Bulletin So fe- ILLINOIS ratura,! History Sux-v-e3) BX7I.LETIM' Largemouth Bass and Other Fishes in Ridge Laite, Illinois 1941-1963 orge W. Bennett Wickliffe Adkins lliam F. Childers NATURAL iliSTORl SURVEY FEB 3 1970 IIBRARY 'E OF ILLINOIS >ARTMENT OF REGISTRATION AND EDUCATION TURAL HISTORY SURVEY DIVISION BANA, ILLINOIS THE U8RARV OF THE JAN 2 7 197Q VOLUME 30, ARTICLi SEPTEMBER, 1969 IX.LINOIS 9'a.tux'a.l History Survey BULLETIN Largemouth Bass and Other Fishes in Ridge Laite, Illinois 1941-1963 iorge W. Bennett Wickliffe Adkins illiam F. Childers TE OF ILLINOIS PARTMENT OF REGISTRATION AND EDUCATION ITURAL HISTORY SURVEY DIVISION BANA, ILLINOIS VOLUME 30, ARTICL SEPTEMBER, 196! STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION BOARD OF NATURAL RESOURCES AND CONSERVATION WnxiAM H. Robinson. Chairman; Thomas Park. Ph.D., Bio/offi/; L. L. Sloss, Ph.D., GeoToj/y; Rooeb Adams, Ph.D., D.Sc, Chemistry; Robert H. Anderson, B.S.C.E., Engineering; Chables E. Olmsted, Ph.D., Forestry; W. L. Evebitt, E.E., Ph.D., Representing the President of the University of Illinois; Roger E. Beyler, Ph.D., Representing the President of Southern Illinois University. NATURAL HISTORY SURVEY DIVISION, Urbana. Illinois SCIENTIFIC AND TECHNICAL STAFF George SPRUOEn:-, Jr., Ph.D., Chief Herbert H. Ross, Ph.D., Assistant Chief AxiGE P. Campbell, B.A., Secretary to the Chief SECTION OF ECONOMIC ENTOMOLOGY William H. Luckmann, Ph.D.. Entomologist and Bead Willis N. Bruce, Ph.D., Entomologist Wayne L. Howe, Ph.D., Entomologist Stevenson Moore, III, Ph.D., Entomologist, Extension Howard B. Petty, Ph.D., Entomologist, Extension James E. Appleby. Ph.D., Associate Entomologist Edward J. Armbrust, Ph.D., Associate Entomologist Marcos Kogan, Ph.D., Associate Entomologist Joseph V. Maddox, Ph.D., Associate Entomologist Ronald H. Meyer, Ph.D., Associate Entomologist Robert D. Pausch, Ph.D., Associate Entomologist Ralph E. Sechriest, Ph.D., Associate Entomologist Clarence E. White, B.S., Assistant Entomologist Keun S. Park, M.S., Assistant Chemist Sue E. Watkinb, Supervisory Assistant Donald E. Kuhlman, M.S.. Instructor, Extension Roscoe Randell. M.S., Instructor, Extension Stephen Sturgeon, B.S., Assistant Specialist, Extensio: Jeian G. Wilson, B.A., Research Associate Keturah Reinbold, M.S., Research Assistant Stephen Roberts, B.S., Technical Assistant Douglas K. Sell, B.S., Technical Assistant SECTION OF WILDLIFE RESEARCH Glen C. Sanderson, Ph.D., Wildlife Specialist and Head Frank C. Bellrose, B.S., Wildlife Specialist Richard R. Graber, Ph.D., Wildlife Specialist Harold C. Hanson, Ph.D., Wildlife Specialist William L. Anderson, M.A., Associate Wildlife Specialist W. W. Cochran, Jr., B.S., Associate Wildlife Specialist William R. Edwards, M.S., Associate Wildlife Specialist Jack A. Ellis, M.S., Associate Wildlife Specialist Ronald F. Labisky, Ph.D., Associate Wildlife Specialist Stanley L. Etteb, M.S.. Assistant Wildlife Specialist RoBEET E. Greenberg, M.S., Assistant Wildlife Specialist G. Blair Joselyn, M.S., Assistant Wildlife Specialist Paul J. Matthews, B.S., Assistant Wildlife Specialist Geohge B. Rose, Ph.D., Assistant Wildlife Specialist Keith P. Thomas, M.S.. Assistant Wildlife Specialist Ronald L. Westhmeiehi, B.S., Assistant Wildlife Specialist Ronald E. Duzan, Technical Assistant Carolyn S. E\'ees, B.A., Technical Assistant Mary Ann Johnson. Technical Assistant Helen C. Schultz, M.S.. Technical Assistant Eleanore Wilson, Technical Assistant Robert D. Crompton, Field Assistant SECTION OF BOTANY AND PLANT PATHOLOGY Junius L. Fobsberq, Ph.D., Plant Pathologist Eugene B. Hemelick, Ph.D.. Plant Pathologist R. Dan Neely, Ph.D., Plant Pathologist D. F. ScHOENErwEisB. Ph.D., Associate Plant Pathologist J. Leland Crane, Ph.D., Assistant Mycologist Walter Hartstirn, Ph.D., Assistant Plant Pathologist Betty S. Nelson, Technical Assistant Gene E. Reid, Technical Assistant SECTION OF FAUNISTIC SURVEYS AND INSECT IDENTIFICATION Herbert H. Robs, Ph.D., Assistant Chief and Head Wallace E. LaBerge, Ph.D., Taxonomist Milton W. Sanderson, Ph.D., Taxonomist Philip W. Smith, Ph.D., Taxonomist Lewis J. Stannard, Jr., Ph.D., Taxonomist John D. Unzickeb, Ph.D., Assistant Taxonomist Donald W. Webb, M.S., Assistant Taxonomist Bernice p. Sweeney, Technical Assistant SECTION OF AQUATIC BIOLOGY George W. Benneh-t, Ph.D., Aquatic Biologist and Head D. Homer Buck, Ph.D., Aquatic Biologist R. Weldon Larimore, Ph.D., Aquatic Biologist William C. Starrett, Ph.D., Aquatic Biologist Robert C. Hiltibran, Ph.D., Biochemist Willlam F. Childers, Ph.D., Associate Aquatic Biologist Donald F. Hansen, Ph.D., Associate Aquatic Biologist Richard J. Baur, M.S., Research Assistant Dennis L. Dooley, Technical Assistant Mary Frances Martin, Technical Assistant C. Russell Rose, Field Assistant SECTION OF ADMINISTRATIVE SERVICES Robert 0. Watson, B.S., Administrator and Head Supporting Services WiLMA G. DnxMAN, Property Control and Trust Accounts Robert O. Ellis, Supervisory^ Assistant Lloyd E. Huffman, Stockroom Manager J. William Lusk, Mailing and Distribution Services Melvin E. Schwartz, Financial Records James E. Sergent. Greenhouse Superintendent Publications and Public Relations Owen F. Glissendorf, M.S., Technical Editor Robert M. Zewadski, M.S., Associate Technical Editor Phyllis K. Bonfibld, B.J., Assistant Technical Editor Richard M. Sheets, Technical Illustrator WiLMER D. Zehr, Technical Photographer Technical Library Doris F. Dodds, B.A., M.S.L.S., Technical Librarian CONSULTANTS: Parasitology, Norman D. Levine, Ph.D., Professor of Veterinary Parasitology and Veterinary Research, Unive7-sity of Illinois; Wiij)LIfe Reseiarch, Willard D. Klimstra, Ph.D., Professor of Zoology and Di- rector of Cooperative Wildlife Research, Southern Illinois University; Statistics, Horace W. Norton, Ph.D., Pro- fessor of Statistical Design and Analysis, University of Illinois. i-30 CONTENTS Acknowledgments 2 Original Stocking and History 3 Creel Censuses 4 Draining Censuses 5 Standing Crops of Fishes 8 Standing Crops of Largemouth Bass 12 Standing Crops of Bluegills 12 Standing Crops of Warmouths 14 Biennial Culling of the Fish Population 14 Period of Annual Fall Drawdowns 16 Stable Water Period 19 Competition: Hybrid Sunfishes Versus Bluegills 19 Size Distribution of Largemoxjth Bass and Bluegills 20 Largemouth Bass 22 Bluegais 24 Bass Spawn Inventory 24 Survival Ratios of Bass: Fry to 2-Year-Olds 26 Relationships Between Bass Spawners, Bass Fry, and Total Fish Population Density 27 Expansion Potential of Bluegills in Ridge Lake 28 Mortality Factors and Length of Life 29 Effects of Censusing and of Culling Small Fishes on the Exploitation Rate 36 Angling as a Test for Management Techniques 39 Warmouths in Ridge Lake 41 Channel Catfish in Ridge Lake 44 Other Fishes in Ridge Lake 45 Relationships Between the Fish Population and the Hook-and-Line Catch 45 The Effects of Management Techniques on Fish Populations and Angling 52 Discussion 54 Summary 61 Literature Cited 64 Index 65 This report is printed by authoritij of the State of Illinois, IRS Ch. 127, Par. 58.12. It is a contribution from the Section of Aquatic Biology of the Illinois Natural History Survey. George W. Bennett is Aquatic Biologist and Head, Section of Aquatic Biology, Illinois Natural History Survey. H. Wickliffe Adkins is Head, Science Department, Benjamin Franklin Junior High School, Champaign, Illinois, and has been employed hy the Illinois Natural History Survey each summer since 19.S2 as Biologist in Charge at Ridge Lake. William F. Childers is an Associate Aquatic Biologist, Illinois Natural History Survey. Cover design hy Richard M. Sheets. (6835—5000—9-69) X Largemouth Bass and Other Fishes in Ridge Lake, Illinois, 1941-1963 George W. Bennett H. Wickliffe Adkins William F. Childers THE RESULTS OF STUDIES of fishes in the small artificial impound- ment known as Ridge Lake (Frontis- piece) in Fox Ridge State Park, Coles County, Illinois, have been presented in several publications. The first two were semipopular articles on the efficiency of various baits for largemouth bass, Micropterus sahnoides (Lacepede), (Durham & Bennett 1949, 1951). Also in 1951 the same authors published an Illinois Natural History Survey Bio- logical Note, Cost of Bass Fis/imq at Ridge Lake, Coles County, Illinois, in which they estimated that fishermen were spending approximately $1.22 per hour for travel, meals, equipment, and licenses to fish in the lake. When these average hourly costs were assigned to the average catch in pounds of bass per hour, the money spent to catch a pound of bass was calculated to be $8.66. In 1954 the senior author prepared a bulletin entitled Largemouth Bass in Ridge Lake, Coles County, Illinois (Ben- nett 1954fl ) which covered the complete Ridge Lake investigation from its be- ginning in 1941 through a 10-year period of biennial drainings and censusings of the fishes. This report was followed by a preliminary one on "The Effects of a Late-Summer Drawdown on the Fish Population of Ridge Lake, Coles County, Illinois" (Bennett 1954/j), describing the changes in the fish population resulting from two severe earh' September draw- downs by comparing it with the fish populations exposed in the five draining censuses of the previous 10 years. Experiments with the Ridge Lake fish population have continued, and during the years since 1953 we have made additional studies of the effects of draw- downs, stable water levels, and the in- troduction of hybrid sunfishes. This re- port will caiTy these studies (in part) through 1963. Ridge Lake has been of particular in- terest in experimental fish management because it can be drained completely and because it was built on a watershed somewhat larger than necessary or rec- ommended on the basis of Illinois rain- fall and runoff. Consequently, we know that when we drain the lake basin com- pletely or partially in late fall or early .spring, it will refill again in a minimum time. Since 1941 the lake has always refilled during the winter following fall drawdowns or drainings and has com- pletely refilled following six spring drain- ings out of eight (between March and May). In those springs when it did not refill completely, the lake basin was more than half full by June. This large watershed also has had its disadvantages in that the extent of soil erosion has been greater than it would have been in a smaller drainage basin. This factor and the fact that ravines above the lake are steep sided and the soil is light have made silting in the upper reservoir of sufficient magnitude to reduce the lake surface area by about 1 acre (0.4 hectare) in 10 years; that is, while the original surface area of the lake in 1941 was 18 acres (7.28 hectares), its area by 1951 had been reduced to 17 acres (6.8S hectares) and by 1963 to about 16 acres, or 6.48 hectares. At this point it is evident that we are about to become involved in the con- fusion of English versus metric systems of measurements, and to give both En- Illinois Natural History Survey Bulletin Vol. 30, Art. 1 glish and metric measurements in a re- port of this length becomes redundant. Therefore, throughout this report the metric system will be followed. For those unfamiliar with or who have forgotten the English-metric equivalents, we are including them here. Area: 1 hectare 1 acre 2.471 acres 0.4047 hectare Weight: 1 kilogram 2.205 pounds 1 pound 453.6 grams or 0.4536 kilogram Length : 1 meter 1 inch 39.37 inches 25.4 millimeters or 2.54 centimeters 1 kilometer 0.621 mile 1 mile 1.609 kilometers Pounds per acre may be converted to kilograms per hectare by multiplying the former by 1.121. Kilograms per hectare may be con- verted to pounds per acre by multiply- ing by 0.892. Some physical, chemical, and limno- logical characteristics of Ridge Lake have already been described (Bennett 1954fl) and will not be repeated here except to restate that the growing season for fishes is 6—6/2 months. Under conditions of stable water levels Ridge Lake might be expected to sup- port a mixed fish population of around 100,000 individuals larger than 65 mm total length, or 12,000-15,000 per hec- tare, weighing around 280 kg per hectare. The lake shows intermediate "natural" fertility because the soil type in which it is built is less fertile than the black prairies of central Illinois and more fertile than the Ozark hills of southern Illinois. The fertility of the lake may have been increased somewhat over the past 23 years because of an influx of leaves and other organic matter from the surrounding hills and because nearly all flat lands in the Ridge Lake watershed are now rather intensively fertilized for increased production of com and soy- beans. One of the more important aspects of the Ridge Lake study is that, because it is a long-term investigation, it demon- strates the variability of a fairly simple population of common fishes, not only in numbers and total weight, but also in the yield obtainable from angling. These variations are partly related to the ap- plication of various management tech- niques, but they are more importantly related to the incomplete ecosystem represented by the habitat and its plant and animal associations—incomplete be- cause certain components are absent. This situation, we believe, is more or less the case with all artificial lakes and reservoirs and of many natural lakes. ACKNOWLEDGMENTS Nearly everyone who has been em- ployed on the permanent or temporary staff of the Aquatic Biology Section of the Illinois Natural History Survey since 1941 has assisted in some capacity in the Ridge Lake investigation. In the early years Mr. Bruno von Limbach, Dr. Louis A. Krumholz, and Dr. Philip W. Smith contributed much time to general col- lections. On draining censuses the crew consisted of six to eight individuals and has included (in the order of the first census on which each worked) Dr. Donald F. Hansen, Mr. von Limbach, Dr. Krumholz, Mr. Jacob H. Lemm ( de- ceased), Mr. Daniel Avery (deceased), Mr. Paul G. Bainickol, Dr. Arthur Witt, Jr., Dr. Leonard Durham, Dr. R. Weldon Larimore, Dr. William C. Starrett, Dr. James S. Jordan, Dr. William F. Childers, Dr. Robert C. Hiltibran, Mr. H. Wick- liffe Adkins, Mr. Richard Ward, Mr. Howard Crum, Mr. Robert T. Crompton, Mr. Richard Bass, Mr. David McGinty, Mr. Ronald Havelka, and others. Also several members of the Illinois Depart- ment of Conservation have helped with one or several censuses: Mr. Sam A. September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake Parr (deceased), Mr. William J. Harth, Mr. Glee Fogelman (deceased), Mr. James Holmes (deceased), Mr. Quentin Pickering, Mr. George Kuhn ( deceased ) , VIr. Ora Price, Mr. Bruce Muench, Mr. Arnold Fritz, and Mr. Rudy Stinauer. As members of the Survey staff for varying periods, several persons gathered limnological samples and statistics on the anglers' catch: Mr. Robert G. Ren- nels. Dr. Smith, Mr. Vernon A. Ander- son, Mr. Charles D. Kemp, Mr. W. W. Fleming, Dr. Morris Brehmer, and Mr. Adkins. Mr. G. H. Boewe, Mr. Frank G. Bell- rose, and VIr. Fleming made special studies of the flora of the lake. Dr. Witt and Dr. Durham studied the growth of Ridge Lake bass and bluegills from scale collections. The manuscript of this paper was read and criticized by Dr. Horace W. Norton, Professor of Statisti- cal Design and Analysis, Department of Animal Science, University of Illinois, and it was edited by Mr. Robert M. Zewadski. ORIGINAL STOCKING AND HISTORY In 196.3 the Ridge Lake experiment was in its 23rd year. In the spring of 1941 this newly completed 7.28-ha arti- ficial impoundment was stocked with 435 largemouth bass, Miciopterus sal- moides (Lacepede), (Bennett 1954a: 2.36). These bass multiplied and their offspring have constituted the bass pop- ulation of Ridge Lake during the entire period of its existence. More than 29,700 bass have been permanently removed from Ridge Lake by pole-and-line fish- ing and by Survey biologists during lake draining operations. The bass appeared to be as numerous in 1963 as in 1942. Tliere was some evidence, however, that they were more difficult to catch in 196.3-1968 than they were 25 years earlier. Bluegills, Lepomis macrochirus Ra- finesque, were first stocked in Ridge Lake in June and July 1944 when 129 were released (Bennett 1954a :236). These began to produce young almost at once, and it was estimated that more than 10,000 small ones were present when the lake was drained in the early spring of 1945. About .390,000 bluegills have been permanently removed from Ridge Lake through fishing and drain- ing operations. On the basis of the number of blue- gills removed in 20 years as compared with the largemouth bass removed in 23 years, it was evident that the bluegills were much more prolific and /or capable of surviving than were the bass. When the lake was drained in the spring of 1949, we made a first attempt to remove the bluegills completely. However, enough bluegills gained entrance from outside sources or survived in the feeder sheam, in spite of an attempt to poison them, to repopulate the lake with their next spawn. In the spring of 1949, 1.38 wannouths, Chacnohryttufi "uJosiis (Cuvier), were stocked in Ridge Lake. In contiast to the blucgill population, the number of wannouths has always remained small, and this fish has contributed very little to the hook-and-line yield. Four stocks of channel catfi.sh, Icta- hinis punctatus ( Rafinesque ) , have been released in Ridge Lake. Those released prior to 1963 were: May 1, 1951, 675 fish 2.3-33 cm total length November 5, 1952, 599 fish 1.3-46 cm total length December 17, 1957, 473 fish 19-29 cm total length The catfish were furnished by the Illi- nois Department of Conservation and were trapped in backwaters of the Mis- sissippi River. Channel catfish grew well in Ridge Lake, and to fishermen they represented a "bonus" fish. They were never stocked in large enough numbers to contribute, in any 1 year, more than 20-30 percent of the total weight of the catch. One of these catfish grew to Illinois Natural History Survey Bulletin Vol. 30, Art. 1 weigh 7.7 kg and several have weighed more than 4.5 kg; these large fish added to the general excitement of fishing at Ridge Lake by usually breaking lines when hooked. In 1960, after an attempt was made to remove the bluegills by leaving the lake basin dry over the winter of 1959—1960 ( Fig. 1 ) , approximately 4,500 small hy- brid sunfishes were stocked. This oper- ation will be described in greater detail in a later section. Also in 1960, 585 lake chubsuckers, Erimyzon sucetta (Lacepede), were stocked. Other fishes which found their way into Ridge Lake were green sunfish, Lepomis cyanellus Rafinesque; longear sunfish, Lepomis megalotis (Rafines- que); yellow bullheads, Ictalurits na- talis (Lesueur); black bullheads, Ic- talurus melas (Rafinesque); carp, Cy- prinus carpio Linnaeus; black buffaloes, Ictiobus niger ( Rafinesque ) ; white suck- ers, Catostomus commersoni (Lacepede); and several species of stream minnows. The only members of this list which contributed to the fishermen's catch were green sunfish, yellow bullheads. black bullheads, and carp. All of these miscellaneous fishes were removed from the lake whenever found in draining censuses. These fishes probably moved into the lake from above as inhabitants of the Dry Run Creek watershed or were illegally stocked by persons unkown. CREEL CENSUSES From 1942 through 1963 (the end of the period covered by this report) Ridge Lake has been open to public fishing from eight Survey-owned boats during June, July, and August of each year except 1943. The lake was closed to fishing on Mondays and Tuesdays and open during the other 5 days of the week. Boats were furnished free and could be reserved in advance for the period from 6 to 10 am or for 3 to 8 pm. When boats were not reserved, anyone could obtain permission to use them during the morning or afternoon periods. Fishermen were checked out onto the lake in boats by the biologist at the laboratory pier and off the lake when they returned to record their catches and retrieve their state fishing licenses, Fig. 1. — The dry basin of Ridge Lake during the winter of 1959-1960. The basin was allowed to dry completely and Dry Run Creek was permitted to run unimpeded through the lake basin to the Em- borras River below the lake. September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake held by the biologist during each fishing period. Thus it was possible to collect information on the time spent in fishing; the catch in kinds, numbers, and weights; and the types of baits used. No re- strictions were placed on baits, but if live minnows were brought to the lake, the biologist inspected them to forestall the escape of any carp, goldfish, or other undesirable species. Tliis method of taking a creel census gave a complete record of the time spent in fishing and the fishes caught. Signs on the lake dam and on the park roads warned that the lake was closed to fish- ing except from boats in this specific summer period, and it is believed that very little poaching took place. DRAINING CENSUSES A description of the method used in making a draining census at Ridge Lake was given in an earlier bulletin (Ben- nett 1954a: 23 1-236). In the 1956 cen- sus a Wolf-type weir ( Wolf 1951 ) built in the drain tunnel opening on the down- stream side of the dam replaced the permanent vertical screen supported by concrete uprights and located about 15 meters below the oudet. Tlie Wolf-type weir is an open-end box frame that is secured with its open end upstream in the lake outlet tunnel (Fig. 2). Tlie sloping bottom of this frame as well as its sides are covered with 25-mm mesh hardware cloth, allowing a flow of water through its bottom as well as its sides. Water falls through the weir bottom by gravity. This arrangement is much more efficient in passing water than a vertical screen and much less likely to become clogged with leaves and debris. Fishes entering the weir with the water were deposited on the sloping Fig. 2. —-Body of the Wolf-type weir that fits in the outlet tunnel on the down stream side of the Ridge Lake dam. A wire mesh covered holding box (not shown) fits tightly against the open end of the weir [held by the biologist) and extends down into the water below while the weir is supported above the stream bottom. Woter from the lake outlet enters the weir (ot right) and falls through the mesh bottom of the weir, leaving the fishes to flop down the slope into the holding box. Illinois Natural History Survey Bulletin Vol. 30, Art. 1 hardware clotli bottom as the water passed through and they flopped do\vn the sloping bottom into a submersed wire-mesh catch basin at the down- stream end of the weir. The fact that the weir was in the outlet of the drain tun- nel instead of in the stream channel some distance below eliminated the need to pump out pools and pockets in the stream channel between the outlet and the vertical screen to capture the last few fishes escaping from the lake. Except for using the weir instead of the vertical screen, the draining cen- suses were all made in about the same manner. However, the census of 1959 was made in October, while all others were made in late March or early April. The fall of 1959 was a poor time to drain Ridge Lake because very little water was flowing in Dry Run Creek; consequently, many of the fishes that remained longest in the lake basin above the gate valve were forced to move about in an emulsion-like suspension of silt and water that tended to clog the fishes' gills and apparently had a high biological oxygen demand. This mud "soup" was quickly toxic to the fishes, and many died before we could get them into clean water. In spring drain- ing operations a small stream of clean water was always flowing in Dry Run Creek, and fishes that collected in the lake basin immediately above the outlet were supplied with a source of clear, oxygenated water. During all draining operations some very small fishes escaped being washed out of the lake with the water or being captured in the screen and censused by remaining in pools of Dry Run Creek above the dam. Later, when water was again impounded behind the dam, they moved down into the refilling basin where they were subjected to predation from the larger fishes put back after the census. Tliere is also a possibility that small numbers of fishes escaped from farm ponds in the Ridge Lake watershed in times of floods and passed down Dry Run Creek into Ridge Lake. These ponds may have been the source of the bluegills and warmouths that appeared in Ridge Lake in 1960 after the lake basin had remained dry during the fall and winter of 1959-1960. Such typical pond species as bluegills and war- mouths, if washed from a pond into a stream, usually would move down- stream in search of quiet water. A work camp for processing the fishes was set up between the stilling basin and the lake outlet channel below the dam ( Fig. 3 ) . Fishes to be returned to Ridge Lake after a census were held alive in the water filled stilling basin of the surface spillway until the censusing was complete. Then, after a small vol- ume of water had collected in the lake basin above the dam, the fishes were re- captured (Fig. 4), weighed, measured, "scaled" for age determinations, and re- turned to Ridge Lake. All of the largemouth bass returned to the lake after a census bore fin clip marks ( either the new mark of the cur- rent census or a mark of some previous census) prior to release; therefore, any unmarked bass taken in a fishing season following a spring census (except the current year-class spawned in the lake) were fish that had escaped being cap- tured in the draining operation. Bluegills were not usually fin clipped, because even when censuses were made at 2-year intervals, the high mortality rate of blue- gills assured that relatively few marked ones would be present at the next census. The 25-mm mesh used in the fish screens and in the construction of the Wolf-type weir allowed small fishes to escape with the water as the lake was drained. No attempt was generally made to estimate the number of fishes that es- caped through the mesh, but at certain censuses many more small fishes were present than at others. The census tabu- lations ( unless otherwise specified ) rep- resent bluegills 64 mm or more in total length and largemouth bass 100 mm or more in total length. During the first 10 years the lake was September, 1969 Bennett et ah: Lahgemouth Bass in Ridge Lake drained completely and the fishes were censused at 2-year intervals ( 1943, 1945, 1947, 1949, and 1951) Following each census small fishes were culled. About half of the small bass were removed in the 1943 census, bass smaller than 25 cm total length were removed in the 1945 and 1947 censuses, bass smaller than 23 cm were removed in the 1949 census, and those smaller than 20 cm were re- Fig. 3 — Fish censusirg camp at the time of a sp the lake are stored in the water •filled stilling basin (right to allow the fishes to be returned. )ining census. Fishes to be replaced in snough water collects in the lake basin Fig. 4.— Recapturing fishes held in the stilling basin. When it is time to return the fishes stored in the stilling basin to the lake, the water is pumped from the basin and the fishes are recaptured with nets and short seines. Illinois Natural History Survey Bulletin Vol. 30, Art. 1 moved in the 1951 census. Bluegills were drastically culled at every census after they were introduced, and attempts were made to remove them completely in 1949 and 1959. The period 1941-1951 constituted the "Biennial Draining Period." A period of testing September draw- downs of the lake level begain in 1951 and extended to the spring draining cen- sus of 1956, with an additional draining census in the spring of 1953. A period of stable water levels when no management practices were applied to either the lake or the fish population extended from the spring of 1956 to October 1959 and included four com- plete fish growing seasons. The lake was drained completely in October 1959, the bass and catfish were removed to a near- by hatchery pond for winter storage, and the basin of Ridge Lake was allowed to dry for about 3 months. In early 1960 Ridge Lake was allowed to refill, the bass and catfish were moved back from the hatchery pond, and hy- brid sunfishes and lake chubsuckers were stocked from outside sources. In the following pages we will con- sider the variations found in the fish populations supported by the lake at the times of the various censuses. Our major objectives are to consider the differences in the nine populations of fishes and the variability of the standing fish crops; to measure the negative relationships in numbers and weights between bass and bluegills; to consider reasons why Ridge Lake appears to have a maximum carry- ing capacity for largemouth bass; to reappraise the effects of early fall draw- downs upon the bass and bluegills of Ridge Lake; and to demonstrate the contrasting effects of stable and fluctu- ating water levels upon the fish popu- lations of this lake. STANDING CROPS OF FISHES Table 1 shows the numbers and weights of largemouth bass, bluegills, and other fishes taken in the nine drain- ing censuses of Ridge Lake. Bass num- bered between 1,500 and 6,200, and their total weight varied between 205 and 412 kg. Bluegills numbered between 7,500 and 93,000 and weighed (exclu- Table 1. — Numbers and weighfs of largemouth bass, bluegills, and other fish taken in nine draining ;uses of Ridge Lake. Census Year September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 2 M „ c c ; = ti o ; = M ^^ '^ 7= 5 .y c S o C •- u c — I c? t^ -H CO -H -H O .-I CO 10 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 sive of the 1945 census when the blue- gill population was just beginning to ex- pand) from nearly 450 to about 1,580 kg. Before 1951 the other fishes were largely black bullheads, green sunfish, and carp, and from 1951 on, warmouths, channel catfish, carp, and lake chub- suckers. In tliree of the censuses, those of 1947, 1959, and 1963, the total popu- lation e.xceeded 1,800 kg in weight, but it varied from 398 kg when the popu- lation was almost entirely bass to 2,100 kg when the largest weight of bluegills was present. In the two or more spawning and growing seasons between censuses, pop- ulations of bass, bluegills, green sunfish, warmouths, black bullheads, channel catfish, carp, and other species had an opportunity to expand. However, large- moutli bass, channel catfish, and war- mouths received greater consideration than bluegills, as most of the larger in- dividuals were returned to the lake after the censuses. This was partly because these species were known to have low population expansion potentials (none at all for tlie channel catfish) and, in the case of largemouths, because we were particularly interested in managing bass as sport fish. Actually, the reduction in the weight of largemouth bass put back after a census represented the removal of small fish and accidental losses of larger fish resulting from handling. The greatest re- duction of bass occurred over the winter of 1959-1960 when the bass and channel catfish were held in a hatchery pond about 19 km from Ridge Lake. When these fishes were recaptured by draining the hatchery pond in the spring of 1960, the total weight of the bass found in the pond was reduced by 72.3 percent from the weight released there in Octo- ber 1959. Bluegills were severely reduced during each of the censuses. In no case were more than 4,500 of the larger bluegills put back after a census; usually the number returned was less than 2,000 (Table 2). Bluegills always showed great capacity for population expansion. As will be discussed later, the factors having a dampening effect on the rate of bluegill population expansion were Table 3. — Numbers per hectare and weights per hectare of largemouth bass, bluegills, and othe fish taken in nine draining censuses of Ridge Lake. September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 11 8 a: 2 =15 tai 12 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 predation by large populations of large- mouths and artificial drawdowns of the lake level. Those who study fish populations may more easily visualize the fishes inhabit- ing ponds and lakes if numbers and weights are expressed in numbers and kilograms per hectare. For this reason we have included Table 3, giving the numbers and weights per hectare of the fishes found in the nine censuses, and Table 4, which gives the numbers and weights of fishes per hectare returned to the lake following each of the nine censuses. The data shown in Table 3 indicated that the maximum weight of fishes that Ridge Lake would support in bass, blue- gills, and such other fishes as have been present was around 280 kg per hectare ( 250 pounds per acre ) . This weight was exceeded slightly in the 1947 census, and the total weights of fishes were only slightly lower than that figure in the 1959 and 1963 censuses. In each of these censuses bluegills made up by far the greatest part of the fish population, both in numbers and weight. Standing Crops of Largemouth Bass When the populations of the species that were most abundant at Ridge Lake are considered as separate units, it may be conjectured that largemouth bass, bluegills, and warmouths have popula- tion maxima beyond which expansion is limited. For example, in the censuses of 1943, 1949, 1951, and 1963 the popu- lation of largemouth bass varied numer- ically between 207 and 904 fish per hectare although in each of these cen- suses the total bass weight was around 56 kg per hectare (54.0, 56.6, 56.0, 52.3). In the 1943 census the bass practically represented a one-species fish population for Ridge Lake, constituting 99 percent of both total number and total weight of all fishes (Table 5). At the other ex- treme when 904 bass per hectare were present ( 1963 census ) and there was a large population of lake chubsuckers to produce young for bass forage, the total weight of bass was only 52.3 kg per hectare. At that time bass made up only 6 percent by number and 19 per- cent by weight of the entire fish popu- J lation. ;l If the standing crop of fishes and the fish-carrying capacity of a body of water are related strictly to available food, we must assume that as much bass food was available when the entire popula- tion of the lake was composed of bass as was available when a variety of fishes was present. This may have been true, as Ridge Lake usually supports a large population of the crayfish, Orconectes virilis (Hagen), which is used exten- sively by largemouths. In the censuses of 1945, 1947, 1956, and 1959 the total weight of bass sup- ported by Ridge Lake ranged from 34.9 to nearly 45 kg per hectare (the 1953 census was excluded because its bass population was aflFected by the severe drawdowns ) . With the exception of the 1945 census when most of the fishes other than bass were bluegill fingerlings, these low weights per hectare of bass were associated with high weights per hectare of other kinds of fishes, sug- gesting competition between largemouth bass and certain other species. Standing Crops of Bluegills Bluegill numbers and total weights were lowest in seasons following the spring censuses because few were re- stocked (Table 4), and in the March census of 1945 after the initial stocking of 129 bluegills in June and July 1944. While the number of bluegills restocked after a census varied from none in 1949 and 1960 (in the latter year we at- tempted to replace bluegills with 654 bluegill X warmouth and red-ear x war- mouth hybrids per hectare) to 653 per hectare in 1963, there was obviously no relationship between the number re- stocked and the number found in the census 2—4 years later. For example, following the 1945 cen- sus, the rate of restocking was eight large bluegills per hectare, yet the weight September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 13 M !» 5 2 i 14 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 of bluegills per hectare in the 1947 cen- sus 2 years later e.xceeded that of any other year (Table 3). The 1959 census exposed 13,469 bluegills per hectare. This was the largest number in any cen- sus and appeared at the end of four grow- ing seasons of stable water levels, sug- gesting that stable waters were favor- able to the buildup of bluegill numbers. However, the number of bluegills pro- duced over the three growing seasons of 1960, 1961, and 1962 and exposed in the March census of 1963 was almost as large ( 12,442 per hectare ) , and bluegills were not even supposed to be present in the lake. In considering the populations of blue- gills in the censuses after that of 1945 but excluding those of 1953 and 1956 ( censuses following fall drawdowns ) , it was evident that there was much vari- ation in the numbers and weights of these fish. Bluegills, unlike largemouth bass whose weights in four censuses were quite similar, achieved no weights similar enough to indicate a maximum standing crop figure for bluegills in Ridge Lake. The figure of 216.7 kg per hectare found in the 1947 census ( Table 3) might suggest that the maximum carrying capacity for bluegills may be around 225 kg per hectare. There were no indications of relationships between the total weights of bluegills and of other fishes except largemouth bass. In years when largemouth bass weights per hectare were highest, bluegill weights per hectare were lowest, and vice versa. This relationship will be considered in more detail later. Standing Crops of Warmouths The warmouth is considered a very satisfactory pond fish (Larimore 1957). It was introduced into Ridge Lake in the summer of 1949 when 138 adult fish were released so that we could gain comparative information about the war- mouth and the bluegill. Even though after each census warmouths were given a special restocking advantage over blue- gills (much higher percentages of total populations were returned to the lake), warmouths never made up more than 5 percent of the total numbers and weights of all fishes in any census ( Table 5 ) . Total numbers of warmouths in the five censuses after 1949 were 916 in 1951, 252 in 1953, 622 in 1956, 2,068 in 1959, and 4,768 in 1963. Warmouths have contributed comparatively little to the Ridge Lake fish population. BIENNIAL CULLING OF THE FISH POPULATION During 1941-1951 Ridge Lake was drained and censused at 2-year intervals and only selected fishes were returned. This operation was described in detail in a previous publication (Bennett 1954a: 231—236) and will only be summarized here. The original stocking of the lake and the methods of operating creel cen- suses and making draining censuses have been described earlier. Briefly, the culling procedure was to remove all bass smaller than 25 cm in the 1945 and 1947 censuses, 23 cm in the 1949 census, and 20 cm in the 1951 census (Table 6). In the 1943 census there were 4,771 bass between 15 and 20 cm. More than half of these fish were removed (2,783) to correct the over- population that had resulted in their stunting. Nearly all of the bluegills were re- moved during each census, and the extent of these removals can be seen in Table 6. Removals of warmouths were relatively small in most censuses. The channel catfish removed were fish that were killed or injured in handling, as we tried to return as many of this species as possible. All other fishes except lake chubsuckers were completely removed from the lake during each census. These "other fishes" were largely bullheads, /. melas and I. natalis; green sunfish; and carp. Small bass (less than 20 cm) and bluegills were culled as a final part of each census after the initial 10-year per- iod. As may be seen in Table 6, the totals of fishes permanently removed from the September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 15 -2 a J* ^S o 05 rt cq ^3 =3^Ma be bc o o o o o TP Oh i-i "t CO O ^ 00 o -* o CO 00 t- —I O Tf S CD => a: o rt o -* in o N in CO od CO ^ 00 CO 03 CO G5 CO rt oq rt CO in t- 05 -H Tj< -^ Tt* ^ lO Gi Ci Ci 3 be be aj o be be rt CO -H CO i-H CD CO lO lO ^ lo CO en rt 05 o 00 in CO CD -^ en 03 03 22 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 rapidly to desirable sizes are decreased. The reverse is also true; smaller numbers of fishes are usually associated with more rapid grov^ rates and larger sizes except in a few situations where the growth of certain pelagic fishes seems to be unrelated to the density of a popu- lation. Where growth rates and large average sizes of fishes are density dependent, fish management must be a compromise. Maximum population numbers must be sacrificed in part to maintain a rate of growth that will produce fishes of catch- able sizes; maximum growth rates and the development of fishes of maximum sizes must be sacrificed in part for the production of suitable numbers for rea- sonably successful anghng. Often it is impossible to apply management at the same efiiciency level to several species of fishes inhabiting the same water that one might apply if he were interested in one species to the exclusion of others. In a simple two-species combination such as the bass-bluegill, one might effectively manage for bass production and disregard the bluegills or manage for bluegills and disregard maximum production of bass. While the produc- tion of fishes for angling can be mate- rially improved in either direction, it may be diEBcult or impossible to attain the maximum for both species at the same time. In the Ridge Lake studies several management techniques were applied. Analyses of the size distribution and hook-and-line yields of the fishes should indicate the effectiveness of the tech- niques in question. These analyses will be presented in the following sections. A consideration of size distribution will come first. Largemoufh Bass The size distribution of largemouth bass found in the nine censuses of Ridge Lake is shown in Tables 7 and 8. Table 7 gives the numbers and weights of largemouths divided into six length- weight categories. If we consider the numbers and total weights of fish in the four length categories from 25.0 cm to 46.9 cm, inclusive, it is quite evident that with the exception of 1943, the Table 8.— Numbers and weights of largemouth bass of small and large sizes found In nine draining censuses of Ridge Lake. September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 23 ^ " I 5 - ^ = ^ - o 'Hi = M CO 00 T)" T}" t-^ r- C3 X in t^ o lo o -H c; -T n ;c c-j — ^ COO CO. I> C5 o' co" C5 —T »-H O — ' lO O -H Ol o o lO OC lO CO ^ t- — ' C^! O lO oi — -H m -H ic o in t~ 05 — I ^ TJ* r}< ^ lO 05 05 05 G5 05 P- '^^ -t; 24 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 largest numbers and weights of bass were found in the period of biennial draining, 1941-1951. Table 8 shows a simplified breakdown of large and small bass taken in the nine censuses. In each census during the first 10 years except that of 1943 when an overpopulation of small bass resulted from the 1941 spawn, the total number and weight of bass 25 cm or longer were more than 370 weighing 215 kg or more. In none of the censuses after 1951 did the number of large bass approach 370 and only in the 1963 census was the total weight of large bass more than 215 kg. Thus, the censuses during the bien- nial draining period, 1941—1951, indi- cate the usefulness of this technique in building up populations of large bass. The relatively high weight of large bass in the 1963 census was chiefly due to the presence of 89 bass in the 1.4—1.8. kg category, which, as will be shown later, were nearly immune to capture by angling. Bluegills The total numbers, total weights, and average weights in three length classes of bluegiUs are shown in Table 9. The first census when numbers of bluegills were available was in 1947, and they have since continued to be present in substantial populations. The largest numbers of bluegills 6.4 cm and longer were present in 1947, 1951, 1959, and 1963, but the best po- tential populations for angling were present in the census of 1947, 1953, 1956, and 1959. By far the largest population of blue- gills of useful sizes was exposed in the 1956 census after three consecutive sea- sons of mild early fall drawdowns. The 8,661 large bluegills (15 cm and over) weighing about 715 kg were about one- third larger in numbers than the next best population ( that of 1947 ) and about two or more times as large in numbers of large bluegills as most other popu- lations. Even following 2 years of severe fall drawdowns the 4,419 large bluegills in the 1953 census were numerically al- most equal to the 4,469 large bluegills of the 1959 census after four seasons of stable water levels. Here is evidence of the importance of drawdowns in bluegill management. Bluegills of 20 cm or more total length were found in the censuses of 1945 and 1947 (survivors of the original stocking of 1944 ) and in the censuses of 1953 and 1956 during the period of drawdowns. In contrast, neither the biennial culling technique nor the periods of stable water levels, 1956-1959 and 1960-1963, pro- duced any bluegills as long as 20 cm. BASS SPAWN INVENTORY The idea of making an annual inven- tory of the schools of bass fry originated on May 29, 1941, when the first schools of young spawned by the original stock were in evidence along the lake shallows (Bennett 1954a: 245). Between May 30 and June 7, 1941, we made daily counts of these schools of fry. The number of schools gradually increased until 38 were counted on June 5. After that date the number of schools decreased, and bass fry from schools that had broken up were scattered along the lake edges in the shallow water over the shore ledge (formed by wave action) where the slope of the natural bank was steep. The estimate of bass fry in the 38 schools was 76,000, or nearly 21,000 per hectare on the basis of the 3.64-ha surface area of the lake at that time. This estimate indicates an average of 2,000 fry per school. Our estimate was probably con- servative, but it was not considered de- sirable or possible to capture an entire school and count the fry. Rough counts were made by estimating the numbers of fry in groups of 100, and it was sel- dom that a school was estimated at more than 3,000 fish; usually they appeared to number 2,000 or less. However, in 1951 a huge school was located around the concrete spillway tower that was estimated at 10,000 fry and probably contained more. This school was found around three sides of the tower, a linear September, 1969 Bennett et al.: Labgemouth Bass in Ridge Lake 25 distance of 10 meters; extended about 2.5 meters out from the tower; and oc- cupied at least 0.6 meter in depth. Conditions for censusing bass fry varied from year to year. Turbid water and wave action sometimes reduced visibility. The schools of fry often moved under floating mats of algae (present in some years) and were difficult to lo- cate. However, rooted vegetation grow- ing on the bottom had not grown suffi- ciently by late May or early June to obscure the schools. A ma.ximum count of schools usually was recorded 3-6 days after the first school was located, and this maximum was considered the number of bass fry for each season. In Table 10 the fry esti- mates are given in terms of numbers per hectare. While the numbers estimated are in no way meaningful as such, the fact that we followed similar methods using identical personnel from year to year has led us to believe that these counts have comparative value. In some years no schools of fry could be found. This did not mean that none were present; rather it probably meant that the number of schools was so small that we were unable to find them or that predation by yearling fishes took place so rapidly that the schools were decimated before the individual fry pro- gressed much beyond the free-swimming stage. The fact that large numbers of fry were found in a given year did not necessarily mean that a large year-class of bass would develop from them. As we shall see in the following section, there were large differences in survival rates from year to year, and it was impossible to predict survival for any given year. The bass fry estimates given in Table 10 have been separated into three groups on the basis of management operations that we believe may have influenced bass fry numbers. The greatest numbers of fry were associated with biennial lake draining and culling operations. These operations removed almost all of the small yearling fishes that would feed upon bass eggs and fry, reduced num- bers of large crayfish that might disturb bass nests, and probably also reduced predacious insect larvae which are known to attack fry. The average num- ber of fry associated with the culling operations in nine draining censuses was 7,917 per hectare. Fall drawdowns of Ridge Lake were believed to have similar but less severe effects upon the small fishes, crayfish, and other aquatic invertebrates. Here the data are less convincing because only .3 years were represented. Thus, the average number of young bass in the censuses associated with drawdowns ( 3,243 per hectare ) suggested that such operations were only about 40 percent as efficient as draining and culling in promoting the successful production of bass fry. There were 10 years when seasons of stable water levels without any type of population reduction preceded bass spawnings. With two exceptions the fry production or fry survival in those years was relatively small. The first exception was in 1942 when the fry count was 3,570 per hectare. At that time the popu- lation of Ridge Lake was composed almost entirely of bass, including a few of the original spawners and the 1941 year-class, fishes ranging in length from IS to 28 cm. These bass were not inter- ested in eating fishes of fry sizes. In 1957 the bass fry estimate was 4,880 per hectare. WTiy the survival of fry to the schooling stage in this year was reasonably good is unknown. \^Tien the 2 exceptional years are included, the average number of fry in seasons follow- ing a year of stable water levels is 1,023 per hectare. If these 2 years had been omitted, the average would have been around 220 per hectare. Thus, the differ- ences in the numbers of bass fry associ- ated with two types of management as compared with the numbers of fry as- sociated with no management appear to be very significant. Several questions arise when large numbers of schooling bass fry are in 26 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 Toble 10. — Estimated numbers of largemouth bass fry per hectare In seasons following culling operations for small blueglHs and age dosses 0+ and 1 "1" bass, 1 or more years of stable water levels, and 1 or more years of early foil drawdowns. September, 1969 Bennett et al.: Labgemouth Bass in Ridge Lake 27 Table H.— Estimated number of largemouth bass fry per hectare in each of five year-classes pro- duced in Ridge Lake, the number of boss per hectare of each year-class either caught by fishermen in the next two fishing seasons after spawning or appearing in the next draining census about 21 months after spawning, and the ratio of fry to fish subsequently taken. These figures indicate survival of fry to become yearlings. Calculations involving water surfoce orea were based on 7.28 ho except where stated otherwise." 28 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 Table 12. — Estimated numbers of bass, bluegills, and other fish per hectare shortly prior to spawn- ing time, and of largemouth bass fry at spawning time, 1941-1953, at Ridge Lake. Calculations involving water surface area were based on 7.28 ha before the 1951 fishing period and 6.88 ha from that time on.° September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 29 Table 13.— Number of bluegllls restocked per hectare following a named census and number per hectare token in the following census 2, 3, or 4 years later. Data ore arranged in order of numbers of bluegills restocked. 30 Illinois Natural Histohv SrnvEY Bulletin Vol. 30, Art. 1 previously so marked. Bass marked at a previous census were not re-marked but were weighed, measured, and "scaled," and the previous fin clip was recorded. After each census a recorded number of marked bass bearing the fin clip of the current census or those of previous censuses were restocked in the lake to be caught by fishermen in the next two, three, or four fishing seasons or to ap- pear as marked individuals in the next draining census. In eight draining censuses prior to the 1963 census 5,373 unmarked bass were fin clipped and restocked in Ridge Lake. As any marked fish may survive one or more periods between censuses, the restocking numbers in Tables 14 and 15 show a total somewhat larger than the total number of bass actually fin clipped. Of the fish restocked, about 59 percent were caught by fishermen, 18 percent were recovered in succeeding draining censuses, and only 23 percent disappeared. Periods between marking and recensusing were 2, 3, and 4 years. Toble 14. — Rates of exploitation and unoccountoble losses of marked lorgemouth bass in Ridge Lake." September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 31 In only a few instances could we fi- nally account for all of the bass in a group of similarly marked fish that were returned to Ridge Lake after a drain- ing census. There were a number of ways, other than being caught, in which a fish might be removed from the popu- lation: (i) Some of the smaller marked bass ( 20—23 cm ) may have been preyed upon by larger bass or may have moved out of the lake over the surface spillway in times of floods, (ii) Some bass of all sizes injured in the draining, censusing, and restocking operation may have died some time after restocking and been torn to pieces on the lake bottom; addi- tionally, a very few large bass may have become buried in the soft mud of the lake basin during the late stages of a census and may not have been recov- ered, (iii) Individual fishes dying of senile degeneration in the period be- tween censuses may have been torn to pieces by crayfish and turtles so that their carcasses never floated to the sur- face. ( iv ) Some fish injured by hooking or trapped on broken lines, on lost stringers, or in lost wire or string mesh fish holding baskets may have died and disintegrated without coming to the sur- face. ( v ) A few marked bass may have been taken by large bird predators, such 32 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 E 5 ^ 0.-8 is September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 33 uQ 34 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 35 1945 period when the fish were still quite small (18—28 cm) was 32.9 per- cent. In the next two 2-year periods, 1945-1947 and 1947-1949, the fish were 4-8 years old and increased in weight from about 0.34 kg each to about 1.8 kg each. The unaccoimtable mortality rate for the 1945-1947 period was 5.4 percent and for the 1947-1949 period, 9.8 per- cent. At least one of these bass lasted for 7 more years, and after 1949 the un- accountable mortality rate again became greater than 30 percent. This change from high natural mor- tality among small bass, followed by low mortality until the fish passed the age of 7-8 years, followed again by high mortality among the older fish seemed to be fairly characteristic of most of the mark groups (Fig. 7). These data have been summarized in Table 16. Natural mortality rates among bass greater than 1.8 kg were relatively high in Ridge Lake, and these fish were very diSicult to catch with hook and line. It was evident from the data presented in Table 16 that more of these large fish died from natural causes than were caught. The oldest largemouth recorded at Ridge Lake was a 1941 year-class fish taken in the 1956 draining census at the age of 15 years. Only four of this year-class lived to be 10 years of age. Table 16. — Nafural, nonfishing mortality rates of various weight ranges of marked largemouth boss In Ridge Lake, tabulated at the beginnings and ends of six 2-year periods and three 3-year periods, 1941-1963. Mortality rates for the 3-year periods were not significantly different from those of the 2-year periods. Weijiht Range 36 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 EFFECTS OF CENSUSING AND OF CULLING SMALL FISHES ON THE EXPLOITATION RATE The marking and counting of bass and large bluegills returned to the lake following each draining census and the complete creel census made in each fishing season allowed us to compare the exploitation rates of largemouth bass and bluegills in the fishing seasons im- mediately before and after draining cen- suses. In postdraining creel censuses the effects of the culling operation were indicated because the March draining eliminated a great many of the small fishes, crayfish, and aquatic invertebrates of value as fish foods. With the im- poundment of new water in April and May the numbers of small aquatic ani- mals, including fishes, undoubtedly in- creased rapidly, but these remained of such small sizes until well into the summer that they were of little interest to the bass of 20 cm and larger. This was not true for bluegills, because all sizes of these fish normally feed on en- tomostraca and small aquatic insect larvae. We have assumed that the fishes put back after a census in March comprised the population of catchable-sized fish present in June when the lake was opened to controlled fishing. Table 17 shows the bass and bluegills per hectare released after each of the eight censuses ( not in- cluding the 1943 census because the lake was not open to fishing in 1943), the fishes caught per hectare in the fol- lowing fishing season, and the percent- ages caught of the total numbers and weights of marked fishes. The bass* re- turned in March probably increased in weight very little during April and May because of a shortage of their larger items of food. Bluegills may have achieved average to rapid growth be- cause of the rapid expansion of popu- lations of entomostraca. Table 17 indicates that the exploita- tion rates of bass numbers in single fishing seasons following draining and culling operations were usually between 37 and 63 percent. The exploitation rate of bass weight reached as high as 73.7 percent. There was no evidence that such exploitation represented overfishing although the total numbers and weights of bass available for replacement after a census varied a good deal. Although Table 17 shows that the removal of bass by angling averaged around 56 percent of these fish in most spring draining census years, this was not true in 1960 and 1963. In 1960 the number of bass brought back to Ridge Lake from the hatchery where they had been kept during the winter was com- paratively small. In 1963 only 116 large bass were available for restocking, but each of these fish exceeded 1 kg in weight. There was a very noticeable shortage of bass in the length range of 25-35 cm (weight range 0.25-0.45 kg). Bass smaller than 25 cm exceeded 6,000 in the census, and more than 2,000 of these small bass were fin clipped and restocked. Fishermen apparently caught and kept relatively few of these small bass. In seasons of postcensus fishing the catch of bluegills returned after census- ing varied between 32 and 41 percent. An exception occurred in 1963 when 966 bluegills of 15 cm or more in length and 3,500 bluegills of less than 15 cm were returned after the draining. This total restocking of almost 4,500 bluegills was not followed by a proportionately large catch of these fishes. It was also possible to estimate less exactly the bass and bluegill exploita- tion rates in summers immediately pre- ceding draining censuses. An estimation of the total populations of bass and blue- gills was made by adding the catch fig- ures for the summer in question to the catchable-sized fish found in the drain- ing following that summer. Obviously, large fish in the draining censuses were present in the lake during the preceding fishing summers and were available to the anglers. Table 18 shows the estimated num- bers and weights of bass and bluegills September, 1969 Bennett ct ai: Largemouth Bass in Ridge Lake 37 1 ^ tt & tt bo 05 p p op lO CO o oi t-^ CO -i o\ oi TT iX) CO lo tt) CD in -H 03 OJ C3^ 05 C3^ I i I i = E g o Sf E - S £ S g !U •a 2 0- c „ — -c S E-H ."5 ;5 a o « i: K ffi CQ S n t-' -H lO CO -^t 05 -H IC 05 Tj< CO CD (M t~^ -H iri -H 05 in ^ CO CO in CO ^ in .-H CO ^ -H T)< rt cOrtcooo(;qinini-< in CD CD O r-i IM CO * rt M CO ^ (N m o -^ (M 05 —I oq o ^ ci CO CD CD CO en 05 Ci O C35 CJl CJS 44 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 flies, and these fish were much heavier than bluegills for any given length. The anglers' catch was usually comparatively small (Table 21). As with bluegills, the largest catches of desirable-sized war- mouths were made in 1955 and 1959. CHANNEL CATFISH IN RIDGE LAKE In the opening pages we described the several introductions of channel cat- fish, the first in May 1951 and others in the fall of 1952 and the winter of 1957. Usually a stocking consisted of about 450-700 fish (62 to somewhat less than 100 per hectare). At Ridge Lake only a few anglers fished for these catfish ( with specialized baits), and usually catches were acci- dental. Most of the channel cats were caught on night crawlers, Lumbricus terrestris, and live or dead minnows. Table 22 shows the catches of channel catfish made in the fishing seasons of 1951-1963, inclusive. Some channel catfish were accident- ally injured or killed during every drain- ing census, partly because of their be- havior. They demonstrated a strong ten- dency to remain in the lake basin in- stead of moving through the gate valve with the outgoing water. As a conse- quence, many of these fish were suffo- cated before they could be placed in the holding basin for live fishes. In addition, 131 catfish died in the hatchery pond at Mattoon over the winter of 1959- 1960. When we add to the 834 channel cats caught by anglers the 13 found in the 1963 census and the 212 lost in other operations, the catfish that were account- able amounted to 1,059 of the 1,747 stocked in Ridge Lake, giving a return of 60.6 percent over a 13-season period. This must be considered a very reason- able return on wild fish trapped in the Mississippi River, handled, and hauled several hundred kilometers by tank truck. Channel catfish grew well in Ridge Lake (Fig. 8). The 13 fish taken in the 1963 census had an average weight of almost 4.45 kg, and the largest weighed 7.71 kg. The greatest weight of channel cat- fish was taken by angling in 1956; the catch was 86 fish weighing 114.3 kg. This catch represented 28.6 percent of the total weight of all fishes caught at Ridge Lake in 1956. Catches of channel catfish after stock- ings of 60-100 per hectare in Ridge Lake exceeded those of Crance & McBay (1966) in Alabama where 247-492 J^^' ' ' September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 45 per hectare were stocked along with estabhshed populations of bass and blue- gills. It is probable that the advantage shown by the Ridge Lake experiment may have been because the channel cats there were 180-300 mm long when stocked, while those stocked by Crance and McBay were only 76-200 mm long, well witliin the size range for bass forage. OTHER FISHES IN RIDGE LAKE As mentioned previously, other fishes in Ridge Lake were mostly green sun- fish, black and yellow bullheads, and carp. When both bluegills and hybrid sunfishes were present, the hybrids are included in the "Other Fish" column of Table 19. On several occasions the total weight of "Other Fish" taken by an- gling exceeded 23 kg and may be of particular interest. For example, the catch in this category in 1948 amounted to 47.1 kg, of which 33.1 kg were black bullheads averaging almost 0.45 kg. These bullheads were all of about the same size and probably represented a single year-class and perhaps part of a single school of bullhead fry produced in the lake or in a Dry Run Creek pool. In 1950, 187 black bullheads were caught along with 36 green sunfish, but the bullheads were considerably smaller than those caught in 1948, and two size classes were present. Black bullheads and green sunfish nearly disappeared after 1953 although 117 black bullheads were in the catch of 1957 along with one carp and 19 bluegill x warmouth hy- brids of small sizes. The 1957 bullheads were of two size categories; 86 were longer than 200 mm and their total weight was 24 kg; 31 smaller bullheads averaged 318 grams. The fishes in the "Other Fish" column in 1961 and 1962 were hybrid sunfishes and were supposed to be the only sun- fishes in the lake. In the 1961 catch 194 bluegill X warmouth and 6 red-ear x warmouth hybrids totaled 23.4 kg. In 1962 the catch was 1,075 bluegill x warmouth hybrids weighing 94.8 kg and 134 red-ear x warmouth hybrids weigh- ing 6.8 kg. Many more of these had been caught in 1961 and thrown back be- cause they were less than the then- required 180 mm total length. In general one may say that black bullheads and green sunfish were con- siderably more numerous in the lake prior to the introduction of warmouths and channel catfish. Whether this was in any measure due to competition from the introduced species is unknown. RELATIONSHIPS BETWEEN THE FISH POPULATION AND THE HOOK-AND- LINE CATCH We assume that there is a positive relationship between the catch of fishes by anglers and the population of fishes from which the catch is taken; this vari- Table 23. — Yields per hectare of all fishes taken by anglers from Ridge Lake, 1942-1963, and man-hours of fishing effort. The lake was not open to public fishing in 1941 and 1943. 46 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 able relationship is affected by species composition, size distribution, density, and behavior of the species involved. At Ridge Lake there was a great deal of variation in hook-and-line yields dur- ing the 21 seasons covered by this report when the lake was opened to controlled public fishing (Table 23). From 1941 to 1945 the fi.sh population of Ridge Lake was composed mainly of largemouth bass, and this was reflected in the catches of 1942, 1944, and 1945. After 1945, when numbers of both bass and bluegills were present, the yields ranged from a low of 3.3 kg per hectare in 1960 to a high of 117.0 kg per hectare in 1959, with an average annual yield of 47.7 kg per hectare. The extent of use of the lake for fish- ing varied directly from season to sea- son as the catch varied. Generally, in years when large weights (and num- bers) of fi.shes were caught, the fi.shing intensity increased, and vice versa. The average fisherman-use level for post- World War II years was 574 man-hours per hectare per season with a range of 240—791. Good and poor fishing years might be defined on the basis of rate of catch and total numbers and weights of fish caught by anglers. These criteria used at Ridge Lake failed to reflect the success of bass fishing in any year. To explore further the relationships be- tween composition of the fish population and catch, we selected 3 of the poorest fishing years, 1947, 1950, and 1963, when the rates of catch per man-hour were Table 24. — Composition of the anglers' catch at Ridge Lake for 3 of the poorest years of fishing. All data are per hectare. September, 1969 Bennett et ah: Largemouth Bass in Ridge Lake 47 0.3, 0.4, and 0.4 fishes, respectively, and 3 of the best fishing years, 1948, 1955, and 1959, when the rates of catch were 1.1, 1.2, and 1.6 fishes per man-hour. Details of the composition of tlie catches in the selected poor and good fishing years are shown in Tables 24 and 25. The most obvious differences in the groupings shown in these two tables are in the numbers of fishes caught. In the 3 poor years the average number of fishes caught each season was 151 per hectare, while in the good years the average number was 1,078 per hectare, or more than seven times as many. These differ- ences were also evident in the average weights of the catches. For the poor years the average weight of the catch was 23.1 kg per hectare; for the good years it was 100.8 kg per hectare. The ratio of large to small fishes caught was about the same in the good fishing sea- sons as it was in the poor ones. Length frequency distributions of bluegills and largemouth bass in the contrasted fishing seasons are shown in Tables 26 and 27. While on the average about 69 percent of the bluegills taken in the good fishing seasons were 15 cm or longer, only about 63 xjercent of those taken in the poor seasons were 15 cm or more ( Table 26 ) . However, these dif- ferences are not significant. The length frequency distribution for bass shows that more bass 43 cm and longer were caught in the poor year of 1963 than in any good year and more bass of less than 23 cm (689) were Toble 25. — Composition of the anglers' catch at Ridge Lake for 3 of the best years of fishing. All data are per hectare. Species 48 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 caught in the good year of 1955 than in any other year of those shown in Table 27. The length frequency distiibution for bass caught in 1949 is included in Table 27 because the rate of catch for largemouths in that year exceeded that of any other. However, the overall fish yield for 1949 was not particularly high because very few fish other than large- mouth bass were present. In considering the size distribution of bass caught in 1949 and comparing this disti-ibution with others in Table 27, it was evident that more bass 25-37 cm long were caught in 1949 than in any other season shown. At the same time 53 bass were caught that ranged from 41 to 56 cm and from about 0.9 to 2.7 kg each. In Tables 28 and 29 we have made estimates of the numbers and weights of largemouth bass and bluegills per hectare in poor (Table 28) and good (Table 29) fishing seasons and com- pared them with numbers and weights per hectare of fishes caught in those same years. Fishes were separated into large and small categories as defined in Tables 24 and 25. In some census years, such as 1947, no small bass or small bluegills were put back after the census. In 1963, another census year, 2,270 small bass were marked and re- stocked, and some bluegills 13—15 cm were restocked. This restocking of small fishes represents rather large differences in numbers restocked; yet fishing was poor in both years. The years 1948, 1950, 1955, and 1959 all preceded censuses so that it was possible to estimate the total population by adding the fish caught in the preceding fishing season to the popu- lation subsequently exposed in the drain- ing census. Upon comparing the data showm in Tables 28 and 29, it became evident that the higher rates of catch in fish per man- hour were dependent upon the catches of bluegills, and high catches of blue- gills combined with high rates of catch were related to large populations of Table 26. —-Length frequency distribution of bluegills caught during years at Ridge Lake. od" and "poor" fishing Length Class Center in Centimeters September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 49 these fish. Bluegill fishing was satisfac- tory if the estimated bluegill population exceeded 2,500 fish per hectare of which more than 1,000 were 15 cm or longer. However, in 1950 the catch of bluegills was poor in spite of the fact that the lake contained 7,138 of these fi.sh per hectare ( Table 3 ) . The poor catch may have occurred because only 149 of the 7,138 bluegills were of desirable sizes (15 cm or longer) and fishermen were soon disappointed by the fact that they were unable to catch bluegills of worth- while sizes. Table 30 shows the average numbers of large and small bass and large and small bluegills and their total weights, respectively, per hectare in 3 poor fish- ing years and 3 good ones. These data are computed from data in Tables 28 and 29. Important differences in blue- gill average numbers and weights in Table 27. — Length frequency distribution of largemouth bass caught during "good" and "poor fishing years at Ridge Loke. Length 50 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 I* .5 ^ 51^ r s X 2 September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 51 52 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 Table 30.— Estimated overage numbers and weights of largemouth bass and bluegllls per hec- tare in Ridge Loke in 3 years when fishing was good and 3 years when fishing was poor. Largemouth Bass Per Hectare Bluegllls Per Hectare Average Average Average Weight Average Weight Num- in Kilo- Num- in Kilo- ber grams ber grams Poor Years Large 59 175 SmaU 123 194 Total 182 41.6' 369 17.1' Good Years Large 73 1,315 Small 158 1,103 Total 231 54.6' 2,418 152.3' «These wei_ghts may be 10-20 percent higher than the actual weights in the lake at the time of fishing because of weight gains in the uncaptured segments of the population in the time between the catch and the next draining census or between the return of fishes after a census and the catch. good and poor years are much greater than are differences in largemouth bass numbers and weights. Also clearly evi- dent are the great differences in the numbers of catchable bluegills per hec- tare in the good and poor years. THE EFFECTS OF MANAGEMENT TECHNIQUES ON FISH POPULATIONS AND ANGLING Four operational techniques were fol- lowed at Ridge Lake in the 1941-1963 period; the results of one of these (the use of hybrid sunfishes) must be disre- garded because circumstances prevented a true test. The others were (i) the bi- ennial draining and culling operation, (ii) the fall drawdowns, and (iii) the period of stable water levels. Each of these operational techniques influenced the catch of fish; they also had marked effects upon the fish populations as ex- posed by draining censuses. The period of biennial draining and culling extended over 10 years, and the culling operations could have affected the catch of fish in 1943-1951. However, the lake was closed to fishing in 1943, and so a consideration of fishing results must be limited to the other 8 years. In all cases fishing during the season immediately following a March draining and culling operation must have been different from fishing during the second fishing season of the biennium because of the spawns of fishes and the growth of fishes to catchable sizes that took place in both years of each 2-year period. Also the period between March 1949 and March 1951 must have been at variance with the others because of the fishes' crowded living conditions in 1949 brought on by the failure of the lake to refill completely. Certainly spawn sur- vival in 1949 must have been lower than usual because of the greater than usual density of the bass population during that season. One would expect the effects of the first September drawdowni of the lake level to be evident in the catch of fishes in the 1952 fishing season. The draw- down of September 1952 undoubtedly had an effect on the fish population ex- posed in the March draining census of 1953. In view of the facts that not all of the fishes taken in the 1953 draining census were returned to the lake and that the complete draining of the lake changed the food-feeder relationships, it would be unreasonable to consider the 1953 catch as being wholly influ- enced by the drawdown. After the 1953 census and fishing season, drawdowns were made in the Septembers of 1953, 1954, and 1955. These drawdowns affected the fishing seasons of 1954 and 1955, and their effects were further exposed in the drain- ing census of 1956. Thus, drawdown- oriented fishing seasons were those of 1952, 1954, and 1955. Of these, that of 1952 was affected by a lake surface area reduction of 69 percent and those of 1954 and 1955 by an area reduction of about 35 percent. These differences had varying effects upon the fish populations (as shown by the censuses of 1953 and 1956 ) and must have affected the hook- and-line catch also. The stable water period described elsewhere lasted from April 1956 when September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 53 the lake had refilled after the March 1956 draining to October 1959 when the lake was again drained. Thus the period of stable waters lasted for three winters and four growing seasons for fishes (April to October). During this period the numbers of fishes were allowed to increase without any culling or the re- strictive effect of the drawdown. Fish- ing in 1956 was more influenced by the spring draining than by the nearly stable water levels that were present during the summer fishing season. However, the constantly stable lake in 1957, 1958, and 1959 must have affected the fish popu- lation and the fishing. Thus, the stable water period may be considered to have lasted about 3 years. In Table 31 an attempt has been made to compare the average catches of desir- able-sized bass ( 25 cm or longer ) , blue- gills, and warmouths (15 cm or longer) made under the three operational tech- niques described above, including eight seasons of biennial culling, three sea- sons of annual fall drawdowns, and three consecutive seasons of stable water levels. It is evident from this table that larger average numbers and total weights of bass were taken per season during the period of biennial culling than under the other management tech- niques. Annual fall drawdowns stimu- lated annual spawns of largemouth bass and increased the numbers of small ones without apparently improving the catch of large bass. The catch of large bass was even smaller under stable waters than under the influence of drawdowns. This reduced catch may have been the result of a large, constantly available supply of small bluegills suitable for bass forage; however, the draining cen- sus of 1959 showed that only 124 bass longer than 24.9 cm were present after the four growing seasons of stable waters (Table 8) although 651 bass longer than 20 cm were put back after the cen- sus of 1956 (Table 2). This reduction in mature bass indicates that the bass population was not holding its numeri- cal strength during this period. "3 2 u>e 2 w ° c-H -5 S 2 t~ -H 54 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 Fig. 9.— Fishermen with their catches on the laboratory pier. Their fish are weighed, measured, and "scaled" for age determination. These data, the time spent in fishing, and the kinds of bait ond tackle used are recorded on individual creel cards. When all of this information has been collected for eoch fisherman, his state fishing license, which has been held at the laboratory, is returned to him. The greatest average numbers and weights of bluegills and warmouths were caught under stable water condi- tions (Fig. 9) although the average sizes of the fishes caught were greater during the drawdown period. As men- tioned previously, the large catch in the stable water period probably was the re- sult of high population density and food competition; the draining census indi- cated that bluegills and warmouths of desirable sizes were more numerous dur- ing the drawdown period. With the con- stant gradual buildup of bluegills during the stable water period, the bluegill population might have eventually be- come so dense as to cause severe food competition and stunting. This com- petition would have created a situation in which many bluegills might have been caught but few would have been of desirable sizes. DISCUSSION The study of the management of the fishes of Ridge Lake over the period 1941-1963 (which still continues) is possibly the longest continuous investi- gation ever made of a warmwater fish population in a small artificial lake. In this 23 years the lake was drained com- pletely and the fish population was cen- sused nine times. Following these cen- suses certain numbers and sizes of fishes of one or several species were returned to the partially reflooded lake basin above the dam and the lake basin was allowed to refill. Each summer, except for those of 1941 and 1943, the lake was opened to con- trolled public fishing to allow us to gather a complete record of fishing; number of fishermen; time spent; catch by species, numbers, and sizes; and kinds of tackle and baits used, inclu- September, 1969 Bennett ct ah: Largemouth Bass in Ridge Lake 55 ding a comprehensive breakdown of types and colors of a huge variety of artificial fish lures. Data presented in this paper do not include an analysis of fish- ing other than the time spent in fishing and the catch of fishes, and these are cited for their relevance to the manage- ment techniques that were applied. The real test of management lies in the rela- tive numbers and sizes of fish caught under each system. No attempt has been made to include growth data based on scale collections made from creel censuses and during lake drainings since 1951. Some of these scales were read to furnish growth data shown in the report of 1954 (Bennett 1954a). Comparative growth of the im- portant species of fish in Ridge Lake under various management techniques will be presented in a future paper. The fish population of Ridge Lake has shown a great deal of variability in species abundance, size distribution, and standing crops and has demonstrated the complexity of fish population dy- namics. This complexity suggests that one might question the validity of cer- tain types of "results" from population studies of short duration. Present and future observations of the responses of this warmwater fish population to new management practices will be particu- larly valuable because of the backlog of data dealing with this population's past variations. At the time the Ridge Lake study was begun, fishermen generally held the mis- conception that natural reproduction and survival were inadequate to maintain populations of game fishes and panfishes and that an annual stocking of finger- lings was necessary to insure good fish- ing. Now, 27 years later, no one familiar with fisheries literature believes that natural reproduction of warmwater fishes is unable to maintain their populations. Thus, one of the original purposes of the study has disappeared: that of test- ing the natiiral fecundities of several important species of warmwater fishes. In this connection it is of some in- terest to note that the 435 largemouth bass released in Ridge Lake in 1941 were the only source of 29,700 bass that have been permanently removed from the lake since then (1941-1967) and that the 129 bluegills released in 1944 have produced more than 400,000 living offspring of which 390,000 have been permanently removed. These figures for the two species probably indicate some- thing of their relative abilities to expand their populations in Ridge Lake, i.e., the bluegills in diis environment were at least 10 times as effective in expanding their populations as were largemouth bass. Within this bass-bluegill complex, warmouths stocked in 1949 (138 fish) produced no more than 10,000 fish (6.5 cm and larger) in 18 years. As was expected, channel catfish failed to reproduce successfully in Ridge Lake. A stream fish that grows well in lakes, the channel cat must have special spawning conditions or it cannot main- tain its numbers. One channel catfish fingerling was captured in one draining census, indicating that these fish had attempted to reproduce or gained access to the lake by some other means. Black bullheads, yellow bullheads, carp, Ni'hite suckers, and green sunfish were indigenous to the Ridge Lake watershed and were exposed as inhabi- tants of Ridge Lake in one or more draining censuses; black bullheads and green sunfish were sometimes caught by fishermen. However, the removal of these fishes whenever they appeared in a drain- ing census was sufficient to keep them from significantly increasing their popu- lations. For unknown reasons, green sun- fish and black bullheads were much less common in the census of 1953 and there- after than they had been in the period 1941-1951. After we compared fishermen's catches made in a season immediately prior to a draining census with the fishes ex- posed in the draining census, it became evident to us that one should use cau- tion in appraising a fish population on the basis of the annual hook-and-line 56 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 catch. For example, in 1962 fishermen caught 145 bass, of which 80 were be- tween 25 and 45 cm and the rest smaller. This was a poor catch of bass, and fishermen agreed openly that the lake contained no large ones. When the lake was drained in March of the following year, it was found to contain 90 bass ranging in length from 46 to 58 cm and in weight from 1.6 to 4.1 kg; in fact, 11 bass belonged to the oldest fin mark group (8—10 years old) and averaged more than 2.9 kg. For unknown reasons fishermen had been unable to catch these large fish. The concept presented by Swingle & Smith (1938, 1939) that single species or mixed populations of warmwater fishes build up to a maximum constant weight within one growing season and then remain at about that weight for an indefinite time has not been demon- strated by the Ridge Lake censuses. Largemouth bass total weights have varied from 240 kg to 412 kg (exclusive of the 1953 census after 2 years of severe drawdowns, when the bass weight was 205 kg); bluegill total weights have ranged from 709 to 1,578 kg, and the total weight for all fishes has varied ( after 1945 and exclusive of 1953 ) from a low of 1,336.7 kg to nearly double that amount-2,092.5 kg (Table 1). In view of such large variations in standing crops of fishes at Ridge Lake, it seems ridiculous to assume that fish populations remain constant in total weight or that annual hook-and-line yields do not vary greatly. D. Homer Buck and Charles F. Thoits have found similar unexplained variations in single- species populations of fishes in 0.4-ha ponds (personal communication 1968 and in press ) . Saila ( 1958 ) published a paper using Ridge Lake data from the 1954 report ( Bennett 1954a ) in which he attempted to demonstrate mathematically that a size limit on largemouth bass would eventually assure a greater number of large fish in the catch than was possible without a size limit. In the early years of fishing at Ridge Lake (1942, 1944, and 1945) we imposed a minimum length limit of 25 cm ( 10 inches ) , while beginning in 1946 fishermen were asked to bring in all bass regardless of length. This change in policy resulted in periods with and without length limits on bass. However, these periods were also marked by different culling lengths for bass in the draining censuses, a point apparently not recognized by Dr. Saila. After about half of the stunted 1941 brood of bass (average length about 18 cm) were removed in the 1943 cen- sus, the minimum culling length was 25 cm (10 inches) in the 1945 and 1947 censuses, followed by 23 cm ( 9 inches ) in the 1949 census and 20 cm ( 8 inches ) in the 1951 census. These lengths were represented by the following average weights for the smallest bass returned to the lake after these censuses: in 1945, 142 fish averaged 0.33 kg (0.72 pound); in 1947, 310 fish averaged 0.41 kg (0.91 pound); in 1949, 917 fish averaged 0.23 kg (0.51 pound); and in 1951, 619 fish averaged 0.27 kg (0.59 pound). These differences in sizes and numbers of fish returned were great enough to influence the numbers and sizes of fish caught by anglers, and it was simply circumstance that controlled the timing of the periods when length limits were enforced and when they were taken off to match the larger and smaller bass culling sizes. In comparing populations of large- mouth bass and bluegills exposed in the nine censuses, it was of particular in- terest that the bass population equaled or approached 56 kg per hectare in four of the censuses, once when the lake contained a nearly pure culture of bass and twice when numbers of bluegills were present. This suggests that 56 kg per hectare may be about the maximum carrying capacity of the lake for bass. No comparable maximum for bluegills was suggested by the census data. The heaviest population of bluegills was found in the census of 1947 when 216.7 kg per hectare were present. The next largest population by weight appeared September, 1969 Bennett et ah: Largemouth Bass in Riix;e Lake 57 in 1959 after four growing seasons of constant water levels when 181.2 kg per hectare of bluegills were present. Other censuses showed lesser weights of blue- gills. There appeared to be an inverse re- lationship between weights of bass and bluegills (r=— 0.91). The lowest weights of bluegills (exclusive of the drawdown period) were present when bass weights were highest and vice versa. The biennial draining operations with the culling of all bass of less than 25, 23, or 20 cm and all bluegills except 1,000-4,500 of the larger ones resulted in a buildup of desirable-sized bass and relatively high hook-and-line catches of these fish. This management technique did not stimulate the development of large bluegill populations, and with one exception seasonal catches of bluegills were much less than 50 kg per hectare. Severe early fall drawdowns that re- duced the lake surface area by 69 per- cent reduced the total weight of the fish population but not in proportion to the lake surface area or volume reduc- tion. More moderate fall drawdo^vns (3 meters, 35-percent surface area reduc- tion) had no significant effect on the total weight of fish. The drawdown technique appears to be the single most important tool in the management of warmwater fish populations inhabiting lakes that can be artificially reduced in area by the release of water. Prior to 1956 we believed that a 50- percent reduction in lake surface area was necessary to effect significant changes in a fish population. After the 1956 draining census which followed 3 successive years of moderate September drawdowns ( 35-percent reduction of the lake surface area) it was obvious that drawdowns to reduce the lake surface area by less than 50 percent were having a beneficial culling effect upon the smaller sunfish species of Ridge Lake without causing any significant reduc- tion in the overall weight of fish that the lake was supporting (Table 3). Bass in the 1956 census were represented by a larger total weight of small fish (less than 25 cm total length) than in any other census except that of 1943 and a smaller weight of large fish than in any preceding census except those of 1943 and 1953 (Table 8). After the mild drawdowns the lake was supporting a substantial population of small bass due to the annual culling action of the draw- downs on the small sunfishes (largely bluegills) that might attack bass fry and limit their survival. The severe drawdowns of 1951 and 1952 caused a drastic reduction in blue- gills so that only 7,500 ( 1,087 per hec- tare) were present in the 1953 census ( Table 3 ) . More than half of these were larger than 15 cm and the rest smaller (Table 9), giving a catchable popula- tion of about 640 bluegills per hectare. According to our creel records, this population of large bluegills was nu- merically too small to give satisfactory bluegill fishing (one or more fish per man-hour ) . After the period of moderate drawdowns in 1953, 1954, and 1955 the bluegill population numbered 17,180 ( 2,497 per hectare ) ( Table 3 ) of which slightly more than half (8,661, or 1,258 per hectare) were of desirable sizes (Table 9). Bluegill fishing was quite good in 1955 ( a year prior to a draining census; the catch was almost one fish—0.94— per man-hour), and the bluegill popu- lation contained more large fish than in any other year of the 19 years when bluegills were present in Ridge Lake. The fact that the fishermen's catch of bluegills in several other years exceeded that of 1955 suggests that a certain amount of food competition is impor- tant in the production of high pole-and- line yields. The knowledge of how to produce superior numbers of catchable- sized bluegills has been carried further since 1963 in a study which will be reported at a later date (Fig. 10). Many small artificial reservoirs re- ceive heavy human use, and as a con- sequence the normal fish predators, such 58 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 as herons, kingfishers, cormorants, and other wild fish-eating birds, are scarce or absent. Also in recent years the num- bers of fish-eating birds are believed to have become considerably smaller than formerly because of their reduced fecun- dity reportedly caused by their ingesting pesticides carried by fishes (Wurster & Wingate 1968). This reduction in the numbers of fish predators has removed a natural check on overpopulation, giv- ing the drawdown technique increased importance as a population regulator. One of the problems associated with drawdowns is to educate fishermen to the usefulness of an annual or biennial water release which may leave imsightly mud flats around the lake edges in early fall and winter. Hopefully, the reservoir will refill again by the next fishing season whi'i the improvement in the fish popu- lation will be reflected in better fishing. There is no longer any question whether a drawdown will cull certain kinds of the smaller fishes in a popula- tion, an action always followed by im- proved survival of bass fry. This obser- vation has also been recorded by Pierce, Frey, & Yawn ( 1965 ) in their draw- downs of Georgia ponds and by Lantz, Davis, Hughes, & Schafer ( 1967) in their drawdowTis of Louisiana reservoirs. Whether these fry will survive in pro- portional numbers to augment the adult bass population is related to the abun- dance of predators of fingerling and yearling bass. However, the evidence indicates that bass are most vulnerable to predation in the embryo, yolk-sac fry, free-swimming fry, and small finger- ling states, i.e., from the time the eggs are laid to the time the small bass are about 25 mm long. During this period they may be affected adversely by weather changes and they are vulnerable to attack by small fishes ( such as stunted bluegills) and predacious aquatic in- sects. When they reach lengths approxi- mating 50 mm, they become strong swimmers and are too large to be eaten by fishes other than the fish-eating spe- cies, such as larger bass, pickerel, gars, and others. Thus, the chances of survival of a new year-class of bass beyond the fry and small fingerling stages may be poor if a lake already contains a large population of yearling bass ( 13-18 cm ) ready to prey upon them. Actually, with Fig. 10.— Fishermen angling for bluegills in deep water using night crawlers or catalpa worms larvae of the catalpa sphinx moth) for bait. The distance from the boat to the pier is about 35 meters. September, 1969 Bennett et ah: Largemouth Bass in Ridge Lake 59 a large yearling bass population already present, there is little need for a strong new year-class to maintain a high popu- lation and replace bass caught by angling. Unfortunately, in planning a draw- down for a specific lake it is impractical to apply "cookbook" methods. Adequate sampling should indicate the level of overpopulation and stunting, and the severity of the drawdown should var\' directly with the severity of stunting. If overpopulation were the only considera- tion, the situation still might be fairly simple. However, lake habitats varv' in amounts of protective cover, and basin contours differ to such an extent that a drawdown designed to give a selected surface area reduction in one lake may not produce a comparable surface area reduction in another. The knowledge of how to use the drawdowTi as a management tool in a specific lake must come through trials and appraisals of their effects. Lantz et al. (1967) and Hulsey ( 1959 ) mention an additional value of drawdowns in controlling pota- mogetons and naiads. However, draw- downs may be responsible for increasing vegetation of certain kinds, such as Potamogeton crispiis L., which may be given an opportunity to get started in deeper water while the lake level is down. ^^'hether a drawdown should be made every year is still an open question and probably depends upon the severity of the stunting problem prior to the pre- liminary' test. At Ridge Lake 2 succes- sive years of severe drawdowns were be- lieved to have reduced the population more than was necessary (Tables 1 and 3, 1953 census ) . Perhaps the lesser draw- downs of 1953-1955 would have im- proved the bluegill population more than they did if the>' had been started in 1951 and carried through 1955 with- out the 1953 draining census. It is evi- dent that testing the drawdown tech- nique is a promising field for a great deal of additional research. The period of stable water levels that extended from April 1956 to the draining census of October 1959 constituted a period of "no management" of the fish population. During this period the bass population reached a weight low (ex- cept for the census of 1953 after 2 suc- cessive years of severe drawdowns ) , and the bluegills reached a numerical high of 13,469 per hectare (Table 3) and a weight high second only to that of 1947. As mentioned above, bluegill num- bers were curtailed by drawdowns and biennial cullings. The latter gave the bluegills two growing seasons to make a comeback (Table 13), and the maxi- mum weight buildup for these 2-year periods occurred in 1945 and 1946, with 9,152 individuals per hectare expiosed in the 1947 census. Stable water levels actually existed in the four growing seasons of 1956-19-59, terminated by the fall census of October 1959, and in the three gro^^'ing seasons of 1960-1962, terminated by the spring draining census of March 1963. The bluegill population was numerically larger in 1963 after 3 years without drainings or drawdowns (Table 13) than it had been in any of the 10 previous 2-year periods be- tween drainings, 1941-1951, and was e\'en larger in 1959 after four seasons without drainings or drawdowns than it had been after three such seasons. \Miile these data are not conclusive, they suggest that the bluegills in Ridge Lake, if left alone, would constantly in- crease in numbers until within a rela- tively short time the lake would become oveqiopulated with a stunted popula- tion of these fish. As described in the section on the stable water period, the test of the use- fulness of hybrid sunfishes in Ridge Lake was invalidated when the lake was contaminated by bluegills and war- mouths, the parent t>'pes of the bluegill X warmouth hybrids being tested. Nei- ther of these two pure species appeared in the creel census of 1960, but a few blue- gills were observed in the lake in 1960 and a few of both species were caught by fishermen in 1961 (Table 19). Both 60 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 species were common during the sum- mers of 1961 and 1962, but the original source of these fishes is unknown. So that Ridge Lake fishermen could legally keep only the largest hybrids, we placed a minimum length limit of 17.5 cm on these fishes. In 1960 fisher- men caught 3,772 of the 4,503 hybrids that had been stocked in April, returning 3,708 and keeping 64. In 1961, after 448 additional hybrids (red-ear x warmouth) had been added in May, fishermen caught 4,890 hybrids, keeping 194 blue- gill X warmouth and 6 red-ear x war- mouth hybrids and returning 4,690. Be- cause the fishermen could not with certainty or did not separate the two kinds of hybrids among the fishes re- leased, it was impossible to compute the ratio of the two kinds in the catch. In 1962 all length restrictions on the hybrids were removed, and fishermen caught and kept 1,075 bluegill x war- mouth and 134 red-ear x warmouth hy- brids. After the 1962 fishing season when hybrids of any length could be taken, the population remaining to be exposed in the 1963 spring draining census con- sisted of only 8 bluegill x warmouth and 64 red-ear x warmouth hybrids. The small numbers of hybrid sun- fishes in the anglers' catch of 1962 and in the spring draining census of 1963 suggest that many of these hybrids died as a result of hooking injuries sustained in being caught and released. This hy- brid study was reported in a junior author's recent publication on hybrid sunfishes (Childers 1967:189). The hy- brid sunfishes in Ridge Lake showed biting characteristics similar to those of hybrid sunfishes in other tests, i.e., they were highly aggressive and bold in tak- ing fishing baits and were very easily caught. It was estimated that in 1962 at Ridge Lake 65 percent of the 1,209 hybrid sunfishes were caught in the first 5 days of fishing and 81 percent were caught in the first 10 days. The catch of largemouth bass during the hybrid sunfishes period, 1960-1962, inclusive, was the poorest of any period between draining censuses (Table 19). This poor catch may have been influ- enced by two factors: (i) the small number and poor physical condition of the bass returned to Ridge Lake after spending the winter of 1959-1960 in a hatchery pond ( which probably slowed the rebuilding of the bass population) and (ii) the introduction in 1960 of 585 lake chubsuckers into the lake (which may have increased the bass food supply and made them less vulner- able to angling). In 1960 the estimated number of bass fry was 3,050 per hec- tare (Table 10). This fry population could have been the origin of a large new year-class of bass. In 1961 no schools of young were seen, and in 1962 only one school was observed. Yet, in the 1963 draining census we found the numerically largest bass population ex- posed in any census (Table 1), 6,218 bass, of which 6,042 ranged in size from 12.7 to 25 cm and were quite obviously members of the 1962 year-class. A com- paratively small number of larger bass (176) was also present, of which 86 were fin clipped from previous censuses. Of the 299 bass moved back to the lake in 1960, 44 were caught in 1960, 48 in 1961, and 15 in 1962, a total of 107 of the 299. Eighty-six marked bass were taken in the 1963 draining census, and only 62 bass representing the 1960 and 1961 year-classes were present. Fisher- men had caught 156 bass of these same year-classes in 1961 and 1962. These figures indicate that the bass population was characterized by low production and survival rates in 1960 and 1961. Only in 1962 was there an unusually high survival of a relatively small spawn. It therefore seems reasonable that, at least prior to 1962, the presence of a dynamic population of lake chubsuckers had little effect on the bass joopulation or on bass fishing although from 1960 to 1963 the chubsuckers increased from .585 to 3,182. One of the most interesting points to September, 1969 Bennett et al.: Largemouth Bass in Ridge Lake 61 come from the study of the fishes of Ridge Lake was the capacity of the largemouth bass and bluegills to expand their populations when their numbers were decimated by artificial culling such as was done in the biennial draining period 1941-1951 and every time we drained the lake thereafter. One might assume from the way these populations recovered that such adversity was com- mon and that these fishes had evolved under environmental catastrophies that produced severe stresses. Even what might appear to be abnormal losses of larger bass through angling—56-63 per- cent of the a\'ailable numbers of marked bass per fishing season ( Table 17 )—were quickly replaced through recruitment and growth. In contrast, stable water levels and insufficient culling (i.e., protection of small fishes) eventually resulted in less desirable fish populations, at least from the standpoint of numbers of large fishes available for angling. This fact indicates that there is a great deal of room for improvement in fish manage- ment to provide better fish populations for angling. But such a potential for improvement cannot become a reality until anglers and fish managers modify much of their present thinking. SUMMARY 1. — Ridge Lake was stocked with 335 yearling largemouth bass and 100 adults in 1941, 129 bluegills in 1944, 138 warmouths in 1949, and var\'ing numbers of channel catfish in 1951, 1952, and 1957. After an attempt to remove all bluegills by draining the lake and leaving the lake basin emptv over the winter of 19.59-1960, 5S5 lake chubsuckers and 4,500 hybrid sunfishes were stocked in the spring of 1960. Since the beginning of this studv in 1941, 29,700 largemouth bass, 390.000 bluegills, and about 10,000 wannouths have been permanently removed from the lake. The lake now ( 1968 ) contains adequate numbers of all species stocked except channel catfish, which did not reproduce successfully in standing water. 2. — A complete creel census has been conducted at Ridge Lake each summer except in 1941 and 1943, when the lake was closed to public fishing. In addition, the lake was drained and the fishes were censused in the springs of 1943, 1945, 1947, 1949, 1951, 1953, 1956, 1959 (fall), and 1963, and selected kinds, sizes, and numbers of fish were held alive and re- stocked (Tables 1-4). 3. — In the nine draining censuses at Ridge Lake bass total numbers varied beUveen 1,500 and 6.000 and their total weights between 205 and 412 kg (Table 1). Bluegill total numbers ranged from 7,500 to 93,000 and their weights from nearly 450 to about 1,580 kg. \\'annouth populations varied but were always small. The total weight of channel cat- fish varied with the number present; a few grew to more than 4.5 kg each. Lake chubsuckers were stocked in 1960. Other fishes in the lake probably came from the M'atershed and were mainh" green sunfish, black bullheads, yellow bullheads, carp, and minnows. These never made up more than a small part of the population. 4. — Standing crops of largemouth bass varied between 35 and 56.6 kg per hectare (Table 3). In four censuses the standing crops of bass approached or slightly exceeded 56 kg per hectare, sug- gesting that this weight may represent the maximum this lake will support. There was no increase in the standing crop of bass when bluegills were present over that of bass by themselves. Stand- ing crops of bluegills varied from 65.3 to 216.7 kg per hectare. There was no suggestion of a maximum standing crop of bluegills. The standing crop of war- mouths never made up more than 5 percent of the total number or \\'eight of any fish population exposed in a drain- ing census. 5. —When substantial numbers of both bass and bluegills were present ( Table 3 ) , the standing crops of all fish 62 Illinois Natt-'ral History Survey Bulletin Vol. 30, Art. 1 in tlie censuses of Ridge Lake varied between 157.2 and 287.4 kg per hectare. Usually when bass weight increased, bluegill weight decreased, and vice versa. 6. — Biennial lake draining with the culling of small bass and bluegills in- creased the numbers of large bass and was selective for fast growing ones, i.e., bass that did not attain lengths of 20-25 cm in two growing seasons were per- manently removed from the lake. 7. — Early fall drawdowns drastically reduced the numbers of small bluegills and allowed an increase in the numbers of large ones because of increased growth rate ( Table 9 ) . Drawdowns maintained large numbers of small bass but did not increase the numbers of large ones (Table 7). The reasons for reduced populations of large bass are unknown. 8. — Four growing seasons without lake drainings or drawdowns resulted in the production of a large numerical population of bluegills and a small population of largemouth bass (Tables 1 and 3). 9. — Hybrid sunfishes were more easily caught than the pure parent species, but offered little competition to the parent species in Ridge Lake. 10. — Bass fry production after a drain- ing and culling of small fishes of all kinds averaged 7,917 per hectare; after drawdowns, 3,243 per hectare; and after 1 or more years of stable water levels, 1,023 per hectare (Table 10). 11. — Tlie ratios between estimated numbers of bass fry produced in census years during the 10-year period of bien- nial drainings and censusings and the number of yearlings of the same year- class caught by fishermen or appearing in the ne.xt census 21 months later varied from 29 to 1 (greatest survival rate) to 196 to 1 (lowest survival rate) (Table 11). Probably all of these ratios were abnormal, as during postcensus summers the numbers of bass fry pred- ators, such as small fishes and preda- cious aquatic invertebrates, were much reduced. 12. — There was no relationship or a negative relationship between the esti- mated numbers of bass spawners and tlie estimated numbers of fry produced (Table 12). However, there appeared to be a definite negative relationship be- tween large numbers of small bluegills and numbers of bass fry. In 1946, 1948, and 1950 when 2,500 or more small bluegills per hectare were present, bass fry survival was negligible (Table 12). 13. — Expansion of the bluegill popu- lation in Ridge Lake was positively re- lated to time and negatively related to drawdowns and to "dominant" popula- tions of bass ( Table 13 ) . However, bass were unable to control bluegills com- pletely except when given the assistance of fall drawdowns. 14. — One largemouth bass belonging to the 1941 year-class and marked in 1943 was taken for the last time in the census of 1956. A few other marked bass lived for 10, 11, and 13 years, but most marked bass disappeared at ages 7-10 years. Seasonal exploitation rates from catches of marked largemouth bass ranged from 1.5 to 63 percent (Table 14). But even with the higher exploitation rates there was no evidence of overfishing, and re- placement rates were increased through recruitment and accelerated growth rates. 15. — Natural, nonfishing mortality for largemouth bass at Ridge Lake ( figured for 2-year periods) was 33 percent for bass weighing 0.07-0.34 kg, about 14 percent for sizes between 0.35 and 1.81 kg, 39 percent for sizes between 1.82 and 2.27 kg, and 73 percent for sizes over 2.27 kg (Table 16). 16. — The nine draining censuses with the culling of small fish and invertebrate fish foods influenced the hook-and-line catch in the postcensus angling seasons to the extent that yields averaged 55.9 percent of the bass available (represent- ing 62.6 percent of their weight) (Table 17), while in precensus fishing seasons, not influenced by culling, an average of 60.3 percent of the number of bass available (representing 39.2 percent of September, 1969 Bennett et al: Largemouth Bass in Ridge Lake 63 their total weight ) were captured ( Table IS). Comparable averages for bluegills for postcensus seasons were 38.1 percent (representing 49.1 percent of weight) and for precensus seasons 49.7 percent (representing 46.0 percent of the total weight of bluegills ) . 17. — Fishing pressures ( from boats only; no bank fishing) at Ridge Lake varied from 222 man-hours to 791 man- hours per hectare per season ( Table 20 ) . Average seasonal rates of catch ranged from 0.1 to 1.8 fish per man-hour; these catches represented average seasonal rates of 7-34 hours to catch 1 kg of fish. These averages include all of the unpro- ductive time spent in fishing by fisher- men who caught nothing as well as pro- ductive time spent bv those who caught fish. 18. — Rates of catch varied so that seasonal fish yields ranged from 3.3 to 117.0 kg per hectare, giving an average for 21 years of 47.7 kg per hectare (Table 23). Five to 10 times as many fishes were caught in good fishing years as in poor ones. 19. — In 3 poor fishing years the aver- age number of large bass present per hectare was 59, and small ones averaged 123, a total of 182 per hectare. For blue- gills the average number of large fish per hectare was 175, and small bluegills averaged 194, a total of 369 per hectare (Tables 28 and 30). In 3 good fishing years the average number of large bass present per hectare was 73; the number of small, 158; the total 231 per hectare. For bluegills the average number of large fish per hectare was 1,315; the number of small, 1,103; the total, 2,418 per hectare (Tables 29 and 30). Num- bers ( and weights ) of fish were the most important differences between good and poor fishing years. The competition, pre- sumably for the available food, produced by large numbers of fishes made fishing returns greater when populations were larger. 20. — The average annual catch of desirable-sized largemouth bass (25 cm or longer) per hectare was 47, weighing 19.2 kg, under biennial draining and culling; 30 per hectare, weighing 11.7 kg, under drawdowns; and 27 per hec- tare, weighing 12.1 kg, under stable water levels. For desirable-sized blue- gills ( 15 cm or larger ) the average an- nual catch per hectare was 133, weigh- ing 13.0 kg, under biennial culling; 304 per hectare, weighing 33.2 kg, under drawdowns; and 472 per hectare, weigh- ing 41.9 kg, under stable water le\'els (Table 31). LITERATURE CITED Bennett, George W. 1954a. Laigeniouth bass in Ridge Lake, Coles County, Illinois. Illi- nois Natural History Survey Bulletin 26(2); 217-276. 1954fc. The effects of a late-summer drawdown on the fish population of Ridge Lake, Coles County, Illinois. North Ameri- can Wildlife Conference Transactions 19: 259-270. _, and Leonard Durham. 1951. Cost of bass fishing at Ridge Lake, Coles County, Illinois. Illinois Natural History Survey Biological Notes 23. 16 p. Chllders, William F. 1967. Hybridization of four species of sunfishes ( Centrarchidae ) . Illinois Natural History Survey Bulletin 29 (3):159-214. Crance, Johnie H., and L. Glenn McBay. 1966. Results of tests with channel catfish in Alabama ponds. Progressive Fish- Culturist 28(4):193-200. DtmHAM, Leonard, and George W. Ben- nett. 1949. Bass baits at Ridge Lake. Illinois Wildlife 4(2): 10-13. , and 1951. More about bass baits at Ridge Lake. Illinois Wildlife 6(2): 5-7. HuLSEY, Andrew H. 1959. A proposal for the management of reservoirs for fisheries. Southeastern Association of Game and Fish Commissioners Proceedings for 1958, 12: 132-143. Lantz, Kenneth E., James T. Davis, Janice S. Hughes, and Harry E. Schafer, Jr. 1967. Water level fluctuation—its effect on vegetation control and fish population man- agement. Southeastern Association of Game and Fish Commissioners Proceedings for 1964, 18:483-494. Larimore, R. Weldon. 1957. Ecological life history of the warmouth (Centrarchidae). Illinois Natural History Survey Bulletin 27 (l):l-83. Markus, Henry C. 1932. The extent to which temperature changes influence food con- sumption in largemouth bass {Huro flori- dana). American Fisheries Society Trans- actions for 1932, 62:202-210. Pierce, Phillip C, John E. Frey, and Henry M. Yawn. 1965. An evaluation of fishery management techniques utilizing winter drawdowns. Southeastern Association of Game and Fish Commissioners Proceedings for 1963, 17:347-363. Saila, Saul B. 1958. Size limits in largemouth black bass management. American Fish- eries Society Transactions for 1957, 87: 229-239. Swingle, H. S., and E. V. Smith. 1938. Man- agement of farm fish ponds. Alabama Poly- technic Institute Agricultural Experiment Station. 6 p. , and 1939. Increasing fish production in ponds. North American Wild- life Conference Transactions 4:332-338. Wolf, Philip. 1951. A trap for the capture of fish and other organisms moving down- stream. American Fisheries Society Trans- actions for 1950, 80:41^5. Wurster, Charles F., Jr., and David B. Wingate. 1968. DDT residues and declin- ing reproduction in the Bermuda Petrel. Science 159(3818): 979-981. 64 INDEX Area reduction, rate of at Ridge Lake, 1 B Bass increased difficulty in catching, 3 length limits on, 56 mortality factors and length of life, 29-35, 62 original stock, 3, 61 population expansion potential of in Ridge Lake, 60-61 removal of from Ridge Lake, 3, 55, 61 Ridge Lake carrying capacity of, 56 vulnerabihty as fry, 26-27, 58 Bass fishing baits, efficiency of, 1 bass removed in 23 years of, 40 best years of, 39^0, 48-49 cost of, 1 length frequency distribution of bass caught in good and poor years, 47^9 Bass fry, survival of as affected by number of bass spawners and fish population density, 27-28, 62 first 2 years, 26-27, 62 Bass spawn method of making inventory, 24-25 survival as related to biennial culhng, drawdowns, and stable water levels, 25-26, 62 Biennial draining of Ridge Lake, 1, 62 method, 5-8 Biennial culling of largemouth bass effects of, 57 minimum sizes returned after censuses, 14 permanent removal of fish after censuses, 15, 62 Biological efficiency, relative, of bass and blue- giUs, 3, 55, 57, 61 BluegiUs largest numbers of in draining censuses, 8, 10, 14 original stock, 3, 61 population expansion potential of in Ridge Lake, 28-29, 60-61 removal attempts, 3, 8, 19-20 removal of from Ridge Lake, 3, 55, 61 Ridge Lake carrying capacity of, 56 Bluegill fishing best years of, 40-41 bluegills removed in 19 years of, 40 effect of hunger on, 41 importance of food competition, 41, 57 length frequency distribution of bluegills caught in good and poor years, 47-48 Buck, D. Homer, 56 Bullheads, black contribution to catch, 4 entry into Ridge Lake, 4, 61 removed in draining, 55, 61 Bullheads, yeUow contribution to catch, 4 entry into Ridge Lake, 4, 61 removed in draining, 55, 61 Carp contribution to catch, 4 entry into Ridge Lake, 4 removed in draining, 55, 61 Carrying capacity of Ridge Lake, variation in, 56 Catch of fish, total for 1941-1963, 39-40 Catfish, channel accidental mortalities, 44 best fishing season for, 40, 44 bonus fish, 3, 44 catch of, 1951-1963, 40, 43^4 contribution to catch, 3 maximum size in Ridge Lake, 3-4, 44 origin of fish, 3 reproduction in Ridge Lake, 55 return of stocked fish, 44 stockings of, 3, 61 Chubsuckers, lake, stocking in 1960, 4 Competition bass versus other species, 12 bluegills versus bluegill x warmouth hy- brids, 59 failure of hybrids to compete with blue- gills, 19-20, 62 Crance, Johnie H., 44 Creel censuses method, 4-5, 54 period of, 4 Davis, James T., 58 Draining censuses, 5-8, 61 culling of small fishes during_7-8 escape of small fishes during, 6 fishes returned after, 7, 9-11, 14, 36-37, 48, 54, 61 fishes taken in, 7-8, 10 holding fishes for restocking, 6-7 marking fish by fin clipping, 6, 29-35 mesh size of fish screens, 6 method, 5-6 mud "soup," 6 removal of indigenous fishes during, 4 wolf-type weir, 5 years and seasons of, 6-7 Drawdowns, 16-19 effect on lake bottom of, 16 effects on fishes of, 8, 10, 16-19, 62 late summer, 1, 16, 52, 57 method, 16 moderate, 16, 52, 57 65 66 Illinois Natural History Survey Bulletin Vol. 30, Art. 1 period of, 8, 16 refilling after, 16 severe, 1, 16, 52, 57 vegetation control by, 59 vegetation spread resulting from, 59 Dry Run Creek, 4, 6, 20, 45 Durham, Leonard, 1 English-metric equivalents, 2 Fertility of Ridge Lake, 2 Fish censusing {see draining censuses) Fish-eating birds, scarcity of, 58 Fish population natural maintenance of, 55, 61 total of Ridge Lake, 8, 10, 61 variability of, 2, 8, 55-56, 61 Fish yields by angling, 39^1, 45, 62-63 differences between lowest and highest, 46^7 Fishes permanently removed during draining, 14-16 Fishing catch per man-hour, 1942-1963, 39-41, 63 estimate of fish population in good years, 48, 51-52, 63 estimate of fish population in poor years, 48, 50, 52, 63 man-hours of per hectare, 39, 41, 45-47, 50-51, 63 Fishing season best for bass (1949, 1951), 39-40, 48^9 boat reservations, 4 daily periods of, 4 days closed, 4 months of, 4 recording fishermen's catches, 4 Fishing statistics, collection of, 5 Frey, John E., 58 M Management, effects of on angling returns, 52-54 Markus, Henry C, 19 McBay, L. Glenn, 44 Minnows inspection of, 5 entry into Ridge Lake of, 4 Mortality of bass, 29-35, 62 fishing and natural niortahty, 30-34 rates related to sizes and ages, 35 removal from the lake by methods other than direct capture, 30-34 effect of removing food during biennial draining, 36 Mortahty of bluegills after biennial draining, small numbers present, 36-37 in seasons prior to draining, 37-39 "Other" fishes, total weight of taken by an- gling, 40, 45 Pierce, Phillip C, 58 Population estimations from fishermen's catches, 55-56 Population expansion potential bass, 60-61 bluegills, 60-61 Rate of catch in fish per man-hour, 39, 41 Restocking after draining censuses, 9-11, 14, 36-37, 48, 54, 61 Ridge Lake area, 1 incomplete ecosystem, 2 location, 1 Growing season of fishes, 2 H Hatchery pond storage, effects of on large- mouth bass and channel catfish, 20 Hughes, Janice, S., 58 Hulsey, Andrew H., 59 Hybrid sunfishes, vulnerability to angling, 60, 62 Lake refilling, 1 Lantz, Kenneth E., 58-59 Largemouth bass (see bass) Lariniore, R. Weldon, 14 Limnology of Ridge Lake, 2 Saila, Saul B., 56 Schafer, Harry E., Jr., 58 Size distribution bass, 21-22, 24 bluegills, 23-24 Smith, E. v., 56 Soil erosion, 1 Stable water levels, 1, 62 allowed bluegill populations to expand, 8, 10, 19, 59, 62 effects on bass, 8, 10, 19, 59, 62 effects on bluegills, 8, 10, 19, 59, 62 period of, 8, 19, 59 Standing crops of fishes, 8-14, 61 bass, 8, 10, 12, 61 bluegills, 8, 10, 12, 14, 61 hypothetical maximum of bass, 12, 56, 61 in numbers and kilograms per hectare, 10 maximum weight supported by Ridge Lake, 12, 56, 61 September, 1969 Bennett et al. : Lakgemouth Bass in Ridge Lake 67 no hypothetical maximum of bluegills, 14, 56-57, 61 percentages by species, 13 range of numbers and weights, 8, 10, 61 reduction of bluegiUs after censuses, 10 reduction of bass after censuses, 10 warmouths, 14, 61 Stocking, original in 1941-1944, 3, 55, 61 Sunfish, green contribution to anglers' catch, 4, 45 entry into Ridge Lake, 4 Sunfish, longear, entry into Ridge Lake, 4 Sunfishes, hybrid, 1, 19-20, 45, 59-60, 62 stocking of, 4, 20, 61 Swingle, H. S., 56 w Warmouths catch of, 1950-1963, 40, 42, 44 caught on surface plugs, 41 efficiency compared to that of bluegills 3, 55 numbers in five censuses after 1949, 14 original stock, 3, 14, 41, 55, 61 Watershed of Ridge Lake, 1 White sucker, entry into Ridge Lake, 4 Wingate, David B., 58 Winter fish storage, 1959-1960 8, 20 Wolf, Philip, 5 Wurster, Charles F., Jr., 58 Thoits, Charles F., Ill, 56 Yawa, Henry M., 58 Some Publications of fhe ILLINOIS NATURAL HISTORY SURVEY BULLETIN Volume 28, Article 2. - The Fishes of Cham- paign County, Illinois, as Affected by 60 Years of Stream Changes. By R. Weldon Larimore and Philip W. Smith. March, 1963. 84 p., frontis., 70 fig., bibliogr., index. Volume 28, Article 3. - A Comparative Study of Bird Populations in Illinois, 1906-1909 and 1956-1958. By Richard R. Graber and Jean W. Graber. October, 1963. 146 p., 4 frontis., 32 fig., bibliogr., index. Volume 29, Article 1. — A Biological Investi- gation of the Fishes of Lake Chautauqua, Illinois. By William C. Starrett and Ar- nold W. Fritz. March, 1965. 104 p., frontis., 40 fig., bibliogr., index. Volume 29, Article 2. ^ Stocking and Sport Fishing at Lake Glendale (Illinois). By Donald F. Hansen. July, 1966. 54 p., fron- tis., 9 fig., bibliogr., index. Volume 29, Article 3. — Hybridization of Four Species of Sunfishes ( Centrarchidae ) . By William F. Childers. September, 1967. 55 p., frontis., 2 fig., color plate, bibliogr., in- dex. Volume 29, Article 4. - The Thrips, or Thysa- noptera, of Illinois. By Lewis J. Stannard. May, 1968. 338 p., frontis., 310 fig., bib- liogr., index. CIRCULAR 39. — How to Collect and Preserve Insects. By H. H. Ross. November, 1966. (Eighth printing.) 71 p., frontis._79 fig. 46. — Illinois Trees: Their Diseases. By J. Cedric Carter. June, 1964. (Third Print- ing, with alterations. ) 96 p., frontis., 89 fig. 49. — The Dunesland Heritage of lUinois. By Herbert H. Ross. (In cooperation with Il- linois Department of Conservation. ) Au- gust, 1963. 28 p., frontis., 16 fig., bibliogr. 51. — Illinois Trees: Selection, Planting, and Care. By J. Cedric Carter. August, 1966. 123 p., frontis., 108 fig. 52. — Fertilizing and Watering Trees. By Dan Neely and E. B. Himelick. December, 1968. (Second printing.) 20 p., 9 fig., bibliogr. 53. — Dutch Elm Disease in Illinois. By J. Cedric Carter. October, 1967. 19 p., fron- tis,, 17 fig. BIOLOGICAL NOTES 53. — Experimental Field Studies on Shade Tree Fertilization. By E. B. Himelick, Dan Neely, and Webster R. Crowley, Jr. June, 1965. 12 p., 8 fig., bibliogr. 54. — A Preliminary Annotated List of the Lampreys and Fishes of Illinois. By Philip W. Smith. June, 1965. 12 p., 3 fig., bib- liogr. 55. — A Guide to Age Determination of Bob- white Quail Embryos. By John L. Rose- berry and Willard D. Klimstra. July, 1965. 4 p., 2 fig., bibliogr. 57. - Man's Effect on the Fish and Wildlife of the IlUnois River. By Harlow B. Mills, William C. Starrett, and Frank C. Bell- rose. June, 1966. 24 p., 16 fig., bibliogr. 58. - The Life History of the Slough Darter, Etheostoma gracile (Pisces, Percidae). By Marvin E. Braasch and Philip W. Smith. June, 1967. 12 p., 8 fig., bibliogr. 59. — Tables for Estimating Ages and Birth Dates of Cottontail Rabbits with Sugges- tions for HandUng Lenses. By William ^. Edwards. December, 1967. 4 p., 2 fig. 60. r- Use of Feather Minerals as Biological Tracers to Determine the Breeding and Molting Grounds of Wild Geese. By Har- old C. Hanson and Robert L. Jones. Feb- ruary, 1968. 8 p., 2 fig., bibUogr. 61. — Waterfowl Migration Corridors East of the Rocky Mountains in the United States. By Frank C. Bellrose. June, 1968. 24 p., 6 fig., bibliogr. 62. — Nightlighting: Its Use in Capturing Pheasants, Prairie Chickens, Bobwhites, and Cottontails. By Ronald F. Labisky. Octo- ber, 1968. 12 p., 8 fig., bibliogr. 63. — Selected Minerals in Soils, Plants, and Pheasants: An Ecosystem Approach to Un- derstanding Pheasant Distribution in Illinois. By Robert L. Jones, Ronald F. Labisky, and William L. Anderson. December, 1968. 8 p., 1 fig., bibliogr. 64. - The Value of In Vitro Fungicide Tests. By Daa Neely. January, 1969. 8 p., bibliogr. 65. — Trends in Pheasant Abundance in Illi- nois: 1958 to 1968. By Ronald F. Labisky. May, 1969. 8 p., 4 fig., bibliogr. List of available publications mailed on request No charge is made for publications of the Illinois Natural History Survey. A single copy of most publications will be sent free to anyone requesting it until the supply becomes low. Costly publications, more than one copy of a publication, and publications in short supply are subjects for special correspondence. Such correspondence should identify the writer and explain the use to be made of the publication or publications. Address orders ond correspondence to the Chief, Illinois Natural History Survey Natural Resources Building, Urbono, Illinois 61801