- cm I ,. .8. F U u . 26¢ - . H. — ~ . ¥ *0 . m .. l.§» ... x. .o . . . firfm .s a Rs: 5.. I. v 3:. 5 . r .. ~v .. .0 2?“ o . . u o I Ln. . I. f “ .1... m . . . H 3... . . .J « a a o .. fl \\ w .0! O o o a. .fi . . . I s\.~ . «SH ‘. o. In! . r .\ rm...‘ ’-v a - n “he . .. . w . my... u. u a o a - I. V \ , A .~ . e m. . ‘ . .. mm. A 1“. a u a." O f V N . . r x p. .m ... . :‘n. \ \. . . «x. I.“ o . n u , l ‘ O H; .H , w- o ‘0 n \ #1 w. . .5. «\u .. .. r \ .a . I .1., r- O . u. .9 I k. u. s . I §. "5 O .5 r .- I'll . \ o .‘o..0” \. . r x u . 9. : .. .O x. a y . .. z. u . H . I ‘IN a V .v- .0 ‘1‘ ‘0 r 4 fun” . . O: o w. .. x. . *3 o n .D. I“ 2. . .. .. n a . v a q . f \ ar‘ \ 'JQI.‘ or \o H .0 . y s . o a I i . .o a .. a u. I o _ a C | H ”a... .- N . . ... t O 2 . . . o a r r... . a .a . v. . a‘ )3 u. o zx \ t .\. a. . 54:33::,,4_,.:=_.:_:::_:,_:_::,,_,,:.,:._ ' Julilluggjjllglufl “ __.-—rrw-. __< _ ,‘ ._ _.——o --—' This is to certify that the ( thesis entitled Growth Characteristics of a Bluegill ' Population in a Michigan Trout Lake presented by Ernest G. Karvelis has been accepted towards fulfillment of the requirements for M. 8. degree in Zoolog 3 RM Q‘RJLQ F Major professor Date Kay 26, 1952. 1‘ 0-169 V_f‘."1r flV-‘* _,-',‘_ fi‘r‘—r I ._l.‘ _. :“wmiifln ‘1' i-I‘ —- .- 'I’ ' .m-F" s.- ( C v ' O ‘L‘ 0 ' ' u . I ' O l 4‘ I‘ . ‘0 D . .. Q I U . '-v i”. ' ‘7'“ §§ ,u e -, . v.‘ .I? - . w" :‘A :’4 w m 5: 1‘ \ L" k. l \V 22*»: 1 W2» ~ . r . ‘t‘; ”I", “furl-Fl: ub‘ ;’1L1?’, I. L“? “fix? ‘ V _. _. A g, A.“ t'l‘é'v: ”S; #é’ 1. 1 _ ‘Ivf‘kl. :1", .xpv'. '. ix. 3? V b. <‘ {of . . ("x ‘Q‘ 15%.,fln‘; fig‘fi' no“ 1 1" ' 3.; ' .:'x “(191“: ‘.lk1‘,,U .‘N' . . 534/ {1" '. gap ‘. t) .- m4. : " 1- r ‘53)“) 1; “vi" " s . . 1‘. H; .m\ .t #4. .' V I357 1' w \ N' “a. ‘1. _ ‘ . ._ 5‘ . . 1r .-v 4 ,. 2“. nq, ~ ‘ m he"! ' \hf‘léx‘ 13“" “was! now ,2; x, 'GROWTH CHARACTERISTICS OF A BLUEGILL POPULATION IN A MICHIGAN TROUT LAKE by ERNEST GENRICK KAREELIS A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology 1952 THESiS ACKNOWLEDGMENTS The investigator extends his appreciation to Dr. Robert C. Ball, Zoology Department, Michigan State College, who has directed this study and whose suggestions and guidance were always available. Thanks is expressed to the personnel of the Pigeon River Trout Experimental Station for the recording and col- lection of bluegill scales and the stomachs of bluegill: and brook trout. s wane 1. .. Q , . ‘ P 9 I . ‘ n 9" 1“ ;| .9 .O ,0 TABLE OF CONTENTS I. INTRODUCTION . . . . . . History . . . . . Description of lake . II. MATERIALS AND METHODS . Field program . . . . Scale sampling . . Stomach sampling . Laboratory examinations Age and growth.determinations Fish food analysis . III. GROWTH ANALYSIS . . . . Validity of scale method Growth increment . Calculated lengths for each age group Comparison with other regions . . IV. EVALUATION OF CHANGES IN LENGTH, WEIGHT, CONDITION OF THE BLUEGILL Average length at time of capture Age of fish to reach 6 inches . Average weight at time of capture Length-weight relationship Condition of Ford Lake bluegills "K" factor from 1948 to 1951 . "K" factor for 1951 Statistical test for homogeneous population "t" test for length "t" test for weight Time of annulus formation Time of spawning . . Page <0 CDN‘I <1 0303 O) 03 $10 V. VI. VII. VIII. IX. Length of growing season Growing season for Growing season for CATCH OF BROOK TROUT . FEEDING HABITS . . . . . Food of bluegill . . Food of brook trout DISCUSSION . . . . . . . SUMMARY . . . . . . . . LITERATURE CITED . . . . 1949 1951 Page 42 45 43 47 48 48 54 65 67 69 INTRODUCTION Michigan has a large number and a great variety of in- land lakes and because of the number and importance of its lakes has become the leading state in the number of licensed fishermen. These lakes can be divided into two general categories on basis of fish-producing potentialities: (l) trout lakes with their colder and usually deeper waters and (2) warmewater lakes with shallower basins and more produc- tive waters. In the course of fisheries surveys throughout the state many lakes have been found that appear to be thermally and chemically suited to trout but are populated with warm-water species of fish. In such lakes there seldom is satisfactory growth.and survival of both types of fish. This appears to be due to the lowered growth rate of the warm-water species in waters below their optimum and inability of the trout to compete successfully with the usually more numerous pan fish. Since such.mixed populations are not successful and because it is desirable to encourage trout production in lakes it has become a part of the lake management procedure to treat lakes to remove such.mixed undesirable fish.popu- lations. An opportunity to study such a lake was presented at Ford Lake (T. 32 N., R. 1 W., 8, Otsego County, Michigan) in 1946. This lake was a trout lake having a stunted bluegill (Lepomis macrochirus) population, (Ball, 1948a) and with.a few of the trout planted surviving to harvestable size. The lake was poisoned in 1946 with the intent of removing all fish. This attempt failed as a few bluegills survived the poisoning. This afforded an opportunity to study the estab- lishment of a bluegill population in a lake where the only predator and competitor was the brook trout (Salvelinus fon- tinalis) and record the interrelationships of these two fishes in competition. History Prior to 1936, Ford Lake was a potential trout lake, but as such it was unproductive of trout due to the pres- ence of a stunted population of yellow perch (£3325_f1aves- 2223). In 1956, the fish population was killed with ro- tenone and dynamite (Eschmeyer, 1937). In 1937, a planting of Montana grayling (Thymallus montanus) was made but did not prove successful due to the unauthorized introduction of bluegills (Leonard, 1939, 1940). By 1959, the bluegill population had become so great that the grayling were not able to compete successfully. Five thousand fingerling brook trout were planted in Sep- tember 1941, but were unable to thrive due to the bluegill population present. In September 1945, young-of-the-year walleyes (Stizo- stedion vitreum) were introduced as a possible means of re- ducing the large number of stunted bluegills to a point where growth would result in legal-sized fish. Gill nets set in the lake in the summer of 1945 failed to show any trout remaining (Ball, 1948a). On August 26, 1946, Ford Lake was poisoned for the second time. In applying the poison, every precaution was made to kill all the fish present so there would be no com- petition for food, as brook trout were to be planted in the fall of that year. After the poisoning, an effort was made to recover all of the fish. The introduction of the walleyes proved of no value, since of the 57,585 bluegills recovered, only 18 were legal-sized (6 inches or longer) and the average length of the fish was 5.9 inches. Of the 168 walleyes planted in 1945, only 17 were recovered and had grown from 5.75-10.50 inches to 17.00-19.75 inches (Ball, 1948a). In the fall of 1946, brook trout were planted, but in 1947, bluegills were found to be present. The bluegills present were believed to have survived the 1946 poisoning. Ball (1948b) states that of 52 Michigan lakes poisoned with rotenone, during 1954-1942, 18 have been recorded as having a complete kill. The personnel of the Pigeon River Trout Experimental Station have taken scale samples of the Ford Lake bluegills beginning in 1948 and continuing to 1951. From the material collected, it was possible to calculate the growth rates of the fish for the different year classes and the relationship of this rate to the population density. An examination of the stomachs of the bluegills and brook trout gave an indication of the food eaten by the fish. In the bluegill growth studies, it was noted that the majority of fish.which survived the 1946 poisoning were fish of the year class 1946. These small fish.may have avoided the poison by burying themselves in the dense Qhara_mats that were on the bottom of the lake. At the time of the poisoning, the lower waters of the lake were devoid of oxy- gen. A few large fish survived but no scales were avail- able from these, however, the spring following the poison- ing the anglers caught a few very large bluegills. Description of Lake Eschmeyer (1957b) describes the lake as having a surface area of 10.7 acres, no inlet or outlet, and a maximum.depth of 10 meters. The lake is situated in the midst of rolling sandy country covered with jack pine and aspen, and receives .a relatively small amount of surface drainage (Leonard, 1959). During a survey conducted by The Institute for Fish- eries Research in 1952, the bottom was found to be composed uniformly of pulpy peat. The rather extensive shoal areas, averaging 175 feet in width, are composed of sand on the north, east, and south sides which.are separated from.the peat by a belt of marl of approximately equal width. MATERIALS AND METHODS Field Program Scale Sampling Scale samples, and accompanying data for 455 bluegills were collected from.Ford Lake during June 1948; June, July, and August 1949; June 1950; and May, June, July, and August 1951. The fish caught did not represent a random sample, but rather a selected sample, since most of the scales col- lected for this study were obtained from anglers. For this reason all but a few of the fish were 6 inches or longer in total length. 1 Collection of bluegills by seining was impossible be- cause of a sharp dropoff and aquatic vegetation in the shallow areas along the lake shore. The scales for the bluegill age and growth studies were removed from the fish in the region between the lateral line and the anterior end of the spinous dorsal fin. These scales were placed in individual envelopes with other per- tinent data. Stomach.Sampling Stomach samples and accompanying data were obtained for 57 bluegills caught with hook and line. The total lengths ranged from.5.5 to 8.0 inches. The date of capture was August 4-5, 1951. During 1950 and 1951, 57 brook trout with total lengths ranging from 5.0 to 12.1 inches were caught by the same method. Of these, 7 were caught in February 1950, 9 in April, 7 in June, and 12 in August of 1951. After recording the length, weight, and date of cap- ture, the stomachs were preserved individually in a formalin solution. Laboratory Examinations Age and Growth.Determination The scales were mounted on slides with a gelatin- glycerin media and examined with the aid of a scale projec- tion machine. From these observations, the age and growth rate of the bluegills were determined. Growth rates were charted by the use of a nomograph.as described by Carlander and Smith (1944). In the use of a nomograph in growth.determinations, it is necessary to know the length of the fish.when the scales ' are laid down. The standard length of bluegills at the time of scale formation was found by Potter (1925) to be 17.0 mm. Using the conversion factor for changing standard lengths to total lengths, as presented by Beckman (1948a), the length of the fish at the time of scale formation was estab- lished as 0.8 inches. As all of the length.measurements were taken in inches and the weight in grams, these units were used in all calcu- lations except for those of the "K" factor. This determina- tion required the conversion of length.of fish to centimeters. Fish.Food Analysis The stomach content of each fish was examined with the aid of a binocular microscope. An estimate was made of the percentage of the total volume contributed by each group of food organisms. GROWTH.ANALYSIS The growth study was carried out to determine whether or not the rate of growth was reduced as the number of blue- gills increased. Such a reduction has been noted in many lakes but the rate at which it proceeds has not been re- corded nor its relationship to the disappearance of trout in the same waters. Age groups of the bluegills are represented by the Roman Numerals I, II, and III. These refer to the number of winters through.which a fish has lived. Thus, a fish having passed one winter will belong to Age Group I and will show one annulus and be in its second summer. In making this growth study, a total of 455 scale samples from bluegills were collected, age determinations made, and length at different year classes calculated. The length of the fish at the time of capture was not used in the growth calculations. If the fish was captured early in the year and had not formed its annulus for that year, that year's growth.was omitted and the only reading taken was that of the calculated length at each annulus. Validity of Scale Method The scale method for determining the growth rate of the bluegill was used. The validity of the scale method for age 10 and growth.determinations for the Centrarchids was demon- strated by Creaser (1926). The following data are presented to justify the use of the scale method for age and growth determinations for the fish population under consideration. The use of this method is based on the assumption that the length of the scale in- creases proportionally to that of the fish. From fish caught in 1951, data wereisaken pertaining to the average lengths of the fish and their scales (Table 1). These data represent true (not calculated) lengths at the time of capture. The length of the scales represents the distance from the focus to the anterior edge of the scale. The data concerning these fish were plotted and the results are shown in Figure 1. In order to have a straight line, there must be a direct relationship between the length of the fish.and the length of the scale. This relationship is exhibited by the plotted line of Figure l. The criteria that the length of the scale increases proportionally with that of the fish is accepted for Ford Lake bluegills. Growth.Increment Table 2 and Figure 2 show the growth increments for the various year classes during the time considered by this study. From these data there is noted a definite decrease in the growth increments as the age of the fish increased, also the 11 TABLE 1 NUMBER, AVERAGE LENGTH OF FISH, AVERAGE LENGTH OF SCALES X 46 Average Average Class length length interval Number fish (inches) (inches) of fish (inches) scales X 46 5.1-5.5 7 5.56 2.25 5.6-4.0 17 5.80 2.70 4.1-4.5 14 4.18 5.05 4.6-5.0 10 4.89 5.44 5.1-5.5 19 5.58 4.00 5.6-6.0 41 5.85 4.59 6.1-6.5 111 6.55 4.77 6.6-7.0 46 6.69 4.98 7.1-7.5 7 7.57 5.19 7.6-8.0 7 7.80 5.96 8.1-8.5 4 8.50 6.60 increments for the same age groups decreased as the number of fish increased. Calculated.1engths for Each Age Group The average calculated lengths for bluegills in each age group for each year class are presented in Table 5 and Figure 5. 233:3 313 Born. toe afinmeoapsnoa summed sauce was new...” aha-Whiu i. . . _ - tilt H 0.33%. mMIoz_ z. Ikozm... Imi m m JCD d d u .1 3e. mmzoz. w z. I u4 0.0H m.bmanfl.flw 0.00 00 H Hmma H0.Hlem.a 00.H 0.m0au0.nma 0.m¢H m.mamum.mmd 0.00m. m HHH 000a mo.mumw.a m>.H 0.00 :0.m0 0¢.wm m.0bano.bmd 0.00H on HH 000d 00.Hnm¢.a mo.a 0.Hm 10.na 00.0H m.¢na:¢.00 0.¢0H b H 000a 0H.mum¢.a H>.H 0.0Hm30.mHH mm.mn~ 0.Hmmwm.>ma m.00m 0m HH mwma mb.Hn00.H 0>.H 0.00 uo.mm 00.H0 m.bmfium.bea ¢.mma m H 000d mH.mum>.H no.m 0.0bd:0.00 nm.mmd m.momua.moa ma.me 0H HH mood. em: noposu em: .msw ea Awaeawv .85 :H A.EEV .neau no macaw Hnwsmo omoom owsAobd omowm unmask, emamm summed 900552 ewd nsow . owmaopm ommaobw man—”gum g Qmom Mom moeo¢m 3M: nz¢ .Bme B .mewzmfl m0¢mm>< amboma m0¢ aamwbdo m¢mM b flnmda 54 of bluegills that covered a considerable period of time were the 282 caught in 1951. The "condition" was calculated for each date of capture and the results are presented in Table 8. TABLE 8 DATE OF CAPTURE, NUMBER, AVERAGE "K" FACTOR, AND PER- CENT or BLUEGILLS HAVING ANNULUS FORMED FOR 1951.‘ Percent hav- ing annulus Date of Average formed for capture Number "K" factor 1951‘ May 5 24 1.54 12.5 May 19 12 1.71 41.6 June 5 & 4 21 1.86 52.4 June 6 50 1.80 54.0 June 7 40 1.88 57.5 June 10 41 1.95 85.0 June 14 44 2.07 65.9 June 17 4 1.55 80.0 July 10 5 1.44 100.0 August 4 & 5 40 1.56 100.0 From the table it can be seen that the "K" factor in- creases from.May 5, to a peak on June 14. A sharp drop then occurred on June 17, followed by a gradual increase to. August 4 and 5. The "K" factors for June 17 and July 10, cannot be re- 55 lied upon because of their small numbers, but they indicate an upward trend. The rise in the "K" factor to June 14 may have been due to enlarging gonads as the spawning season approached. The sharp drop on June 17 could have been caused by spawning. This may be substantiated by the fact that the peak of spawn- ing had passed by June 18, 1951, (as reported by observers at the lake). Lagler (1949) states that a sharp change in the ”K" value may be expected at spawning. Deason and fills (1947) found that the weight loss of male kiyis (Leucichthys kill) at spawning was unimportant, but the loss of weight I for the females at spawning was considerable. Any rapid loss in the weight of the fish would have a marked effect on the condition factor of the fish. The reason the bluegills in Age Group III, caught in 1950, have a lower "K" value than fish of the same age group, but caught in 1951, may be that they were all taken Just after spawning. This is the time when the condition of the fish is the lowest. The fish of the same age group for 1951 were caught over an extended period of time maSking the low values of "K" at the time of spawning. The date of capture appears to have a marked effect on the condition ("K" factor) of the fish. 56 Statistical Test for a Homogeneous Population The data, on the growth rate of the bluegills, indicate that the growth.was probably declining. To substantiate this supposition, a statistical test was made to determine whether or not the populations are homogeneous. The statistical test was the "t" test as shown by Snedecor (1946). If the "t" test shows significant differ- ences, the populations for those age groups and their dates of capture can be said to represent two different populations. "t" Test for Lengths The value of "t" for the lengths (Table 9) reveals a significant difference for all age groups and years of cap- ture with the exceptions of Age Groups I and II for the 1950-1951 dates of capture. "t" Test for weights Table 10 shows the "t" values for the weights of blue- gills and reveals a significant difference for all age groups ‘ and years of capture. The exceptions to this are for Age Group I for the 1950-1951 dates of capture and Age Group II for the 1948-1949 dates. If the "t" value was significantly different for the lengths, it was also significantly different for the weights TABLE 9 57 "t” TESTS FOR LENGTHS 0F FORD LAKE BLUEGILLS LENGTHS Age Group I Years Caught "t" Value 1949-1950 27.55 ** 1949-1951 11.51'** 1950-1951 1.02 Age Group II Years Caught "t” Value 1948-1949 7.89 ** 1948-1950 12.11 ** 1948-1951 8.66 ** 1949-1950 28.94 ** 1949-1951 13.92 ** 1950-1951 1.50 Age Group III Years Caught "t" Value 1950-1951 6.50 ** ** Significant at 99 percent level. TABLE 10 58 "t" TEST FOR THE WEIGHTS OF FORD LAKE BLUEGILLS Age Group I Years Caught "t" Value 1949-1950 1949-1951 1950-1951 Age Group Years Caught 1948-1949 1948-1950 1948-1951 1949-1950 1949-1951 1950-1951 Age Group Years Caught 51.80 ** 16.85 ** .65 II "t" Value .58 14.99 ** 11.94 ** 24.54 ** 21.55 N 2.29 * III "t“ Value 1950-1951 5.88 ** ** Significant at 99 percent level. * Significant at 95 percent level. 59 of the bluegills in Age Groups I and III. In Age Group II this is not true. For 1948-1949, the "t” value of the lengths was found to be significant while that of the weights was insignificant, but for 1950-1951, the opposite was found to be true. These data indicate that the population of Ford Lake bluegills during the period of the investigation is not homogeneous. The "t" test does not indicate whether or not the growth rate is declining. The non-homogeneous popula- tion in the lake supports the previous findings that the growth rate of the bluegills declined. Time of Annulus Formation The annulus is formed in the spring of the year when growth is resumed after a winter period of little or no growth. An attempt was made to determine the date of annulus formation for the Ford Lake bluegills. Since collections for the years 1948, 1949, and 1950 were made after annulus formation, no conclusions as to the time of annulus formation for these years could be made. The date of annulus formation for Ford Lake bluegills (for the year 1951 is presented in Table 8. From the datafi available 80 percent had formed annuli by June 17 and 100 percent by July 10. The rapid increase in the percentage of fish having formed their annuli by June 10 may be due to a larger number 40 of Age Group I fish (5.4-5.8 inches long) present in this collection than in earlier or later collections. Hansen (1956) found that the date of annulus formation for the white crappie (Pomoxis annularis) in Illinois is quite vari- able, varying from May to June or even later. Also, fish from.5.6-5.5 inches long had a peak in annulus formation about the middle of June, while on the same date larger fish (5.6-9.5 inches) had barely begun. He also found that the peak in the annulus formation for the larger fish.came a month later than that of the smaller fish. Carlander (1950) working with saugers (Stizostedipn canadense cangdense) from Lake of the Woods, Minnesota, found the annulus formed in May and early June. Beckman (1945) found that fish of the same region of Michigan as Ford Lake had laid down their annulus by the first part of June. The date for annulus formation of Ford Lake bluegills varies, and a specific date for their formation cannot be given. However, for the year 1951, it can be said that the annulus of the fish was formed during the month of June. Time of Spawning for Ford Lake Bluegills ' In the food analysis of the brook trout, the fish caught in February, 1950 were found to be eating small blue- gills ranging in length from.1.0-l.6 inches. 41 The growth rate of the bluegills shows that the average calculated length of the bluegills at the first annulus was 4.4 inches for the fish hatched in 1946 and 5.1 inches for those of l950Q The smallest calculated length at the first annulus for the fish batched in 1950 was 2.7 inches and 5.0 inches for 1949. The finding of fish of such.small size in the stomachs of the brook trout, indicates that spawning must have occurred late in the summer. 'With the indication that there must have been a wide range in the time of bluegill spawning, an attempt was made to establish the approximate date of the peak. As very little material was available for the years 1948, 1949, and 1950, no attempt was made to determine the time of spawning for those years; however for the year 1951 there is sufficient data to establish the approximate date for the peak of spawning. The Pigeon River Trout Experimental Station reported that the peak of the bluegill spawning had passed as of June 18, 1951. Table 8 gives the average "K" factor of 2.07 for fish caught June 14, 1951 and 1.55 for June 17, 1951. The reason for the rapid decrease may be due to loss in weight I because of the spawning of the fish. Deason and Hile (1947) found the loss of weight for the female kiyis at spawning to be considerable. If this is true it would indicate that the peak of the spawning occurred sometime between the dates of June 14 and June 17, 1951. 42 Morgan (1951), who worked with the bluegills of Buckeye Lake, Ohio, found the fish spawning from early May to the middle of August. Carbine (1959), in his studies of the spawning habits of fish in Deep Lake, Michigan, found the bluegills spawning from June 18 to August 18. With the report from the Pigeon River Trout Experimental Station that the peak of bluegill spawning had passed by June 18, 1951, there is no other definite proof that the bluegills spawned at a later date for this year. The only indication that this may have happened is the presence of the small bluegills in the stomachs of the brook trout caught in February, 1950. The work of Morgan and Carbine also con- firms this supposition. The bluegills spawned over a prolonged period with a fairly rapid increase to a peak, and then declined to‘a point where a few fish spawned sporadically. Length of Growing Season The length of the growing season of fish is variable. An attempt to determine the length of the growing season for -the Ford Lake bluegills was made. It was possible to ob- serve the differences in the length of the growing seasons for the years 1949 and 1951. The growing season for fish starts with an annulus for- mation, then for a short time there is a period of rapid 45 growth which later tapers off. Spoor (1958) observed that suckers (Catostomus commersonnii) in Muskellunge Lake, Wis- consin completed 92 percent of their growth.by mid-July. The average growth for each collection date was calcu- lated for bluegills caught in 1949 and 1951. This was accom- plished by calculating the amount of growth from the time of the last annulus formation to date of capture. Growing Season for 1949 The average length of fish for each date of capture is presented by Table 11. The earliest collection date was late June, which is well into the growing season, so no date for when growth started can be given, but the leveling-off period occurred some time in August. Growing Season for 1951 The results for 1951 (Table 12) are more reliable be- cause of the greater numbers taken at each collection date. The earliest date of capture was May 5, which.was before growth had started, and the latest date of capture was ‘August 4. The calculated growth on May 5, 1951 was 1.0 inches, while on June 10, the growth had decreased to 0.5 inches. The reason being that during May, the fish had not formed their annulus, and as the number of fish forming their annu- 44 TABLE 11 AVERAGE GROWTH FROM THE TIME OF THE LAST ANNULUS FORMATION TO THE TIME OF CAPTURE OF BLUEGILLS CAUGHT IN 1949 Total growth of Average Collection all fish. Number rowth date (inches) of fish inches) June 29 6.1 5 1.2 July 1 5.2 2 1.6 July 4 6.0 4 1.5 July 7 27.9 20 1.4 July 10 17.5 14 1.2 July 17 4.9 4 1.2 July 24 11.5 8 1.4 August 17 1.1 l 1.1 August 25 6.5 4 1.6 August 28 5.1 2 1.6 Totals 87: 6: III-4* * Average growth for all fish. lus increased, the calculated growth.declined until the peak of annulus formation was reached (Table 8 shows June 10 as the peak of annulus formation). The growth increased to 0.9 inches by July 19, then leveled off so that it appeared that the growing season for 1951 was complete. For the year 1951, the growing season appeared to be 45 TABLE 12 AVERAGE GROWTH FROM THE TIME OF THE LAST ANNULUS FORMATION TO THE TIME OF CAPTURE 0F BLUEGILLS CAUGHT IN 1961 Total growth of Average Collection all fish Number growth date (inches) of fish (inches) May 5 25.6 24 1.0 May 19 8.6 12 0.7 June 5 a 4 12.2 21 0.6 June 6 & 7 51.6 89 0.6 June 10 20.7 41 0.5' June 14 24.8 44 0.6 June 17 5.0 5 0.6 July 19 5.2 6 0.9 August 5 & 4 55.4 59 0.9 Totals 185.1 28:, [037* 4 Average growth for all fish. from the middle of June to the latter half of July. Due to the late collection dates for the year 1949, , there was no basis for comparing the start of the growing season with that of 1951. The termination of growth for 1949 was in the latter half of August, while that for 1951‘ was in the latter half of July. The length of the growing season may regulate the amount of growth for the two years. 46 During 1949, the average growth.was 1.4 inches and during 1951, 0.7 inches. Effect of Temperature on Growth Temperature may have had an effect on the length of the growing season. Table 15 shows the average monthly air temperatures of the Ford Lake area from May through.August for 1949 and 1951. May 1951 was warmer than May 1949, but the rest of the months during 1951 were cooler than in 1949. TABLE 15 AVERAGE MONTHLY AIR TEMPERATURE (FAHRENHEIT) FROM MAY THROUGH AUGUST FOR 1949 AND 1951 Year Month May June July August 1949 52.96 67.44 67.91 64.99 1951 56.25 60.55 65.20 61.80 . Beckman (1945) states the time Of annulus formation is correlated roughly with the mean monthly air temperature. If this is true, the fish caught in 1951 started growing before those caught in 1949, but the warmer temperatures during June, July, and August of 1949 may account for the later growing season. 47 CATCH OF BROOK TROUT During 1946, 1947, and 1951 brook trout were planted in Ford Lake at the rate of 500 fingerlings per acre or a total of 17,400 fish. As there was no compulsory creel census before 1949, there is no record of the number of trout caught before this date. During the trout season of 1949, 159 brook trout were caught having an average total length of 8.6 inches and an average weight of 155 grams. In 1950, only 11 trout were caught during the open season. Their average total length was 10.5 inches and their average weight was 222.5 grams. However, on February 9, 1950, a total of 51 brook trout were caught. These fish had an average total length of 9.7 inches and an average weight of 198.1 grams. In 1951, the total catch consisted of 16 legal-sized brook trout with an average total length of 9.6 inches and an average weight of 164.4 grams. During the summer, numer- ous trout below the legal-size of 7 inches were caught but are not included in the tabulation. 17,400 brook trout were planted of which only 197 were known to have been caught, thus revealing a very low return. 48 FEEDING HABITS The feeding habits of the bluegill and broOk trout were studied to determine whether or not they competed for food. Food of the Bluegill During August 4 and 5, 1951 while Obtaining scale samples for bluegills, 57 stomachs were collected for food analysis. The fish were of two length groups, 5.5 to 4.5 inches and 5.5 to 8.0 inches. For the fish in the smaller length group, the results of the food analysis are presented in Table 14, while the results for the fish in the larger length group are presented in Table 15. Table 16 shows the major food groups eaten by the two groups of fish. The food of the smaller sized fish consists primarily of plankton crustaceans (Entomostraca), and in- sects in very small numbers. Ball and Tanner (1951), Ewers and 506861 (1955), and Leonard (1940) who worked with'blue- gills of a smaller size found the fish to be feeding on a similar diet . The food of the large fish presented in Table 16, shows insects making up over one half of the total food eaten and plants accounting for a little under one third of the total. The plankton crustaceans (Entomostracs), mollusks, and fish make up the remainder of the total. Morgan (1946), Morgan Hmoa .m-e eesmoa suppose no open .oEfiaop doom HmpOE mo paooeom mm ozoam .moaoofi 0.n npmaoa aspen oweeopm .apmsea Hence nosed“ 0.4 on m.» .mHHaMpan 0H 00 mdmhawnmrnomEOpm mo mpfldmom 0H canoe 50 m 0H m on mm 0 eeuaeooonfino 0&0paan spooqu H 0H 0H 0H 0 H 000002000 costs 9 m m m.ma m sooeoaoo 00 00 0b 00H 00H 0H snoooomao semaphoEOEEH 0:008000 mamaowwao on» someone nomeOpm msmfiaewao msmaomwno Emansmao Has mom woaofimpooo has Ed has CH moanfiepooo mnaeaspooo 082H0> usomeopn CH 052Ho> HepOp 08§H0> H000» 030080p0 oncogene H0000 Ho oesaop H0000 no poooaoa no poooaom H0000 no no 900852 0200900 no 2200200 00009 90000020 pa0oaom 0wmaobd 00090>41 .thH .0.4 enemas noaeooHHoo to seem .easHos moon H0000 no poooaoa 00 macaw .m0nooH 0.0 apmn0H H0000 000L0>0 .mpwooH H0000 menoeH 0.0 on 0.0 .Ah0080 oqov uHHHmooHn Hm mo mHthoam Someone mo mpHfimom 0H eHnme 52 .H0H900099050 0 00H 00H 00H 0 H 309008 002 0000 0 00 ON 00 0H 0 0H9000 H 0 0 0H 0H 0 000H0 .H00 09 w 00 0 oo 00 m carcass 92909.0 HH 00 00 00 om 0 09000 090H0 0 00 0 or 0H 0 096080000 0000HH02 0 00H 00H 00H 0 H #0900000H00 m 00 00 00 0 H 4093080800 00090 0 0 0 0 H 09000H800 H 0m 0m 0m 0 H 09000000099 0 00H 00H 00H 0 H 0900000000 0008000 0 0H 0 00 0H 0 000H00H00 00 H0 0 00 0b 0H 000H80009H00 09000H0 000000H 0 0 0 0m 00 0 000009000 0 0 0.0 00 00 OH 0900000H0 000900080090 00008000 080Ho0w90 000 0008000 0008000 080H90w9o 080H9009o _80H90090 HH0 900 onoH00coo 080 9H 090 9H 00H9H00800 0909H00900 085Ho> 00008000 0H 085Ho> H0000 088Ho> H0000 00008000 00008000 H0000 00 089Ho> H0000 90 0900900 no 0900900 H0000 00 00 900822 0000900 no 0000900 0000A 00000090 0800900 00090>< 0009090 53 (1951), and Ball and Tanner (1951) also found bluegills of comparable size feeding largely upon insects and plants. TABLE 16 PERCENTAGE OF TOTAL FOOD ORGANISMS FOR TWO SIZE GROUPS OF BLUEGILLS, (AUGUST 4 and 5, 1951) 3.5 to 4.5 5.5 to 8.0 Food organisms inches inches Entomostraca 97* 5 Insecta 3 54 Plant 0 31 Mollusca 0 4 Fish 0 5 * Percent of total food. The above investigation of the food of the Ford Lake bluegill, is based on collections of fish taken in a short span of time and the only conclusion that can be made is that there is a definite difference in the food eaten by the two size groups of fish, at the time of capture. Hile (1951) states that the feeding habits of fish change with their ' growth. As the fish becomes larger, it is capable of seizing and devouring larger prey. This may be the reason for the difference in the food eaten by the two size groups of fish. 54 Food of the Brook Trout Stomach samples of 37 brook trout were collected at the following dates, 9 during February 1950, 9 during April 1951, 7 during May-June 1951, and 12 during August 1951. A small number of fish were examined and can only give an indication as to the food eaten. The food for the four dates of capture are presented in Tables 17, 18, 19, and 20. Table 21 presents the major food groups. No plankton crustaceans (Entomostraca) were found in any of the stomachs. Insects made up the bulk of the food for all dates of cap- ture with the exception of February. Plants contributed very little to the food of the fish.although.small quanti- ties were found in the February and August collections. Mollusks were not found in large numbers. Few were taken during February, and for the other collection dates, their volume varied up to almost one third of the total volume. The stomach analysis for February showed a predominance of fish; whereas relatively few were found in the stomach samples of other months with the exception of August, when none were found. In northern and southern Ontario lakes fish were found to be the main diet for speckled trout (brook trout) over 10.0 inches in length (Ricker, 1930). Insects accounted for the greatest part of the food of brook trout in East Fish Lake, Michigan (Leonard, 1941). This is in agreement with the stomach analysis of the trout in Ford Lake during April, May-June, and August. .0000 0 900 # .HmmH .09009000 0900000 no 0000 .005 1H0» 0000 H0000 00 0000900 00 03000 .0000000 0.0H 00wn0H H0000 0009090 .000wn0H H0000 00000H H.HH 00 0.0 .05090 00090 0 00 0000H000 0008000 00 00H500m .! WUIH.».II .. 0H 0H00E 56 on om on 00 mu 0 3000HE 000 00 00 on 000 000 0 HHfimosam 0000 00090 n n a HH H 0H9000 m m H OH an n 09000 000H0 0 OH 0 00 00 0 0000000000 0000HH00 00090 n n 9 HH H 0900000Hoo H . 0 n m an n 0900000H0¢ . 0000000 00090 m.o m.o «.0 HH H 000000009H0o 0900009 000000H 00000000 000000m90 000 0000000 0000000 000000w9o 000000m90 .00000m9o HH0 900 w000000000 000 00 000 00 w0H0000000 w000000000 V 000H0> 00000000 0H 000H0> H0000 000H0> H0000 00000000 00000000 H0000 no 005H0> H0000 no 0000900 00 0000900 H0000 00 00 900002 0000900 no 0000900 00000 00000090 0000900 0&09094 0w090>¢ .HmmH .Hfigmd oaspmao mo mama .madao> dupe» no psoonom mm agonm .monocH m.m upwcoa prOp mmmnmpw .numcod Haven menoca n.HH on m.> .pfionu #0099 a no mumhawqw nowaopm no mpdfimom ma oflpwa 58 .Hwfinpmonnoat am no 00 or mm a Bounda 652 nmfim ad on ma op «w w «comoapmaw momsHHoz m om om om Ha H «nopmoqmahm H OH 0H 0H Ha a #maopqonpno b ma oa om w¢ ¢ «nonmaamm pH on oa on mm m *unopmooaoo ma mm 0H om mm m unopmomaou m om om om Ha H owuaeocogano a m m m Ha H ¢oauaafingopmoh2 n ma 0H om mm m #owoaaonondnv m ma m on vw w occanonm m 9H m om ¢¢ ¢ owuaoaaso dnmpmwn upcoqu unowEUpm mamaawwho on» nowEOpm nowaopm mamacwwpo namflnwwuo .Emfindmno Had you mcficawpcoo had a“ ham ca madcawpnoo mnacfimuaoo oasaop unodSOpm :H oESHo> Have» oadao> HapOp anom86pm unowscpm prop no oasaop prou mo paoonom Ho unconom HapOp no no nonasz unconom no uncouoq pmdoq pmopaouw sacchom omuno>4 owwnopd .Hmma .OGSb and hwz oazpmmo mo mama eamfido> Hana» no unmonom ma axon» .moflona n.m numdoa wave» omwhmbw .npwcoa Hana» monoaa H.ma on o.m .udoap Mocha b no mfimhaaqu nowsoum no mpazmom ma oanws . .l1‘il....¢ .il Ida II 6O .UoanSoo 6959 cam apan H .Haanmoanoa * n om ON ON wH H annon wH on on on mm m honnHa cg: nuHm mH aw mm on mm m «oomoapmwc doufiHHos HH mr mp mb wH H mHnQoQ m mH mH om mm m *unopmocmahm m om om om HH H ¢aaopmosom w nH 0H mH mm m tuaopmooHou cowan m m m ¢H H anopaooHoo oownu m m m wH H owUHaononono m m m 0H mm m towuHcog IOAOHHOQ mm mm m 00H nw n HoaUHoHHfio mH n¢ 0H. OCH aw n *omUHcHgsm anoumHn upooqu uflodfibpm mSmHzmmho on» nowEOpm nowScpm mEchwmpo naanwwno .EmHnwmno HHw you wankucoo haw nH haw GH wanprcoo wanHmpsoo oasHob unowEOpm nH mESHop prop cabHop Haven unowBOpu anowabuu Have» no ospHo> Have» no paconom no unconom prOp no no nonabz ucooamq no pcoonom pmuon «nonwonw unconom , owwnobd owwno>fi I 5...; . . . J .QOHuuHfinwp qH cocfiHocH pom mango anomEOpm b * .33 84‘ p.334 833:8 no mpwn .oESHo> Have» no unconom mu atone .mmflocH 9.0 npwnoH Hanan ommao>w .npwqu Haney mononH o.b o» m.m .#p:oau #0099 NH 90 mHthwcw nodacpm no mpHdmom om OHQwe 62 .Hdanmonnoa * m mm mm mm om H oHpqswa aoanm panm Hn mu m» om ow m acoqoapmaw womuHHos mH om om om om H «Human mH om om om om H «noanamm H m m m om H unopgooHoo b mH mH om o¢ m towUHEocopHnu mm mm 0H OCH ow m omUHSosoano anmeHn upooqu mnoaadpm machawno on» nowacpm nowaopm maanwwno machwwno aquwwno HHm non manprcoo haw 2H haw qH mankucoo wanprcoo oabHop unowSODa :H oabHo> HmpOp oEsHo> Haven anomaoum «newEOpm Hana» Ho oaSHo> Hanan yo pqoonom no pcoonom Hanan no no 903552 unconom no unoonom pmaoq pmopaopw pnoonom owdho>¢ owwaobd 63 TABLE 21 DATE OF CAPTURE OF BROOK TROUT WITH THE PERCENTAGE OF TOTAL FOOD FOR EACH MAJOR GROUP Major food Date of capture groups February April May and June August 1950 1951 1951 1951 Entomostraca 0* o o o Insecta l 63 71 64 Plant 2 O 0 5 Mollusca 5 16 12 51 Fish 91 21 17 O * Percent of total food. Needham.(1951) and Morofsky (1940), found insects to be the predominate food of the brook trout in streams. Table 22 illustrates the amount of aquatic and terres- trial food taken by the brook trout. The terrestrial foods include the adult forms which have aquatic larvae or nymphs. The water organisms contribute the largest percentage of the food. During the winter when the lake was covered with ice, only aquatic food was taken. As more terrestrial forms of life became present, they were taken in larger numbers. The bluegills have an advantage over the brodk trout in that they have a high breeding potential and reproduce natu- rally in lakes, whereas the trout do not and have to be 64 planted. The only predator of the bluegill is the brook trout which does not seem to be great enough to control their numbers. As the bluegills increase in numbers, they compete strongly with the trout for the same foods. This competition results in a poor showing of the trout. TABLE 22 PERCENT OF TOTAL FOOD AND DATE OF CAPTURE FOR FORD LAKE BROOK TROUT Food types Date caught February April May and June August 1950 1951 1951 1951 Aquatic 100* 68 60 93 Terrestrial O 32 4O 7 * Percent of total food. 65 DISCUSSION Michigan with its large number and great variety of in- land waters has been placing greater attention on the lakes that are suitable for trout. Many of the lakes that are suited for trout have a large population of small warm-water fish. In lakes where trout and warm-water fish live together such.mixed populations are not successful. In the northern part of the lower peninsula of Michigan the accepted lake management procedure is to encourage trout production. In carrying out this policy it is necessary to remove the undesirable fish population and restock with trout. Ford Lake is a lake that is thermally and chemically suited to trout but has been over populated with.small blue- gills. In August of 1946 the lake was poisoned, to remove the fish population for a fall planting of brook trout. After the poisoning it was believed that the bluegill popu- lation was eliminated, however, in the spring of 1947 it was discovered that a few of the bluegills survived the poisoning. This situation gave the opportunity to study the growth rate of the bluegills as they repopulated the lake. The growth studies were made from.433 bluegill scale samples, collected from 1948 to 1951. The scales were mounted on slides with a gelatin-glycerin media and ex- amined with the aid of a scale projection machine. 66 The growth rate of the bluegills was found to decrease as the age of the fish increased. The growth rate for the same age groups of fish also decreased as the number of fish increased. During the investigation an attempt was made to deter- mine whether or not other calculations besides the scale method may be used for growth determinations. It was found that these calculations could not be used. However, with the scale method they help substantiate the findings. From the creel census it was found that very few brook trout were caught, indicating that the growth and survival of the trout was very poor. Stomach samples of 37 bluegills and 37 brook trout were analyzed and it was found that the larger sized bluegills competed for food with the brook trout. The relationship between the bluegill and brook trout is one in which the bluegill becomes the numerically domin- ant fish and the trout eventually disappears from.the lake. If a lake is to have a good trout production it is necessary to keep the warm-water fish out of the lake. 1. 8. 67 SUMMARY Growth.analysis of the bluegill revealed a decrease in the growth rate as the age of the fish increased, also the growth rate of the same age groups decreased as the number of fish in the lake increased. The bluegills caught in 1948 and 1949 attained a length of 6 inches some time during their second summer of life. Those caught in 1950 and 1951 did not reach this length.until the third summer. The lengths and weights of Ford Lake bluegills increased proportionally. The condition ("K" factor) of a fish.population does not indicate whether there is poor growth.by a low "K" value. The date of capture has a marked effect on the "K" fac- tor of the fish. Increasing from the start of the grow- ing season to spawning, accounting for the sharp drop, then increasing for the remainder of the growing season. Ford lake bluegills laid down their annulus during the month of June. ' Bluegills spawned over a prolonged period of time with a fairly rapid increase to a peak, and then declining to a point where a few fish spawned sporadically. For the year 1951, the growing season was from the middle of June to the latter half of July. Of 17,400 brook trout planted in Ford Lake, the records 10. 11. 12. 68 reveal only 197 legal-sized trout caught. Food of bluegills in the length group, 3.5 to 4.5 inches, was almost exclusively plankton crustaceans (Entomos- traca) with a few insects. Food of the larger sized bluegills, 5.5 to 8.0 inches, was chiefly insects, which accounted for over one half of the total amount of food taken, plants a little under one third, with plankton crustacenas (Entomostraca), mollusks, and fish almost equally divided for the re- mainder. The food of the brook trout for February consisted of fish.(bluegills) in such numbers as to almost exclude all other organisms. In April insects made up the greatest percent of the total food taken, with.mollusks second. May and June collections had a greater per— centage of insects than the April collection'but had a smaller percentage of fish and mollusks. In the August sampling, insects were the dominate food fol- lowed by mollusks and plants. 69 LITERATURE CITED Ball, Robert C. 1948 Recovery of marked fish following a second poison- ing of the population in Ford Lake, Michigan. Trans. Am. Fish. Soc., 1945, 75: 36-42. 1948 A summary of experiments in Michigan lakes on the elimination of fish population with rotenone, 1934- 1942. Trans. Am. Fish. Soc., 1945, 75: 139-146. ----------- and Howard A. Tanner 1951 The biological effects of fertilizer on a warm-water lake. Tech. Bull. 223, Michigan State College Agr. EXP. Sta. Beckman, William.C. 1943 Annulus formation on the scales of certain Michi- gan game fishes. Papers Mich. Acad. Sci. Arts and Letters., 1942, Vol. XXVIII: 281-312. 1948 The length-weight relationship, factors for con- versions between standard and total lengths and coefficients of condition for seven Michigan fishes. Trans. Am. Fish. Soc., 1945, 75: 237-256. 1948 The age and growth of fishes. Michigan Conserva- tion, Vol. XVII, No. 7: 8-9. - 1949 The rate of growth and sex ratio of seven Michigan fishes. Trans. Am. Fish. Soc., 1946, 76: 65-81. Carbine, W. F. 1939 Observations on the spawning habits of Centrarchid fishes in Deep Lake, Oakland County, Michigan. Trans. Fourth.North.Am. Wildlife Conf., pp. 275-287. Carlander, Kenneth D. and Lloyd L. Smith.Jr. 1944 Some uses of nomographs in fish growth studies. Copeia, No. 3: 157-162. dense canadense) (Smith) and yellow perdh, (Perca flavescens) (Mitchill) from Lake of the Woods, MIn- nesota., Trans. Am. Fish. Soc., 1949, 79: 30-42. 70 Creaser, Charles W. 1926 The structure and growth of the scales of fishes in relation to the interpretation of their life history, with special reference to the sunfish (Eupomotis gibbosus). Misc. Pub. No. 17, Univ. oT‘Michigan, Museum of Zoology Deason, Hilary J. and Ralph Hile 1947 Age and Growth of the kiyi, (Leucichthys ki i) (Koelz) in Lake Michigan. Trans. Am. Fis . oc., 1944, 74: 89-142. Eschmeyer, R. W. 1937 Some characteristics of a population of stunted perch. Papers Mich. Acad. Sci. Arts and Letters, Vol. XXII: 613-628. 1937 Experimental management of a group of small Michigan lakes. Trans. Am. Fish. Soc., 1937, 67: 120-129. Ewers, Lela A. and M. W. Boesel 1935 The food of some Buckeye Lake fishes. Trans. Am. Fish. Soc., 1935, 65: 57-70. Hansen, Donald F. 1936 The date of annulus ring formation in the scales of the white crappie. Trans. Am. Fish. Soc., 1936, 66: 227-236. Hile, Ralph 1931 The rate of growth of fishes of Indiana. Inves- tigations of Indiana lakes, No. 2, Indiana De- partment of Conservation, Pub. No. 107: 8-55. Lagler, Karl F. 1949 Studies in freshwater fisheries biology. J. W. Edwards, Ann Arbor, Michigan, 231 pp. Leonard, Justin W. 1939 Feeding habits of the Montana grayling (Thymallus montanus), (Milner) in Ford Lake, Michigan. Trans. Am. Fish. 300., 1938, 68: 188-195. 1940 Further observations on the feeding habits of the Montana grayling (Thymallus montanus) and the blue- gill (Le omis macrEEhIrus) in Ford Sake, Michigan. Trans. A5. FIsh. Soc., 1939, 69: 244-256. 71 Leonard, Justin W. 1941 Notes on the feeding habits of brook trout in East Fish Lake, Montmorency County, Michigan, Hunt Creek Experimental Area, during the summer of 1940. Inst. for Fish. Research. Rept. 663 (unpub.). Lewis, William M. 1950 Fisheries investigations on two artificial lakes in Souther Iowa II. Fish pepulations. Iowa State College Journal of Science, Vol. 24, No. 3: 287-324. Mackenthun, Kenneth.M. 1947 Age and growth of Southern Wisconsin bluegills, (UIIEIIE macrochirus). Wisconsin Conservation B e n, VoI. XII, No. 5: 20-22. Morgan, Ann H. 1946 Food of game and pan fishes of the 1945 biological survey. Fisheries report for lakes of Central Massachusetts, 1944-1945: 70-74. Morgan, George D. 1951 The life history of the bluegill sunfish, (Le omis macrochirus), of Buckeye Lake, Ohio. Den son University Bulletin, Journal of the Scientific Laboratories, Vol. 42, No. 4: 21-59. Morofsky, W. F. 1940 A comparative study of the insect food of trout. Jour. Econ. Ent., 33, 3: 544-546. Murphy, Garth I. 1951 The fishery of Clear Lake, Lake County, Califor- nia. California Fish and Game, Vol. 37, No. 4: 439-484. Needham, Po Re 1931 Studies on the seasonal food of brook trout. Trans. Am. Fighe $000, 1931, 60: 73-880 Parsons, John W. 1950 Life history of the yellow perch, (Perca flaves- cens) (Mitchill), of Clear Lake, Iowa. Iowa State College Jour. Sci. 25 (1): 83-97. Potter, George ( ) ( ) 1925 Scales of the bluegill Legomis pallidus Mitchill . Trans. Am, Micros., Vol. , o. : - 7. 72 Ricker, William E. 1930 Feeding habits of speckled trout in Ontario waters. Trans. Am. Fish. Soc., 1930, 60: 64-72. Snedecor, George W. 1950 Statistical Methods. Iowa State College Press, Ames, Iowa, 485 pp. Spoor, William A. 1938 Age and growth of the sucker, (Catostomus com- mersonnii) (Lacepede), in MuskeIIunge Lake, VIlas Academy of Sciences, Arts and Letters. Vol. XXXI: 457-505. Taube, Clarence M. 1948 A progress report for 1947 and 1948 on the pro- ductivity-stunting-survival experiments run in a hatchery pond. Inst. for Fish. Research. Rept. .- t? ',’ ' 2.5 ‘.:’..’_dj'(:"' 4 H ’- ' 7' — ) ink-u- . ' 9 ‘.‘ A J 'j - ‘ -.. 1 : . ‘ . . ‘. k "“143“. . ."ED N‘ If r’fixn‘a'A‘”: % |£J :.\~l '72 k 1" t». I; t‘h. I}. x- ‘2?~.‘°¢" ”‘- - "' I -. ' 41‘" {.r L4,} .vlfb ' r ‘a g I. A La. -' ' 'La .t . ’twn'fu J \.\ J o" '44 5 L, "a" ‘1 ...\ ta “I'\ y‘: 7%. v: .. AH :-',‘.’1.1‘Y:tti ‘- 3 a ' ' 3 .-:~‘. '4‘ .513; ' ' .e.>’-'-~’x'=~' ‘ I. .7"? .‘ . v. ‘ l .7,- 3 7" I‘, 4‘: . .':’_- w. ‘ :‘Ei “ ‘ t 7’?" '_. '. _ ‘. ‘*'-)~I.- Qe.~,~'- (535‘. . 7 U.- u «a..- HICHIGRN STQTE UNIV. LIBRQRIES Ill 1 0852 lllllfl llllllHl Nlll Ill! 9 312 3103 illl 7