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UBC Theses and Dissertations

Character displacement and variability in lacustrine sympatric and allopatric Dolly Varden (Salvelinus… Armitage, Godfrey Norman 1973

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CHARACTER DISPLACEMENT AND VARIABILITY IN LACUSTRINE SYMPATRIC AND ALLOPATRIC DOLLY VARDEN (Salvelinus malraa) POPULATIONS by GODFREY NORMAN ARMITAGE B.A., Oxon., 1970 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Zoology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1973 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of ZOOLOGY  The University of British Columbia Vancouver 8, Canada i i ABSTRACT The object of t h i s study was to investigate character displacement (Brown and Wilson, 1956) and reduction of phenotypic v a r i a b i l i t y with reduction i n niche width (Van Valen, 1965)• D o l l y Varden from one sympatric (Loon Lake) and two a l l o p a t r i c (Dickson and Foley Lake) populations were compared. F i e l d studies showed that the niche width of sympatric D o l l y Varden was l e s s than that of a l l o p a t r i c D o l l y Varden owing to food and s p a t i a l segregation, confirming r e s u l t s of an e a r l i e r study (Andrusak and Northcote, 1971). Character displacement was evident i n p y l o r i c caeca numbers and i n cert a i n behavioural responses ( s p a t i a l d i s t r i b u t i o n and feeding) observed i n the laboratory. These were accompanied by reduced v a r i a b i l i t y , also apparent i n length d i s t r i b u t i o n s within year classes, i n the sympatric population compared with an a l l o p a t r i c population (Dickson Lake). However, character displacement and reduced v a r i a b i l i t y could not be demonstrated f o r most morphometric characters, presumably because of the complexity of growth processes involved. E f f e c t s of overlapping adjacent year classes and of continuous growth of f i s h body parts ( i n contrast to comparable studies with birds) obscured in t e r p r e t a t i o n of such c h a r a c t e r i s t i c s . i i i TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS i i i LIST OF TABLES v LIST OF FIGURES v i LIST OF APPENDIX TABLES i x ACKNOWLEDGEMENTS x i I. INTRODUCTION 1 I I . DESCRIPTION OF THE STUDY AREAS 3 1. Loon Lake 3 2. Dickson Lake 3 3. Foley Lake 6 I I I . MATERIALS AND METHODS 8 A. F i e l d Study 8 1. Temperature • 8 2. Bottom fauna 9 3. Zooplankton. 9 4. Use of g i l l nets 10 5. Echo sounder records. 12 6. Fish c o l l e c t i o n s 12 7. Morphometries and meristics 13 8. Age analysis of f i s h 13 9. Stomach analysis 14 B. Laboratory Study 15 1. Methods of capture 15 2. Holding f a c i l i t i e s 16 3. Observation f a c i l i t i e s 17 4. Stomach pump 17 5. Experimental procedures 18 C. S t a t i s t i c a l Analysis. 20 1. M e r i s t i c s . 20 2. Morphometries and length-weight rela t i o n s h i p s 20 3. Canonical c o r r e l a t i o n 20 4. Comparison of means using a modified ' t ' test to correct f o r unequal sample variances 21 i v Page IV. RESULTS 22 A. F i e l d Study 22 1 . Temperature 2 2 2 . Bottom fauna 2 4 3 . Zooplankton 27 4 . Fish d i s t r i b u t i o n 30 i . Loon Lake 30 i i . Dickson Lake 3 4 i i i . Foley Lake.. 40 5 . Food 4 3 i . Seasonal changes 4 3 i i . Number of food categories taken per f i s h . 50 i i i . Factors a f f e c t i n g food taken 50 6. Length frequency and age categories.... 5 4 7 . M e r i s t i c counts... 59 8 . Morphometric comparison of the three Dolly Varden populations 65 9 . Length-weight relationships 72 1 0 . Morphometric differences between cutthroat trout and Do l l y Varden 7 3 B. Laboratory Observations. 7 5 1 . S p a t i a l d i s t r i b u t i o n 7 5 2 . Presentation of novel prey 7 8 i . Earthworms. 7 8 i i . Chironomid larvae 7 9 3 . E f f i c i e n c y of feeding on planktonic Chaoborus larvae by sympatric and a l l o p a t r i c D olly Varden 8 0 V. DISCUSSION 8 3 VI. CONCLUSIONS 9 9 BIBLIOGRAPHY 1 0 2 APPENDIX 1 0 7 V LIST OF TABLES TABLE Page I Morphometric and discharge c h a r a c t e r i s t i c s of the study lakes... 8 II Sizes of D o l l y Varden held, December 1 9 7 1 . . 1 5 I I I Size frequency of bottom organisms from Foley and Dickson Lake f a l l samples, separated by eye 27 IV Numbers of D o l l y Varden and cutthroat trout captured i n duplicate 1 . 4 m deep g i l l nets fished on the bottom at 1 0 m i n Loon Lake i n 1 9 7 2 32 V Numbers of D o l l y Varden and cutthroat trout captured i n summer nettin g series i n Loon Lake during 1 9 7 0 lnd 1 9 7 1 32 VI Numbers of D o l l y Varden i n inshore and offshore g i l l nets i n the upper 5 m of Dickson Lake i n 1 9 7 2 4 0 VII Seasonal differences i n v e r t i c a l d i s t r i b u t i o n of Dolly Varden i n surface-bottom g i l l nets set at 5 and 1 0 m i n Foley Lake 4 3 VIII Relationship of numbers of p y l o r i c caeca and g i l l rakers to diet 5 4 IX Means and variances of meristic counts f o r D o l l y Varden from Loon, Dickson and Foley Lakes 6 2 X Summary of morphometric comparisons of the three Dolly Varden populations 7 1 XI Results of s p a t i a l d i s t r i b u t i o n and a c t i v i t y comparisons... 7 6 XII Comparison of numbers of a l l o p a t r i c and sympatric D o l l y Varden eating chironomid larvae during t h e i r f i r s t 1 0 minute exposure to 2 0 larvae scattered on a sand and leaf l i t t e r substrate 8 0 v i LIST OF FIGURES FIGURE Page 1 Morphometry of Loon Lake 4 2 Morphometry of Dickson Lake (adapted from Andrusak, MS 1968) 5 3 Morphometry of Foley Lake 7 4 Temperature p r o f i l e s of the three study lakes 23 5 Depth d i s t r i b u t i o n of major benthic organisms i n the three study lakes during summer 1972. 26 6 Zooplankton abundance i n Loon, Dickson and Foley Lakes 28 7 Seasonal changes i n average percent composition of zooplankton samples i n the three study lakes during 1972 29 8 V e r t i c a l d i s t r i b u t i o n of sympatric Loon Lake Dolly Varden and cutthroat trout i n nets set from surface to bottom at 5t 10 and 20 m, day and night, i n 1972 31 9 V e r t i c a l d i s t r i b u t i o n of sympatric Loon Lake Dolly Varden and cutthroat trout i n nets set from surface to bottom at 5 and 10 m, day and night, i n f a l l 1970 33 10 V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c Dickson Lake D o l l y Varden i n nets set from surface to bottom at 51 10 and 20 m, day and night, i n summer 1971 and 1972 35 11 Echo sounding traces made on a standard transect i n Dickson Lake over a 24 hour period i n August 1971, showing onshore movements of a l l o p a t r i c D o l l y Varden at night 36 12 Echo soundings made on a standard transect i n Dickson Lake over a 24 hour period i n Jul y 1972 37 v i i FIGURE Page 13 V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c Dolly Varden i n nets set i n Dickson Lake by Andrusak i n I967 (Andrusak, MS 1968) 39 14 V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c Foley Lake Dolly Varden i n nets set from surface to bottom at 5, 10 and 20 m during 1 9 7 2 . . . . 41 15 Echo sounding records showing evidence of a l l o p a t r i c D o l l y Varden throughout the water column i n Foley Lake i n 1972......... 42 16 Stomach contents (average percent volume) of adult sympatric D o l l y Varden and cutthroat trout i n Loon Lake i n 1970 (October) and 1972 45 17 Percent occurrence of copepods and cladocerans i n stomach contents of planktivorous Dolly Varden and cutthroat trout from a l l regions sampled i n Loon Lake 46 18 Stomach contents (average percent volume) of adult sympatric (Loon Lake) and a l l o p a t r i c (Dickson and Foley Lakes) Dolly Varden 48 19 Mean number of major food categories taken per i n d i v i d u a l Dolly Varden 51 20 Size related differences i n stomach contents (average percent volume) of sympatric Loon Lake and a l l o p a t r i c Dickson Lake Dolly Varden i n 1972 53 21 Seasonal changes i n length frequency d i s t r i b u t i o n of Dolly Varden and cutthroat i n Loon Lake during 1972 56 22 Length frequency histograms f o r Dolly Varden captured i n Foley and Dickson Lakes i n 1972 57 23 Fork length d i s t r i b u t i o n of J u l y samples of Dolly Varden from Loon and Dickson Lakes. 58 24 Relationship of p y l o r i c caeca numbers to fork length 60 v i i i FIGURE Page 25 Relationship of g i l l raker numbers to fork length 6 1 26 D i s t r i b u t i o n of p y l o r i c caeca numbers i n Dolly Varden from Loon, Dickson and Foley Lakes.... 63 27 D i s t r i b u t i o n of g i l l raker numbers on the anteriormost right hand g i l l arch i n D o l l y Varden from Loon, Dickson and Foley Lakes.. 6 4 2 8 Relationship of head length to standard length f o r the three Dolly Varden populations... 6 6 29 Relationship of upper jaw length, distance from snout to back of eye, and eye length to standard length f o r the three Dolly Varden populations. 67 30 Relationship of least fleshy i n t e r o r b i t a l width, length of longest g i l l raker, and weight to standard length f o r the three D o l l y Varden populations 6 8 3 1 Relationship of upper jaw length to standard length f o r Dolly Varden smaller than and larger than 14-0 mm (approximately 1 5 5 mm fork length) f o r the three populations • 70 32 Relationship of upper jaw length, eye length, and weight to standard length f o r Loon Lake D o l l y Varden and cutthroat taken i n May 1 9 7 2 7 4 3 3 Correlation of time spent i n upper h a l f of observation tank with a c t i v i t y 7 7 3 4 E f f i c i e n c y of capture of Chaoborus larvae by sympatric and a l l o p a t r i c D olly Varden... 8 1 35 E f f i c i e n c y of capture (catch/grab) of Chaoborus larvae by sympatric and a l l o p a t r i c Dolly Varden i n successive t r i a l s 8 2 ix LIST OF APPENDIX TABLES APPENDIX TABLE Page I Seasonal changes of stomach contents (average percent volume) of Loon Lake Dol l y Varden and cutthroat i n 1 9 7 2 . . . . . . 107 II Seasonal changes of stomach contents (average percent volume) of a l l o p a t r i c D o lly Varden from Dickson and Foley Lakes 108 III Average number of major food categories taken per i n d i v i d u a l Dolly Varden 109 IV Size related differences of stomach contents (average percent volume) of Loon and Dickson Lake Dolly Varden i n 1972 110 V Relationship of head length to standard length I l l VI Relationship of upper jaw length to standard length 112 VII Relationship of snout-to-back-of-eye length to standard length..... 113 VIII Relationship of eye length to standard length 113 IX Relationship of maximum g i l l raker length to standard length, 114 X Relationship of predorsal length to standard length 114 XI Relationship of i n t e r o r b i t a l width to standard length 115 XII Relationship of the distance from the anal f i n base to the pectoral f i n base to standard length 115 XIII Size related differences i n the r e l a t i o n s h i p of upper jaw length to standard length f o r the three Dolly Varden populations 116 X APPENDIX TABLE Page XIV Relationship of weight to standard length 117 XV Relationship of upper jaw length, eye length and weight to standard length fo r cutthroat and D o l l y Varden using log-transformed spring 1972 data from Loon Lake 118 XVI Times to f i r s t bottom grab (seconds) during 10 minute exposure period to red chironomid larvae on sand and l e a f l i t t e r substrate 119 x i ACKNOWLEDGEMENTS Fina n c i a l support f o r t h i s study came from a National Research Council grant to my supervisor, while I was supported on a Canadian Commonwealth Scholarship. I am most g r a t e f u l to my supervisor. Dr. T.G. Northcote, f o r h i s encouragement and guidance during t h i s study. Drs. N.J. Wilimovsky, J.D. McPhail and R.'Liley read the manuscript and offered useful suggestions. I thank Mr. Harvey Andrusak f o r the loan of o r i g i n a l data from Dickson and Marion Lakes. I am g r a t e f u l to Mr. J . Walters and members of the U.B.C. Research Forest s t a f f f o r access to and accomodation at Loon Lake; also Canadian Forest Products Ltd. f o r arranging access to Dickson Lake, and to the B.C. Fish and W i l d l i f e Branch f o r the loan of much f i e l d equipment. I am p a r t i c u l a r l y g r a t e f u l to the many individ u a l s who gave me assistance i n the f i e l d ; Mr. Kim Waterman and Miss Regina Clarotto also assisted with analysis of benthos and plankton samples. My thanks go to Mr. B i l l Dunford f o r help with analysis of stomach contents, to Mrs. Dolores Lauriente f o r the computer data analysis, to Mrs. Gayle Burnison f o r assistance with figures and to Miss A l i c e Fedorenko f o r t r a n s l a t i o n of Russian papers. F i n a l l y I wish to thank my wife Frances f o r her continual encouragement, patience and assistance throughout the study and fo r typing the manuscript. 1 INTRODUCTION Coexisting populations of trout and char d i f f e r considerably i n t h e i r s p a t i a l d i s t r i b u t i o n and diets, both from one another and from populations of the same species l i v i n g s i n g l y i n a l l o p a t r y . This has been shown fo r brown trout (Salmo trutta) and A r c t i c char (Salvelinus alpinus) by Nilsson (summarized i n Nilsson, 1967) and f o r cutthroat (Salmo c l a r k i c l a r k i ) and D o l l y Varden (Salvelinus malma) by Andrusak and Northcote (1971). Schutz and Northcote (1972) showed i n laboratory experiments that D o l l y Varden from a population coexisting with cutthroat i n Marion Lake, near Squamish, B.C., were more substrate oriented and more e f f i c i e n t substrate feeders than troutj the trout, i n contrast, hovered i n midwater and were more e f f i c i e n t surface feeders. E c o l o g i c a l character displacement (Brown and Wilson, 1956; Kohn and Orians, 1962) or ec o l o g i c a l segregation c e r t a i n l y appears to occur when the two species are l i v i n g i n sympatry. Nilsson ( I 9 6 7 ) , using Brian's (1956) terminology, describes the segregation between trout and char as •interactive* as opposed to ' s e l e c t i v e * . Differences between the two species, when cohabiting, are magnified by in t e r a c t i o n , e i t h e r through dir e c t interference between indi v i d u a l s or by one species e x p l o i t i n g prey with greater e f f i c i e n c y . Selective segregation, i n contrast, refers to situations where species are segregated either because of 2 differences evolved i n c i d e n t a l l y i n a l l o p a t r y or through reinforcement of e x i s t i n g differences i n sympatry, involving a period of i n t e r a c t i v e segregation u n t i l preferences for the reduced ec o l o g i c a l niches (Hutchinson, 1 9 5 7 ) are s t a b i l i z e d i n t h e i r respective genotypes. Schutz and Northcote ( 1 9 7 2 ) , although acknowledging that ' i t i s d i f f i c u l t to decide at what point i n t e r a c t i v e segregation becomes selec t i v e segregation i f continuous evolutionary d i f f e r e n t i a t i o n i s involved', state that i n t e r a c t i o n between the two species i s probably a minor factor and that innate morphological and behavioural differences seem l a r g e l y responsible f o r t h e i r segregation when cohabiting i n small coastal lakes. The aim of t h i s study i s to examine i n more d e t a i l the ec o l o g i c a l segregation of D o l l y Varden coexisting with cutthroat trout, and to determine whether morphological or behavioural character displacement occurs, i n order to reveal, i f possible, mechanisms of segregation. Morphological character displacement may indicate whether sel e c t i o n f o r greater s p e c i a l i z a t i o n has occurred. In addition, phenotypic v a r i a b i l i t y may be decreased by reduction i n 'niche width' (Van Valen, 1 9 & 5 ) due to the presence of the second species or to the absence of major prey types. This p o s s i b i l i t y i s considered i n terms of morphological and behavioural characters. Populations from three lakes were chosen f o r the study; Loon and Dickson Lakes are si m i l a r l i m n o l o g i c a l l y and contain sympatric and a l l o p a t r i c populations of Dolly Varden respectively. Foley Lake, quite d i s t i n c t l i m n o l o g i c a l l y from the other two lakes, contains an a l l o p a t r i c population of Do l l y Varden. I I . DESCRIPTION OF THE STUDY AREAS 1. Loon Lake Loon Lake (49° 18' 20" N, 122° 35 ' 45" W) i s located i n the U.B.C. Research Forest, approximately 47 kilometres east of Vancouver at an a l t i t u d e of 343 metres. The lake consists of two basins - a steepsided main basin with a maximum depth of 62 metres and a smaller outlet basin with a maximum depth of 15 metres (Fig. 1 ) . The two basins are connected by a shallow arm, the most extensive l i t t o r a l area i n the lake. Bottom sediments consist mainly of soft mud. The lake contains D o l l y Varden and a large population of cutthroat trout but no other species of f i s h . 2 . Dickson Lake Dickson Lake (49° 19' 0" N, 122° 5 ' 30" W) i s located 84 kilometres east of Vancouver at an a l t i t u d e of 671 metres (Fig. 2 ) . I t i s deep, with a maximum depth of 76 metres, and steepsided, except near the outlet and i n the south-east bay which was used as the study area. Much of the east side of the watershed was logged 4 FIGURE 1. Morphometry of Loon Lake. X and Y indicate 1971 and 1972 limnological stations respectively; ——-• arid • • indicate surface-bottom and bottom fished nets respectively, i n 1971 (open) and 1972 ( s o l i d ) . Depth contours i n metres. FIGURE 2. Morphometry of Dickson Lake (adapted from Andrusak, MS 1968). Map shows limnological s t a t i o n (X), netting s i t e s i n 1971 (o d) and 1972 (• • ) and echo sounding transects i n 1971 ( ) and 1972 (——— ) , Depth contours i n metres. 6 i n I 9 6 3 . Gravel deltas and sand beaches have formed near the mouths of creeks owing to the f r i a b l e nature of the surrounding granite. Sediments i n the l i t t o r a l area consist of mud and sand or l e a f l i t t e r . Further offshore, they consist of mud mixed with flakes of clay. The lake has a large population of D o l l y Varden, the only species of f i s h present. A study of these was made i n 1967 (Andrusak and Northcote, 1971). 3 . Foley Lake Foley Lake (49° 7' 30" N, 1 2 1 ° 24' 45" W) i s located 120 kilometres E-S-E of Vancouver at an a l t i t u d e of 550 metres ( F i g . 3 ) . I t was apparently formed about a century ago by a rockslide which dammed Foley Creek, a major t r i b u t a r y of the Ghilliwack River. Large stands of trees, mainly Western Red Cedar, remain i n the eastern h a l f of the lake, flooded to a depth of 20 metres; most have been trimmed to lake l e v e l by logging operators. The major inflow i s Foley Creek which enters the lake at the east end; a secondary inflow enters on the north side. The drainage area of the lake i s r e l a t i v e l y large which, together with i t s small surface area, contributes to i t s short retention time (Table I) and to i t s r a p i d l y f l u c t u a t i n g t u r b i d i t y and l e v e l during the spring runoff. The eastern h a l f of the lake i s steepsided, f a l l i n g r a p i d l y to 20 metres. The western h a l f of the lake i s shallower with more extensive l i t t o r a l areas; t h i s was 7 FIGURE 3. Morphometry of Foley Lake. Map shows limnological station (X), netting s i t e s (• • ) and spring ( ) and summer/fall ( —) echo sounding transects. Depth contours i n metres. 8 used as the study area. Bottom sediments here consisted of soft mud. Water leaves the lake through some wide, shallow pools and then plunges over rockslide debris f o r several hundred metres before returning to the o r i g i n a l stream gradient. This constitutes an e f f e c t i v e b a r r i e r to upstream migration; rainbow trout (Salmo gairdneri) occur below the rapids but not above (Hartman and G i l l , 1968). There i s a small population of Do l l y Varden, the only f i s h species present, i n the lake. TABLE I Lake LOON DICKSON FOLEY Morphometric and discharge c h a r a c t e r i s t i c s of the study lakes. 2 3 Area (m ) Volume (nr) 4.5 x 10 5 10.8 x 10 6 9.7 x 10 5 38 x 10 6 1.1 x 10- 1.4 x 10* Approximate Estimated drainage retention area (km ) time* 4.5 9 45 1 year 6 months 3 days *based on very approximate estimates of average annual discharge I I I . MATERIALS AND METHODS A. F i e l d Study 1. Temperature Temperature was recorded with a Lakes Instrument Co. combined oxygen-temperature probe Mark 2. Readings 9 were taken every metre down to 10 metres and usually at greater i n t e r v a l s thereafter at limnological stations shown on Figures 1, 2 and 3 . 2 . Bottom fauna Benthos samples were col l e c t e d with an Ekman p dredge (225 cm ) near each of the main netting s i t e s . Spring and summer samples were s t i r r e d thoroughly; a 1200 ml subsample of the approximately 3800 ml collected was sieved through a screened-bottom bucket ( 0 . 8 5 mm square mesh opening). F a l l samples were sieved i n e n t i r e t y . Material remaining i n the sieve was preserved with 10$ formalin and was sorted l a t e r using a binocular microscope (20-30x magnification). The macrobenthos was i d e n t i f i e d , grouped into f i v e major categories, and expressed as 2 numbers per 100 cm . 3 . Zooplankton Plankton samples were taken i n the spring, summer and e a r l y f a l l at Loon and Foley Lakes and i n the summer only at Dickson Lake i n 1972. Collections were made using a Wisconsin net with 25 cm i n t e r n a l diameter and 100 micron mesh s i z e . V e r t i c a l hauls from 5 m to the surface, from 15 to 10 and from 10 to 5 m were made close to the 20 m netting s i t e s . V e r t i c a l hauls were also made from 5 m to the surface close to the 5 m netting s i t e s , i n water about 6 m deep. Samples were co l l e c t e d at midday and midnight. 10 Samples were preserved i n the f i e l d with 5% formalin. Zooplankton were i d e n t i f i e d into major categories using a binocular microscope (20 x 30x magnification). Numbers i n each category i n the Loon Lake f a l l samples were estimated by d i v i d i n g the sample into s i x equal subsamples by volume, analysing one subsample, and returning i t to the o r i g i n a l sample which was then s t i r r e d and subsampled again; the mean of the two subsamples was taken f o r each of the categories. Numbers i n each category fo r a l l other samples were counted d i r e c t l y . Average numbers of major categories were calculated f o r day and night samples at each depth range. Sample sizes were small, so no s i g n i f i c a n t differences could be established between day and night samples or between inshore and offshore samples. The average of day and night samples was calculated f o r each depth range; r e s u l t s f o r the uppermost 5 m are given as the average of inshore and offshore r e s u l t s . 4 . Use of g i l l nets F l o a t i n g monofilament g i l l nets, 5 or 10 m deep, were marked h o r i z o n t a l l y every metre to determine capture depth of each f i s h . Each net was composed of three 5 m sections with stretched mesh sizes of 2 5 . 4 , 38.1 and 50.8 mm. One of the 10 m f l o a t i n g nets was converted for use as a sinking net by the addition of an extra lead l i n e during the spring and summer series at Loon Lake. 11 Sinking nets were 1.4 m deep, 35 m long, and composed of f i v e 7 m sections of stretched mesh sizes 2 5 . 4 , 3 8 . 1 , 6 3 . 5 . 79.8 and 95.2 mm. Float i n g nets, 3 and 6 m deep (smallest stretched mesh size 38.1 mm) and sinking nets, 5 m deep (stretched mesh size 38.1 mm) and 2 m deep (stretched mesh sizes 2 5 . 4 , 3 8 . 1 , 5 0 . 8 and 63.5 mm) were used i n Loon Lake i n July 1970 only. During the f a l l of 1970, two netting series were made i n Loon Lake using r e p l i c a t e f l o a t i n g nets set p a r a l l e l to shore and sinking nets set perpendicular to shore. Nets were set from midday to dusk i n both series and, i n one, f o r a further f i v e hours s t a r t i n g from dusk. During the summer of 1971. three netting series were made i n Loon Lake and one i n Dickson Lake? single nets were u s u a l l y fished f o r three hour periods and, when pulled, were immediately replaced with i d e n t i c a l nets. Nets were set perpendicular to the shore (Figs. 1 and 2 ) . During 1972, nets were set p a r a l l e l to the shore to f i s h the whole water column at 5 m and at 10 m i n each lake; 1.4 m nets were sunk to f i s h the bottom at 10 m i n Loon Lake and, i n the spring and summer, i n Foley Lake (Figs. 1, 2 and 3 ) . At 20 m, 1.4 m sinking nets were fished at the bottom and 5 m f l o a t i n g nets were fished at the surface except i n the spring and summer Loon Lake series when a sinking 10 m and a f l o a t i n g 10 m net were fished 12 close together to sample the whole water columnj no nets were fished at 20 m i n Foley Lake during the f a l l of 1972. Day and night nets were usually set fo r about ten hours each. 5. Echo sounder records A Furuno Model FM-22D echo sounder with a 50 kHz transducer was used to obtain bottom p r o f i l e s f o r depth contour maps of Loon and Foley Lakes and to provide addi t i o n a l information on f i s h d i s t r i b u t i o n . The zero band on the sounder obscured the upper one to three metres. A l l traces were made i n a boat moving at approximately 2 km/hour. 6. Fish c o l l e c t i o n s A l l nets were picked immediately a f t e r they were pulled, with the exception of the September 1970 night s e r i e s . A number-coded waterproof tag was slipped into the mouth of each f i s h , following i t s removal from the net, and the code number and depth of capture of each f i s h were recorded together with pertinent net set data. A l l D o l l y Varden were fix e d i n 10% formalin, as were a l l trout from Loon Lake p r i o r to the 1972 summer se r i e s . During the summer and f a l l series i n Loon Lake, a l l trout from bottom-fished nets were immediately fi x e d . A l l trout from surface-to-bottom nets were measured (fork length) to the nearest millimetre? those captured i n the same depth i n t e r v a l as char, and subsamples from other depths, were then fi x e d to provide shrinkage and stomach content data. 13 Following several weeks i n formalin, the f i s h were rinsed and transferred to 40$ isopropanol f o r storage,- preservation schedules were kept as s i m i l a r as possible f o r a l l specimens. ?. Morphometries and meristics A l l counts and measurements follow Hubbs and Lagler (1958) except snout-to-eye; t h i s was measured from the t i p of the snout to the hindmost border of the o r b i t . A l l measurements were made on the l e f t side of the specimen with d i a l c a l i p e r s reading to 0.1 mm, except f o r g i l l raker counts and measurements which were made on the f i r s t r i g h t -hand g i l l arch; t h i s was dissected out of the specimen and examined under a stereo-binocular microscope (12x magnification) using a seeker, where necessary, to detect rudimentary g i l l rakers. Measurements from males and females were not treated separately. 8. Age analysis of f i s h Length frequency d i s t r i b u t i o n s were analysed using fork length data from separate netting s e r i e s . Data were plotted on p r o b a b i l i t y paper (Cassie, 1954). Males and females were not distinguished. Scales taken from the ri g h t side behind the dorsal f i n were examined under a stereo-binocular microscope at 80x magnification. Interpretation was very d i f f i c u l t as the scales were so small. O t o l i t h s were taken from a number of f i s h f o r comparison. 14 9. Stomach analysis Contents of the digestive t r a c t from the oesophagus to the p y l o r i c sphincter were taken f o r food analysis. The material from i n d i v i d u a l stomachs was either preserved i n k0% isopropanol and f i l t e r e d with a 100 micron mesh p r i o r to examination, or removed d i r e c t l y from the stomach p r i o r to examination. The damp material was sorted under 20x magnification into the same major food categories as used by Andrusak (MS 1968), except that gastropods and Simulium larvae were included with the more motile benthic forms such as amphipods and nymphs, and Chaoborus larvae were placed i n the ' s t a t i c benthos' category with chironomid larvae and Pisidium. I f a sizeable amount of a given category was present, i t was transferred to a graduated centrifuge tube and i t s volume measured to the nearest 0 . 0 5 ml by volume displacement, adding a known volume of water from a graduated pipette. The volume of small amounts of material was measured using a method based on that of Hellawell and Abel (1971). Two microscope s l i d e s were glued onto the sides of a glass plate, 80 x 100 mm, to form a c e l l approximately 1 mm deep. Stomach material of a given category was placed, s l i g h t l y moist, on the plate and covered with an i d e n t i c a l upper plate, squashing out the material. The number of squares of mm graph paper covered by the area of the squash was counted and recorded. 1 5 The c e l l was cali b r a t e d by p i p e t t i n g known volumes of water onto i t , covering i t with the second plate and counting the number of squares covered by the water. From the r e s u l t i n g c a l i b r a t i o n curve, volumes as small as 0.001 ml could be estimated. counted under 12-20x magnification. Items that were too thoroughly digested to be i d e n t i f i e d were ignored. Results are presented as the average of volume percentages (Andrusak, MS 1968). B. Laboratory Study 1. Methods of capture D o l l y Varden from Dickson Lake were captured i n August and October 1971, by angling with a surface-fished l u r e . Those from Loon Lake were captured i n August and September 1971 with sinking nets fished at 10-12 m. F i s h were removed as quickly as possible from the net and placed i n cold oxygenated water. Table II shows the average sizes of the f i s h held. TABLE I I . Sizes of D o l l y Varden held, December 1971. Numbers of prey items i n each food category were Lake Fork length, mm Mean Range Number held LOON 197 170-230 9 DICKSON 1 9 8 1 7 5 - 2 6 5 1 8 16 2. Holding f a c i l i t i e s Dickson and Loon Lake f i s h were always kept separate. I n i t i a l l y , they were held i n outdoor wooden flume tanks, through which a slow flow of water was maintained. A l l Loon and some Dickson Lake f i s h were l a t e r transferred to laboratory f i b r e g l a s s holding tanks; the average number to a tank was three, the maximum s i x . Holding tanks were 110 cm long and 60 cm wide, with a central standpipe 35-40 cm high. Lighting was completely a r t i f i c i a l , being provided by 60 watt incandescent bulbs controlled by an Intermatic T101 time switch at approximately natural photoperiod; daylength was adjusted every two weeks. A l l tanks were covered with wire mesh screens over which was stretched black polyethylene sheeting with openings 50 x 50 cm by the l i g h t s , which were between 50 and 100 cm from the water surface. C i t y water was fed into each tank at 1 to 3 l i t r e s per minute; i t s temperature ranged from 6°C i n winter to 12°C i n summer. Water pipes passed through a large thermostatically controlled water bath to minimise temperature f l u c t u a t i o n . Aeration was provided i n every tank using Metaframe Bubble-up corner f i l t e r s . A l l f i s h were conditioned to feed on small pieces of chicken l i v e r , which floated on the surface. They were occasionally fed l i v e plankton. 17 3 . Observation f a c i l i t i e s Two observation tanks of grey painted plywood with p l e x i g l a s s fronts, each 1 2 2 x 6 1 x 6 1 cm, also used by Schutz (MS I 9 6 9 ) , were set side by side 1 . 3 m from a wall of the laboratory, behind which was an observation chamber. This section of the laboratory was t o t a l l y screened o f f with black polyethylene sheeting to minimise disturbance. Water was run through the tanks at approximately § litre/minute and the tanks were aerated p r i o r to introduction of a f i s h . Lighting was provided by two 60 watt incandescent l i g h t bulbs 2 0 cm above the water and 2 2 cm from the ends of the tank? t h i s gave uniform l i g h t i n g 1 1 cm above the bottom of the tank, as measured by a GM submersible photometer. The substrate was grey painted wood fo r the s p a t i a l t e s t s and the earthworm feeding t e s t s . Chironomid and Chaoborus feeding t e s t s were conducted with a substrate composed of sand, gravel and debris sieved from lake mud. 4. Stomach pump This was used only f o r the Chaoborus feeding experiments. I t s basic design followed that of Seaburg ( 1 9 5 7 ) • The sampler used had a 0 . 8 mm i n t e r n a l diameter p l a s t i c i n l e t tube and a 6 . 3 5 mm i . d . p l a s t i c outlet tube. Rather than stomach pump f i s h to standardize hunger p r i o r to experimentation, as done by Schutz (MS 1 9 6 9 ) , 18 f i s h were tested at least three days a f t e r feeding. Fish were usually fed to s a t i a t i o n every three to four days. 5. Experimental procedures For the s p a t i a l t e s t s , a horizontal l i n e on the pl e x i g l a s s front divided the tank into equal upper and lower halves and a v e r t i c a l l i n e s i m i l a r l y divided the tank into two halves, r i g h t and l e f t . T r i a l s were run during the winter of 1971» usually i n the mornings p r i o r to feeding. Fish were tested s i n g l y and once only; an i n d i v i d u a l was transferred from a holding tank to one of the observation tanks, and observations were started a f t e r t h i r t y minutes when the f i s h began to show exploratory c r u i s i n g behaviour. During the t h i r t y minute t r i a l the time of each t r i p into the upper h a l f was recorded cumulatively on a stopwatch. Each complete journey from one end of the tank to the other was recorded as one a c t i v i t y unit, using a mechanical counter? a s o r t i e into the other h a l f of the tank of no more than one body length from the middle of the tank, followed by a return, was also recorded as a single a c t i v i t y u n i t . Chaoborus feeding experiments were conducted during the summer of 1972 with water temperatures between 13 and 16°C i n the observation tank. Two hundred 4th i n s t a r Chaoborus t r i v i t t a t u s larvae were introduced to the tank and the water flow was cut o f f during the test to minimise loss of larvae through the outflow pipe. 19 Fish were introduced i n d i v i d u a l l y to the tank. The time that elapsed before the f i r s t grab at prey and the t o t a l number of grabs during the following 10 minutes were recorded. Following the tes t , the f i s h were anaesthetized i n d i l u t e MS-222 u n t i l they were limp and then t h e i r stomachs were flushed with three aspirator b u l b s - f u l l of water ( t o t a l 75 ml) using the stomach pump. Nearly a l l the Chaoborus larvae were washed out i n the f i r s t 25 ml and none were i n the l a s t ; i t was therefore assumed that recovery was 100$. Following recovery from the anaesthetic, f i s h were returned to t h e i r holding tanks and an hour l a t e r each i n d i v i d u a l was fed approximately one quarter of the s a t i a t i o n volume of chicken l i v e r recorded f o r i t during t e s t s i n the preceding month. The next t e s t was run two days l a t e r and only traces of l i v e r appeared i n the washings. Tests were repeated three times f o r each f i s h . The number of larvae taken by the f i s h was replaced with fresh Chaoborus to bring the number to 200 again. As each series took two days, the water flow through the tank was switched on again i n the evenings to maintain the temperature at approximately 13°C and a net was set at the end of the outflow pipe to c o l l e c t those larvae that were washed out; the number i n the tank was made up to approximately 200 i n the morning before tests were started again. Four sympatric Dolly Varden from Loon Lake and 20 f i v e a l l o p a t r i c D o l l y Varden from Dickson Lake were tested. A l l had been feeding reg u l a r l y on chopped chicken l i v e r . Three of the sympatric f i s h (#2, #3 and #4) were recent captures. C. S t a t i s t i c a l Analysis 1. M e r i s t i c s Means, 95 and 99% confidence l i m i t s were calculated f o r the raw data. Variances were calculated from log-transformed data to correct for the e f f e c t s of unequal means on the variances ( c f . Van Valen, 1965; Lewontin, 1966) and the two t a i l e d F test was used to test whether variances d i f f e r e d s i g n i f i c a n t l y from one another. 2 . Morphometries and length-weight relationships Regressions were calculated for various body parts and weight against standard length, using log-transformed data. The log-transformation was used to investigate the presence of allometric growth (Huxley, 1932), and to correct f o r the size related change i n variance (Lewontin, 1966). Pairs of l i n e s were compared using analysis of covariance. 3 . Canonical c o r r e l a t i o n Canonical c o r r e l a t i o n analysis i s used to r e l a t e one set of random variables, U, to another set of random variables, V, where K U = a^x^ and J ( 1 4 3 ) . The c o e f f i c i e n t s are chosen to give the largest possible c o r r e l a t i o n between the sets U and V (Lee, 1971). with the r e s t r i c t i o n that they be independent of previously derived l i n e a r combinations of c o e f f i c i e n t s (Green, 1972). This was used as an exploratory t o o l to determine i f r e l a t i o n s h i p s existed between diet and meristie counts. Diet was expressed as a l i n e a r combination of eight major food categories. Calculations were performed on the IBM 360 computer using a program available at the U.B.C. computing centre, BMDi 06M. Canonical correlations were tested f o r significance using B a r t l e t t ' s c r i t e r i o n (Lee, 1 9 7 1 ) for detection of the simultaneous departure of several roots from zero: which follows approximately a Chi-square d i s t r i b u t i o n with (pj - r + l ) ( p 2 - r + 1) degrees of freedom. N i s the t o t a l number i n the sample, p^ and p 2 the number of random variables i n the f i r s t or second set respectively, and }\ ^  i s the i canonical root. where i=r+l Comparison of means using a modified ' t' test to correct f o r unequal sample variances Variances d i f f e r e d s i g n i f i c a n t l y i n the s p a t i a l 22 d i s t r i b u t i o n laboratory tests and the following approximation was used f o r the comparison of means (Bailey, 1959)i d = x l ~ x2  2 2 s/(s1 /n± + s 2 /n 2) i s treated as being d i s t r i b u t e d approximately as 'Student's' t with f degrees of freedom where f = 1  u 2 / ( n j - 1) + (1 - u ) 2 / ( n 2 - 2) 2/ and u = s l / n l s l 2 / n l * s2 2/ n2 IV. RESULTS A. F i e l d Study 1. Temperature Loon Lake i s usually frozen from mid-December to mid-February though ice cover i s not always complete during t h i s period (information from U.B.C. Research Forest s t a f f ) . A thermocline may develop by the end of May and s t r a t i f i c a t i o n i s well developed f o r the whole summer. The thermocline becomes deeper as the summer progresses and at the end of September 1970 i t lay between 8 and 10 m ( F i g . 4). Dickson Lake usually does not become icefree u n t i l the middle of May and ice may remain on the surface u n t i l early June (L. Liberty, pers. comm.). The lake 23 WATER TEMPERATURE (°C) Loon Lake Foley Lake 1 ~ 10 -15 -20 • 31 May 1972 7~~ 20 July 1972 13 Sept. 1972 FIGURE 4. Temperature p r o f i l e s of the three study lakes. 24 developed a thermocline between 3 and 6 m by the end of July i n 1967 (Andrusak and Northcote, 1971), but not by mid-July i n 1972. At the end of August 1971 the surface temperature had r i s e n to 21.0°C, with a thermocline at 5 m (Fig. 4 ). A weak thermocline persisted between 9-11 m at the end of September 1972 and as la t e as mid-October i n 1967. Foley Lake usually freezes over i n mid-December and becomes icefree at the end of February. However, i n 1972 the lake had ice cover u n t i l the end of March following a hard winter (B. Walton, pers. comm.). During the summer of 1972, no s t r a t i f i c a t i o n developed ( F i g . 4), probably because of the short retention time of the lake (Table I ) . The temperature at 15 m rose s t e a d i l y from 4.9°C i n the spring to 10.6°C i n early f a l l , and the maximum recorded surface temperature was 15.5°C. 2. Bottom fauna Densities of bottom organisms at 10 and 20 m were lower i n Loon and Dickson Lakes than i n Foley Lake (Fig. 5) as they decreased with increasing depth, while i n Foley Lake the density of bottom fauna increased with increasing depth. In Loon Lake at 5 m oligochaetes made up most of the fauna followed by chironomid larvae. At 10 m, chironomid larvae were most common; Pisidium spp. and Chaoborus larvae were also taken i n small numbers at t h i s depth. The only organisms recorded at 20 m were chironomid larvae. Small 25 amounts of motile benthos were obtained at 5 m; t h i s category included amphipods, S i a l i s and caddis larvae, although the l a s t were only represented by t h e i r empty l a r v a l cases. In Dickson Lake, Pisidium spp. were more abundant than i n Loon Lake but densities of other categories were si m i l a r . Motile benthos, consisting of amphipods, planorbid gastropods and caddis larvae were co l l e c t e d i n small numbers at 5 and 10 m. Pisidium spp. were abundant i n Foley Lake, p a r t i c u l a r l y i n l i t t o r a l areas. Densities of chironomid larvae were greatest at 10 m and were much more abundant at t h i s depth and at 5 m than i n the other two lakes. Oligochaetes became more common with increasing depth and at 10 and 20 m accounted f o r much of the increased density of bottom fauna i n Foley Lake r e l a t i v e to the other two lakes. In the motile benthos category, caddis larvae and planorbid gastropods were collected; mayfly nymphs were not taken i n benthos samples but were evident i n submerged vegetation i n the l i t t o r a l area. Both chironomid larvae and Pisidium spp. were separated into two d i s t i n c t size classes. Chironomid larvae longer than 10 mm and Pisidium spp. with s h e l l diameter greater than 1.5 mm were c l a s s i f i e d as 'large'. A l l Loon Lake chironomid larvae and Pisidium were i n the small category. Foley Lake had proportionately more large Loon Dickson Foley Numbers per 100 c m 2 FIGURE 5. Depth d i s t r i b u t i o n s of major benthic organisms i n the three study-lakes during summer 1972. Sample s i z e s i n parentheses; mean and range of numbers per 100 cm2 shown. A. T o t a l B. Pisidium C. Chironomids D. Oligochaetes E. Motile Benthos. 27 chironomid larvae and Pisidium spp. than Dickson Lake (Table I I I ) . TABLE I I I . Size frequency of bottom organisms from Foley and Dickson Lake f a l l samples, separated by eye, Chi- Significance chironomids >10 mm 382 5 <10 mm 220 82 Pisidium ^1.5 mm 107 6 <1.5 mm 478 137 430 p< 0.001 400 p<0.001 3. Zooplankton Zooplankton i s considerably more abundant i n Loon Lake than i n Dickson Lake, and Foley Lake contains only small amounts (Fig. 6). Loon Lake also shows a s i g n i f i c a n t increase i n numbers per haul i n the top 5 m as the season progresses (F i g . 6k). Calanoid (Diaptomus spp.) and cyclopoid copepods formed a considerable percentage of the plankton i n Loon Lake i n each sampling series (Fig. 7). Numbers of Daphnia spp. increased through the season; Bosmina l o n g i r o s t r i s showed a peak i n the summer and Diaphanosoma leuchtenbergianum were most abundant i n the f a l l . Other species present included Holopedium gibberum, Polyphemus p e d i c u l i s . Leptodora  k i n d t i and Scapholebris k i n g i . Water mites (Acarini) were taken occasionally. In Loon Lake, numbers of cladocerans 28 A S p r i n g Total No. of Zooplankters/5 m Vertical Haul 0 1 10 1 0 2 1 0 3 -N^ I i i I I I 111 I i i I I I 111 i 1 i i i i 1 1 1 i 1 I I i i 1 1 1 ' . • ! 5 12 c o 52 Summer-CD W Fall-^ r-2 0 I 4 3 12 -A— i—Sj^ -i \ ^ 9 0 1 10 10' 1 0 " B - \ I I I I I I 111 I 1 I I I I I I I I I I I I 1111 1 I I I I 1 1  L Cladocera 0 - 5 - B 5 - 1 0 E 1 0 - 1 5 / K i — i CO > c a cu Q 0 - 5 5 - 1 0 1 0 - 1 5 Copepoda I — 0 - 5 5 - 1 0 1 0 - 1 5 Total 12 f-\ \ \ • X 3 13 I is I 0 i I / ' 5 FIGURE 6. Zooplankton abundance i n Loon (•), Dickson (*) and Foley (•) Lakes. Mean numbers and range per 5 metre v e r t i c a l stage haul shown; number of samples indicated. A. Seasonal changes. B. Depth d i s t r i b u t i o n during summer. 100 r L O O N 29 c 0 o •0 0. 0 D) CO 60 40 20 Key D ICKSON CLADOCERA O Daphnia 0 (20) Diaphanasoma Bosmina • o COPEPODA e D • Calanoid Cyclopoid • Harpacticoid /s Chironomid and 1 1 ™ Chaoborus larvae. X .Acar ini SPRING SUMMER FALL FIGURE ?. Seasonal changes i n average percent composition of zooplankton samples i n the three study lakes during 1972. Number of samples i n parentheses. 30 were highest between 5 and 10 m, while copepod numbers decreased with increasing depth (Pig. 6B). In the one Dickson Lake sampling series, Bosmina  l o n g i r o s t r i s was the most abundant species present (Fig. 7). Calanoid copepods (several Diaptomus spp.) were common; cyclopoid copepods were scarce. Daphnia were present; Diaphanosoma, Holopedium and Scapholebris were not recorded i n plankton samples but were present i n f i s h stomachs. Cladocerans and copepods were f a i r l y evenly d i s t r i b u t e d i n the top 15 m of Dickson Lake. In Foley Lake, cyclopoid copepods were the most important items i n the sparse plankton, followed by Daphnia. Turbulence, caused by spring runoff water, was probably responsible f o r the appearance of harpacticoid copepods, chironomid larvae and nematodes as important constituents of the plankton i n the spring and summer samples. 4, Fish d i s t r i b u t i o n i . Loon Lake Sympatric D o l l y Varden were mainly associated with the bottom i n May 1972 ( F i g . 8). Most were captured inshore, and here some were taken i n midwater. They were also taken i n large numbers i n bottom nets at 10 m (Table IV); more were captured i n the lower than i n the upper half of these nets (Chi-square = 7.53? p<0.01). Cutthroat trout were taken i n large numbers throughout the water column inshore ( F i g . 8). Offshore, they were predominantly M a y D A Y N I G H T Ju ly D A Y N I G H T September D A Y N I G H T • one fish FIGURE 8. V e r t i c a l d i s t r i b u t i o n of sympatric Loon Lake Dolly Varden (DV, shaded) and cutthroat trout (CT, blank) i n nets set from surface to bottom at 5, 10 and 20 m, day and night, i n 1972. Catches expressed as number per p a i r of nets. 32 associated with the surface. During the day, cutthroat trout were taken i n smaller numbers than at night; D o l l y Varden were taken only at night. D o l l y Varden had moved into deeper water by Ju l y 1972 and remained near the bottom (Fig. 8). Here, they were taken i n about equal numbers with cutthroat trout (Table IV). Summer nettin g series i n previous years confirmed that D o l l y Varden were only taken i n nets that fished the bottom and that cutthroat were not excluded from t h i s region (Table V). Cutthroat were deeper than i n May and were the only species taken during the day. TABLE IV. Numbers of Dolly Varden and cutthroat trout captured i n duplicate 1.4 m deep g i l l nets fished on the bottom at 10 m i n Loon Lake i n 1972. Month D o l l y Varden Cutthroat trout May 42 4 J u l y 24 19 September 55 9 TABLE V. Numbers of Do l l y Varden and cutthroat trout captured i n summer netting series i n Loon Lake during 1970 and 1971. Depth range fished Depth at netting s i t e E f f o r t * D o l l y Varden Cutthroat trout 0 - 5 m 12 m 900 0 5 5 - 10 m 12 m 360 0 36 Bottom 1.4 m 10 - 15 m 4340 79 33 *Effort» product of the length of net (metres) and the time fished (hours) 28 September DAY NIGHT 18 October DAY CT . DV CT DV CT DV D Single fish FIGURE 9. V e r t i c a l d i s t r i b u t i o n of sympatric Loon Lake D o l l y Varden (DV, shaded) and cutthroat trout (CT, blank) i n nets set from surface to bottom at 5 and 10 m, day and night, i n f a l l 1970. Catches expressed as number per ^ three nets. ^ 3 4 In mid-September 1972, D o l l y Varden were confined to the bottom at 10 m (Fig. 8). Few cutthroat trout were captured i n t h i s region (Table IV), but they were often taken i n midwater and at the surface, both day and night. In late September 1970 (Fig. 9), more D o l l y Varden were captured inshore and i n the water column than i n J u l y and mid-September 1972 netting s e r i e s . However, a preference f o r the bottom was s t i l l evident, but t h i s disappeared by October 1970. Cutthroat trout were widely d i s t r i b u t e d i n the water column, both day and night i n the f a l l . In summary, Do l l y Varden were c l o s e l y associated with the substrate i n Loon Lake during the summer, and t h i s association was f a r more d i s t i n c t than that reported by Andrusak and Northcote (1971) f o r Dolly Varden i n Marion Lake. Although Dolly Varden appeared to be confined to the bottom few metres from spring to early f a l l , cutthroat were not excluded from t h i s part of the water column. Later i n the f a l l , D o l l y Varden moved into the water column and were also taken during the day. i i . Dickson Lake A l l o p a t r i c D o l l y Varden i n Dickson Lake were widely d i s t r i b u t e d throughout the water column, inshore and offshore, both day and night during the summer and f a l l . G i l l netting r e s u l t s and echo sounding records (Figs. 10, 11 and 12) both showed t h i s pattern. FIGURE 10. V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c Dickson Lake D o l l y Varden i n nets set from surface to bottom at 5» 10 and 20 m, day and night, i n summer 1971 and 1972. Catches expressed as number per p a i r of nets. FIGURE 11. Echo sounding traces made on a standard transect in Dickson Lake over a 24 hour period i n August 1971, showing onshore movements of a l l o p a t r i c D o l l y Varden at night. Thermocline present from 4 to 6 metres. FIGURE 12. Echo soundings made on a standard transect i n Dickson Lake over a 24 hour period i n July 1972. No thermocline present. 38 Wide d i s t r i b u t i o n of D o l l y Varden i n the upper 10 m of Dickson Lake at night was also shown i n a previous study (Andrusak and Northcote, 1971). However, numbers captured during the day (Fig. 13) were small compared with the present study; the short duration of day net sets (average 3 hours, maximum 6 hours; Andrusak, MS 1968) may be part of the reason that so few were taken then i n that study. Echo sounding records i n 1967 showed no evidence of f i s h above 25 m during the day (Andrusak and Northcote, I97I). However, the upper 1-2 m are always obscured by the 'zero band' on the echo sounding record. In 1972, the majority of f i s h taken i n 5 m surface nets offshore at the 20 m depth contour, both day and night i n J u l y and September, were captured i n the uppermost 2 metres ( F i g . 10). Numerous observations of f i s h r i s i n g at the surface, p a r t i c u l a r l y f o r several hours a f t e r dawn and at dusk, i n 1971 and 1972, also showed that a l l o p a t r i c D o l l y Varden i n Dickson Lake were not confined to deeper water during the day. Although there was no evidence f o r extensive d i e l v e r t i c a l movements of f i s h within the lake from g i l l n e t t i n g or echo sounding r e s u l t s , netting r e s u l t s from July 1972 (Table VI) and echo sounding records made over 2k hours i n August 1971 ( F i g . 11) suggest that an onshore migration occurred at night during the summer. I t was not DAY N IGHT H Two fish FIGURE 13. V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c D o l l y Varden i n nets set i n Dickson Lake by Andrusak i n 1967 (Andrusak, MS 1968). 40 TABLE VI. Numbers of Do l l y Varden i n onshore and offshore g i l l nets i n the upper 5 m of Dickson Lake i n 1972, Day Night Chi-square J u i y Onshore Offshore 17 28 68 8 42 September  Onshore Offshore 17 15 17 12 0.05 apparent i n late September 1972 (Table VI). To conclude, i n contrast to the sympatric Loon Lake population, a l l o p a t r i c D o l l y Varden i n Dickson Lake were widely d i s t r i b u t e d throughout the water column during summer and autumn. i i i . Foley Lake Catches of D o l l y Varden were small r e l a t i v e to nettin g e f f o r t i n each of the sampling s e r i e s . Day and night d i s t r i b u t i o n s did not d i f f e r s i g n i f i c a n t l y from one another, so were combined for each series; s i m i l a r l y spring and summer d i s t r i b u t i o n s did not appear to d i f f e r from one another and these r e s u l t s were also combined (Fig. 14). In the spring and summer series, the majority of f i s h were captured within one metre of the bottom ('bottom f i s h * ) . In the f a l l series, more f i s h were captured i n the water column ('midwater f i s h ' ) and fewer near the bottom (Table VII). The small number of 'midwater f i s h ' i n the spring and summer serie s may be an underestimate Spring and Summer Fall FIGURE 14. V e r t i c a l d i s t r i b u t i o n of a l l o p a t r i c Foley Lake D o l l y Varden i n nets set from surface to bottom at 5. 10 and 20 m during 1972. Day and night data combined; catches expressed as number per four nets. 42 D A Y N I G H T Spr ing 15 L FIGURE 15. Echo sounding records showing evidence of a l l o p a t r i c D o l l y Varden throughout the water column i n Foley Lake i n 1972. Long v e r t i c a l marks may be submerged logsj v e r t i c a l reference l i n e s should be ignored. 43 TABLE VII. Seasonal differences i n v e r t i c a l d i s t r i b u t i o n of D o l l y Varden i n surface-bottom g i l l nets set at 5 and 10 m i n Foley Lake. Spring and Summer (pooled data) F a l l •Midwater f i s h ' 2 8 •Bottom f i s h ' 21 4 D i s t r i b u t i o n s d i f f e r t p< 0.001 (Fisher Exact Test) of the actual proportion present i n the water column as marks, probably representing f i s h , were present here on the spring and summer echo sounding records ( F i g . 15); f i n e red s i l t , which accumulated on the meshes of the g i l l nets, rendering them conspicuous, may have been p a r t l y responsible f o r low net catches i n midwater during the spring and summer se r i e s . In summary, although data were limi t e d , a l l o p a t r i c D o l l y Varden i n Foley Lake appeared to be present throughout the water column} they were, however, more c l o s e l y associated with the bottom than those i n Dickson Lake, but not nearly as d e f i n i t e l y as the sympatric population i n Loon Lake. 5. Food i . Seasonal changes Loon Lake Sympatric D o l l y Varden i n Loon Lake took a progressively greater proportion of benthic prey from spring 44 to e a r l y f a l l ; t h i s was composed increasingly of organisms taken from within the substrate, such as chironomids and Chaoborus larvae and Pisidium spp. ( F i g . 16). The proportion of i n d i g e s t i b l e items taken (mud, seeds and leaf debris) increased concomitantly. Water column prey, s o l e l y zooplankton, decreased i n importance from spring to e a r l y f a l l , but i n October, when Dolly Varden were present throughout the water column, zooplankton again became the major prey category. 'Motile benthos', an important food i n the spring, was a minor item i n early f a l l , when Do l l y Varden were absent from inshore regions. Cutthroat trout caught i n the same depths as D o l l y Varden were subject to sp e c i a l study ( F i g . 16); they took an increasing amount of benthic prey from spring to ea r l y f a l l . In contrast, benthic prey was of l i t t l e importance to cutthroat trout caught i n midwater, surface and onshore regions of Loon Lake ( F i g . 16). Cutthroat trout throughout the lake fed predominantly on water column prey (Fig. 16), mainly zooplankton and, to a small extent, chironomid pupae. The percent occurrence of cladocerans decreased whereas copepods increased from spring to early f a l l , although cladocerans were always more commonly taken ( F i g . 1?). In the spring, when cutthroat trout were not present i n as large numbers as D o l l y Varden at the 10 m depth zone (Table IV), planktivorous D o l l y Varden fed mostly on cladocerans. 45 FIGURE 16. CD E > Cutthroat trout - same depths as Dolly Varden c CD O i_ CD CL CD D) CO i_ <D > < 50 -midwater, surface and onshore 100 50 May July Key: • • v o o o o 20 °°°< $8 _ 0 ° oo .v ° 0 0 0 o o 0 '°°°o :-.V •VTTS 63 25 1 r ••• 1 " ^ Sept. Oct. Surface insects Water column prey (zooplankton and chironomid pupae) Salamanders Motilo benthos Y/. Static benthos Stomach contents (average percent volume) of adult sympatric Dolly Varden and cutthroat trout i n Loon Lake i n 1970 (October) and 1972. Number sampled indicated; balance (unshaded) composed of i n d i g e s t i b l e material e.g. seeds, mud. 46 Dolly Varden t ^ ^ l Copepoda I I Cladocera FIGURE 17. Percent occurrence of copepods and cladocerans i n stomach contents of planktivorous D o l l y Varden and cutthroat trout from a l l regions sampled i n Loon Lake. Percent occurrence of planktivores i n parentheses. 47 In the summer, when cutthroat and Dolly Varden were taken i n about equal numbers there, fewer Dolly Varden fed on zooplankton and, i n those that did, the percent occurrence of copepods was greater than that of cladocerans. In early f a l l , when s p a t i a l segregation between the two species was most pronounced (Table IV; F i g . 8), the few planktivorous D o l l y Varden fed l a r g e l y on cladocerans ( F i g . 17). This suggests that i n the summer, when the two species overlapped s p a t i a l l y and fed on the same general food category, zooplankton i n the water column, they nevertheless concentrated on d i f f e r e n t prey items within that category. Cutthroat trout throughout the lake, p a r t i c u l a r l y i n spring and f a l l , fed on surface insects. These were of l i t t l e importance to Dolly Varden. A few larger cutthroat trout took salamanders, but D o l l y Varden did not eat any vertebrate prey. In summary, sympatric Dolly Varden i n Loon Lake fed p r i m a r i l y on bottom fauna i n summer and early f a l l ; zooplankton was predominant i n t h e i r d i e t s i n spring and i n October. Their diet d i f f e r e d most from that of cutthroat i n e a rly f a l l . Dickson Lake Water column prey became increasingly important i n the d i e t of a l l o p a t r i c Dickson Lake D o l l y Varden as the season progressed ( F i g . 18). Surface insects, the most important food category i n the spring (Andrusak and Northcote, D O L L Y V A R D E N 48 Sympat r ic - Loon Lake 100 T Key: Surface insects • • ° Water column prey (zooplankton - except Foley; chironomid pupae) Salamanders - Loon ; Dolly Varden - Dickson; tadpoles - Foley vCvc Motile benthos Static benthos FIGURE 18. Stomach contents (average percent volume) of adult sympatric (Loon Lake) and a l l o p a t r i c (Dickson and Foley Lakes) D o l l y Varden. Sample sizes indicated! balance (unshaded) composed of i n d i g e s t i b l e material e.g. seeds, mud. •data from Andrusak (MS 1968) 49 1971)» decreased i n importance during summer and autumn. Water column prey was composed increasingly of zooplankton, l a r g e l y Bosmina and Daphnia spp., and decreasingly of chironomid pupae between June and October. Benthic organisms were of l i t t l e importance. Individual D o l l y Varden started to feed on members of t h e i r own species when as small as 140 mm (fork length); exceptionally large f i s h taken i n 1967 and 1972 (360 and 380 mm fork length respectively) had both fed exclusively on f i s h . Cannibalism, however, was uncommon and the average percent occurrence of f i s h remains i n 371 adults examined i n 1967, 1971 and 1972 was only 3.3%. The most marked differences between diets of sympatric Loon and a l l o p a t r i c Dickson Lake D o l l y Varden were the importance of benthic prey to the former and of surface insects to the l a t t e r ( F i g . 18). They d i f f e r e d most i n early f a l l when Loon Lake Dolly Varden took mostly benthos and very l i t t l e water column prey. Foley Lake Motile benthos, mainly Heptageneidae (Ephemeroptera) larvae with a few large plecopteran and trichopteran larvae, was the most important prey category of a l l o p a t r i c Foley Lake Dolly Varden (F i g . 18). I t comprised 80% of the average percent volume i n the spring, but dropped to 33% i n the summer when 22% of the average percent volume was s t a t i c benthos; t h i s was l a r g e l y composed of chironomid larvae 50 with some large Pisidium. Surface insects, and to a less e r extent chironomid pupae, increased i n importance through the season. Tadpoles were an important constituent of the diet i n the summer; i n d i v i d u a l f i s h preyed heavily on them. i i . Number of food categories taken per f i s h A l l o p a t r i c D o l l y Varden from Dickson and Foley Lakes took a wider range of major food categories per f i s h than sympatric D o l l y Varden from Loon Lake ( F i g . 19). D o l l y Varden from Loon Lake showed a decrease i n the range of food categories taken as the season progressed; i n the f a l l , the range taken per i n d i v i d u a l was s i g n i f i c a n t l y l e s s (p< 0.05) than that i n the spring. V a r i a b i l i t y i n range of food categories taken between i n d i v i d u a l s was greatest f o r Foley Lake Dolly Varden (Appendix Table I I I ) ; i n the summer and f a l l the variance of the number of major categories taken was greater f o r Foley Lake D o l l y Varden than f o r D o l l y Varden from Dickson and Loon Lakes (F r a t i o s give p<0.01 i n a l l cases). i i i . Factors a f f e c t i n g food taken The diet of sympatric D o l l y Varden i n Loon Lake was evidently influenced by t h e i r association with the bottom, benthos being important at a l l times i n t h e i r diet and surface insects n e g l i g i b l y so. In contrast, cutthroat trout captured i n the same depth i n t e r v a l s as Dolly Varden were not so r e s t r i c t e d and fed on insects as well as 51 5 r JZ CO c CD _ i 03 -*—< CO CD — . O O) CD -4—• CO o T3 O O U_ — . o CO o 1 o z c CO CD 0 (12) (57) Spr ing Sum mer F a l l Loon & Dickson O Foley • FIGURE 19. Mean number of major food categories taken per i n d i v i d u a l Dolly Varden. 95% confidence l i m i t s of mean shown; sample size i n parentheses. (See Appendix Table III) 52 zooplankton and benthos ( F i g . 18) Relative proportions of food categories eaten by sympatric D o l l y Varden i n Loon Lake changed with increasing body s i z e . F i sh larger than 155 mm fork length, a c r i t i c a l length as shown i n the morphological section (Fig. 31). ate a greater proportion of benthos ( F i g . 20) than smaller f i s h . Average numbers of chironomids taken per f i s h by large and small f i s h i n Loon Lake i n the f a l l were 98 (12 f i s h sampled) and 6.7 (10 f i s h sampled) respectively; the average volume of i n d i v i d u a l chironomids eaten by large D o l l y Varden was over twice that of those taken by small f i s h . More mud and debris was also taken by the large f i s h . Small f i s h took more zooplankton. The same changes with increasing size were reported f o r Marion Lake (Andrusak, MS 1968). Food taken by a l l o p a t r i c Dolly Varden i n Dickson Lake was not c l e a r l y related to the depth at which they were captured. Some f i s h caught at the bottom at 20 m had eaten insects and motile benthos, and others caught at the surface at 20 m had eaten s t a t i c and motile benthos prey types. This suggests considerable v e r t i c a l and onshore-offshore movement by D o l l y Varden i n Dickson Lake, a behavioural pattern corroborated by netting data there. A l l o p a t r i c Dickson Lake Dolly Varden, with fork length l e s s than 155 mm, took more zooplankton both i n the summer and i n the f a l l than larger f i s h ( F i g . 20). In the summer, larger f i s h took a greater proportion of insects L O O N L A K E D I C K S O N L A K E <155 mm 100 50 0 E o > - o-c o o 0. cn CO \ o > < 100 50 Key: >155 mm May July Surface insects Sept. <155 mm >155 mm July o°o« Water column prey (zooplankton, chironomid pupae) V\>NN Motile benthos '//• Static benthos Dolly Varden - Dickson o „ ° Sept. FIGURE 20, Size related differences i n stomach contents (average percent volume) of sympatric Loon Lake and a l l o p a t r i c Dickson Lake D o l l y Varden i n 1972. Sample sizes indicated; balance (unshaded) composed of indigestible material e.g. seeds, mud. 54 than smaller ones but t h i s was reversed i n the f a l l , when lar g e r f i s h took more motile benthos. S t a t i c benthos and f i s h were proportionately more important i n the diets of large f i s h than small i n both summer and f a l l . In Foley Lake, i n d i v i d u a l a l l o p a t r i c D o l l y Varden made simi l a r v e r t i c a l movements to those i n Dickson Lake. Fi s h taken at 17 m depth i n the summer, close to the substrate, had eaten insects shortly before capture; others that had f r e s h l y eaten insects were taken at 10 m i n the spring and f a l l . Most f i s h were captured close to the substrate and the amount of benthos eaten was correspondingly high. Canonical correlations (Lee, 1971) showed that food of i n d i v i d u a l D o l l y Varden was not correlated with the number of g i l l rakers or p y l o r i c caeca i n any of the three lakes (Table VIII). TABLE VIII. Relationship of numbers of p y l o r i c caeca and g i l l rakers to diet; data within lakes are combined. Canonical correlations and t h e i r significance Lake N I C h i 2 d.f. II C h i 2 d.f. LOON 160 0.272 17.5 27 NS 0.190 5.7 16 NS DICKSON 205 0.177 10.8 27 NS 0.148 4 . 4 16 NS FOLEY 47 0.442 14.8 27 NS 0.368 6.0 16 NS 6. Length frequency and age categories The length frequency d i s t r i b u t i o n s of Loon Lake D o l l y Varden ( F i g . 21) are d i s t i n c t l y more polymodal than 55 those of Dickson Lake f i s h ( F i g . 22). This d i s t i n c t i o n i s shown well when frequency d i s t r i b u t i o n s of D o l l y Varden captured i n J u l y over a number of years from Loon and Dickson Lakes are plotted on p r o b a b i l i t y paper (Fig. 23). These suggest that there i s l e s s v a r i a b i l i t y i n fork length within year classes i n Loon Lake than i n Dickson Lake. Scale samples taken from a small number of Loon Lake D o l l y Varden i n the f a l l showed that the winter checks corresponding to the f i r s t , second and t h i r d winters occurred when f i s h were approximately 80, 125 and 175 mm i n fork length respectively. This showed that yearling f i s h (1+) started to enter the catch i n the f a l l ( F i g . 21). Most cutthroat trout captured i n Loon Lake were between 160 and 200 mm i n fork length; winter checks corresponded to fork lengths of approximately 60, 110 and 160 mm. Fork lengths f o r a given year class appeared to overlap considerably with those of Dolly Varden from the same year c l a s s . Dickson Lake Dolly Varden were d i f f i c u l t to separate into year classes using length frequency histograms owing to the v a r i a b i l i t y i n length within year classes and the overlap between adjacent year classes (Figs. 22 and 23). Ageing with o t o l i t h s proved impractical as they were d i f f i c u l t to clear; an i n d i v i d u a l of fork length 173 mm was shown to have overwintered three times (J.D. McPhail, pers. comm.). A few scales were read, but r e s u l t s were uncertain; 56 301 20-10-0 -10-CI 1 + 2 + Fa l l 3 + 40-> 30-o 20-z UJ 10 o 0 UJ 10-cc u_ 0 Summer Spring 2 + 3 + 125 150 175 200 225 F O R K L E N G T H (mm) 250 FIGURE 21. Seasonal changes i n length frequency d i s t r i b u t i o n of D o l l y Varden (shaded) and cutthroat (blank) i n Loon Lake during 1972. Probable age categories shown on some histograms. 57 101 0 Foley Lake Fall 10 0 10 Summer >-O z UJ D o UJ tr J 1 U Spring 175 200 Diekson Lake 225 250 275 300 20 10 0 30 20 10 0 . , . , „ . , , Fall \ Summer 125 150 175 200 225 FORK LENGTH (mm) FIGURE 22. Length frequency histograms for D o l l y Varden captured i n Foley and Dickson Lakes i n 1972. 2 2 0 -2 0 0 X h-^ 1 8 0 z UJ o 1 6 0 1 4 0 1 2 0 Loon Lake ( 8 4 ) Dickson L a k e oss) 0 . 1 0 . 2 0 . 5 1 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 9 5 9 8 9 9 9 9 . 5 9 9 8 9 9 . 9 C U M U L A T I V E P E R C E N T FIGURE 2 3 . Fork length d i s t r i b u t i o n s of J u l y samples of Dolly Varden from Loon and Dickson Lakes. Samples from several years are pooled i n each case. Sample sizes i n parentheses. 00 59 probably most of the f i s h taken i n 1972 netting with fork lengths between 130 and 160 mm were f i s h that had over-wintered twice. In August 1971. a sample of young of the year was co l l e c t e d by dip netting i n an inflow creek mouth; they ranged i n fork length from 28 to 50 mm with a mean of 37 mm. Foley Lake Dolly Varden were considerably larger than D o l l y Varden from Loon and Dickson Lakes ( F i g . 22). Young of the year, with fork length of approximately 50 mm, were observed i n side channels of the main inflow, Foley Creek, i n September 1972. 7. M e r i s t i c counts Numbers of p y l o r i c caeca are not correlated with fork length for Loon and Foley Lake D o l l y Varden, but c o r r e l a t i o n i s evident f o r the Dickson Lake population (Fig. 24). This may account f o r part of the greater v a r i a b i l i t y i n p y l o r i c caeca number of the Dickson Lake population (Table IX). Mean numbers of p y l o r i c caeca are greater i n both a l l o p a t r i c populations than i n the sympatric Loon Lake population. G i l l raker numbers are correlated with fork length fo r Loon Lake D o l l y Varden ( F i g . 25); t h i s may account i n part for the high v a r i a b i l i t y i n g i l l raker numbers of the Loon Lake population (Table IX). Numbers reach an asymptote at approximately 140 ram fork length. G i l l raker numbers are not correlated with fork length f o r the two a l l o p a t r i c 60 35 30 25 • 20 15 r 10 5 CO 0 o CD 35 • O 30 -o 25 • o 20 ->. 0 - 15 -H — 10 -o 5 -CD JQ 0 E 3 35 " z 30 25 20 15 10 5 -Loon Lake R = 0 0 5 2 p > 0-1 Dickson Lake R = 0-227 p < 0-001 • • • Foley Lake R z 0-172 p > 0 1 100 200 Fork Length (mm) 300 FIGURE 24. Relationship of p y l o r i c caeca numbers to fork length? c o r r e l a t i o n c o e f f i c i e n t s (R) and p r o b a b i l i t y of significance (p) are shown. 61 20 15 ***** *•••*« • H l | ) l W « H * ' *«• 10 5 - Loon Lake R = 0-419 p < 0001 CD CO or 20 15 -O 1° n E — « . » * O f t » t > » » + f r » * » » » « « Dickson Lake R = 0 0 6 7 p > o -1 20 15 10 5 Foley Lake R = 0-144 P > 0-1 0 100 200 300 Fork Length (mm) FIGURE 2 5 . Relationship of g i l l raker numbers to fork length; c o r r e l a t i o n c o e f f i c i e n t s (R) and p r o b a b i l i t y of significance (p) are shown. 62 TABLE IX. Means and variances of meristic counts for D o l l y Varden from Loon, Dickson and Foley Lakes. 1. P y l o r i c caeca 99% confidence Variance of Population Mean range of mean log (count) N LOON 24.23 23.77 - 24.68 0.0088 168 DICKSON 25.90 25.35 - 26.46 0.0145 209 FOLEY 25.89 24.76 - 27.02 0.0128 46 DICKSON and FOLEY means> LOON mean, 1% si g n i f i c a n c e . F r a t i o (two t a i l e d test) to compare variances: DICKSON: LOON = 1.648; p<0.0l FOLEY: LOON = 1.454; p<0 . 0 5 DICKSON: FOLEY = 1.133: NS 2. G i l l rakers on the anteriormost r i g h t hand g i l l arch 99% confidence Variance of Population Mean range of mean log (count) N LOON 17.31 17.06 - 17.56 O.0058 177 DICKSON 17.46 17.27 - 17.66 0.0043 221 FOLEY 17.00 16.47 - 17.52 0.0056 49 There i s no s i g n i f i c a n t difference between the means. F r a t i o (two t a i l e d test) to compare variances: LOONt DICKSON = 1.349; NS LOON: FOLEY = 1.036; NS FOLEY: DICKSON = 1.302; NS See Figures 26 and 27. 30 20 >" 10. O Z o UJ ZD 30 O UJ 20-DC LL 10-Loon Lake Dickson Lake i i' - Foley Lake •x&v: ::::::ivi* • . . . 1 H . 1 . 1 1 1 1 I •v.v.-.v|.v.v.v.^ ..,..t1  20 22 24 26 28 30 32 NUMBER OF PYLORIC C A E C A 34 FIGURE 26. D i s t r i b u t i o n of p y l o r i c caeca numbers i n D o l l y Varden from Loon, Dickson and Foley Lakes. ON 64 60-50-404 30-| 20 >" 10 O Z o LU 3 80-| a LU 7 0 50 40 30-20-10 0 Loon Lake Dickson Lake Foley Lake 1 1 1 >X;X>v, 12 14 16 18 20 N U M B E R OF GILL R A K E R S FIGURE 27. D i s t r i b u t i o n of g i l l raker numbers on the anteriormost r i g h t hand g i l l arch i n Dolly Varden from Loon, Dickson and Foley Lakes. 65 populations. Mean numbers of g i l l rakers do not d i f f e r s i g n i f i c a n t l y between the three populations. 8. Morphometric comparison of the three D o l l y Varden populations Growth of the head ( F i g . 28) and predorsal length i n r e l a t i o n to standard length i s greatest f o r Loon Lake D o l l y Varden and least f o r the Foley Lake population (Table X). Similar differences i n r e l a t i v e growth of other head parts, upper jaws, snout-to-back-of-eye, eye ( F i g . 29) and longest g i l l raker ( F i g . 30) are found between the three populations. Although r e l a t i v e growth rates of these body parts are greater f o r Loon and Dickson Lake Dolly Varden, i n most cases they are proportionately smaller than i n the Foley Lake f i s h for much of the size range captured. For example, upper jaws of Loon Lake Dolly Varden are smaller than those of Foley Lake f i s h of corresponding size u n t i l they reach 230 mm standard length (Fig. 2 9 ) . Relative growth rates of the eye vary greatly between the populations, that of Loon Lake D o l l y Varden being the greatest; both Loon and Dickson Lake D o l l y Varden have larger eyes than sim i l a r sized Foley Lake f i s h over the size range captured ( F i g . 29) as the growth rates of t h e i r eyes i n r e l a t i o n to standard length are so much lar g e r than that of Foley Lake D o l l y Varden (Appendix Table VIII). Contrary to expectation, v a r i a b i l i t y (mean square FIGURE 28. Relationship of head length to standard length f o r the three D o l l y Varden populations. 15. 10. UJ Si 15. 10. i ' l I I I I I H 1 I I I I I 15. 10... H 1 1.. 50. 100. 300. 50. 100. 300. 50. STANDARD LENGTH (MM) 100. H 1 300. FIGURE 2 9 . Relationship of upper jaw length, distance from snout to back of eye, and eye length to standard length f o r the three D o l l y Varden populations. 68 50° 100. 300« 50« 100. 300. 50» 100. 300. FIGURE 3 0 . Relationship of least fleshy i n t e r o r b i t a l width, length of longest g i l l raker, and weight to standard length f o r the three Dolly Varden populations. 69 deviation) about the regression i s greatest f o r the sympatric Loon Lake population for head, predorsal, upper jaw, snout-to-back-of-eye, eye and longest g i l l raker lengths (Table X). The v a r i a b i l i t y i s s i g n i f i c a n t l y greater than that of Dickson Lake Dolly Varden i n every case and i t i s greater than that of Foley Lake D o l l y Varden i n upper jaw, longest g i l l raker and predorsal lengths. Examination of the regressions of head (Fig. 28), upper jaw, snout-to-back-of-eye and eye ( F i g . 29) lengths on standard length f o r Loon Lake Dolly Varden suggests an i n f l e c t i o n , p a r t i c u l a r l y marked for the upper jaw, at 140 mm (approximately 155 mm fork length) towards greater r e l a t i v e growth of each of these body parts i n larger f i s h . The i n f l e c t i o n must contribute considerably to the increased mean square deviations of these body parts of the Loon Lake population with respect to the a l l o p a t r i c populations. Regressions calculated separately f o r f i s h smaller than and larger than 140 mm ( F i g . 31) eliminate the eff e c t of the i n f l e c t i o n , and v a r i a b i l i t y within each size group of the Loon Lake f i s h i s no longer s i g n i f i c a n t l y greater than that of f i s h from equivalent size classes from the other two populations (Appendix Table XIII). The i n f l e c t i o n s noted f o r the r e l a t i v e growth of the head, snout-to-back-of-eye and eye lengths f o r Loon Lake Dolly Varden suggest that a l l these characters are in t e r r e l a t e d with upper jaw length i n the same 'morphogenetic f i e l d of influence* 50. 10. 5TAN0ARD LENGTH LESS THAN 140 MM-LOON 50 DICKSON 50. FOLEY lZU-M io. -H-50. 100. 300. 50. 100. — I 1° 300. 50 M i l l 100. 300. 3 50. 10. STANDARD LENGTH GREATER THAN 140 MM-LOON 50- DICKSON 50. FOLEY l l l l 50. 100. — I io 300. 50 +4- H 1 1°' 100. 300. 50. 100. 300. FIGURE 31. Relationship of upper jaw length to standard length f o r Dolly Varden smaller than and larger than 140 mm (approximately 155 mm fork length) f o r the three populations. TABLE X. Summary of morphometric comparisons of the three D o l l y Varden populations. Body part Head Upper jaw Slope L and D > F L >D > F Relative size of body part at given standard length F > L > D for a l l lengths measured F > L for f i s h > 300 mm Appendix V a r i a b i l i t y Table L > D V L > F and D VI F > D for f i s h > 300 mm Snout-to-back-of-eye L > D > F F > L and D for f i s h > 250 mm L and F > D VII Eye L > D > F F > D F >L D >L for for for f i s h > 110 mm f i s h > 150 mm f i s h > 160 mm L and F > D VIII Length of longest g i l l raker L > D and F F > D > L L>D >F for for f i s h > 150 mm f i s h > 150 mm L > D and F IX Predorsal L > D > F F > L >D for a l l lengths L > D > F X I n t e r o r b i t a l width Anal to pectoral f i n base No differences F > D > L measured F > L > D f o r a l l lengths L > D > F measured F > D > L for a l l lengths F > D > L measured XI XII L = Sympatric Loon Lake Dolly Varden D = A l l o p a t r i c Dickson Lake Dolly Varden F = A l l o p a t r i c Foley Lake Dolly Varden A l l differences are s i g n i f i c a n t at p 4 0 . 0 5 . 72 (Huxley, 1932). The three populations do not d i f f e r i n r e l a t i v e growth of the i n t e r o r b i t a l width ( F i g . 30; Table X), a measure of head width. However, Dickson Lake D o l l y Varden have considerably narrower heads than Dolly Varden from the other two lakes i n the size ranges measured. Foley Lake Dolly Varden smaller than 180 mm standard length have r e l a t i v e l y wider heads than Loon Lake Dolly Varden of corresponding sizes? larger Foley Lake f i s h have r e l a t i v e l y narrower heads. Loon Lake D o l l y Varden again vary most f o r t h i s character (Table X). The distance from the anal base to the pectoral f i n base, a measure of body length, i s greatest i n Foley Lake f i s h and le a s t for Loon Lake D o l l y Varden f o r f i s h of any size i n the range measured. Growth of t h i s character i n r e l a t i o n to standard length, and i t s v a r i a b i l i t y about the regression l i n e are greatest i n a l l o p a t r i c Foley Lake Dolly Varden and least i n sympatric Loon Lake D o l l y Varden, the reverse of the s i t u a t i o n f o r the head-related body parts (Table X). 9. Length-weight rel a t i o n s h i p s The c o e f f i c i e n t s (b) i n the equation log W = log a + b(log L) are 3.071, 2.835 and 2.573 f o r the Loon, Foley and Dickson Lake populations r e s p e c t i v e l y and these d i f f e r s i g n i f i c a n t l y (Appendix Table XIV). The Loon Lake Dolly Varden grow 73 heavier f o r t h e i r length with increasing length (slope departs from isometry, where b = 3»0; p<0 .05); f i s h from Foley and Dickson Lakes become l i g h t e r f o r t h e i r length at increasing lengths (p< 0.01 and p< 0.001 r e s p e c t i v e l y ) . For a l l standard lengths captured, Dickson Lake Dolly Varden are l i g h t e r than s i m i l a r sized f i s h from the other two populations, and have a s i g n i f i c a n t l y greater mean square deviation about the regression i n d i c a t i n g greater v a r i a b i l i t y ( F i g . 30). Foley Lake f i s h with standard lengths l e s s than 300 mm are heavier than s i m i l a r sized Loon Lake f i s h . 10. Morphometric differences between cutthroat trout and D o l l y Varden The average rate of growth of the upper jaw i n r e l a t i o n to standard length ( F i g . 32) i s the same for both cutthroat and D o l l y Varden from Loon Lake (Appendix Table XV), but the upper jaw length of cutthroat i s proportionately larger than that of s i m i l a r sized D o l l y Varden, comparing smaller f i s h . This s i t u a t i o n also occurred i n Marion Lake (Schutz and Northcote, 1972); Dolly Varden there, l i k e small Loon Lake D o l l y Varden, had smaller maxillaries than cutthroat and d i f f e r e d from the general description i n Clemens and Wilby (1961) i n having small subterminal mouths. However, owing to the marked increase i n r e l a t i v e growth of the upper jaw of Loon Lake D o l l y Varden larger than 140 mm standard length ( F i g . 32), t h e i r jaw length approaches that i 3 7^  LX3LTN LAKE SPRIN3 rjDLLY VARDEN QJTTr-RDAT 50. 100. 300-50. 10- ++ 50. 100. 300-Ui 15 10 .J. I I I I I 50. 100. H 1 300. 15. 10... I 1 I I I 50. 100. H 1 300-STANDARD LENGTH (MM) FIGURE 32. Relationship of upper jaw length, eye length, and weight to standard length f o r Loon Lake Do l l y Varden and cutthroat taken i n May 1972. 75 of cutthroat at standard lengths greater than 220 mm. Foley Lake D o l l y Varden smaller than 170 mm standard length ( F i g . 29) have larger jaws than si m i l a r sized cutthroat; the upper jaws of Dickson Lake Dolly Varden, on the other hand, are proportionately smaller than those of cutthroat at a l l lengths measured. Relative growth of the eyes of the two species do not d i f f e r i n Loon Lake, but cutthroat have proportionately larger eyes. Cutthroat trout are proportionately heavier than D o l l y Varden i n Loon Lake but the rate of increase of body weight with length i s the same f o r both populations. B. Laboratory Observations 1. S p a t i a l d i s t r i b u t i o n A l l o p a t r i c Dickson Lake Dolly Varden spent a greater percentage of a test period i n the upper h a l f of the tank than sympatric Loon Lake Dolly Varden (Table XI). The former also showed s i g n i f i c a n t l y more v a r i a b i l i t y between in d i v i d u a l s i n the amount of time spent i n the upper h a l f than the l a t t e r . The amount of time spent i n the upper h a l f of the tank by sympatric D o l l y Varden was not correlated with a c t i v i t y , but was so f o r a l l o p a t r i c Dolly Varden ( F i g . 33), because one i n d i v i d u a l was exceptionally active and spent over 70% of the t r i a l i n the upper h a l f , and another rested frequently on the substrate. The mean 76 TABLE XI. Results of s p a t i a l d i s t r i b u t i o n and a c t i v i t y comparisons. A. S p a t i a l d i s t r i b u t i o n * Arcsin transformed data % Number Population Mean time up Variance Mean time up tested LOON 36.46 36.94 35.3 9 DICKSON 48.62 171.74 56.3 13 Mean time up; DICKSON > LOON; p<0.01 from d = 2.925 with 18 d.f. using a modified "t* test to compare means of small samples with unequal variances (Bailey, 1959). Variance of time spent up: DICKSON> LOON F = 4.648; one t a i l e d test gives p<0.02. B. A c t i v i t y : Number Population Mean Variance tested LOON 77.2 415 9 DICKSON 98.9 2413 13 Mean a c t i v i t y : No difference. p> 0 . 1 0 from d = 1.426 with 17 d.f. using the modified ' t ' t e s t . Variance of a c t i v i t y : DICKSON > LOON F = 5.807; one t a i l e d test gives p< 0 . 0 1 . C. Correlation of time spent i n upper h a l f with a c t i v i t y : A l l f i s h A l l o p a t r i c Sympatric R ( c o r r e l a t i o n c o e f f i c i e n t ) 0.61 0.73 0.05 p <0.01 <0.01 NS 90° 77 80^  70" 60" °50° 0 E 40u CO a 30° Q. 0 20 w 10° o < 0^  0 o o O Oj o o o o Dickson Lake (allopatric) Loon Lake (sympatric) 100 Activity units 200 FIGURE 33: Correlation of time spent i n upper half of observation tank with a c t i v i t y . (See Table XI C) 78 a c t i v i t i e s of the two populations did not d i f f e r s i g n i f i c a n t l y ; however, a l l o p a t r i c D olly Varden showed more v a r i a b i l i t y i n a c t i v i t y between indivi d u a l s than did the sympatrics. 2. Presentation of novel prey Following capture and while being held i n outdoor stream tanks, Dolly Varden from Loon Lake took longer to condition to feed on small cubes of chicken l i v e r , presented s t i l l frozen at the surface where i n i t i a l l y they f l o a t e d . A l l Dickson Lake f i s h were eating such items within 5 days of capture (18 i n d i v i d u a l s observed) while Loon Lake f i s h required 14 days before a l l were feeding (12 indiv i d u a l s observed). Dickson Lake f i s h r a p i d l y learned to take l i v e r at the surface or while i t sank but usually rejected i t on the substrate. Loon Lake Dolly Varden i n i t i a l l y took l i v e r as i t sank but took 3 0 days to condition to take l i v e r from the surface; t h e i r surface grabs were rapid and they frequently missed the food item. Two experiments were conducted i n the observation tanks i n the spring of 1972 to t e s t whether a l l o p a t r i c Dolly Varden responded f a s t e r to novel prey than sympatric Dolly Varden a f t e r 6 months feeding on chicken l i v e r . A l l f i s h had been fed to s a t i a t i o n on chicken l i v e r three days before the test i n an attempt to standardize hunger l e v e l s , i . Earthworms Ten earthworms of uniform size were placed on the 79 bare substrate of the observation tank p r i o r to the introduction of a test f i s h . The f i s h was allowed ten minutes i n the tank to respond to the prey, before being returned to i t s holding tank. Three out of f i v e a l l o p a t r i c f i s h and none of the f i v e sympatric f i s h ate earthworms (p = 0.085» Fisher Exact Test); although t h i s was not s t a t i s t i c a l l y s i g n i f i c a n t , the difference was i n the expected d i r e c t i o n . i i . Chironomid larvae Twenty larvae were scattered randomly over the sand and l e a f l i t t e r substrate. Fish were introduced i n d i v i d u a l l y f o r a 10 minute te s t period. The time to the f i r s t grab was recorded (Appendix Table XVI). At the end of the t e s t period the f i s h was removed and the remaining chironomid larvae were counted to determine how many had been eaten. Following the tes t , each f i s h was fed to s a t i a t i o n with chicken l i v e r , and the tes t was repeated three to four days l a t e r , A l l o p a t r i c f i s h responded f a s t e r to the prey than sympatrics, considering up to three successive tests to encourage unresponsive f i s h to feed (Appendix Table XVI). A l l o p a t r i c Dolly Varden appeared to eat larvae more r e a d i l y during the f i r s t 10 minute test than did sympatric D o l l y Varden (Table XII). The one a l l o p a t r i c f i s h which did not feed then fed immediately when i t was tested a second time, as did one of the sympatric Dolly 80 TABLE XII. Comparison of numbers of a l l o p a t r i c and sympatric D o l l y Varden eating chironomid larvae during t h e i r f i r s t 10 minute exposure to 20 larvae scattered on a sand and l e a f l i t t e r substrate. A l l o p a t r i c Sympatric Feeding 7 1 Not feeding 1 3 p = 0.065, Fisher Exact Test Varden. The l a t t e r , however, only took one l a r v a and f a i l e d to eat on the t h i r d t e s t . The two remaining sympatric D o l l y Varden f a i l e d to feed on chironomid larvae during any of the three t e s t s although, l i k e a l l the other f i s h , they were active during the t e s t period. The one sympatric i n d i v i d u a l that fed on the f i r s t t e s t ate 75$ of the larvae presented; most of the a l l o p a t r i c f i s h took more than t h i s . A l l o p a t r i c D olly Varden took more larvae on the f i r s t t est than sympatric D o l l y Varden (p = 0.014; Mann Whitney U test f o r non-normal data, where U = 3, n 1 = 8, n 2 = 4; Siegel, 1956). 3. E f f i c i e n c y of feeding on planktonic Chaoborus larvae by sympatric and a l l o p a t r i c Dolly Varden In three successive exposures of sympatric and a l l o p a t r i c D o l l y Varden to planktonic Chaoborus larvae, the capture e f f i c i e n c y of the sympatric f i s h lay well within the range of that of the a l l o p a t r i c f i s h , considering only t e s t s 81 1.0-0.9-0.8-0.71 V— a • S 0.6-0.5-*- 0.4-•o 0.3-ro o 0.2-ro O 0.1-A. 0 o Allopatric A Sympatric » 2 *1 40 80 120 160 Number of grabs per 10 mi nutes(ef f ort) B. 200 e o o o o o o o o o ro CL E >» co ro a o FIGURE 34. E f f i c i e n c y of capture of Chaoborus larvae by sympatric and a l l o p a t r i c Dolly Varden. A. In re l a t i o n s h i p to e f f o r t . B. For those ind i v i d u a l s making an e f f o r t greater than 8 grabs/minute. 1.0 1 1 *T Test 1 Test 2 Test 3 FIGURE 35. E f f i c i e n c y of capture (catch/grab) of Chaoborus larvae by sympatric and a l l o p a t r i c D o l l y Varden i n successive t r i a l s . 83 i n which i n d i v i d u a l s made more than 8 grabs per minute (F i g . 3^). This l e v e l of e f f o r t was chosen to eliminate r e s u l t s from two sympatric indiv i d u a l s (#2, #3). whose catch e f f i c i e n c i e s decreased markedly through the te s t series, neither of them capturing any prey i n the f i n a l t e s t ( F i g . 35). Both f i s h were recent captures and presumably were unused to handling. V. DISCUSSION The aim of t h i s study was to investigate the nature and extent of the character displacement evident i n sympatric and a l l o p a t r i c Dolly Varden populations i n small lakes. This follows from studies conducted by Andrusak (MS 1968) and Schutz (MS 1969)? more emphasis was placed on f i s h from a l l o p a t r i c populations, both i n the f i e l d and i n laboratory observations. Loon and Dickson Lake D o l l y Varden populations were chosen f o r the primary comparison as these two lakes were f a i r l y s i m i l a r i n t h e i r limnology, although Dickson Lake had a shorter summer and plankton abundance was les s i n the summer than i n Loon Lake. Foley Lake was quite d i f f e r e n t , with abundant benthos and n e g l i g i b l e amounts of zooplankton. D o l l y Varden were associated with the substrate i n Loon Lake and moved out of the s u b l i t t o r a l zone into deeper water i n late summer. In autumn, they were found 84 inshore again and also i n the water column, showing a s i m i l a r breakdown i n s p a t i a l segregation to that reported by Andrusak (MS 1968) f o r Marion Lake. S p a t i a l segregation i n summer was f a r more apparent i n Loon than i n Marion Lake. Cutthroat trout were more abundant i n Loon than i n Marion Lake; capture r a t i o s of char to trout were 3«25 and 0.34 respectively. In Marion Lake, Dolly Varden were captured i n the water column throughout the summer, mainly i n the lower h a l f . In Loon Lake, D o l l y Varden were confined to the substrate during the summer and early f a l l ; cutthroat were not excluded from t h i s region although numbers here were low i n early f a l l . In Dickson Lake, Dolly Varden were captured throughout the water column i n July, August and September both day and night. These r e s u l t s appear to c o n f l i c t with those of Andrusak (MS 1968), but re-examination of his o r i g i n a l data suggests that f i s h may have been captured during the day. Stomach contents provided i n d i r e c t evidence for v e r t i c a l migration of some ind i v i d u a l s and t h i s may be a thermoregulatory mechanism for energy conservation i n the face of lim i t e d food resources, s i m i l a r to that proposed by Brett (1971) f o r juvenile sockeye salmon (Oncorhynchus  nerka). The close association of the f i s h with the thermocline i n August 1971 and t h e i r more random d i s t r i b u t i o n i n J u l y and September 1972, when thermoclines were absent or only weakly present, suggests a possible r e l a t i o n s h i p 85 of t h e i r d i s t r i b u t i o n with temperature. Nilsson (1965) points out that Salvelinus alpinus are eurythermal: A r c t i c char captured at 30 m had f r e s h l y caught imagines of Lycoridae i n t h e i r stomachs. D o l l y Varden captured i n Dickson Lake at 20 m had eaten adult dipterans. Groups of D o l l y Varden were observed feeding at the surface f o r several hours at a time when the surface temperature was 21°C i n August 1971» showing that they were not excluded by these high temperatures from any portion of the lake. D o l l y Varden from Foley Lake were mostly captured close to the substrate but they were not confined there; some were caught at the surface i n the middle of the lake. Echo sounding records suggest a more midwater d i s t r i b u t i o n than do the netting r e s u l t s . In general, the sympatric Dolly Varden were associated with the substrate and with greater depths, as reported f o r a number of other lakes i n B r i t i s h Columbia where they coexist with trout species (Andrusak and Northcote, 1970), while the a l l o p a t r i c Dolly Varden were not so s p a t i a l l y r e s t r i c t e d . Loon Lake Do l l y Varden fed increasingly on benthos and l e s s on zooplankton as the season progressed, u n t i l October, when they moved back into the water column and zooplankton became more important. Large f i s h became even more benthophagic than small f i s h i n the summer and f a l l ; they took less zooplankton than small f i s h presumably 86 because at t h e i r s i z e , i t was no longer e f f i c i e n t to do so.. Andrusak (MS 1968) showed si m i l a r size related changes i n the diet of Marion Lake Dolly Varden. As summer progressed and they became more benthophagic, Loon Lake Dol l y Varden became les s s i m i l a r i n diet to Dickson Lake D o l l y Varden as well as to cutthroat trout. The diet of the cutthroat trout i s f a i r l y s i m i l a r to that of Dickson Lake Dolly Varden although zooplankton, more abundant i n Loon Lake, i s more important f o r trout. Cutthroat trout mainly took zooplankton, the percentage occurrence of copepods increasing, as i n Marion Lake (Andrusak, MS 1968), and of cladocerans decreasing through the season. As i n Marion Lake, many Dolly Varden took cladocerans and there was a similar peak percent occurrence of copepods i n midsummer. Insects were important to cutthroat i n the spring and f a l l and some chironomid pupae were eaten i n the spring and summer, but f a r less than i n Marion Lake. Increasing amounts of chironomids and Chaoborus larvae taken by trout caught at the same depths as Do l l y Varden i n ea r l y f a l l suggest that competition may st a r t to occur f o r t h i s prey category as cutthroat invade the food refuge. However, Andreasson (1971) states that s i m i l a r i t y of d iet indicates lack of competition owing to superabundance of a common prey. One would have to determine l e v e l s of prey production and requirements of the two competitors to be able 8? to state whether competition i s occurring or not) however, i t i s d i f f i c u l t to determine whether demand exceeds supply i n the f i e l d (Northcote, 1954). Dickson Lake Dolly Varden fed on a l l categories of food that were av a i l a b l e . Cannibalism occurred but was not common. The small sizes of prey available i n Dickson Lake may put a l i m i t on the size to which Dolly Varden grow, owing to energy expenditure required to capture s u f f i c i e n t food, unless the f i s h become piscivorous (Andreasson, 1971; Nikolsky, 1963» p. 277). Fish larger than 210 mm were rare, although two f i s h of 360 and 380 mm fork length were caught i n 1967 and 1972 respectively. The absence of smaller f i s h i n Foley Lake may be explained on t h i s basis; there were n e g l i g i b l e amounts of zooplankton and the remaining prey items were probably a l l too large f o r small f i s h to capture or to handle e f f i c i e n t l y , e s p e c i a l l y large nymphs. These made up a large proportion of the food taken throughout the season. Small f i s h presumably stayed i n the inflow creek u n t i l they were over at least 150 mm fork length before entering the lake. The wide range of prey exploited, p a r t i c u l a r l y by some ind i v i d u a l s , i s probably p a r t l y due to the large size of these f i s h compared to those from Loon and Dickson Lakes, as well as to the absence of a competitor i n Foley Lake. Reduction i n niche width i s well i l l u s t r a t e d by the average number of prey categories taken per i n d i v i d u a l 88 i n the three lakes. The two a l l o p a t r i c populations take consistently more categories than the sympatric D o l l y Varden population. The reduction i n average number of prey categories per i n d i v i d u a l as the season progresses i n Loon Lake i s probably a r e s u l t of lower amounts of insects and motile benthos being taken by sympatric D o l l y Varden, which are no longer present i n surface and onshore regions of the lake. Around Loon Lake there appeared to be few suitable spawning s i t e s . Loon Lake D o l l y Varden entered the creeks i n the f a l l and cutthroat moved into the creeks l a t e r i n the winter (P r o v i n c i a l Fish and W i l d l i f e trap records, I969-70). I t i s possible that spawning trout interfered with Dolly Varden redds; the low population l e v e l s of Dolly Varden i n Loon Lake may r e s u l t p a r t l y from t h i s . Loon Lake D o l l y Varden became proportionately heavier with increasing length suggesting that food was r e a d i l y available f o r the larger size classes. The size classes were d i s t i n c t from one another even i n older age classes; t h i s may be due both to the small population and to the probable short spawning season. Spawning s i t e s appeared to be abundant i n Dickson Lake. Absence of a competitor may r e s u l t i n a longer spawning season; t h i s , coupled with marked growth depensation (Brown, 1946; Poliakov, 1958; Magnuson, 1962) owing to high recruitment and concomitant low food a v a i l a b i l i t y would 89 r e s u l t i n considerable size differences among the f r y i n the spawning creeks. Interactions among similar sized f r y are greatest (Chapman and Bjornn, 1968)? dominant f i s h can e s t a b l i s h higher growth rates (Onodera, 1967) which enable them to feed on larger organisms, as the size of food taken i s related to the size of the predator. Spreading of the length frequency d i s t r i b u t i o n i n the a l l o p a t r i c s i t u a t i o n may allow the population as a whole to exploit a wider size range of foods. Adjacent year classes start to overlap as fast growing i n d i v i d u a l s catch up with slow growing i n d i v i d u a l s of the previous year class; t h i s can be seen from the length frequency data presented f o r Dickson Lake where year classes were hardly separable on such a basis. V a r i a b i l i t y about the regression of weight on standard length was s i g n i f i c a n t l y greater for Dickson Lake D o l l y Varden than f o r the other two populations; t h i s may be another expression of growth depensation. In addition, Dickson Lake f i s h departed considerably from isometry and grew proportionately l i g h t e r with increasing length. These e f f e c t s could both be due to low food l e v e l s i n the lake, the plankton being one tenth the abundance of Loon Lake and lar g e l y composed of small Bosmina i n the summer. Although corresponding age classes of Loon Lake Dol l y Varden and cutthroat were f a i r l y s i m i l a r i n length throughout the season, adult cutthroat trout had 90 proportionately larger upper jaws than sympatric D o l l y Varden f o r most of the length range measured; trout i n Marion Lake also had proportionately larger jaws (Schutz, MS 1969). This may enable them to take a larger range of prey size s (Northcote, 1954; Keast and Webb, 1966) than Do l l y Varden of the same age; both Marion and Loon Lake cutthroat trout took vertebrates while Dolly Varden i n these lakes did not. Schutz (MS 1969) suggested that the small scoop-like mouths of D o l l y Varden were well adapted to bottom feeding. However, Do l l y Varden from Foley Lake had proportionately larger jaws than cutthroat, comparing f i s h smaller than 170 mm standard length; from the time they enter the lake, Foley Lake Dolly Varden must spec i a l i z e on r e l a t i v e l y large benthic prey whereas the other Dolly Varden populations and the cutthroat population can take zooplankton when small. Unlike r e l a t i v e growth of the upper jaws of both cutthroat and Loon and Dickson Lake Do l l y Varden, which was p o s i t i v e l y allometric, growth of the upper jaw i n r e l a t i o n to standard length i n Foley Lake f i s h was isometric i n the range measured (suggesting an e a r l i e r growth stanza i n which r e l a t i v e growth may have been much greater i n response to the large prey available (Martin, 1949)) . The proportional size of the jaws of Dickson Lake Do l l y Varden increased r e g u l a r l y with increasing standard length; concomitantly, more benthic prey and other larger items such as the occasional conspecific were taken. In 91 contrast, the Loon Lake Do l l y Varden showed a marked s h i f t to benthic prey at standard lengths greater than 140 mm (155 mm fork length); before a t t a i n i n g t h i s s i z e , r e l a t i v e growth of t h e i r upper jaws was negatively allometric, but a marked i n f l e c t i o n was evident at t h i s length. Relative growth became so strongly p o s i t i v e l y allometric that upper jaw lengths of the largest Loon Lake Dolly Varden captured were almost the same as those of cutthroat of the same length. Relative i n t e r o r b i t a l width, probably a f a i r measure of jaw width, appears s i m i l a r l y to r e f l e c t the influence of benthic feeding. That of Dickson Lake Dol l y Varden was smallest while Foley Lake f i s h had wider heads than Loon Lake Do l l y Varden up to a standard length of 180 mm. A benthic form of stickleback, Gasterosteus sp. i n Paxton Lake, B.C., with a proportionately wider mouth than a coexisting limnetic form took l a r g e l y macrobenthos while the l a t t e r took l a r g e l y zooplankton (Larson, MS 1972). Martin (1949) showed that differences i n body form could be produced by c o n t r o l l i n g diet during early growth i n rainbow trout (Salmo g a i r d n e r i ) . R e l a t i v e l y large eyes and heads resulted from malnutrition. Whereas most differences i n body proportions were re l a t e d to d i f f e r e n t body sizes at the time of e a r l i e r growth i n f l e c t i o n s , differences i n t h i s case appeared to r e s u l t from changes i n regression slope. I t appears that the 92 d i f f e r e n t r e l a t i v e growth rates reported here f o r the three D o l l y Varden populations may also he related to changes i n d i e t . The proportions of these body parts and t h e i r r e l a t i v e growth h i s t o r i e s are affected by environmental factors and must c e r t a i n l y also be influenced by the genotype. The growth i n f l e c t i o n contributed considerably to the increased v a r i a b i l i t y (mean square deviation) of the upper jaw length of sympatric Loon Lake Dolly Varden i n r e l a t i o n to standard length when compared with the a l l o p a t r i c populations. Comparisons of r e l a t i v e upper jaw growth of Loon Lake D o l l y Varden smaller than 140 mm (standard length) with f i s h of similar size from Dickson Lake, and of f i s h larger than 140 mm with f i s h of sim i l a r sizes from Dickson and Foley Lakes showed that the v a r i a b i l i t y within each stanza of the upper jaws of the sympatric D o l l y Varden was no greater than that of the a l l o p a t r i c populations. Similar i n f l e c t i o n s were apparent i n the r e l a t i v e growth of several other head parts of the Loon Lake Dolly Varden. These head parts are probably a l l i n t e r r e l a t e d i n the same 'morphogenetic f i e l d o£ influence* (Huxley, 1932; Kanep, 1971); McCart (MS 1963) demonstrated that heads, eyes and jaws of d i f f e r e n t whitefish populations showed p a r a l l e l r e l a t i v e growth patterns. Such growth i n f l e c t i o n s may also contribute towards the higher v a r i a b i l i t y of these 93 head parts compared with those of the a l l o p a t r i c populations. Phenotypic v a r i a b i l i t y , i f expressed as the mean square deviation about regression of the body part on standard length, i s not reduced i n the population with reduced niche width, i e . i n sympatric Loon Lake Do l l y Varden. However, owing to more d i s t i n c t modality of the length d i s t r i b u t i o n within year classes i n Loon Lake Dol l y Varden, jaw lengths are also d i s t r i b u t e d as a series of modes ( F i g . 32); i n the a l l o p a t r i c Dickson Lake population, jaw lengths are more evenly d i s t r i b u t e d ( F i g . 29) over the size range of f i s h captured, owing p a r t l y to the large population size but also to the greatly increased growth depensation i n t h i s lake. This allows e x p l o i t a t i o n of a wider range of prey by each year class with overlap of prey size requirements of adjacent year classes. Thus, i n e f f e c t , i t appears that Van Valen's (I965) hypothesis may be supported; the phenotypic v a r i a b i l i t y , i f expressed as the v a r i a b i l i t y of jaw size within a year class, may be less i n the population with reduced niche width. I t can be seen that continuous growth of f i s h leads to complicated interpretations of character displacement and of v a r i a b i l i t y changes r e s u l t i n g from the presence of competing species, even though one species may be compared i n the presence or absence of only one competitor. Work with birds usually involves a large number 94 of other species present, but complications owing to continuous growth are minimised. Van Valen (1965) compared the v a r i a b i l i t i e s of b i l l measurements of several species of birds on mainland A f r i c a and on the Canaries or Azores and showed increased v a r i a b i l i t y on the islands where he assumed niche widths were greater. This approach has been used by numerous other authors (eg. Crowell, 1962; Grant, 1968). Use of meristic counts lessens the problems associated with growth as the counts were not, i n most cases, correlated with body length f o r these sizes of f i s h . Loon and Dickson Lake Dolly Varden populations did not d i f f e r s i g n i f i c a n t l y from one another i n g i l l raker numbers, nor from Loon Lake cutthroat. G i l l rakers i n both species were r e l a t i v e l y short unlike the long g i l l rakers associated with planktivores l i k e Coregonus peled (Kanep, 1971), where numbers of g i l l rakers correspond to actual conditions of feeding and growth i n lakes. Foley Lake D o l l y Varden, which took no zooplankton, had a s l i g h t l y lower (NS) average number of g i l l rakers; i n s u f f i c i e n t numbers of lakes were studied to determine i f c o r r e l a t i o n between di e t and g i l l raker number existed as shown by Kliewer (19^9) f o r Coregonus. The a l l o p a t r i c Dickson and Foley Lake populations, which consumed vertebrates and considerable amounts of insects, had higher numbers of p y l o r i c caeca, although 95 food s p e c i a l i z a t i o n by indi v i d u a l s correlated with t h e i r caeca numbers was not evident. V a r i a b i l i t y was also greater i n the a l l o p a t r i c populations. P i t t and Chehalis Lake Dolly Varden resemble Loon Lake Dolly Varden i n having low mean p y l o r i c caeca numbers of 22.1 and 24 respectively (McPhail, 1961)} i n both lakes, one or more species of trout i s present. P y l o r i c caeca act as extensions to the anterior end of the in t e s t i n e and have been shown to have p r o t e o l y t i c functions (Dobrovolov, 1966). Piscivorous Baikal grayling (Thymallus a r c t i c u s baicalensis) have an average of 19.1 caeca while grayling (T. a r c t i c u s baicalensis infrasubsp. brevipinnis) which feed on amphipods and caddis larvae have an average of 15.3 (Svetovidov, 1953). Savvaitova (I96I) reported a c o r r e l a t i o n of p y l o r i c caeca number with diet i n Kamchatka Salvelinus alpinus. The piscivorous form had most p y l o r i c caeca; the form feeding on aquatic insect larvae had the l e a s t , while numbers were intermediate i n the form that ate molluscs. Martin and Sandercock (1967). however, could not f i n d a c o r r e l a t i o n i n diet with p y l o r i c caeca number i n the three populations of S. namaycush that they studied. Diet i s probably not the only factor determining p y l o r i c caeca numbers (McPhail, MS 1959). Winters are more severe i n Dickson and Foley Lakes and lower temperatures are often correlated with an increase i n meristic counts 96 (Barlow, 1961). I f , as i s suggested above, a l l o p a t r i c D o l l y Varden spawn over a longer period also, some w i l l develop i n warmer weather, but no warmer than i n Loon, P i t t or Chehalis Lakes. This should set a lower l i m i t on the range of p y l o r i c caeca numbers? i t i s 19 f o r a l l but the Chehalis Lake population, where i t i s 22. In the laboratory, i n d i v i d u a l Loon Lake Do l l y Varden spent a smaller proportion of a te s t period i n the upper h a l f of an observation tank compared with Dickson Lake Dolly Varden. This p a r a l l e l s t h e i r behaviour i n the f i e l d ? however*, i t cannot be argued that t h i s demonstrates selec t i v e segregation. The Loon Lake f i s h , captured as adults, may have learnt to avoid unpleasant encounters with trout or to exploit benthos more e f f i c i e n t l y than trout by c r u i s i n g close to the substrate; Loon Lake Dolly Varden and cutthroat trout were held together i n the laboratory so reinforcement f o r such behaviour probably continued. Sympatric and a l l o p a t r i c D olly Varden should be reared under i d e n t i c a l conditions i n laboratory stream tanks and then tested to determine whether such behaviour patterns p e r s i s t . Similar experiments could be performed on groups of each population reared with s i m i l a r sized cutthroat. The stenophagia shown by Loon Lake Dolly Varden may r e f l e c t the low average number of prey items per i n d i v i d u a l i n the lake. Prey switching does, however, occur i n the f i e l d as seasonal changes i n stomach contents 97 suggest; 'superabundant' insects i n the spring on the surface of Marion Lake are preyed on by D o l l y Varden but, unlike the cutthroat, they did not feed on them immediately (Andrusak and Northcote, 1971). In the laboratory, they were slower than trout to switch to surface prey and increased s t e a d i l y i n e f f i c i e n c y over four days (Schutz and Northcote, 1972). Dickson Lake D o l l y Varden were, however, r e l a t i v e l y euryphagic and learned to switch prey rapidly; t h i s p l a s t i c i t y of behaviour may be advantageous when food a v a i l a b i l i t y i s low (Nikolsky and Pikuleva, 1958) as well as probably r e f l e c t i n g the wide range of food items taken by f i s h i n the lake. Both Dickson and Loon Lake Do l l y Varden hunted the substrate i n a s i m i l a r way to that described f o r Marion Lake D o l l y Varden (Schutz and Northcote, 1972), with f a s t c r u i s i n g and frequent turning e s p e c i a l l y following a prey capture; they both fed on planktonic Chaoborus with s i m i l a r e f f i c i e n c y i f they made more than a threshold amount of e f f o r t . With no food present on the bottom i n the s p a t i a l tests, sympatric D o l l y Varden s t i l l swam closer to the substrate than a l l o p a t r i c Dolly Varden, The only difference i n treatment was that they had been held with trout while the a l l o p a t r i c f i s h had been held with other a l l o p a t r i c i n d i v i d u a l s , or alone i n several cases; thus sympatric D o l l y Varden may eat l a r g e l y benthic food because 98 they swim closer to the substrate than a l l o p a t r i c D o l l y Varden. Evidence provided i n t h i s study confirms work by Andrusak (MS 1968) which showed that coexisting D o l l y Varden and cutthroat are segregated, though not completely, with respect to food and space, i n p a r t i c u l a r during the summer. The patterns of change of growth rate of the upper jaw may be connected with changes i n the diet, larger jaws giving an obvious advantage i n feeding on larger and more varied prey. Diet i s influenced to a large extent by the presence or absence of a competitor, but as can be seen from comparisons of Dickson and Foley Lakes, population numbers, a v a i l a b i l i t y of small sized prey f o r small f i s h and a v a i l a b i l i t y of intermediate and large prey sizes f o r larger f i s h also influence the diet of the f i s h , complicating discussion of character displacement as a response to the presence of a competing species. P y l o r i c caeca numbers are also influenced by d i e t , but again t h i s character may be influenced to a greater or l e s s e r extent by environmental factors such as the temperature regime of development. As body form i s determined by both genetic and environmental e f f e c t s and behaviour by both the genotype and the e f f e c t s of learning, i t i s impossible to state c a t e g o r i c a l l y to what extent the segregation observed between the two coexisting species i s 'i n t e r a c t i v e ' or ' s e l e c t i v e ' . 99 VI. CONCLUSIONS 1. Coexisting D o l l y Varden and cutthroat trout were s p a t i a l l y segregated i n Loon Lake; Dolly Varden were confined to deep water close to the bottom during the summer while cutthroat trout were widely d i s t r i b u t e d throughout the lake. A l l o p a t r i c D olly Varden i n Dickson and Foley Lakes were present throughout the water column during the summer. 2. The average number of prey categories taken per i n d i v i d u a l by sympatric Dolly Varden was l e s s than that taken by a l l o p a t r i c Dolly Varden. Sympatric Dolly Varden ate mainly benthos; smaller i n d i v i d u a l s took more zooplankton. Dickson Lake Dolly Varden took mainly water column and surface food, although larger individuals took more benthos and some cannibalism occurred. Foley Lake f i s h took l a r g e l y benthic prey, though chironomid pupae, tadpoles and surface insects were also eaten. 3. Loon Lake D o l l y Varden grew proportionately heavier with increasing length. The year classes remained d i s t i n c t and the population size was small, possibly due to l i m i t e d spawning f a c i l i t i e s and interference of redds by later-spawning cutthroat. Considerable overlap i n length between year classes occurred i n Dickson Lake. The small c o e f f i c i e n t and large mean square deviation from regression 100 i n the allometric length-weight equation are probably-further indications of the unfavourable r e l a t i o n s h i p of population size to food. Few small f i s h were taken i n Foley Lake, possibly due to s c a r c i t y of suitable small sized food. 4. A l l o p a t r i c populations of Dolly Varden had higher mean p y l o r i c caeca counts than did the sympatric population. This was interpreted i n terms of character displacement r e s u l t i n g from a wider spread of diet i n the absence of trout. 5. Proportionately larger upper jaws appeared to be correlated with increased consumption of benthic prey. Separation of the growth stanzas showed that v a r i a b i l i t y of the r e l a t i v e upper jaw length within each stanza of the sympatric Loon Lake population was no greater than that of the a l l o p a t r i c Dickson Lake f i s h of corresponding s i z e s . Relative growth of the upper jaws i n Foley Lake D o l l y Varden d i f f e r s from that of the other two populations, perhaps owing to the need f o r larger jaws i n small f i s h when faced only with r e l a t i v e l y large prey items. 6. Laboratory studies showed that a l l o p a t r i c D o l l y Varden were l e s s substrate oriented and more variable i n s p a t i a l preferences than sympatric D o l l y Varden. They 101 were also more euryphagic, taking novel prey more r e a d i l y . Both populations could feed with si m i l a r e f f i c i e n c i e s on planktonic Chaoborus when they exerted more than a threshold amount of e f f o r t . These studies suggest that behavioural character displacement occurs i n the sympatric population. Whether these t r a i t s have been selected for i n the sympatric population, s t a b i l i z i n g them i n the genotype, was not established. 102 BIBLIOGRAPHY Andreasson, S.t 1971. Feeding habits of a sculpin (Cottus gobio L. 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Toronto, Stud., B i o l . Ser., No. 58. Publ. Ontario Fi s h . Res. Lab., No. 70. 91 pp. Nikolsky, G.V., 1963. The Ecology of Fishes, t r . L. Bir k e t t . A.P., London and New York. 352 pp. Nikolsky, G.V. and V.A. Pikuleva, 1958. Adaptive significance of the range of v a r i a b i l i t y i n s p e c i f i c features of organisms. Zool. Zhurn., 37t 972-986. (In Russian; English summary) Nilsson, N.-A., I965. Food segregation between salmonid species i n North Sweden. Rept. Inst. Freshwater Res., Drottningholm, 46s 58-78. Nilsson, N.-A., I967. Interactive segregation between f i s h species, pp. 295-313 i n S.D. Gerking (ed.), The B i o l o g i c a l Basis of Freshwater Fish Production. Blackwell S c i . Publ., Oxford and Edinburgh. Northcote, T.G., 1954. Observations on the comparative ecology of two species of f i s h , Cottus asper and Cottus rhotheus, i n B r i t i s h Columbia. Copeia: 25-2BT Onodera, K., 1967. Some aspects of behaviour influencing production, pp. 345-355 i n S.D. Gerking (ed.), The B i o l o g i c a l Basis of Freshwater Fish Production. Blackwell S c i . Publ., Oxford and Edinburgh. Poliakov, G.D., 1958. The adaptive significance of the v a r i a b i l i t y of the weight of yearling carp. Zool. Zhurn., 37* 403-414. (In Russian; English summary) Savvaitova, K.A., I96I. I n t r a s p e c i f i c b i o l o g i c a l forms of Salvelinus alpinus (L.) i n Kamchatka. Vopr. I k h t i o l . , It 695-706. (Fish. Res. Bd. Canada Trans. No. 795) Schutz, D.C., MS I969. An experimental study of feeding behaviour and in t e r a c t i o n of coastal cutthroat trout (Salmo c l a r k i c l a r k i ) and Dolly Varden (Salvelinus malma). M.Sc. Thesis, Department of Zoology, University of B r i t i s h Columbia. 81 pp. 106 Schutz, D.C. and T.G. Northcote, 1972. An experimental study of feeding behaviour and int e r a c t i o n of coastal cutthroat trout (Salmo c l a r k i c l a r k i ) and Dolly Varden (Salvelinus malma). J . Fish . Res. Bd. Canada, 29s 555-565. Seaburg, K.G., 1957. A stomach sampler f o r l i v e f i s h . Prog. Fish-Cult., 19: 137-139. Siegel, S., 1956. Nonparametric S t a t i s t i c s for the Behavioural Sciences. McGraw-Hill Book Co. Inc., New York. 312 pp. Svetovidov, A.N., 1953. On the cor r e l a t i o n between the numbers of p y l o r i c caecae and the feeding behaviour of f i s h e s . In Essays on General Problems i n Ichthyology, U.S.S.R. Academy of Sciences Press. (In Russian) Van Valen, L., 1965. Morphological v a r i a t i o n and width of e c o l o g i c a l niche. Am. Nat., 99s 377-390. APPENDIX TABLE I. Seasonal changes of stomach contents (average percent volume) of Loon Lake Do l l y Varden and cutthroat i n 1 9 7 2 . Benthic prey Water column prey 1 2 1 Chironomid Surface Season N Stati c Motile Vertebrates J pupae Zooplankton insects Miscellaneous D o l l y Varden» Spring 75 9.5 32.0 0 0.8 53.4 1.1 4.7 Summer 33 22.1 23.0 0 t r 39.3 4.9 9.7 F a l l 6 4 62.4 10.8 0 0.2 13.1 0 13.4 Cutthroat captured i n the same depth i n t e r v a l s as Dolly Varden: Spring 2 4 0 7.7 4.2 6.6 41.4 2 8.4 11.7 Summer 33 8.0 7.2 0 9.1 6 4.4 7.8 3.8 F a l l 20 12.8 3.4 6.1 2.0 63.6 9.6 2.4 Cutthroat captured i n midwater and at the surface: Spring 63 0.1 2.3 0.1 9.5 47.1 36.3 4.6 Summer 2 5 0.7 8.1 0 16.1 59.1 14.7 1.4 F a l l 38 2.1 2.3 2.5 0.6 71.0 16.7 4.6 1. Chironomid and Chaoborus larvae and Pisidium spp. 2. Aquatic insect larvae, amphipods, planorbid gastropods. 3. Salamanders. APPENDIX TABLE I I . Seasonal changes of stomach contents (average percent volume) of a l l o p a t r i c D olly Varden from Dickson and Foley Lakes. Month N Benthic S t a t i c 1 prey M o t i l e 2 Vertebrates-^ Water column prey Chironomid pupae Zooplankton Surface insects Miscellaneous Dickson Lake* *June 29 5 1 3 16 0 75 0 J u l y 147 6.2 12.8 1.0 9.8 36.3 26.8 7.1 *July 30 0 5 3 7 31 47 7 September 75 1.7 13.4 1.3 4.9 49.8 22.7 6.2 •October 15 9 1 0 0 67 18 5 Foley Laket May 21 0.4 80.2 2.5 4.0 0 9.8 3.2 J u l y 14 22.4 32.8 16.0 5.9 0 12.2 10.7 September 11 7.7 56.5 0 9.0 0 22.9 3.9 1. Chironomid larvae, Pisidium spp. 2. Aquatic insect larvae, amphipods (Dickson Lake only), planorbid gastropods, Simulium larvae (Foley Lake only). 3. D o l l y Varden (Dickson Lake only), tadpoles (Foley Lake only). * 1967 data from Andrusak (MS 1968). A l l other data from 1972. O co 109 APPENDIX TABLE I I I . Average number of major food categories taken per i n d i v i d u a l D o l l y Varden. Lake LOON Number Season of f i s h Spring Summer F a l l DICKSON Summer F a l l FOLEY Spring Summer F a l l 57 36 69 148 77 21 16 12 Mean and 99% confidence l i m i t s Variance 2.24 + 0.30 1.37 1.89 ± 0.37 1.31 1.68 + 0.20 0.69 3.00 + 0.19 1.42 2.86+0.18 O.69 3.05 ± 0.53 1.55 3.37 ± 0.94 3.72 3.00 + 0.80 2.00 As Simulium larvae were not present i n Loon or Dickson Lakes, Simulium occurring i n Foley Lake f i s h stomachs were grouped together with 'motile benthos' as t h i s was the category with which they were most often associated. APPENDIX TABLE IV. Size related differences of stomach contents (average percent volume) of Loon and Dickson Lake Dolly Varden i n 1972. Benthic prey Water column prey 1 2 ~ 2i Chironomid Surface Season Size N Stati c Motile^ Vertebrates pupae Zooplankton insects Miscellaneous Loon Lakes Spring >155 35 15.9 29.4 0 1.0 40.9 1.3 9.8 <155 40 8.3 31.3 0 0.6 58.0 1.0 0.2 Summer >155 25 22.6 25.2 0 t r 36.0 2.4 12.5 <155 8 20.4 16.3 0 0 50.0 12.5 0.8 F a l l >155 54 61.6 11.0 0 t r 10.0 0 14.5 <155 11 55.8 9.1 0 0.9 27.0 0 7.1 Dickson Lakes Summer >155 56 7.5 3.3 1.7 13.4 17.9 34.6 9.9 <155 92 5.1 12.3 o.5 7.6 47.2 21.8 5.3 F a l l >155 25 2.5 21.3 3.9 7.3 37.8 21.2 5.7 ^155 50 1.0 8.7 0 3.7 56.7 23.9 5.8 1. Fork length (mm). 2. Chironomids, Pisidium spp. and Chaoborus larvae (Loon Lake only). 3. Aquatic insect larvae, amphipods, planorbid gastropods (Dickson Lake only). 4. Dolly Varden (Dickson Lake only). I l l For APPENDIX TABLES V - XIV: Relationships of body parts or weight (y) to standard length (x) are given using log-transformed 1972 data. Y = A + b(X - 1) was calculated where Y = l°g ey and X = log ex.. Differences i n mean square, slope and A between the D o l l y Varden populations are shown when s i g n i f i c a n t at p «0.05, calculated using analysis of covariance. APPENDIX TABLE V. Relationship of head length to standard length. Lake Mean square Slope A Number of f i s h LOON 1.772 x 10"3 1.057 3.560 177 DICKSON 1.057 x 10~3 1.015 3.475 232 FOLEY 1.430 x 10"3 0.932 3.991 49 Differences s i g n i f i c a n t at p^0.05: Mean square: LOON >DICKSON Slope: LOON and DICKSON >FOLEY A: FOLEY >LOON >DICKSON See Figure 28. 112 APPENDIX TABLE VI. Relationship of upper jaw length to standard length. Lake Mean square Slope A Number of f i s h LOON 6.327 x 10~ 3 1.288 2.799 177 DICKSON 3.762 x 10~ 3 1.200 2.710 231 FOLEY 2.798 x 10" 3 1.024 3.355 49 Differences s i g n i f i c a n t at p< 0.05s Mean squares LOON> FOLEY and DICKSON Slope: LOON >DICKSON >FOLEY A: FOLEY>LOON and DICKSON See Figure 2 9 . To determine the significance of departures from isometry, i . e . B = 1.00 (Bailey, 1959)1 Lake b 2 t=(b-B)/s h d.f,=n-2 Significance LOON 1.288 9.26 X -4 10 ^ 9.0 175 p < 0.01 DICKSON 1.200 10.05 x 6.3 229 p < 0.01 FOLEY 1.024 18.03 x 10-* 0.565 47 NS 113 APPENDIX TABLE VII. Relationship of snout-to-back-of-eye length to standard length. Lake LOON DICKSON FOLEY Mean square 2.700 x 10"3 1.761 x 10~3 2.367 x 10~3 Slope A Number of f i s h 1.057 2.805 177 0.993 2.732 233 0.868 3.188 49 Differences s i g n i f i c a n t at p<0.05: Mean square: LOON and FOLEY>DICKSON Slope: LOON > DICKSON > FOLEY A: FOLEY > DICKSON See Figure 29. APPENDIX TABLE VIII. Relationship of eye length to standard length. Lake Mean square Slope A Number of f i s h LOON 4.476 x 10~3 0.809 1.969 177 DICKSON 2.588 x 10"3 0.677 1.949 233 FOLEY 4.702 x 10"3 0.550 2.176 49 Differences s i g n i f i c a n t at p<0.05: Mean square: LOON and FOLEY> DICKSON Slope: LOON > DICKSON >FOLEY A: FOLEY 7 LOON > DICKSON See Figure 29. 114 APPENDIX TABLE IX. Relationship of maximum g i l l raker length to standard length. Lake Mean square Slope A Number of f i s h LOON 2.367 x 10~2 1.291 1.023 177 DICKSON 1.715 x 10"2 1.097 0.974 219 FOLEY I.I67 x 10"2 0.936 1.426 49 Differences s i g n i f i c a n t at p 40.05: Mean square. LOON > DICKSON and FOLEY Slope: LOON > DICKSON and FOLEY A: FOLEY > LOON >DICKSON See Figure 30. APPENDIX TABLE X. Relationship of predorsal length to standard length. Lake Mean square Slope A Number of LOON 1.012 x 10 - 3 1.020 4.086 28 DICKSON 0.938 x 10'3 0.974 4.099 28 FOLEY 0.825 x 10~3 0.955 4.535 14 Differences s i g n i f i c a n t at p«0.05: Mean square: LOON >DICKSON > FOLEY Slope: LOON >DICKSON > FOLEY A: FOLEY >DICKSON > LOON Not i l l u s t r a t e d . 115 APPENDIX TABLE XI. Relationship of i n t e r o r b i t a l width to standard length. Lake Mean square Slope A Number of f i s h LOON 5.486 x 10" 3 1.080 2.442 177 DICKSON 4.291 x 10~ 3 1.002 2.263 233 FOLEY 1.780 x 10~ 3 0.964 2.827 49 Differences s i g n i f i c a n t at p<0.05« Mean square1 LOON> DICKSON >FOLEY Slopet No differences A« LOON and FOLEY >DICKS0N See Figure 30 APPENDIX TABLE XII. Relationship of the distance from the anal f i n base to the pectoral f i n base to standard length. Lake Mean square Slope A Number of f i s h LOON 0.813 x 10~3 1.053 4.187 28 DICKSON 1.173 x 10~3 1.068 4.247 28 FOLEY 1.554 x 10~3 1.085 4.632 14 Differences s i g n i f i c a n t at p*s0.05» Mean square1 FOLEY >DICKSON > LOON Slope i FOLEY >DICKSON > LOON As FOLEY > DICKSON >LOON Not i l l u s t r a t e d . 116 APPENDIX TABLE XIII, Size related differences i n the relati o n s h i p of upper jaw length to standard length f o r the three Dolly Varden populations. Standard length (mm) Lake Mean square Slope A Number of f i s h 140 LOON 2.900 x 10~3 0.866 2.499 64 DICKSON 2.952 x 10~3 1.081 2.620 154 140 LOON 7.398 x 10**3 1.401 2.968 113 DICKSON 5.314 x 10"3 1.285 2.891 77 FOLEY 2.785 x 10~3 1.062 3.373 47 The following differences were shown to be s i g n i f i c a n t at p ^  0 . 0 5 i i ) Small f i s h i i ) Within Loon Lake i i i ) Within Dickson Lake iv) Large f i s h Mean square* Slopes A: Mean squares Slope s A: Mean squares Slopes A: Mean squares Slopes As No difference DICKSON > LOON DICKSON >L00N large f i s h > small f i s h large f i s h > small f i s h No difference large f i s h > small f i s h No difference No difference LOON and DICKSON > FOLEY LOON >FOLEY} DICKSON intermediate FOLEY > LOON and DICKSON 117 APPENDIX TABLE XIV. Relationship of weight to standard length. Lake Mean square Slope A Number of f i s h LOON 7.020 x 10~3 3.071 3.793 177 DICKSON 1.604 x 10"2 2.573 3.383 224 FOLEY 6.098 x 10~3 2.835 4.978 46 Differences s i g n i f i c a n t at p^O.05* Mean square: DICKSON >FOLEY and LOON Slope: LOON > FOLEY > DICKSON A: FOLEY > LOON >DICKSON See Figure 30. To determine significance of departure from isometry i . e . B = 3.00 (Bailey, 1959): Lake b s^ t=(b-B)/s^ d.f,=n-2 Significance LOON 3.071 10.26 x lO"^ 2.22 175 p<0.05 DICKSON 2.573 43.79 x 10"^ 6.48 222 p<0.01 FOLEY 2.835 40.30 x 10"^ 2.60 44 p<0.01 118 APPENDIX TABLE XV. Relationship of upper jaw length, eye length and weight to standard length f o r cutthroat and Do l l y Varden using log-transformed spring 1972 data from Loon Lake. A. Upper jaw length against standard length* Species Mean square Slope A Number of f i s h D o l l y Varden 6.O85 x 10~ 3 1.312 2.682 71 Cutthroat 2.447 x 1 0 " 3 1.338 3.101 105 Differences s i g n i f i c a n t at p< 0 . 0 5 : Mean square: Dolly Varden >cutthroat Slope: No difference A: Cutthroat >Dolly Varden B. Eye length against standard length: Species Mean square Slope A Number of f i s h D o l l y Varden 3.231 x 1 0 " 3 0.795 I . 8 8 9 71 Cutthroat 2.252 x 1 0 " 3 0.905 2.161 105 Differences s i g n i f i c a n t at p ^ 0 . 0 5 : Mean square: Dolly Varden>cutthroat Slope: No difference A: Cutthroat >Dolly Varden C. Weight against standard length: Species Mean square Slope A Number of f i s h D o l l y Varden 3.160 x 1 0 " 3 2.832 3.430 71 Cutthroat 4 .601 x 1 0 " 3 2.763 3.929 44 Differences s i g n i f i c a n t at p«i0.05» Mean square: Cutthroat >Dolly Varden Slope: No difference A: Cutthroat >Dolly Varden Regressions and analyses of covariance calculated as on p.111. 119 APPENDIX TABLE XVI. Times to f i r s t bottom grab (seconds) during 10 minute exposure period to red chironomid larvae on sand and l e a f l i t t e r substrate. A l l o p a t r i c Sympatric 72 375 135 980* 35 1800+** 65 1800+** 600* 90 0 130 *Fish which did not respond during the f i r s t 10 minute test but did during a subsequent t e s t . **Fish which were tested three times but did not respond to the chironomid larvae on any of these occasions. The time to the f i r s t grab i s less f o r a l l o p a t r i c s than f o r sympatrics, s i g n i f i c a n t at p<0.01 using the Mann Whitney U test; U = 1, n 1 = 8, n ? = 4. 

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