Bulletin STATE OF ILLINOIS DwiGHT H. Green, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Frank G. Thompson, Director NATURAL HISTORY SURVEY DIVISION Theodore H. Frison, Chief Volume 23 BULLETIN Article 3 Overfishing in a Small Artificial Lake Onized Lake Near Alton^ Illinois GEORGE W. BENNETT Printed by Authority of the State of Illinois URBANA, ILLINOIS May 1945 STATE OF ILLINOI S DwiGHT H. Green, Governor DEPARTMENT OF REGISTRATION AND EDUCATION Frank G. Thompson, Director BOARD OF NATURAL RESOURCES AND CONSERVATION Frank G. Thompson, Chairman William Trelease, D.Sc, LL.D., Biology* Arthur Cutts Willard, D.Eng., LL.D., Ezra J. Kraus, Ph.D., D.Sc, Forestry President of the University of Illinois L. R. HowsoN, B.S.C.E., C.E., Engineering Norman L. Bowen, Ph.D., Geology Roger Adams, Ph.D., D.Sc, Chemistry NATURAL HISTORY SURVEY DIVISION Urbana, Illinois Scientific and Technical Staff Theodore H. Prison, Ph.D., Chief Florence A. Nyberg, Assistant to the Chief Section of Economic Entomology G. C. Decker, Ph.D., Entomologist M. D. Farrar, Ph.D., Research Entomolo- gist J. H. Bigger, M.S., Associate Entomologist S. C. Chandler, B.S., Southern Field Ento- mologist James W. Apple, M.S., Northern Field Ento- mologist B. G. Berger, M.A., Assistant Entomologist John M. Wright, B.A., Assistant Entomolo- gist (on leave) H. B. Petty, Jr., M.A., Associate in Ento- mology Extension C. J. Weinman, Ph.D., Special Research Assistant Willis N. Bruce, B.S., Special Research Assistant Section of Insect Survey H. H. Ross, Ph.D., Systematic Entomologist Carl O. Mohr, Ph.D., Associate Entomolo- gist, Artist (on leave) B. D. Burks, Ph.D., Assistant Entomologist (on leave) Milton W. Sanderson, Ph.D., Assistant Entomologist Kathryn M. Sommerman, M.S., Artist, Entomological Assistant Phyllis A. Beaver, Laboratory Assistant Section of Forestry James E. Davis, M.F., Extension Forester Lee E. Yeager, Ph.D., Forester Section of Aquatic Biology George W. Bennett, Ph.D., Limnologist D. F. Hansen, Ph.D., Assistant Zoologist Paul G. Barnickol, M.A., Ichthyologist Bruno von Limbach, M.S., Special Researd Assistant Section of Game Research and Management R. E. Yeatter, Ph.D., Game Specialist Section of Wildlife Experimental Areas Arthur S. Hawkins, M.S., Game Technicia, (on leave) F. C. Bellrose, Jr., B.S., Assistant Game Technician Harold C. Hanson, M.S., Assistant Game Technician Section of Applied Botany and Plant Pathology L. R. Tehon, Ph.D., Botanist J. C. Carter, Ph.D., Assistant Botanist G. H. Boewe, M.S., Field Botanist J. L. Forsberg, M.S., Research Pathologist Bessie B. Henderson, M.S., Research Assistant Section of Publications James S. Avars, B.S., Technical Editor Eleanor G. Wolff, B.Ed., Assistant Tech nical Editor Technical Library Marguerite Simmons, M.A., M.S., Tcchnica Librarian Consultants in Herpetology: Howard K, Gloyd, Ph.D., Director of the Museum, Chicago Academy of Sciences; Clifford H. Pope, B.S., Curator of Amphibians and Reptiles, Chicago Natural History Museum. •Deceased January 1, 194S. This paper is a contributionfrom the Section of Aquatic Biology. (79323—3M—3-45) CONTENTS Page Acknowledgments 375 Characteristics of Onized Lake 375 Evidences of Overfishing 378 Analysis of the Population 382 Effects of Overfishing 383 Largemouth Bass 385 Black Crappie 388 Bluegill 392 Warmouth Bass 395 Green Sunfish 397 Yellow Bass 398 Bullheads 399 Golden Shiner 400 Miscellaneous Fish 402 Age Distribution of Fish 402 Discussion 404 Summary 405 Literature Cited 406 Some of the largemouth bass taken in th final census of Onlzed -Lake in 1941. W. \^ Wood, inspecting fish, and Lyle Walker, hold ing them, are two of the several members c the Onized Club who assisted in the census. Overfishing in a Small Artificial Lake Onized Lake Near Alton, Illinois GEORGE W. BENNETT BEFORE North America was exten- sively settled, native fish were the staple food for a wide variety of predatory mammals, birds and reptiles, as well as for adult game and other piscivo- rous fishes. With few exceptions, the nat- ural predators captured small individuals of the various fish species in proportion to the relative abundance of such fish ; as the larger individuals were less subject to attack than the smaller individuals, an accumulation of large fish resulted. Under conditions involving extensive juvenile mortality, the survival of any species of fish depends upon a high repro- ductive potential, adjusted to compensate for large losses. Most species that exist today have a high reproductive potential. The species that produce comparatively few eggs have unusual behavior patterns that offer special protection to their spawn. As the human communities have spread to cover the continent, native fishes have been subjected to a different kind of «A Onized Lake as seen when looking east from the spillway toward the lower end of the larger bay. The fairly steep banks surrounding the lake are well grassed except where worn by traffic. On the hill above the fishing pier, left, are brick grills, picnic tables and a shelter. [373] 374 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 attack. Man has become a selective preda- tor of large fishes. He has waged contin- ual warfare on other fish predators, has passed laws directed at controlling any inclination on his part to take small fish, and has developed an artificial propaga- tion and stocking program to augment the supply of small fish. Because the high reproductive potential of the fishes has remained unchanged, there has been a great increase in the survival of young fish, resulting in added competition for food and space, in overpopulation of waters and in stunting of fish. Intensive inter- specific competition among the fishes them- selves may be the key factor responsible for eliminating or reducing populations of many of the more desirable game fishes in some waters, because the young of these species are unable to compete with the young of others under crowded conditions. A common belief among anglers is that, in lakes in which the annual yield of game fish has declined over a period of years, intensive fishing is responsible for the pro- gressively poorer catches. In most instances in which an actual decline may be proved, no data are at hand as to the kinds and quantities of fish that remain in the lake at the time of low production. However, in 22 artificial lakes in Illinois, most of which were censused at a time of low pro- duction, only one showed a decline in yield associated with intensive fishing. Whether intensive angling is o.r has been directly responsible for a reduction in game fish yields of other Illinois lakes, particularly those larger than 25 acres, is subject to question. The efficiency of angling devices is so low, and the patience of the average angler so short, that, long before the pop- ulation of the selected species has been reduced to the danger point below" which it cannot reproduce itself, the fishing for that species has become so uninteresting that it is greatly reduced, or it may even be stopped. It is not uncommon for populations of desirable fish to become depleted in, or disappear from, waters that are fished very little. This occurrence is frequent in arti- ficial lakes and reservoirs where preda- tors of small fish are at a minimum. Here competition among those desirable species artificially introduced, along with compe- tition from undesirable kinds that gain entrance through feeder streams, eventu- ally crowds out the more desirable species. The term "overfishing" as it relates to lakes is loosely used by anglers. By some it is applied to a process characterized by the depletion of a single select species, a depletion attributed to more or less inten- sive fishing (usually an unspecified num- ber of man-hours) for that species. Actu- ally this decrease in yield may result from competition with other fish wherein the select species is gradually replaced by an- other or several other species, less desir- able to anglers. In such a case the water cannot be said to be overfished, for it sup- ports a fish population at least as great in total weight as that when the select species was present in numbers. In the strict sense, the term overfishing involves the entire fish population of a body of water. The yield taken by anglers is not restricted to one or a few species but includes all or almost all in near pro- portion to their relative abundance. This yield, considered in pounds of fish flesh, is removed at a rate faster than it can be replaced by conversion of available natural food into flesh, and the poundage of fish supported by the water remains below the carrying capacity of that water for all fish. Overfishing as defined here is a con- dition that is extremely rare because it requires a very great intensity of angling. The only case of overfishing ever observed in Illinois by Natural History Survey aquatic biologists occurred under conditions favorable for study, 1938-1941. Evidence of overfishing was available from well-kept records of hook-and-line catches for two complete fishing seasons and parts of two others, and from sample catches made with test hoopnets in 1938 and 1940. In 1941 the lake was treated with a plant alkaloid to kill the fish, and a careful cen- sus of the fish population was made. This investigation would have been impossible without the continual interest and cooperation of members of the Fish-i ing Club of the Owens-Illinois Glass Com- pany of Alton, Illinois. Overfishing in Onized Lake was the result of an intensity of angling far greater than that observed in most waters. Only I under conditions of heavy use of a small body of water by a club, community or industry, where fishing is associated with other forms of outdoor recreation, would this intensity of fishing be duplicated. f May, 1945 Bennett: Overfishing, Onized Lake 375 Acknowledgments Mr. Bruno von Limbach, Assistant Zool- ogist with the Illinois Natural History- Survey, has given able assistance in many phases of the field work, and is in no small measure responsible for the completeness of the final census. Others to whom I am indebted for assistance are Mr. W. W. Wood, Mr. Austin Vincent and Mr. John Conrad of the Owens-Illinois Glass Com- pany, who helped to make this study possi- ble ; Mr. Robert G. Rennels, who assisted in the final census; Mr. Gernon P. Hes- selschwerdt, who tabulated the creel cen- sus data; and Mrs. Bruno von Limbach, who assisted in growth calculations. Characteristics of Onized Lake The Owens-Illinois Glass Company of Alton sponsors an extensive indoor and outdoor recreation program. The outdoor program is centered on a tract of land of 23 acres about 8 miles northwest of Alton. Here facilities are available for picnics, hiking, softball and fishing. The property, leased from C. W. Terry, consists of open Hats suitable for ball diamonds and other playgrounds, and steep-sided, well-wooded ravines, attractive for hiking. Several buildings have been erected, which are useful for indoor activities and serve as shelters in case of sudden storms. John Conrad acts as general caretaker during the season the area is open for use. Onized Lake is located in the northeast part of the tract within 100 yards of the entrance gate, fig. 1. The location of the lake in relation to the entrance and gen- eral headquarters for the area makes for convenience in checking fishermen and recording catches. The lake is a small artificial body of water of approximately 2 acres, built by Mr. Terry in 1933 by damming a steep- sided ravine. It is roughly V-shaped, with the main arm extending northward and Lotus and pond lilies in the smaller bay of Onized Lake. The lotus plants were started from a few seeds that were thrown into the lake several years ago. They have spread to cover most of the shallow water in this bay and are now a great nuisance to fishermen. 376 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 the other extending north-northwest. Sur- face water entering the smaller arm drains from a cultivated field, and that running into the main arm drains from a pasture and barnlot, the latter located about 200 yards from the lake. The entire drainage area is not more than 15 or 20 acres. The banks of the ravine in which Onized Lake was built are relatively steep except toward the upper ends of the two arms, resulting in little shallow water along most of the shore line. Soundings indi- cate a maximum depth of 21 feet in the southwest part of the lake near the dam, and much of the lake is from 10 to 14 feet in depth. The average depth is approxi- ONIZED LAKE AND ONIZED CLUB GROUNDS (NORTH SECTION) AREA OF LAKE - 2 ACRES DRAINAGE FROM BARNVARD Fig. 1.—Map of Onized Lake and the north section of the recreation area used by the Owens- Illinois Glass Company employees. Fishermen entering and leaving the lake are readily checked by the custodian at his headquarters. I May, 1945 Bennett: Overfishing, Onized Lake 377 mately 8 feet. Although the drainage area is small, the water level rarely fluctuates more than 2 or 3 feet during the year. A 12-inch tile serves adequately as a spill- way. The area immediately around the lake is used extensively for picnics. Large oaks are scattered over this area, and the shores are well grassed except where heavily shaded or worn by traffic. Aquatic plants are cattails, Typha lati- foUa L. ; pickerelweed, Pontederia cor- data L. ; arrowhead, Sagittaria spp. ; Table \.—Vertical series of temperatures and oxygen samples from Onized Lake during very hot weather, 10:00 a.m., August 29, 1938. 378 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 applying copper sulfate have been only partially satisfactory. A sample of water collected from the lake was analyzed by the State Water Survey, table 2. The presence of 1.7 parts per million of ammonium indicates pollution from barnyard waste. Other parts of this analysis, as compared with similar analyses from many other Illinois ponds, show that the water of Onized Lake is somewhat softer than that of most other ponds. Further indications of pollution from the barn lot came to light in hoopnet fish- ing operations in the terminal portion of the main arm in the summers of 1938 and 1940. Most of the fish caught in hoop- nets set in the shallow water of this arm, and left overnight, died, while those caught in other parts of the lake, and sim- ilarly treated, lived. No loss of fish has been observed in Onized Lake outside of nets, and it is probable that fish move out of the upper end of the larger arm or bay when periods of oxygen reduction occur. Undoubtedly, the waste from the barnyard has stimu- lated the growth of fish food organisms and, hence, the fish production of the lake. Evidences of Overfishing Onized Lake was stocked with 10,000 fingerling fish in 1934, from the state hatchery near Lebanon. No record is available of the kinds of fish used, but it is believed that largemouth bass and crap- pies predominated in this group. The next year, 1935, 2,000 fish, species unknown, from the Lebanon hatchery, were placed in Onized Lake, when it was found that the water level in a pond near Brighton, for which they had been intended, was dangerously low. Fishing in Onized Lake was begun in 1937 and it is probable that at that time, with 12,000 fish that had been stocked plus their young of 1935, 1936 and 1937, the lake was overpopulated and the fish already stunted. L. H. Nicolet of the Owens-Illinois Glass Company estimates that over a 5- year period an average of 125 families fished the lake each year. Fishing permits were issued to about 100 families in 1939, and to a few less in 1940 and 1941. In addition, approximately 95 special passes were issued each year. Near the end of the fishing season of 1938, the Natural History Survey fur- nished the Onized Lake caretaker with a creel census record book in which records could be made for each fishing trip, includ- ing the date, name of fisherman, number of hours of fishing, kinds of fish caught, numbers caught and their total weight. Mr. Conrad, in charge of the grounds, was much interested in the returns from fishing and checked each fisherman on entering and leaving the area. Fishing was heaviest on week-ends, beginning on Friday and usually reaching a peak on Sunday. Few fishermen appeared on Monday. As the custodian was on duty over the week-end, he was allowed a free day on Tuesday. Although some Tues- day fishermen were interested enough in keeping records to inform Mr. Conrad of catches made on that day, others did not take the trouble to do so ; therefore, the Tuesday record is not complete. No attempt has been made to estimate either the total Tuesday catch or the fishing intensity for that day, so that figures listed in the tables dealing with catch and fish- ing intensity are somewhat lower than if this information could have been included. The evidence for overfishing originates from three sources: (1) a creel census; (2) hoopnet samples of the population and (3) comparison of the poisoned fish population of June, 1941, with figures from the creel census and the hoopnet sampling. The first and probably the best evidence of overfishing in Onized Lake is from the creel census. A comparison of the total weight of fish taken by anglers during the fishing seasons of 1939 and 1940, table 3, indicates that a considerable drop in yield occurred in the latter year, after nearly 700 pounds of fish had been removed from Onized Lake in 1939. Apparently the 1939 catch was greater in pounds than could be replaced by the assimilation of the natural food supply. The fact that! about 1,000 fewer fish were caught in 1940 than in 1939 does not necessarily mean that the actual number of fish pres- ent in the lake had been reduced. No fig- ures are available on the abundance of natural spawn, but a. few successful indi- vidual broods could easily have replaced the numbers taken. It rather suggests that the number of fish of desirable sizes May, 1945 Bennett: Overfishing^ Onized Lake 379 Table 3.—Statistics on anglers' catch of fish from Onized Lake, 1938-194L Date Number of Number of Man-Hours Fish OF Fishing Caught 1938 September. . . 117.00 October 17.75 Season 134 . 75 1939 April 163.25 May 717.50 June 847.25 July 602 . 50 August 251.00 September. . . 135.25 October 113.00 Season 2,829.75 1940 April 30.50 May 995.80 June 947.20 July 459.00 August 484.00 September... 343.00 October 35.00 Season 3,294.50 1941 April 267.30 May 652.70 June 347.90 Season 1,267.90 Grand total.. 7,526.90 23 5 28 147 834 793 299 40 14 33 2,160 25 370 290 89 328 71 2 1,175 143 255 236 634 3,997 Total Weight OF Fish, Pounds 21.50 4.25 25.75 51.38 259.72 246 . 56 79.75 24.00 27.00 11.50 699.91 7.60 93.75 76.15 20.83 66.44 17.26 3.00 285.03 40.75 63.24 37.75 141.74 Average Weight OF Fish, Pounds 0.93 0.85 0.92 0.35 0.31 0.31 0.27 0.60 1.93 0.35 0.32 0.30 0.25 0.26 0.23 0.20 0.24 1.50 0.24 0.28 0.25 0.16 0.22 Number of Fish Per Man-Hour Pounds of Fish Per Man-Hour 0.197 0.282 0.208 0.900 1.162 0.936 0.496 0.159 0.104 0.292 0.763 0.820 0.372 0.306 0.194 0.678 0.207 0.057 0.357 0.535 0.391 0.678 0.500 1,152.43 Grand average 0.531 0.184 0.239 0.191 0.315 0.362 0.291 0.132 0.096 0.200 0.102 0.247 0.249 0.094 080 0.045 0.137 0.050 0.086 0.086 0.152 0.097 0.108 0.112 0.153 was smaller and that the new broods of young were unable to grow fast enough to reach the size range of interest to anglers. No accurate records were made of the number of small fish returned to the lake by fishermen, but verbal informa- tion obtained from persons familiar with the situation suggests that in 1940 many more fish were returned than were taken. Table 3 shows also that the average weight of fish taken in 1940 was considerably less than that in 1939. The fishing intensity actually increased in 1940 over that of 1939 by about 16 per cent. In both 1939 and 1940, more fish were caught in May and June than during other months, with the exception of August of 1940 ; also, the fishing intensity was greater in May and June than at other times. The catch per man-hour was highest during May of 1939 when 1.162 fish were taken per hour of effort. June of 1939 was also a productive month, although the rate dropped to 0.936 fish per man-hour. The unusual August rate of catch in 1940 Table 4.—Hook-and-line yield and fishing intensity per acre of water in Onized Lake, area 2 acres, 1938,* 1939, 1940 and 194Lt Number of Weight Man-Hours Year of Fish of Fish, of Caught Pounds Fishing 1938*. 1939. . 1940. . 1941t. 14 380 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 of 0.678 fish per man-hour was due to abnormal success in angling for bluegills. The average catch for the period covered by the census was 0.531 fish per man-hour. Throughout the creel census period there was a gradual reduction in the aver- age weight of fish caught ; average weights were 0.92 pound in 1938; 0.32 in 1939; 0.24 in 1940 and 0.22 in 1941. Abnor- mally high average weights may be observed for September and October of 1938, August and September of 1939, and October of 1940. These were due to the influence of proportionally larger catches of largemouth bass, a fish that averaged heavier than other species. As a brief summary of fishing at Onized Lake it may be stated that, during the period of study, this 2-acre lake produced a hook-and-line yield of 3,997 fish, weigh- ing 1,152.43 pounds, requiring fishermen to expend 7,526.9 man-hours in return for an average catch of 0.531 fish per man- hour, table 3. Statistics on fishing intensity and yield from widely scattered investigations are Table 5.—Analysis of the hook-and-line catch by species, Onized Lake, 1938,* 1939, 1940 and 1941.t Year Statistics ffi H O S w O M b! en < < 1-1 m Cl. 0. < u o .J I— ( o a pa May, 1945 Bennett: Overfishing, Onized Lake 381 Table 6.—Hoopnet catches of fish from Onized Lake, August 28-30, 1938 (9 net-days of fish- ing), and July 10-15, 1940 (36 net-days of fishing). Species Number 382 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 ported to a breeding pond below the lake dam. The hoopnet catches for the two seasons are shown in table 6. Although the total catch in number of fish was larger in 1940 than in 1938, the total weight of the catch was less; the number per net-day was 3.37 times as great in 1938 as in 1940. Only two species of fish, black crappies and blue- gills, were numerous enough in these catches for comparison. Both of these species readily enter the nets. In 1938, crappies were caught at the rate of 23.78 per net-day, while in 1940 the catch was The evidence of a reduced population of fish of desirable sizes in 1940 is not as strong from a comparison of the rate of catch of hoopnets, as from the anglers' records, but both census methods indicate a striking reduction in the numbers of these fish. Analysis of the Population On June 24, after Onized Lake had been fished for 3 months in the 1941 sea- son, the fish remaining in the lake were poisoned with the object of making a Table 7.—Census of all fish in Onized Lake, area 2 acres, June 24-28, 1941. Fish Species Number May, 1945 Bennett: Overfishing^ Onized Lake 383 Table 8.—Fish of desirable sizes* in Onized Lake at the time of the final census, June 24-28, 194L Species Per Cent of Number Total Number of Named Species Weight, Pounds Per Cent of Total Weight of Named Species Largemouth bass 47 Black crappie 7 Bluegill 325 Warmouth bass 13 Green sunfish 9 Yellow bass 4 Black bullhead 2 Yellow bullhead 36 Carp 1 Golden shiner 37 Total 481 17.1 31,8 5.0 0.8 3.7 100.0 100.0 10.4 100.0 41.1 5.2 101.8 2.2 55.6 2.3 1.6 3.1 2.8 10.7 12.0 4.2 196.3 93.6 68.3 23.9 8.0 24.6 100.0 100.0 28.9 100.0 58.5 44.4 Arbitrarily set at 10 inches for largemouth bass, 8 inches for black crappies, 7 inches for yellow bass, bullheads and golden shiners, and 6 inches for bluegills, warmouth bass and green sunfish. tive numbers of fishes of desirable* sizes then remaining in the lake; (3) the indi- vidual ability of various species present to withstand overfishing; and (4) the effect of overfishing on the growth rates of all species. A careful census was made during the period of June 24 to 28, inclusive, and data on a small number of dead fish found after June 28 were tabulated by Austin Vincent and John Conrad of the Owens- Illinois Glass Company. Table 7 lists the kinds of fish collected and gives details as to numbers and weights. The lake contained a total population of 9,171 fish weighing 442.17 pounds, or, on the basis of an acre, 4,586 fish weighing 221.09 pounds. It is of interest to note that the 1939 yield in pounds per acre was greater than the weight of all fish per acre at the itime of the complete census in 1941. All I species of fish that were taken in the creel census were present in the final census. In addition, there were one carp, one common sucker and one blunt-nosed minnow; these i probably represented escaped bait. Fish- ermen were allowed to use "minnows" in fishing, but were asked to deposit them [with the caretaker after fishing, rather than release them in the lake. Of the 9,171 fish collected in the final census, 481 or 5.2 per cent were of desir- able sizes. However, these fish represented 44.4 of the weight of all fish. Listed in Desirable size is arbitrarily set as at least 10 inches for largemouth bass, 8 inches for black crappies, 7 inches r yellow bass, bullheads and golden shiners and 6 "dies for bluegills, warmouth bass and green sunfish. table 8 are the number and weight of the fish of desirable sizes of each species; also, the percentage of each species, by weight and by number, in the desirable size class. All the yellow bass were of desirable size. On the other hand, only 5.0 per cent of all bluegills present were of desirable size ; their weight was 23.9 per cent of the weight of all bluegills. The number of bluegills of desirable size, 325, was much larger than that of any other species ; also the bluegills of all sizes were more numer- ous than fish of other species. Although only 17.1 per cent of the largemouth bass were of legal size, the weight of these fish was 93.6 per cent of the total weight of all largemouth bass. Eflfects of Overfishing No fish population analysis may be con- sidered complete unless the age composi- tion of that population is known. In fishes, where the pattern of growth may vary a great deal with the amount of available food, the length of the growing season, and the potential size and age for a selected species, the scale method of age determina- tion and its corollary, the calculation of growth from scale measurements, is inval- uable. Samples of scales were taken from many fish collected in the final, or poison, cen- sus of 1941. Because the accuracy of growth calculations depends, among a number of other factors, upon the accu- racy of length measurements, fish badly 384 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 Table 9.—Number of fish used in a study of the growth of Onized Lake fish. Kind FixAL Census May, 1945 Bennett: Overfishing, Onized Lake 385 taken from a random sample of smaller fish measured individually, and individual length measurements were taken on many more fish. Finally, if a large number of a given kind of fish still remained after these samples were taken, they were sorted to size, weighed collectively and counted. Thus, the age-length frequency tables are based on data derived from (1) 577 fish, measured individually, the ages of which were determined from scales; (2) an addi- tional number of fish, also measured indi- vidually, sorted into age groups on the basis of measured lengths; and finally (3) unaged fish, unmeasured individually but of known length range, sorted into age groups on the basis of age-length relation- ships. Table 10 lists the numbers of the various kinds of fish in each of the above groups. The status of the population of each species of fish present in Onized Lake at the time of the final census was influenced by fishing pressure and by the ability of that species to reproduce successfully, as well as to compete with other species of fish. In the following discussion, individ- ual species of fish are considered separately in an attempt to integrate the information furnished by the creel census, hoopnet sampling, the final census, age determina- tions and growth rates. Largemouth Bass Huro salmoides (Lacepede) The largemouth bass population' at Onized Lake was, at the time of the final census in 1941, one of the best observed in 22 artificial lakes in Illinois (Bennett 1943), not only from the standpoint of number and weight per acre of lake surface, but also with reference to rates of growth and range of sizes. This population con- tained individuals belonging to six annual broods (one brood spawned each season, 1936-1941), and the lengths of fish recov- ered ranged from li/^ to 22 inches. Forty- seven bass, or 17.1 per cent of the 275 present, were of legal lengths, tables 7 and 8 ; Onized Lake contained over 23 legal- sized bass per acre in spite of very heavy fishing from 1939 through part of 1941. The greatest catch of bass occurred in 1939 when 62 individuals of legal sizes were taken, table 5 ; 29 were taken in the season of 1940 and 8 in 1941 from May 15 to June 24. These, and 13 others taken in September and October of 1938, make a total of 112 captured during the period of the creel census. While the hook- and-line catch of largemouth bass made up only 2.8 per cent of the total number of fish removed by anglers, their com- bined weight was 179.1 pounds, or 15.5 per cent of the weight of all fish caught, table 5. Possibly all of the legal-sized bass in Onized Lake had become "edu- cated" to avoid both artificial and natural baits offered by fishermen. The lake is so small that an experienced bait caster may cover the entire water area from the shore in about an hour. The fact that the lake still contained 47 bass of legal sizes in 1941, including 12 fish that ranged from 3 to 6 pounds in weight, suggests that fac- tors other than angling may be responsi- ble for low populations of bass in many Illinois waters less intensively fished. The lengths and ages of the bass col- lected from Onized Lake are shown in table 11. The smallness of the number of bass in the group (spawned in May, 1941) is due partially to predation at the time of poisoning. Small fish are affected by the treatment first, and all carnivorous fish of larger sizes quickly feed upon them, as they are readily captured at this time. Also, many small fish sink to the bottom of the lake as they die and are eaten or torn to pieces by crayfish and turtles. A fish census made by the poisoning method is inaccurate in the numbers of small fish of all kinds. The natural spawn and survival of young bass in Onized Lake is considered to have been adequate to maintain the pop- ulation of this fish at a high level—much higher than is usual in artificial lakes con- taining several species of fish (Bennett 1943). As largemouth bass are known to spawn successfully in mud-bottomed ponds, it seems likely that low populations in many lakes are the result of loss of eggs through silting, through the roiling of waters by fish (bullheads, carp and other bottom feeders), or through the nest raid- ing activities of sunfish and other species when they are overlv abundant (Swingle & Smith 1943). The growth rate of largemouth bass in Onized Lake was faster than in most Illi- nois waters. Average calculated lengths by years of life of 81 fish measured and 386 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 "scaled" during the fish census of June 24-28, 1941, table 12, indicate that these fish reached legal length (10 inches) dur- ing the second summer of life and contin- ued to grow rapidly throughout their life span. Fig. 2 shows a growth curve of Onized Lake largemouth bass, based on calculated lengths from scale measure- ments, with a similar growth curve for the bass in Sportsmen's Lake, a small sec- tion of the gravel pit lakes near Lincoln, Illinois (Thompson & Bennett 1939). At the time of the poison census of Sportsmen's Lake, May 20, 1938, that Table 11.—Age-length frequencies of the 275 largemouth bass collected from Onized Lake in the census of June 24-28, 1941. The census was made about l'/^ months after the spawning season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Length in May, 1945 Bennett: Overfishing^ Onized Lake 387 Table 12.—Average calculated total lengths in inches of 81 largemouth bass collected from Onized Lake in the census of June 24-28, 194L Brood Number OF Fish Average Calculated Length by Years of Life Average Total Illinois Natural History Survey Bulletin Vol. 23, Art. 3 YEARS Fig. 3.—Average rate of growth of largemouth bass taken from Onized Lake, from Wiscon- sin and from Louisiana. The Onized Lake bass averaged about the same size as the Wisconsin bass in the first year and approached the size of the Louisiana bass during the second and third years. their growth rate was slow. Once the young bass became large enough to prey on other fish, they began to grow rapidly. Black Grappie Pomoxis nigro-maculatus (Le Sueur) The black crappie population at the time of the 1941 census had become re- duced to 22 fish. Information gathered from net fishing in 1938 and 1940, and from the catch of black crappies made by fishermen in 1939, 1940 and 1941, indi- cates that the lake contained a large crap- pie population at the beginning of the 1939 fishing season and a somewhat larger pop- ulation in 1940 than was taken in the 1941 census. The lengths of the 22 crappies taken in the 1941 census are recorded in table 13. Only seven were large enough to interest fishermen; the others were second sum- mer fish of small size. Although a few small fish undoubtedly belonging to the group (spawned in 1941) were seen when the poison was applied, none were col- lected, and it is probable that they were eaten by fish, turtles and crayfish, or were lost among the mats of vegetation. It is impossible to say whether the crap- pies could have returned to their former population level in Onized Lake in compe- tition with the other species of fish pres- ent. Certainly the number taken in the final census was sufficient to replenish this population with a single successful spawn, if the young were able to survive predation from a strong bass population. Studies of crappies in other lake census work in Illinois (Bennett 1943) indicate that the black crappie is rarely as numer- ous as the white crappie, Po/noxis annula- ris Rafinesque, in small artificial lakes. Not only were there more stunted popula- tions of white crappies than black in the lakes censused, but in 14 lakes where both species were present the white crappies. were more abundant in all but 2. May, 1945 Bennett: Overfishing, Onized Lake 389 Black crappies taken in hoopnets from Onized Lake in 1940. These crappies were li and 21 years old. Scales and total length measurements from crappies taken from hoopnet collec- tions in 1938 and 1940, and from 21 of the 22 fish taken in the final census, were used in calculating the lengths shown in tables 14, 15 and 16. The lengths of black crappies collected from Onized Lake are plotted in fig. 4. No crappies older than four summers are known to have been taken from the lake during this study. Calculated lengths of the 1938 and 1941 crappie collections showed relatively slow growth rates for the first year, and a marked increase dur- ing the second growing season. The 1940 collection included 226 crappies in their second summer of life (1939 brood) that averaged 4.02 inches for calculated first year growth, or about a half more than the first year lengths for the other collec- tions. Most of the fish of the 1940 collec- tion were spawned in the year of the great- icst hook-and-line yield, and their rapid Igrowth may have been related to an abun- jdant food supply resulting from the re- moval of many fish. Growth stimulation caused by an increased amount of avail- able food brought about by one of several possible situations has been observed in Table 13.—Age-length frequencies of the 22 black crappies collected from Onized Lake in the census of June 24-28, 194L The census was made about V/i months after the spawn- ing season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Length 390 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 Table 14.—Average calculated total lengths in inches of 98 black crappies collected with hoopnets from Onized Lake, August 29-31, 1938. Brood Number OF May, 1945 Bennett: Overfishing, Onized Lake 391 Table 15.—Average calculated total lengths in inches of 234 black crappies collected with hoopnets from Onized Lake, July, 1940. Brood Number OF Fish Average Calculated Lengths by Years of Life 1 Average Total Length at Time OF Capture 1938... 1939... Total. . . .Average . 226 334 2.24 4.02 3.96 8.03 8.03 10.55 6.87 Table 16.—Average calculated total lengths In inches of 21 black crappies collected from Onized Lake in the census of June 24-28, 1941. Brood Number OF Fish Average Calculated Lengths by Years of Life 1 Average Total Length at Time OF Collection 1939... 1940... Total. . . Average . 6 15 3.48 2.66 2.89 7.82 7.82 8.62 5.29 14 12 (f) r Z 10 I- o Z 6 l(J < 1- O 2 I- 392 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 of age group II of the 1939 collection, shows the largest first-year growth. Schoffman's data are based on the average actual lengths of fish on which ages were determined. Points at the extremities of the Norris Reservoir and the Onized Lake curves represent average actual lengths of fish at the time of capture. As shown in fig. 5, the growth curve of the black crap- pies from Onized Lake lies between the other two, indicating that the Onized Lake fish grew faster than those of Reelfoot, hut less rapidly than those of Norris Res- ervoir. The excessive cropping of Onized Lake resulted in an unusually rapid rate of growth of black crappies. Schoffman (1940) in his study of Reelfoot Lake black crappies suggests that the minimum legal length of crappies in Tennessee be increased from 8 to 9 inches, in order to give them greater protection and "since the greatest weight per length is reached in the 8th summer." An assumption of this kind is not valid, because fish growth, within limits, is a reflection of food abundance. Bluegill Lepomis macrochirus Rafinesque Bluegills apparently thrive under con- ditions of intensive fishing. Not only did this species make up 60.9 per cent of the number and 48.1 per cent of the weight of all fish taken bv fishermen from Onized Lake, 1938-1941, table 5, but, in the final fish census, bluegills represented 71.4 per cent of all fish present, and their weight was 52.7 per cent of the weight of all fish. As recorded in the creel census, the aver- age weight of 2,433 bluegills caught was 0.23 pound, table 5 ; a fish of this weight has a length of slightly more than 6 inches. The largest bluegill recorded by the custo- dian weighed approximately 1 pound. Bluegills caught and recorded in the creel census of 1939 averaged larger, weighing 0.25 pound each, than in succeeding years; in 1940, the average weight was 0.21 pound and, in 1941, 0.18 pound, table 5. Table 17 gives the age-length frequencies of the bluegills taken in the 1941 census. As many of these fish were not accurately aged or measured, but sorted into age groups on the basis of their size range, this table is an estimate of the actual age- length distribution of the population. No fish in the collections were much more than 3 years (in fourth summer) of age. As in similar tables for other species, the number recorded for 1941 brood blue- gills does not represent the actual number in the lake at the time of poisoning. The 1941 brood probably exceeded the 1940 brood in number of individuals. The number of individuals of desirable sizes listed in table 8 represents an accurate Table 17.—Age-length frequencies of the 6,545 bluegills collected from Onized Lake in the census of June 24-28, 1941. The census was made about II/2 months after the spawning sea- son, and the lengths shown for each age include the growth increment for the early part of the' 1941 season. Length in- May, 1945 Bennett: Overfishing, Onized Lake 393 count ; great care was taken in sorting out individuals of 6 or more inches in length. The ratio of bluegills of desirable sizes to those smaller was 1 :19; that is, the num- ber of bluegills of desirable sizes repre- sented about 5 per cent of the total num- ber of bluegills. Because an accurate count of the 1941 brood could not be made, the calculated percentage of large fish was much larger than the actual percentage. Tables 18, 19 and 20 show calculated lengths of bluegills taken in the hoopnet collections of 1938 and 1940, and in the census of 1941. Growth curves based on these lengths, fig. 6, show some variation in growth rates of bluegills represented by each of these three collections. Unlike the black crappies, bluegills spawned in 1939 apparently made no abnormal growth increment during that year. Abnormal growth in bluegills spawned early might be obscured by the growth figures of those spawned in July and August ; it also seems that the growth of bluegills was less stim- ulated by the results of heavy fishing than was that of most other species. Other sources of information relative to bluegill growth in Illinois are available. Table 18.—Average calculated total lengths in inches of 53 bluegills collected with hoopnets from Onized Lake, August 29-31, 1938. Brood Number OF Fish Average Calculated Lengths BY Years of Life 1 Averag 394 Illinois Natural History Survey Bulletin Vol. 23, Art. 1 Measurements of 1938 brood bluegills taken from Fork Lake during 1939 (Ben- nett, Thompson k Parr 1940) indicate that under uncrowded conditions this species may grow rapidly to useful sizes. Table 21 gives the numbers and average Table 21.—Numbers and average total lengths in inches of 1938 brood bluegills col- lected, March through November, 1939, from Fork Lake near Mount Zion, Illinois. Month March April May June July August September October November Total 773 May, 1945 Bennett: Overfishing^ Onized Lake 395 Table 22.—Average growth of bluegills in Illinois, based on growth in five large bodies of water representing northern, central and southern locations, and three types of lakes. Average Total Length in Inches at End of Growing Season First 396 Illinois Natural History Survey Bulletin Vol. 23. Art. 3 Table 23. Age-length frequencies of the 1,638 warmouth bass collected from Onized Lake in the census of June 24-28, 1941. The census was made about 1 Vi months after the spawning season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Age in Years Length in Inches 1 2 .... 1 2 • • • 3 .... 1 2 . . . . 4 .... 1 2 • 5 .... 1. 2 • • • • 6 .... 1 2 • • • 7 ... 1 2 • 8 ... Total. 33 555 474 56 47 -Desirable Size- 1,165 64 169 179 40 - 2 3 1 466 2 3 1 1 Fig. 8—Average rate of growth of warmouth bass in Onized Lake and in Reelfoot Lake , The warmouth bass in Onized Lake grew at approximately the same rate as the green sunfish:] lig. 9, and neither of these species was of great importance in the hook-and-line catch. May, 1945 Bennett: Overfishing, Onized Lake 397 Table 24.—Average calculated total lengths in inches of 101 warmouth bass collected from Onized Lake in the census of June 24-28, 194L Brood Number OF Fish Average Calculated Lengths bv Years of Life 1 Average Total Length at Time of Capture 1938 7 1939 63 [940 31 Total 101 Average 2.13 1.19 L77 1.43 4.35 3.91 3.95 6.12 6.12 6.61 4.87 2.88 growth rate was slower than that in Reel- foot during the first 3 years of life. Only a few of the warmouth bass in Onized Lake had survived to begin the fourth summer. The warmouth bass may have some potential value as a fish for managed ponds, but it seems unable to produce usable fish in combination with other spe- cies in unmanaged small lakes. Green Sunfish Lepomis cyanellus Rafinesque Green sunfish were more important than warmouth bass in the creel census from Onized Lake, but they failed to make up as much as 10 per cent by weight of the fishermen's catch, 1938-1941, table 5. In the 1941 census, green sunfish were greatly outnumbered by warmouth bass and blue- gills, table 7. Table 25 gives the age-length frequen- cies of green sunfish. With the exception of one fish of the 1937 brood, the green sunfish collected in the 1941 census be- longed to the 1938, 1939 and 1940 broods. The 1941 brood was lost in the process of censusing. The age distribution pattern of green sunfish was nearly identical with that of the warmouth bass, tables 23 and 25. Only 9 of the 245 green sunfish were 6 inches or more in length. The average weight of this fish in the 1941 census was 0.026 pound, while that of the bluegill Table 25.—Age-length frequencies of the 245 green sunfish collected from Onized Lake in the census of June 24-28, 194L The census was made about l'/2 months after the spawning season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Length in Inches Age in Years 2 . 1 2 3 . 1 4'. i 2 • 5 . 1 2 10 398 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 Table 26.—Average calculated total lengths in inches of 95 green sunfish collected from Onized Lake in the census of June 24-28, 1941. Brood May, 1945 Bennett: Overfishing^ Onized Lake 399 Table 27.—Average calculated total lengths in inches of two yellow bass collected from Onized ^ake in 1938, one in 1940 and three in the final census of June 24-28, 1941. Brood Number OF Fish Average Calculated Lengths by Years of Life Average Total Length at Time OF Collection i935... ;936... Total. . . Average. [936... .936... 1 1 2 400 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 Table 28.—Hypothetical age-length distribution of the 347 yellow bullheads collected from Onized Lake in the census of June 24-28, 1941. Ages have been assigned on the basis of length. The census was made about I'/z months after the spawning season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Length in Inches Age in Years 4 i 5 X 2 6 2 7 Desirable Size- \ 2 8 1 2 9 2 10 1. 2 11 1 2 12 1 2 13 i 2 14 Total 22 53 98 58 53 27 22 333 1 2 5 2 9 1 2 they suggest three age groups. Young bullheads are spawned during May in Onized Lake, and it is unlikely that any of the 4-inch fish taken in the census be- longed to the brood of the 1941 season. Therefore, it is assumed that the 4- to 7- inch group represented the 1940 brood; the ^Yz- to lOi/2-inch group the 1939 brood; and the 12- to 14-inch group the 1938 brood (possibly the 14-inch fish be- longed to the 1937 brood, although this seems unlikely, as bullheads are readily caught). The assumption of these various age groups has a validity it would not pos- sess if the ranges of length in this species had overlapped. Table 28 shows the age-length frequen- cies of yellow bullheads, sorted according to their hypothetical ages determined on the basis of their lengths. Onized Lake is probably a poor habitat for bullheads, because of the steep slope of its basin and its limited shoal water. These characteristics, coupled with the complete absence of oxygen in the deeper waters in summer, result in a limited habi- tat for bottom-living species such as the black and yellow bullheads. Golden Shiner Notcmigonus crysoleucas auratus (Rafinesque) Golden shiners are not usually consid- ered hook-and-line fish, but Onized Lake fishermen caught and kept them in 1940 and 1941. Certainly, desirable sizes of these fish cannot be less than 7 inches. The creel census records show 40 golden shiners, weighing a total of 7.7 pounds, table 5. In the 1941 final census, 90 shiners were collected, of which 37 were 7 or more inches long, tables 7 and 8. The age-length distribution is given in table 29. This table shows that these golden shiners in Onized Lake made rapid growth and reached comparatively large sizes for min- nows. Only fishermen and the larger bass could utilize the larger shiners. Calculated lengths based on scale meas- urements of 87 golden shiners are given in table 30. These lengths are plotted as a growth curve in fig. 10. May, 1945 Bennett: Overfishing, Onized Lake 401 Table 29.—Age-length frequencies of the 90 golden shiners collected from Onized Lake in the census of June 24-28, 1941. The census was made about l'/2 months after the spawning season, and the lengths shown for each age include the growth increment for the early part of the 1941 season. Length in Inches Age in Years 1 ... i 2 • • 2 ... 1 '> . . . 3"... 1 4"... 1 s' ... 1 2 • • • 6 . . . 1 1' ... 1 8"... 1 2 • • 9 ... Total. 4 2 3 1 18 14 1 -Desirable Size- 38 6 19 9 3 1 38 1 1 1 1 1 1 6 Table 30.—Average calculated total lengths in inches of 87 golden shiners collected from Onized Lake in the census of June 24-28, 1941. Brood Number OF Fish Average Calculated Lengths by Years of Life 1 Average Total Length at Time of Collection 1938 5 1939 36 1940 38 1941 8 Total 87 Average 2.76 4.24 3.31 3.70 6.28 6.82 6.75 7.51 7.51 1 .16 7.19 5.25 2.20 Table 31.—Size frequencies for each group of female golden shiners taken from the Huron River at Ypsilanti, Michigan, May 19, 1934 (from Cooper 1935, rearranged). Age in Years Number of Fish Average Standard Length Millimeters Inches Average Total Length, Inches* 1 127 2 83 3 37 4 10 5 2 70.7 93.4 104.3 120.8 126.5 2.78 3.68 4.11 4.76 4.98 3.48 4.60 5.14 5.95 6.23 Standard length converted to total length by the formula- of Illinois golden shiners. T.L. S.L. = 1.25. The formula is based on measurements 402 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 YEARS OF LIFE Fig. 10.—Average rate of growth of golden shiners in Onized Lake and in the Huron Rive at Ypsilanti, Michigan. Also in fig. 10 is shown a second curve based on female golden shiners collected and aged by Cooper (1936). These fish were taken from the Huron River at Ypsi- lanti, Michigan, May 19, 1934. Coop- er's data, summarized in table 31, offer evidence that the females of golden shin- ers live to a greater age and grow some- what faster than males, and suggest that females predominated among the larger shiners in Onized Lake. In Onized Lake, the first-year growth rate was essentially the same as in the Michigan collection of Cooper. How- ever, Onized Lake shiners continued to grow at a rapid rate during the second year, while the rate of growth of the Michigan fish was much slower. Probably because of competition with other young fish, Onized Lake shiners grew less rapid- ly in their first year than might normally be expected in the southern part of Illinois. The origin of the Onized Lake golden shiners is unknown. Possibly they wer stocked as forage for bass. Or they mai represent escaped bait. Miscellaneous Fish One carp, one common sucker and on blunt-nosed minnow were taken in thj 1941 census. i This miscellaneous assortment of roug j and forage fish probably represents bai that escaped the hooks of fishermer Onized Lake is some distance from othe water containing a variety of fish, and i is improbable that these fish were carrie to the lake by fish-eating birds. Age Distribution of Fish The overfished population of Onize Lake was of particular interest from tl standpoint of its age composition. As mjj be seen from table 32, overfishing tende to limit the life span of the fishes to tl May, 1945 Bennett: Overfishing, Onized Lake 403 Table 32.—Age composition of the fish population of Onized Lake; census of June 24-28, 194L Age in Years Species Largemouth bass 33 Black crappie Bluegill 236 Warmouth bass Green sunfish rellow bass Black bullhead i'ellow bullhead Carp Common sucker Golden shiner 8 Blunt-nosed minnow Total 277 1 Total 195 15 3,369 1,165 187 333 1 38 I 5,304 24 7 2,857 466 49 1 12 83 7 1 2 38 6 3,454 115 lis 22 6,545 1,638 245 4 2 347 1 1 90 1 9,171 approximate length of time that was re- quired for them to reach desirable sizes. These sizes were attained by most species during the latter part of the second grow- ing season. Some fish escaped being caught during the third season, but only a few remained to begin the fourth or fifth. Of these, the largemouth bass is the most nota- ble and its survival is believed to hinge upon the probability that, of all species represented, it is the most wary and best able to learn from experience. Moreover, the life span of the largemouth is normally somewhat longer than that of other Illi- nois lake fishes. Lines representing a pyramid of num- bers of Onized Lake fish have been super- imposed upon lines representing a similar pyramid for a theoretical fish population (Bennett 1943), fig. 11. This figure MOSTLY 1941 BROOD LOST IN THE JUNE 24, 1941 CENSUS OF \ Fig. IL—Diagram representing the age-frequency distribution of Onized lake fish, final 1941 census, superimposed upon a pyramid of numbers representing a theoretical fish popula- tion. This diagram suggests that overfishing tends to remove most of the older and larger fish, Dut has little effect upon the production of adequate broods of young. 404 Illinois Natural History Survey Bulletin Vol. 23, Art. 3 illustrates the tendency of overfishing to remove the larger and older fish. The 1941 census was made shortly after com- pletion of the 1941 spawn, and, as the 1941 brood was composed of very small fish, most of which were lost in the census, this brood is represented as the pyramidal base enclosed in dotted lines. When quad- rilaterals representing the 1940 and 1939 broods are superimposed upon the theoreti- cal pyramid, with the lines for the 1940 brood coinciding with the limits of the theoretical quadrilateral for 1940, the lines for the 1939 brood extend beyond the lim- its of the theoretical quadrilateral for the corresponding year. The figure representing the 1938 brood shows that this brood was only a small fraction of the size of the 1939 brood and much smaller than the theoretical quadrilateral for 1938; the effects of overfishing are thus indicated. Older broods are represented by a spearhead extending toward the apex of the theoretical pyramid. Discussion All sources of evidence point to the hypothesis that Onized Lake was severely overfished. Yet every species of fish known to be once numerous in the lake was pres- ent in the final census, perhaps due to the fact that fishing pressure drew its quota from all kinds of fish present, rather than from one or two of the more desirable species. The many fishermen using the lake represented a cross section of anglers, their fishing gear running the gamut from willow-pole to flyrod. The fish in this lake were presented with a variety of baits and hook sizes, attractive to all but the smallest. It is possible that if the fishing intensity had been directed toward a certain species, to the exclusion of others, that species might have been entirely eliminated. This could be expected to occur, not directly through intensive fishing, but indirectly through the inability of reduced numbers of spawn or young of the selected species (because of fewer breeding adults) to com- pete with the more numerous young and adults of other species not affected by fish- ipg. For all practical purposes, the lake would have become "fished out" for the selected species before all of the adults had been caught, but it is rather unlikely that the few remaining could have pro- duced enough young to compete with young of the more numerous species. In the 1941 census, the black bullheads and yellow bass were only a few in number, but in view of the fact that the hook-and- line catch was made up of only small num- bers of yellow bass and bullheads, and the hoopnet collections of 1938 failed to indi- cate abundant populations of these fish, the conclusion must be reached that some factors other than heavy fishing kept them from becoming numerous. The black crappies of Onized Lake were nearer extermination than any other spe- cies known to be numerous in the past. However, the creel census does not indi- cate that particularly large catches of these fish were made, fig. 5. Only during 1939 were appreciable numbers taken. In that year the crappie catch ranked second to the bluegill in numbers and well ahead of any other species. In 1940, the total hook-and- line catch of crappies was only 56; yet hoopnets set during July of that year caught 234 black crappies, more than twice the number of bluegills and many times the numbers of other fish caught, table 6. The fact that only 56 crappies were taken by anglers in 1940, and 31 in 1941, fol- lowing a catch of 502 in 1939, suggests a natural die-off of the older fish during the latter half of the summer of 1940. The only other evidence for the natural die-off •assumption is that large numbers of crap- pies were not present in the final census. All species of fish in Onized Lake from which scales were studied showed poor growth during the first season, and all but one, the warmouth bass, grew at an excep- tionally rapid rate throughout later years of life. This situation can be explained by assuming that the constant drain on the adult fish population through heavy fishing allowed increased success in spawning and greater survival of young fish. Thus, foods suitable for small fish were at a pre- mium, and early growth was slow. How- ever, once the young fish reached sizes large enough to allow them to feed upon larger food organisms, they grew rapidly, because the constant take of adults eased the food competition in this size range. The fishing intensity at Onized Lake during the period of this study was so great that most of the fish were caught be- fore they reached the age of 3 years; a May, 1945 Bennett: Overfishing, Onized Lake 405 few managed to escape for two more sum- bers of fish per acre ranged from 10,119, mers. None had completed the sixth year where a large number of minnows were of life. present, to 1,124; the average number per The hook-and-line yield of 349.95 acre was 3,434. The fact that Onized pounds per acre in 1939, table 4, is judged Lake contained more than the average Much of the angling at Onized Lake is done by families or other small groups that use the club grounds for picnics. Because fishing is incidental to other uses, the angling pressure on this body of water is less closely related to the catch of fish than on most other lakes. to be about three-fourths of the carrying capacity of Onized Lake for the species of fish then in the lake. The carrying capac- ity, on the basis of that found in other similar ponds, is believed to lie between 450 and 500 pounds of fish per acre, as the average for Onized Lake and 21 other small Illinois lakes censused was 446.5 pounds per acre (Bennett 1943). In the final census of 1941, the total weight of fish in Onized Lake was only 221.09 pounds per acre, table 7, plus a few pounds for the numerically abundant 1941 brood that was not recovered. The number of fish collected per acre was 4,586. In the 21 other small lakes mentioned above, which were censused in a manner similar to the census of Onized Lake, the num- number of fish per acre, although over- fished, indicates that numerically the pop- ulation was maintaining itself (in spite of no additional stocking), and that, with reduced fishing pressure, the population would have increased rapidly in total weight, until it approached the carrying capacity of the lake. Summary 1. Onized Lake, a small pond of 2 acres, offered an excellent opportunity to study overfishing because it was fished in- tensively and a creel census was made of the catch. 2. The creel census covered September and October of 1938, the fishing seasons 406 Illinois Natural History Survey Bulletin Vol. 23, Art.] of 1939 and 1940, and April, May and June of 1941, The fishing intensity was light in 1938 (end of the season), but for the 1939 season it was 1,414.9 man-hours per acre; for 1940, 1,647.3 man-hours per acre; and, for April, May and June of 1941, 634.0 man-hours per acre. Hook- and-line fish yields were, for 1939, 349.95 pounds per acre; for 1940, 142.5 pounds per acre; and, for 3 months of 1941, 70.9 pounds per acre. Hoopnet sampling of August 28-30, 1938, compared with catches made with nets July 10-15, 1940, indicated a reduction in the population of large-sized fish between these two sam- pling periods. 3. A poison census was made on June 24, 1941. At this time the lake contained 9,171 fish weighing 442.17 pounds. The kinds of fish present were largemouth bass, black crappies, bluegills, warmouth bass, green sunfish, yellow bass, black bull- heads, yellow bullheads and golden shin- ers, as well as one carp, one common sucker and one blunt-nosed minnow. ^ 4. Fish were relatively stunted during the first year of life, but most species grew at an exceptionally rapid rate during later years. The oldest fish were in their sixth 1 summer of life, and nearly all of these were largemouth bass. Most of the fish were taken when in their third summer. 5. A large population of black crappies had been reduced to 22 fish by the time of the final census. This reduction was apparently not due to hook-and-line fish- ing. Largemouth bass and bluegills re- mained numerous, although they had made up an important part of the hook-and-line catch. 6. In spite of heavy fishing, the natural spawn of fish was obviously sufficient to insure replacement of those fish removed, and under reduced fishing intensity the lake would have returned to its former carrying capacity. LITERATURE CITED II Beckman, William C. 1941. Increased growth rate of rock bass, Ambloplites rupestris (Rafinesque), following reduc- tion in density of the population. Am. Fish. Soc. Trans. 70:143-8. Bennett, George W. 1937. Tl^e growth of the large mouthed black bass, Huro salmoides (Lacepede), in the waters of Wisconsin. Cope. 1937(2) :104-18. 6 figs. 1943. Management of small artificial lakes, a summary of fisheries investigations, 1938-1942. III. Nat. Hist. Surv. Bui. 22(3) :357-76. 7 figs. Bennett, George W., David H. Thompson and Sam A. Parr 1940. Lake management reports. 4. A second year of fisheries investigations at Fork Lake, 1939. 111. Nat. Hist. Sqrv. Biol. Notes 14. 24 pp., 10 figs., 4 pis. Cooper, Gerald P. 1936. Age and growth of the golden shiner (Notcmigonus crysoleucas auratus) and its suita- bility for propagation. Mich. Acad. Sci., Arts and Letters Papers 21:587-97. 3 figs. Eschmeyer, R. W., and Alden M. Jones 1941. The growth of game fishes in Norris Reservoir during the first five years of impound- ment. N. Am. Wildlife Conf. Trans. 6, 1941:222-40. 4 figs. |M| Hubbs, Carl L., and Gerald P. Cooper ^ 1935. Age and growth of the long-eared and green sunfishes in Michigan. Mich. Acad. Sci., Arts and Letters Papers 20:669-96. 5 pis. Schloemer, Clarence Louis 1939. The age and rate of growth of the bluegill, Helioperca macrochira (Rafinesque). Doc- toral Dissertation, University of Wisconsin. jH Schoffman, Robert J. "" 1940. Age and growth of the black and white crappie, the warmouth bass, and the yellow bass in Reelfoot Lake. Reelfoot Lake Biol. Sta. Rpt. 4:22-42. 9 figs. Swingle, H. S., and E. V. Smith 1943. Factors affecting the reproduction of bluegill, bream and largemouth black bass in ponds. Ala. Ag. Exp. Sta. Circ. 87:1-8. Thompson, David H., and George W. Bennett 1939. Lake management reports. 3. Lincoln Lakes near Lincoln, Illinois. 111. Nat. Hist Surv. Biol. Notes IL 24 pp., 8 figs. I Recent Publications A.—ILLINOIS NATURAL HISTORY SURVEY BULLETIN. Volume 21, Article 3.—Studies of Nearctic Aquatic Insects. By H. H. Ross and T. H.] Frison. September, 1937. 52 pp., frontis. + 86 figs., bibliog. 50 cents. Volume 21, Article 4.—^Descriptions of Nearctic Caddis Flies (Trichoptera), wit special reference to the Illinois species. By Herbert H. Ross. March, 1938. 84 pp., frontis. + 123 figs., foreword, index. $1.00. Volume 21, Article 5.—Preliminary Studies on Parasites of Upland Game Birds and] Fur-Bearing Mammals in Illinois. By W. Henry Leigh. August, 1940. 10 pp.,j frontis. + 2 maps. | Volume 21, Article 6.—^Preliminary Investigation of Oak Diseases in Illinois. Byj J. Cedric Carter. June, 1941. 36 pp., frontis. + 51 figs., bibliog. (Bound with| Article 7.) Volume 21,' Article 7.—A Needle Blight of Austrian Pine. By Robert L. Hulbary.l June, 1941. 6 pp., frontis. -f 3 figs., bibliog. (Bound with Article 6.) ] Volume 21, Article 8.—Duck Food Plants of the Illinois River Valley. By Frank C] Bellrose, Jr. August, 1941. 44 pp., frontis. + 35 figs., bibliog., appendix. Volume 22, Article 1.—The Plant Bugs, or Miridae, of Illinois. By Harry H. Knight September, 1941. 234 pp., frontis. + 181 figs., bibliog., index. $1.25. Volume 22, Article 2.—Studies of North American Plecoptera, with special referenc to the fauna of Illinois. By T. H. Frison. September, 1942. 122 pp., frontis. -f 126 figs., bibliog., index. $1.00. Volume 22, Article 3.—Management of Small Artificial Lakes: a summary of fisheries investigations, 1938-1942. By George W. Bennett. February, 1943. 20 pp., frontis. 4- 7 figs., bibliog. Volume 22, Article 4.—The Prairie Chicken in Illinois. By Ralph E. Yeatter. May, 1943. 40 pp., frontis. 4- 18 figs., bibliog. (Bound with Article 5.) Volume 22, Article 5.—Preferential Rating of Duck Food Plants. By Frank C. Bell- rose, Jr., and Harry G. Anderson. May, 1943. 16 pp., frontis. -|- 16 figs., bibliog. (Bound with Article 4.) Volume 22, Article 6.—Survey of the Illinois Fur Resource. By Louis G. Brown and Lee E. Yeager. September, 1943. 70 pp., frontis. + 33 figs., bibliog. (Bound with Article 7.) Volume 22, Article 7.—Illinois Furbearer Distribution and Income. By Carl 0. Mohr. September, 1943. 33 pp., frontis. + 24 figs., bibliog. (Bound with Article 6.) Volume 23, Article 1.—The Caddis Flies, or Trichoptera, of Illinois. By Herbert H. Ross. August, 1944. 326 pp., frontis. + 961 figs., bibliog., index. $1.50. Volume 23, Article 2.—Duck Populations and Kill. By Frank C. Bellrose, Jr. Novem- ber, 1944. 46 pp., frontis. -}- 27 figs., bibliog. B.—ILLINOIS NATURAL HISTORY SURVEY CIRCULAR. 32.—Pleasure With Plants. By L. R. Tehon. November, 1942. (Second printing, with revisions.) 32 pp., frontis. + 9 figs. 33.—Controlling Peach Insects in Illinois. By S. C. Chandler and W. P. Flint. August, 1939. 40 pp., frontis. + 32 figs. 34.—Rout the Weeds! Why, When and How. By L. R. Tehon. August, 1943. (Third printing.) 47 pp., color frontis. + 13 figs. 35.—Diseases of Small Grain Crops in Illinois. By G. H. Boewe. September, 1939. 130 pp., frontis. -f 47 figs. 36.—Planting and Care of Shade Trees. By J. E. Davis. March, 1941. 23 pp., frontis. + 16 figs. 37.—Outwitting Termites in Illinois. By W. E. McCauley and W. P. Flint. August, 1942. (Second printing.) 23 pp., frontis. -f 19 figs. 38.—Windbreaks for Illinois Farmsteads. By J. E. Davis. February, 1942. (Second printing.) 24 pp., frontis. -J- 19 figs. 39.—How to Collect and Preserve Insects. By H. H. Ross. May, 1944. (Second print- ing, with additions.) 55 pp., frontis. -f 63 figs. 40.—Control of Roundheaded Apple Tree Borer. By S. C. Chandler and W. P. Flint. April, 1942. 8 pp., 6 figs. C—ILLINOIS NATURAL HISTORY SURVEY MANUAL. 1.—Fieldbook of Illinois Wild Flowers. By the staff. March, 1936. 406 pp., color frontis. -\- 349 figs., index. $1.50. 2.—Fieldbook of Illinois Land Snails. By Frank Collins Baker. August, 1939. 166 pp., color frontis. -f 170 figs., 8 pis. $1.00. 3.—Fieldbook of Native Illinois Shrubs. By Leo R. Tehon. December, 1942. 307 pp., 4 color pis. + 72 figs., glossary, index. $1.25. List of available publications, about 400 titles, mailed on request. Address orders and correspondence to the Chief ILLINOIS NATURAL HISTORY SURVEY Natural Resources Building, Urbana, Illinois Pay inetit ia the form of U. S. Poat Office taoney order made out to State Treasurer of Illinois, Springfield, Illinois, must accompany requests for those publications on which a price is set.