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UBC Theses and Dissertations

A study of the production of Kamloops trout (Salmo gairdnerii Kamloops Jordan) in Paul Lake, British… Anderson, George Cameron 1949

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A STUDY: QF THE PRODUCTION CF KAMLOOPS TROUT (Salmo gairdnerii kamloops Jordan) i n PAUL LAKE, BRITISH COLUMBIA by George Cameron Anderson A Thesis submitted i n p a r t i a l fulfillment of the requirements for the degree of MASTER OF ARTS i n the Department of ZOOLOGY. The University of B r i t i s h Columbia September, 1949. ABSTRACT An investigation of the limnology and the Kamloops trout population of Raul Lake, British Columbia, from the summer of 1947 to the end of the summer of 1949, i s presented. Comparisons of the conditions found by the writer are made with those conditions reported by Drs. C.McC. Mottley, D.S. Rawson and D.C.G. MacKay.in previous investigations of Paul Lake. Analysis of the environmental conditions indicated extreme annual variations i n the summer heat income, an abundance of oxygen at a l l depths, minor annual fluctuations i n the quantity of plantkon, a significant decrease in the quantity of bottom fauna which was believed due to the depletion of the Gammarus population, and a f a i r l y large supply of available food. Another species of f i s h , the redside shiner, has made i t s entry into Paul Lake. The statistics of the trout population has shown a decrease in the average size of the age classes of trout since 1931, a large proportion of the younger age classes of trout i n the anglers' catch and i n the spawning run and a decrease in the size of eggs and number of eggs per female. A large year class resulting from 1945 has been followed through the fishery. The main effects of this year class appear to have been a greater survival of trout and a restoration of older age classes i n the anglers' catch and i n the spawning run. A comparison of the 1949 creel census data with that for 1936 has indicated a two-fold increase i n fishing intensity, a slight decrease i n the total catch and a decrease of two-thirds i n the catch per unit e f f o r t . A revised stocking policy, patterned after the 1945 year class, i s outlined. 3. ACKN CWIEDGEMENTS The writer wishes to express his sincere appreciation to Dr. W.A. Clemens, head of the Department of Zoology, for suggesting the problem and for his guidance and keen interest in the work. The writer is indebted to Dr. P.A. Larkln for his valuable criticisms and constant help in the preparation of the manuscript. Special thanks are due to the following: The University of British Columbia and the Provincial Game Commission for financial support which made the field work possible. The International Pacific Salmon Commission for the use of a Promar scale projector. The staff of Echo Lodge, especially Mr. J.R. Morrill, for their co-operation with the creel census and the field work as a whole. Dr. D.C.B-. MacEay for use of data in his unpublished report. Dr. C.McC. Mottley and Dr. D.S. Rawson for supplying unpublished information pertinent to the problem. Hatchery officers P. Pells and P. Martin for their assistance in sampling the spawning run. A sincere acknowledgement is also made to a l l my classmates who assisted in the field work. TAB IE OF CONTENTS. page INTRODUCTION 1 ACKNOWLEDGEMENTS 3 LOCATION AND MORPHOMETRY 4 PHYSICAL AND CHEMICAL CONDITIONS 6 TEMPERATURE 6 OXYGEN CONCENTRATION 9 FAUNA OF THE LAKE 10 PLANKTON 10 BOTTOM FAUNA 13 Numerical analysis .... .... .... 13 Gravimetric analysis 14 Discussion 13 FISH FAUNA 21 FOOD SUPPLY OF THE TROUT 24 VOLUME OF STOMACH CONTENTS 24 ANALYSIS OF STOMACH CONTENTS 26 DISCUSSION 27 STATISTICS OF THE TROUT POPULATION 31 HISTORY OF THE STOCKING POLICY .... 31 ANGLERS' CATCH 33 Average measurements 34 Age composition 35 Catch curve analysis .... .... 36 page Length frequency distribution .... 39 Growth of the trout 39 Sex ratio 4-9 CREEL CENSUS 52 SPAWNING RUN 54 DISCUSSION 59 SUMMARY AND CONCLUSIONS 64 REFERENCES • 66 APPENDIX A 68 APPENDIX B 73 1. A STUDY OF THE PRODUCTION OF KAMLOOPS TROUT (Salmo gairdnerii kamloops Jordan) i n PAUL IAKE, BRITISH COLUMBIA. INTRODUCTION This report deals with an investigation of the limnology and the Kamloops trout population of Paul Lake, British Columbia, from the summer of 1947 to the end of the summer of 1949. The purpose has been to provide a contribution to the solution of the problem concerning the propagation and conservation of Kamloops trout, particularly i n Paul Lake, but also i n other lakes of the province. Originally, Paul Lake was barren of f i s h , but i t was stocked i n 1909 by the Domini on Department of Fisheries. The species of f i s h selected for stocking was the Kamloops trout, Salmo gairdnerii kamloops Jordan. The lake was suitable for investigation because Kamloops trout was the only species present, the spawning run could be controlled, and a creel census was practical. E a r l i e r investigations of this lake have provided a valuable background. In the period from 1931 to 1936, a major study was carried out by the Fisheries Research Board of Canada. Dr. C.McC. Mottley investigated the l i f e history, population and culture of the trout. Dr. D.S. Rawson, i n 1931, made a special study of the limno-l o g i c a l conditions. In 1946, Dr. D.C.G. MacKay conducted a general survey involving plankton collections, temperature, oxygen and pH determinations and samplings of fis h from the anglers' catch. 2. The material for the present report consists of data obtained in the summer of 1947 by Dr. W.A. Clemens and that obtained by the writer in the summer of 1948 and 1949 including the addition of bottom samples, assessments of the spawning runs and a creel census in 1949. Further, winter samples of plankton, temperatures and trout were taken in December, 1948. Comparisons of the physical and chemical conditions, the food supply and the statistics of the trout population, as found by the writer, are made with those conditions reported by Drs. Mottley, Eawson and MacKay. On this basis, recommendations are advanced for the future scientific management and continued investigation of Paul Lake. It is hoped that the findings may find some application to the problems in other lakes. LOCATION AND MORPHOMETRY Paul Lake lies in a narrow rocky valley at an altitude of 777 m. (2542 ft .) , 19.2 km. (12 mi.) north east of Kamloops. It has a length of 6.1 km. (3.8 mi.) and an average width of 0.48 km. (0.3 mi.). The area is approximately 3.9 sq. km. (1.5 sq.mi.) while the maximum depth observed was 55.5 m. (182 ft . ) . The lake has one major inlet, Paul Creek, which drains Pinantan Lake. There are also a few mountain streams entering the lake which become dry in the summer months. There is only one outlet, Paul Creek. An outline map of Paul Lake is shown in figure 1. Figure 1. Outline map of Paul Lake (from Rawson, 1934). S - station S.S. - sub station D.S. - dredging series. 6. PHYSICAL AND CHEMICAL CONDITIONS TEMPERATURE. Series of temperatures were taken at various stations during the summers of the investigation. Tabulated results are shown in Appendix A. The locations of the stations are shown in figure 1. Rawson (1934) has described the thermal stratification of Paul Lake. After the spring turnover, the upper 10 m. gradually warms up to midsummer conditions. The thermocline is located in the 4.5 to 15 m. region, varying with the annual climatic coniitions. The average depth of the upper limit of the thermocline is approximately 5 m. There is very l i t t le mixing of water below the thermocline at any time during the summer. The surface temperature may reach a high of 21.5 deg. C. during the summer while the bottom temperature may reach a high of 4.8 deg. C. approximately at the same time. Typical midsummer thermal conditions in Paul Lake are shown in figure 2. The following figures show the summer heat income* for 1931, 1946, 1947, 1948 and 1949. These have been calculated according to the method of Barge and Juday (1914)> and are expressed in gram calories per square centimetre of lake surface. 1931 - 19,562 gm. cal. 1946 - 16,142 gm. cal. 1947 - 15,937 gm. cal. * The summer heat income is the amount of heat necessary to raise the water from 4 deg. C. to the maximum summer temperature. The formula used to calculate the heat income was as follows: Dm (Tm - 4 deg.C.) • gm. cal/sq. cm. of lake surface. Dm - mean depth in cms. Tm - mean temperature. 7 1948 - 11,423 gm. cal. 1949 - 13,612 gm. cal. The summer heat income for Paul lake shows definite annual fluctuations. The greatest variation can be noted in a comparison of the heat incomes for 1931 and 1948. The difference was in the order of 8,000 gm. cal. The summer heat income in Paul Lake in 1931 is similar to that found in Cultus Lake by Ricker (1937), who stated that the heat budget of Cultus Lake was a direct reflection of the generally equable climate of the region. However, the summer heat income for Paul Lake in 1948 was similar to that of Maligne Lake (Rawson 1942) which is described as an extreme "mountain type". Annual fluctuations of this magnitude in the summer heat income of a lake might be expected to have definite ecological effects. However, no direct relation could be found between the summer heat income and the growth rates of the trout. Possibly some other aspect of temperature conditions might show a correlation to the growth rate of trout. TEMPERATURE. °C. Figure 2. Midsummer thermal conditions i n Paul Lake, August 3, 1949. 9 OXYGEN CONCENTRATION. Oxygen determinations using the Winkler, method were made at intervals throughout the summer of 1947 and one determination was made in the summer of 1948. Midsummer oxygen conditions are shown in Table I . Table I . Midsummer oxygen determinations in Paul lake, 1931, 1946-1948. (p.p.m.) 1931 1946 1947 Depth Aug. 22. Aug 17. Aug 21. Aug. 18. (m). 0 6.3 8.3 9.2 8.4 12 9.4 15 6.3 - 9.2 9.3 5 0 4.4 7.0 . 5.6 4-7 There does not appear to be any appreciable difference in dissolved oxygen among the records of the last three years. The oxygen content for 1931 is lower probably because of the higher water temperatures prevailing in 1931 and possibly the results of the determinations are somewhat low due to the use of Miller's method.which apparently under certain conditions may give low results. Rawson (1934), has stated that the oxygen supply is always abundant and thus does not act as a limiting factor for the life in the deep waters. 10. FAUNA OF THE LAKE PLANKTON. Plankton hauls were taken periodically throughout the summers of the investigation. Figure 1 shows the locations of the plankton stations. The plankton nets used were modified closing nets of the Wisconsin type (Juday 1916). The net had an aperture of 23 cm., inside diameter, and a f i l t e r i n g area of approximately 3,000 sq. cm. Nets were made up of number twenty bolting s i l k , 77 meshes to the centimetre, and number ten bolting s i l k , 44.5 meshes to the centimetre. The method used i n obtaining a l l of the plankton samples was a t o t a l v e r t i c a l haul taken at a speed of half a metre per second. The samples were then preserved i n weak formalin. Volumes of plankton were obtained by allowing the sample to settle for twenty-four hours i n a graduated centrifuge tube. Centrifuged volumes were obtained by centrifuging each sample for ten minutes at a rate of approximately 1,800 revolutions per minute. Table II shows the settled and centrifuged volumes of the to t a l vertical hauls of plankton. Ricker (1937) has shown that a net of number twenty s i l k strains a volume of water which varies with a number of conditions, and hence is. of l i t t l e use quantitatively unless frequently standardized. He has also shown that a net of number ten s i l k appears to be "unusually constant", even over long periods, and makes an excellent sampling apparatus for adult Entomostrada. In the series i n Table II, the efficiency of the number twenty net has been calculated, using the number ten net as a standard. The relative efficiency of the number twenty net ranges from 13 per cent to 71 per cent. 11. TAB IE I I . Volumetric plankton analyses, Paul Lake, 1947-194-9. Year Date - Station SIC net #20 net Settled Centri- Settled Centri- Effic-volume fugal volume fuge! iency (c.c.) vol (cc] (c.c.) vol (cc) » ) 1947 Jul 22 S.S. 113 9.2 4.8 3.5 1.7 35.4 Jul 26 5.7 3.1 2.5 1.5 48.4 Aug 21 5.2 2.7 1.8 1.2 44.4 Sep 2 4.6 2.9 3.3. 1.0 34.5 Jul 23 S.S. II 12.1 7.2 7.4 3.6 50.0 Jul 28 16.9 10.2 4.5 3.0 29.4 Aug 21 5.9 3.0 1.3 0.9 30.0 Aug 29 6.5 3.6 2.7 0.9 25.0 Sep 2 5.0 2.4 3.3 1.1 45.8 1948 Jul 24 S. 1 19.1 13.1 2.7 1.75 13.4 Jul 29 15.1 9.7 3.0 1.8 18.6 Aug 9 5.3 3.5 3.1 1.85 52.9 Aug 18 3.9 2.6 1.1 0.75 28.8 Sep 10 5.3 3.5 1.55 1.0 28.6 Dec 17 S.S. I 0.9 0.7 0.8 0.5 71.4 1949 May 10 S. I 1.25 0.8 Jun 25 3.1 2.1 Aug 3 3.1 1.9 May 10 S.S. I 0.4 0.25 Jun 25 2.3 1.7 Aug 4 3.1 2.1 12. It is interesting to note that the efficiency was lowest when plankton was abundant (July 24-29) and was highest when plankton was scarce (December), The peak of plankton production appeared in late July in 1947 and 1948. In 1949 the peak of production was missed. It is probable that i t occurred earlier in July and the plankton was on a downward trend when the sample was taken on August 3. The winter sample (0»7 c .c ) , taken in December 1948, indicates a fairly large quantity of plankton for this season in comparison with the sample (o.25 c.c.) obtained in May 1949 at the same location. The mean quantities of plankton taken in July and August in 1931, 1946, 1947 and 1948 are given in Table III. Figures for 1931 have been taken from Clemens, Rawson and McHugh (1939) and figures for 1946 have been taken from MacKay (unpub.). TAB IE III. Mean volumes of total vertical plankton hauls taken in July and August, Paul Lake, 1931, 1946-1948. -5k* Year Settled Volume (c.c.) Centrifugel Volume (C.C.) Settled Volume (c.c.) Centrifugal Volume (c.c.) 1931 - 4.4 -1946 - 2.15 - 0.6 1947 10.35 6.0 4.0 2.1 1948 10.85 7.2 2.5 . 1.5 The average amount of plankton recorded for 1946 was low in comparison with that of the other years. Figures for 1947 and 1948 13 indicate a definite increase i n the plankton population over that shown for 194-6. Rawson (1934), states that the plankton i s only moderate i n quantity but that i t might indicate efficiency of u t i l i z a t i o n i n the rapid "turn over" and non-accumulation of nutrient materials. BOTTOM FAUNA. Series of bottom dredgings were taken i n 1948 and 1949 with a 523 sq. cm. Ekm/zfin dredge. A to t a l of 68 dredgings were made, 15 collected i n 1948 and 53 collected i n 1949. Locations of the dredging series are shown i n figure 1. In order to make the dredgings comparable with those taken by Rawson i n 1931, the samples collected i n 1949 were taken i n approximately the same locations that Rawson used i n 1931. The samples were washed through a coarse and a fine mesh screen (225 meshes per sq. cm.) and the visible organisms preserved i n alcohol. Reference has been made to Ward and I h i ^ l e (1918) and Needham and Needham (1941) for the identification of organisms. Numerical Analysis Each group of organisms was counted and the results are recorded numerically i n table IV, according to the different depth zones. The to t a l number of each group of organisms and the tot a l number of organisms have been calculated for the entire area of the lake. These totals have been weighted for the areas of the depth zones. Figures for 1931 have been taken from Rawson (1934). Several variations i n the abundance of groups of organisms can be noted i n 1949 when compared with those numbers recorded i n 1931. The Chiromonidae were almost twice as abundant i n 1949/ and made up 75 per cent of the t o t a l number of organisms. There was also a larger number of L4. Planorbis, Zygoptera and Awisoptera, Ephemeroptera, and Ollgochaetes in 1949. h^e Gammarus and Hyalella populaiflons have been reduced considerably, especially the Gammarus. The numbers of Sphaeriidae and Hirudinea have also decreased. The total number of organisms per sq. m. in the lake as a whole was larger than that recorded in 1931. Figure 3 represents the average number of organisms for the various depth zones in 1931 and 1949. The greatest number of organisms for both years occurred in the 0 to 5 m. zone. There was a sharp drop in numbers in the 5 to 10 m. zone in both cases. In 1931 there was an increase in numbers in the 10 to 20 m. zone, almost equaling that of the 0 to 5 m. zone. This was followed by a steady decline in numbers down to 55 m. In 1949 the numbers of organisms levelled off at the 10 to 40 m. zone and then dropped sharply down to 55 m. The numerical analysis shows fluctuations in the populations of the different groups of organisms but gives no indication of the quantitative nature of the food supply. Gravimetric Analysis Each sample was weighed individually after carefully blotting the excess moisture. In this manner the wet weight of the sample was obtained. The weight of Mollusc shells was deducted according to Rawson (1934). Twenty per cent of the total wet weight of Physa and thirty-two per cent cffthe total wet weight of other Molluscs is the amount contributed by the shell. The number of dredging samples taken in 1948 is small and therefore a comparison with the quantity of bottom fauna in 1931 gives somewhat doubtful results. The mean wet weight of organisms of eight dredgings in the 0 to 10 m. zone in 1948 is 1.35 gms. in comparison TAB IE IV Numerical analysis of bottom dredgings, Paul lake, 1949 as compared to 1931. Depth Zone (m.) Organisms 19A9 1931 , 0 - 5 5-10 10 - 20 20-30 30-40 40-50 50-55 &0-55 *0-55 , Chironomidae 2,110 1,651 1,343 1,767 1,545 595 1,121 672 Hyalella 969 7 - mm - mm - 101 198 Gammarus 8 22 1 - 3 - 4 166 Physa 14 57 3 - - mm - 8 7 Limneq 6 100 1 - - - mm 11 4 Planorbis 253 342 1 - - mm - 62 -Spbaeriidae 67 40 259 - ;;95 - - 70 247 Zygoptera 113 62 - - - ' - - 18 3 Anisoptera 84 19 - . - - - - 11 2 Trichoptera 21 7 - - - - - 3 3 Ephemeroptera 71 2 - - - mm - 8 -Hirudinea 12 9 - - - - - 2 19 Plawaria 14 28 51 57 41 57 - 34 30 Oligochaeta - - 7 47 70 89 38 a 10 Miscellaneous 6 - 4 - - mm - 1 2 Totals 3,74-8 2,346 1,670 1,871 1.754 741 38 1,495 1,363 * weighted average. Figure 3 . Average number of bottom organisms at various depths i n Fata Lake, 1931, 1949. 1931 1949 4000 D E P T H I N M E T E R S 18 with 2.39 gms. in 1931. This suggests a decrease in the quantity of bottom fauna in the lake. In 1949, a thorough investigation of the bottom fauna was made. The results are tabulated in Table V along with results from 1931 which have been taken from Rawson (1934). Detailed results of the gravimetric analysis for 1948 and 1949 are shown in Appendix A. From an examination of the mean wet weights, there appears to be a decrease, in a l l depth zones, in the wet weight of bottom organisms in 1949 as compared with 1931. The data were subjected to an analysis of variance modified for a weighting procedure as described by Snedecor (1946, pp. 462, 463). A Summary of the analysis Is as follows: Year Mean (gm.) Sx Variance "t" value in comparison 1931 o.955 0*151 0.022796 ^ 3 85 1949 0.399 (}.054 0.002919 The size of the sub samples (number of dredgings in each depth zone) is small, varying from 4 to 28, so that the significance of a wt" value is difficult to assess, particularly with the complication of the weighting procedure. Assuming that n t n is distributed normally in this type of calculation, the value of 3.85 has a probability of <~ .001 which is highly significant. It is probably safe to conclude that the total quantity of bottom fauna in Paul Lake in 1949 is significantly less than that in 1931. Discussion. A numerical and a gravimetric comparison of the bottom fauna in Paul Lake in 1931 and 1949 has been made. The numbers of organisms have increased while the amount of bottom fauna has decreased. The T A B I E V Gravimetric analysis of the bottom fauna. Depth Zones (m.) Area of Depth Zone (*) 1949 >31 No. of Samples Mean Wet weight (gm.) S 2 Weighted mean (gm.) No. of Samples Mean Wet weight (gm.) S 2 Weighted mean (gm.) 0-10 10.4 28 1.765 1.851 .184 20 2.514 3.891 .261 10-20 17.9 13 .289 .358 .052 9 1.710 4.088 .306 20-40 24.5 8 .262 .027 .064 11 .852 .849 .209 40-55 47.3 4 .083 .020 .039 11 .378 .074 .179 Weighted mean - .339 gm. Weighted mean - .955 gm. (al l depths) (all depths) 20. Increase in numbers has been mainly due to one group of organisms, the Chironomidae. These are small organisms which require large numbers to contribute significantly to the total weight. The group_pf organisms that have shown a definite decrease in numbers are the Gammarus,. < Gammarus are usually relatively large organisms which contribute a large proportion to the total weight.of a sample i f found in moderate numbers, so that the decrease in quantity of bottom fauna appears to be mainly due to the decrease in the population of Gammarus. The decrease in the Gammarus population might possibly be due to overgrazing by the trout since 1931, as in that year the stock of trout was depleted (Mottley 1932). If this is the case, i t would appear that the bottom fauna was being more efficiently utilized in 1949 than in 1931, as there did not appear to be a significant decrease in the available food of the trout which is shorn in a later section of the paper. The phenomenon of complete removal of Gammarus populations has havo been reported in other small lazkes in British Columbia (Larkin, unpub. verbal information). Another possible explanation for the reduction in the Gammarus population is that of natural annual variation. A poor spawning season or some detrimental ecological effect might be the cause of the variation observed in Paul Lake. Lundbeck (1926) and Aim (1922), cited by Rawson (1930), have observed two-fold annual variations in the total quantity of bottom fauna in some localities. It was not specified whether the variation was due to fluctuations in one group or a l l groups of bottom organisms. 21. FISH FAUNA. The redside shiner, Richardsonius balteatus (Richardson). i s the only species of f i s h other than Kamloops trout which occurs i n Paul Lake. This species, i n 194B, made i t s way down from the upper lakes i n the same chain as Paul Lake, where i t had been introduced by anglers. The shiners i n Paul Lake are best treated as a potential source of food rather than available food, particularly since observations made i n other lakes would suggest that the trout may eventually feed upon the shiners. In two small lakes i n the same chain as Paul Lake, Hyas and Pinantan lakes, the trout do feed upon shiners. In these lakes, i t i s alleged that after the appearance of shiners, fishing was poor. After three or four years, the trout "obtained the habit" of eating shiners and fishing gradually returned to i t s previous standard. Mr. CC. Lindsey (unpub. verbal information) has made interesting observations on shiners and eastern brook trout, Salvelinus  fontinalis (Mitchell), in Rosebud Lake i n the West Kootenay. Shiners are extremely abundant i n this small lakej seine haftls of 500 to 1,000 individuals are readily taken. They are a major item i n the diet of the brook trout and i t would seem that with such a high density of shiners, the trout would exhibit a relatively fast rate of growth and the shiner^ population^ would be depleted. However, Mr. Lindsey has observed that the brook trout have great d i f f i c u l t y i n catching the shiners. He records the observation that a brook trout may make many attempts to catch one of a large school of shiners, but w i l l usually he unsuccessful. If dead shiners are thrown i n the water, the brook trout show no hesitation i n taking them. 22 It might be surmised from these observations that i t i s only when shiners are extremely abundant that they are sufficiently available for trout to u t i l i z e as an item of their diet. In the f i r s t few years following their introduction into a lake, the shiners would be at a low density and their occurrence i n trout stomachs would be rare. At a higher density, shiners would be more readily available to trout and their occurrence i n trout stomachs would be more common. It might also be supposed that i n the f i r s t few years after their introduction into a lake, the increase i n the numbers of shiners would be exponential. Consequently, the a v a i l a b i l i t y and the occurrence of shiners i n trout stomachs would also increase exponentially and would give the impression that trout had suddenly "obtained the habit" of eating shiners. It would be expected then, that i n Paul Lake, records of shiners i n the stomachs of trout w i l l be occasional i n the f i r s t few years following the entry of shiners into the lake. In three or four years time the shiners may attain a sufficiently high density that they w i l l be commonly taken by trout, as i s now apparently tine case i n Hyas and Pinantan lakes. The question of the effect the shiners w i l l have upon the fishing at Paul Lake can only be answered by future observations. Their beneficial effects may be (1) to increase the available food supply for the larger trout and thus increase their rate of growth, (2) to u t i l i z e food organisms i n the lake that are not commonly taken by trout, e.g., Copepoda, and thus increase the efficiency with which the primary f i s h food organisms (plankton and bottom fauna) are converted into trout fles h . 23. Their main detrimental effect appears to be that of competition for food with the trout. In an analysis of seventeen shiner stomach contents, Copepoda, Cladocera, Ephemeaoptera and Chironomidae predominate i n the order named. Carl and Clemens (1948) state that the shiners of Okanagan Lake fed mainly upon Copebda, Cladocera, and Chironomidae. The ultimate effect of the presence of a large shiner population i n Paul Lake is worthy of study. 24. FOOD SUPPLY OF THE TROUT In this section, only the food organisms found in the trout stomachs wi l l be dealt with. Al l other organisms found in the lake, exclusive of those found in the trout stomachs, may be classified as indirect or potential food for the trout. Stomach contents were preserved from approximately one third of the. trout sampled from the angler's catch from 1947 to 1949. Samples were taken from various sizes of fish which were caught either by fly fishing or trolling. Collections were made from spring through to fa l l so that variations in the available food supply during the fishing season could be observed. Winter samples were obtained in December, 1948, by means of g i l l netting. VOLUME OF STOMACH CONTENTS. Individual stomach contents were placed on paper towels to absorbtthe excess moisture. The volume in c.c. of each stomach content was then obtained by placing the contents in a graduated centrifuge tube along with a known amount of water. Results for July and August of 1947 and July, August, and December of 1948 along with figures taken from Mottley and Mottley (unpub.) for 1932 to 1935 are shown in Table VI. The factor, mean length of the trout divided by the mean volumes of the stomach contents is meant to show the condition of the available food supply. That is, a high value for the factor indicates a low available food supply while a low value for the factor indicates a relatively large available food supply. A linear relation between the length of the fish and the volume of the stomach was assumed. TAB IE VI. Volumetric analysis of trout stomach contents, Paul Lake, 1932-1935, 1947, 1948. Year Month Number of Stomachs Number of Empty Stomachs Mean Length of f i s h (c.m.) Mean Volume of Stomach contents (c.c.) Factor Mean length Mean volume 1932 Julwand Aug 157 13 35.2 * 2.96 11.9 1933 Jul,and Aug , 51 10 35.9 1.81 19.8 1934 Jul, and Aug, 33 6 36.2 2.49 U . 5 1935 Jul,and Aug. 55 18 31.0 0.91 34.1 1947 Jul and Aug • 37 7 32.6 1.73 18.8 1948 Jul" and Aug „ 69 4 37.1 1.74 21.3 December 29 1 28.8 0.99 29.1-26. Mottley and Mottley (unpub.) have inferred that the change i n amount of food eaten from 1932 to 1935 directly reflects a decrease i n the availability of food of the trout, which might indicate correspond-ing changes i n the food supply of the lake. They have also observed a significant downward trend i n the available food supply from spring to f a l l of each year. The volumes for July and August of 1947 and 1948 show what would appear to be a significant increase i n available food over that of 1935. The low summer heat income i n Paul Lake i n 1948 could possibly be a contributing factor i n the relatively lower supply of available food i n comparison with 1947. The winter samples taken i n 1948 show a rela t i v e l y large supply of available food for this season. Evidence to support the fact that the mean volumes of stomach contents i s a f a i r estimate of the available food supply can be seen i n the percentage of empty stomachs noted 'during the different years. The samples for 1948 should be deleted owing to the extreme environmental changes. When the available food supply i s high, the percentage of empty stomachs i s low. Conversely, the percentage of empty stomachs increases when the available food supply decreases. A Chi square analysis comparing the r a t i o of empty stomachs to f u l l stomachs gave the following results: 1932 vs. 1935 p. .01 significant 1948 vs. 1935 p. ^ .01 significant 1932 vs. 1948 p. >- .7 non significant ANALYSIS OF STOMACH CONTENTS. A microscopic examination of each stomach sample was made and the groups of organisms identified. An estimate of the percentage volume of each group of organisms was made for each sample. The percentage 27. volume was converted into c c . as a function of the t o t a l volume of the stomach sample. Total percentage volumes for each group of organisms were then calculated, taking into account the volume i n c c . each group of organisms contributed to the total volume of a l l the stomach samples i n one season. This method of representation i s not meant to show the feeding habits of the trout, but i s devised to show the quantitative importance of each group of organisms i n regard to the t o t a l volume of stomach contents for any one season. The results are shown i n Table VII. Daphnia pulex. Odonata, Gastropoda, and Hyale 11a were the most abundant food organisms i n the diet of the trout and predominated i n the order named. Daphnia pulex was the dominant item of food i n " a l l seasons except May, 1949, when i t was surpassed by Anisoptera and Hymenoptera. In a l l seasons sampled i n 1947, 1948 and 1949, Gammarus made up a very small percentage of the stomach contents with the exception of December, 1948, when i t contributed 18.8 per cent to the total volume. These data would bear out Rawson's observation that the trout ate large quantities of insects i n May and June while the water was sufficiently cool to allow feeding at or near the surface. In t h i s investigation, the trout were found to eat large quantities of bottom and surface insects i n May and June and large quantities of bottom insects i n December. Discussion. It i s apparent that there are conspicuous seasonal and annual differences i n the diet of trout which presumably re f l e c t seasonal and annual variations i n the availability and abundance of the different food organisms. Rawson (1934) observed that Gammarus was the main food item of trout i n Paul Lake i n 1931 and Daphnia pulex was next i n order. In the period from 1947 to 1949, i t was found that Gammarus made up only Year Date May o CO fc- ^ Cj( .§£ £g n I £ WH ro ON vO O <I CO 521 0 o § 1 H> & P CD g-18.3 • •OIMMO •J H TOvO .... . . H UJ Daphnia pulex UJ * CO • . • • UJ ON -0 1 o . ro Gammarus Q 1 a, $ to H • UJ ro « o M ro UHHO) .... H fO O H 1 • ON Hyalella Q 1 a, $ to g vn U> H • • 1 o 0s 0s  . O Ui ON H Awisoptera Q 1 a, $ to UJ • 09 CO i ro i • • 1 1 Zygoptera Q 1 a, $ to . UJ p CO o ro H co • • . . .£» ro UJ v£> 1 o^ • CO Trichoptera Q 1 a, $ to o UJ • H H O 1 H . . . H H O 1 1 Ephemeroptera Q 1 a, $ to vO • O • O O O O . • • • <J ^- UJ 1 1 Coleoptera Q 1 a, $ to ro • ro O O O H . • • • £» VJl . . ro ON Chironomldae Q 1 a, $ to 21.3 1*11 CO 1 1 Hymenoptera Q 1 a, $ to i \-> o «J UJ • • • • CO O UJ CO H -3 UJ . . ON H Physa Q 1 a, $ to UJ • vO M co ro M .... ro vO o vO 1 o CO Llmnea Q 1 a, $ to 1 H 1 O O CO UJ vO 1 o • ro Planorbis Q 1 a, $ to 1 1 O 1 o H H 1 1 Sphaeriidae Q 1 a, $ to 1 1 1 H UJ 1 Hirudinea Q 1 a, $ to • o i to o to ... CO -0 . . vO ON Miscellaneous Q 1 a, $ to (D 4 o I SB TO CD •i CD I O 4 TO to CD 4 CO 6 a to 5 is •2Z 29 a minor item of the diet of the trout which reflects a decrease i n the Gammarus population which was indicated by the analysis of the bottom fauna. It might also be said that annual and seasonal climatic conditions may act as limiting factors i n the a v a i l a b i l i t y of trout food. The temperature of the upper layer of water appears to govern, to a large extent, the feeding habits of the trout. It has been shown i n an analysis of the trout stomachs and also by Rawson (1934) that the trout in Paul Lake do not generally feed i n the shallow shoal area where food i s abundant, after the temperature of the water has reached summer conditions. A long warm season would apparently cause the trout to feed mainly i n deeper water where the bottom fauna is not as abundant either i n species or i n quantity, whereas a long cool season would be conducive to feeding at or near the surface where there i s an abundance of both' species and numbers of organisms. Mottley and Mottley (unpub) observed that for the years 1932 to 1935, the volume of food eaten by trout i n the spring was high and dropped progressively u n t i l f a l l . This was probably due to the fact that the trout were forced to feed i n depper water during the summer months. conditions (and possibly by other factorsj for example, oxygen depletion, pH, light intensity), would indicate that the relation between the quantity of bottom' organisms and plankton and their a v a i l a b i l i t y i s complex and variable. For example, bottom organisms may be extremely abundant in the shoal area, but w i l l not be available to the trout at those times when the water temperature i n this area i s high enough to force them into deeper water to feed. It might be concluded that The r e s t r i c t i o n of feeding areas by unfavorable temperature 3 0 . because Kamloops trout feed on such a variety of organisms i n a l l ecological zones within a lake, and because variations i n environmental factors may exclude them from time to time from some of these zones, that i s i s d i f f i c u l t to assess the relation between the quantity and quality of food organisms and their a v a i l a b i l i t y to trout. 31. STATISTICS CF THE TROUT POPULATION HISTORY OF THE STOCKING POLICY. A record of the plantings of eggs and fry in Paul Lake is given in Table VIII. TABLE VIII. Distribution of fry and eggs in Paul Lake. Year Number 1909 5,000 fry 1922 42,500 eggs 1923 139,250 eggs 1925 107,000 eggs 1927 100,000 eggs 1928 165,000 eggs 1929 200,000 fry 1930 378,000 eggs 1931 185,000 fry 1932 200,000 fry 1933 200,000 fry 1934 200,000 fry 1935 200,000 fry 1936 200,000 fry 1937 175,000 fry 1938 150,000 fry-1939 ISO, 000 fry 1940 200,000 fry 1941 200,000 fry 1942 200,000 fry 1943 250,000 fry 1944 250,000 fry 1945 100,000 fry 1946 200,000 fry 1947 200,000 fry 1948 n i l 1949 300,000 fry In 1909, Paul Lake was stocked with 5,000 Kamloops trout fry from Adams Lake. The lake had been "barren" previous to this period. The ini t ia l stocking was successful and a relatively high rate of growth was realized (Mottley, 1932). In 1922, Paul Creek was planted with 42,500 eggs obtained from an egg collecting hatchery which was built 32. near the lake i n that year. Surplus eggs collected were used to stock other "barren" lakes i n the province. Following this, the plantings i n Paul Lake were .irregular u n t i l 1931. J An investigation into the propagation and conservation of Kamloops trout was begun i n 1931 by the Biological Board of Canada. Rawson (1934) i n his study of the productivity of the lake found that the "nutritive" condition of the lake was di s t i n c t l y oligotrophic. He concluded that the bottom fauna was e f f i c i e n t l y u t i l i z e d by the trout and that Paul Lake appeared to be capable of supporting a relatively large population of Kamloops trout. Mottley (1932) made a study of the trout population of Paul Lake and found that depletion had occurred. The causes of depletion were believed to be the increased fishing intensity since 1921 and drying up of Paul Creek i n August of certain years, with a consequent trapping of the f r y and the destroyal of the eggs. To remedy the l a t t e r situation he recommended the planting of fry i n the lake. Mottley (1932) outlined a stocking policy for Paul lake which he believed would (1) e f f i c i e n t l y u t i l i z e the food supply of the lake, (2) counteract the depletion of rrtrout that he had observed and (3) satisfy the intensity of the fishing at that time. He assumed that the shoreline of the lake was equally as productive as the best type of stream and that the potential feeding ground around the shore was seven miles long and th i r t y feet wide. Calculations of the f i s h carrying capacity of this area were made according to Embody (1927), cited by Mottley (1932). On the basis, Mottley calculated that the f i s h carrying capacity of the lake was probably not less than 200,000 fry annually. In later studies, Mottley (1940) observed that the lake was producing approximately 33. ten pounds of trout per acre per year, 10,000 pounds i n a l l , and he believed that this figure might be taken as the lake's productivity. In 1937, the stocking was reduced to 175,000 f r y and was reduced further i n 1938 and 1939 to 150,000 fry per year. This reduction i n the number of fry planted was recommended by Mottley due to the decrease in average size of the trout (Clemens, 1937). The stocking was again increased to 200,000 fry i n 194-0, and was continued u n t i l 1942. A further increase to 250,000 fry per year was made i n 1943 and 1944. High waters i n 1945 damaged the f i s h trap and fence. As a result, most of the spawning run escaped to spawn naturally. Therefore, the stocking i n this year was reduced to 100,000 fry, as i t was believed that the natural spawning would make up the balance. In 1946 and 1947 the stocking was 200,000 fry per year. The water in Paul Creek reached flood conditions i n 1948 and again resulted in the escape of most of the spawning run. A r t i f i c i a l planting was not carried out i n this year. In 1949, a further experiment was begun on the lake and a planting of 300,000 fry was made. This experiment i s discussed i n a later section of the paper. ANGIERS' CATCH. Trout were sampled from the anglers' catch at Echo Lodge as time and opportunity permitted, during the summers of the investigation. These f i s h were sampled as soon after being caught as was possible i n order to minimize error from loss of weight in storage. The sex, weight, standard and fork lengths, and state of maturity were recorded for each f i s h . A scale sample was taken below the insertion of the dorsal f i n , immediately above the lateral l i n e . Stomach contents were preserved from 34. approximately one th i r d of the f i s h sampled. Average measurements. The average measurements of the trout sampled are shown in Table 3X. Average weights of trout from 1932 to 1936 have been taken from Mottley (1940) and were converted from pounds to grams. Unfortunately, figures are lacking for the standard and fork lengths of trout from 1932 to 1936. TAB IE. IX Average measurements of trout i n the anglers 1 catch from Paul lake, 1932-1936, 1946-1949. Year Weight Standard Fork (gm.) Length Length (cm.) (cm.) 1932 675.8 - -1933 693.0 - -1934 530.7 - -1935 426.4 - •-1936 453.6 - -1946 324.4 26.7 28.6 1947 399.9 28.4 32.2 1948 594.4 32.8 36.5 1949 469.4 30.2 33.5 Mottley (1941) has shown that there was a significant decrease from 1932 to 1935, i n both length and weight of the immature yearling and two-year-old female trout of Paul Lake. He believed that these changes were related to the increase in the stock of trout i n the lake. 35. Figures from 1946 to 1948 show a steady increase in both length and weight. The 1949 measurements show a slight decrease from those in 1948. Age composition. The scale samples taken were mounted in glycerine jelly and were viewed under a Promar scale projector.. The data^ were then grouped / into age classes. A discussion of scale reading and the driteria used by the writer in interpreting the scales is given in Appendix B. The percentages of age classes in the anglers' catch are given in Table X. Table X. Percentage age composition of the anglers' catch from Paul lake, 1946-1949. Year Age Glasses I II III IV 1946 63.0 19.7 12.3 4.9 -1947 24.4 36.7 34.4 3.3 1.1 1948 1949 10.6 50.2 36.2 3.0 -28.3 3.5.0 26.7 10.0 -A large year class can be followed through the fishery beginningnwith the one-year-old fiyat in 1946. In this year, they were the dominant age class and made up 63 per cent of the anglers' catch. In 1947 the two-year-old fish were dominant and made up 37 per cent of the catch. The three-year-old fish made up 36 per cent of the catch in 1948. The four-year-old fish contributed 10 per cent of the catch in 1949. This is a high percentage when compared with percentages of 36. / foyr-year-old f i s h i n other years. The large year class can probably be attributed to the floods i n 194-5 which allowed natural spawning. The natural spawn coupled with the 100,000 fry planted i n 1945 likely resulted i n a great influx of f r y into the lake and thus produced a dominant one-year-old class i n 1946. The number of fry that reached the lake was probably greater than the usual stocking of 200,000 f r y annually. The anglers, therefore, caught a much greater percentage of one-year-old f i s h i n 1946 and this brought about the low average size for trout i n this year. In 1948 there was s t i l l an -abundance of the large year class that had not been fished out i n the s , / z e previous two years. This would account for the high average Aof fish caught i n 1948. The large year class had decreased considerably i n numbers i n 1949, due to the extensive fishing i t had undergone i n the previous three years. As a result, the average size of fish i n th i s year was reduced somewhat, as the younger age groups were contributing a larger percentage to the t o t a l catch. The proportions of age classes making up the t o t a l catch i n different years i s instrumental i n explaining the fluctuations i n average size of fish from 1946 to 1949. That i s , the average size of f i s h caught i n these years would be approxiiEtely equal, i f the percentages of each year class i n the catch were similar. Therefore, the reason for the fl u c t u a t i o n / i n average size of trout from 1946 to 1949 was mainly due to the age composition of the catch rather than to large variations in the growth of the trout, variations i n the growth of the trout are discussed i n a later section of the paper. Catch curve analysis. The anglers' catches are represented graphically i n figure 4. 37. The method chosen has been to plot catch curves. Loge of the frequency of occurrence was plotted directly against the age classes. The resulting figure shows the trends of the trout population over a period of four years and also shows the survival of the older age groups. Ricker (194-8) described a catch curve as having a steeply ascending l e f t limb, a dome shaped portion and a long descending right limb. Deviations from the theoretical may arise from violent fluctuations i n reproduction and therefore recruitment to the fishery. The ascending l e f t limb and the dome of a catch curve represent age classes which are incompletely captured by the gear used to take the sample: that i s , they are taken less frequently i n relation to their abundance than are older f i s h . In the case of the trout fishery i n British Columbia, there i s a legal size limit of eight inches which must be observed and would there-fore result In an inadequate sampling of the one-year-old f i s h . The catch curve for 1946 deviates from the theoretical in that i t lacks a l e f t limb and a dome shaped portion. This would bear out the statement made previously that the stocking was great enough' in 194-5 to produce a dominant one-year-old class. The one one-year-old class was large enough to dominate the catch, although i t was not as subject to heavy fishing as the older age classes. The 1947 catch curve i s characteristic i n that i t has the essential parts described above. The large age class is now shown by the two-year-old f i s h . The one-year-old class was due to the usual stocking of 200,000 fry i n 1946. The 1948 and 1949 catch curves are somewhat similar to each other and to the 1947 curve. It can be seen that the large jear class originating in 1945 has been surpassed by the two-year-old f i s h i n 1948 Figure 4. Catch curves of the anglers' catch, Paul Lake, I946-I949. . Legend: 1946 , 1947 1948 1949 39. and by a l l age groups i n 1949. A high survival of the four-year-old f i s h can be noted i n 1949 i n comparison with the previous years. A high percent-age of one-year-old f i s h i n the catch i n 1949 serves to indicate a successful natural spawning in 1948 as no a r t i f i c i a l stocking was carried out i n that year. Length frequency distribution. Figure 5 represents a method of graphically i l l u s t r a t i n g the anglers' catch, where the standard lengths rather than the ages of.the f i s h are taken into consideration. Length classes of 3.0 cms. were ar b i t r a r i l y chosen and the frequency of occurrence of trout were calculat-ed for the different classes. The frequency of occurrence was plotted d i r e c t l y against the length classes. The large year class resulting from 1945 can be readily followed through the fishery by noting the peak of the curve i n each year il l u s t r a t e d . In 1946, the peak occurred at the 20.5 to 23.4 cms. length class. In 1947, the peak had moved over to the 29.5 to 32.4 cms. length class.. The large year class had been reduced considerably by 1949 and, i n this year, did not form the major peak i n the curve. However, the frequency of occurrence of trout i n the 35.5 to 41.4 cms. length class was high i n comparison with the previous years. Growth of the trout. Figure 6 represents the growth, in centimetres, of trout ranging i n age from one to four years. The average fork lengths have been plotted against the age classes for five different years. The figures for 1931 have been taken from Mottley (1932) and were converted from inches to centimetres. This method of i l l u s t r a t i o n i s not meant to show an accurate rate of growth of the trout. The growth shown for 1931 was high i n comparison with the other Figure 5. Length frequency curve of the anglers' catch, Paul Lake, 1946-1949. Length classes: *1. 17.5 - 20.4 cm. 2. 20.5 - 23.4 cm. 3 . 23.5 - 26.4 cm. 4. 26.5 - 29.4 cm. 5. 29.5 - 32.4 cm. 6 . 32.5 - 35.4 cm. 7. 35.5 - 38.4 cm. 8. 38.5 - 41.4 cm. 9. 41.5 - 44.4 cm. %rout are illegal below 20.3 cm. Legend: 1946 1947 1948 1949 Figure 6. Growth of trout in the anglers' catch, Paul lake, 1931, 1946-1949. Legend: 1931 1946 1947 1948 1949 44. years illustrated. In this period, the lake was showing signs of depletion of trout and would account for a relatively rapid rate of growth. There was l i t t l e difference i n the growth from 1946 to 1949 with the exception that 1947 showed a s l i g h t l y smaller growth. The'mean standard lengths of age classes of trout from 1946 to 1949 are shown in Table XI. The standard deviation and the standard error were calculated for each mean. TABIE XI. Mean standard lengths (cm.) and standard errors of age classes of trout i n the anglers 1 catch, Paul Lake, 1946-1949. Age Class 1946 1947 1948 1949 I 22.77 *; .183 22.17 1^318 21.78 ±y.734 22.29 +/.507 II 31.73 ± .465 28.87 t.884 32.94 t .267 29.08 t .746 III 35.97 ± .472 31.52 ±.721 35.35 1 .281 34.63 ± .737 IV 39.33 ± .85 33.63^1.415 40.1 t .964 37.39t 1.041 A s t a t i s t i c a l comparison, using values of n t M , was made between the age classes of trout to determine significant variations i n length. The results of the comparisons are shown i n Table XII. 45. TAB IE XII. Results of the Mt n value comparisons of the standard lengths of age classes of trout in the anglers1 catch, Paul Lake, 1946-1949. Years compared Age Class 1946,1947 1946,1948 1946,1949 1947,1948 1947,1949 1948,1949 I N.S. N.S. N.S. N.S. N.S. N.S. II S. S. S. S. N.S. s. III s. N.S. N.S. S. S. N.S. IV s. N.S. N.S. S. N.S. N.S. S - significant N.S. - non significant Five percent level. There was no significant difference between the lengths of one-year-old fish in any of the years compared. The outstanding feature of this comparison is in the 1947 catch. In the majority of cases, the average length of each age class in this year, excluding the one-year-, old fish,, was significantly smaller than corresponding age classes in the other three years. In 1946, due to the large 1945 year class, the population of trout probably exceeded the optimism capacity for the lake. The food supply appeared to decrease as was indicated by the plankton samples taken in 1946. As a result, there was a reduction of the growth of trout in the period 1946 to 1947, which could be attributed to increased competition as an effect of the decrease in available food, so that a lower average length of trout was observed in 1947. A large proportion of the dominant year class was fished out in 1946 and 1947, and the growth 46. of trout increased i n the period 1947 to 1948. An explanation for the fact that the one-yaar-pld f i s h i n 1947 were not found to be smaller i s that this age class was not representatively sampled} that i s , the smaller one-year-old f i s h are not of legal size. Values for the standard deviations are shown i n the following table. TAB IE XIII. Standard deviations of the mean standard lengths of age classes of trout i n the anglers' catch, Paul Lake, 1946-1949. Age Class 1946 1947 1948 1949 I 2.448 1.492 3.672 2.211 II 3.478 5.081 2.896 4.477 III 2.793 4.016 2.589 3.458 IV 3.182 2.451 2.55 3.447 "z" values were calculated according to Fisher (1948) • Significance was determined by comparing calculated values of H z " with tabled values of »z n at the % level of probability. Results of the comparisons are shown i n the foliosing table. TABLE XlVa. Results of the "z" value comparisons of the standard deviations of age classes of trout i n the anglers' catch, Paul Lake, 1946-1949. Age Class Years compared 1946-1947 1946,1948 1946,1949 1947,1948 1947,1949 1948,1949 I S. S. N.S. S. S. S. II S. N.S. S. S. N.S. S. III S. N.S. N.S. S. N.S. S. Iff N.S. N.S. N.S. N.S. N.S. N.S. 47 TABLE XlVb. Results of the "z" value comparisons of the standard deviations of age classes of trout i n the anglers* catch, Paul lake, 1946-1949. Age classes compared Year I, II II,III III,IV 1946 S. N.S. N.S. 1947 S. N.S. N.S. 1948 N.S. N.S. N.S. 1949 S. N.S. N.S. S. - significant N.S. - non significant Five per cent le v e l . The best comparisons may be noted i n the two-year-old and three-year-old age classes. Age classes for one-year-old f i s h are poor for comparison as they are not adequately represented i n the anglers* catch, with the result that only the larger one-year-old f i s h were taken. This would tend to reduce the values of the standard deviations. The sample sizes far four-year-old fi s h were very small and l i t t l e confidence can be placed i n the results. Comparisons of the two-year-old f i s h show that the standard deviations for 1947 and 1949 were significantly higher than for 1946 and 1948. There was no significant difference between the standard deviations for 1946 and 1943 and between those for 1947 and 1949. A repetition of the above i s found i n three-year-old class, with the exception that there i s no significant difference between 1946 and 1949. In three out of four cases, 1946,1947 and 1949, there were significant differences i n the standard deviations between the one- and 48 two-year-old age classes, the two-year-old fish having the higher standard deviations. There were no significant differences in the standard deviations between the two- and three- and between the three- and four-year-old age classes for each year represented. Two factors might account for the high standard deviation of the two-year-old fish in 194-7. These are competition for food and length of time spent as a stream dwelling fish. It was suggested in a previous section of this paper that a more acute competition for food probably resulted from the large stock of fry introduced in 194.5. This increased competition apparently resulted in a decrease in the rate of growth, increased individual variation in growth rate and thus a higher value for the standard deviation. There were probably a large number of fry, from the natural spawning in 194-5, that remained in the stream for one year. In an analysis of the 1948 spawning run, which is discussed in a later section of the paper, i t was found that approximately 42 per cent of the three-year-old fish of the spawning run had apparently spent a part or a l l of their first year in the stream. The Criterion used in determining "stream type" fish is given in Appendix B. Mottley (1932) has observed that trout "prefer" the stream in their first year at least, and that these "stream type" fish usually do not reach the legal size limit until their second year. There-fore, a large proportion of these "stream type" fish from the 1945 spawning run did not enter the fishery until 1947. The "stream type" fish coupled with the lake dwelling fish for the two-year-old age class in 1947 would give a greater dispersion in size range than usual and would therefore tend to increase the value of the standard deviation. The factor of competition for food would help to explain the high standard deviation 49. for the three-year-old f i s h i n 1947. Sex ratio. Chi square values were calculated to determine significant variations from the theoretical 1:1 sex ratio for the different age classes of the anglers' catch. The results are shown i n Table XVa. In 1946 and 1947, there were no significant departures from the 1:1 ratio, although the females predominated i n the majority of cases. In 1948 and 1949, there were significant variations, and in a l l cases, female trout dominated the catch. Table XVb. shows the four years of data grouped together. In a l l cases, except the one-year-old f i s h , the anglers were selecting female trout. The data were then analysed i n the following manner. Year, classes were followed through the fishery, were grouped and sex ratio comparisons were made. It was again found, i n most cases, that the females dominated the fishery. A possible explanation for the fact that the anglers catch a significantly greater number of female trout than male trout involves the length of time for each sex to attain sexual maturity. Male trout generally spawn earli e r i n l i f e than female trout (Mottley, 1940). Observations made during scale reading showed that both males and females usually spawn each year after their f i r s t spawning. Therefore, female trout might be said to spend a longer period of l i f e as non spawners than y do male trout. This would possibly produce a preponderance of male spawners i n the lake as compared with female spawners. After a trout has spawned, i t is i n "poor condition" insofar as the angler i s concerned, / so that a larger number of male f i s h would be discarded by the a n g l e r s 50. and would give the impression that the anglers were selecting female f i s h . This does not appear significantly i n the one-year-old class as few f i s h tend to spawn this early i n l i f e . TAB IE XVa. Sex ratio comparisons of trout i n the anglers' catch, Paul Lake, 1946-194-9. Age Class Male Female I II III IV Total. 1946 93 N.S. p'* .3 SI 22 N.S. p > .2 31 14- N.S. p > .2 21 3 N.S. p 7.05 10 132 N.S. p > .5 14-3 I II III IV Total. 194-7 10 N.S. p y.3 6 11 N.S. p > .2 17 11 N.S. p > .1 19 2 N.S. p > .5 1 34- N.S. p > .3 4-3 I II III IV Total. 1948 3 S. p/.01 22 41 S. p<.01 76 35 N.S. p > .1 4-9 3 N.S. p > .2 7 82 S. p-c.01 154-I II III IV Total. 194-9 6 N.S. p •> .1 13 12 S. p<.05 24-9 N.S. p > .3 13 2 S. p<C.05 9 29 S. p<.01 59 S. - significant N.S. - non significant P. - probability Five per cent l e v e l . 51 TABLE XVb. Sex ratio comparisons of trout i n the anglers' catch, Paul Lake, 1946-1949. Age Class Male Female I 112 N.S. p / .5 122 II 86 S. p< .01 148 III 69 S. p< .02 102 IV 10 s. p< .01 27 Total. 399 s . p< .01 277 S. - significant -N.S. - non significant p. - probability-Five per cent l e v e l . 52, CREEL CENSUS. A voluntary creel census was taken at Raul Lake during the fishing season of 1949. Creel census cards were pointed and were distributed to Echo Lodge and to the cottages. A creel census sign and box was erected at the outlet of the lake. In this location, i t was clearly visible to a l l those leaving the lake. Publicity was given by the Kamloops Sentinel newspaper and by a radio sports broadcast. Letters urging co-operation from the anglers were distributed to the cottages and whenever possible, the writer personally talked with the anglers. An estimated 90 per cent efficiency of returns was obtained by Mr. J.R. Mo r r i l l of Echo Lodge. Unfortunately, very l i t t l e co-operation was received from the cottages. The unit chosen for representing the fishing e f f o r t i s the "boat-day". One "boat-day" i s equal to two anglers fishing for five hours. This was the unit chosen by Mottley (1934). The catch per "boat-day" for the three months of data available i s as follows: May - 3.0 f i s h June - 2.0 f i s h July - 4.5 f i s h . May, June and July - 3.2 f i s h . An attempt has been made to estimate the t o t a l catch for the 1949 fishing season as i t might be useful far comparison with previous years. The estimate i s based on the returns from Echo Lodge. It was assumed that a 90 per cent efficiency of returns was obtained from the lodge, that May, June and July was one half of the tot a l fishing season and that the cottagers' boats were used one third as much as the lodge boats. The following data have been used i n the calculations. The t o t a l 53 number of fis h recorded at the lodge during May, June and July was 1,870 while the total number of "boat-days" recorded was 588.4. The lodge had 27 boats im operation while the cottagers had a total of 70 boats. With these facts and assumptions, the estimated total catch i n Paul lake i n 1949 i s 7,743 trout and the estimated t o t a l number of "boat-days" i s 2,436. This estimate i s only approximate and at best can be used only for a rough comparison with previous years. Table XVI shows a comparison of these estimated totals with previous data obtained by Mottley (1940) . TABLE XVI. Production of trout i n Paul Lake, 1932-1936, 1949. Year Total catch of trout "Boat-days" k Number of f i s h : per "boat-day" Total weight of f i s h (lbs) 1932 3,000 750 4 4,500 1933 6,000 1,000 6 9,200 1934 8,000 5-, 000 8 9,300 1935 12,000 1,200 10 11,300 1936 10,000 1,100 9 10,000 1949 7,743 2,436 3.2 8,050 The estimated total number and weight of f i s h produced i n 1949 i s equal to approximately four f i f t h s of the total produced i n 1936. I t may be noted also, that the fishing intensity has more than doubled, while the catch per unit effort has decreased by two thirds i n comparison with 1936. From these comparison^, i t would appear that the total stock of trout i n the lake i n 1949 has been reduced considerably since 1936. The 54. 1949 production figures compare most closely with those figures for 1932 when the lake was in the process of recovering from a state of depletion. A fishing Intensity twice as great as previously, and a reduced total catch should immediately suggest that the lake is once again tending towards depletion. SPAWNING RUN. The spawning run at Paul Lake takes place during May and the first half of June of each year in Paul and Agnes Creeks. The majority of the run enters Paul Creek. Mottley (1933) has indicated that the difference between the number of fish entering Paul and Agnes creeks was proportional to the volume of water leaving each stream. In 1933, approximately one fiftieth of the spawning run entered Agnes creek. There is likely a high mortality of eggs and fry in Agnes creek as only the lower reaches, apprcodLmately 100 yards, of the creek continue to flow during the summer. A fish fence and traps are situated on Paul creek, approximately one half a mile from the lake. The spawning trout are counted and stripped and the eggs are then transported to Lloyd's creek hatchery. An effort is made to handle a l l of the fish in the spawning run, although this has usually not been possible as there are a few "stragglers" that enter the creek after the fence has been removed. The spawning run at Paul creek was sampled during the spring of 1948 and 1949. In 1948, sampling was carried out in June, shortly after the high waters from the flood had receded. The total number of trout sampled in this year was 90. In May and June of 1949, 195 spawning trout were sampled. These totals were comprised of 27 males and 63 55. females in 1948, and 92 males and 103 females in 1949. An analysis of the data showed the spawning trout to have average fork lengths of 36.5 cm. in 1948 and 39.5 cm. in 1949. The scale samples were mounted and read, and arranged into age classes. The results are shown in the following table. TABLE XVII Percentage age composition of the spawning run, Paul lake, 1948, 1949. Year Sex Age classes II III IV V 1948 Male 22.2 59.3 14.8 3.7 Female 20.6 54.0 25.4 -1949 Male 4.5 36.4 47.7 11.4 Female 2.0 24.5 60.2 13.3 The large year class resulting from 1945 can be detected again in analysis of the data. In this case, the large year class dominates the spawning run as three year old fish in 1948 and as four year old fish in 1949. There was a greater percentage of males in the younger age classes, while the females were dominant in the older age classes. This would indicate that male Kamloops trout tend to spawn earlier in l i fe than female trout (Mottley 1940). Records of the spawning run at Paul creek have been kept by the hatchery officials.. These data are shown in the following table. 56. TABLE XVIII. Statistics of the spawning run, Paul Lake, 1932 - 1949. Year Number of Spawners Number of Eggs number of eggs per female Number of Eggs per f l u i d ounce. Male Female 1932 - - 265,000 - 250 1933 •* - 841,000 - 250 1934 - - 837,000 - 250 1935 - - 388,000 - 250 1936 1,022 1,011 1,419,500 1,404 250 1937 802 1,019 1,530,000 1,501 250 1938 452 504 806,000 1,599 250 1939 566 543 1,103,000 2,031 250 1940 743 759 1,680,000 2,213 250 19a 366 373 850,000 2,279 250 1942 822 900 1,800,000 2,000 240 1943 771 819 1,870,000 2,283 250 1944 620 675 1,155,000 1,711 250 1945 286 317 485,000 1,530 250 1946 2,077 1,784 2,135,000 1,197 330 1947 1,255 1,155 1,350,000 1,169 375 1948 237 258 352,500 1,366 380 1949' 975 1,095 1,853,000 1,692 300 57. A comparison i s shown of the numbers of male and female spawners, the number of eggs obtained, the number of eggs per female, and the number of eggs per f l u i d ounce. Data for 1945 and 1948 were biased due to flood conditions and therefore, total numbers cannot be compared with other years. Chlgquare values were calculated for the numbers of male and female trout i n each year, i n order that significant variations from the theoretical 1:1 sex ratio might be determined. Significant variations were found in 1937, 1946, and 1947. In 1937, the females dominated the run, while i n 1946 and 1947, the males dominated the run. An analysis of the anglers' catch showed the fishermen to be significantly selecting female trout. This would tend to explain the preponderance of males i n the spawning run i n 1946 and 1947. Another reason far the preponderance of males i n these years i s that the males from the large year class resulting i n 1945, would make up a large proportion of these runs. The females would make up only a small percentage of these runs as they tend to spawn mainly i n their fourth year. In 1949, the females dominated the run, although the numbers were not significantly larger. The number of eggs per f l u i d ounce remained f a i r l y constant, 250 eggs per f l u i d ounce, from 1932 to 1945. The only deviation noted was i n 1942, when -the size increased to 240 eggs .per f l u i d ounce. The period 1946 to 1948 showed a decrease i n the size of eggs which corresp-onded to a low point i n the number of eggs per female. This would seem to indicate a decrease i n the average size of trout i n the spawning run during this period. The size of eggs, eggs per female and average size of trout had begun to increase i n 1949, which was probably due to a relatively high proportion of the large 1945 year class that reached 58. maturity. An examination of the figures for the number of eggs per female shows the high point to occur in the period 1939 to 1944. This period corresponds very closely to the war years when the fishing intensity was likely reduced significantly. If this is the case, there was likely a larger proportion of the older age classes that were not fished out and were given the chance to reach maturity. Generally speaking, the older fish are larger in size and have a greater number and size of eggs than the younger fish. This would account for the large number of eggs per female in these years. Since the war years, fishing intensity has likely increased rapidly. Consequently, the numbers of older fish spawning were reduced, and the number of eggs per female and average size of eggs decreased. The total number of eggs obtained in each year from 1932 to 1944 appears to' show a periodic cyclical fluctuation. If the spawning run is divided into three year periods, beginning with 1932 to 1934, a regular recurring low point in egg production in the first year of each period may be observed. The egg production is a direct reflection of the number of females in the spawning run and the number of eggs per female. Figures from 1945 to 1949 are biased due to flood conditions in 1945 and 1948. No explanation can be offered for this cyclical fluctuation because of the absence of pertinent data but there is a possibility that i t is a natural phenomenon in the trout population and might warrant investigation in other lakes. 59 DISCUSSION. The preceding sections of this paper have dealt with two fundamental aspects of the problem of the productive capacity of lakes. These are the study of the environment of the f i s h population and the study of the v i t a l s t a t i s t i c s of the f i s h population. Either aspect of the problem may be used as an index of the productivity of a lake. The study of the environmental conditions i n a lake serves to indicate the general suitability of the physical and chemical conditions for the bottom fauna and flora, the plankton and the f i s h population. Also, a knowledge of the fauna and the available food supply i n relation to the area of the lake i s obtained which provides an index to the product-ive capacity of the lake i n terms of f i s h . However, because Kamloops trout feed on a variety of organisms i n a l l ecological zones within a lake and because variations i n environmental factors may exclude them from time to time from some of these zones, i t is d i f f i c u l t to assess the relation between the quantity and quality of food organisms and their a v a i l a b i l i t y for the production of trout. It i s for t h i s reason that our knowledge of the relation of the environment to the production of trout i s empirical. In the absence of comparable data from other lakes, the s t a t i s t i c s of the trout population affords a better direct index of the degree to which the resources of the lake are being u t i l i z e d . That i s , a knowledge of the f i s h population provides a stronger basis for the formulation of *be suitable management policy. A combination of both indices i s more valuable i n that the pros and cons arising from each index can be weighted according to their relative importance. Environmental conditions that would appear 60. detrimental to the f i s h population might be disregarded, within limits, i f i t was found that the trout population did not show the effects. For example, the quantity of bottom fauna i n Paul Lake has decreased, but an analysis of the f i s h population did not appear to show a corresponding decrease i n available food. A selection of the most promising line of attack can then be made. Drs. Mottley and Rawson have outlined the conditions that existed i n Paul lake during a previous investigation. A summary of the conditions i n 1949 and variations from the previous investigation i s outlined below. The environmental conditions d i f f e r somewhat since 1931. The summer heat incomes have shown extreme downward fluctuations since 1931 although other physical and chemical conditions have remained relatively constant. The plankton i s moderate i n quantity. Fluctuations have occurred, especially i n 1946 when a downward fluctuation was observed, but no permanent quantitative change has been observed. The bottom fauna was described as of average richness i n 1931 but has decreased i n quantity by two-thirds since then. The available food supply of the trout as indicated by the volumes of the stomach contents has shown a decrease i n amount from 1932 to. 1935, an increase i n amount from 1935 to 1949 and a slight decrease i n amojtnt from 1932 to 1949. Another species of f i s h , the redside shiner, has made i t s entry into Paul Lake. The s t a t i s t i c s of the trout population have also indicated significant variations since 1931. The average size of the age classes of trout has decreased slightly since 1931. The anglers have recently been catching a large proportion of the younger age classes of trout. These younger age groups of trout have also constituted a major portion of the 61 recent spawning runs, causing a reduction i n the size of eggs and numbers of eggs per female. A large year class resulting from 194-5 has been followed through the fishery. The main effects of this year class appear to have been a greater survival of trout and a restoration of older age y classes i n the anglers' catch i n 1940 and 194-9 and i n the spawning run i n 1949. A comparison of the 1936 records with those from 194-9 has indicated a two-fold increase i n fishing intensity, «*4 a slight decrease i n the total catch and a large decrease i n the catch per unit effort. From an examination of these conditions, i t would seem that the previous stocking policy of 200,000 f r y per year has been a f a i r average and has gradually adjusted to the resources of the lake. Conditions i n 194-9, such as a large increase i n the fishing intensity and a large decrease i n the catch per unit effort would suggest that the previous management policy might be revised. The problem appears to be a matter of too small a stock- of f i s h to satisfy the increasing fishing intensity. This condition might be improved i n two ways; by decreasing the catch limit per person or by increasing the stock of trout i n the lake either by increasing the annual planting or possibly by i n i t i a t i n g a c y c l i c a l fluctuating stocking policy patterned after the 1945 year class. A reduction i n the catch l i m i t alone would have to be drastic. I t was found i n an analysis of the creel census i n 1949 that a reduction to five f i s h per person per day eliminated only six per cent of the t o t a l catch. A reduction i n the catch l i m i t would possibly result i n a more even distribution of f i s h to the anglers and would probably not decrease the t o t a l catch to any extent. In order for this method to function e f f i c i e n t l y , i t would be necessary to reduce the catch l i m i t even further. The result of the 1945 year class was observed with both i t s 62 detrimental and beneficial effects. The main beneficial effect was the change i n the quality of f i s h as evidenced by the increase i n numbers of older and larger f i s h i n the anglers 1 catch and i n the spawning run. This was due to a high survival of f r y and thus a high survival of the older age groups of the year class even though they were intensively fished i n the years between. The increase i n numbers of older and larger f i s h i n the spawning run produced corresponding larger and greater numbers of eggs. The detrimental effects appeared to be that of a decrease of plankton i n the year following the origin of the year class and a slight decrease i n the growth of trout during the period of low plankton production. Therefore, for purposes of f i s h culture and for experiment, i t i s suggested that the future stocking policy be patterned after the 1945 year class. This could be i n i t i a t e d by the following procedure. Year I. Introduce a stock of 300,OCX) fry and produce a dominant year class. This has been carried out i n the 1949 stocking. Year I I . Introduce a stock of 100,000 fry as conditions for survival and for growth may be poor i n this year due to the large stock preceding i t . Year III. Introduce a stock of 200,000 fry as conditions for survival and for growth should be improving. Year IV. Repeat the process. It i s also suggested that the catch limit be reduced to five f i s h per person per day. The c y c l i c a l fluctuating stocking policy should result i n an improvement i n the quality of f i s h i n the anglers 1 catch and i n the spawning run, and i f i t also results i n an increase of 63. the stock i n the lake by virtue of a more efficient u t i l i z a t i o n of the food resources, the reduction to five f i s h per person per day might decrease the total catch^by a greater percentage than i t would i n 194-9, thus leaving a largerifood stock i n the lake. If the suggested management policy does not increase the stock, the reduced catch limit may act as a safeguard against overfishing. At the end/ of three years, the effects of the revised stocking e.ry policy on the fishifig should be observed. I f i t i s found that the t o t a l y i e l d and the oatch per unit effort of trout have not increased, the t o t a l stocking could then be increased i n multiples of the ratio 3:1:2 provided that the food resources of the lake would warrant an increase i n the stock. Effects of the stocking could be observed by the collection and analysis of the following data; data of the trout i n the spawning r u n ^ including age composition, t o t a l numbers and average size of f i s h , number of eggs per female and number of eggs per f l u i d ounce, and data of the trout i n the anglers' catch, including age composition, average size and catch per unit effort. 64. SUMMARY AND CONCLUSIONS A definite summer thermal st r a t i f i c a t i o n was observed i n Paul Lake. The summer heat incomes have shown extreme annual fluctuations. Oxygen was abundant at a l l depths. The plankton was moderate i n quantity and has shown minor annual fluctuations. There was a reduction i n quantity of plankton during the winter but appeared to indicate a f a i r l y large supply for the winter season. There was a relatively large supply of bottom fauna. However, there was a significant reduction i n the quantity of bottom fauna since 1931. This reduction i n amount appeared to be due to the depletion of the Gammarus population. The redside shiner, Richardsonius balteatus. has made i t s entry into Paul Lake. Analysis of the stomach contents showed the shiners to be directly competing with the trout for food. The available food supply for the trout appeared to have increased slightly since 1935. The winter sample indicated a large supply of available food i n view of low temperature conditions. A large year class was found to have resulted from the floods in 1945. This year class probably exceeded a stocking of 200,000 f r y as i t could be traced throughout the fishery. The beneficial effects appeared to outweigh the detrimental effects. 65. The anglers selected significantly mere female than male trout, which was possibly due to a preponderance of male spawners i n the lake. The fishing intensity has doubled, the total catch has decreased by one f i f t h and the catch per unit effort has decreased by two thirds. The stock of the trout i n the lake i s tending towards depletion under the present fishing intensity. The large year class from 1945 has increased the numbers of older f i s h i n the spawning run. Also the number of eggs per female and the size of eggs were increased due to this large year class. A cyclical fluctuation i n egg production was noted. A revised stocking policy, patterned after the 194-5 year class, has been outlined. 66 REFERENCES. Birge, E.A. and C. Jnday. 1914. A limnological study of the Finger Lakes of New York. B u l l . U.S. Bur. Fish. j[2:525-609. C a r l , G.C. and W.A. Clemens. 1948. The fresh-water fishes of British Columbia. Publ. B r i t . Col. Prov. Mus. Handbook 5. Clemens, W.A. 1937. Report of the Pacific Biological Station, Nanaimo, British Columbia, for 1936. Annual Rept. B i o l . Bd. Can. 1936. p.p. 28-35. Clemens, W.A., D.S. Rawson and J.L. McHugh. 1939. A biological survey of Okanagan Lake, Bri t i s h Columbia. B u l l . Fish. Res. Bd. Can. j>6: 1-70 Fisher, R.A. 1948. S t a t i s t i c a l methods for Research Workers. London. Juday, C. 1916. Limnological apparatus. Trans. Wis. Acad. S c i . 18 (2)-.566-592 MacKay, D.C.G. Paul Lake trout investigation. Unpublished M.S. A/ Mottley, CMcC. 1932. The propagation of trout i n the Kamloops Dis t r i c t , B r i t i s h Columbia. Trans. Am. Fish. Soc. 62;144-151 . 1932. Investigation of trout i n British Columbia i n 1931. Annual Rept. B i o l . Bd. Can. 1931. p.p. 77,78. . 1933. The spawning migration of rainbow trout. Trans. Am. Fish. Soc. 63_: 80-84 , 1934, The fishing effort at Paul Lake. Annual Rept. B i o l . Bd. Can. 1933. p.p. 89,90. , 1940. The production of rainbow trout at Paul Lake, Bri t i s h Columbia. Trans. Am. Fish. Soc. 62:187-191 . 1941. The effect of increasing the stock i n a lake on the size and condition of rainbow trout. Trans. Am. Fish. Soc. 6 7 . 70:414-420 — — - — . Kamloops trout scales. Unpublished M.S. Mottley, CMcC. and J.C. Mottley. The effect on the food supply of increasing the stock of rainbow trout i n a lake. Unpublished M.S. Needham, J.G. and P.R. Needham. 1941 . A guide to the study of fresh-water biology. New York. Rawson, D.S. 1930. The bottom fauna of lake Simcoe and i t s role i n the ecology of the lake. Univ. of Toronto studies 34. Publ. Ont. Fish. Res. Lab. 4^0:5-183. -. 1934. Productivity studies i n lakes of the Kamloops region, British Columbia. B u l l . B i o l . Bd. Can. 42:1-31. — .-. 1942. A comparison of some large alpine lakes i n western Canada. Ecology. 23. (2) :1A3-161. Ricker, W J E . 1937. Physical and chemical characteristics of Cultus Lake, B r i t i s h Columbia. Jour. Fish. Res. Bd. Can. ^ (4):363-402. . 1938. On adequate quantitative sampling of the pelagic net plankton of a lake. Jour. Fish. Res. Bd, Can. £ (l):19-32. . 1948. Methods of estimating v i t a l statistics of f i s h populations Indiana Univ. Publ. S c i . Series 15. p.p. 1-101. Snedecor, G.W. 1946. S t a t i s t i c a l methods. Ames, Iowa. Ward, H.B. and G.C. Whipple. 1918. Fresh-water biology. New York. 68. APPENDIX A. 69. TABLE XlXa. Temperature series, Paul Lake, 1947. C. Depth Sub station I I I . Sub station II. (m.) Jul 25. Aug 21. Aug 28. Aug 29. Jul 28. Aug 29. Sep 2. 0 20.0 17.6 19.0 19.2 19.0 19.1 19.4 3 19.5 - 18.5 - - 18.5 18.4 6 18.6 - 17.6 - 17.6 17.9 17.8 7.5 15.2 17.3 - 17.4 16.1 17.0 17.1 9 32.9 14.6 11.9 - 12.5 11.9 14.5 15 mm 6.6 5.8 6.4 6.2. 6.7 6.6 30.5 4.7 4.7 - 4.7 - 4.7 4.7 Bottom 4.5 4.5 4.7 4.7 4.5 4.7 4.6 TABLE XLXb. Temperature series, Paul Lake, 194S. *C. Depth Station I. (*.) Jul 23. J u l 24. Jul 29. Aug 5. Aug. 9. Aug 18. Sep 10. 0 20.4 19.5 19.0 19.8 20.1 19.0 18.1 3 19.9 19.4 18.4 19.2 19.1 18.7 16.6 4.5 19.6 17.1 16.2 18.2 18.5 18.6 16.2 5.5 14.7 1A.2 12.9 16.0 17.4 16.0 -6 12.0 10.5 11.4 14.0 14.7 14.9 15.2 7.5 7.6 8.8 7.8 8.7 9.8 8.8 11.0 9 - 7.0 7.4 6.9 8.1 15 5.2 5.3 5.2 5.1 5.2 5.1 5.4 30.5 4.6 4.6 4.6 4.6 4.6 4.6 4.7 53.5 4.4 4.4 4.6 4.4 4.4 4.4 4.5 70. TAB IE XIXc. Temperature series, Paul Lake, 1948. * C. Depth Sub station I. Sub station II. (*.) Jul 31 Aug 16 Sep 6 Aug 5 Dec 17 Aug 1 Aug 5 Sep 6 0 19.7 19.3 19.8 16.3 1.2 21.5 19.1 16.3 3 18.4 19.2 18.8 15.8 2.4 19.2 19.1 16.2 4.5 17.2 19.2 18.6 15.7 - 17.9 19.0 15.8 5.5 10.9 18.4 18.6 - - 16.9 15.0 -6 9.6 13.6 17.4 12.3 2.8 14.8 12.2 15.4 7.5 7.4 8.5 12.6 8.9 - 8.0 7.8 12.4 9 - 6.5 9.5 7.1 2.9 6.8 6.6 8.2 15 5.2 5.1 5.3 5.2 - 5.2 5.1 5.1 24.5 4.7 4.8 4.9 4.8 3.1 - - -30.5 4.6 4.5 4.5 48 * 4.4 4.4 4.4 TABLE XlXd. Temperature series, Paul Lake, 1949. ° C Depth (m.) Station I. May 15 Jun 23 Aug 3 0 15.3 16.1 20.8 3 11.4 16.1 20.0 4.5 10.0 15.3 18.9 6 6.7 13.3 16.4 7.5 6.4 9.2 11.9 9 5.5 6.7 8.9 15 - 4.4 6.4 53.5 4.4 3.9 4.4 71, TABLE XX. Dredging Samples, Paul Lake, 1948, Date Dredging Depth % e t Weight Series (m.) Aug 19 S.S. I. 2.0 .4497 11.5 .1621 25.0 .0498 26.0 .0856 H.5 .2384 1.5 .8449 Aug 20 S. I. 9.0 .5889 55.0 .0075 25.5 .1091 5.5 3.1530 1.5 1.5392 Aug 27 S.S. II 2.0 2.2527 8.0 .5276 13.0 .0668 2.0 1.4146 % e i g h t of Mollusc shells has been deducted. 72. TABLE XXI. Dredging Samples, Paxil Lake, June 18-25, 1949. Dredging Depth % e t Weight Dredging Depth % e t Weight Series (m.) (gm.) Series (m.) . (gm.) D.S. I. 2.5 1.949 D.S. V. 1 2.121 10.5 2.259 2 3.909 25.5 .107 17.5 .066 16.5 .062 45 .005 9 .591 19 .278 2 3.073 7 .826 0.5 2.952 D.S. I I . 2.5 1.600 D.S. VI. 2.5 .883 2.5 .507 9 1.395 6.5 1.178 11 .076 14.5 .226 13 .030 30 .367 13.5 .226 10.5 .084 33 .267 5 1.438 41 .293 2 1.032 49.5 .031 7 .437 1.5 .173 D.S. III. 1.5 1.361 D.S. VII. 1 3.688 4 5.961 5 3.745 9 .730 21 .441 39 .359 35 .032 11 .034 19.5 .224 2.5 .349 7 .951 1.5 .698 30 .433 D.S. IV. 2.5 2.814 10.5 .123 55 .002 31.5 .093 7.5 1.241 7.5 2.338 1.5 1.495 19.5 .066 % e i g h t of Mollusc shells has been deducted. 73. APPENDIX B. 74. SCALE READING. Scale reading i s a highly subjective undertaking and requires a good deal of experience. Thus, significant variations i n results are not uncommon when a comparison i s made with results from other scale readers. The writer has spent a large proportion of time i n familiar-izing himself with Kamloops trout scales and has devised a f a i r l y objective interpretation of them. Mottley (unpub.) gave an outline of scale reading from which constant reference was made. A trout scale i s composed of an anterior embedded portion which i s made up d§ concentric rings or c i r c u l i . The posterior or exposed portion i s heavily pigmented and usually lacks c i r c u l i . A small area i n the centre of the scale Is called the nucleus. The winter check or annulus was the feature used to determine the age of a f i s h from i t s scales. Winter checks are due to a sudden decrease in the rate of growth and make their appearance among the c i r c u l i i n the latero-posterior radius of the scale. A count of the winter cheks indicated the age. Scales that presented much d i f f i c u l t y i n reading were not used in the results. The following c r i t e r i a were used i n determining a winter check. 1, A notch or wedge among the c i r c u l i . 2. Cutting over. The f i r s t summer ring may cross sharply over the winter rings and give the impression that the winter rings have been cut off. 75. 3. C i r c u l i spaced closely together. Confusion i n identifying winter checks might possibly occur due to the following factors. 1. Summer check. Available food may become scarce, growth i s retarded, and a check occurs. Summer cheks are usually not as well defined as a winter check. (Mottley, unpub.) 2. Injury to f i s h . Growth rate may be retarded and a check may occur. 3. Absence of winter check. Growth rate may not slow down significantly during the winter and therefore, a check may not occur i n the scale. 4. Spawning scar. The resorption of the scale during spawning may be great enough to eliminate previous annuli. 5. Regenerated scale. Annuli are not present i n regenerated portions of scales. A Kamloops trout scale from Paul Lake, indicating some of the above features i s shown in figure 7. It has been suggested by Mottley (1932) that stream dwelling f i s h can be differentiated from lake dwelling f i s h . He has indicated that scales from stream dwelling f i s h are characterized by eight or less c i r c u l i i n one year's growth. However, there are a great deal of "border line" cases when making this separation. Therefore, for the 76. purposes of this investigation, there has been l i t t l e attempt to make the separation. F i g u r e 7» Kamloops t r o u t s c a l e , P a u l l a k e . 1„ Nucleus 2 0 Winter check 3„ Summer check Jj-o L a t e r o - p o s t e r i o r r a d i u s Figure 7. Kamloops trout scale, Paul Lake. 

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