - o l d mussels  Channel, w h i l e 6-yr-old mussels In comparison,  Kautsky  (1980) r e p o r t e d t h a t  routine  populations,  in this  Sea r o u t i n e l y  (an e x t r e m e  and Bayne and W o r r a l l l o s s o f t i s s u e s was  for culture  and m o r t a l i t y ,  i n the B a l t i c  dry t i s s u e weight  loss.  and B.C.  1971;  mussels  during which  observed i n the present  Summer m o r t a l i t y northeast P a c i f i c  i s well-documented  ( Q u a y l e , 1978;  Skidmore  and Chew, 1985;  Atlantic  ( I n c z e e t al.,  Emmett 1980),  ( W o r r a l l and Widdows, 1 9 8 4 ) . by W o r r a l l  and Widdows  f o r mussels  Heritage, et a l . ,  1983;  Emmett,  1984;  1987), t h e n o r t h w e s t  and t h e n o r t h e a s t  Atlantic  Summer m o r t a l i t y was  (1984)  i n the  investigated  i n a mussel p o p u l a t i o n  from t h e  E n g l i s h Channel which e x h i b i t e d r e d u c e d scope f o r growth following  s p r i n g spawning.  month a f t e r  Non-predatory m o r t a l i t y peaked  s p a w n i n g when m e t a b o l i c c o s t s were h i g h and  r e s e r v e s were a t a minimum.  T h e r e may  between i n c i d e n c e o f m o r t a l i t y population,  s i n c e mussels  have b e e n  i n larger  size  i n v e s t i g a t i o n by  I n c z e and L u t z  reduced  food r a t i o n  i n Maine  in this  classes exhibited  and h i g h e r r e p r o d u c t i v e e f f o r t .  edulis  energy  correlation  and r e p r o d u c t i v e e f f o r t  higher mortality  c u l t u r e d M.  a  both  In a n o t h e r  (1980), m o r t a l i t i e s  on  were t h o u g h t t o have been  during metabolic stress  one  c a u s e d by  raftc a u s e d by high  temperatures.  In t h e p r e s e n t mussels* Thus,  s t u d y , summer m o r t a l i t i e s  mean c a r b o h y d r a t e c o n t e n t was  o c c u r r e d when t h e  a t an i n t e r m e d i a t e  i t appeared that mussels d i e d d e s p i t e b e i n g  competent.  T h i s prompted  i n August,  r e g a r d was  between  i n mussels at the time o f  as compared  with A p r i l  c a r b o h y d r a t e r e s e r v e s were l o w e s t and m o r t a l i t y insignificant.  energetically  questioning of the r e l a t i o n s h i p  e n e r g y r e s e r v e s and e n e r g y b u d g e t s worst m o r t a l i t y  level.  A comparison of A p r i l  when  was  and A u g u s t m u s s e l s  made by c o m b i n i n g p h y s i o l o g i c a l  e n v i r o n m e n t a l p a r a m e t e r s , some m e a s u r e d  in this  characteristics  in this  and  s t u d y and some  83 taken  from t h e l i t e r a t u r e  points 3-m  of interest  station  ( d a t a shown i n T a b l e 1 ) .  from the t a b l e  deficits  o f 2-3  positive  scope  kJ'h  - 1  ),  f o r growth  but i n A p r i l  f o r growth,  regard,  to April,  food concentration.  The  with those of Worrall (1980), who  results  deficient  (1984), and  only although  f o r reasons  Incze et  t o energy  the production  r e l a t e s t o maximum s i z e : exceed  60 mm  (Heritage,  northwest A t l a n t i c 1979),  M. 1983;  1976).  cultured  Emmett e t al.,  coast  1987),  of Spain a t t a i n  In S p a n i s h waters  region.  mussels  i n B.C.  (Freeman  and  o f mussels i n  and E u r o p e a n  commonly r e a c h 70 mm  and on t h e A t l a n t i c  (Korringa,  edulis  al.  deficiency.  t o a much g r e a t e r e x t e n t t h a n i n e i t h e r A t l a n t i c A n o t h e r d i f f e r e n c e between l o c a l  low  accord  i n E n g l i s h Channel  respectively,  cripples  a  o f c a r b o h y d r a t e i n August  summer m o r t a l i t y  However, summer m o r t a l i t y  mussels had  of the present study thus  and Widdows  attributed  August  t o h i g h t e m p e r a t u r e and p o s s i b l y  northwest A t l a n t i c mussels,  B.C.  D e p a r t u r e Bay  t h e y were e n e r g e t i c a l l y  o f i n c r e a s e d m e t a b o l i s m due  2)  energy  and 3) t h e r e f o r e ,  t h e mussels had a g r e a t e r p r o p o r t i o n relative  (with  and Genoa Bay m u s s e l s were  marginally negative i n this  at the  longer-lasting  as compared w i t h A u g u s t ,  e x h i b i t e d a n e g a t i v e scope  main  cultured  of both s i t e s possessed a p o t e n t i a l l y  carbohydrate reserve i n A p r i l mussels  a r e : 1) m u s s e l s  The  rarely but i n the  and  Dickie,  80-90  mm  i n c r e a s e d g r o w t h may  t o warmer t e m p e r a t u r e s , b u t t h e n o r t h w e s t A t l a n t i c  and  be  due  northeast  84  T a b l e 1. E n e r g y r e s e r v e s and e n e r g y b u d g e t s o f m u s s e l s c u l t u r e d i n D e p a r t u r e Bay and Genoa Bay a t t h e 3-m s t a t i o n . Data — p r e s e n t e d a r e f o r m u s s e l s o f t h e mean w e i g h t s and c a r b o h y d r a t e c o n t e n t s f o r A p r i l and A u g u s t 1989.  85  Genoa Bay April August  Departure Bay April August  Culture Characteristic  149 4.8 0.117 10 13.4  360 15.5 0.934 17 4.4  173 3.2 0.927 10 11.4  480 13.5 1.085 17 5.4  37 1.00  283 0.44  43 0.59  354 0.31  ENERGY IN (kJ/h) 0.137 ENERGY OUT (kJ/h) 0.112 SCOPE FOR GROWTH (IN- OUT, kJ/h) 0.025  0.135 2.147 -2.012  0.115 0.158 -0.043  0.194 3.561 -3.367  Total dry tissue weight (mg) CHO content (% dry wt) , Equivalent CHO reserve (kJ) Water temperature (°C) Seston concentration (ng/L) Energy Metabolism Estimated V 0 (ml 02/h) Longevity of CHO reserve (h) 2  2  Energy Budget 3  1  The e n e r g y  content  g e n e r a l i z e d heat 2 V0  2  o f known w e i g h t  o f carbohydrate  o f combustion o f carbohydrates,  r e s e r v e was c a l c u l a t e d f r o m a  1.68  kJ-kg  w a s c a l c u l a t e d u s i n g summer a n d w i n t e r e q u a t i o n s  t i s s u e weight f r o m Widdows  from Bayne  (1973)  (Church  - 1  and Pond,  1982).  f o r oxygen consumption based on d r y  corrected t o the appropriate  temperature  using  Q^Q  values  (1973).  3 These v a l u e s were c a l c u l a t e d u s i n g a g e n e r a l i z e d o x y c a l o r i f i c c o n v e r s i o n f o r carbohydrate  of  20.9  kJ-L  0  2  - 1  (Church and Pond,  * V a l u e s f o r "ENERGY I N " a r e d e r i v e d converted t o estimated energy  content  1982).  from t h e present  from estimates o f a b s o r p t i o n e f f i c i e n c y a t v a r y i n g r a t a b a s e d o n a n i m a l s i z e f r o m d a t a i n Widdows 5  of  formulated  20.1 k J - L 0  2  _ 1  .  f o r M. edulis  et al. (1979), a n d c a l c u l a t e d  food concentration and o f f i l t r a t i o n  (1978).  V a l u e s f o r " E N E R G Y OUT" a r e c a l c u l a t e d u s i n g V0  conversion,  data on seston concentration  f r o m d a t a i n Widdows  2  values from g e n e r a l i z e d o x y c a l o r i f i c  e a t i n g a mixed a l g a l d i e t  (Widdows a n d H a w k i n s ,  1989)  Pacific is  not  are s i m i l a r caused  by  i n temperature.  temperature alone.  d i f f e r e n c e s between E u r o p e a n and 1983;  Emmett e t al.,  study)  may  a shorter l i f e  settlement  edulis  s p a n and  higher  Mytilus  edulis  et  1990;  al.,  and  d i f f e r e n c e s may  be  operations.  history  (Heritage, present  strategy.  r e p r o d u c t i v e output as e a r l y  i n l o c a l mussels:  i n B.C.  identified  i n Europe,.local populations  t o the  Notably,  1-2  months  1981) .  of  Mytilus  r e g i o n s have b e e n made; overall  production  success  o f M.  of  edulis  in  r e l a t i o n s h i p between s p a w n i n g and  seasonal  1987). to  Although  c o n f e r no  particular  m u s s e l s i n B.C. plentiful,  and  are  the  (Emmett e t  b e e n shown i n t h e p r e s e n t  advantages with  fast-growing,  B.C.  changes i n energy  i s also distinct  p o l y c u l t u r e has  r e s p e c t t o mussel  potential  m u s s e l c u l t u r e i n B.C.  such  local  summer m o r t a l i t y , and  i n local populations  earlier  after  seems p o t e n t i a l l y more l i m i t e d by  reserves  In  seem t o have  a t an  between p o p u l a t i o n s  other geographic critical  as  Suchanek,  Many p o i n t s o f d i s t i n c t i o n  culture  B.C.  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