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A study of the effects of Toxaphene on the bottom fauna of Paul Lake, British Columbia Ellickson, Peter Joseph 1965

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A STUDY OF THE EFFECTS OF TOXAPHENE ON THE BOTTOM FAUNA OF PAUL LAKE, BRITISH COLUMBIA by PETER JOSEPH ELLICKSON B.Sc, University of B r i t i s h Columbia, 1961 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 standards THE UNIVERSITY OF BRITISH COLUMBIA December, 1965 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l m a k e i t f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may b e g r a n t e d by t h e H e a d o f my D e p a r t m e n t o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n D e p a r t m e n t o f T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r 8, C a n a d a . i i ABSTRACT The d e n s i t y of the animals forming the bottom fauna of P a u l Lake, B r i t i s h Columbia has been estimated f o r two s u c c e s s i v e seasons, based on 250 Ekman dredge sam-p l e s from a l l zones f o r each year. A f t e r the sampling of the f i r s t year, the lake was t r e a t e d with .004 p.p.m. Toxaphene. D e n s i t y changes i n the i n v e r t e b r a t e popula-t i o n were c o n s i d e r e d on the b a s i s of i n c r e a s e , decrease and changes i n z o n a l d i s t r i b u t i o n . F o l l o w i n g p o i s o n i n g and e l i m i n a t i o n of pr e d a t o r y f i s h , d e n s i t y i n c r e a s e s o c c u r r e d i n the Physidae, Lymnae-idae, O l i g o c h a e t a , P l a n o r i b a e , and H i r u d i n e a . D e n s i t y decreases o c c u r r e d i n the Watermites, Amphipods, C h i r o n -omidae, P l a n a r i a , S p h a e r i i d a e and Odonata. T r i c o p t e r a , Ephemeroptera and Ceratopogonidae were not taken i n any of the samples a f t e r p o i s o n i n g . i i i TABLE OF CONTENTS Page INTRODUCTION 1 DESCRIPTION OF THE STUDY AREA 4 LOCATION AND MORPHOMETRY 4 PHYSICAL AND CHEMICAL PROPERTIES 6 MATERIALS AND METHODS 9 RESULTS 12 GRAPHICAL RESULTS . . . . . . . 12 STATISTICAL RESULTS 12 DIVERSITY OF ANIMALS 21 HISTORY OF BOTTOM FAUNA ESTIMATES IN PAUL LAKE 21 DISCUSSION 27 METHODS 27 TIME OF SAMPLE-TAKING 28 THE EFFECT OF TOXAPHENE 30 (a) Animals Which Increased i n D e n s i t y i n P o s t - P o i s o n i n g Samples 31 (b) Animals Which Decreased i n D e n s i t y i n P o s t - P o i s o n i n g Samples 38 (c) Species O c c u r r i n g i n New Zones i n P o s t - P o i s o n i n g Samples . 45 (d) Species O c c u r r i n g i n Zones i n 1962 and Not Present i n 1963 . 45 SUMMARY 48 LITERATURE CITED 50 i v LIST OF TABLES Table Page I. Midsummer oxygen determinations for Paul Lake (Rawson, 1934 and Larkin, 1950) 8 II . Average numbers of animals per m^  by zone i n 1962 and 1963 i n Paul Lake . . . . 14 I I I . Results of analyses of variance f o r in d i v i d u a l species f o r two years (1962/63) 19 IV. Results of analyses of variance for t o t a l numbers of organisms f o r two years (1962/63) . 20 V. Percentage increase or decrease of average numbers of animals/m2, by zone between 1962 and 1963 22 VI. Animals forming 90% of the t o t a l popu-l a t i o n i n 1962 and 1963 by zone 24 VII. Average density of the bottom fauna estimated i n the l i t e r a t u r e for Paul Lake since 1931 25 VIII. Weighted average of bottom organisms for the whole of Paul Lake from date published since 1931, per meter squared. 26 IX. Percentage of Chironomidae of varying sizes captured i n a sieve of mesh aperture 0.56 mm. square (Hamilton, 1965) 29 X. Percentage increase i n density by zone, and average percentage increase in density i n a l l zones i n 1963 32 XI. Percentage decrease i n density by zone, and average percentage decrease i n density i n a l l zones i n 1963 34 V Table Page XII. Groups occurring in pre-poisoning samples but not occurring i n post-poisoning samples, by zone 46 v i LIST OF FIGURES Figure Page 1. Paul Lake showing depth contours, streams and access road 5 2. Temperature curve for September 8, 1962 7 3. Map giving locations of sampling pat-tern in Paul Lake i n la t e summer 1962 and 1963 '". 11 4. Average number/m^ of Oligochaeta and Hirudinea by zones i n 1962 and 1963, . . . . 15 5. Average number/m^ of Gammarus l a c u s t r i s and H y a l e l l a azteca by zone i n 1962 and 1963 . . . . . . 15 6. Average number/m2 of Watermites and Planaria by zone i n 1962 and 1963 16 7. Average number/m^ of Lymnaeidae and Physidae by zone i n 1962 and 1963 16 8. Average number of animals per metre square of Planorbidae and Sphaeriidae by zone i n 1962 and 1963 17 9. Average number per metre square of Anisoptera and Zygoptera by zone in 1962 and 1963. 17 10. Average number per metre square of Ephemeroptera and Tricoptera by zone in 1962 and 1963 18 11. Average number per metre square of Chironomidae and Ceratopogonidae by zone i n 1962 and 1963. 18 12A. Number of taxa making up 90% of the t o t a l population by zone, i n 1962 and 1963 23 v i i Figure Page 12B. Number of taxa making up 50% of the t o t a l population by zone, i n 1962 and 1963. 23 v i i i ACKNOWLEDGEMENTS The study of the e f f e c t s of Toxaphene on the bot-tom fauna of Paul Lake, B r i t i s h Columbia, was suggested to the author by Dr. P.A. Larkin, Director, P a c i f i c B i o l o g i c a l Station, F i s h e r i e s Research Board of Canada, Nanaimo, B.C., for whose encouragement the author i s g r a t e f u l . Dr. I.E. Efford was most h e l p f u l i n preparation of the manuscript. Drs. J. Adams, G.G. Scudder and T.G. Northcote c r i t i c a l l y read the manuscript, and offered many he l p f u l suggestions. Their advice was greatly appreciated. Dr. J.T. McFadden was most patient and generously spent many hours compiling computer programs and suggesting approaches to the s t a t i s t i c a l techniques. His assistance was invaluable. The author wishes to thank the Zoology Department, University of B r i t i s h Columbia (Teaching Assistantships 1963/64) fo r f i n a n c i a l support, and Dr. N.J. Wilimovsky, Director, I n s t i t u t e of Fisheries for h i s patience and f i n -a n c i a l support. The B r i t i s h Columbia Department of Recreation and Conservation, Fish and Game Branch, financed the f i e l d work. Mr. George Stringer, Regional Fi s h e r i e s B i o l o g i s t , was most h e l p f u l i n the c o l l e c t i o n of the data, and with technical advice. 1 INTRODUCTION The e f f e c t s of Toxaphene on bottom fauna are not well known. Two aspects of e f f e c t s are of p a r t i c u l a r i n t e r e s t , the actual toxic e f f e c t on the invertebrates, and the e f f e c t on the density of the invertebrate popula-ti o n after removal of the f i s h predators. Several studies have been published which treat these two aspects, notably the work of Hooper and Grzenda (1955), Cushing and Olive (1956), and Hilsenoff (1965). Other workers, Brown and B a l l (1942), and B a l l and Hayne (1952) did s i m i l a r studies, using Rotenone (derris root) as the agent for f i s h removal. A t h i r d group, Morretti (1948), and Schoettger and Olive (1961) considered, only the toxic e f f e c t s of Toxaphene on the invertebrates. Studies of the Kamloops trout (Salmo gairdneri) i n Paul Lake, B r i t i s h Columbia, have been carried on since 1931. Rawson (1934) noted that adult trout ate Gammarus, Daphnia, Insecta, Gastropoda, and Hirudinea i n that order of preference. Larkin et a l . , (1950) point out that stomach-content analyses of trout indicate the depletion of Gammarus i n the bottom fauna, and the increased impor-tance of plankton i n the d i e t of trout. P r i o r to 1950 the Redside Shiner (Richardsonius balteatus) had been i n t r o -duced, and, at the time of Larkin's (1950) study, was well 1 INTRODUCTION The e f f e c t s of Toxaphene on bottom fauna are not well known. Two aspects of e f f e c t s are of p a r t i c u l a r interest, the actual toxic e f f e c t on the invertebrates, and the e f f e c t on the density of the invertebrate popula-tion after removal of the f i s h predators. Several studies have been published which treat these two aspects, notably i s the work of Hooper and Grzenda (1955), Cushing and Olive (1956), and Hilsenoff (1965). Other workers, Brown and B a l l (1942), and B a l l and Hayne (1952) did s i m i l a r studies, using Rotehone (derris root) as the agent for f i s h removal. A t h i r d group, Morretti (1948), and Schoettger and Olive (1961) considered only the toxic e f f e c t s of Toxaphene on the invertebrates. Studies of the Kamloops trout (Salmo gairdneri) in Paul Lake, B r i t i s h Columbia, have been carried on since 1931. Rawson (1934) noted that adult trout ate Gammarus,  Daphnia, Insecta, Gastropoda, and Hirudinea in that order of preference. Larkin e_t a_l., (1950) point out that stomach-content analyses of trout indicate the depletion of Gammarus in the bottom fauna, and the increased impor-tance of plankton i n the diet of trout. P r i o r to 1950 the Redside Shiner (Richardsonius balteatus) had been i n t r o -duced, and, at the time of Larkin's (1950) study, was well 2 established, and suspected of being an important predator on the bottom fauna, and a competitor of trout. Larkin and Smith (1953) note that the adult shiners crop the amphi-pods, leaving "almost none" for the trout, the r e s u l t being the loss of the equivalent of one year's growth by the trout. The trout are compensated by an increase i n growth rates when they are large enough to use shiners as food, but t h i s i s o f f s e t by the fact that they are exposed to an additional year of natural mortality. Crossman and Larkin (1959) found that the summer diet of trout other than gammarids was bottom fauna and shiners, the l a t t e r making up 95% of the d i e t . The winter diet of small and medium sized trout was 95% bottom fauna, and no shiners, while large trout alone, ate shiners, which composed only 10% of the t o t a l d i e t . Johannes and Larkin (1961) show that both shiners and trout prefer amphipods, but due to the low numbers of the l a t t e r , they both have substitute d i e t s . Trout are at a disadvantage i n Paul Lake i n the presence of shiners, as shown by Johannes and Larkin (1961). The bottom fauna in Paul Lake, as food of trout and shiners, has been well studied, with p a r t i c u l a r emphasis on the amphipods. However, the population trend of the bottom fauna, in the absence of f i s h predators, has never been considered i n Paul Lake. Since predation by fishes i s considered by some, Gerking (1962), to account for a 3 larger proportion of the losses of the l a r v a l insect popu-l a t i o n than emergence, i t i s important to consider the effect of predator removal on the density of the bottom fauna. In 1962 the B r i t i s h Columbia P r o v i n c i a l Government, Department of Recreation and Conservation, Fish and Game Branch, treated Paul Lake with .004 p.p.m. Toxaphene in order to remove a l l the f i s h from the lake, preparatory to re-stocking the lake with trout. This afforded the oppor-tunity for the study of the ef f e c t s of the removal of f i s h predators from the invertebrate l i f e of a lake, as well as the opportunity to examine the e f f e c t s , i f any, of Toxaphene on the bottom fauna of a lake. 4 DESCRIPTION OF THE STUDY AREA LOCATION AND MORPHOMETRY Paul Lake i s situated twelve miles north-east of Kamloops, B r i t i s h Columbia, i n a narrow rocky valley, at an altitude of 775.3 metres (2,542 f e e t ) . It has a length of 6,114 metres (3.8 miles) and an average width of 482.7 metres (0.3 miles). The area of the lake was described by Rawson (1934) and Larkin (1950) as 3.9 square kilometers (1.5 square miles), but i n a survey by B r i t i s h Columbia P r o v i n c i a l Government, Department of Recreation and Conser-vation, Fish and Game Branch in 1962, the area was found to be 2.72 square kilometers (1.05 square miles). Irregu-l a r i t y of the shoreline, as expressed by the Welch (1948) term "shore development" i s 5.55 units, i n d i c a t i n g a large amount of shoreline i n r e l a t i o n to the area of the lake. Maximum depth i s 55.5 metres (182 fe e t ) , and approximately 33% of the area l i e s below the 50 metre contour (Fig. 1). Mean depth i s 34.2 metres (112 f e e t ) , and the shore slopes at an angle of 20/25 degrees. The lake has one major i n l e t , Upper Paul Creek, which drains Pinantan Lake, and several mountain streams, which are dry in summer, known c o l l e c t i v e l y as Agnes Creek. There i s one outlet, Lower Paul Creek, which joins the North Thompson River. Rawson (1934) states that there was no flow through Lower Paul 6 Creek, due to the low l e v e l of the lake during his survey. This was an unusually dry year and s i m i l a r conditions have not been repeated since then. PHYSICAL AND CHEMICAL PROPERTIES Figure 2 shows a temperature curve for September 8, 1962, which i s t y p i c a l for late summer in Paul Lake. The thermocline i s located i n the 15 to 50 feet region, as found by Larkin e_t a l . (1950) . There i s l i t t l e warming below th i s l e v e l . t Midsummer oxygen determinations are given for 1963, 1948, 1947, 1946, 1931 i n Table I. Oxygen determinations were by the "Winkler" method except i n 1931 when the " M i l l e r " method of oxygen determin-ation was used. Oxygen supply i s abundant even in the very deep waters, and Rawson (1934) has stated that, in his opinion, i t does not act as a l i m i t i n g factor for l i f e in the deep waters. Degrees Centigrade O 5 IO 15 2 0 25 I ' 1 7 2.5 4Q5. 43. F i g u r e 2. Temperature curve f o r September 8, 1962, Table I. Midsummer oxygen determinations f o r Paul Lake (Rawson, 1934 and Larkin, 1950). Percent Saturation Depth in Metres 1931 1946 1947 1948 1963 0 76 100 106 100 122 15 59 81 84 82 57.7 50 37 78 48 40 41 9 MATERIALS AND METHODS In summer 1962 a series of bottom fauna dredgings were taken over a three month period. This series was for comparison with the data of Rawson (1934) and Larkin et a l . (1950) and samples were taken at stations approximating the sampling locations of Rawson (1934). In late summer 1962 a concentrated series of bottom fauna dredgings was taken. The lake was divided into ten areas, A to J, f o r sampling (Fig. 3). Within each zone, f i v e samples, evenly spaced over the depth range, were taken from each of the L i t t o r a l Chara (0-10 metres), L i t t o r a l Non-Chara (0-10 metres), S u b l i t t o r a l (10-20 metres), and Profundal (> 20 metres)zones, giving a t o t a l of 250 samples f o r the whole lake. The presence of the stonewort Chara i n shoals around 95% of the lake in the L i t t o r a l Zone (0-10 metres), and on the lake bottom offshore, determined by the slope of the basin and the penetration of l i g h t , necessitated the sampling of the L i t t o r a l Zone in two sections v i z . , L i t t o r a l Chara Zone and L i t t o r a l Non-Chara Zone. A Standard Ekman Dredge of 523 square centimetres was used, and the counts of organ-isms are t o t a l counts, i . e . , no sub-samples were taken. Mesh size of screen f o r washing dredgings was 31 meshes to 10 the l i n e a r inch, with an aperture of 0.56 mm. square. In late summer 1962, after the above sampling was completed, the lake was treated with 0.004 p.p.m. Toxaphene, i n an attempt to remove the large numbers of redside shiners (Richardsonius balteatus) Richardson which, together with the rainbow trout (Salmo gairdneri), are the only species of f i s h which occur in Paul Lake. In late summer 1963, a series of dredgings was taken following the same pattern of samplings as the 250 series taken i n 1962. 12 RESULTS GRAPHICAL RESULTS The graphical r e s u l t s are presented in Table II and Figures 4 to 11. STATISTICAL RESULTS The re s u l t s of the analyses of variance for the ind i v i d u a l species for two years to assess the sign i f i c a n c e of the main e f f e c t s and interactions are shown i n Table II I . P r o b a b i l i t i e s of chance occurrence are indicated. The analysis of variance for the t o t a l number of organisms for two years, 1962 and 1963 (Table IV) shows highly s i g -n i f i c a n t differences between years, between zones, and between species. The analyses i n d i c a t e : — (1) That both i n the pre-poisoning and post-poisoning samples there are s i g n i f i c a n t differences between species and between zones, and highly s i g n i f i c a n t interactions, i n d i c a t i n g that species tend to be associ-ated with p a r t i c u l a r zones. (2) Comparing the two years, there are s i g n i f i -cant differences between the years, and s i g n i f i c a n t interactions between years and areas; years and species; 13 and years and zones, i n d i c a t i n g thjat Toxaphene acts d i f -f e r e n t l y on s p e c i e s , and d i f f e r e n t l y i n d i f f e r e n t h a b i t a t s , presumably the l a t t e r v i a d i f f e r e n t i a l a c t i o n on spe c i e s . r- r- H 1 1—1 M r-co (0 CD CO CO CO CO CO CO CO CV 0) 05 05 05 05 05 05 05 05 co to CO to CO to CO to CO to H - > *0 •a CO co tr 1 tr* tr 1 f P < c c H * H - H - H * CD (t) o o cr cr c t C t c t r t hb H ) M t—• c t C t c t c t S3* P rr P c c H - H - 0 O O O o orq 0 Oq 13 c t r t 4 4 M (D a. a c t c t P P P P (D (D P P o 0 1—1 I—1 M h-M I—1 r- 0 M 0 p P 25 O O P • P J . M I—1 0 O ST tr W \ * r \ a P P (0 s (D 3 1 i 4 to to o o P p 3* tr P P p P to to o> CO 05 to C5 0 0 <l CO CO \-> CO CO o to cn 0 0 cn <l M CO >u CO 0 0 h-1 to CO CO 0 0 05 O o CO M o r- r- 05 0 0 to 05 05 l - 1 05 O cn CO cn to • M 05 cn CO co M r-1 oo 0 0 cn CD to 0 0 o H i - 1 M to CO cn o o o o • • • M • r-" cn 0 0 0 0 O • to oo K- to o h-1 to (0 O o CO CO o CD 0 0 • • CO cn 1— to CO cn to o 0 0 o <l M CO 0 0 05 05 CO 4t cn CO H Cn o 0 0 o o • tO • 05 r- to 0 0 0 0 to to o to Cn CO 1—1 CO • CO M to o <I 0 0 »u 0 0 o h-1 l-> o CO 05 M 0 0 • CO CO Cn CO CO CO 0 0 h-1 CO CO to to to 05 O o to to O o • to • cn CO r- 0 0 <l to 1— o 1— CO co cn to CO 05 *> o o • to 0 0 1—1 to o • 1— CO o - © 1— <l • CO o • CO o <l o 0 0 O to to ANISOPTERA ZYGOPTERA OLIGOCHAETA CHIRONOMIDAE EMERGED & PUPAE CERATOPOGONIDAE GAMMARUS LACUS-TRIS HYALELLA AZTECA HIRUDINEA HYDRACARINA PHYS ID AE PLAN0RBIDAE LYMNAEIDAE SPHAERIIDAE TRICOPTERA EPHEMEROPTERA PLANARIA 15 120, — A — 1962 — o — 1 9 6 3 120 3 p O Q — A -— e • •1962 -1963 Figure 5. Average number/nr4 of Gammarus l a c u s t r i s and Hy a l e l l a azteca by zone in 1962 and 1963. 16 60. SO 40 30 -20; IO 180. — a —1962 — o —1963 Littoral Litforal Sub" Profundal Chara Non Chara littoral WATERMITES Littoral Littoral Sub Profund Chara NonChara littoral PLANARIA Figure 6. Average number/m^ of Watermites and Planaria by zone i n 1962 and 1963. 2.1 OO, —A— 1962 — o—1963 Littoral NonChara Sub- Profundal littoral Figure 7. LYMNAEIDAE 0 PHYSIDAE Average number/m^ of Lymnaeidae and Physidae by zone i n 1962 and 1963. 17 Littoral Littoral Sub- Profundal Chara Non Chara littoral PLANORBIDAE Littoral Non Chara SPHAERIIDAE Sub- Profundal littoral Figure 8. Average number of animals per metre square of Planorbidae and Sphaeriidae by zone in 1962 and 1963. 240 I20. IOO 80 | 6 0 z < 4 0 — A —1 9 6 2 — o — 1 9 6 3 2 0 Littoral Non Chara ANISOPTERA Sub- Profundal littoral Littoral Chara Littoral Non Chara S u ^ Profundal littoral ZYGOPTERA Figure 9. Average number per metre square of Anisoptera and Zygoptera by zone in 1962 and 1963. 12. 24, — A — 1 9 6 2 — e 1963 18 EPHEMEROPTERA TRICOPTERA Figure 10. Average number per metre square of Ephemerop-tera and Tricoptera by zone i n 1962 and 1963. I.SOO Chara Non Chara littoral CHIRONOMIDAE — A —1962 — e —1963 CERATOPOGONI DAE Figure 11. Average number per metre square of Chironomidae and Ceratopogonidae by zone i n 1962 and 1963. Table I I I . Results of analyses of variance for i n d i v i d u a l species f o r two years (1962/ 63) . Species Source of Variation years zones areas yearsXzones yearsXareas zonesXareas yearsXzone: Anisoptera .05 .01 NS .01 NS .05 NS Zygoptera .01 .01 NS .01 NS NS NS Oligochaeta .01 .01 .01 NS NS .01 .01 Ceratopogonidae NS NS NS NS NS NS NS Gammarus lacus-t r i s NS NS NS NS NS NS NS H y a l e l l a azteca .01 .01 NS .01 .05 NS .05 Watermites .01 .01 .05 .01 .05 .05 .05 Physidae NS .01 .05 .01 NS NS NS Planorbidae NS .01 NS NS NS NS NS Lymnaeidae .01 .01 NS .01 NS NS NS Spaeriidae NS .01 NS NS NS NS NS Tricoptera .01 .01 .01 .01 .01 .01 .01 Ephemeroptera .01 .01 .01 .01 .01 .01 .01 Planaria .01 .01 .01 .01 NS .01 NS Hirudinea .01 .01 NS .01 NS NS NS Emerged & Pupal Chironomidae .01 .01 NS .01 .01 .01 .05 Chironomidae .01 .01 NS .01 NS .05 NS Table IV. Results of analyses of variance f o r t o t a l numbers of organisms f o r two years (1962/63). Main E f f e c t s Interactions Years = .01 Years X Areas .01 Zones = .01 Years X Zones .01 Species = .01 Years X Species - .01 Areas = N.S. Areas X Zones = .01 Areas X Species = .01 Zones X Species = .01 Years X Areas X Zones .01 Years X Zones X Species .01 Years X Areas X Species = N.S. Areas X Zones X Species .01 Years X Areas X Zones X Species .01 CO o 21 DIVERSITY OF ANIMALS Table V shows the percentage increase or decrease of the average number of animals per metre squared, by zone, between 1962 and 1963. Several groups were taken i n the 1963 samples i n zones in which they were not found i n 1962, these are indicated by ++. Animals not taken i n 1963, but occurring in 1962, are indicated by x. Figure 12A shows the number of taxa making up 90% of the t o t a l population i n 1962 and 1963, and Table VI shows the animals forming 90% of the population i n 1962 and 1963. Figure 12B shows the number of taxa making up 50% of the t o t a l population in 1962 and 1963. HISTORY OF BOTTOM FAUNA ESTIMATES IN PAUL LAKE Table VII shows the average number of bottom organisms estimated in published data since 1931, and includes figures for thi s study. Table VIII shows a weighted average of t o t a l bottom organisms i n the whole lake, from published data since 1931. The low weighted average number (799) i n 1948 can be p a r t l y accounted f o r as due to the small t o t a l number of samples (15) taken, on which estimates for the whole lake were based. Table V. Percentage i n c r e a s e or decrease of average numbers of animals/m 2, by zone between 1962 and 1963. < « w ft o m M Z < tt w a 8 < EH w < o o < Q M S o z o « t—i K U a o tt < Q o a o « w < w s tt H H « < Q w « ft < a CQ tt O 55 «J ft < tt w < < EH < Q tt ft a w o HH w EH tt W tt ft < W o < o w s X S3 ft tt ft W EH W + 786 -87 X x + 512 -96 X X + 290 X X X tt < ft L i t t o r a l Chara -65.2 x +288 -97 L i t t o r a l Non-Chara -24.5 -76.9 -47.9 -85 S u b l i t t o r a l -22.2 -99.7 P r o f u n d a l -14.8 -95.6 -80 x X X ++ -97.5 -97.2 +62 + 24.6 x x +57 -20 -99.4 38 49 + 325 +300 ++ ++ -65.4 ++ (1) Percentage i n c r e a s e i n d i c a t e d by +, percentage decrease i n d i c a t e d by -. (2) Groups found i n 1963 and not o c c u r r i n g i n those zones i n 1962 are i n d i c a t e d by ++ . (3) Species o c c u r r i n g i n zones i n 1962 i n which they were not taken i n 1963 are i n d i c a t e d by x. to to c CD to N O S j O 0 3 CD c t cr *• tr CD CD 4 H-P f t 0 O Hj I—1 c t ( O f f r t CO p to X •a p p o P XS 3 a C P M ?r i — • P H-CO f t S3 C5 H-aq CO o • S3 C XJ cr v- to o <59 N O Of T a x a M a k i n g Up 9 0 % O f The Total P o p u l a t i o n .— ro to i n o 9 -3 3 z R Q. O cr 3 —•» c _ D aq c l-i CD to 03 O Hj - S3" (D S3 f t O I—1 f t CO P CT1 I—1 to XJ P o S3 -a a. c CD w 25 c 3 cr o o Hj f t P p 3 P M ST P H-f t 0 H-aq o P c cr «< t n o o o — — o o o r Q O 9_ • a c C L Q No. O f T a x a M a k i n g Up 5 0 % Of The Total P o p u l a t i o n — IU W > U l I I I i vO O S3 24 Table VI. Animals forming 90% of the t o t a l population i n 1962 and 1963 by zone. Zone Year Animals L i t t o r a l Chara 1962 Hy a l e l l a azteca Physidae Planorbidae Chironomidae Lymnaeidae Anisoptera Planaria (38.4%) (17.5%) (13.2%) (11.3%) ( 4.6%) ( 4.3%) ( 3.3%) L i t t o r a l Chara 1963 Lymnaeidae Physidae Planorbidae (63.6%) (17 %) (10.5%) L i t t o r a l Non-Chara 1962 Hy a l e l l a azteca Chironomidae Oligochaeta Sphaeriidae Hirudinea (60.2%) (12.2%) (12.2%) ( 4.6%) ( 2.0%) L i t t o r a l Non-Chara 1963 Hy a l e l l a azteca Lymnaeidae Physidae Oligochaeta Planorbidae Hirudinea (24.8%) (20.1%) (16.6%) (16.3%) ( 7.3%) ( 6.4%) S u b l i t t o r a l 1962 Chironomidae Oligochaeta (55.0%) (38.8%) S u b l i t t o r a l 1963 Oligochaeta Planorbidae (88.8%) ( 3.8%) Profundal 1962 Oligochaeta (95.9%) Profundal 1963 Oligochaeta (99.2%) Table V I I . Average d e n s i t y of the bottom fauna estimated i n the l i t e r a t u r e f o r P a u l Lake s i n c e 1931. 1931 1949 1962 Summer 1962 F a l l 1963 Depth i n Meters 0-10 10-20 >20 0-10 10-20 > 20 0-10 10-20 > 20 0-10 10-20 > 20 0-10 10-20 > 20 Chironomidae 169 949 2270 3761 1343 5028 5317 872 571 982 1567 18 78 5 0.8 H y a l e l l a a z t e c a 2983 40 976 1 101 1671 3955 2 0.5 367 0.4 Gammarus sp. 111 510 137 30 3 7 175 80 4 2 Physidae 212 2 71 1 4 509 2 938 8 785 34 0.4 Lymnaeidae 49 13 106 1 11 244 283 0.8 0.6 2391 24 P l a n o r b i d a e 5 595 1 62 1513 2 1 731 1 446 4 0.8 Sp h a e r i i d a e 44 482 1307 107 259 165 142 1 177 3 0.2 11 Zygoptera 86 175 18 190 142 8 A n i s o p t e r a 19 103 11 345 272 101 T r i c o p t e r a 64 2 28 2 142 1 33 0.4 Ephemeroptera 4 73 8 37 12 0.4 H i r u d i n e a 103 80 21 2 101 1 133 3 192 5 P l a n a r i a 78 45 131 42 51 189 934 3 5 202 107 3 37 0.4 O l i g o c h a e t a 29 7 39 7 292 1091 458 103 408 1106 447 255 861 381 to Table VIII. Weighted average of bottom organisms for the whole of Paul Lake from date published since 1931, per meter squared. Time 1931 1948 1949 1962 1963 Average No. per m2 1363 799 1490 1491 932 27 DISCUSSION METHODS Before any conclusions can be reached on the res u l t s i t seems f i t t i n g to define the l i m i t a t i o n s of the methods of sampling, and of the apparatus used. An Ekman Dredge samples the bottom. Depending on the type of sub-strate, mud, rooted aquatics, shale, or rock, the dredge takes a sample of varying amount. During the clo s i n g of the dredge i t i s possible to lose parts of the sample through the jaws. Again, during the ascent of the dredge through the water i t i s possible to lose some of the sam-ple. A l l these factors can contribute a large error to the sample, and th i s error i s introduced before the sample i s landed. The sample, once taken, i s washed through a screen to remove mud etc., and the remainder of the sample i s picked through by hand to remove the animals which i t contains. The type of mesh used in the screen through which the sample i s washed can contribute errors f a r surpassing those introduced in the c o l l e c t i n g technique. Jonasson (1955) states that "the numbers captured are a function of the mesh gauge". He f e e l s that figures reached on animal density must be altered materially when an adequate gauge 28 capturing the animals quantitatively i s used. Hamilton (1965) has calculated the percentage of Chironomidae of varying sizes taken i n a sieve with a mesh aperture of 0.56 mm. square. His findings are presented in Table IX. Jonasson (1955) with a si m i l a r test concluded that the width of the head capsule of chironomids was correlated with the e f f i c i e n c y of the various mesh gauges. TIME OF SAMPLE-TAKING The time (late summer 1962 and 1963) at which the 250 series of samples were taken, introduces a further error i n the c a l c u l a t i o n of numbers of animals, insofar as i t e f f e c t s those insects that have a l a r v a l or pupal stage in the water, while the adults are t e r r e s t r i a l . In th i s study no account has been given to emergence of the Diptera, Odonata, Ephemeroptera and Tricoptera, and f i n a l c a l c u l a -tions of the density of these insects must be i n error. The error factors introduced i n the stages of sampling, as well as the time of sampling, introduce errors which render the f i n a l figures highly suspicious, and not valuable as calculations of t o t a l density, being of value only as comparable material. Table IX. Percentage of Chironomidae of varying sizes captured i n a sieve of mesh aperture 0.56 mm. square (Hamilton, 1965). Size of Animals i n mms. 1.5 2 3 4 5 6 7 8 mm. mm. mm. mm. mm. mm. mm. mm. Tanypodinae 0 15.5 43.5 76 76 67 92 100 Other Chironomidae 0 11.5 29 48.5 72.5 83 91 98 to to © 3 +J ed U 30 THE EFFECT OF TOXAPHENE Toxaphene has long been used as an in s e c t i c i d e and a f i s h poison. The Council on Pharmacy and Chemistry of the American Medical Association (1952) describe Toxa-phene as a chlorinated camphene, with the average empirical formula CioH^oClg. i n s e c t i c i d a l effectiveness i s caused by combined contact and stomach poison e f f e c t s . The s i t e of the action of Toxaphene has not been established for invertebrates, but ch r o n i c a l l y poisoned vertebrates are characterized by degenerative changes in the renal tubules and the l i v e r parenchyma. Since the s i t e of the action of Toxaphene i s i n such doubt, assessment of the ef f e c t s of the poison on the various groups can only be made on the end r e s u l t s i . e . were the animals k i l l e d , or not, by the poison. Comparisons can be made with documented data of the e f f e c t s of the poison on invertebrates under conditions s i m i l a r to thi s study. The percentage increase or decrease of animals, by zone, i s given i n Table V, thi s i s calculated on the changes in density per metre square, between 1962 and 1963. These animals f a l l into four main groups:— (a) Those animals that increase i n number per metre square after the poisoning. 31 (b) Those animals that decrease i n number per metre square after the poisoning. (c) Species found i n zones i n 1963, i . e . , after the poisoning, in which they did not occur in 1962. (d) Species found in zones i n 1962, and not occurring in those zones i n 1963. Table X shows the percentage increase i n density of animals by zone i n 1963, and the average percentage increase over the whole lake. (a) Animals Which Increased i n Density in Post-Poisoning Samples As seen in Table X, Physidae with an average increase of 706.5% i n a l l zones, shows maximum increase, followed by Lymnaeidae (529%), Oligochaeta (288%), Planor-bidae (219.3%), and Hirudinea (47.8%). These increases can be grouped into increases i n the Gastropoda, and increases i n others, thus allowing consideration of the taxa of maximum increase as a unit. A l l three taxa (Lymnaeidae, Physidae and Planorbidae) are pulmonate animals, and may be expected to migrate to the surface in order to breath. For thi s reason i t would be unusual f o r them to occur i n deep water, Table X. Percentage increase i n density by zone, and average percentage increase i n density i n a l l zones i n 1963. Physidae Lymnaeidae Oligochaeta Planorbidae Hirudinea L i t t o r a l Chara 786% 288% 62% L i t t o r a l Non Chara 1088% 512% 138.5% . 24.6% S u b l i t t o r a l 325% 290% 300% 57% Profundal ++ Average % Increase In A l l Zones 706.5% 529% 288% 219.3% 47.8% 33 thought Cheatum (1934), suggests that pulmonate s n a i l s are capable of f i l l i n g the pulmonate sac with water and using i t as a g i l l . One i n d i v i d u a l Physidae alone was found in the Profundal Zone i n a l l the samples taken. In view of t h i s low number i t i s considered that the Gastropoda of Paul Lake are L i t t o r a l - S u b l i t t o r a l animals. A l l three Gastropoda occurring are hermaphroditic, and isolated individuals have been observed to produce young (Pennak, 1953). Lymnaeidae increased i n numbers i n a l l zones, but Physidae (-38%) and Planorbidae (-49%) decreased in numbers i n the L i t t o r a l Chara Zone (see Table XI), i n d i -cating either a change to the L i t t o r a l Non-Chara and Sub-l i t t o r a l Zones, or d i f f e r e n t i a l mortality in the various zones. Hooper and Grzenda (1955) in a study on the Toxaphene treatment of a lake, found that the Gastropoda did not appear to be harmed by Toxaphene. Hilsenoff (1965) found that the Physidae increased i n density after Toxa-phene treatment, and were reduced in density on the i n t r o -duction of f i s h . Rawson (1934) shows that the Gastropoda in Paul Lake, while making up only 9% of the t o t a l bottom fauna i n the lake, contributed 4.4% of the t o t a l food Table XI. Percentage decrease i n density by zone, and average percentage decrease i n density i n a l l zones in 1963. L i t t o r a l Chara L i t t o r a l Non Chara S u b l i t t o r a l Profundal Average % Increase In A l l Zones Watermites 99.4% 99.4% Gammarus l a c u s t r i s 97.5% 97.5% Chironomidae 97% 85% 99.7% 95.6% 94.3% Sphaeriidae 87% 96% 91.5% Planaria 98.8% 97.3% 65.4% 87.2% Zygoptera 76.9% 76.9% H y a l e l l a azteca 97.2% 98.4% 20% 71.8% Planorbidae 49% 49% Anisoptera 65.2% 24.5% 44. 8% Physidae 38% 38% Oligochaeta 47.9% 22.2% 14.8% 28.3% 35 eaten by trout, and t h i s , before the introduction of shiners, and the consequent reduction of Amphipods. This figure had increased (Larkin, 1950) to 9.9% of a l l food taken. It seems then, that predation was heavy on the Gastropoda of Paul Lake. Lehman (1948), speaking of vertebrates, states that Toxaphene i s p r i n c i p a l l y a l i v e r poison. The l i v e r (digestive gland) of the Gastropoda functions p r i n c i p a l l y i n the production of a c e l l u l o s e - d i s s o l v i n g ferment, and has not the many functions of the mammalian l i v e r . D i f -f e r i n g i n s t r u c t i o n and function, as the Gastropoda l i v e r does, i t does not seem to be effected by Toxaphene, or at least, i s not effected to the same extent, as the mammalian l i v e r . Pennak (1953) points out that the presence of dissolved s a l t s , in p a r t i c u l a r , calcium carbonate, i s ess e n t i a l i n the determination of the habitat of gastropods. Paul Lake has dense masses of Chara impregnated with calcium carbonate, i n the L i t t o r a l Zone, as well as r i c h marl deposits i n the S u b l i t t o r a l Zone. It i s suggested then, that i n Paul Lake, i n the presence of what seems to be an unlimited supply of food, i n the form of algae, as well as calcium carbonate, for s h e l l production, the gastropods occupy an i d e a l habitat. The e f f e c t s of Toxaphene seem less on the gastropods than on the vertebrates. The animals are, i f necessary, functional hermaphrodites. Predation, on the gastropods by fi s h e s , based on stomach-content analyses, seems heavy. On the removal of the predators, conditions seem i d e a l for an increase i n den-s i t y . Predation seems to be the major regulatory mechan-ism of the population density of gastropods in Paul Lake. No explanation for the decrease of the Physidae (-38%) and the Planorbidae ( -49%) i n the L i t t o r a l Chara Zone i s f o r t h -coming from the present data. Increases i n the Oligochaeta was maximal i n the L i t t o r a l Chara Zone, with a decrease (Table XI) i n the S u b l i t t o r a l Zone. Cushing and Olive ( 1 9 5 6 ) found that Toxaphene had no adverse e f f e c t s on the population density of the Oligochaetes, and accounted f o r the increase i n density, which they found, as being due to the presence of decomposed f i s h which resulted from the poisoning. These findings were confirmed by Hooper and Grzenda ( 1 9 5 5 ) . Morgan ( 1 9 3 0 ) holds that decayed organic matter i s the main d i e t of Oligochaetes. Oligochaetes occupy a habitat which renders them less susceptible to predation by fishe s , than any other member of the bottom fauna community. Increased food, as suggested by Cushing and Olive ( 1 9 5 6 ) , and 37 removal of what predation, i f any, there was, remain as the reasons for increase i n density of the Oligochaeta, after Toxaphene treatment. It should be pointed out that counts on samples of Oligochaetes taken, are more suspect than indicated at the beginning of t h i s section for other ani-mals, due to the fact of'the Oligochaetes being segmented anatomically, and s p l i t t i n g off of segments may have been accomplished mechanically when washing through the sieve. This could res u l t in a mature in d i v i d u a l being broken, and counted as several animals. Hirudinea are the only other Annelida present i n Paul Lake. These show an increase i n a l l zones except the Profundal Zone, amounting to a calculated average of 47.8%. No record of the e f f e c t s of Toxaphene on the Hirudinea i s available. It can be presumed from the present data that the detrimental e f f e c t s of Toxaphene on the Hirudinea are not great. Larkin (1950) records 0.8% as the percentage volume of Hirudinea as food i n the average trout stomach. Predation from f i s h e s , while i t occurs, does not seem to be very heavy. The main food item in the diet of leeches i s dead animal matter, but more commonly they are c a r n i -vorous, and feed on gastropods, oligochaetes, and other small invertebrates. Removal of predation, small though i t may have been, and increased food supply, with the 38 increase in dead f i s h , and no known adverse e f f e c t s of Toxaphene, accounts for the increase in density of the Hirudinea i n a l l zones i n which they occur, after the Toxaphene treatment of the lake. (b) Animals Which Decreased in Density i n Post-Poisoning Samples. Table XI shows the animals that decrease i n density i n post-poisoning samples. The Chironomidae show a decrease i n density in a l l zones i n the post-poisoning samples amounting to an average of 94.3%. Predation by trout on the chironomids in Paul Lake i s indicated by Rawson (1934) as 6.8% of a l l food taken i n May and August, and by Larkin (1950) as a mean of 1.7% over a two year period. This shows a d e c l i n -ing predation by trout on chironomids after introduction of shiners to the lake. There i s no data available on the amount of predation by shiners on chironomids. Hooper and Grzenda (1955) found that chironomids survived for a few weeks after Toxaphene poisoning, and were then k i l l e d , with a spectacular repopulation after eleven months, reaching a density l e v e l "much higher" than the o r i g i n a l population l e v e l . Cushing and Olive (1956) found that chironomid larvae died three days after Toxaphene poisoning, but returned on repopulation. Moretti (1948) found that a l l 39 larvae were k i l l e d on Toxaphene treatment. Hilsenoff (1965) shows that the population of chironomids were stable for a month after Toxaphene treatment, but i n four months had increased two hundred times i n density. The Hilsenoff (1965) study was on a thermally s t r a t i f i e d lake, and he implies that the chironomids were not exposed to the Toxa-phene. He also states that the numbers of chironomids were reduced on the introduction of f i s h . The duration of the l i f e cycle i n the Chiron-omidae i s variable, some forms have several generations in one year, and others have one generation in a year. M i l l e r (1941) considers that predation on the chironomids by fishes i s heavy, and that the standing crop i s replaced eight to nine times i n summer in the epilimnion, and two or three times in the hypolimnion. In Paul Lake i t seems that the chironomid population was completely eliminated by Toxaphene. The population sampled i n the post-poisoning survey seems to be a repopulation, with the suggestion that i n the prolonged absence of predation, i t can increase beyond the density l e v e l of the pre-poisoning population. The Watermites show a decrease in density in post-poisoning samples amounting to 99.4% of the pre-poisoning f i g u r e s . The l i t e r a t u r e gives no indications of known ef f e c t s of Toxaphene on Watermites. The method of 40 sampling bottom fauna, as used (Ekman Dredge) in th i s study cannot f a i l to be a poor method for c o l l e c t i n g Watermites, so any figures r e s u l t i n g from t h i s sampling are suspect. The Watermites seem to have suffered severe adverse e f f e c t s of Toxaphene in Paul Lake. Gammarus l a c u s t r i s , never taken in zones other than the L i t t o r a l Chara, shows a decrease i n population density of 97.5%. The occurrence of one specimen from the S u b l i t t o r a l Zone i s ignored as an a r t i f a c t of sampling. The history of the Amphipoda i n Paul Lake i s well known. Larkin, e_t al_. , (1950), Larkin and Smith (1953), Crossman and Larkin (1959), and Johannes and Larkin (1961), a l l trace the decline of the amphipods in trout d i e t to increased predation on the amphipods by shiners. Cooper (1964) says "the lack of any apparent l i m i t a t i o n , and th e i r gregarious nature, leave predation as the major regulatory mechanism of the amphipod population". Hooper and Grzenda (1955) found the gammarids most sensi t i v e to Toxaphene. This seems to be the case i n Paul Lake. Given the oppor-tunity to increase i n density, in the absence of predators, the Gammarus l a c u s t r i s population of Paul Lake can be expected to increase u n t i l an equilibrium i s reached, determined by factors other than predation. The Sphaeriidae decreased i n population density 41 to an average of 91.5% i n both the zones of the L i t t o r a l i n which they occur, aft e r treatment of the lake with Toxaphene. Diet of freshwater clams consists of zooplank-ton, phytoplankton and organic d e t r i t u s . Larkin (1950) calculates the occurrence of sphaeriids i n trout stomachs at such a low figure for a two year period as to be almost n e g l i g i b l e . Hooper and Grzenda (1955) state that i n t h e i r lake under study "the Sphaeriidae did not appear to be harmed by Toxaphene". With l i t t l e or no predation on sphaeriids i n Paul Lake, we are forced to conclude, that, Hooper and Grzenda (1955) r e s u l t s notwithstanding, the Sphaeriidae i n Paul Lake were severely effected, and popu-l a t i o n density was decreased by Toxaphene. Planaria shows a decrease i n population density i n a l l zones after Toxaphene treatment, amounting to an average of 87.2%. Predation by fishes on Planaria, i n Paul Lake, i f present, i s not shown i n any of the previous studies. Pennak (1953) holds that the T u r b e l l a r i a are seldome an important element i n the diet of other animals. Food of Planaria i s usually small invertebrates, and dead animal matter. No data i s available from the l i t e r a t u r e on the e f f e c t s of Toxaphene on Planaria, but in view of the figures from the present study, they must be greatly affected by Toxaphene. 42 The Zygoptera f a i l e d to be taken i n the L i t t o r a l Chara Zone in post-poisoning samples, an area i n which they occurred in pre-poisoning samples, and were reduced 76.9% in the L i t t o r a l Non-Chara Zone. No data i s available on the e f f e c t s of Toxaphene on the Zygoptera. As an item in trout d i e t , the Zygoptera was estimated by Larkin (1950) as a mean of 1.7% over a two year period. Food of Zygop-tera consists mainly of aquatic insects, molluscs, C r u s t -acea, and annelids. Only the nymphal stages of the insect are aquatic. One year l i f e cycles are the most common, but there are many exceptions. Emergence extends the whole of the summer. Again, as with the Chironomidae, i t i s d i f -f i c u l t to place much reliance on the sampling figures of an emerging group as estimates of t o t a l population density. However, a decrease of 76.9% i s so great that i t seems safe to presume, even i n the absence of f i s h predators, and what seems to be unlimited food, that Toxaphene had a severe adverse e f f e c t on the population density increase of the Zygoptera. The l i f e cycle i s of such duration that the period between pre-poisoning and post-poisoning sampling was not s u f f i c i e n t l y long to allow for repopulation by Zygoptera from outside Paul Lake. H y a l e l l a azteca was reduced i n a l l zones to a calculated average of 71.8%. In the S u b l i t t o r a l Zone, an 43 area i n which H y a l e l l a azteca occurred i n pre-poisoning samples, no specimens were taken i n the post-poisoning seri e s of samples. As with Gammarus l a c u s t r i s , H y a l e l l a seems to have been severely adversely effected i n density increase by Toxaphene. The Planorbidae show a decrease i n the L i t t o r a l Chara Zone, amounting to 49% of the 1962 figures for that zone. In a l l other zones the orb s h e l l s increase. No explanation for the r e s u l t s has any basis i n fact, and there i s no means of knowing from the data whether the apparent decrease i s the r e s u l t of a change i n habitat of the Planorbidae from the L i t t o r a l Chara Zone to the L i t -t o r a l Non-Chara Zone, or i s i n fact the r e s u l t of an adverse e f f e c t by the Toxaphene on the Planorbidae in the L i t t o r a l Chara Zone. The Anisoptera show a decrease in both the L i t t o r a l Zones amounting to an average of 44.8%. With a mode of l i f e s i m i l a r to the Zygoptera, s i m i l a r e f f e c t s occur to the Anisoptera. Predation by trout on these animals i s indicated by Larkin (1950) as 7.5% of the t o t a l volume of food organisms i n trout stomachs, as an average over two years. No data i s available from the l i t e r a t u r e on the e f f e c t s of Toxaphene on Anisoptera. Occurring only in the L i t t o r a l Zone, the data from t h i s study indicates 44 that the population density decreased, even i n the absence of f i s h predators and unchanged available food. It seems that Toxaphene has had an adverse effect on the population density. As with the Planorbidae, the Physidae show an increase i n a l l zones except the L i t t o r a l Chara, where they show a decrease amounting to 38% of the population density i n t h i s zone i n the pre-poisoning samples. Again as with the Planorbidae, there i s no means of knowing from the data i n t h i s study whether the decrease i n density i n the L i t t o r a l Chara Zone i s the res u l t of a change of habi-tat of the Physidae, or i s due to t h e i r being k i l l e d by the action of the Toxaphene. The Oligochaeta show a decrease i n a l l zones except the L i t t o r a l Chara Zone, amounting to an average of 28.3% of t h e i r o r i g i n a l density i n those zones. The increase i n the L i t t o r a l Chara Zone (288%) more than com-pensates for the t o t a l decrease (84.9%) i n a l l zones. Cushing and Olive (1956) found that Toxaphene had no adverse e f f e c t s on the population density of the Oligo-chaeta, findings confirmed by Hooper and Grzenda (1955). Ignoring the detailed estimates, in the present data, an o v e r a l l increase of 203.1% r e s u l t s as the post-poisoning density figures. No explanation can be suggested for the 45 d i f f e r e n t i a l e f f e c t s of the Toxaphene i n the d i f f e r e n t zones, i f indeed there i s a d i f f e r e n t i a l e f f e c t , and not a change of habitat. (c) Species Occurring i n New Zones i n Post-Poisoning Samples. Three groups, the Ceratopogonidae, Physidae and Planorbidae, a l l occur i n the Profundal Zone i n the 1963 samples, an extension of depth range on the data from the 1962 samples. They occurred 4, 4, and 8 times respec-t i v e l y . It i s d i f f i c u l t to decide on those low figures whether a change of habitat i s indicated, or the figures are merely a r t i f a c t s of the sampling. (d) Species Occurring i n Zones i n 1962 and Not Present in 1963. Some group or groups occur i n zones i n the pre-poisoning samples, and f a i l to occur i n those zones i n the post-poisoning samples. These are tabulated i n Table XII. It w i l l be noticed that i f any group f a i l s to occur i n a zone i n which i t occurred i n pre-poisoning samples i t also shows a decrease i n density for a l l other zones in which i t does occur. It seems that the absence Table XII. Groups occurring i n pre-poisoning samples but not occurring i n post-poisoning samples, by zone. L i t t o r a l Chara L i t t o r a l Non-Chara S u b l i t t o r a l Profundal Zygoptera (107/m2) Ceratopogonidae (18.4/m2) Gammarus l a c -u s t r i s (4/m2) Lymnaeidae (0.7/m2) Ceratopogonidae (0.4/m2) Watermites (18.4/m2) Hya l e l l a azteca (2/mZ) Sphaeriidae (0.2/m2) Tricoptera (12/m2) Tricoptera (21.4/m2) Ceratopogonidae (0.8/m2) Ephemeroptera (l/m2) Ephemeroptera (10.8/m2) Sphaeriidae (3/m2) Tricoptera (.4/m2) Ephemeroptera (0.4/m2) 47 of a group from a zone of expected occurrence i n 1963 indicates that the ef f e c t s of Toxaphene on that group are progressively more severe and are maximal ( i . e . the group i s eliminated) in the zone of non-occurrence. 48 SUMMARY 1. Bottom fauna sampling with an Ekman Dredge, and stand-ard screening procedures, provides, at most, a r e l a t i v e estimate of population density, which can best be used for comparisons with data co l l e c t e d by s i m i l a r sampling. 2. The s i t e of the action of Toxaphene on invertebrates i s not known. The e f f e c t s of Toxaphene on the i n d i v i d u a l groups of a population can, for the present, only be measured empirically. 3. The animals that increased in density, and so were presumed to have been unaffected by Toxaphene and the absence of predatory f i s h were the Gastropoda, O l i o -chaeta, and the Hirudinea. 4. The animals that decrease i n density, and were presumed to have been severely effected by Toxaphene, were the Watermites, Amphipods, Chironomidae, Planaria, Sphaeriidae, Odonata, and the Oligochaeta (in a l l zones other than the L i t t o r a l Chara). 5. Tricoptera, Ephemeroptera, and Ceratopogonidae a l l seem to have been adversely effected by Toxaphene, and to have been completely eliminated from the lake. Certain others show a decreasing trend (Table XII). 49 6 . C a l c u l a t i o n s of the f i g u r e s f o r s p e c i e s o c c u r r i n g i n new zones, c o u l d be a r t i f a c t s of sampling. 50 LITERATURE CITED American Medical Association. 1952. Council on Pharmacy and Chemistry. Pharmacological Properties of Toxa-phene, a Chlorinated Hydrocarbon Insecticide. Jour. Amer. Med. Assoc., 149;1135-1137. Ball, R.C. and D.W. Hayne. 1952. Effects of the removal of a fish population on the fish food organisms of a lake. Ecol., 33:41-48. Brown, C.J.D. and R.C. Ball. 1942. A population study of Third Sister Lake. Trans. Am. Fish Soc, 72:177-186. Brown, C.J.D. 8B R.C. Ball. 1942. An experiment in the use of derris root (rotenone) on the fish and fish food organisms of Third Sister Lake. Trans. Am. Fish. Soc, 72:267-284. Cheatum, E.P. 1953. Limnological investigations on res-piration, annual migratory cycle, and related phenomena in freshwater pulmonate snails. Trans. Am. Microscop. Soc., 53:348-407. Cooper, W.E. 1964. Population dynamics, production and regulation of a natural population of a freshwater amphipod Hyalella azteca. Ph.D. Thesis, University of Michigan, 96 pp. Crossman, E.J. and P.A. Larkin. 1959. Yearling liberations and change of food as effecting rainbow trout yield in Paul Lake, British Columbia. Trans. Am. Fish. Soc, 88:36-44. Cushing, C.E. and John R. Olive. 1956. Effects of Toxa-phene and Rotenone upon the macroscopic bottom fauna of two Northern Colorado Reservoirs. Trans. Am. Fish. Soc, 86:294-301. Gerking, S.D. 1962. Production and food uti l i z a t i o n in a population of Bluegill Sunfish. Ecol. Mono., 32:31-78. Hamilton, A.L. 1965. An analysis of the freshwater benthic community, with special reference to the Chironomidae. Ph.D. Thesis, University of British Columbia, 96 pp. Hilsenoff, W.L. 1965. The effect of Toxaphene on the benthos of a thermally st r a t i f i e d lake. Trans. Am. Fish. Soc, 94:210-213. 51 Hooper, F.F. and A.R. Grzenda. 1955. The use of Toxaphene as a f i s h p o i s o n . Trans. Am. F i s h . S o c , 85:180-190. Johannes, R.E. and P.A. L a r k i n . 1961. Competition f o r food between Redside s h i n e r s ( R i c h a r d s o n i u s b a l t e a t u s ) and Rainbow t r o u t (Salmo g a i r d n e r i ) i n two B r i t i s h Columbia l a k e s . J . F i s h . Res. Bd. Canada, 18:203-220. Jonasson, J . 1955. E f f i c i e n c y of s i e v e s . Oikos, 6:183-207. L a r k i n , P.A., G.C. Anderson, W.A. Clemens and D.C.G. Mackay. 1950. The p r o d u c t i o n of Kamloops t r o u t (Salmo  g a i r d n e r i i kamloops Jordan) i n P a u l Lake, B r i t i s h Columbia. S c i . Publ., B r i t i s h Columbia Game Comm., No. 1, 37 pp. L a r k i n , P.A. and S.B. Smith. 1953. Some e f f e c t s of the i n t r o d u c t i o n of the Redside s h i n e r on the Kamloops t r o u t i n P a u l Lake, B r i t i s h Columbia. Trans. Am. F i s h . S o c , 83:161-175. Lehman, A.J. 1948. The pharmacology of the newer i n s e c t i -c i d e s . U.S. Food and Drug. Adm. Proc. I n t . Congr. Trop. Med. and M a l a r i a . M o r e t t i , G.P. 1948. C h l o r i n a t e d i n s e c t i c i d e s and t h e i r t o x i c i t y to c e r t a i n arthropods and v e r t e b r a t e s . A t t i . s o c i t a l . s c i . nat. e museo c i v i c o s t o r i a nat. Milano., 87:5-39. A b s t r a c t i n Chemical A b s t r a c t s , 45:3979f ,~T951. Morgan, A.H. 1930. F i e l d book of ponds and streams. New York. G.P. Putnam's Sons, 449 pp. M i l l e r , R.B. 1941. A c o n t r i b u t i o n to the ecology of the Chironomidae of C o s t e l l o Lake, Algonquin Park, O n t a r i o . Univ. Toronto S t u d i e s , B i o l . S e r i e s No. 49, 63 pp. Pennak, R.W. 1953. Freshwater i n v e r t e b r a t e s of the United S t a t e s . New York. The Ronald Press Company, 769 pp. Rawson, D.S. 1934. P r o d u c t i v i t y s t u d i e s i n l a k e s of the Kamloops Region, B r i t i s h Columbia. B i o l . Bd. Canada, B u l l . 42:1-31. Schoettger, R.A. and J.R. O l i v e . 1961. Accumulation of Toxaphene by f i s h food organisms. Limnol. Oceanogr., 6:216-219. Welch, P.S. 1948. L i m n o l o g i c a l Methods. New York. McGraw-Hill Book Company, Inc. 381 pp. 

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