Bulletin / J ILLINOIS a^tura.! History Survey BULLETIN JUiNi 2 91973 The Effects of Supplemental Feeding and Fall Drawdowns on the Largemouth Bass and Bluegills at Ridge Lake, Illinois rge W. Bennett Vickliffe Adkins iam F. Childers ; OF ILLINOIS ARTMENT OF REGISTRATION AND EDUCATION rURAL HISTORY SURVEY DIVISION )ANA, ILLINOIS THE LIBRARr OF THE '^^^3 1973 ISL \ini iiur 01 ADTini c i ILLIMTOIS ia^turail History Sii.]:**vey jorge W. Bennett iWickljffe Adkins lliam F. Childers BULLETIN The Effects of Supplemental Feeding and Fall Drawdowns on the Largemouth Bass and Bluegills at Ridge Lake, Illinois rE OF ILLINOIS iPARTMENT OF REGISTRATION AND EDUCATION TURAL HISTORY SURVEY DIVISION JBANA, ILLINOIS STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION BOARD OF NATURAL RESOURCES AND CONSERVATION WiLuiAM H Robinson Chnirman: Thomas Park. Ph.D., ISinlngij: L. L. Sloss. Ph.D.. Geology: (Vacant). Chcmiatry Robert H. Anderson. B.S.C.E.. Kmiimyriiia: Charles E. Olmsted. Ph.D.. Forcs(ry; "' ' EVERITT. E.E., Ph.D.. Rrprracniiiifl thr l>rtsl Section of Wildlife Research Glen C. Sanderson. Ph.D., Wildlife Specialist and Head Frank C. Bellro'^e. 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 Charles M. Nixon, M.S., Associate Wildlife Specialist Robert E. Greenberg. M.S., Assistant Wildlife Specialist G. Blair Joselyn. M.S., Assistant Wildlife Specialist David R. Vance. M.S., Assistant Wildlife Specialist Ronald L. Westemeier. B.S.. Assistant Wildlife Specialist Ronald E. Duzan. .Junior Professional Scientist Helen C. Schultz. M.A., Technical Assistant Hilda Wiesenmeyer, Technical Assistant Eleanore Wilson. Technical Assistant Robert D. Crompion. Field Assistant James W. Seets. Laboratory Assistant Section of Administrative Services Robert O. Watson. B.S., Administrator and Head Supporting Services Wilma G. Dillman. Property Control and Trust Accounts Robert O. Ellis, Assistant for Operations Lloyd E. Huffman, Stockroom Manager J. William Lusk. Mailing and Distribution Services Melvin E. Schwartz. Financial Records James E. Sergent. Greenhouse Superintendent Section of Aquatic Biology George W. Bennett. Ph.D., AQuatie Biologist and Head D. Homer Buck, Ph.D., Aquatic Biologist R. Weldon Larimore, Ph.D., Aquatic Biologist Robert C. Hiltibran. Ph.D., Biochemist William F. Guilders, Ph.D.. Associate Aquatic Biologist Donald F. Hansen. Ph.D., Associate Aquatic Bi- ologist Richard E. Sparks, Ph.D., Assistant Aquatic Bi- ologist Arnold Gnilka, Ph.D.. Junior Professional Scientist Richard J. Baur. M.S., Research Assistant Dennis L. Dooley, Technical Assistant Linda Klippert. B.S.. Technical Assistant Mary Frances Martin. Technical Assistant Kenneth R. Walker. Technical Assistant C. Russell Rose. Field Assistant CONSULTANTS AND RESEARCH AFFILIATES: Systematic Entomology, Roderick R. Irwin, Chi- cago. Illinois; Wildlife Research, Willard D. Klimstra, Ph.D.. Professor of Zoology and Director of Co- operative Wildlife Research. Sunihern Illinois Univcrsitir. Parasitology, Norman D. Levine, Ph.D.. Profes- sor of Veterinary Parasitology. Vctrrinani Research, and Zoology and Director of the Center for Human Ecology. University of Illinois: Entomology. Robert L. Metcalf, Ph.D., Professor of Zoology and of En- tomology and Head of the Department of Zoology, University of Illinois: and Gilbert P. Waldbauer, Ph.D., Professor of Entomology. University of Illinois: Statistics, Horace W. Norton, Ph.D., Professor of Sta- tistical Design and Analysis, University of Illinois. Publications and Public Relations Owen F. Glissendorf, M.S., Technical Editor Robert M. Zewadski, M.S., Associate Technical Editor Shirley McClellan, Assistant Technical Editor Lloyd LeMere. Technical Illustrator WiLMER D. Zehr, Technical Photographer Technical Library Doris F. Dodds, M.S.L.S., Technical Libr Doris L. Sublette, M.S.L.S., Assistant Technical Libr //6or^./'WAiwr CONTENTS AcKNOWLEDGjrENTS 3 The 1963 Restocking of Ridge Lake 3 The Feeding Program 3 Fall Drawdowns 6 Population Dynamics of Fishes During the Feeding-Drawdown Period 8 Largemouth Bass 8 Bluegills 10 Warmouths 11 Channel Catfish 12 The Effects of Early Fall Drawdowns in Reducing Bluegill Numbers in Ridge Lake 13 A Comparison of the Effects of Various Management Techniques ON Angling Yields 14 The Effects of Supplemental Feeding and Drawdowns on the Condition of Largemouth Bass and Bluegills 17 The Growth of Bass and Bluegills in a Feeding-Drawdown Program 19 Discussion 22 Summary 25 Literature Cited 26 Index 27 This report is printed by authority of the State of Illinois, IRS Ch. 127, Par. 58.12. It is It 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 by the Illinois Natural History Survey each summer since 1952 as Resident Biologist at Ridge Lake. William F. Childers is an Associate Aquatic Biologist, Illinois Natural History Survey. (45582—5M—1-73) 1,1 .*?v* .\^ :J^^i^ ^(^ ;j^M;,.'' i The Effects of Supplemental Feeding and Fail Drawdowns on the Largemouth Bass and Biuegiiis at Ridge Izke, Illinois George W. Bennett H. Wickliffe Adkins William F. Childers IN 1963 WHEN THE PROGRAM described here was begun, studies of the fish population of Ridge Lake had been going on for 21 years (Bennett 1954a and 19546; Bennett & Durham 1951 : Durham & Bennett 1949 and 1951: Bennett, Ad- kins, & Childers 1969), These studies involved annual controlled public fishing during June, July, and August and drain- ing censuses (usually in the spring) to gain estimates of the total population of fishes in the lake. Between these draining censuses we applied several types of pri- mary or secondary population manipula- tion, or none at all, to explore the effects of these manipulations upon the fish pop- ulations and the yields of fishes. This jjeriod included 10 years of biennial drain- ing of the lake and culling of small fishes; 5 years of fall drawdowns of the lake, with one draining census after 2 years and one after 3; 4 years of stable water levels and no manipulation of the fish popula- tion ; and 3 years of testing the value of hybrid sunfishes for angling (Childers 1967:189). In the period 1941-1970, Ridge Lake has been completely drained and the fishes have been censused 10 times: in 1943, 1945, 1947, 1949, 1951, 1953, 1956, 1959 (in the fall), 1963, and 1970. On the basis of complete creel censuses in all years (except 1942, when the lake was closed to fishing) we were able to measure with some degree of cer- tainty the type of fish population the lake would support and the efl'ects of \arious management efforts on that population. The fishes included in this investiga- tion were largemouth bass, Micropterus salmoides (Lacepede) ; bluegills, Lcpomis macrochirus Rafinesque; warmouths, Lc- pomis gulosui (Cuvier) ; lake chubsuckers, Erimyzon sucetta (Lacepede) ; and chan- nel catfish, Ictaluriis punctatus (Ra- finesque). Any other fishes that gained entrance to the lake through fishermen's minnow buckets or from the drainage basin were removed during the draining censuses. All of the fishes in the Ridge Lake population descended from 435 largemouth bass stocked in 1941, 129 bluegills storked in 1944, 138 warmouths stocked in 1949, 558 lake chubsuckers stocked in 1960, and several groups of 6- to 12-inch channel catfish stocked in 1951. 1952, 1957, and 1969. The several stockings of catfish were necessary be- cause channel catfish usually cannot re- produce successfully in Ridge Lake. All of the other fishes (bass, bluegills, war- mouths, and chubsuckers) have main- tained adequate populations through nat- ural reproduction and survi\al with no stocking but the original one. Experimental drawdowns were begun at Ridge Lake in 1951. In the spring of that year the lake was drained ; the fishes were censused; and selected numbers of largemouth bass, bluegills, and warmouths were returned to the partially filled basin. The lake refilled before June 1 and was opened to controlled public fishing during the summer imtil September 1. Fishing was then terminated and the lake level was lowered 4.6 meters (15 feet), reduc- ing the surface area from 6.9 to 2.0 ha (17 to 5 acres) and the maximum depth from 7.6 meters to 3 meters (25 to 10 Frontispiece.—A 3-meter (10-toot) drawdown at Ridge Lake. About one-third of the lake bottom, mostly in the upper end of the impoundment, is exposed by such a drawdown. Illinois Natural History Survey Bulletin Vol. 31, Art. 1 feet) without allowing any fishes to es- cape with the water. Thus, the fish population that had developed through natural reproduction and growth to fill a volume of water represented by a sur- face area of 6.9 ha^ (17 acres) became concentrated in a volume represented by 2 ha (5 acres), a minor fraction of the full lake. In 1952, after the lake had been open to public fishing during the summer, the lake level was again drawn down 4.6 meters (15 feet) in early September. In late March of 1953 the lake was complete- ly drained, the fish were censused, and selected individuals were returned to the lake. These studies were reported in several papers (Bennett 1954a and 1954fo; Bennett et al. 1969). The effect of the 4.6-meter drawdowns in 1951 and 1952 upon the bluegills was severe, reducing their numbers to the point that fewer small bluegills survived than did large ones. To insure the survival of enough bluegills to maintain successive year classes for fishing, it was decided to limit drawdowns to 3 meters (10 feet), leaving a maximum lake depth of 4.6 meters (15 feet) near the dam and a lake surface area of about 4.5 ha (11 acres). This procedure was followed in early Septem- ber of 1953, 1954, and 1955, and the lake was drained again in the spring of 1956 and a census was inade of the fishes. The lesser drawdowns of 1953—1955, inclusive, allowed the survival of a greater number of bluegills (both larger and smaller than 1 50 mm, or 6 inches, the length at which this fish was considered useful) than the 4.6-meter drawdowns allowed. Following the spring lake draining and fish census of 1956, selected bass, blue- gills, warmouths, and a few channel cat- fish were rctiuned to the lake; the basin refilled by May. From March 1956 until October 1959 the water level in Ridge Lake was allowed to fluctuate around the crest of the tower spillway, i.e., without any drawdowns and with only minor fluc- tuations caused by rimoff from rains in > Ricli-r Lakr oriijinaliy li.itl a surf.ice area ot 7.3 ha (18 acres); .silt deposits in the upper lake had re- duced the area to al)Out G.9 lia by 1953 and to 6.5 ha hy 19C3. the lake watershed. In October 1959, after four growing seasons for fishes, the lake was again drained completely and the fishes were censused. As in the years of the drawdowns, the lake was open to controlled public fishing during the sum- mers of 1956-1959. Thus, as a background for the experi- ment reported here, the authors had in- formation on anglers' catches and total fish populations from 10 years of biennial draining of the lake and culling of the fishes, 5 years of drawdowns, and 4 years of stable water levels (including that part of 1959 important for fish reproduction and growth). From the lengths, weights, and scales of individual fishes taken by fishermen in 1951-1959 and from similar data gathered from fishes during the draining censuses of 1953, 1956, and 1959, it was possible to compare the growth rates of bluegills and their relative plump- ness (condition) under a program of an- nual fall drawdowns and under another of stable water le\-els. In the fish censuses of 1953 and 1956, many of the bluegills were of exceptional sizes but appeared to be comparatively thin. The supplemental feeding proposed at the beginning of the experiment re- ported on here was in part related to this observation. Our laboratory production and culture of hybrid .sunfishes (Childers 1967) had demonstrated that most species of sun- fishes (Centrarchidae) quickly learn to feed upon commercial trout food if the pellets are small enough for them to swal- low. Bluegills in laboratory aquaria be- came plump and grew rapidly on a trout ]5ellet diet. ^If bluegills in Ridge Lake could be trained to eat fish food pellets to supplement their diet of natural foods, this additional food supply should be re- flected in improved bluegill growth and condition. We wished to discover wheth- er enough improvement in bluegill yield would occur to make artificial feeding practical. In 1963 following the spring fish census, we decided to combine Sep- tember drawdowns of Ridge Lake (for the control of bluegill numbers) with supplemental feeding to increase the Jan., 1973 Bennett et al.: Effects of Feeding and Dra\vdo\vns on Fishes 3 growth rate, condition, and yield of these fish. Results would determine whether such a program was practical. ACKNOWLEDGMENTS Mr. H. VVickliffe Adkins, stationed at the Ridge Lake Laboratory during the simimer months, supervised the fishermen and recorded their catches, fed the fishes twice daily, made daily observations on schools of bass fry and on the nesting of bluegills, assisted in age and growth analy- ses from fish scales, and recorded many biological happenings of importance to this study. Dr. ^Villiam F. Childers planned and superxised the draining cen- suses in 1963 and 1970. Many people assisted in the fish censuses; these included Mr. Robert O. Ellis, Mr. Howard Crum (deceased), Mr. Robert T. Crompton, Mr. Dennis Dooley, Dr. D. Homer Buck, Mr. Richard Baur, Mr. Russell Rose. Dr. R. Weldon Larimorc, Mr. H. \V. .\dkins. Mr. Ronald Havelka, Mr. David Mower. Mr. Edward Doyle, and Dr. George Spru- gel, Jr., of the Illinois Natural History .Siu'vey staff"; Mr. Alvin C. Lopinot, Mr. .'\rnold Fritz, and Mr. Rudy Stinauer of the Illinois Department of Conser\ation; and Dr. Leonard Durham and Scott Buck and other students from Eastern Illinois L'niversity. The manuscript of this paper was read and criticized by Dr. Horace W. Norton, Professor of Statistical Design and Analysis, Department of Animal Sci- ence, University of Illinois, and it was edited by Mr. Robert M. Zewadski of the Natural History Survey. THE 1963 RESTOCKING OF RIDGE LAKE Following the draining census of April 8-13, 1963, Ridge Lake was restocked with 2,270 small bass and 116 large ones, 4,492 bluegills, 1,335 warmouths, 1,020 lake chubsuckers, and 1 1 large channel catfish, a total of 9,244 fishes weighing 510.6 kg (1,125.5 poimds) (Table if. The weight of these fishes was 78.8 kg per hectare, or 70.3 pounds per acre. Be- fore the restocking, the lake contained 287 kg per hectare (256 pounds per acre), almost four times the weight of fish returned to the lake. A total of 1,000 channel catfish were stocked on May 21 and 29, 1969. These were Age III fish with an average total length of 259 mm (10.2 inches) and an average weight of 127 grams (0.28 pound) ; their total weight was 127 kg (280 potmds). On October 20 and 21^, after the 1969 growing season was nearly over, an additional 1,000 channel catfish were released. These were also Age HI fish, a\eraging 234 mm (9.2 inches) in total length and 113 grams (0.25 pound) and ha\ing a total weight of about 1 13.4 kg (250 pounds). All of these catfish originated in Arkansas in 1968 and were held in ponds on the Sam A. Parr Co- operative Fisheries Research Center in Marion Countv, III., until stocked in 1969. Alter the spring draining and restock- ing of 1963. the fish population was fishetl by the public during the summers of 1963 and 1964 imder the regular creel census- ing system. Otherwise, the restocked fish ]3opulation of Ridge Lake was allowed to expand for almost 2 years before any ex- perimental management program was ap- plied. During the summer of 1963 fish- ermen caught 299 largemouth bass, 358 bluegills, 49 warmouths, and 1 1 hybrid sunfishes, weighing a total of 113.4 kg (250 pounds) in 1,816 hours; the catch in 1964 was composed of 554 bass, 1,287 bluegills, 108 warmouths, and 65 miscel- laneous hybrid simfishes, weighing a total of 232.2 kg (512 pounds) in 2,346 hours of fishing. While the total yield per hectare in 1964 was twice that of 1963 (1963, 17.5 kg per hectare, or 15.6 pounds per acre; 1964, 35.9 kg per hectare, or 32 pounds per acre), both must be con- sidered much below the average of the hook-and-line yields of fishes from Ridge Lake in the 1 94 1 - 1 963 period . THE FEEDING PROGRAM In May 1965, a supply of Splash Ex- panded Fish Food was purchased from the Ralph G. Wells Company of Mon- mouth, 111. This food consisted of fish Illinois Natural History Survey Bulletin Vol. 31, Art. 1 X^On S'^ l£> "*• CM O tD CO CM O —< t^ O CM —• CM (D CM — CO to IT) CO CO lO r^ CM (J> Tj" T}- O) I^ CM CO 00 — r^ O lO CM CM ^ uo moo CO CO (O o in CO — o o o d 6 Tj. o d d CM o d d ^ m CT) CO in CM CM * en (D m to in CM ^ (O CI -^ CM — CO * CO --• 00 d CM !N •* — lo o lo ^ o >" CO CO — CM 5" ss Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 5 meal, corn distillers' dried solubles, meat and bone meal, soybean meal, cottonseed meal, wheat shorts, dehydrated alfalfa meal, brewers' dried yeast, yellow hominy feed, salt, vitamin A and D oils, vitamin A palmitate, D-activated plant sterol, d- alpha tocopherol acetate, thiamin hydro- chloride, riboflavin supplement, calcium pantothenate, niacin, choline chloride, vitamin B-12, and trace amounts of nine additional compounds. The food was 32 percent protein and 4 percent fat. Total calories of energy per pound of fin- ished feed were recorded as 1,884. The original pellets were too large for most bluegills to swallow, but they soon learned to pick at the pellets until they could break off pieces small enough to swallow. After the first season, we pur- chased smaller pellets. About half of the pellets would float for several hours. The rest would become waterlogged and sink almost at once. Feeding was begun in late May or early June, and bluegill spawning beds were selected as feeding areas along with the area around the boat dock, where blue- gills were observed to congregate (Fig. 1 ) . The fishes were fed twice each day at 10:30 AM and 6:30 PM; the dry fish food pellets were broadcast by hand from a boat. The authors assumed that food pellets that sank into bluegill nests would be picked up by the guarding males for removal from the nests, at which time these fish would discover that the pellets were edible. This was exactly what happened, and bluegills were active- ly foraging for pellets after less than a week of daily feeding. In less than 2 Fig. 1.—H. W. "Wick" Adl Qj CM — -H Th CO ci d cvi — d CO CS CM -«*- CM * CT^ "i d CM -^ o -^ Q, CD CO — O O *-i CO (M CM CO — cvj rN. ^ CO -^ — *^ r^ CO CM CO — to O CO —' CO lO Qi CO tJ* o r^ ci^ -^ r^ CO lO lO O CO CD CO CM Tf" CM CO CO CT) ^ ^ •^ lO CO CO CO (£1 ^O CO CO CTJ — CO -^ t-- CO lO CO CM ^ Tf to CO CO — ^ D CO r^ O -^ •^ — — . — . CM — ^^ I CO r^ CO CD _' CO CO CO COD O^ D O^ D0-Q to CO CO CO ' Illinois Natural History Survey Bulletin Vol. 31, Art. 1 POPULATION DYNAMICS OF FISHES DURING THE FEEDING-DRAWDOWN PERIOD Table 2 shows the yields of the four species of fishes taken by anglers in the fishing seasons 1963-1969, inclusive. This table also shows the averages of the yields for the 2 years when no sup- plemental feeding or drawdowns were conducted and for the 5 years of the feed- ing-drawdown program. From these aver- ages it was obvious that a large difTerence occurred in the yield of bluegills, so large a difference that the average bluegill yield during the feeding-drawdown (f-d) period was about six times that for the pre-experimental 2 years. This difference occurred partly because the fish popula- tion was expanding in 1963—1964, and many of the bluegills were too small to interest anglers. This lack of interest in the small bluegills was further demon- strated by the light fishing pressure in those years (46 man-hours per hectare, or 114 man-hours per acre, in 1963; 56 man-hours per hectare, or 138 man-hours per acre, in 1964) , as annual fishing pres- sures below 125 man-hours per hectare per season (309 man-hours per acre) in- dicated the poor quality of the fishing. However, the eight boats available for angling were seldom, if ever, used to the maximum during August in any year. Annual fishing eflfort, 1963-1969, is shown in Table 3. Because the fish population was enu- merated in total at the fish census and Table 3.—Fishing effort, in man-hours per hec- tare and per acre, expended by fishermen during the seasons 1963-1969, inclusive, at Ridge Lake. Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 9 ^Q, mc5 X 10 Illinois Natural History Survey Bulletin Vol. 31, Art. ] spawning season, and successive strong year classes were produced, some of which were later reduced by predation from a preceding year class. This cycle of pro- duction created by the drawdown caused severe competition and slow growth among the small bass and rapid growth among the few that survived the food competition, stranding, and predation of their first season and the fishing pressure of their second season. Severe predation upon small fishes oth- er than bass was indicated by changes in the population of lake chubsuckers in the 7 years of this experiment. In 1963, 1,020 lake chubsuckers were restocked, totaling 110 kg (243 pounds) and averaging 108 grams (0.24 pound) each. Only 232 chubsuckers, weighing 44.7 kg (98.5 pounds) and averaging 193 grams (0.42 pound), appeared in the 1970 census. These fish were too large to be preyed upon by any but the very largest bass and catfish; none smaller had managed to survive. Bluegills A total of 4,492 bluegills, mostly within the 100- to 140-mm (4- to 5.5-inch) length range were returned to Ridge Lake after the spring census of 1963 (Table 5) . These bluegills constituted a popula- tion of 693 per hectare (281 per acre). With such a small population, very few were caught in 1963, but by 1964 enough bluegills were present to increase food competition and improve the catch. Large catches of bluegills exceeding 150 mm (6 inches) in total length were made in each year from 1965 to 1969, inclusive, or throughout the f-d period (Table 5 and Fig. 2 ) , and quite large numbers of small FiQ- 2.—Fishermen returning to the laboratory pier with large catches of bluegills. Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 11 Table 5.—Population dynamics of bluegills in Ridge loke, 1963-1970, including the feeding- drawdown period (1965-1969). 12 Illinois Natural History Survey Bulletin Vol. 31, Art. 1 anglers' yield in every phase of experi- mental fish management that has been tested, including the f-d program. Channel Catfish Eleven large channel catfish appeared in the census of 1963 and were returned to Ridge Lake (Table 7). These were all very large fish, averaging 4 kg each (8.9 pounds) . No catfish was caught by fishermen until 1965 when two small fish weighing 172 grams each (0.38 pound) were taken. These were believed to rep- resent survivals from a spawn produced in the lake in 1963. Others of this year class probably survived because some cat- fish were taken each year, 1966-1969, in- clusive (Table 7). These catches prob- ably represented this same year class, be- cause their average size moved progres- sively upward with each successive sea- son: 1966, 1 kg; 1967, 2.3 kg; 1968, 3 kg; 1969, 3.4 kg (2.3, 5.1, 6.6, 7.5 pounds). It appears improbable that any of the 11 catfish returned to the lake in 1963 were caught. However, it is likely that the 32 large catfish caught by fishermen, 1966-1969, and the 22 large fish taken in the census of 1970 were all survivors from a year class of fish produced in Table 7.—Population dynamics of channel catfish in Ridge Lake, 1963-1970, including the feeding-drawdown period (1965-1969). The large catfish restocked in 1963 apparently produced a few young in 1963 or 1964. length. Approximately 1,330 of the larg- er ones were restocked following the cen- sus (Table 6). The catch of both large and small warmouths was quite insig- nificant, 732 large warmouths and 418 small ones being brought in by fishermen in 7 years. There were 556 warmouths in the cen- sus of April 1970, and only 134 of these were more than 150 mm (6 inches) in total length. That the total number of warmouths was reduced during this period suggests that the drawdown was not obviously ef- fective in stimulating an increase in the warmouth population. Warmouths have been observed to eat the pelleted food, and they presumably grow well on it. In 1966, for example, the 74 warmouths that comprised that part of the catch which exceeded 150 mm in total length averaged 251 grams (0.56 pound) each, or more than twice as much as the aver- age weight of large bluegills caught in that year. The warmouths, as is usually the case in Illinois (Larimore 1957:70), in com- petition with largemouth bass and blue- gills in Ridge Lake, have contributed very little to the fish population and to the Smaller Than 304 mm (12 inches) 304 mm or Larger Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 13 Ridge Lake, probably in 1963. These channel catfish were able to sundve in 1963 because the fish population was well below the carrying capacity of the lake in that year, and predation pressure was probably low. THE EFFECTS OF EARLY FALL DRAWDOWNS IN REDUCING BLUEGILL NUMBERS IN RIDGE LAKE With stable water levels, the bluegill population of Ridge Lake increases rapid- ly in total number with each successive spawning season and with apparently little regard for the number of largemouth bass present. In 1949 and 1950 the bass pop- ulation of Ridge Lake was exceptionally large, and no bluegills other than those that remained in pockets of the old stream channel during the 1949 census were left in the lake. Yet the population found in the 1951 census amounted to 51,963 bluegills larger than 65 mm (Table 8). The 66,600 bluegills that appeared in the 1947 census originated from 61 large blue- gills returned to the lake following the 1945 census. If the period between cen- suses is longer than 2 years, the numbers of bluegills become larger. For example, the 3-year period 1960-1962 started with zero bluegills and a dry lake basin over the winter of 1959-1960. A few bluegills appeared in 1960 from an unidentified source. These multiplied in competition with 4,500 hybrid sunfishes and a bass population that was building up to 6,000 small fishes. In 3 years the bluegills numbered 85,500. Still larger numbers of bluegills were present after the four growing seasons with stable water lev'els, beginning in March 1956 and continuing until October 1959. After the 1956 census, 1,008 blue- gills were restocked, and in the 1959 cen- sus the bluegill population was 92,700. It is impossible to suggest how much this population might increase numerically, but it seems apparent that in a relatively short period, say 7—10 years, the bluegills would become so dominant as to curtail the success of bass reproduction. Within the range of bluegill numbers (and time) shown in Table 8, there was no evidence of a reduction of bass numbers; in fact, the 6,200 bass exposed in the 1963 census, when 85,500 bluegills were present, was the largest population of small bass ever recorded for Ridge Lake. The effects of the drawdowns on the Table 8.—Total numbers and total weights in kilograms of fishes collected in several draining censuses at Ridge talce when bluegills were present and when water levels were stable for two or nore seasons prior to the census. Similar data are presented for censuses following 2^5 years of early 14 Illinois Natural History Survey Bulletin Vol. 31, Art. 1 bluegill populations become evident when the bluegill numbers at the bottom of Table 8 are compared with those at the top. Also, a direct relationship apparent- ly exists between the severity of the draw- down and the extent of bluegill popula- tion reduction, as indicated by the 1953 and 1956 census figures. During a drawdown, small bluegills are more vulnerable to stranding and preda- tion than are bluegills larger than a cer- tain minimum size (25-100 mm). The larger fishes may live through several drawdowns, while relatively few of the small ones survive. The reduced popula- tion remaining in Ridge Lake after a drawdown (10,000-20,000 fishes instead of 50,000-100,000) becomes an expand- ing population in the refilled lake, with plenty of available food and space for reproduction and growth in the growing season following a fall drawdown. Table 8 shows no large differences be- tween the numbers of largemouth bass with and without drawdowns. Draw- downs are associated with successful re- production of largemouth bass during the following spawning season, but when a drawdown is scheduled for every fall the young bass of each spawning season may be decimated by yearling bass from the previous year class. The discovery that drawdowns are almost always followed by successful bass fry production and the survival of these little fish beyond the size subject to predation by bluegills sug- gests a "surefire" method of producing a new year class of bass when a stunted bluegill population has been curtailing all bass reproduction. It is evident that annual drawdowns, with or without sup- plemental feeding, do not result in bass populations with superior potential for bass fishing although they probably should not be considered below average. A COMPARISON OF THE EFFECTS OF VARIOUS MANAGEMENT TECHNIQUES ON ANGLING YIELDS To make a comparison of management techniques, data from several fishing sea- sons directly affected by these techniques were selected and averaged (Tables 9 and 10). For example, several years in the biennial draining-and-culling period, 1941-1951, were characterized by large catches of largemouth bass. The year 1948 was selected because of the alternate years in which the lake was not drained, it was the year of the largest catch of bass. In the first period of drawdown studies, 1951-1956, catches for the years 1951 and 1953 were omitted because they followed spring censusing operations in which the lake was completely drained and selected fish were returned. These operations also affected all other aquatic biota. While the fish returned to the lake after the 1953 census must have been influenced by the drawdowns of the fall seasons of 1951 and 1952, the fish population re- turned was probably more a reflection of the draining and censusing operation than of the drawdowns. The draining opera- tion of 1956 again upset the replacement fish population.' It marked the beginning of the "steady-state" period which lasted from May 1956 to October 1959. Only the years 1957, 1958, and 1959 were used to represent this period of stable water levels. In the f-d period the years 1965-1969 were included because, as mentioned pre- viously, feeding was begun during the summer of 1965 and the first drawdown was made in the fall of 1965. In Table 9, statistics are shown for a comparison of the yields of the four major species of fishes in Ridge Lake for the several periods mentioned above. The average yield of bass of 18 kg per hectare (16.1 pounds per acre) for the f-d period is lower than that of any of the other periods shown and was exceeded by nearly twice this average in 1948, one of the best bass fishing seasons. It seems safe to assume that annual fall drawdowns at Ridge Lake did not result in the production of large numbers of desirable-sized bass. Bass fishing was con- siderably better in the period when we drained the lake every 2 years and re- moved bass smaller than 200-255 mm (8-10 inches) along with large numbers of smaller bluegills. Under this culling Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 15 E ^- o i 2 -9 3< CO OD 2 "o 2 « ^2 L CO « _ X J3 j; u "O en — — « — — ""O « 16 Illinois Natural History Survey Bulletin Vol. 31, Art. 1 O -D u Jan., 1973 Bennett et al.: Effects of Feeding and Drawdowns on Fishes 17 THE EFFECTS OF SUPPLEMENTAL FEEDING AND DRAWDOWNS ON THE CONDITION OF LARGEMOUTH BASS AND BLUEGILLS We believed that the effects of supple- mental feeding of the fishes of Ridge Lake would become evident through changes in the growth rate and in the relative plumpness of the fishes. The procedure of allowing two seasons to pass after the restocking of the lake before any experi- mental management or feeding was be- gun gave results from those 2 years that we could compare with results from 5 years of f-d operations. Also, results from the 5-year f-d period could be compared with results from previous Ridge Lake studies (Bennett 1954a; Bennett et al. 1969) : 5 years of drawdowns without feeding, 10 years of biennial draining of the lake and culling of the fishes, and 4 years of stable water levels. It is convenient to begin by comparing the condition of bass and bluegills col- lected in 1963 and 1964, when no supple- mental feeding or drawdowns were con- ducted, with collections made in 1965- 1969, inclusive, when the fish were fed daily during the summer and the lake level was dropped 3 or more meters each fall and held down as long as the weather was waiTTi. FisheiTnen's catches at Ridge Lake were measured as total lengths in tenths of inches and weights in hundredths of pounds. Therefore, it was convenient to use the Index of Condition, C, formulated by Thompson & Bennett (1939:16-17) W 10,000 I? in which W is weight in pounds and L is length in inches. To interpret results from this formula, one must know that bluegills showing an index of condition, C, of 6.0-7.0 are in poor flesh; those showing a condition of 7.1-8.0 are in the range of average plump- ness; and those showing a condition of 8.1 or above are obese and usually show internal fat deposits. The largemouth bass, having more elongated shapes than the shapes of blue- gills, have a lower condition index range. In bass, condition indices of 3.5-4.5 are related to a thin body; bass in the range of 4.6-5.5 are about normal; and those within the range of 5.6 or higher are obese. Bluegills are known to have an annual cycle of condition (Bennett, Thompson, & Parr 1940:6), with condi- tion being lowest during winter, gradual- ly rising in March and April, and reach- ing a peak in late May or early June at the beginning of the spawning season. During the long spawning season extend- ing throughout the summer, bluegill con- dition usually drops. Sometimes it rises in late August and early September, drop- ping again to the winter low. No annual condition cycle has been reported for largemouth bass. Average indexes of condition are shown in Table 1 1 . Data were taken from creel cards recorded for all fishes by the first junior author when fishermen returned to the laboratory pier with their catches. Length-weight data from fishes caught by anglers during early June, the first Table 11.—Average index of condition, C, of monthly samples of largemoutti bass and bluegills token by fishermen from Ridge Lake during the summer fishing periods, 1963-1969. Month 18 Illinois Natural History Survey Bulletin Vol. 31, Art. 1 part of July, and the first part of August were used, and the numbers of fish rec- ords ranged between 17 and 337, depend- ing on the numbers available. Indexes of condition were calculated for bass within the length range of 173- 399 mm (6.8-15.7 inches) and for blue- gills within the range of 147-246 mm (5.8-9.7 inches) . Fishes were separated into 25-mm (1-inch) length groups (e.g., 147-172 mm, 173-198 mm, etc.) so that any great variations in the relative plump- ness of these length groups would be ex- posed. Bluegills were fairly consistent in condition within the size groups recorded, but bass more than 12 inches long were heavier in proportion to their length than were shorter bass. Indices of condition for both bass and bluegills caught by an- glers at any one time (within a period of a few days) were quite uniform for their species, although occasionally a few in- dividuals varied widely. The bass con- dition data in Table 1 1 emphasizes the fact that in most months the bass aver- aged slightly below normal, or average, plumpness. In general, all bass were thin, but some were more so than others. During the summer of 1963 the blue- gills were thin (Fig. 3) , but they improved to average plumpness in 1964 before any supplemental feeding was begun. Appar- ently, the feeding program in 1965 was not reflected in the condition of the blue- gills in that year although they were, on the average, somewhat plumper than they were in 1964. The eflfects of supplemen- tal feeding were evident in the collections for June in 1966, 1967, and 1968 (Fig. 3) when the average C values for blue- gills were in the fat category. The con- dition cycle for this species was evident in most years. Bluegill plumpness in July and August was usually lower, on the average, than it was in June, with mid- and late-summer condition falling below the fat classification in all years except 1967. In 1968, bluegills were in fat con- dition in June, and large bluegills again reached that level in August. In that same year, a high survival rate oc- curred among the small bluegills of a very large year class. This high rate of sur- vival became evident in 1969 when many bluegills were too small to interest anglers but were numerous enough to reduce the overall effect of the supplemental feeding. Fig. 4 shows the average condition for Length Group Millimeters incties 147-170 5.8-6.7 17! -196 6.8-77 197- 221 78 - 8.7 Wtd.Avg, 'FAT"CONDITION "THIN" CONDITION Fig. 3.—Indices of Condition of three length groupings of bluegills and the weighted average for all groupings in summers of the f-d experiment. Supplemental feeding was begun in 1965, and the first drawdown of this program was conducted in the fall of 1965. Jan., 1973 Bennett et al. : Effects of Feeding and Drawdowns on Fishes 19 7.0- A.O-' Length Group Millimeters Incties 147-170 5.8-6.7 171 -196 6.8-77 197-221 78-8.7 Wtd. Avg. "FAT" CONDITION AVERAGE PLUMPNESS -V AUGUST "THIN" CONDITION AUGUST 1954 1955 Fig. 4.—Indices of Condition of ttiree length groupings of bluegills and ttie weigtited average for all groupings tal