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Habitat shifts and behavioural interactions between sympatric and experimentally allopatric cutthroat.. Andrew, Joyce H. 1985

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HABITAT SHIFTS AND BEHAVIOURAL  INTERACTIONS  BETWEEN SYMPATRIC AND EXPERIMENTALLY  ALLOPATRIC  CUTTHROAT TROUT AND DOLLY VARDEN CHAR by JOYCE H. ANDREW B.Sc,  Simon Fraser  University,  1975  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF. MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard  THE UNIVERSITY OF BRITISH COLUMBIA December 1985 ©  Joyce H. Andrew, 1985  ln  presenting  degree freely  at  this  the  available  copying  of  department publication  of  in  partial  fulfilment  of  the  University  of  British  Columbia,  I  agree  for  this or  thesis  reference  thesis by  this  for  his thesis  and  scholarly  or for  her  of  T h e U n i v e r s i t y o f British 1956 M a i n M a l l Vancouver, Canada V6T 1Y3  DE-6(3/81)  Columbia  I further  purposes  gain  shall  that  agree  may  representatives.  financial  permission.  Department  study.  requirements  It not  be  that  the  Library  permission  granted  is  by  understood be  for  allowed  an  advanced  shall for  the that  without  head  make  it  extensive of  my  copying  or  my  written  ii  ABSTRACT The  role  of  community of two Richardson) and was  competition  in  salmonid s p e c i e s ,  cutthroat  D o l l y Varden char  investigated  utilization  of  coexistence  with  in  both  three  alone  that  littoral,  sampled. habitats Char  utilized  generalist  all  feeding  epipelagic) habitats  Walbaum),  lakes.  Habitat and  in  determined by  gill  surfaces  behaviour  to  epibenthic  sympatry  mainly and  allopatry,  and  exhibited  opportunistically  utilizing  However, i n sympatry, char s h i f t e d to deeper In  abundance v a r i e d between sampling  sympatry,  spatially  segregated with depth.  was  pronounced.  not  The  trout  and  However, temporal  habitat  habitats  char  s h i f t by char supports char  r e s o u r c e s , where c o m p e t i t i o n a c t s more s t r o n g l y  However,  food  abundance  partly  were  segregation  h y p o t h e s i s of c o m p e t i t i o n between sympatric t r o u t and habitat  surface  allopatry.  periods.  trout.  such  h a b i t a t s were  habitats  occupied by  prey  by  bottoms  different  not  as  in in  (Salmo c l a r k i  malma  June to October, t r o u t u t i l i z e d  ( l i t t o r a l and  lacustrine  (allopatric)  e p i p e l a g i c , p e l a g i c , and  From  B.C.  (sympatric) was  n e t t i n g at depth contours from lake  a  trout  (Salvelinus coastal  species  each other  structuring  explained  patterns  an for  on  char.  in  fish  distribution. The trout  h y p o t h e s i s that h a b i t a t and  char  investigated the with  type  is  based  in laboratory  and  irradiance  intensity level  on  segregation behavioural  experiments. of  that  between  sympatric  interactions  There were changes  i n t e r a c t i o n between t r o u t and were  was  consistent  with  in char  their  distribution  and  depth of h a b i t a t .  such as occur i n s u r f a c e  habitats,  At high i r r a d i a n c e  t r o u t were more a g g r e s s i v e to  char than at low i r r a d i a n c e l e v e l s .  In  sympatry  char may seek refuge from a g g r e s s i o n by t r o u t with in  lower i r r a d i a n c e interspecies  decreasing feeding  pairs  The feeding  dominated  by  with  i n deeper  irradiance  of  these  char  trout  did  trout, habitats  performance of char increased  i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s .  performance  not  behaviours  dominant t r o u t .  confined  Whether the s h i f t  sympatric  i s not c l e a r .  while  in  improve  an  t o deeper h a b i t a t s  However, an h y p o t h e s i s i n v o l v i n g an  of  segregation  irradiance  l e v e l gradients  and  interference  at low display  aquarium  char i s a r e s u l t of i n t e r f e r e n c e  mechanism  with  However, the  l e v e l s , presumably because char continued to  subordinate  dwelling  levels.  levels  by  with lake-  mechanisms interactive  c o m p e t i t i o n along  cannot be r e j e c t e d by t h i s study.  TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES iv LIST OF FIGURES v ACKNOWLEDGEMENTS vi 1 .0 INTRODUCTION 1 2.0 MATERIALS AND METHODS 7 2.1 Study Area 7 2.2 S p a t i a l and Temporal D i s t r i b u t i o n 10 G i l l Netting 10 L i m n o l o g i c a l Sampling 13 Data Analyses 14 2.3 Laboratory Experiments 16 2.3.1 I r r a d i a n c e L e v e l s 19 2.3.2 B e h a v i o u r a l I n t e r a c t i o n s 20 2.3.3 Data Analyses 22 3.0 RESULTS 23 3.1 Study Lake Environmental C o n d i t i o n s 23 3.1.1 Morphometric Comparisons 23 3.1.2 Temperature, Oxygen, and I r r a d i a n c e L e v e l s .... 23 3.1.3 F i s h Prey D i s t r i b u t i o n s 27 3.2 Length, Weight, and Age of Trout and Char 29 3.3 E f f e c t s of Coexistence on S p a t i a l and Temporal Distribution 35 3.3.1 Trout 37 Sympatric Trout i n Loon Lake 37 A l l o p a t r i c Trout i n Eunice Lake 40 Sympatric versus A l l o p a t r i c Trout 40 3.3.2 Char 45 Sympatric Char i n Loon Lake 45 A l l o p a t r i c Char i n K a t h e r i n e Lake 48 Sympatric versus A l l o p a t r i c Char 51 3.3.3 Trout versus Char 54 3.4 E f f e c t s of I r r a d i a n c e L e v e l on B e h a v i o u r a l and Feeding I n t e r a c t i o n s 59 3.4.1 General Behaviour 59 Establishment of Dominance 59 Swimming Behaviour 61 Feeding Behaviour 63 3.4.2 B e h a v i o u r a l I n t e r a c t i o n s 64 3.4.3 Feeding Performance 69 4.0 DISCUSSION 76 4.1 S p a t i a l and Temporal D i s t r i b u t i o n 76 4.2 B e h a v i o u r a l I n t e r a c t i o n s and I r r a d i a n c e L e v e l 93 4.3 Concluding Statement 102 5.0 REFERENCES 105  V  LIST OF TABLES Table 1. F i s h sizes and order of irradiance level treatments Table 2. A g o n i s t i c , swimming, and feeding behaviours recoreded i n the experiment Table 3. P h y s i c a l and chemical characteristics of Loon, Eunice, and Katherine lakes, University of B r i t i s h Columbia Research F o r e s t Table 4. Zooplankton species in Loon, Eunice, and Katherine l a k e s Table 5. Comparison of fork l e n g t h of t r o u t and char captured i n Loon, Eunice, and K a t h e r i n e lakes i n 1976 and 1982 Table 6. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric trout by time of day, h a b i t a t , and month Table 7. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Eunice Lake a l l o p a t r i c trout by time of day, h a b i t a t , and month Table 8. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric trout versus Eunice Lake a l l o p a t r i c t r o u t by l a k e , time of day, h a b i t a t , and month Table 9. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net catch per u n i t e f f o r t f o r Loon Lake sympatric char by time of day, h a b i t a t , and month Table 10. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r K a t h e r i n e Lake a l l o p a t r i c char by time of day, h a b i t a t , and month Table 11. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t effort f o r Loon Lake sympatric char versus Katherine Lake a l l o p a t r i c char by l a k e , time of day, h a b i t a t , and month Table 12. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net catch per u n i t e f f o r t f o r Loon Lake sympatric t r o u t and char by s p e c i e s , time of day, h a b i t a t , and month Table 13. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net catch per u n i t e f f o r t f o r Eunice Lake a l l o p a t r i c t r o u t versus Katherine Lake a l l o p a t r i c char by s p e c i e s , time, h a b i t a t , and month Table 14. Swimming activity of t r o u t and char i n f e e d i n g t r i a l s and t r i a l s without prey present  18 21 24 28 30 39 42  43 47 50  52 55  57 65  LIST OF FIGURES F i g u r e 1. Map of g i l l net sampling stations and lake h a b i t a t s used i n the a n a l y s i s of s p a t i a l d i s t r i b u t i o n of trout and char i n Loon, Eunice, and Katherine l a k e s , U.B.C. Research F o r e s t F i g u r e 2. Temperature, dissolved oxygen concentration, Secchi depth, and midday i r r a d i a n c e p r o f i l e s of Loon, Eunice, and K a t h e r i n e l a k e s F i g u r e 3. Length frequency d i s t r i b u t i o n of t r o u t and char captured from Loon, Eunice, and Katherine l a k e s F i g u r e 4. Length-weight relationship and functional r e g r e s s i o n l i n e s of t r o u t and char from Loon, Eunice, and Katherine lakes F i g u r e 5. Age composition of t r o u t and char from Loon, Eunice, and Katherine l a k e s F i g u r e 6. Age-length r e l a t i o n s h i p of t r o u t and char from Loon, Eunice, and K a t h e r i n e l a k e s F i g u r e 7. S p a t i a l and temporal d i s t r i b u t i o n of sympatric t r o u t i n Loon Lake F i g u r e 8. S p a t i a l and temporal d i s t r i b u t i o n of a l l o p a t r i c t r o u t i n Eunice Lake F i g u r e 9. S p a t i a l and temporal d i s t r i b u t i o n of sympatric char i n Loon Lake F i g u r e 10. S p a t i a l and temporal d i s t r i b u t i o n of a l l o p a t r i c char i n Katherine Lake F i g u r e 11. Behaviours a s s o c i a t e d with the establishment of dominance of t r o u t over char. . J F i g u r e 12. H o r i z o n t a l p o s i t i o n i n aquarium d u r i n g the establishment of dominance of t r o u t over char F i g u r e 13. Type and i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s between dominant t r o u t and subordinate char at four irradiance levels F i g u r e 14. Swimming activity of dominant t r o u t and subordinate char at four i r r a d i a n c e l e v e l s F i g u r e 15. E f f e c t of b e h a v i o u r a l interactions between dominant trout and subordinate char on the f e e d i n g performance of char F i g u r e 16. Feeding performance of dominant trout and subordinate char at four i r r a d i a n c e l e v e l s F i g u r e 17. Type and i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s between dominant trout and subordinate char during feeding at four i r r a d i a n c e l e v e l s F i g u r e 18. Swimming activity of dominant t r o u t and subordinate char during f e e d i n g at four irradiance levels F i g u r e 19. V e r t i c a l position i n the water column of subordinate char at four i r r a d i a n c e l e v e l s F i g u r e 20. Schematic diagram of habitat overlap of sympatric Loon Lake t r o u t and char and e x p e r i m e n t a l l y a l l o p a t r i c Eunice Lake t r o u t and K a t h e r i n e Lake char. ..  8 25 31 33 34 36 38 41 46 49 60 62 66 68 70 71 72 74 75 83  vii  ACKNOWLEDGEMENTS I am g r a t e f u l to my s u p e r v i s o r , Dr. Tom Northcote, f o r the opportunity to conduct this study, f o r r e s e a r c h funding and summer support, and v a l u a b l e c r i t i c i s m on my work. C o n s t r u c t i v e comments on my research p r o p o s a l s and t h e s i s manuscript were a l s o made by my other research committee members, Dr. B i l l N e i l l , Dr. Kim Hyatt, and Dr. J . Don McPhail. I thank the many individuals at the I n s t i t u t e of Animal Resource Ecology who helped me develop my ideas while p r o v i d i n g encouragement and support, especially Dave Bernard, Sandie O ' N e i l l , Alistair B l a c h f o r d , Linda Berg, Dr. Lee Gass, and Dr. Tony S i n c l a i r . Accomodation i n the U.B.C. Research F o r e s t was k i n d l y provided by the r e s e a r c h f o r e s t s t a f f . My c o l l a b o r a t o r s i n the f i e l d study, Dr. Bror Jons'son, K j e t i l Hindar, and Nina Jonsson, provided v a l u a b l e e x p e r t i s e i n g i l l n e t t i n g techniques and many weeks of f i s h d i s s e c t i o n s and age determination. Field assistance was provided by Dr. Tom Johnston, A l S t o c k w e l l , and B r i a n Emerson. Video equipment f o r the l a b o r a t o r y study was p r o v i d e d by Dr. Kees Groot, Dr. C a r l Walters, and Dr. Lee Gass. Most of a l l , I am g r a t e f u l to those i n d i v i d u a l s who encouraged me to pursue an M.Sc. i n f i s h e r i e s b i o l o g y , namely my f a t h e r Fred Andrew, B i l l P h i l l i p s , and Dr. Glen Geen, and to my f a m i l y f o r t h e i r continued support throughout my s t u d i e s .  1  1.0 INTRODUCTION The role  c o n t i n u i n g debate d u r i n g the past twenty years over the  of  interspecific  communities  has  competition  remained  largely  Roughgarden 1983, S i m b e r i o f f has  focused  on  same  niche  unresolved  1983).  A great  non-interbreeding  cannot  E i t h e r one  species  1957),  ecological  or  structuring  t e s t i n g the 'competitive  which s t a t e s that two the  in  coexist  will  become  and the two  species  niches.  Interspecific  deal  research  occupying  (Harden  1960).  (Hutchinson  between the s p e c i e s w i l l be  will  segregate  competition  determines  into  different  the  number of  levels  l i m i t s the s i m i l a r i t y of competing s p e c i e s  in  i n an area, relation  the abundance and d i v e r s i t y of c r i t i c a l  resources  Therefore,  i s potentially  interspecific  1983,  principle',  locally  s p e c i e s that can c o e x i s t at s t a b l e p o p u l a t i o n and  of  populations  indefinitely  differences  magnified  (Connell  exclusion  extinct  animal  competition  (Werner  to  1977).  strongest  between c l o s e l y r e l a t e d s p e c i e s because t h e i r  preferred  are  s h i f t s i n food or  often  similar  or  overlapping.  h a b i t a t u t i l i z a t i o n between s p e c i e s one  l o c a t i o n and s e p a r a t e l y  are g e n e r a l l y supporting of  considered  Niche coexisting  niches  (sympatric)  (allopatric) in different locations  to  produce  the  the premise that competition  strongest  evidence  i n f l u e n c e s the s t r u c t u r e  p a r t i c u l a r communities (Zaret and Rand 1971, Schoener  1975,  Werner and H a l l  removal  of  1976,  competitors  l e v e l s of competition Competition  in  Connell  1983).  The  1974a,  addition  or  a l t e r s niches or abundances by v a r y i n g  (Connell  1975, C o l w e l l and Fuentes 1975).  has been i m p l i c a t e d as an  important  selective  2  force  in  number  fish  of  communities  studies  competition  between  p a r t i t i o n i n g , and 1983,  have  Connell Fish  particular  (Yoshiyama 1980, Schoener 1983). demonstrated  fishes  temporal  as  exclude  potential  habitats  by  either  depleting  competition)  two  selective -  in  that  types fish  ecological  selective  their  a l s o B r i a n 1956). behaviours  spatial  (Kalleberg  and  habitat  in  Schoener  and  food  aggressive  Nilsson  such  as food or h a b i t a t interaction,  occurs between s p e c i e s which have great  to  be  ecologically  of one or more c r i t i c a l resources (see  Many f i s h  s p e c i e s possess  a broad  repertoire  (Hoar 1951), and s e v e r a l s t u d i e s have shown that of  species  territorial  results  behaviour  from  interspecific  of salmonids i n streams  1958, Hartman 1965, Hartman and  Gill  1968,  Everest  and Chapman 1972, Cunjak and Green 1984) as w e l l as other on  coral  review (1983)  reefs  (Low  1971,  of 164 s t u d i e s on found  and  segregation  through d i r e c t b e h a v i o u r a l  use  (1967)  - interactive  Interactive  differences  from  resources  through  competition).  sufficiently  segregation  aggression  of  competitors  segregation  segregation  differences in  of  or  communities.  s e l e c t i o n are magnified  of  (reviews  may  identified  isolated  food  species  ( i . e . interference  evolved  as  segregation  interactions  while  well  occurrence  1983).  (i.e. exploitative  implies  the  A  that  Myrberg and Thresher  competition  territorial  among  competition  1974).  animals,  fishes In a  Schoener  prevailed  among  fishes. N a t u r a l sympatric  populations  of  two  salmonid  species,  3  D o l l y Varden char  ( S a l v e l i n u s malma Walbaum) and c u t t h r o a t t r o u t  (Salmo  Richardson),  clarki  Individuals  from  segregated  in  these  coexist  populations  1974 - 1976  (Hume  t r o u t ) and D o l l y Varden char and  Katherine  were  1978),  a l l o p a t r i c p o p u l a t i o n s of c u t t h r o a t t r o u t  Eunice  i n Loon  B.C.  experimentally thereby  creating  (herein r e f e r r e d t o as  (herein r e f e r r e d  lakes,  Lake,  to  respectively.  as  char)  in  These a l l o p a t r i c  p o p u l a t i o n s are s e l f - s u s t a i n i n g , and s e v e r a l n a t u r a l l y  produced  generations are now present i n these l a k e s . S p a t i a l s e g r e g a t i o n between t r o u t and char i n Loon Lake and other  nearby  Northcote  lakes  was  clearly  (1971), Armitage  (1973) and Hume  char segregate with depth, zones  and  char  demonstrated  trout  occupying  by Andrusak and  (1978).  Trout  i n h a b i t i n g s u r f a c e and midwater  deeper  water.  Evolved d i f f e r e n c e s  between t h e s e ' p o p u l a t i o n s have a l s o been demonstrated. and p a i r e d t r o u t and char differ  in their  from  orientation  s t u d i e s (Schutz and Northcote than  the other  height  at  There  (Armitage  1972) and each  prey  i s more  and Northcote  i s a major d i e t a r y o v e r l a p i n l i m n e t i c  efficient  1972, Hume zooplankton efficiencies  s p e c i e s (Hume 1978).  important  factor  (1985) found that i r r a d i a n c e  which  determines  a c q u i s i t i o n by t r o u t and char i n Loon Lake. at  populations  i n the water column i n l a b o r a t o r y  (Schutz  Henderson and Northcote an  sympatric  1973) although t r o u t have higher capture  on zooplankton  is  natural  Solitary  f e e d i n g on prey items a t i t s own p r e f e r r e d  i n the water column  1978).  and  detection  and  foraging e f f i c i e n c y  level  the success of prey Trout a r e s u p e r i o r i n r e l a t i v e l y high  4  irradiance  (e.g. l i t t o r a l  char  superior  are  benthic  and  pelagic  (e.g. d i u r n a l feeding). in  deep  Despite  interspecific  Northcote been  1972)  populations  is  However,  as  sympatric  trout  of  but  various  that trout  previous  in  by  char  need  not  when  trout  selective  morphological  and  Loon  Lake  objective  that  segregation  always  be  has  of  lake  interactive. between  interactive  i n the  early  or  stage  outcompetes char  for  cause g e n e t i c changes  in  behavioural characters, resulting  two  major  objectives in this  i s due  to competitive  i s t o d e t e r m i n e whether trout  would  are  and  char  support  interspecific tested  it  (1982),  d e t e r m i n e whether h a b i t a t s e g r e g a t i o n  between  and  in  segregation.  There are  in  1978),  than  may  char  (Schutz  rather  occur  of  water  over  that segregation  d o m i n a t e s and  pressures  shallow  trials  (Rosenau  Henderson  and  irradiance  were dominant  studies  selective  low  nocturnal  feeding  aquaria  habitats)  chemoreception  relatively  h a b i t a t s and  i n stream  and  d e t e c t i o n and  in  used  largely  limnetic  I n t e r a c t i v e s e g r e g a t i o n may  then  selective  to  pairs  indicated  coexistence  food,  prey  evidence  in  shallow  visual  water  and  concluded  selective.  at  and  a  aggressive  as f o l l o w s :  differed  study.  The  between t r o u t  interaction,  and  and the  the  behavioural  with  irradiance level  hypothesis  of  interactions.  segregation The  first  is  char second  interactions in a  based  hypotheses to  way on be  5  1. Trout and/or char have undergone a spatio-temporal h a b i t a t shift  from sympatry to a l l o p a t r y such that  segregated  trout  and  char  experimentally  occupy more s i m i l a r h a b i t a t s  than when i n sympatry. T h i s hypothesis temporal those  will  be  examined  h a b i t a t uses by sympatric  of  by  comparing  spatial  and  p o p u l a t i o n s i n Loon Lake with  experimental a l l o p a t r i c p o p u l a t i o n s of t r o u t and char  (Loon Lake stock) i n Eunice and K a t h e r i n e  lakes,  respectively.  If  suggest  that h a b i t a t  differences  are  found,  this  would  segregation may be due to c o m p e t i t i o n between the two populations. that  the  sympatric  A h a b i t a t s h i f t by only one s p e c i e s would species  which  does  not  shift  is  the  study  reported  indicate superior  competitor. Based on the r e s u l t s of the f i e l d the  following  possible  hypothesis  relationship  will  be  between  tested  from  t o i n v e s t i g a t e the  irradiance  e f f e c t i v e n e s s of a g g r e s s i v e behaviour  herein,  level  by t r o u t  and  the  i n e x c l u d i n g char  habitats:  2. There  are  behaviour irradiance  changes i n the i n t e n s i t y and type of a g o n i s t i c between  trout  level  that  d i s t r i b u t i o n with depth T h i s hypothesis w i l l be using  interspecific  and are  of  in  changes  consistent  a  trout  r e d u c t i o n i n a g g r e s s i v e behaviours level,  with  with  in their  i n Loon Lake.  examined  pairs  char  laboratory  and char.  with  experiment  I f there i s a  decreasing  irradiance  low i r r a d i a n c e h a b i t a t s may p r o v i d e r e f u g i a f o r char (the  inferior  competitor,  according  to  the f i e l d  r e s u l t s reported  6  herein)  if it  habitats. 3.  The of  is  able  Therefore,  to  the  acquire  i s reduced  resources  following hypothesis  r a t e of p l a n k t i v o r o u s trout)  food  by  feeding  aggressive  of c h a r  will  be  ( i n the  behaviour  in  these  tested: presence  of t r o u t .  7  2.0 MATERIALS AND  2.J_ The  present  oligotrophic Research 1).  study  lakes  in  F o r e s t (49°  The  lakes  Study  19'N,  are  Area  was  the  METHODS  conducted  University  in  of  three  British  small, Columbia  122° 34'W), near Haney, B.C.  situated  in  (Figure  c o a s t a l mountain uplands at  e l e v a t i o n s between 340 m (Loon Lake) and 505 m (Katherine Lake). The  surrounding topography  covered  by  western  and p l a n t e d Douglas outcrops Research till wet over  of  is  fir  (Feller  iodite  F o r e s t and gradual  in  in  1975). the  slopes  1967).  There  northern of  (Roddick and Armstrong  and m i l d ( E f f o r d  by  steep  slopes  hemlock f o r e s t with stands of a l d e r ,  quartz  i n the south  characterized  are  birch,  granitic  portion  of the  forest-covered  glacial  1956).  Eunice and Katherine  The c l i m a t e i s lakes  freeze  winter but Loon Lake i s i c e - c o v e r e d only i n o c c a s i o n a l  winters. Each of the three l a k e s i s almost f o r e s t to the water's  edge.  pads (Nuphar polysepalum)  the  s h o r e l i n e , and beds of h o r s e t a i l  end of the l a k e . vegetation Similarly lily  along  but  by  along approximately one-fourth of (Equisetum  i n the l i t t o r a l  fluviatile)  zone near the  and  south  In Eunice Lake, there are f l o a t i n g mats of bog the south shore of the main p a r t of the l a k e .  to Loon Lake, Eunice Lake c o n t a i n s  pads,  surrounded  Loon Lake c o n t a i n s patches of water  lily  pondweed (Potamogeton spp.)  entirely  also  has  sparse  ( L y s i c h i t o n americanum), f e r n s , and  patches  patches of  shrubs near  of  skunk the  water cabbage  shoreline.  2  &  1 0 SAMPLING  Figure  20 DEPTH  40 CONTOUR  (m)  1. Map of g i l l net sampling s t a t i o n s and lake h a b i t a t s used i n the a n a l y s i s of s p a t i a l d i s t r i b u t i o n t r o u t and char i n Loon, Eunice, and Katherine l a k e s , U n i v e r s i t y of B r i t i s h Columbia Research F o r e s t .  9  Katherine in  Lake  the l i t t o r a l  has  more abundant growth of a q u a t i c  zone than the other  i t s north and  south ends.  grasses  reeds  and  submerged  Lake  cutthroat  littoral  (Graminae),  contains  trout  lily  near  patches of  pads,  and  Dolly  Varden  native  and  other  char,  populations but  no  Abundance of a d u l t s of these s p e c i e s was  fish,  the p e r i o d  r e s p e c t i v e l y (Hume 1978).  were  both  1976,  a t o t a l of  were  transplanted  fishless  respectively sufficient  1571  Loon  1978).  assume  stocks  populations  reproduced  systems so that by  1974.  cutthroat from  (Hume to  until  transplanted  1982  881  Eunice numbers  in  Katherine  there  have  could  recruited  to  1974  lakes  and  Katherine  The  each  June char  lakes,  generations  that completed t h e i r e n t i r e l i f e  were  donor  and cycle  and  transplanted  of the new  been  them  by  to be 7300 and  between  1980).  successfully  fish  transferred  homogeneity Stahl  other  D o l l y Varden  and  year  lakes.  classes  Eunice and  t r o u t and  The  (Ryman and  - 1976  of  estimated  Between October  to  genetic  1974  successive  recipient  especially  zone c o n t a i n s  water  coexisting  the Schnabel method during 3100  lakes,  vegetation.  Loon  species.  The  two  macrophytes  up  to  lake eight  at l e a s t  two  within  the  10  2.2 Spatial  Spat i a l and Temporal D i s t r i b u t i o n  distributions  of  fish  p o p u l a t i o n s were assessed  d u r i n g three sampling  p e r i o d s i n 1982:  (hereafter  referred  to as the June sampling  25 August,  and  30  (3)  September  r e f e r r e d to as the October  (1) 22  to  10  June  to  5  July  p e r i o d ) , (2) 16 to October  (hereafter  sampling p e r i o d ) .  G i l l Netting  gill  Fish  were  captured i n nylon monofilament g i l l  net  gang  was  increasing  mesh  composed  sizes  (20,  s t r e t c h e d d i a g o n a l mesh). and  lakes  were  located  c o n t o u r s , and contours  25,  31,  5 m 38,  long 44,  panels  51, and  Nets were e i t h e r 2, 5, or  (8.0  (Figure  ± 4.5  sampling  Sampling along  stations  the  2,  at  5,  of  60  10 m  h)  and  1).  Stations  the study. night  were  Gill  (13.5  Loon  10, and  marked  nets were  ± 4.0  and  10, 20, and  i n Katherine Lake at the 2, 5,  r e t a i n e d throughout  set  seven  Each  mm  deep  were marked at 1 m i n t e r v a l s to f a c i l i t a t e d e t e r m i n a t i o n of  capture depth of f i s h .  at  of  nets.  40 m 20 m  with set  h) p e r i o d s .  Eunice depth depth  buoys and during  During each  p e r i o d a l l s t a t i o n s were sampled from s u r f a c e to bottom  l e a s t twice.  At the  s u c c e s s i v e l y so  10, 20, and  that  all  40 m s t a t i o n s g i l l  depths  at  every  nets were  station  sampled.  For example, at the 40 m s t a t i o n , a 10 m deep g i l l  was  at  set  day  0-10  m,  10-20  s e q u e n t i a l days to complete one experimental  sampling,  m,  20-30  "day  m,  sample".  an e x t r a set was  and  were net  30-40 m on four In  performed  addition  to  i n Katherine  11  Lake  to  supplement  low  August  overnight on the bottom 2 m,  catches.  The  the net extending  net  was  set  from the shore to  deep benthic h a b i t a t s of the l a k e . One  potential  problem  c a t c h per u n i t e f f o r t may each and  station. two  first  with  t h i s sampling  decrease  with  Since each depth was  repeated  was  sampling  sampled four times  day  be higher  if  the  r e s p e c t i v e l y a day or a night s e t .  Day  and  night catches per u n i t e f f o r t were s i g n i f i c a n t l y  different  each p o p u l a t i o n i n June (x =3.84, p<.05, d f = l ) , and four  the  f i s h p o p u l a t i o n s the g r e a t e r c a t c h was  time  consistent  with  first  net  obtained d u r i n g  exposure.  However,  d i f f e r e n c e s i n day and night catches should not a f f e c t of  my  study whose purpose was  t h i s part  to compare d i s t r i b u t i o n s of  not  exposure  may  bring  population  i n the v i c i n i t y of each s t a t i o n so  first  the shallower l a y e r s of the water column, the catches  at  about  depths of 10 m to 40 m  distributions  and  p o p u l a t i o n was  fished  therefore  would  make  be  catch  in  a  may  between non-random  be  reduced,  lakes.  depletion that  which  them appear s h a l l o w e r . the  biased  same  manner  i n the same way  First  fish  p o p u l a t i o n s and  at  total  for  i n three out  2  of  at  (two  night s e t s ) , day or n i g h t catches may sampling  design i s that  by  of  net the  fishing  would  bias  However, every  and  distributions  i f such d e p l e t i o n s  occur. There are some d i f f i c u l t i e s d i s t r i b u t i o n by (Andreev  1955),  i n f e r e n c e from  i n determining results  of  f i s h d e n s i t y and  gill  net  sampling  although r e s e a r c h e r s f r e q u e n t l y have used  nets f o r t h i s purpose (e.g. Horak and Tanner  1964).  Gill  gill nets  12  are to  passive their  sampling d e v i c e s  swimming  entangled. or  into  activity),  in that sample. perceive  and  than n i g h t . irradiance  the  a higher  becoming  avoid  mainly  fish  may  capture by g i l l  level  diel  and  activity  of  be  However, c o n d i t i o n s  fish,  of i r r a d i a n c e  activities  fish.  them would be biased Fish  removed  is In  gill  l a b o r a t o r y at Loon Lake. i n t e r v a l s ) was the  laboratory,  capture, of  recorded  sexual  maturity  any  case,  of  pinhead s i z e and  and  related  a  unit  habitat  biases  in  the  similar  for  nets  way. sampled  at  Depth of capture  (within  1  as f i s h were removed from g i l l  were  depth  catch per  were  (± 1.0  varies  with  are o b v i o u s l y  indicative  same  s p e c i e s , date and  fork length  the  h a b i t a t s so that comparisons between  in much the from  with  Furthermore,  measurement of catch per u n i t e f f o r t probably were l a k e s , and  day  c y c l e were s i m i l a r among lakes  by these a c t i v i t i e s  populations,  the  " f i s h density"  "importance" of h a b i t a t s to f i s h , a higher  to  or  visually  varies  sampling dates of f i s h p o p u l a t i o n s .  "useful"  day  the accuracy of  to the  e f f o r t biased  to  nets  f o r a g i n g or r e p r o d u c t i v e  all  and  foraging  able  gill  u n i t e f f o r t as  illumination  to  since  is  gilled  nets b e t t e r during  Because the e f f i c i e n c y o.f  h a b i t a t s , and  which  due  c a t c h per u n i t e f f o r t w i l l r e s u l t  In a d d i t i o n ,  between samples. the  and  (presumably due  i n t e r p r e t a t i o n of catch per  and  net  is  If f i s h are more a c t i v e at c e r t a i n times of the  in c e r t a i n h a b i t a t s  spawning  i n that the capture of f i s h  mm),  l o c a t i o n (lake and weight  recorded.  (± 0.1 Females  males with t e s t e s enlarged  a m  field depth  nets.  At  s t a t i o n ) of  g), sex and  state  with eggs up  up to h a l f the  to  body  13  cavity  length  were  recorded  gonad development was was  recorded  were  as  immature ( j u v e n i l e ) f i s h .  more advanced the s t a t e of sexual  as mature ( a d u l t ) ,  following  determined l a t e r using o t o l i t h s  Dahl  If  maturity  (1917).  Ages  ( d e t a i l s i n Jonsson et a l .  1984).  Limnoloqical  Sampling  To t e s t the hypothesis and  sympatric  be  identical  prey  types and  met  in  populations  that niche u t i l i z a t i o n  of  allopatric  i s the same, lake environments  with respect to l i m n o l o g i c a l f e a t u r e s , as w e l l as sizes.  whole  Such i d e a l c o n d i t i o n s are r a r e l y  lake experiments.  there were important  prey  types  differences  were  netting periods. and  light  point  of  conducted  between  each  during  Temperature, d i s s o l v e d  penetration lake  concentration  were  15 m c a b l e and  probe.  lakes  3 1 Van  Dorn  standard  but  and  measured  bottle.  sampling  oxygen  gill  concentration,  1).  Temperature  u s i n g a YSI  and  oxygen  Model 57 meter with a  Measurements of temperature and d i s s o l v e d using the  same  samples were brought to the s u r f a c e in a Light  penetration  was  measured  by  a  Secchi d i s c and/or L i c o r Model LI-185A l i g h t meter.  Invertebrate  prey  determined by Hindar et study  seasonal  p r o f i l e s were determined at the deepest (Figure  water  ever  each of the three  oxygen at depths g r e a t e r than 15 m were obtained apparatus,  if  However, to determine whether  d i f f e r e n c e s w i t h i n l a k e s , l i m n o l o g i c a l measurements and of  should  and  are  types, d e n s i t i e s and d i s t r i b u t i o n s were a l . (in  summarized  in  prep.)  concurrently  S e c t i o n 3.1.3.  with  my  Zoobenthos were  14  sampled in  with a 9 x 9" Ekman dredge at the g i l l  a l l sampling  periods.  Five p a r a l l e l  each s t a t i o n .  Zooplankton were sampled  Clarke-Bumpus  gear  (0.08 mm  netting  stations  samples were taken at  by d i a g o n a l  hauls  with  net) from the depths 0-5, 5-10, 10-  20, and 20-40 m.  Surface a r t h r o p o d s were  (frame  x 30 cm, 0.2 mm mesh) at d i s t a n c e s of 50-150 m  size  30  sampled  towed from the bow of a boat along the shore l i n e water  with  and  a  net  in  mid-  (6 samples per lake per month).  Data Analyses Numerical  catch  data  from  the  three l a k e s were used to  determine s p a t i a l and temporal h a b i t a t use. of  trout  The  and a l l o p a t r y  distribution  of each s p e c i e s i n sympatry  and  compared to determine whether one or both s p e c i e s had a  habitat  shift.  use  in  was  undergone  A second t e s t was performed t o determine the  relative similarity comparing  char.  of  habitat  use  by  the  two  h a b i t a t use by t r o u t and char i n sympatry allopatry.  species  by  with h a b i t a t  An h y p o t h e s i s of c o m p e t i t i o n p r e d i c t s that  the two s p e c i e s p r e f e r more s i m i l a r h a b i t a t s than they occupy i n sympatry. S p a t i a l and compared  using  temporal the  distributions  Kruskal-Wallis  of  populations  e x t e n t i o n t o two and three  f a c t o r nonparametric a n a l y s e s of v a r i a n c e on ranked v a l u e s 1984,  p.219-222,  249).  depth  is  confounded  (Zar  In the model f o r a n a l y s i s of v a r i a n c e  (ANOVA), depth i s nested i n s t a t i o n , because v a r i a t i o n with  were  by  the  sloping  in  catch  lake bottom.  For  example, the c a t c h at depth equal t o .2 m at the 2 m contour  has  15  a benthic depth  i n f l u e n c e whereas t h i s component i s absent at the same  at  the  other  r e s u l t s from g i l l four  stations.  To  n e t t i n g s t a t i o n s and  h a b i t a t zones.- The  littoral  s t a t i o n s , the e p i p e l a g i c h a b i t a t 10 m, the  20 m,  and  5 to 15m  effort  the  40 m contour.  effort  latter  All  seasonal  catch  net  samples  per  occurred  or  set was  between  Lake), sampling multiple  sampling  to be  one  to catch per  unit  net area/12 h s e t ) . fish  u n i t e f f o r t ANOVAs were determined with and  sampling month.  Diel  and  i n lake h a b i t a t s changed with  respectively.  sympatric  to lake  month,  comparison  and.  Whether  of  habitat  allopatric  time  of  means  day,  and  (p=.05)  used throughout the  analyses.  was  shifts  populations either  (Loon Lake versus Eunice or  homogeneous sets of means from ANOVAs (Zar software was  included  temporal d i s t r i b u t i o n of  unit e f f o r t  month,  with respect  the  5 to 35 m depth  considered  determined by c a t c h per u n i t e f f o r t ANOVAs of char  of  of f i s h between h a b i t a t s were i n f e r r e d when  r e l a t i v e c a t c h per  time of day  5 m  reduced  were c o r r e c t e d  to h a b i t a t , time of day, movements  the 2 m and  three h a b i t a t zones because i t lacked a  To determine the s p a t i a l and  the  Lake had  2  populations,  to  the p e l a g i c h a b i t a t  Katherine  A 5 m deep g i l l  unit.  assigned  i n c l u d e d the upper 5m  ( i n d i v i d u a l s captured/100 m  respect  depths were  depth zone at the 20 m s t a t i o n and 40 m s t a t i o n .  sampling  t h i s confoundment,  zone i n c l u d e d  40 m s t a t i o n s , and  zone at the in  avoid  was  trout  or  Katherine  habitat.  Tukey's  used to determine  1984,  p.199).  Genlin  16  2.3 Laboratory  Experiments  Trout and char were c o l l e c t e d  i n May  1984 from experimental  a l l o p a t r i c p o p u l a t i o n s (Hume and Northcote Katherine  lakes,  monofilament  respectively.  gill  nets  of  1985) from Eunice and  Collections  stretched  numbers  experiments  were  started.  temperatures  fed  in  The two s p e c i e s were  seasonally  ranging  from x  p r o v i d i n g water replacement  daily  the  70  held  s e p a r a t e l y at  6.0 to 12.5 °C i n l a r g e cm  deep)  with  every 2.3 hours.  r a t i o n s of chopped c h i c k e n l i v e r ;  flow-  F i s h were  some char would  l i v e r and were f e d Neomysis mercedis, a mysid  shrimp.  used  i n the experiments  rest  and  held  were segregated from  the  not Fish  of  the  i n d i v i d u a l l y or i n mixed-species p a i r s f o r 3-6  days i n s i m i l a r but s m a l l e r a q u a r i a with water replacement of  mm.  laboratory,  eat  stock  with  maintained there f o r four months before  o v a l f i b r e g l a s s a q u a r i a (137 x 78 through  made  mesh s i z e s 20 to 60  Despite a r e l a t i v e l y high i n i t i a l mortality adequate  were  approximately one hour  (112 x 50 x 36 cm deep).  rates  These  fish  were f e d ad l i b i t u m d a i l y r a t i o n s of Neomysis mercedis. A g o n i s t i c behaviour of s i x mixed-species p a i r s of t r o u t and char  was recorded at four i r r a d i a n c e l e v e l s .  was c o n s i d e r e d to be one r e p l i c a t e . days  at  the  highest  irradiance  Each p a i r of f i s h  Each p a i r was h e l d f o r level  "dominant" and the other " s u b o r d i n a t e " .  until Based  one f i s h  in  Loon  t h e r e f o r e only p a i r s i n which the t r o u t was dominant were  used i n the experiment. out  became  on the r e s u l t s of  my f i e l d study, t r o u t are s u p e r i o r competitors to char Lake,  2-5  of  the  ten  Although t r o u t were dominant  size-matched  interspecies  in  eight  p a i r s used i n the  17  l a b o r a t o r y , there was no frequency size  significant  difference  at  p=.05  in  of dominance by t r o u t and char with t h i s small sample  (binomial t e s t , o n e - t a i l e d , p=.055).  l e v e l was the experimental  treatment,  Since decreased  the  highest  light  irradiance  l e v e l was the c o n t r o l , and was used t o e s t a b l i s h b a s e l i n e l e v e l s of a g g r e s s i o n . three  The three l e v e l s were then presented  c o n s e c u t i v e days.  at each treatment pair  fish  pairs  l e v e l , behaviours were recorded f o r each  fish  at each treatment  Rather  level.  to a v o i d l o g i s t i c a l problems, inferential levels.  i n the next  statistics  of  than using d i f f e r e n t  Although  t h i s procedure  i t violated independence  To p a r t i a l l y circumvent  the of  was  used  assumption  of  data a t treatment  t h i s problem,  treatments  presented to f i s h p a i r s i n random order so that p r i o r at  other i r r a d i a n c e l e v e l s was randomized  allowed at l e a s t one day of  acclimation  before  were  data  on  behaviour  minutes d u r a t i o n were performed after PST.  feeding.  experience  (Table 1). to  each  recorded.  Two  F i s h were  light  t r i a l s of 30  between  10:00  and  Each r e p l i c a t e p a i r was h e l d i n the experimental  Following  each  phenoxyethanol  at each l i g h t  replicate,  fish  and were measured and  matching of p a i r s  level  each day, one before and another  T r i a l s were conducted  u n t i l data on behaviour  were  l e v e l had were  been  aquarium recorded.  anaesthetized  weighed  to  17:00  verify  in  2-  size-  (Table 1).  P a i r s were h e l d together i n the experimental aquarium p r i o r to treatments aggression  u n t i l the f i s h were a c c l i m a t e d to the aquarium and  between  Sect ion 3.4.1).  the  trout  and  char  had  s t a b i l i z e d (see  18  Table  1.  F i s h s i z e s and order of i r r a d i a n c e  level  treatments.  Trout Replicate 1 2 3 4 5 6 1 2  Pair  Order of Treatments  1  T1--C1 T2--C2 T3--C3 T3--C4 T4--C5 T4--C6  2  I-111 -IV -II I-I I -III -IV I - I V - III -II I - I I -IV- III I-111 -II -IV I-111 -IV -II  T = t r o u t ; C=char I r r a d i a n c e l e v e l treatments: I = 3.0 X 1 0 photons/m /s II = 1.5 X 1 0 photons/m /s III = .5.0 X 1 0 photons/m /s IV = 3.0 X 1 0 photons/m /s 1 8  2  1 6  2  1 5  1 5  2  2  Length (cm) 24 22 25 25 24 24  1 4 5 5 0 0  Weight (gm) 1 25 0 1 1 50 1 57 5 1 57 5 1 22 5 1 22 5  Char Length (cm) 23 22 25 26 23 24  0 3 8 5 2 .5  Weight (gm) 1 1 25 98 0 1 56 0 1 75 5 108 .0 1 1 4.0  19  During the establishment of dominance data r e c o r d i n g , f i s h rations  of  tunnel.  therefore  not  both  present  of  were fed d a i l y  Neomysis were c o l l e c t e d  planktonic  or  in  Eunice  s p e c i e s were e q u a l l y  t h i s prey p r i o r to the experiment. large  period  of the F r a s e r R i v e r , east of the George Massey  Neomysis were  lakes,  the  i n the experimental aquarium  25 l i v e Neomysis mercedis.  from the Main Arm  and  and  Katherine  i n e x p e r i e n c e d with  Neomysis  is  a  e p i b e n t h i c i n v e r t e b r a t e , and  relatively i t s swimming  movements make i t a h i g h l y v i s i b l e prey to both t r o u t and  char.  The  (mean  mean  length  of  Neomysis  used  was  11.23  ± 2.76  mm  ± standard d e v i a t i o n ) t o t a l l e n g t h ( a n t e r i o r end of carapace tip  of  telson),  and  was  not s i g n i f i c a n t l y d i f f e r e n t  to  between  samples ( F - t e s t , p>.05, F=2.46, df=4,115).  2.3.]_  I r radiance L e v e l s  Experiments aquarium through  were conducted  i n a g l a s s - f r o n t e d brown  (118 x 56 x 30 cm deep) with a sand s u b s t r a t e and flowproviding  temperature  water  replacement  v a r i e d s e a s o n a l l y from 9.0  i l l u m i n a t e d by two V i t a - l i t e  sun  every  to 13.0  fluorescent  l i g h t - p r o o f housing and suspended The  wooden  1.8 h.  °C.  tubes,  The tank mounted  in  a  that of the  h i s Figure 2).  The three lower  irradiance  l e v e l s were obtained  by  board  lengthwise  0.64  the  cm  slit  c l o t h over the  1982,  was  50 cm above the water s u r f a c e .  s p e c t r a l d i s t r i b u t i o n of V i t a - l i t e s approximates (Henderson  Water  under  sliding housing,  a  with  a  and p l a c i n g l a y e r s of black  slit.  The h i g h e s t i r r a d i a n c e l e v e l used  (3.0 x 1 0  18  photons/m /s) 2  20  was  g r e a t e r than the s a t u r a t i o n  char and near that of t r o u t . irradiance  that  and Northcote  irradiance  threshold  (SIT) of  The SIT i s the minimum q u a n t i t y of  maximizes r e a c t i o n d i s t a n c e t o prey  1985).  (Henderson  A c c o r d i n g t o Henderson and Northcote,  both  s p e c i e s use v i s u a l prey d e t e c t i o n above the SIT and t r o u t always use v i s u a l prey d e t e c t i o n . (3.0 x 1 0 (VIT)  lowest  irradiance  photons/m /s) was at the v i s u a l  1 5  of  The  2  trout  prey, 10  15  7.0  x  10 "  photons/m /s  1  categories  aggression  Despite  reaction  trout  to  (3.0 x  and  char,  1985).  and  improved  of a g o n i s t i c behaviour, which i n c l u d e d  submission,  visibility  were  limited.  Therefore,  only  were recorded to ensure subtle  raising)  not  (Table  irradiance  2).  levels  were  r e l a t i v e l y obvious b e h a v i o u r a l a c t s  r e g u l a r i t y and r e l i a b i l i t y  behaviours  were  recorded  t o the observer u s i n g the s p e c i a l  video camera, o b s e r v a t i o n s at the lower  More  zero  Behavioural I n t e r a c t i o n s Several  both  for  2  r e s p e c t i v e l y ; Henderson and Northcote  2.3.2  in  The VIT i s the  below which prey t a r g e t s are not d e t e c t e d v i s u a l l y and  used  irradiance threshold  but g r e a t e r than that of char.  maximum q u a n t i t y of i r r a d i a n c e r e s u l t i n g  level  such  recorded.  as  threat  in recording.  postures  (e.g.  fin  S i m i l a r procedures were used on  i n t e r - and i n t r a s p e c i f i c p a i r s as w e l l as s o l i t a r y f i s h  of  both  spec i e s . O b s e r v a t i o n s of f i s h room  which  housed  were made from o u t s i d e the l i g h t - p r o o f  the experimental aquarium.  For purposes of  o b s e r v a t i o n , the aquarium was i l l u m i n a t e d with i n f r a r e d l i g h t of  21  Table 2. A g o n i s t i c , swimming, and feeding behaviours recorded i n the experiment. B e h a v i o u r a l Act  Description  A. A g g r e s s i v e Behaviour Charge  Aggressor r a p i d l y d a r t s at body of submissive f i s h , but aggressor does not chase submissive f i s h i f i t attempts to escape.  Chase  Aggressor chases submissive f i s h down length of aquarium, u s u a l l y at burst swimming speed.  Nip  Aggressor b i t e s or nips t a i l p a r t s of submissive f i s h .  or other body  B. Submissive Behaviour Avoidance  Submissive f i s h a v o i d s an a g g r e s s i v e i n t e r a c t i o n by f a s t swimming ( u s u a l l y < burst speed) down l e n g t h of aquarium when the aggressor approaches.  C. Swimming Behaviour Swimming a c t i v i t y  Movement i n h o r i z o n t a l p o s i t i o n i n aquarium to a d i f f e r e n t q u a r t i l e = one u n i t of activity. Recorded only d u r i n g l u l l s i n aggression.  Bottom r e s t  Occurred i n char only; r e s t i n g on s u b s t r a t e on p e c t o r a l and caudal f i n s .  Diagonal hover  Submissive f i s h hovers i n water column, u s u a l l y near s u r f a c e , i n a n o n - h o r i z o n t a l p o s i t i o n (approximately 30° angle) with i t s head up. F i s h may be s t a t i o n a r y or move forward slowly, but most movements are b a l a n c i n g movements, mainly of the p e c t o r a l fins.  D. Feeding Behaviour Feeding s t r i k e  Rapid forward movement at prey, not n e c e s s a r i l y r e s u l t i n g in capture; occurred in feeding t r i a l s only.  22  two  incandescent  88A  filters.  aquarium near lites. of  The  12.7  cm Kodak Wratten  lamps were p l a c e d at an angle on top of the  the f r o n t so as not to block l i g h t  from the  t r o u t and  x 10  char  were  not  significantly  or absence of i n f r a r e d and  17  3.0  x 10  l i g h t when V i t a - l i t e  photons/m /s  15  different  2  for  trout  and  light  740  up  to  nm  evidence that salmonids sufficient  light  (Beauchamp et a l .  25 mm  sensitive  to  far-red  there i s no  do not have s i m i l a r high red  sensitivity  on  (R.D.  a  Beauchamp, p e r s . comm.).  video  S i l i c o n Diode video camera (VCS 1:1.4  char,  1979), and  intensity  F i s h were observed  the  l e v e l s were  However, other f i s h s p e c i e s can p e r c e i v e  EE  Vita-  in  respectively.  in  Series  Henderson (1982) found that the mean r e a c t i o n d i s t a n c e s  presence 4.2  lamps s h i e l d e d by  monitor  through  a  3000) f i t t e d with a F u j i n o n  Sanyo T.V.  p h o t o m u l t i p l i e r l e n s and a V i t i c o n tube which i s infrared  e l e c t r o n i c hand-held  light.  event  Behaviours  were recorded on an  recorder (Observational  Systems  OS-  3) .  2.3.3  Data The  Analyses statistical  r e s u l t s was repeated  test  one-way ANOVA  measures  (Winer  the number of b e h a v i o u r a l log,o(behavioural  for  to  analyze  the  single-factor  1971,  + 1.0)  was  experimental  experiments  Rodgers 1977).  interactions  interactions  d i s t r i b u t i o n of the data. the a n a l y s e s .  used  with  In a l l ANOVAs,  transformed  using  to normalize the Poisson  M i n i t a b software was  used  throughout  23  3.0 RESULTS  3.j_ Study Lake Environmental  Conditions  3_.j_.j_ Morphometric Comparisons Loon  Lake  lakes based on  i s l a r g e r and deeper than Eunice and Katherine surface  area,  (Table 3 ) . Loon Lake has over of  either  2.2  (Loon  and  volume  comparisons  twice the s u r f a c e area and volume  of the other two l a k e s .  The three lakes have s i m i l a r  ( D t ) , which ranges from 1.5 (Eunice  s h o r e l i n e development to  depth,  Lake).  However,  Katherine  Lake  Lake)  has a l a r g e r  percentage of i t s s u r f a c e area formed by l i t t o r a l  zone than does  Eunice or Loon Lake (Table 3 ) . Almost one-fourth  of the s u r f a c e  area of Katherine Lake i s l e s s than Eunice have much smaller l i t t o r a l s u r f a c e areas,  2 m  deep,  while  Loon  and  zones (7.1% and 10.4% of t h e i r  respectively).  3^J_.2 Temperature, Oxygen, and I r r a d i a n c e L e v e l s During  each  of the three sampling  thermally s t r a t i f i e d 2).  with  p e r i o d s , a l l lakes were  well-developed  thermoclines  (Figure  The e p i l i m n i a l depths were s i m i l a r f o r a l l lakes (Table 3 ) .  Maximum  epilimnial  (approximately  temperatures-  were  20 °C) d u r i n g summer but decreased  deepened (6.5-8.5 m) d u r i n g  autumn.  epilimnia  turnover  had begun but f a l l  During  similar  each  of  In  i n a l l lakes (12-15 °C) and  October,  erosion  of  had not yet o c c u r r e d .  the three sampling  p e r i o d s , the d i s s o l v e d  24  T a b l e 3. P h y s i c a l and c h e m i c a l c h a r a c t e r i s t i c s of L o o n , E u n i c e , and K a t h e r i n e l a k e s , U n i v e r s i t y of B r i t i s h C o l u m b i a R e s e a r c h Forest. Loon E l e v a t i o n (m) Surface area (ha) Maximum d e p t h (m) Mean d e p t h (m) Volume (m x 10 ) S h o r e l i n e development (Dt) S h a l l o w l i t t o r a l a r e a (0-2 m) ( p e r c e n t of l a k e a r e a ) E p i l i m n i o n d e p t h i n 1982 (m) June August October Secchi disc transparency i n 1982 (m) June August October Irradiance extinction c o e f f i c i e n t (TJ) pH C o l o r (Pt u n i t s ) Total d i s s o l v e d s o l i d s (mg/L) 3  4  .  1  1  2  2  'Hume 1978 N o r t h c o t e and C l a r o t t o  2  1975  2  340 48. 6 62 27. 5 1 336 2. 2  Eunice 480 18.2 42 15.8 288 1 .5  Katherine 505 20.7 29 7.5 175 1.9  7. 1  10.4  24.5  5. 5 6. 5 8. 5  3.5 6.0 6.5  4.5 6.0 7.5  9. 3 8. 1 7. 5  8.5 4.0  9.1 7.3  1. 1 6.4-6. 7 <5 32  -  1 .7 6.4 1 5 1 6  -  1 .4 6.6 1 0-15 1 5  25  LOON  EUNICE  TEMPERATURE 0  KATHERINE  (C) AND DISSOLVED OXYGEN (mg/L)  5 10 15 20 25  0  5 10 15 20 25  0  5 10 15 20 25  c z m  o TEMPERATURE o CO  o  ' y  l  S\  /  '  o.  UJ  a  /  /  /  /  /  1 / 1 1 1( 1 /  > c c cn  /  1  o n -* o ro m 33  .15  10  10  17  10  19  10'"  10" 10  17  IRRADIANCE LEVEL  Figure  10  19  10  21  „15  10" 10  19  10  21  10  (photons/m /s)  2. Temperature, d i s s o l v e d oxygen c o n c e n t r a t i o n , midday i r r a d i a n c e p r o f i l e s of Loon, Eunice, and Katherine lakes. (Surface conditions in October: x 1 0 photons/m /s; f l a t c a l m ; no c l o u d ) 1  S  2  and 7.53  26  oxygen  profiles  heterograde  of  the  curves.  lakes  The  usually  only  exhibited  exceptions  positive  were Katherine and  Eunice l a k e s i n October, where  dissolved  oxygen  concentration  decreased  dissolved  oxygen  concentration  result  of  maximum  with at  depth.  the  solubility  of  temperatures, clinograde  thermocline oxygen  in  reduction  was  may  the  with  be  a  epilimnion  oxygen consumption  phytoplankton at the process  The  due  decreased  to high summer  i n the hypolimnion  (typical  of  depth), and p r o d u c t i o n of oxygen by  thermocline  (Wetzel  1983).  The  latter  probably not important, as d i s s o l v e d oxygen maxima  seldom exceeded 110%.  Eunice Lake was  anoxic near the  sediment  in deep p a r t s of the lake d u r i n g August. Secchi d i s c t r a n s p a r e n c i e s of the lakes were s i m i l a r d u r i n g June  (Table  between  June  phytoplankton profiles  In  and  all  perhaps  over  the  due  growth  to  decreased  accumulated  season.  Irradiance  i n d i c a t e that l i g h t e x t i n c t i o n with depth i s  i n Eunice and  3).  l a k e s , water transparency  October,  biomass  i n October  more r a p i d (Table  3).  However,  Katherine the  lakes  pattern  than  in  Loon  of l i g h t e x t i n c t i o n  Lake i n the  three l a k e s i s t y p i c a l of c o a s t a l o l i g o t r o p h i c l a k e s .  and  The  study lakes tend to be s l i g h t l y  Pt  v a l u e s range  Lake has approximately  from <5-15  units  acidic  (Table 3).  (pH  6.4-6.7),  Although Loon  twice the t o t a l d i s s o l v e d s o l i d s  content  of Eunice or Katherine l a k e s , a l l three l a k e s are w i t h i n the low range  typical  Larkin  1956).  of c o a s t a l B r i t i s h Columbia  l a k e s (Northcote and  27  F i s h Prey D i s t r i b u t i o n s  3.j_.2  The  study  densities,  lakes  and  share  similar  distributions  prey  (Hindar  d e n s i t i e s of s u r f a c e arthropods  e_t  types  (Table  4),  a l . in prep.).  The  (mainly winged i n s e c t s ) were not  s i g n i f i c a n t l y d i f f e r e n t between the lakes in 1982, than 2 i n d i v i d u a l s / m in  August  and  The  2  Limnetic  was  zooplankton  samples except highest  at  individuals/m depths  3  in  0-5  m  of  July  m,  and in  Eunice  m).  relatively  depth  Katherine  densities  contour  lakes,  proportion  chironomid  at 5-10  of  in  in July.  and  larvae,  and  m versus  8734 at  than  There was  of  all  (mainly  lakes  3  a  zooplankton  Hyalella  l a r v a e ) were highest at  a significant  the  489-1887 i n d i v i d u a l s / m  zoobenthos  Profund a l  was  3  littoral  of l a r g e (£8 mm)  density  individuals/m )  respectively).  in  in a l l  20-40 m sampling i n t e r v a l s )  Lake i n August.  October  i n October.  densities  i n Eunice  There was  2  Katherine  the  low p r o p o r t i o n of l a r g e s i z e c l a s s e s  individuals/m ). the  3  surface  depth  From s p r i n g to autumn,  3  exceeded 4  (9000 - 23000  with  when  Eunice  mm)  highest  October,  a z t e c a , Pisidiurn sp., and chironomid 2 m  (^4  decreased  i n Loon (379-4264  in a l l lakes i n J u l y and The  both  i n Katherine  were  (287-1023 i n d i v i d u a l s / m and  large  and  g r e a t e r than 10 m (10-20 and  lakes  when  (18846 i n d i v i d u a l s / m  at 0-5  were always higher other  in  Katherine  5-10  October,  densities  at  3  in  proportion  highest  individuals/m )  were l e s s  during a l l sampling p e r i o d s except  Katherine  individuals/m . arthropods  2  and  (1500  the  - 2200  i n c r e a s e with depth in  zoobenthos i n a l l lakes except  zoobenthos was  almost  exclusively  showed d e n s i t y maxima at 40 m in Loon,  Table 4. Zooplankton lakes.  s p e c i e s i n Loon, Eunice, and Katherine  1  , Cladocera Daphnia rosea Bosmina l o n g i r o s t r i s Holopedium gibberum Diaphanosoma brachyurum Polyphemus p e d i c u l u s Leptodora k i n d t i i Ceriodaphnia p u l c h e l l a , Copepoda Diaptomus Diaptomus Diaptomus Diaptomus Cyclopoda  kenai leptopus oregonensi s tyrrelli  Loon  Eunice  Katherine  *** 2 ***  *** *** *** *** ** ** *  **  ** **  ** **  ** **  ** **  **  ** **  **  *** ** ** *** ***  ***  *** ** **  Data from Hindar e t a_l. i n prep., Hume and Northcote 1985, and Northcote and C l a r o t t o 1975. 2*** y common; ** common; * uncommon; - rare 1  v e r  29  u s u a l l y at 20 m i n Eunice, and at 10 m i n Katherine Lake.  3.2 Length, Weight, and Age of Trout and Char S i z e d i f f e r e n c e s between f i s h populations  i n sympatric  and  allopatric  were not as pronounced i n 1982 as they were i n 1976  (Table 5 ) . Trout and char t r a n s f e r r e d i n 1974 - 1976 to and  Katherine  experimental abundant  lakes,  length-weight individual  In  1976,  and  237.2 mm,  fish  the  Six  mm,  (Hume  and  comparisons  fishless  lakes  with  Northcote  1985).  This  of  length  distributions,  and i n c r e a s e s i n the growth r a t e s  from sympatric  and  allopatric  mean l e n g t h s of a l l o p a t r i c  populations.  t r o u t and char  was s t i l l  r e s p e c t i v e l y ) were s i g n i f i c a n t l y g r e a t e r than mean in their  sympatric donor p o p u l a t i o n s (180.0  l a t e r , the mean l e n g t h of a l l o p a t r i c char s i g n i f i c a n t l y g r e a t e r than sympatric char  two-tailed,  and  mm) was s i g n i f i c a n t l y two-tailed,  (197.2  mm)  (182.2  mm;  p<.00l) although the d i f f e r e n c e was not so  great as i n 1976, but the mean l e n g t h of a l l o p a t r i c  test,  (209.9  r e s p e c t i v e l y ; t - t e s t s , t w o - t a i l e d , p<.00l; Hume 1978).  years  t-test,  on  previously  relationships,  l e n g t h s of f i s h 172.0  to  resources  c o n c l u s i o n was based  of  r e s p e c t i v e l y , grew q u i c k l y f o l l o w i n g the  transfers  food  Eunice  l e s s than sympatric t r o u t  p<.00l;  trout  (178.4  (165.9 mm;  t-  Table 5, F i g u r e 3 ) . D i f f e r e n c e s i n  f i s h s i z e s between years may be a t t r i b u t e d t o the wider  range of  gill  in  net mesh  sampling  sizes  used  in  1982  (20-60 mm)  than  1976  (25-51 mm s t r e t c h e d d i a g o n a l mesh).  Since  trout  and  char  are  native  i n Loon Lake and have  c o e x i s t e d f o r c e n t u r i e s , these p o p u l a t i o n s may be assumed to  be  30  Table 5. Comparison of fork l e n g t h of t r o u t and char captured in Loon, Eunice, and Katherine lakes i n 1976 and 1982. Fork Length (mm) Range min,max  N  Mean  A. 1976 (Hume 1978) Trout Loon 218 1 1 1 ,233 180.0 Eunice Char Loon  Eunice Char Loon Katherine 1  116,310  209.9  41.8  25  112,217  1 72.0  24.8  237.2  45.4  0  3  1066  77,332  178.4  30. 1  917  82,270  1 65.9  26.5  288  96,220  182.2  14.7  392  100,323  1 97.2  43.4  t-Test Between Years (df )  1  7 . 272*** (430)  2  3  6.957*** (148)  .000ns 21 .776*** (1282) (1981) 19.311*** (1129) 5.633*** (678)  3.105** (31 1 ) 8.861*** (515)  H : Mean l e n g t h i n experimental lakes = mean l e n g t h i n Loon Lake H : Mean l e n g t h i n 1976 = mean l e n g t h i n 1982. * * * p<.00l; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05 0  2  18.4  214  Kather ine 1 25 134,337 B. 1982 Trout Loon  Standard Deviat ion  t-Test Between Lakes (df)  31  TROUT  o in  CHAR  o in (1066)  o  60.0 (291)  o  in  o in  o  o  o  -< z "0  CO  >  OJ  > 2 u  z  3 a  ui cr ««- o  }— z 111  g  UJ  t=4-  o  o o in  m  O  (922)  -  (462)  o  a. o  o  o  o  CV)  CM  o  O  o  J  r o •a >  —< 33  n  J  <99  120  160  200  240  »260  <99  FORK LENGTH  Figure  120  160  200  240  £260  (mm)  3. Length frequency d i s t r i b u t i o n of t r o u t and c a p t u r e d from L o o n , E u n i c e , and K a t h e r i n e l a k e s . ( S a m p l e s i z e s a r e shown i n p a r e n t h e s e s . )  char  32  stable,  and the Malthusian parameter  et a l . 1984). differ  ( r ) equal to zero  The mean l e n g t h of t r o u t  significantly  in  Loon  Lake  (Jonsson d i d not  between 1976 and 1982 ( t - t e s t , t w o - t a i l e d ,  p>.05), but that of char was s i g n i f i c a n t l y  longer  test,  f o r char, however, i s  two-tailed,  p<.0l).  q u e s t i o n a b l e due to the (n=25).  The  result  relatively  sample  s h o r t e r than those  trout  and  char  size  in  1976  t r o u t and char i n 1982  in  1976  captured  p a t t e r n s of l e n g t h versus weight Functional  (t-tests,  two-  regression  as  i n 1982 had the same  those  captured  of the l o g s of weight  of 1982 Loon t r o u t r e s u l t e d i n a  slope  which  95% c o n f i d e n c e l i m i t s of the length-weight  1976  (slope=2.73 ± 0.105, c f F i g u r e 4 ) . Loon char also  had a length-weight  95% c o n f i d e n c e l i m i t s of ± 0.305,  i n 1976.  and l e n g t h (Ricker  the  1982  1982 ( t -  p<.00l).  Sympatric  1973)  low  mean l e n g t h s of a l l o p a t r i c  were s i g n i f i c a n t l y tailed,  The  in  overlapped  relationship for captured  in  r e l a t i o n s h i p that overlapped the  those  captured  in  1976  (slope=2.82  c f F i g u r e 4 ) . T h i s p r o v i d e d f u r t h e r evidence that the  n a t i v e f i s h p o p u l a t i o n s i n Loon Lake were s t a b l e with respect to their  length-weight  relationship.  Trout and char captured i n 1982 ranged and  12+  years  determined paper  and  (Hume  (Armitage  age  between  0+  5 ) . F i s h captured i n 1975 - 1976 were  t o be a maximum of age  analysis  analysis  (Figure  in  4+  years  using  probability  1978), which was c o r r o b o r a t e d with s c a l e  1973).  The maximum age of f i s h between  1976  1982 probably d i d not d i f f e r by e i g h t y e a r s , but r a t h e r the  age d i f f e r e n c e i s an a r t i f a c t of the d i f f e r e n c e  i n technique  of  33  o o in  A. TROUT Sympatric  Log Wt=2.81(Log Len)-4.57 Slope+95% C.L.=2.81+.079 N=624 r=.98  Allopatric Log Wt=2.51(Log Len>-3.91  o o  Slope+95% C.L. = 2.51+.076 N=663 r=.93  o in  SYMPATRIC ALLOPATRIC  in I 19 UJ  o o in  B. CHAR  /  Sympatric Log Wt=2.62(Log Len)-4.16  /  Slope+95% C.L. = 2.62+145  / /  N=185 r=.82  /  Allopatric Log Wt= 3.01 (Log Len)-5.02  o o  /  /  Slope+95% C L =3.01+. 116  /  /  N=286 r=.99  o in  / / /  /  / /  /  /  / /  // ///  yy  /  /  /  in 50  //  200  100 LENGTH  400  (mm)  Figure 4 . Length-weight r e l a t i o n s h i p and f u n c t i o n a l r e g r e s s i o n l i n e s of t r o u t and char from Loon, Eunice, and Katherine l a k e s . (Data p o i n t s are omitted f o r clarity.)  34  TROUT  CHAR  o in o  (291)  cn -< z u >  O  u z  UJ  o UJ cr u. z UJ  u tr UJ  a.  m o  01 i ii  II  il  o  (462)  > r r  o  Q  o ru  "0 >  EL  n  10  12  AGE IN YEARS  F i g u r e 5. Age composition of t r o u t and char from Loon, Eunice, and K a t h e r i n e l a k e s . (Ages were determined using o t o l i t h s . Sample s i z e s are shown i n parentheses.)  i  35  age  determination.  relatively (Figure (Figure trout  strong  5).  Allopatric  age  This  3+  and  i s also  shorter  at  a  a l l o p a t r i c char are longer difference  in  but  growth  In  a  classes,  (Figure  6).  Allopatric  age than sympatric t r o u t , but  (Figure  6 ) . There was no s i g n i f i c a n t  between  char  had  allopatric a  faster  and  sympatric  growth  rate than  (Jonsson et a_l. 1984, t h e i r Table 2 ) .  given  length  c l a s s e s of a l l o p a t r i c t r o u t  tended  to  i n Loon Lake (Hume 1978).  rates  in  and  weigh more than the same  In 1982, t h i s was s t i l l  of char, but a l l o p a t r i c t r o u t were not able growth  respectively  r e f l e c t e d i n length d i s t r i b u t i o n s  1976, the l a r g e r length  of  species  year  sympatric char had  given  rate  allopatric  sympatric char  char  4+  and  3) and age-length r e l a t i o n s h i p s are  trout,  trout  true  t o maintain the same  weight throughout the lengths sampled  (Figure  4).  3.3  E f f e c t s of Coexistence on S p a t i a l and Temporal D i s t r i b u t i o n In Tables 6-7 and  differences habitat  in  use  of  "time*habitat", use  9-10,  spatial  the  use of h a b i t a t  individual respectively.  and  in  populations  are  the  "lake*time*habitat",  are  by  the  "month*time*habitat",  spatial  and  that  that  respectively.  provide  respectively.  terms  and  in habitat  interaction  information  d i e l use of h a b i t a t s  interaction  indicate  "habitat"  Seasonal d i f f e r e n c e s  Tables 8 and 11, the ANOVA terms differences  terms  and d i e l d i f f e r e n c e s i n  populations  and d i e l movement a r e i n d i c a t e d  "month*habitat"  ANOVA  between  "lake*habitat",  terms In on fish and  In Tables 12-13, the ANOVA  36  TROUT  CHAR  156  (1066)  O O•  cn  o o•  274  219  220  6 ,6  2  2  10  (0 6  -H-H-  81  CM  75  (922)  125  7  1  29  u.  •  i  i i  (291)  o o' cn 9  6  _368 237  o o  54  1  i i' i 2 1  107 1  o o•  "0 •  H n  RANGE  r—  cr o  x STANDARD DEVIATION  / O  13 Z UJ  <  ,  i  i  i i  (462)  65  r r o  104  2  76  46  "D > H 31  70  M  •A  n  2 /  0  2  4  6  8  10  12  0  2  4  6  8  10  12  AGE IN YEARS  F i g u r e 6. Age-length r e l a t i o n s h i p of t r o u t and char from Loon, Eunice, and Katherine l a k e s . (Sample s i z e s are shown on b a r s . T o t a l sample s i z e s are shown i n parentheses. )  37  terms that  indicate differences  habitats  between t r o u t and  terms  "species*habitat"  in  spatial  char p o p u l a t i o n s and  and  diel  are the  use  of  interaction  "species*time*habitat",  respectively.  3 . 3 . j_ Trout  Sympatric Trout  i n Loon Lake  Sympatric  t r o u t mainly occupied  June to October  (Figure 7), and  that CPUE was  highest;  secondarily  in  were most dense  see S e c t i o n  epipelagic  depths between 0-10  2.2)  relative  CPUEs  between h a b i t a t s  r e f e r r e d to  as  H-test),  significant  diel  June to October  or  in l i t t o r a l  habitat,  e s p e c i a l l y p e l a g i c h a b i t a t s were l i t t l e  while  the  epibenthic  utilized,  Table  6).  sense  habitat,  according  ( K r u s k a l - W a l l i s H-test  p<.00l;  seasonal  (in  m from  There  and and to  (herein were  no  movements between h a b i t a t s from  (H-test, p>.05;  Table  6).  (Movement  between  habitats  i s i n f e r r e d when the r e l a t i v e CPUEs change between  day  and  ( d i e l ) or from month to month (seasonal  see  night  Section  2.2).  However, there was  movement at night a greater this Table  extent  trend 6D).  was  (Figure 7).  some evidence of  Trout  statistically  a  shoreward  u t i l i z e d pelagic habitat  i n October than d u r i n g not  movement);  to  June and  August although  significant  (H-test, p>.05;  DAY  NIGHT  zzzr VAVAA (96)  (236) c  o  2 m  CM  (170)  22  Ind./ 100m  / 1 2h  2  (93)  x r— O. Ill Q  o .  >15 S.1-15 o .  2.1-5  CO  y//Y/AV/// ML (114)  •  0.1-2 0  (357)  yA/VAAYAA/ yA/V/AA/Ayo 22  o H O  CD  m  73  10  10  SAMPLING DEPTH CONTOUR  20  40  (m)  Figure 7 . S p a t i a l and temporal d i s t r i b u t i o n of sympatric t r o u t i n Loon Lake. (Mean c a t c h per u n i t e f f o r t i n 5 deep g i l l net sets i n u n i t s of i n d i v i d u a l s / 1 0 0 m net area/12 h s e t . Numbers of i n d i v i d u a l s captured are shown i n parentheses.) 2  39  Table 6. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric t r o u t by time of day (D=day, N=night), h a b i t a t ( L = l i t t o r a l , E P = e p i p e l a g i c , P=pelagic, EB=epibenthic), and month (j=June, A=August, O=0ctober).  ANOVA F a c t o r  H-statistic, Deg. Freedom  Probability of H  A. June (N=332) time of day habitat time*habitat  2 .97, 1 50 .52,3 .93,3  ns  B. August (N=263) time of day habitat t ime*habitat  .05, 1 42 .03,3 .30,3  ns  C. October (N=471) time of day habitat time*habitat  .91,1 39 .68,3 .54,3  ns  D. Pooled (N=1066) sampling month time of day habitat month*time month*habitat time*habitat month*time*habitat  4 .15,2 2 .93, 1 1 17.33,3 1.22,2 3 .43,6 .80,3 .87,6  ns ns  2  ** *  ns  ***  ns  ***  ns  ***  ns ns ns ns  Tukey M u l t i p l e Comparison of Means (p=.05) 1  ns L EP EB P ns ns L EP EB P ns ns L EP P EB ns ns ns L EP EB P ns ns ns ns  'Factor l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . 2 * * * <.001; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05 P  40  Allopatric  Trout i n Eunice Lake  From June to depths  October,  from 0-5 m (Figure  h a b i t a t and s e c o n d a r i l y epibenthic  habitats  in  habitat  August  or  significant  June to October  zone  at  little  utilized  (Table  occupied  (Table seasonal  pelagic 7).  7B  and  was not maintained no  movements between h a b i t a t s  from  Table  C).  There  7).  In  August  (Figure 8 ) , but t h i s trend was not s t a t i s t i c a l l y  (H-tests,  p>.05; Table 7B and C ) .  Trout  trout  were d i s t r i b u t e d d i f f e r e n t l y  (H-tests, p<.05; Table 8B and D). order of d e c r e a s i n g  l i t t o r a l , pelagic, were  most  epipelagic, epibenthic,  then  epibenthic abundant  between h a b i t a t s (in  CPUE) l i t t o r a l ,  then  in  trout u t i l i z e d habitats. littoral  epipelagic,  However, and  trout  was  In g e n e r a l , more  sympatric t r o u t .  the v e r t i c a l d i s t r i b u t i o n  restricted  to  shallow  both  epipelagic  h a b i t a t s , while fewer t r o u t were found i n e p i b e n t h i c habitats.  and  Sympatric t r o u t u t i l i z e d  h a b i t a t s , whereas a l l o p a t r i c  populations  and  seemed to be a shoreward movement to the l i t t o r a l  In August and i n a l l sampling months pooled, sympatric  pelagic  in  were  p>.05;  Sympatric versus A l l o p a t r i c  allopatric  and  In June,  h a b i t a t was higher than  7D), but t h i s p a t t e r n  (H-tests,  night  significant  or  mainly  h a b i t a t , while  in epibenthic  October  diel  October, there  in l i t t o r a l  (Table  trout  8), and were most dense i n e p i p e l a g i c  were  the mean CPUE of t r o u t pelagic  allopatric  and p e l a g i c  of  allopatric  h a b i t a t s than that of  There was no d i f f e r e n c e i n  diel  patterns  of  41  DAY  NIGHT  £  x o. i-  HI Q  10  20  40  S A M P L I N G D E P T H C O N T O U R (m)  F i g u r e 8. S p a t i a l and temporal d i s t r i b u t i o n of a l l o p a t r i c t r o u t i n Eunice Lake. (Mean c a t c h per u n i t e f f o r t i n 5 m deep g i l l net s e t s i n u n i t s of i n d i v i d u a l s / 1 0 0 m net area/12 h s e t . Numbers of i n d i v i d u a l s captured are shown i n parentheses.) 2  42  Table 7. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Eunice Lake a l l o p a t r i c t r o u t by time of day (D=day, N=night), h a b i t a t (L= l i t t o r a l , EP=epipelagic, P= p e l a g i c , EB=epibenthic), and month (J=June, A=August, O=0ctober)  ANOVA F a c t o r  H-statistic, Deg. Freedom  Probability of H  Tukey M u l t i p l e Comparison of Means (p=.05) 1  A. June (N=411) time of day habitat time*habitat  1.32, 1 48 .66,3 8 .51,3  ns *** ns  ns EP L EB P ns  B. August (N=176) time of day habitat time*habitat  .07, 1 40 .09,3 .46,3  ns *** ns  ns EP L P EB ns  C. October (N=330) time of day habitat time*habitat  .02, 1 42 .87,3 1.32,3  ns *** ns  ns EP L P EB ns  D. Pooled (N=917) sampling month time of day habitat month*time month*habitat time*habitat month*time*habitat  5 .05,2 .24, 1 1 30.70,3 1.50,2 3 .74,6 1.12,3 1.74,6  ns ns *** ns ns ns ns  ns ns EP L P EB ns ns ns ns  1  2  2  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . * * * p<.00l; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05  43  Table 8. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric t r o u t versus Eunice Lake a l l o p a t r i c t r o u t by lake (L= Loon, E=Eunice), time of day (D= day, N=night), h a b i t a t ( L = l i t t o r a l , EP= e p i p e l a g i c , P=pelagic, EB=epibenthic), and month (j=June, A=August, O=0ctober).  ANOVA F a c t o r  H-statistic, Deg. Freedom  Probability of H  A. June (Loon N=332, Eunice N=411) lake .27,1 time of day .06, 1 habitat 90.31 ,3 lake*time 4.10,1 lake*habi t a t 1.13,3 t ime*habitat .41,3 lake*time*habitat 1.75,3  ns ns *** * ns ns ns 2  B. August (Loon N= 263; Eunice N= 1 76) 1.71,1 lake ns time of day .13,1 ns *** habi t a t 72.35,3 l a k e * t ime .00, 1 ns * lake*habi t a t 9.60,3 t ime*habi t a t lake*time*habitat  .62,3 .17,3  ns ns  C. October (Loon N =471; Eunice N = 330) 1.87,1 lake ns time of day .61,1 ns *** habitat 78.35,3 lake*time .26, 1 ns lake*habitat 3.35,3 ns time*habitat 1.78,3 ns lake*time*habitat .33,3 ns  Tukey M u l t i p l e Comparison of Means (p=.05) 1  ns ns EP L EB P E-D L-N E-N L-D ns ns ns ns ns L EP EB P ns L-L E-EP L-EP E-L L-EB L-P E-P E-EB ns ns ns ns L EP P EB ns ns ns ns ..Continued  44  Table 8.  Continued  D. Pooled (Loon N=1066; Eunice N=917) lake ns 1 .85 1 * month 7, 08, 2 time of day .68, 1 ns *** habitat 236.02 3 lake*month 68 ns 2.68,2 lake*time ns 2.33,1 * lake*habitat 10.45,3 month*habitat time*habitat lake*month*habitat lake*time*habitat  3.67,6 1.62,3 3.55,6 .33,3  ns ns ns ns  ns 0 J A ns L EP P EB ns ns L-L E-EP L-EP E-L L-EB L-P E-P E-EB ns ns ns ns  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . 2*** p^.001; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05 1  45  habitat in  use  habitat  char  habitat,  epipelagic H-test,  (H-test,  p=.05,  was  June  were were  in pelagic  sparse  sympatric  p>.05;  (H-test,  than  5  diel  movements  and  depths  p<.0l;  between was  night that  p<.0l;  0-10 m a t  in  (Figure p=.05,  pattern  of  T a b l e 9B) and  the usual l e v e l  of  exception  than e p i p e l a g i c h a b i t a t  night,  i n the d i s t r i b u t i o n  of  in  habitats  most  char  t h e 5-20 m c o n t o u r s . char  There between  T a b l e 9 D ) , w h i c h i n v o l v e d a movement in  June  habitats  some e v i d e n c e  spawn d u r i n g  to  (Figure  habitats 9).  p>.05;  that  utilized  char  (Figure  autumn.  9).  greater  T h e r e were no  (H-test,  i n August and O c t o b e r  char  habitat  This  Table 9 A ) , a l t h o u g h at  shallow habitats  there  thirdly  T a b l e 9C) w i t h t h e  in l i t t o r a l  CPUE i n  the u s u a l l e v e l of 9D).  m deep i n August and O c t o b e r  at  habitat,  (H-test,  p=.058;  highest  n o t d i s t r i b u t e d d i f f e r e n t l y between  differences  from r e l a t i v e l y  the  in l i t t o r a l  Table  i n August  were more d e n s e  seasonal  noted  p=.068;  s i g n i f i c a n t at  f o u n d between  habitats  with  a l t h o u g h not s i g n i f i c a n t at  (H-test,  although  a n d most  found  C h a r were  habitats  be  secondarily  at  was  October  October.  captured  a l t h o u g h not s i g n i f i c a n t at  significant  char  were  habitat,  distribution  in  T a b l e 8D) between  differences  C h a r i n Loon Lake  epibenthic  that  p>.05;  nor s e a s o n a l  trout.  Sympatric  was  Table 8),  Char  ,Sympatric  9;  p>.05;  use ( H - t e s t ,  allopatric  3.3.2  (H-test,  Table  9),  shallower It  should  A l t h o u g h many c h a r  in  NIGHT  DAY  Y//X//A (8)  (109)  I c 2  m  I  (31)  m  m.  '////,  5  10  20  SAMPLING  Figure  40  2  DEPTH  6 1 0  CONTOUR  20  40  (m)  9. S p a t i a l and t e m p o r a l d i s t r i b u t i o n o f s y m p a t r i c c h a r i n Loon L a k e . (Mean c a t c h p e r u n i t e f f o r t i n 5 deep g i l l net s e t s i n , u n i t s of i n d i v i d u a l s / 1 0 0 m net area/12 h s e t . Numbers o f i n d i v i d u a l s c a p t u r e d a r e shown i n p a r e n t h e s e s . ) 2  47  Table 9. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric char by time of day (D= day, N=night), h a b i t a t (L= l i t t o r a l , EP=epipelagic, P=pelagic, EB=epibenthic), and month (J=June, A=August, O=0ctober).  H-statistic, Deg . Freedom  ANOVA F a c t o r A. June (N=117) time of day habitat time*habitat B. August (N=54) time of day habitat time*habitat  C. October (N=117) time of day habitat time*habitat D. Pooled (N=288) sampling month time of day habitat month*time month*habitat time*habitat month*time*habitat 1  Probability of H  Tukey M u l t i p l e Comparison of Means (p=.05) 1  ** 2 ns ns  N D ns ns  .78, 1 14.52,3 1 .09,3  ns ** ns  ns EB P EP L ns  2.05,1 7.49,3 3.47,3  ns ns ns  8.79,1 5.07,3 .69,3  3  ns ns ns  (EB P L EP)  3.59,2 9.34,1 7.14,3 2.29,2 18.28,6  ns ns ** N D ns" ns (EB P EP L) ns ns ** J-EP O-EB A-EB 0-P A-P O-L J-L J-EB J-P O-EP A-EP A-L4 1.10,3 ns ns ns 5.35,6 ns A  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d .  2*** < . o o i ; p=.058 p=.068 p  3  fl  ** p < . 0 l ;  * p<.05; ns=not  significant  p>.05  48  spawning c o l o r a t i o n were captured aggregations  Allopatric  char  bottom of Katherine between  P<.01; Table  10).  depths  (Figure  habitats  In June and  in  either  10A  and  in  August  captured  and  15.24  char/100  The  supplemental In and  extra g i l l 11.71  littoral  the the  day  distributions  char  most  dense  June  were  These  experimental  in  epipelagic  l e a s t dense i n p e l a g i c 10C).  During  and  October,  f o r s u r f a c e prey over the whole l a k e .  (N=16)  "driven"  littoral  Lake  habitat,  habitat.  sample s i z e s of a l l o p a t r i c char,  in  thirdly  i n Katherine  the r e s u l t s from  and  in  ( H - t e s t s , p<.05; Table  epibenthic  were  habitat,  number of char captured the  in  (H-test, p<.05; Table  small  highest  h a b i t a t , and  set overnight  corroborated  October,  were  (H-test,  2  2  the  distributed  char/100 m /l2 h in l i t t o r a l  char were observed to r i s e  from  CPUEs  in l i t t o r a l  net  were  each sampling month  August,  m /l2 h  catches  epibenthic habitat  during  but  p e l a g i c or e p i p e l a g i c h a b i t a t  B).  to  spawning  from the s u r f a c e to  10),  in  epibenthic habitat, secondarily  sampling.  no  Lake  occupied Lake  differently  Due  October,  were observed.  A l l o p a t r i c Char in Katherine  habitat  during  by  at night  zone and  and  August  nocturnal i n October  were c h i e f l y  especially  (N=2),  catches.  The  (N=209) came  the large mainly  l a r g e a d u l t males  and  females i n spawning c o l o r a t i o n . Although there were no s i g n i f i c a n t d i e l habitats was  (H-test,  p>.05;  a marked increase  Table  10),  movements  between  in June and October  i n the d e n s i t y of char i n l i t t o r a l  there  habitat  DAY  NIGHT  SAMPLING DEPTH CONTOUR  Figure  (m)  10. S p a t i a l and temporal d i s t r i b u t i o n of a l l o p a t r i c char i n K a t h e r i n e Lake. (Mean c a t c h per u n i t e f f o r t i n 5 m deep g i l l net sets in u n i t s of i n d i v i d u a l s / 1 0 0 m net area/12 h s e t . Numbers of i n d i v i d u a l s captured are shown i n parentheses. Note change i n depth s c a l e from F i g u r e s 9-11.) 2  50  Table 10. K r u s k a l - W a l l i s a n a l y s e s of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Katherine Lake a l l o p a t r i c char by time of day (D=day, N=night), h a b i t a t ( L = l i t t o r a l , E P = e p i p e l a g i c , P= p e l a g i c , EB=epibenthic), and month (J=June, A=August, O=0ctober)  ANOVA F a c t o r  H-statistic, Deg. Freedom  Probability of H  Tukey M u l t i p l e Comparison of Means (p=.05) 1  A. June (N=112) time of day habitat time*habitat  1 1 .92, 1 9.05,3 3.35,3  *** 2  ns  N D EB L P EP ns  B. August (N=27) time of day habitat time*habitat  15.91,1 15.51,3 5.97,3  ** * ns  N D EB L EP P ns  5.92,1 5.58,3 5.53,3  ns * ns  ns EP L P EB ns  C. October (N=253) time of day habitat time*habitat D. Pooled (N=392) sampling month time of day habitat month*time month*habitat ,time*habitat month*time*habitat  *  25.60,2 *** 14.86,1 *** 3.48,3 ns 1.59,2 ns 18.44,6 ** O-P A-EB O-EB J-P 5.51,3 5.33,6  ns ns  0 J A N D ns ns Q-EP Q-L J-EB J-L A-L A~EP J-EP A-P ns ns  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . 2*** <.001; ** p^.01; * p<.05; ns=not s i g n i f i c a n t p>.05 1  P  51  at night ( F i g u r e 10).  Sympatric  versus A l l o p a t r i c  In June and October, distributed  sympatric  differently  between  P<.01, r e s p e c t i v e l y ; Table months  pooled,  distribution The  there  Char and  allopatric  habitats  was  no  significant  between  p o p u l a t i o n s were most dense i n allopatric littoral char  char  were  found  between  in  significantly  habitats  differences  in  (H-test,  habitat  Sympatric  different  habitat  were  Table due  There was between 11).  but a l l o p a t r i c char  i n June and August and  sympatric  in  both  August,  and  11D).  to  allopatric movements Seasonal  o p p o s i t e trends of Sympatric  char  epibenthic habitat  utilized  epibenthic  shallower h a b i t a t s i n October.  no s t a t i s t i c a l d i f f e r e n c e i n d i e l use of h a b i t a t s  sympatric However,  obscured  Although  seasonal  shallow h a b i t a t s i n June and mainly  in August and October,  have  habitat  v e r t i c a l movement between the two p o p u l a t i o n s . utilized  D).  g r e a t e r r e l a t i v e abundance i n  p<.00l;  use  habitats.  epibenthic  h a b i t a t than sympatric char.  exhibited  11B and  i n August c r e a t e d a r e l a t i v e l y  l a r g e v a r i a n c e i n c a t c h per u n i t e f f o r t which may distribution  in a l l  d i f f e r e n c e in t h e i r  between h a b i t a t s ( H - t e s t s , p>.05; Table  in  were  ( H - t e s t s , p<.05 and  11A and C), but i n August and  small number of char captured  differences  char  and  in  allopatric  October,  there  char was  ( H - t e s t s , p>.05; Table some  evidence  that  char used shallower p a r t s of the water column at night  while a l l o p a t r i c char  (mainly spawners) used l i t t o r a l  a g r e a t e r extent at n i g h t than d u r i n g the  day.  h a b i t a t to  52  Table 11. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric char versus Katherine Lake a l l o p a t r i c char by lake (L=Loon, K=Katherine), time of day (D=day, N=night), h a b i t a t ( L = l i t t o r a l , EP= e p i p e l a g i c , P= p e l a g i c , EB=epibenthic), and month (J=June, A=August, O=0ctober)  ANOVA Factor  H-statistic, Deg . Freedom  A. June (Loon N=117; Katherine 7.11,1 lake time of day 20.12, 1 habitat 1.66,3 lake*tirne .58, 1 lake*habitat 1 1 . 17,3  Probability of H N=112)  ** 2  *** ns ns *  0  time*habitat lake*time*habitat  2.53,3 1 .20,3  B. August (Loon N = 54; Katherine .02, 1 lake time of day 4.86,1 habitat 22.05,3 1.87,1 lake*time lake*habitat 3.66,3 time*habitat 3.60,3 lake*time*habitat .66,3  ns ns N=27) ns * *** ns ns ns ns  C. October (Loon :N=117; Katherine lake 19.09,1 time of day 3.29,1 habitat .42,3 l a k e * t ime .00,1 lake*habitat 12.20,3 time*habitat lake*time*habitat  6.75,3 .60,3  N=253) *** ns ns ns ** ns ns  Tukey M u l t i p l e Comparison of Means (p=.05) 1  K L N D ns ns K-L K -EB L-L L -EB ns ns  K-P L- EP L-P K- EP  J  ns N D EB P L E-P ns ns ns ns K L ns ns ns K-EP L-EB ns ns  K-L  K-P K-•EB  L-P  L-L L-•EP  ..Continued  53  Table  11.  Continued  D. Pooled (Loon N= 288; Katherine N=392) *** lake 18.31,1 *** month 19.21,2 *** time of day 22.79,1 habitat 6.12,3 ns ** lake*month 10.70,2 lake*time lake*habitat month*habitat time*habitat lake*month*habitat  L-A-L lake*time*habitat  1.29,1 2.93,3 10.26,6 5.06,3 23.86,6  1.99,3  ns ns ns ns ***  K L 0 J A N D ns K-0 K-J L-0 L - J j L-A K-A ns ns ns ns K-O-EP K-O-L K-J  ns  ns  f a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d , z*** <.001; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05 P  54  3>.3.3 Trout versus Char There  were  significant  differences  sympatric t r o u t and char d u r i n g sampling  months  pooled  s e g r e g a t i o n between differences trout  were  dense  in  October,  each  (H-tests,  sympatric  sampling  dense  epipelagic  trout  differences  in l i t t o r a l  habitat.  month  and a l l  and  char  was  based  on  and l i m n e t i c zones, where h a b i t a t and char were most  However,  during  and  e p i p e l a g i c h a b i t a t s and  and  all  between  utilized  There were s i g n i f i c a n t  allopatric  Although  epibenthic  differences  in habitat  t r o u t and char d u r i n g June, August, and  sampling months pooled (H-tests,  D).  mainly  were  and  segregation with depth, where t r o u t u t i l i z e d mainly l i t t o r a l char  utilization  August  on  use  habitat  In June,  based  pelagic habitats.  in  use between  p<.00l; Table 12).  i n u t i l i z a t i o n of l i t t o r a l most  in habitat  differences  in  p<.00l; Table 13A,  habitat  B,  utilization  and  between  a l l o p a t r i c t r o u t and char were mainly based on depth of h a b i t a t , littoral  h a b i t a t was among the two more  f o r both t r o u t and char. use  were  not  so  were  significant  then e p i b e n t h i c in used  pelagic  most  13C).  habitats.  between  habitats  in habitat  a s ' d u r i n g other months In  October,  both  However, t r o u t were much habitats  relative  ( e p i p e l a g i c and l i t t o r a l ) h a b i t a t s no  habitats  significant between  a l l o p a t r i c t r o u t and char i n any  month  pelagic,  less  dense  t o the two h e a v i l y  (Table 13C).  difference  sympatric  (H-test,  allopatric  dense i n e p i p e l a g i c , l i t t o r a l ,  and e p i b e n t h i c  There was  used  During October, d i f f e r e n c e s  p>.05 (cf p<.00l); Table populations  heavily  in  diel  movements  t r o u t and char or between or  pooled  months  (H-  55  Table 12. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Loon Lake sympatric t r o u t and char by s p e c i e s (T=trout, C=char), time of day (D=day, N=night), h a b i t a t ( L = l i t t o r a l , EP=epipelagic, P=pelagic, EB=epibenthic), and month (J=June, A=August, O=0ctober).  ANOVA Factor  H-statistic, Deg. Freedom  Probability of H  A. June (Trout N=332; Char N=117) spec i e s 12.27,1 time of day 8.21,1 habitat 34.38,3 species*time .31,1 species*habitat 16.89,3  ** *** ns ***  time*habitat species*time*habitat  ns ns  .54,3 .72,3  * * *  2  B. August (Trout N=263; Char N=54) spec i e s 12.06,1 *** time of day ' .39,1 ns habitat 11.23,3 * species*time .11,1 ns *** species*habitat 45.62,3 time*habitat species*time*habitat  .70,3 .13,3  ns ns  C. October (Trout N=471; Katherine spec i e s 17.93,1 t ime of day 1.83,1 habitat 11.98,3 species*time .00,1 species*habitat 34.40,3  N=117)  time*habitat species*time*habitat  ns ns  1.02,3 1.10,3  ***  ns ** ns ***  Tukey M u l t i p l e Comparison of Means (p=.05) 1  T C N D. EP L EB P ns T-L T-EP C-EP T-EB C-L C-EB T-P C-P ns ns •  )  T C ns L EP EB P ns T-L T-EP C-EB T-EB. C-P T-P C-EP C-L ns ns T C_ ns L EP P EB ns T-L T-EP C-EB T-P, C-P T-EB C-L C-EP ns ns .Continued  56  Table  12.  Continued  D. Pooled (Trout N=1066; Katherine N=288) 40.41,1 species *** 6.66,2 month * 7.88,1 time of day ** 47.88,3 habitat *** .31,2 ns species*month .32, 1 ns species*time *** 89.14,3 spec i e s * h a b i t a t month*habitat time*habitat species*month*habitat species*time*habitat  8.96,6 .87,3 5.39,6 .50,3  ns ns ns ns  T C 0 J A D N L EP EB P ns ns T-L T-EP C-EB T-EB. C-P T-P C-EP C-L ns ns ns ns  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . 2*** <.001; ** p<.0l; * p<.05; ns=not s i g n i f i c a n t p>.05 1  P  57  Table 13. K r u s k a l - W a l l i s analyses of v a r i a n c e of g i l l net c a t c h per u n i t e f f o r t f o r Eunice Lake a l l o p a t r i c t r o u t versus Katherine Lake a l l o p a t r i c char by s p e c i e s (T=trout, C=char), time of day (D=day, N=night), h a b i t a t ( L = l i t t o r a l , EP= e p i p e l a g i c , P=pelagic, EB=epibenthic), and month (J=June, A= August, O=0ctober).  ANOVA F a c t o r  H-statistic, Deg. Freedom  Probability of H  A. June (Trout N=411 ; Char N=112) spec i e s 5.78,1 time of day 1 .29, 1 habitat 32.62,3 spec i e s * t i m e 8.79,1 spec i e s * h a b i t a t 31 .07,3 time*habitat species*time*habitat  1.69,3 1.83,3  * 2  1  ns *** ** ***  T C ns L EP EB P T-D C-N T-N C-D T-EP T-L C-L C-EB, C-P T-EB T-P C-EP  ns ns  ns ns  ***  T C_ ns EP L EB P ns T-EP T-L C-EB T-P C-L C-EP C-P T-EB ns ns  B. August (Trout N=176; Char N=27) spec i e s 12.83, 1 time of day 2.13,1 habitat 24.30,3 species*time 1.05,1 species*habitat 26.22,3  ns *** ns ***  time*habitat species*time*habitat  ns ns  1 . 04 , 3 1.23,3  Tukey M u l t i p l e Comparison of Means (p=.05)  C. October (Trout N=330; Char N=253) spec i e s .13,1 ns time of day .98,1 ns habitat 49.40,3 *** species*time .40,1 ns species*habitat 5.39,3 ns time*habitat 5.68,3 ns species*time*habitat 1.24,3 ns  ns ns EP L EB P ns ns ns ns .Continued  58  Table  13.  Continued  D. Pooled (Trout N=917; Char N=392) ** 9.08,1 spec i e s 19.16,2 month *** * time of day 3.89,1 *** habitat 95.77,3 * spec ies*month 8.12,2 spec i e s * t ime species*habitat  6.48, 1 53.61,3  * ***  month*habitat time*habitat spec ies*month*habitat spec i e s * t ime*habitat  11.07,6 4.75,3 7.50,6 1.62,3  ns ns ns ns  T C 0 J A N D EP L EB P C-0 T - J T-0 T-A C-J C-A T-D C-N T-N C-D T-EP T-L C-EB C-L . C-EP C-P T-P T-EB ns ns ns ns  F a c t o r l e v e l s are l i s t e d i n descending order of means; homogeneous subsets are u n d e r l i n e d . 2*** < . o o i ; ** p < . 0 l ; * p < . 0 5 ; ns=not s i g n i f i c a n t p>.05 1  p  T  59  t e s t s , p>.05; Tables some evidence allopatric During  12 and 13).  of a d i f f e r e n c e i n the p a t t e r n of d i e l movement of  trout  June,  and char  although  e p i p e l a g i c and l i t t o r a l more and  However, d u r i n g June there was  between h a b i t a t s ( F i g u r e s 8 and 10).  allopatric  trout  were  most  dense  in  h a b i t a t s during day and n i g h t , they were  dense i n e p i b e n t h i c h a b i t a t during the n i g h t than the day, although  allopatric  char  were  most  dense  in  h a b i t a t o v e r a l l , they were more dense i n l i t t o r a l  epibenthic  h a b i t a t during  the night than the day.  These d i e l h a b i t a t s h i f t s  both  and char make n o c t u r n a l use of h a b i t a t s  allopatric  trout  which are t y p i c a l of the other  i n d i c a t e that  species.  3_.£ E f f e c t s of I r r a d i a n c e L e v e l on Behavioural  and  Feeding  Interactions  _3.4.1 General Behaviour  Establishment The  establishment  experimental To  of Dominance of  dominance  fish  aquarium  and  11.  although  Initially,  response  was  followed  i n t e r a c t i o n and reduced swimming was  to  behaviour.  established.  the  fish  explored  swimming a c t i v i t y of both f i s h  r e l a t i v e l y high, there were few b e h a v i o u r a l  trout  prior  t h i s p a t t e r n , a g o n i s t i c i n t e r a c t i o n s of one p a i r  of f i s h are shown i n F i g u r e  initial  pairs  treatments f o l l o w e d a r e g u l a r p a t t e r n of  illustrate  the  in  by  interactions.  a phase of r e l a t i v e l y  activity,  when  dominance  was This high by  Once e s t a b l i s h e d , t h e i r dominance was  60  Figure  11. Behaviours a s s o c i a t e d with dominance of t r o u t o v e r c h a r .  the  establishment  of  61  maintained f o r the d u r a t i o n of the experiment of  aggression,  but  the  in  regular  number of a g g r e s s i v e i n t e r a c t i o n s and  time spent i n bouts markedly  decreased  (Figure  11). During  phase, the swimming a c t i v i t y of the char was very use  of  the aquarium  the char s t r a y e d "responded"  this  position,  aggressive  the  behaviour.  e s t a b l i s h e d , a l l a g g r e s s i v e behaviours trout  low  this  and i t s  was r e s t r i c t e d t o one end (Figure 12).  from  with  bouts  trout  Once  were  immediately  dominance  performed  and a l l submissive behaviours by the char.  If  was  by the  Although data  on establishment of dominance were not recorded f o r a l l p a i r s of fish,  t h i s sequence of behaviours was easy t o r e c o g n i z e , and i n  each  replicate,  i r r a d i a n c e l e v e l treatments were not commenced  u n t i l a g o n i s t i c behaviours had s t a b i l i z e d .  Swimming  Behaviour  The swimming a c t i v i t y of t r o u t than  that  of  char  interspecific pairs replicate  (F-test,  was  significantly  p<.00l,  F=37.55,  df=1,23) i n  (e.g. days 4-6, F i g u r e 11B). Char i n  or hovered a t the o p p o s i t e end t o the char Char  always  had  a  different  Char o f t e n " r e s t e d " swam  or  hovered  position on in  the  irradiance  levels char  and  behaved  always i n the  substrate,  the end  same  tank  i n the water column than  the water  at  the  (e.g. F i g u r e 12).  way,  whereas  column.  i n t e r s p e c i f i c p a i r s r e s t e d on the s u b s t r a t e more  Solitary  every  spent the m a j o r i t y of t h e i r time a t e i t h e r end of the  aquarium, whereas t r o u t e i t h e r swam back and f o r t h i n  trout.  greater  of but  trout  Char  often  in  a t low  the aquarium. rested  more  62  A.  QUARTILE  I  (LEFT-HAND  END) CHAR  TROUT  ~n B.  rm  E3n QUARTILE  H  1  II  o in  P7  o • C.  QUARTILE  D.  QUARTILE  V I I I  _C1 IV  &]  (RIGHT-HAND  EL END)  1 3 DAY  Figure  12. Horizontal position establishment of dominance  in of  aquarium during the trout over char.  63  frequently  near  seemed  "prefer"  to  interspecific attempt to  of  resting  on  the  aquarium.  the  substrate,  from aggression from t r o u t .  continue  char  char  in  the  bout.  Char  often  swam  d u r i n g an a g g r e s s i v e bout,  t h i s p o s i t i o n only to a v o i d the t r o u t to  Although  have assumed t h i s r e s t i n g posture i n an  bottom and became very s t i l l  leaving again  centre  p a i r s may  to escape  the  the  However,  if  it  approached  i n some p a i r s ,  trout  i n i t i a t e d a g g r e s s i v e bouts when char assumed a r e s t i n g p o s t u r e . Another in  swimming behaviour performed  interspecific  pairs  was  position.  T h i s behaviour was  never  solitary  by  by char but not  hovering  performed  individuals  or  in  a  non-horizontal  by subordinate f i s h ,  dominant  Although the relevance of t h i s behaviour  trout  or  Feeding  s i z e from a v e r t i c a l  char. be  their  viewpoint.  Behaviour  During  feeding  changes i n Neomysis,  trout  trials,  and  behavioural  char.  there  interactions  10 min while the f i s h  interactions  between  trout  decreased w i t h i n 30 minutes. difference  were  Following  approximately  several the  introduction  were reduced exploited  behavioural  the  of  i n i t i a l l y for prey,  then  and char became very frequent, but However, there was  no  significant  i n the i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s between  feeding and non-feeding The  and  i s not known, i t may  used by subordinate f i s h as a submissive d i s p l a y to reduce apparent  trout  trials  ( F - t e s t , p>.05, F=3.25, df=1,23).  i n c r e a s e i n swimming a c t i v i t y of both t r o u t  F=20.67, df=1,23) and char  ( F - t e s t , p<.0l,  ( F - t e s t , p<.00l,  F=9.31., df = 1,23)  was  64  highly  significant,  (Table  14).  significantly present  mainly due t o i n c r e a s e d s e a r c h i n g a c t i v i t y  However,  the  greater  than  swimming  activity  that  char  of  ( F - t e s t , p<.00l, F=14.73, df=1,23)  of  trout  whether or  was  prey were  absent  (F-test,  P<.001, F = 37.55, df=1,23) . The  vertical  position  of  char i n the water column ( i . e .  " r e s t i n g " on bottom, swimming i n the water column, hover) was not changed from non-feeding  or  diagonal  trials.  2L4.2! B e h a v i o u r a l I n t e r a c t i o n s The char  frequency of b e h a v i o u r a l i n t e r a c t i o n s between t r o u t and  was  reduced  with  decreasing irradiance l e v e l  two-way ANOVA ( i r r a d i a n c e l e v e l p<.05,  F=4.52,  df=3,l0;  (repeated measures) and  Figure  levels  significantly (F-test  were, presented  affect  order),  13). There were v i r t u a l l y no  i n t e r a c t i o n s at the lowest i r r a d i a n c e l e v e l . irradiance  (F-test in  to  The order i n which  each  pair  did  not  the frequency of b e h a v i o u r a l i n t e r a c t i o n s  i n two-way ANOVA ( i r r a d i a n c e l e v e l  (repeated  measures)  and o r d e r ) , p>.05, F=0.23, d f = 2 , l 0 ) . At  a l l irradiance  predominantly three  lowest  levels,  b e h a v i o u r a l i n t e r a c t i o n s were  submissive a c t s of avoidance irradiance  levels,  there  by the char. was  an  predominance of submissive a c t s by the char, and the  even g r e a t e r  aggression  by  t r o u t was v i r t u a l l y n i l ( F i g u r e 13), although the dominance  r e l a t i o n s h i p was maintained a t a l l i r r a d i a n c e At the lower by  At the  levels.  irradiance l e v e l s , v i s u a l perception  t r o u t may be l i m i t e d due t o reduced  of  char  swimming a c t i v i t y of the  65  Table 14. Swimming a c t i v i t y of t r o u t and char i n f e e d i n g (F) and t r i a l s without prey present (NF). (Data from a l l i r r a d i a n c e l e v e l s pooled; N=24.)  NF  Trout  Swimming a c t i v i t y per 30 minutes 43.9±21 .2 (mean ± standard d e v i a t ion)  F  107 .6±83.5  NF  Char  9.8±17.2  trials  F 31.9±48.6  A. IRRADIANCE LEVEL 3.0 x 10 93.55 ± 31.02 a c t s  o o rvj  18  prtotons/m /s 2  Avoid  o in  Change Chase  o  o  Nip o in  LH z  n  a  T  Q ro "s cn r-  u <  _J < cr o  > < X UI  ca  2  J  zzzz  B. IRRADIANCE LEVEL 19.39  ±  1.5  X  10  16  p h o t o n s / m  2  / s  a c t s  10.79  o o  a in  o  J  C. IRRADIANCE LEVEL 5.0 x 10 9.19 ± 4.53 a c t s  15  photons/m /s  D. IRRADIANCE LEVEL 3.0 x 10 0.50 ± 0.34 a c t s  15  photons/m /s  2  o in  o  J  a in  o  2  J  1  2  3  4  5  6  REPLICATE  gure 13. Type and i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s between dominant t r o u t and subordinate char at four irradiance levels. (Mean b e h a v i o u r a l a c t s per 30 min standard e r r o r are shown.)  67  trout. char  With d e c r e a s i n g i r r a d i a n c e , t r o u t must a c t i v e l y seek out in  order  significant  to  perform  difference  aggressive  in  swimming  acts.  There  activity  of  was  no  trout  in  i n t e r s p e c i f i c p a i r s with char with d e c r e a s i n g  irradiance  (F-test,  However, s o l i t a r y  p>.05, F=1.32, df=3,15; F i g u r e 14).  t r o u t and i n t r a s p e c i f i c t r o u t activity  with  solitary  and  interspecific  decreased  pairs  irradiance level.  intraspecific pairs  exhibit  with  pairs  trout  reduced  level  swimming  The same i s true of  of  char,  showed  a  but  char  highly s i g n i f i c a n t  r e d u c t i o n i n swimming a c t i v i t y with d e c r e a s i n g i r r a d i a n c e (F-test,  p<.0l,  F=5.44,  df=3,15;  swimming a c t i v i t y of t r o u t presence  of  char.  n=23) but not char intensity  F i g u r e 14).  appears  Swimming (p>.05,  to  be  n=24)  was  low  behaviours  irradiance,  char  continue  to  less  several avoid  active  than  dominant or s o l i t a r y  t r i a l s at the lower trout,  irradiance  the  (p<.05, r=.43,  correlated  It  appears  exhibit  with  and  (3.0  x  respond to nudging  irradiance  some  char  10  photons/m /s)  1 5  by t r o u t .  appeared 2  levels, to  irradiance  subordinate fish.  be  because  that  submissive  ( i . e . "avoidance"; Table 2) used at higher  l e v e l s to a v o i d a g g r e s s i o n by t r o u t , and that are  by  of b e h a v i o u r a l i n t e r a c t i o n s , although the r value f o r  t r o u t was not much g r e a t e r than that of char. under  level  T h e r e f o r e , the  influenced  a c t i v i t y of t r o u t  r=.37,  in  char  However, i n  char torpid they  d i d not i n low d i d not  68  A. IRRADIANCE LEVEL 3.0 x 10 photons/m /s TROUT 34.96 + 8.15: CHAR 30.44 ± 10.27 u n i t s 18  o m  2  CHAR TROUT  o  in tL I B. IRRADIANCE LEVEL 1.5 x 10 photons/m /s TROUT 51.47 ± 4.50; CHAR 2.76 + 1.52 u n i t s 16  o m  z  2  x o ro  o  <  1  LI  . C. IRRADIANCE LEVEL 5.0 x 10 photons/m /s TROUT 52.90 + 9.97: CHAR 2.26 ± 0.91 u n i t s 15  o .  Z n X X  00  on  o  1  IRRADIANCE LEVEL 3.0 x 10 photons/m /s TROUT 35.81 + 10.01: CHAR 3.46 ± 1.58 u n i t s 15  o m  o  l Figure  2  1  I  jzm.  3 4 REPLICATE  2  I L  14. Swimming a c t i v i t y of dominant t r o u t and subordinate char at four i r r a d i a n c e l e v e l s . (One swimming a c t i v i t y u n i t i s entry to a new h o r i z o n t a l q u a r t i l e of aquarium. Mean a c t i v i t y per 30 min ± standard e r r o r are shown.)  69  3._4.3 Feeding Performance The  feeding  dominated  by  performance  trout  increased  behavioural  interactions  df=4; F i g u r e  15).  of  char  with  (t-test,  in interspecific pairs  decreasing two-tailed,  Data used i n t h i s  test  intensity  of  p>.05, t=5.41,  were  restricted  to  feeding  t r i a l s at i r r a d i a n c e l e v e l s that maximized the r e a c t i o n  distance  f o r both s p e c i e s  The  difference  interspecific  (3.0 x 1 0  i n feeding  pairs  dominated  1 8  photons/m /s). 2  performance of t r o u t and char  by t r o u t was h i g h l y s i g n i f i c a n t  ( F - t e s t , p<.00l, F=24.29, df=1,23; F i g u r e feeding  strikes  than  16).  Trout made  (Replicate  2; F i g u r e  ( F - t e s t , p>.05, F=2.39, df=3,l5) nor char under  Neither  ( F - t e s t , p>.05,  less  level.  performance of t r o u t d e c l i n e d  feeding  frequently  16C).  F=1.92, df=3,15) fed The  more  char i n a l l r e p l i c a t e s at a l l i r r a d i a n c e  l e v e l s except f o r one t r i a l trout  in  lower  irradiance more r a p i d l y  with i r r a d i a n c e l e v e l than d i d that of char although t h i s r e s u l t was not s t a t i s t i c a l l y During feeding non-feeding t r i a l s , activity, As  and  s i g n i f i c a n t (Figure 16).  t r i a l s , char maintained s i m i l a r behaviour t o i n c l u d i n g subordinate  orientation  behaviours,  i n the water column (Figures  i n t r i a l s without prey p r e s e n t , there was a  i n t e n s i t y of i n t e r a c t i o n a t the three highest but  there  was  a  relatively  the was  17, c f F i g u r e  13).  at  variable  irradiance levels,  in  feeding  trials  However, t r o u t were dominant even a t  lowest i r r a d i a n c e l e v e l , and the feeding affected  17-19).  low i n t e n s i t y of i n t e r a c t i o n and  v i r t u a l l y no a g g r e s s i o n at the lowest l e v e l (Figure  highly  swimming  a l l irradiance  levels.  performance of char There was a h i g h l y  70  Figure  15. E f f e c t of b e h a v i o u r a l i n t e r a c t i o n s between dominant t r o u t and subordinate char on the feeding performance of char. ( I r r a d i a n c e l e v e l = 3.0 x 1 0 photons/m /s. Bars i n d i c a t e ± standard e r r o r . Sample s i z e s are shown i n parentheses.) 1 8  2  71  A. IRRADIANCE LEVEL 3 .0 x 10 photons/m /s TROUT 27.92 + 5.83; CHAR 8.76 ± 3.86 s t r i k e s 18  2  o  1/  TROUT  O  1  CHAR  1  o  o m  B. IRRADIANCE LEVEL 1 5 x 10 photons/m /s TROUT 19.10 + 4.68 CHAR 2.08 + 1.24 s t r i k e s 16  2  O CM  in  UJ 1771  C. IRRADIANCE LEVEL 5 0 x 10 photons/m /s TROUT 13.70 ± 3.33 CHAR 4.57 t 2-50 s t r i k e s 15  (ft  LO Z n Q UJ UI U.  O  O CM  1 1 <2  o CM  3 4 REPLICATE  Figure  L  D. IRRADIANCE LEVEL 3.0 x 10 photons/m /s TROUT 11.90 + 4.43; CHAR 1.28 ± 0.92 s t r i k e s 15  o  2  2  ia I 1  16. Feeding performance of dominant t r o u t and subordinate char at four i r r a d i a n c e l e v e l s . (Mean feeding s t r i k e s per 30 min ± standard e r r o r are shown.)  72  A. IRRADIANCE LEVEL 3.0 X 10 54.72 + 26.84 a c t s  a in  18  photons/m /s 2  a o o in  mi  i — i  B. IRRADIANCE LEVEL 1.5 x 10 41.94 ± 22.62 a c t s  O  16  in o ro \ ui Iu <  2  I  ttmH  o o  Y///A  |  Avoid Change  Chase Nip  o in  m  _J < tr O i-t >  C. IRRADIANCE LEVEL 5.0 X 10 49.71 t 25.28 a c t s  <  I UJ CD  photons/m /s  15  photons/m /s 2  a in  o o Q  m o o in  J  m  L  0. IRRADIANCE LEVEL 3.0 X 10 8. 13 + 2.01 a c t s  3  1  photons/m /s 2  1  I  J_C  15  A  REPLICATE  Figure  17. Type and i n t e n s i t y of b e h a v i o u r a l interactions between dominant t r o u t and s u b o r d i n a t e char during feeding at four i r r a d i a n c e l e v e l s . (Mean behavioural a c t s p e r 30 m i n ± s t a n d a r d e r r o r a r e s h o w n . )  73  s i g n i f i c a n t decrease trials  with  was  irradiance  significantly  similarly  greater  df=1,40)  v a r i e d between replicate  (Figure individual  4 hovered  than any other char.  exception  used bottom highest  of  irradiance  (F-test,  p<.00l,  char  feeding  in  with  irradiance  ( F - t e s t , p<.001, F=9.84, char  in  s i m i l a r between f e e d i n g and non-  19). char.  However, For  vertical example,  orientation the  i n a d i a g o n a l p o s i t i o n much more  char  in  frequently  At the three lowest i r r a d i a n c e l e v e l s , the hover  r e p l i c a t e 2 at 1.5 x 1 0  resting  feeding  The o r i e n t a t i o n of  f i v e other char never used the d i a g o n a l the  of  decreased  to non-feeding t r i a l s  the water column was remarkably trials  level  in  than non-feeding t r i a l s (F-  but  df=1,15; F i g u r e 18, cf F i g u r e 14).  feeding  interactions  The swimming a c t i v i t y  t e s t , p<.0l, F=9.31, level  behavioural  decreasing  F=15.13, df=3,40). trials  in  behaviour  level.  more  1 6  behaviour  (with  photons/m /s), but  frequently  2  than  at  the  74  g„  A.  IRRADIANCE TROUT  o o  I  LEVEL  202.26  3.0  ± 42.15;  o o•  1 I  C.  z  n  z x  I  VTA  IRRADIANCE TROUT  L9  18  76.70  LEVEL  photons/m /s 2  CHAR 9 3 . 0 7  I  TROUT  CU  u <  10  CHAR  IRRADIANCE L E V E L 1 . 5 TROUT 9 0 . 4 6 ± 2 8 . 5 8 :  o ro v. >-  X  x  ± 12.36:  units  I  1  1 0 photons/m /s CHAR 9 . 2 1 + 3 . 9 7 units  x  2  16  I  5.0  ± 24.17  10  1 5  CHAR  photons/m /s 2  19.61  ± 10.66  units  o o• CU  n Z  I 0.  IRRADIANCE TROUT  60.81  LEVEL  3.0  ± 10.76;  x  10  CHAR  1  1 5  photons/m /s 3 . 9 3 ± 1 . 5 5 units 2  o oH cu  3 4 REPLICATE  Figure  m  18. Swimming a c t i v i t y of dominant t r o u t and subordinate char during feeding at four i r r a d i a n c e levels. (One swimming a c t i v i t y u n i t i s entry to a new h o r i z o n t a l q u a r t i l e of aquarium. Mean a c t i v i t y per 30 min ± standard e r r o r are shown.)  75  A. IRRADIANCE LEVEL O  •  3.0 x 10 photons/mVs 18  O f f Bottom  ^3  Diagonal Bottom  o.  OJ  o.  B. IRRADIANCE LEVEL  1.5 x 10  16  C. IRRADIANCE LEVEL 5.0 x 10  1S  D. IRRADIANCE LEVEL 3.0 x 10  15  photons/mVs  O . OJ  c E LU  3E  NF F 1  Figure  NF F 2  NF F  NF F  3 4 REPLICATE  photons/mVs  photons/m  NF F  NF F  5  6  /s  19. V e r t i c a l p o s i t i o n i n the water column of subordinate char at four i r r a d i a n c e l e v e l s . (NF=no prey present; F= Neomysis mereedis p r e s e n t . See text for e x p l a n a t i o n of terms.)  76  4.0  DISCUSSION  4.J_ S p a t i a l and Temporal D i s t r i b u t i o n Habitat p a r t i t i o n i n g 1967,  Keast  1970,  et a l . 1977, a  1978,  i s common in f i s h communities ( N i l s s o n Zaret and  Gorman and Karr  particular  kind  (e.g. l i t t o r a l  of  zone),  Rand 1971,  1978).  Moyle 1973,  A "habitat" i s a place  environment  inhabited  i r r a d i a n c e l e v e l , other organisms).  and  The  type of food resources  bottom,  proximity  present.  The  boundary.  Each h a b i t a t had  temperature,  oxygen,  In a d d i t i o n , prey abundance  used  boundaries:  a  surface  to  the  bottom;  to n e i t h e r  s i m i l a r environmental c o n d i t i o n s irradiance level  types were  distributed  i n the study  in  my  epipelagic,  to both; and p e l a g i c , p r o x i m i t y  and  in  to e i t h e r the lake  among h a b i t a t s in the lakes  similar  of  lakes.  relative  (with some exceptions,  as  below).  If resource competitive competitors response,  use  patterns  interactions, should cause  are  affected  then  species  addition to  "shift"  by  interspecific  or their  e i t h e r away from or towards the resources  competitor, or  temperature,  habitats  to the s u r f a c e ; e p i b e n t h i c , p r o x i m i t y proximity  role  (e.g.  p r e f e r r e d h a b i t a t of  or a combination of the two  littoral,  discussed  organisms  i s commonly thought to be based mainly on the abundance  study were d e f i n e d by t h e i r p r o x i m i t y or  by  with  where "environment" i s a c o l l e c t i v e term  for the c o n d i t i o n s i n which an organism l i v e s  species  Werner  r e s p e c t i v e l y (Eadie  set  of  1982).  A niche  is a  removal  of  niche  in  used by  the  particular  r e l a t i o n s h i p s of an organism i n an ecosystem,  77  which  may  be  geographical  filled areas.  the most important  1975).  different  of which are t r o p h i c and  temporal  Species  may  dimensions of t h e i r n i c h e . sympatric  part  the pressure of Although  undergo  Dill  most  important  partition  or time of  shifts  A habitat shift  in  may  between  habitats  means  often  i s the divergence  Northcote  Hall  1981, An  1974a,  fish  Connell  by  (Magnuson  which  1976,  as  1962,  1974a).  1977,  is  1979,  hypothesis of competition  1974b,  captured  in f i s h 1975,  N i l s s o n and  Larson  and  Moore  between t r o u t and char i n or  both  s i g n i f i c a n t d i f f e r e n c e s between h a b i t a t use of  and experimental all  habitat  1974c,  Werner 1977, 1982,  the  species  competition  allopatry.  and  e_t a l . of  or  s p e c i e s between sympatry and  August  contained  similar  by a h a b i t a t s h i f t i n one  the sympatric  usually  Gustafson  Niche  of  Schoener  Magnan and F i t z g e r a l d  were  a  1980).  by h a b i t a t i s one  evidence  1963,  space  ecologically  (Schoener  cited  for  Loon Lake would be supported  There  of  occupies  f o r food resources  Segregation  ( N i l s s o n 1960,  and  particular  compete f o r space per se (e.g. Fausch and  food resources  communities  activity  (Schoener  e_t a_l. 1981).  are  habitat  competition  particular  1985).  relationships,  dimension  c l o s e l y a s s o c i a t e d with competition  Werner  "dimensions",  thereby a l l o w i n g c o e x i s t e n c e under  species  1969,  different  of the s i t e ,  White 1981), competition  shifts  in  s p e c i e s from each other so that each then  different  within  species  A niche i s composed of many  or s p a t i a l dimension, (Pianka  by  sampling  allopatric  months pooled.  i n g r e a t e s t r e l a t i v e abundance i n  trout  populations  in  A l l o p a t r i c t r o u t were epipelagic  habitat,  78  sympatric  t r o u t were captured i n g r e a t e s t r e l a t i v e abundance in  littoral  h a b i t a t , and e p i b e n t h i c and p e l a g i c h a b i t a t  utilized  by both p o p u l a t i o n s .  between  Loon  apparent  habitat  prey  and  Eunice  shift.  were d i s t r i b u t e d  and August, abundant  except  in  individuals/m ) Allopatric  could  Zoobenthos,  surface  (4.06  part  arthropods 2  August  explain  (Hindar  were  surface  much  more  than i n Loon  (0.23  e_t  have u t i l i z e d  August to consume s u r f a c e a r t h r o p o d s .  and  this  w i t h i n each lake i n June  individuals/m )  Eunice t r o u t may  in Eunice mainly  in  less  distributions  zooplankton,  i n a s i m i l a r way  during  2  lakes  that  Eunice  D i f f e r e n c e s i n prey  were  a_l. i n  prep.).  e p i p e l a g i c h a b i t a t in  The d i s t r i b u t i o n of trout  i n the upper 5 m of  the  water  column  rather  than the upper 10 m as i n Loon i s c o n s i s t e n t with the hypothesis that  trout  in  epipelagic habitat  abundant s u r f a c e  arthropods  al.  found  (in  consumed  prep.) the  proportions apparent sympatric  in  that  i n Eunice were consuming the  August.  However,  sympatric  and  same  prey  types,  and  in  during  each  month.  In  any  p r e f e r e n c e of a l l o p a t r i c trout  probably  trout  preferred  epipelagic  habitat,  epipelagic habitat  in  Loon  allopatric similar case,  littoral  despite  over  char  were  Lake.  There  was  allopatric  trout.  I  in  habitat,  by  char  no  significant sympatric  conclude that these data p r o v i d e no  c l e a r evidence of a h a b i t a t s h i f t allopatry  the  not abundant in  d i f f e r e n c e between d i e l or seasonal use of h a b i t a t s by and  trout  epipelagic  excluded  because  e_t  relative  for epipelagic  h a b i t a t , or at l e a s t were not outcompeted or from  Hindar  i n t r o u t between sympatry  and  h a b i t a t use, d i e l d i f f e r e n c e s i n use of h a b i t a t s ,  79  or  seasonal d i f f e r e n c e s  i n use of h a b i t a t s .  There were s i g n i f i c a n t d i f f e r e n c e s i n h a b i t a t sympatric  and  difference  in  allopatric  char  h a b i t a t s but including trout.  allopatric  char  August  in  or  were  most  sympatric  epipelagic  This shift  hypothesis  of  to  typical  littoral  h a b i t a t s most  However,  in  Zygoptera  l a r v a e , which a_l. i n  pooled.  attraction  of  equally,  were  utilized  used  most  than  of  to  attracted  char  trout  a l l o p a t r i c char. to  by  support  an  which  the by  were  more  epibenthic allopatric  and char.  were  abundant  in  the  littoral  was zone  The high abundance of t h i s prey i n  char  In October,  heavily  strong  influence  to l i t t o r a l ,  and  possibly  the r e s u l t s of h a b i t a t  by  and  littoral  allopatric  on  shifts  habitats  char were l e a s t  These r e s u l t s support  an  c o m p e t i t i o n between t r o u t and char i n Loon Lake,  because sympatric similar  utilized  food item of a l l o p a t r i c char  by the sympatric p o p u l a t i o n .  hypothesis  not  habitats  c o n t r a d i c t those of June, as e p i p e l a g i c that  June,  a l l habitats  utilized  allopatric  epibenthic, habitats.  In  no  littoral  Katherine Lake d u r i n g June probably had a the  but  e p i b e n t h i c and  i n June does  habitat  main  prep.).  October,  h a b i t a t that was  to  heavily  the  and  between  between t r o u t and char i n Loon Lake  shifted trout  June,  in  utilized  i n h a b i t a t use  similar  e_t  dense  and l i t t o r a l  competition  June  a l l months  char  because sympatric char  (Hindar  in  use  shifted  habitat  than  to  habitats  that  were  h a b i t a t s used most h e a v i l y  During October, a l l o p a t r i c char were the  epipelagic  arthropods, as t h i s prey type was  less  zone over  to twice  prey as  upon dense  by  probably surface during  80  t h i s sampling p e r i o d (4.5 i n d i v i d u a l s / m ) than i n any other lake 2  or  month  (Hindar  et a l . i n p r e p . ) .  During October  were observed to r i s e to the lake s u r f a c e  to  1982,  consume  floating  prey items, and s u r f a c e arthropods were a more important item  to  char than i n any other lake or month.  allopatric habitat  char  (0-5  were  m)  probably  not  During  attracted  to  char  dietary October,  epipelagic  to consume zooplankton prey, as t h i s prey  was  more dense at 5-10  of  surface  m in pelagic habitat.  arthropods  in  Loon  Lake  Since the  during  comparable to that i n K a t h e r i n e Lake, h a b i t a t interpreted  with  caution,  e x p l a i n the  shift.  because  prey  density  October  shifts  type  was  not  should  be  abundance may  partly  The d i s t r i b u t i o n of a l l o p a t r i c char from the s u r f a c e to the bottom of the lake and of sympatric char from approximately deep and  to  the lake bottom a l s o support the h y p o t h e s i s that  char  difference  compete in  Loon  seasonal  a l l o p a t r i c char. mainly  in  surface  The  use  Lake.  There  in  June  (H-test,  sympatric  a  h a b i t a t s that are not u t i l i z e d  by  undergo  this shift  p<.00l;  i n a g r e a t e r s e g r e g a t i o n between sympatric  undergo  also  char  char  a  habitat  shift  and from  to p r i m a r i l y e p i b e n t h i c and  and char from June to August and October. that  significant  seasonal movement of sympatric  habitats  resulted  a  m  trout  of h a b i t a t s between sympatric  p e l a g i c h a b i t a t s i n August and October 12D)  was  5  These  data  habitat  shift  trout.  Sympatric  Table trout  indicate  i n October char  to may  i n August, but the evidence f o r  i s not c o n c l u s i v e .  There were  no  statistical  differences  between  the  two  81  populations October  in  there  diel was  use  of  some  h a b i t a t s , although i n August and  evidence  that  sympatric  char  shallower h a b i t a t s at n i g h t , while a l l o p a t r i c char used h a b i t a t more at night than d u r i n g the day. the  used  littoral  P r i o r to sampling i n  l a k e s , I p r e d i c t e d that sympatric, but not a l l o p a t r i c ,  would move at n i g h t to shallow h a b i t a t s i r r a d i a n c e l e v e l s decreased. could  exploit  abundant  zooplankton  of prey a t low i r r a d i a n c e l e v e l s though  by  trout  as  In shallow h a b i t a t s at n i g h t , char  prey, s i n c e char are more e f f i c i e n t  Even  occupied  char  or even s u r f a c e arthropod  than t r o u t  (Henderson  i n the d e t e c t i o n  and Northcote  sympatric char do not c l e a r l y  1985).  show t h i s p a t t e r n of  d i e l movement, the d i e l v e r t i c a l movement of a l l o p a t r i c char puzzling.  Why  are  a l l o p a t r i c char not d i s t r i b u t e d  h a b i t a t s d u r i n g the day? avian  predation  habitats. foraging al.  than  Risk of p r e d a t i o n i s known to a f f e c t  the  by  greater  fish  Belted kingfisher  at  the  (Mittlebach  1981,  (Meqaceryle  i n shallow  that  surface  habitat  1983).  heron  is  One p o s s i b l e reason i s  is  risk  of  i n deeper choice  of  1984, Werner et  alcyon),  great  blue  (Ardea h e r o d i a s ) , and common loon (Gavia immer) have been  observed  i n the U.B.C. Research F o r e s t ( J . Werring, p e r s . comm.)  and, although these b i r d s p e c i e s are  not  common,  may  a c t as  p r e d a t o r s at the lake s u r f a c e d u r i n g the day but not at night at all  three  study l a k e s .  Another  reason may be that char p r e f e r  the deepest water and lowest  i r r a d i a n c e l e v e l that s t i l l  maximum  to  reaction  perception habitats  of may  distance  food  items,  prey.  utilizing  p r o v i d e concealment  Without low  allows  hindering visual  irradiance  from p r e d a t o r s .  level  The r e a c t i o n  82  d i s t a n c e of char level  (>3.0  i s maximized at  x 10  (>40  m  depths  this  decrease,  1985,  irradiance  char  must  reaction  t h e i r F i g u r e 5).  level  is  littoral  irradiance  migrate  to  distance  and  1985,  levels  shallower  (Henderson  their all  water  and  to  Northcote  These data do not provide evidence that  a l l o p a t r i c char used  niche  shift,  as  shallower l i m n e t i c or  h a b i t a t s at n i g h t .  Lake p r e d i c t s , species,  i n a d d i t i o n to h a b i t a t  that  habitat  utilization  s i m i l a r when both  species  coexist  in  Lake.  versus  char,  Loon and  of  are  in  shifts  of  of the two allopatry  Habitat u t i l i z a t i o n allopatric  trout  Tables  12  and  13).  significant difference populations sympatric  (H-test,  However,  in  Table  or  they  of sympatric  trout  char  there  while  that  12C).  the  of h a b i t a t o v e r l a p shown i n F i g u r e 20.  differences  populations  or  in  diel  between  use  i n October  of  allopatric  However, at n i g h t i n June,  habitats  is  no  the  (H-test, with  There were  between  was  of  consistent  populations there  was  between a l l o p a t r i c  P<.001; Table pattern  result  were  ( H - t e s t s , p<.00l;  p o p u l a t i o n s remained s i g n i f i c a n t l y d i f f e r e n t The  both  when  October,  13D),  i n Loon  s p e c i e s i s more  versus  in habitat u t i l i z a t i o n p>.05;  one  than  s i g n i f i c a n t l y d i f f e r e n t d u r i n g June and August  October.  deep  at  An h y p o t h e s i s of competition between t r o u t and char  no  1985)  relatively  i n sympatry with t r o u t undergo a temporal sympatric  irradiance  2  However, at n i g h t , when  maintain maximum  both  low  on a c l e a r J u l y day; Henderson and Northcote  Figure 4).  char  relatively  photons/m /s; Henderson and Northcote  16  and d u r i n g the day  a  from some  sympatric June to evidence  83  A.  SYMPATRIC  CHAR  >u  z  UJ Z> C3 UJ  tr  DEPTH  OF  HABITAT  F i g u r e 20. Schematic diagram of h a b i t a t o v e r l a p of sympatric Loon Lake t r o u t and char and e x p e r i m e n t a l l y a l l o p a t r i c Eunice Lake t r o u t and K a t h e r i n e Lake char.  84  that a l l o p a t r i c and  t r o u t moved to t y p i c a l char h a b i t a t ( e p i b e n t h i c )  allopatric  Fish  char moved to t y p i c a l t r o u t h a b i t a t  distributions  competition  in  between  comparison of populations  trout  habitat  with  the  fact  and  of  evidence  significantly  the  an  char  Loon Lake based on a  habitat  different  in  between  hypothesis  the  two  of  sympatric  the two a l l o p a t r i c p o p u l a t i o n s , but i n June and August to support the  The lack of evidence that  support  separation  that  there i s i n s u f f i c i e n t hypothesis.  October  (littoral).  at  i n June and August i s due  utilization a l l times,  to  of t r o u t and char was thereby  preventing  " q u a n t i f i c a t i o n " of niche s e p a r a t i o n . Although  trout  d i d not undergo a h a b i t a t  their vertical distribution char  and  layers  expansion  of  the  hypothesis  that  in  as  of  to the s u r f a c e with  the  shift  by  char  i s c o n s i s t e n t with the h y p o t h e s i s that competition  evidence  are s p e c i f i c c r i t e r i a  Although niche s h i f t s are g e n e r a l l y  of c o m p e t i t i o n w i t h i n communities, there that must be met f o r c o m p e t i t i o n to occur.  Competition occurs when two or more same  shift  i s consistent  In a d d i t i o n , the h a b i t a t  a c t s more s t r o n g l y on char. accepted  allopatry  or expand  i n t e r s p e c i f i c c o m p e t i t i o n occurs between t r o u t  and char i n Loon Lake. but not t r o u t  i n a l l o p a t r y , the h a b i t a t  of t h e i r h a b i t a t u t i l i z a t i o n  lake  shift  resources  that  organismic  units  use the  are i n short supply, and t h i s reduces the  f i t n e s s and/or e q u i l i b r i u m p o p u l a t i o n s i z e of each (Pianka 1983, p.184). least  Trout and char p o p u l a t i o n s  in  Loon  Lake  consume  at  some of the same prey s p e c i e s (Schutz and Northcote 1972,  Hume and Northcote  1985, Hindar e_t a_l. i n p r e p . ) .  In a l l o p a t r y ,  85  s i m i l a r g e n e t i c stocks of these  s p e c i e s consume v i r t u a l l y a l l of  the same prey c a t e g o r i e s as each other, although r e l a t i v e proportions  (Hindar  et a_l. i n p r e p . ) .  of Loon Lake t r o u t and char fishless 1985)  stocks  Lake.  The  likely  limited  results  ( i . e . fecundity) reduces t h e i r  in and  reduced  potential  fish  Part of the d i f f i c u l t y field  experiment  experimental Although fish  food-limited  population  prey  study  is  may  potential  s i z e , and t h e r e f o r e  they c o u l d provide a focus f o r  populations.  i n drawing a strong c o n c l u s i o n  lake  environments.  even  influence  subtle how  differences  fish  development,  and  i n v e r t e b r a t e d i s t r i b u t i o n s are probably  not  of these  intraspecific  factors  especially  in  competition  difficult The  f a c t o r s on h a b i t a t u t i l i z a t i o n  among In  influences  how  pressure  and  The r e l a t i v e by  littoral  experiment.  respond to i n t e r s p e c i f i c competition,  been addressed i n t h i s experiment.  of these  this  lake  habitats.  lake  populations  morphometry,  utilize  in  in  addition,  from  the lack of a r i g i d c o n t r o l f o r the  Differences  the most important  Loon  lakes had s i m i l a r l i m n o l o g i c a l f e a t u r e s and  distributions,  environments  in  i n Loon Lake most  reproductive  t r a n s f e r of f i s h between whole  the  previously  Although Pianka's c r i t e r i a have not been  i n t h i s study,  f u r t h e r s t u d i e s on these  this  are  to  (Hume and Northcote  growth of t r o u t and char  fitness.  addressed d i r e c t l y  species  The r a p i d growth  transferred  lakes with abundant food resources  i n d i c a t e s that these  not i n the same  trout  this  has  importance  and  char  is  to quantify. c o n c l u s i o n that t r o u t i s a s u p e r i o r competitor  t o char  86  is  corroborated  performance  by  based  evidence  on  growth  t r o u t , showed a niche s h i f t donor  from  diets  and  and  size.  rates  in diet  relative  stock (Hindar et a l . i n p r e p . ) .  physiological Char, but not  to  Sympatric  the  and a l l o p a t r i c  t r o u t had a marked food resource o v e r l a p from June and  f e d mainly  cladocerans. resources  on  littoral  Sympatric  i n October  zoobenthos,  zoobenthos,  and  surface  Sympatric  chironomids,  arthropods  (Hindar et a l . i n p r e p . ) . the  sympatric  population  v a r i a b l e s growth r a t e p<.00O,  longer,  October,  s u r f a c e i n s e c t s , and in  food  only, although food resource a v a i l a b i l i t y  and  a l l o p a t r i c char consumed mainly l i t t o r a l August,  to  and a l l o p a t r i c char overlapped  may p a r t l y e x p l a i n t h i s r e s u l t . littoral  sympatric  and  char consumed zooplankton,  zooplankton  respect  (higher, p < . 0 0 l )  whereas  zoobenthos i n June in  A l l o p a t r i c char improved with  mainly  to  and  size  while growth r a t e of a l l o p a t r i c  October  relative  the  and  to  life  history  (fork  length  t r o u t was the  same as that of the sympatric stock (p>.05) and mean fork l e n g t h was  shorter  However,  (p<.00l;  et  a_l. 1984,  their  Table  Lake  stocks as i n d i c a t o r s of c o m p e t i t i v e  must  be  interpreted  with  pressure  caution,  p o p u l a t i o n s i n Loon Lake a r e s t a b l e habitat  not  the  ( S e c t i o n 3.2).  s e g r e g a t i o n of t r o u t and char i n Loon Lake i s  mainly with depth of h a b i t a t . are  in  as a l l o p a t r i c  p o p u l a t i o n s are not n e c e s s a r i l y a t c a r r y i n g c a p a c i t y , while  The  2).  d i f f e r e n c e s i n growth r a t e s and s i z e between sympatric  and a l l o p a t r i c Loon  Jonsson  common.  s p e c i a l i z a t i o n s , or  The selective  Seasonal  and  morphological differences,  daily and of  differences ecological  these  closely  87  related use.  s p e c i e s are i n accordance  with t h e i r p a t t e r n of h a b i t a t  Char feed more s u c c e s s f u l l y on benthic prey, and t r o u t  surface  prey  in  laboratory  experiments  i n d i v i d u a l s and i n t e r s p e c i e s p a i r s exposed  involving t o food  on  solitary  in benthic,  s u r f a c e , and both l o c a t i o n s  (Schutz and Northcote  1972, see a l s o  Hume  i n f e e d i n g performance  on prey types  1978).  Differences  may be r e l a t e d t o d i f f e r e n c e s char  (Hespenheide  1973).  i n mouth morphology of  trout  and  The mouth of char i s subterminal and  " d i r e c t e d " downwards at b e n t h i c prey whereas the mouth of is  terminal,  which may allow t r o u t to feed more e f f e c t i v e l y on  zooplankton or s u r f a c e prey.  Deep-dwelling  VIT  and  two  orders  of  the  more  that  are  one  r e s p e c t i v e l y , than those (Henderson  trout  and  Northcote  1985).  char have a SIT of  magnitude  and  lower,  surface-dwelling  trout  These d i f f e r e n c e s i n v i s u a l  a b i l i t y of t r o u t and char are r e l a t e d to d i f f e r e n c e s i n the morphology  and  the  ratio  of  rods  to  cones  in  eye  the r e t i n a  (Henderson  1982), and enable each s p e c i e s to d e t e c t prey i n i t s  habitat.  In  addition  to  capable of chemoreception  of  v i s u a l p e r c e p t i o n of prey, char are prey  below  their  VIT,  and  the  g r e a t e r maximum r e a c t i o n d i s t a n c e and f o r a g i n g v e l o c i t y of t r o u t enable  trout  to  v i s u a l l y search a volume of water seven  times  g r e a t e r than char f o r a zooplankter such as Diaptomus kenai on a summer day (Henderson of  trout  make  and Northcote 1985).  The  specializations  i t s u p e r i o r t o char i n the e x p l o i t a t i o n of food  resources i n shallow, w e l l - i l l u m i n a t e d h a b i t a t s , and v i c e for  char  in  deeper,  less well-illuminated habitats.  these s p e c i a l i z a t i o n s do not e x p l a i n the absence  of  versa  However, char  from  88  shallow h a b i t a t s i n sympatry with t r o u t In  addition  to  r e s o u r c e s , t r o u t and factors cue  such  as  selection  char  may  temperature  of  also and  i n Loon Lake. habitat use  in prey type and abundance with depth, are  important (Fry  homogeneous determinant  1971).  documented Coutant  The  of  many  Apart the  from  differences  limnetic  respects.  physiological  1958,  and.  Brett  the  1971,  success  food  environmental  zones  and  biochemical  rates  is well-  N e i l l and Magnuson  of  a  of  Temperature i s an  b e h a v i o u r a l thermoregulation of f i s h  (Ferguson  1977),  in  other  on  i r r a d i a n c e l e v e l to provide a  f o r h a b i t a t p a r t i t i o n i n g with depth.  lakes  based  fish  1974,  in achieving i t s  fundamental thermal niche can c o n t r i b u t e to i t s f i t n e s s i n terms of growth ( B r e t t have  1970,  documented  Magnuson et  thermal  habitat  bottom h a b i t a t (Brandt et along  temperature  habitat and  Magnuson  complementarity lake  1975, in  animal's  seasonal  (Matthews  Crowder  the  use  et  and  a l . 1985),  thermal  Magnuson  (Beitinger  1982),  20  °C.  trout,  which  and  of food and thermal h a b i t a t s i n a Magnuson  et  a l . (1979)  niche.  The  stressed  i s one a x i s of an  fundamental  temperature  niche of t r o u t and char i s probably s i m i l a r to that of rainbow  i n lake shifts  i s an e c o l o g i c a l resource and  multidimensional  studies  habitat  from c o m p e t i t i v e i n t e r a c t i o n  (Crowder et a l . 1981).  that temperature  Recent  p a r t i t i o n i n g by f i s h  a l . 1980),  gradients  shifts resulting  a l . 1979).  juvenile  McCauley and Pond (1971) found to be  17-  I t i s i n t u i t i v e that the fundamental i r r a d i a n c e niche of  both t r o u t and char to prey t a r g e t s .  i s one which maximizes the r e a c t i o n d i s t a n c e  Therefore, habitat preference  of  both  trout  89  and is  char  based on temperature and i r r a d i a n c e l e v e l  i n warm e p i l i m n i a l waters of l i t t o r a l  Since  the  reaction  distance  i r r a d i a n c e l e v e l than t r o u t fundamental  habitat  fundamental  preferences. the  water  or e p i p e l a g i c  char  i s maximized at a lower  (Henderson and Northcote  In a l l o p a t r y niche  Although column  and  based  sympatric  than  on  sympatry,  trout,  Therefore,  irradiance  s e l e c t i o n based  p r e f e r e n c e s i s supported to  a  lesser  niche. on  temperature  and char  with  and  to  be  interference aggressive  char.  hypothesis  1983,  and  hypothesis of  The h a b i t a t s h i f t of char i n irradiance levels  that competition  i s in  between t r o u t  of  of  competition  phenomena  individuals  and  producing  from  competition  1983).  limiting  i n d i v i d u a l s of the b e n e f i t s to be  If competitive a b i l i t y  E l t o n and M i l l e r Pianka  utilization  exploitative•  encounters,  of  direct  r e s o u r c e s , the mechanism  a competitor  mechanism 1947,  an  preferred  trout  d e p r i v e s other  from those  prevent  their  i n Loon Lake a c t s more s t r o n g l y on char.  resources  said  to  by the d i s t r i b u t i o n of a l l o p a t r i c  When competition concerns  gained  in  level  extent  the  occupy  irradiance  sympatry t o c o l d e r h a b i t a t s with lower accordance  trout  i n a l l o p a t r y they are found i n  thermal  and,  the  char occupy h a b i t a t s deeper  similar  habitat  1985),  temperature and i r r a d i a n c e  shallower h a b i t a t s that a r e more and  habitat.  of char extends deeper i n the water column  than that of t r o u t . their  of  preferences  gaining  harm  toxins,  and  access  to  i s based on  each so  is  other on,  resources,  by  which the  i s s a i d to be i n t e r f e r e n c e (Crombie  1954, B r i a n 1956, M i l l e r  1967,  Schoener  L o c a l e x t i n c t i o n occurs only where s p e c i e s  90  niches  overlap,  contiguous gopher  thereby  allopatry  species,  allowing  (Miller  Miller  populations  1964).  (1964)  whenever  competitive  fundamental  niche  one  fundamental niche specialized survive. present  of  must  be the  where  the  and  the  within  the  s p e c i e s with  the  s u p e r i o r competitor i n order  to the  ( i . e . fundamental  that of char,  and  H a l l (1977), and  similar results.  trout  is  Connell  Nilsson  found  (1960,  that  the  Cthamalus s t e l l a t u s s u r v i v e d at a l l water l e v e l s i n the zone, but p e r s i s t e d i n competition  competitor Balanus balanoides environment  where  i n h a b i t a t use  with the  only by occupying a  B. balanoides  H a l l found that b l u e g i l l  sunfish  did  not  superior  part  survive.  of  the  Werner  and  (Lepomis macrochirus) were more  than green s u n f i s h (L. c y a n e l l u s ) , which  were l i m i t e d to l i t t o r a l  habitats.  In sympatry with  green s u n f i s h , b l u e g i l l s s h i f t e d to s m a l l e r ,  aggressive  less preferred  food  i n the open water column, while green s u n f i s h remained i n  littoral  water  general  occurs  first  preferred habitat  (1961), Werner and  a l s o obtained  intertidal  the  in  competitor.  Connell  items  a  M i l l e r ' s r e s u l t s are p a r a l l e l e d by the r e s u l t s of  the s u p e r i o r  flexible  as  included  of another s p e c i e s , the  niche  study,  barnacle  that,  is  coexist  on h i s work with  exclusion  species  niche) of t r o u t i s i n c l u d e d w i t h i n  1963)  Based  stated  principle,  to  zone and  column  which handled sunfish. a r c t i c char  exploited larger  provided small  Nilsson  a  foods found  food  competitive more that  (Salvelinus alpinus)  in  The  refuge f o r the  efficiently brown  items.  trout Sweden  than  open  bluegill, did  green  (Salmo t r u t t a ) preferred  and  similar  91  prey,  but i n sympatry, char s h i f t e d to o f f s h o r e prey,  zooplankton, whereas t r o u t continued to feed on types  i n the l i t t o r a l zone.  char i n e x p l o i t i n g p r e f e r r e d  The  primarily  preferred  t r o u t were more e f f e c t i v e  prey  items  and  were  much  t e r r i t o r i a l and a g g r e s s i v e i n i n t e r s p e c i f i c encounters. case  cited  above,  the  h a b i t a t or food s e l e c t i o n a  was  the g e n e r a l i s t Habitat organisms in  a s p e c i a l i s t in  (e.g. t r o u t  i n the present study)  the mechanism of  selection  behaviour  of  species  such  behaviour  can  i n p r e d i c t a b l e environments  be  perhaps  specialist  due  the  than  very  organisms exact  However,  competitors  (Morse  competitors. of  study both demonstrated  18 mo  Northcote  following 1985).  trout  segregation Both  and  plasticity in  1974  populations  Chaoborus l a r v a e i n p e l a g i c h a b i t a t s .  char  used  in  - 1976  switched  (Hume to  However, t h i s  and  abundant switch  type  represented a g r e a t e r change i n h a b i t a t s e l e c t i o n  char  than  trout.  benthofagous  in  Individual sympatry  with  shallow h a b i t a t s i n Loon Lake.  char  were  trout,  the  i n prey s e l e c t i o n i n  prey  to  and  to t h e i r c o m p e t i t i v e e x c l u s i o n by s u p e r i o r  A l l o p a t r i c populations present  evolves because  (Krebs 1978).  g e n e r a l i s t s o f t e n occur where they have few 1980),  of  from i t s usual h a b i t a t .  habitats;  specialized  was  (e.g. c h a r ) , exclusion  i n some h a b i t a t s leave more descendants  other  In each  that  i n t e r f e r e n c e c o m p e t i t i o n was  than more  competitor  s u p e r i o r competitor to the g e n e r a l i s t competitor  and  prey  previously  in by  highly  whereas t r o u t occupied  T h e r e f o r e , char can be  be more g e n e r a l i s t , o p p o r t u n i s t i c p r e d a t o r s than  concluded  trout.  In  92  the  present study, a l l o p a t r i c  utilization different expansion  than t r o u t . prey  However, f l u c t u a t i o n s i n abundances may  partly  (Hindar et a_l. i n p r e p . ) .  to l e s s p r e f e r r e d h a b i t a t s  that  trout  were  Schutz  aggressively  interspecies pairs in laboratory that  trout  were  more  The  apparent d i e t have had  habitat  i n the presence  based on i n t e r f e r e n c e by t r o u t .  found  the  of  f l u c t u a t i o n s i n food types and abundances than Loon  or Eunice lakes  found  explain  of a l l o p a t r i c char because Katherine Lake may  more e r r a t i c  char  types  char were more general i n h a b i t a t  and  shift  of t r o u t may  Northcote  of be  (1972)  dominant to char i n most,  aquaria, aggressive  and  Rosenau  than  (1978)  char i n stream  aquaria. In summary, the present study with  the  showed  evidence  hypothesis that t r o u t and char were i n competition i n  Loon Lake.  Based on d i s t r i b u t i o n between h a b i t a t s  char are g e n e r a l i s t s i n h a b i t a t s e l e c t i o n and specialists. similarly  consistent  in a l l o p a t r y ,  t r o u t are  In sympatry,  trout  remain  in  allopatric  trout,  and may  competitively  to  char from t h i s zone.  D i e l and  relative  shallow, h a b i t a t s exclude  seasonal temporal d i f f e r e n c e s are  not important to h a b i t a t u t i l i z a t i o n  of t r o u t .  The mechanism of  c o m p e t i t i o n of t r o u t and char i n Loon Lake i s at l e a s t p a r t i a l l y e x p l o i t a t i v e , based on s e l e c t i v e species.  differences  the  two  However, a mechanism of e x p l o i t a t i v e competition does  not e x p l a i n why  char are not present i n t y p i c a l  Other  suggest  studies  that  trout  habitat.  interference competition i s usually  the mechanism of c o m p e t i t i o n when excluded  between  a  generalist  competitor  from the p r e f e r r e d h a b i t a t of a s p e c i a l i s t  is  competitor.  93  In a d d i t i o n , the s u p e r i o r a g g r e s s i v e n e s s with  an  hypothesis  of  interference competition. are  segregated  with  segregation  with  I t i s suggested  depth  c o m p e t i t i o n by t r o u t , and irradiance  of t r o u t  is  consistent  depth  based  that t r o u t  and  on char  i n Loon Lake based on i n t e r f e r e n c e  that t h i s mechanism  l e v e l , an environmental  is  moderated  by  cue which p r o v i d e s s t r u c t u r e  in the p e l a g i c environment.  4.2 If  Behavioural I n t e r a c t i o n s and  Irradiance Level  i n t e r a c t i v e s e g r e g a t i o n occurs between p o p u l a t i o n s ,  f o l l o w i n g c r i t e r i a must be 1. The  populations  the  met:  must  be  segregated  spatially  temporally, at l e a s t d u r i n g c r i t i c a l p e r i o d s  of  and/or resource  acquisition. 2. The  populations  competitors,  must  be  competitors,  f o r an e s s e n t i a l resource  or  such  potential  as  food  or  space. 3. The  populations  recognizable aggressive  must  signals, or  have which  a  communication  may  a g o n i s t i c behaviours  or t e r r i t o r i a l i t y  take  the  system of form  of  that s i g n a l dominance  to i n d i v i d u a l s or groups  of  the  other  population. 4. To  a v o i d l o c a l e x t i n c t i o n , both p o p u l a t i o n s must be able  to maintain growth and In accordance are segregated  reproduction.  with C r i t e r i o n  1, t r o u t and char  s p a t i a l l y with depth (Armitage  1973,  i n Loon Lake Hume  1978,  94  my  field  study).  presented  Furthermore,  evidence  competition.  i n my  field  study that t r o u t and char are i n  In sympatry, there i s a h a b i t a t s h i f t  t r o u t occupy t h e i r p r e f e r r e d h a b i t a t . char  in  Loon  Lake  d i s t r i b u t i o n s as t r o u t most  dense  with C r i t e r i o n 2 , I  i n accordance  have  Trout  similar  in a l l o p a t r y i n  in l i t t o r a l  in  sympatry  spatial Eunice  by char, but  and  Lake;  and e p i p e l a g i c h a b i t a t s .  relation  allopatry,  to  char  in  allopatry  they  are  distribution  Katherine  Lake.  In  char occupy the e n t i r e water column, but i n sympatry  with t r o u t , char are found concluded  in  temporal  However, char  in Loon Lake have a r e s t r i c t e d s p a t i a l and temporal in  with  from the f i e l d  in  deep  limnetic  water.  It  was  study that t r o u t and char i n Loon Lake  are i n c o m p e t i t i o n and that t r o u t  is  the  superior  competitor.  However, at t h i s p o i n t i t has not been shown whether c o m p e t i t i o n is  of  the  experiments  exploitative address  or  i n t e r f e r e n c e type. 3  Criteria  behavioural i n t e r a c t i o n  4,  and  My l a b o r a t o r y  and  investigate  ( i n t e r f e r e n c e competition) as a p o s s i b l e  mechanism of i n t e r a c t i v e s e g r e g a t i o n between t r o u t and In  conjunction  with  establishment of a dominance system  aggressive  relationship  The  repertoire  behaviours  "agonistic defense  of  of  performed  submissive behaviours performed  overt  one is  requisite a  dominant  by subordinate  behaviour". its  behaviours  by  territory  t h r e a t e n i n g , or d i s p l a y s which may  of the  communication  of r e c o g n i z a b l e s i g n a l s between dominant and  individuals.  termed  3,  Criteria  char.  subordinate encompassing  individuals individuals  The aggressor i s i d e n t i f i e d as  attacking,  chasing,  be overt or r i t u a l i z e d  and are by or  (Morse  95  1980).  I n t e r s p e c i f i c p a t t e r n s of a g g r e s s i v e behaviour  groups  studied  1980,  p.267),  to  date resemble  i n animal  i n t r a s p e c i f i c patterns  (Morse  and i n c l o s e l y g e n e t i c a l l y r e l a t e d s p e c i e s such as  t r o u t and char, communication s i g n a l s may be more  similar  b e h a v i o u r a l s i g n a l s of s p e c i e s which are not c l o s e l y Aggressive  behaviour  and dominance-mediated  than  related.  interspecific  r e l a t i o n s h i p s have been r e p o r t e d f o r many animal taxa, i n c l u d i n g mammals, b i r d s , crustaceans, p.267).  fish,  l i z a r d s , salamanders,  spiders,  and  limpets  starfish,  (reviewed  including  both  strict  territorial  ones i n which no s t a t i o n a r y area i s defended the  dominance  i s a s s o c i a t e d with a c l e a r  (concept  developed  s i t u a t i o n s and  (Morse  by  reference  Schjelderup-Ebbe  1980).  to  resources  (e.g. food,  space,  or  in  cited  space  i n Morse  mates)  r e s t r i c t i n g the a v a i l a b i l i t y of resources to another  If  aggressive  point  1922,  social  The f u n c t i o n of a g g r e s s i v e behaviour, then, i s to  access  or  of  r e l a t i o n s h i p involves t e r r i t o r i a l i t y ,  behaviour  1980).  i n Morse 1980,  These r e l a t i o n s h i p s occur over a wide range  situations,  insects,  gain while  individual  group. In  trout  accordance and  Aggressive  char  with  possess  behaviours  Criterion  3,  a  system  common  t h e r e i s evidence that of  communication.  of t r o u t such as n i p , charge, and chase,  and the submissive behaviour of char such as a v o i d i n g or f l e e i n g from i t s aggressor combined t o produce a dominance in  interspecies  pairs  in  the  present  r e l a t i o n s h i p i n the l a b o r a t o r y aquarium territoriality,  as  study.  may be  relationship The dominance  associated  with  evidenced by the r e s t r i c t i o n of char to one  96  end,  and the more general use of the aquarium by dominant  (Figure  12).  Fish  visually  locate t e r r i t o r i e s .  absence of such pelagic  may  use  the aquarium w a l l s or s u b s t r a t e to However, there would seem to be an  s p a t i a l markers to l o c a t e  environments.  trout  Unless  territories  in  lake  f i s h are c l o s e l y a s s o c i a t e d with  the lake s u r f a c e or bottom, there are few v i s u a l cues f o r a  fish  as to i t s l o c a t i o n .  Loon  T h e r e f o r e , how  i s segregation between  Lake p o p u l a t i o n s of t r o u t and char One  environmental  cue  maintained?  which  " s p a t i a l " marker f o r t r o u t and char level.  Irradiance  level  is  d i f f e r e n c e s between the two resources  (Henderson  p e r c e i v e prey  i n low  an  may  i n Loon Lake important  char  a  is  factor  vertical  irradiance in selective  s p e c i e s i n the procurement  1982).  Since  trout  are  of  less  If trout  i n Loon Lake, char w i l l experience  are  strong a g g r e s s i o n i n flee  to  i r r a d i a n c e h a b i t a t s to seek refuge. The  for  able to  dominant  h i g h i r r a d i a n c e h a b i t a t s occupied by t r o u t and char may low  food  i r r a d i a n c e , the p r e f e r r e d h a b i t a t s of t r o u t  have r e l a t i v e l y high i r r a d i a n c e l e v e l s . to  provide  l a b o r a t o r y experiments r e p o r t e d h e r e i n p r o v i d e  reduced  i n t e n s i t y of b e h a v i o u r a l i n t e r a c t i o n s between t r o u t  and char as i r r a d i a n c e decreases trout.  Assuming  to  that  aggression  e x p l a n a t i o n f o r reduced  aggression  irradiance  evidence  level  is  that  the  the  threshold  of  i s based on v i s u a l cues,  one  by  ability  visual  trout of  with  decreasing  t r o u t to v i s u a l l y  p e r c e i v e char d e c l i n e s over the range of experimental i r r a d i a n c e tested.  The  prey of t r o u t  v i s u a l a b i l i t y with respect to r e a c t i o n d i s t a n c e to and  char  certainly  declines  over  this  range  97  (Henderson In  1982).  a d d i t i o n to the reduced c a p a b i l i t y of t r o u t to see char  with d e c r e a s i n g i r r a d i a n c e l e v e l , i s another contact trout  f a c t o r which would a f f e c t  of in  char  t r o u t were  of  by  trout.  interspecific  significantly  presence  with  less  pairs  to  in  reinforce  almost  fifty  did  not  would  likely  ( F - t e s t , p>.05), s o l i t a r y  irradiance.  dominance  in  Therefore,  experience  as  small  their  the  fish  similar  Lake, t r o u t would have very l i t t l e  in  close  proximity  trout  irradiance  relationship  persisted.  char  that  observed  decreased  to  threshold,  a  the  char  of  proportion  i n c r e a s e d with d e c r e a s i n g i r r a d i a n c e l e v e l . dominance  relationship  very  low  dominance  Although most b e h a v i o u r a l submissive  the  due  activity.  i n t e r a c t i o n s at a l l i r r a d i a n c e l e v e l s were ( i . e . "avoidance"),  in  v i s u a l c o n t a c t with char  i n t e n s i t y at t h e i r v i s u a l with  to  swimming  i r r a d i a n c e h a b i t a t s i n Loon  to reduced v i s u a l a b i l i t y and swimming by  than  n a t u r a l environment.  confined  T h e r e f o r e , i n low  aggression  The  laboratory  they are i n experimental a q u a r i a , t h e i r  a c t i v i t y would probably be more  Although  activity  relationship.  relatively  in  with  trout.  the  times the n a t u r a l f i s h d e n s i t y i n Loon  i n Loon Lake are not  solitary  decrease  s t i m u l a t e the swimming  the  Since t r o u t char  visual  level  Lake " f o r c e d " more i n t e n s e i n t e r a c t i o n s between they  of  char  low  confinement of t r o u t and char at  frequency  with  irradiance  active  the  Although the swimming a c t i v i t y of  of subordinate char may  trout  aquaria  the swimming a c t i v i t y of t r o u t  between i n d i v i d u a l  acts  submissive In  Loon  by acts  Lake,  a  i n t e r a c t i n g p a i r s of  98  t r o u t and  char would p o s s i b l y  persist  as  be able  be e s t a b l i s h e d  to f l e e from i t s aggressor.  low  nor  would  it  observed in the experiments, because the char would  char would have a r e l a t i v e l y the  not  low  In low  irradiance  habitats,  encounter rate with t r o u t ,  i n t e n s i t y of a g g r e s s i o n might then not  be  strong  and  enough  to e s t a b l i s h a dominance r e l a t i o n s h i p . In Loon Lake, t r o u t and irradiance level  gradient,  habitats  irradiance  gradient, with  and  char  these  use  of  relatively  deeper  high  habitats  inferior  aggression  the d i s t r i b u t i o n of the  differences.  If  irradiance  char level  by  two can  maintained  competitively  by  superior  char to a s s o c i a t e not  tested  in  laboratory and  on  experiments  this  consistent  to  associate i n t e n s i t y of segregation  interactions  t r o u t cannot be r e j e c t e d .  The  i r r a d i a n c e l e v e l with a g g r e s s i o n by  required  particularly  to  test  the  by  ability trout  their  natural  lake  direct  application  study to i n t e r a c t i o n s of t r o u t and environment.  of was  char at  field of  this  irradiance  A more  rigorous  t e s t of the h y p o t h e s i s that s e g r e g a t i o n between t r o u t  char i s maintained by a mechanism of  based  is  habitat  interspecific  investigations,  o b s e r v a t i o n s , are  levels  along  i n t h i s study.  Further  laboratory  aggressive  lower  experience  trout  with a greater  an  irradiance  char  learn  on  with  species  a g g r e s s i o n from t r o u t , the h y p o t h e s i s that is  spatially  r e l a t i v e l y high  Competitively  in i n t e n s i t y and  segregate  where t r o u t use  levels.  differences  char  irradiance to  mine  levels but  would  be  i n t e r a c t i v e segregation to  in larger aquaria.  conduct Use  of  similar 10 x  10m  99  aquaria  would  scale  approximately  the  the  probably  probably  may  be  i n t e r a c t i o n s between  be much l e s s intense than  reflect  interaction.  fish  density  n a t u r a l d e n s i t y in Loon Lake.  t h i s s i z e , behavioural would  experimental  more  accurately  However, the r e s u l t s of my  In a q u a r i a of  interspecies I observed,  the  to  pairs  but would  natural  rate  of  l a b o r a t o r y experiments  i n d i c a t i v e of i n t e r a c t i o n s that take p l a c e in the n a t u r a l  environment in a more s u b t l e form. The  fourth c r i t e r i o n  populations maintain  must  be  growth  extinction.  is  that  reproduction, not  i n Loon Lake are at s t a b l e l e v e l s but the f a c t  that  char  persisted  Lake  the  for  trout  local  populations  Loon  whether  avoiding  char  in  known  thereby  to  and  have  is  segregation  able to o b t a i n adequate food resources  and  It  for i n t e r a c t i v e  many  decades i f not  c e n t u r i e s i n d i c a t e s that they have been able to o b t a i n food  resources  for  growth and  Jonsson et §_1. 1 984).  longterm  However,  in  t r o u t and char, the e x c l u s i o n of char or  d i s t r i b u t i o n probably  than  optimal  foraging  ultimately  based  in  individual  (Alcock  1975,  energy prey,  intake  per  patches, its  One  (see a l s o  populations  of  from i t s p r e f e r r e d h a b i t a t  since  habitat to  Werner et a l . 1981). effort  selection  fitness A  of  reduction  by char due  is the in  to l e s s dense  i n c r e a s e d search and/or h a n d l i n g time i n in decreased  in f i t n e s s would r e s u l t  the p o p u l a t i o n .  coexisting  contribution  such patches o b v i o u s l y r e s u l t s reduction  reproduction  means that char are r e s t r i c t e d to l e s s  foraging  smaller prey, and  adequate  mechanism  fitness.  A  strong  i n the eventual e x t i n c t i o n of  the  char  may  use  to  obtain  100  adequate forage of  resources  i s to occupy low  unhindered by a g g r e s s i v e  char  feeding the  food  may  trout.  improve when aggression  hypothesized mechanism of l e v e l gradients My  of  aggressive  reaction  char  on  The  of  distance  (3.0  Lake  trout  would presumably not  present,  char  (3.0  2  x 10  below  threshold  feeding  rate  dominant  of  model  of  a f f e c t e d by  more  behavioural  visual  15).  irradiance  Northcote  not  1985)  and  stimulus  for  Moreover, below t h i s  threshold,  feeding performance of char through as  visually  i f t r o u t were not  to  their  x 10 * photons/m /s), and 1  2  char  was  visual  below t h i s  (Henderson 1982).  inferior  to  that  of  t r o u t at a l l i r r a d i a n c e l e v e l s above the  irradiance threshold  foraging  feeding  2  items  (7.0  the  photons/m /s), t r o u t would  15  char c o u l d forage  prey  nearly  s t r i k e s (Figure  the  (Henderson and  the  very  adversely  see char, thereby removing the  restrict  detecting  aggressively  irradiance  irradiance level  photons/m /s),  l e v e l d e t e c t i n g prey using chemoreception The  on  and  Char which had  habitats  behaviour, and  irradiance  18  of  mercedis was  behaviour of t r o u t .  t r o u t would not aggressive  x 10  Neomysis  prey items v i s u a l l y  aggressive  c o n s i s t e n t with an  in an  with t r o u t made fewer feeding  However, in Loon threshold  char was  evidence that  behaviour of t r o u t .  interactions  visual  performance  t r o u t i s reduced.  i n t e r a c t i v e segregation  experiments provide  maximized that of t r o u t  detect  by  feeding  in Loon Lake.  maximized  rate  The  to  experiments in t h i s study were performed to t e s t whether  feeding performance of t r o u t and  that  irradiance habitats  of  trout.  Henderson and  As  Northcote  described (1985), the  in  the  greater  101  r e a c t i o n d i s t a n c e and swimming a c t i v i t y of t r o u t  ( F i g u r e s 14 and  18) allowed t r o u t to search a l a r g e r volume of water thereby  i n c r e a s i n g prey encounter  rate.  In my  than  char  experiment,  char  were subordinate at a l l i r r a d i a n c e l e v e l s and were r e s t r i c t e d to one end of the aquarium. predators,  and  were  They only  behaved  able  to  h e m i s p h e r i c a l volume of water, with radius.  The  feeding performance  dominated by t r o u t  (8.76  ± n=6)  solitary  ± 6.86  was  char  (48.14  ± 7.81,  n=2  feeding  attacks  on  in  Neomysis strikes  prey,  standard  of  the pairs  deviation)  (27.4  ± 20.1,  n=2),  char  respectively).  but  dominating n=4  and  The  7.72  feeding  reduced with d e c r e a s i n g by  trout  declined  I t should be  probably  i t was  expected  that  the  noted  increased  for trout.  proportion with  was  that the feeding performance  less frequent.  above the v i s u a l  irradiance  performance  t r o u t was  of  of  trout,  s u p e r i o r to that of char  the  of char  aggression  However, at a l l i r r a d i a n c e threshold  of  decreasing  P r i o r to performing  would improve with d e c r e a s i n g i r r a d i a n c e l e v e l while trout  as  a  l e s s than that of  that  ( F i g u r e 16).  and  irradiance level, especially  by  prey  s t r i k e s i n c l u d e d both s u c c e s s f u l and u n s u c c e s s f u l  unsuccessful  experiment,  ±  However, f e e d i n g s t r i k e s  more r a p i d l y than those of char that  from  both t r o u t and char was  irradiance l e v e l .  for  s t r i k e s per 30 minutes,  or i n t r a s p e c i f i c p a i r s  of  wait"  distance  significantly  s t r i k e s per 30 minutes,  performance  reaction  (mean  was  not s i g n i f i c a n t l y d i f f e r e n t  interspecific  search  " s i t and  of char i n i n t e r s p e c i f i c  9.47  s t r i k e s per 30 minutes,  like  the  levels feeding  ( F i g u r e 16).  T h i s i s probably because the dominance r e l a t i o n s h i p between  the  1 02  f i s h p e r s i s t e d to the v i s u a l reasons  i r r a d i a n c e t h r e s h o l d of t r o u t .  a l r e a d y g i v e n , i n Loon Lake, the dominance r e l a t i o n s h i p  would probably  break  down  in  low  t h e r e f o r e the f e e d i n g performance In  (Henderson  habitats,  of char might then  and  improve.  of  food  resources  and Northcote  1985).  in  low  irradiance  habitats  Henderson showed t h a t ,  although  maximum r e a c t i o n d i s t a n c e f o r v i s u a l prey d e t e c t i o n by char  at t h e i r v  irradiance  any case, char are c e r t a i n l y more capable than t r o u t of  procurement  the  For  saturation  i r r a d i a n c e l e v e l of 3.0 x 1 0  char use v i s u a l prey d e t e c t i o n down to t h e i r threshold  of  7.0  chemoreception detection  x  10  of prey.  down  to  14  photons/m /s,  1 6  photons/m /s, 2  visual  irradiance  below which they use  2  Trout a r e only able to use v i s u a l an  irradiance  level  of  3.0  prey  x  10  1 5  photons/m /s, which corresponds t o a depth of below 40 metres i n 2  Loon Lake on a sunny summer day. night,  approximately  5.5 h  per  not even s u r f a c e waters a r e i l l u m i n a t e d s u f f i c i e n t l y f o r  prey d e t e c t i o n by t r o u t Figure  For  5).  Therefore  (Henderson char  and  Northcote  1985,  their  a r e able to capture prey i n these  darker s p a t i o - t e m p o r a l h a b i t a t s i n the absence of t r o u t .  4.3 Concluding Statement Segregation of t r o u t and char i n selective  due  physiological acquisition. utilization habitats  to  behavioural  (Henderson However,  1982)  Loon  is  certainly  (Schutz and Northcote  1972) and  differences  competition  plays  of sympatric t r o u t and char.  whether  allopatric  Lake  that a  Trout  role  affect  prey  in habitat  occupy  or i n sympatry with char.  surface On the  1 03  other hand, char undergo a h a b i t a t s h i f t allopatry.  In  allopatry,  s e a s o n a l l y , in accordance char  shift  to deeper,  char  occupy  that  shift  different  not  by  trout  and  by char, although t h i s r e s u l t  habitat u t i l i z a t i o n . the  field  Difficulties  r e s u l t s a r i s e due  in such whole lake experiments. d i f f e r e n c e s in l i t t o r a l habitat u t i l i z a t i o n Other  the  have  1978)  laboratory  between  dominant  irradiance level.  that  distributions  1972)  studies.  and  habitats.  Char  do  on  stream  I t i s concluded  behavioural char  interactions decrease  I f t h i s holds t r u e i n lake environments, trout switch  sympatry with t r o u t , but whether t h e i r Lake  controls  to q u a n t i f y .  subordinate  seek refuge from a g g r e s s i o n by  irradiance  explain  strong conclusions  prey  Northcote  aquarium  and  partly  that t r o u t are very a g g r e s s i v e  and  experiments trout  based  In p a r t i c u l a r , the i n f l u e n c e of  shown  laboratory  is  accompanying  to the l a c k of r i g i d  by f i s h are d i f f i c u l t  studies  from my  may  It  i s i n t e r p r e t e d with  i n drawing  development and  towards char i n lake (Schutz (Rosenau  Temporal  pronounced.  c a u t i o n s i n c e d i f f e r e n c e s i n prey d i s t r i b u t i o n s  from  sympatry,  t r o u t are c o m p e t i t i v e l y s u p e r i o r to char, shift  and  habitats  less well-illuminated habitats.  on the lack of h a b i t a t habitat  sympatry  with food abundance, but i n  segregation between t r o u t and char was concluded  between  by to  shifting such  habitat  with char  to  low  habitats  shift  in  in  Loon  i s a r e s u l t of i n t e r f e r e n c e mechanisms i s not c l e a r .  This  r e l a t i o n s h i p might be confirmed i n an a p p r o p r i a t e study, based f i e l d observations. improves  with  Although the f e e d i n g  decreasing  performance  of  on  char  i n t e n s i t y of a g g r e s s i o n by t r o u t ,  my  104  l a b o r a t o r y experiment d i d not show  that  l e v e l per se produced the same e f f e c t . in  my  decreasing  irradiance  T h i s i s probably  because  experiment, the dominance r e l a t i o n s h i p between t r o u t  char p e r s i s t e d  in  conditions  of  low  irradiance  due  to  and the  continued confinement of f i s h p a i r s i n a q u a r i a . This  study c o r r o b o r a t e s the s c e n a r i o proposed by Henderson  (1982) that when t r o u t and char through  invade a  fishless  lake,  t h e i r a g g r e s s i v e h i g h l y c o m p e t i t i v e behaviour,  to occupy t h e i r restrict by char  i n sympatry with t r o u t may  food,  competition,  and  habitat  be  predators  are  important  populations  need  and although  the segregation of t r o u t and char  selective,  each  "optimal" f o r char,  the  not  for  species.  segregation  hypothesis and  i r r a d i a n c e l e v e l g r a d i e n t s cannot be r e j e c t e d .  variables  an  of  interactive,  i n Loon  involving  interference  since  Segregation  be e x c l u s i v e l y s e l e c t i v e or  an  and  However, the h a b i t a t occupied  determining  mechanism of  are able  " o p t i m a l " h a b i t a t based on food p r e f e r e n c e s  char to other p o r t i o n s .  certainly  trout  Lake  is  interactive  competition  along  105  5.0 REFERENCES  Alcock, J . 1975. 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