mm. LI B R.ArLY OF THE U N IVERSITY or ILLINOIS NArURAL HISTORY SURVEY State of Illinois Henry Horner, Governor LAKE MANAGEMENT REPORTS 1. Horseshoe Lake near Cairo, Illinois David H. Thompson and George W. Bennett Department of Registration and Education John J. Hallihan, Director Division of the Natural History Survey Theodore H. Prison, Chief Biological Notes No. 8 Urbana, Illinois September, 1938 [Printod by authority of the State of Illinois] LAKE MANAGEMENT REPORTS 1. Horseshoe Lake near Cairo, Illinois David H. Thompson and Illinois Natural H For many years the Illinois Natural History Sur- vey has been measuring fish populations and fish production. Among the various types of Illinois waters studied, it has been found that each tends to have the capacity to support a certain number of pounds of fish per acre which is constant from year to year. This number of pounds per acre remains constant even though there may be ten times as many fish (of one-tenth the average weight per fish) in some years as in others. When this amount of fish flesh per acre is disturbed by putting in or taking out fish or by floods or drouths, readjust- ment takes place much more rapidly than is popu- larly supposed. When a new lake is stocked with a few breeder fish the saturation point is usually reached in about a year. When one-fourth, or less, of the total amount of fish in a lake is removed during the course of a season, readjustment takes place so rapid- ly that changes in abundance are not detectable. This means that the yield of game fishes from an acre of water can be many times the amount taken out by ordinary fishing. Geokce W. Bennett istory Survey Fish grow to more desirable sizes and furnish a better quality of food and sport when their numbers are reduced enough to give rapid growth rates. Good farmers understand this view of livestock and crop production and practice it continually. The follow- ing is an account of the changes which have taken place in Horseshoe Lake since its reconstruction in 1931. Description Horseshoe Lake embraces about 2.400 acres of water with a 1,400-acre island in the center. The Illinois Department of Conservation owns the island and about two-thirds of the water surface and main- tains it as a waterfowl refuge. The lake is located about 12 miles northwest of Cairo on Highway 150. Horseshoe Lake is part of a former channel of the Mississippi which has grown up in cypress. Cypress, gum, willow and buck brush grow throughout all parts of the lake, although the trees are more scat- tering along the east side, leaving considerable areas of open water. With the exception of some flooded pasture lands, the remainder of the lake is grown up in timber and brush. The east side of the lake has a uniform depth of about six feet; the remainder is KINDS, SIZES AND NUMBERS OF FISH IN HORSESHOE LAKE Kind Largemouth Bass . White Crappie ... Black Crappie . . . White Bass Yellow Bass Warmouth Bass . . Bluegill Green Sunfish .... Flier Sunfish Grass Pike . . Spotted Gar . Dogfish Channel Cat Black Bullhead . . Yellow Bullhead . Gizzard Shad . . Golden Shiner . Carp Rcdmouth Buffalo. . . Mongrel Buffalo. . . . Smnllinouth Buffalo . Quillback Redhorsc Spotted Sucker Chub Sucker Total Total No. Handled 1934-38 Average Total Length in Inches 235 1,044 3.913 3 IS 9 969 2 825 14 2 17 9 1,122 329 1,244 11 217 618 33 12 9 1 139 1 10,793 1934 12.4 10.3 6.3 7.3 5.3 9.1 10.8 9.1 19.8 13.8 15.2 12.9 1936 16.2 10.7 7.9 6.9 6.0 10.0 10.9 9.7 20.8 17.0 20.3 16.2 1937 15.4 10.9 7.6 6.8 5.8 10.5 12.1 10.4 21.5 17.9 22.7 16.8 1938 Estimated Number in Lake during the Past Year 16.2 8.5 7.9 6.8 5.9 11.1 11.4 10.7 22.6 18.1 21.7 17.7 5,000 to 10,000 250,000 to 350,000 500,000 to 700,000 150,000 to 250,000 4,000 to 15,000 150,000 to 250,000 35,000 to 50,000 50,000 to 200,000 25,000 to 50,000 25,000 to 100,000 1,000 to 5,000 5,000 to 20,000 1,200,000 to 2,000,000 —2— (Left) Cypress Trees Grow in the Open Waters of the Lake (Right) Don Hansen Measures a Carp at the Ferry Landing t K more shallow with depths ranging from one to six feet. A small creek about 25 feet wide feeds Horseshoe Lake from a large area to the north and east. In addition, a dredge ditch about six feet deep drains the hills from the north and west. During heavy rains these streams bring in a great deal of muddy water which often extends well down the lake. Al- though Horseshoe Lake is brownish in color, it is sufficiently transparent to allow bottom to be seen in one to three feet of water. Submerged aquatic vege- tation is scanty. The climate of this southern tip of Illinois is much milder than most upstate citizens realize. Cotton is grown in this vicinity; mistletoe parasitizes the elms and maples; and cane brakes are scattered in the low- lands. The fish have a growing season nearly twice as long as that of northern Illinois and pole-and-line fishing goes on throughout most winters. History In 1930 the old dam holding Horseshoe Lake washed out. The lake drained and lay completely dry for a year. The only water left was in the dredge ditch which feeds the lake. A permanent dam of concrete with deep foundations was built in 1931. Rains in late summer and early fall of that year par- tially filled the lake. In December, 1931, a stock of small bass, crappies, bluegills, channel cat, bullheads, small carp and buffalo were brought from the Illinois River at Havana and put in Horseshoe Lake. This was followed by some larger bass stocked in the early spring of 1932. Apparently a few other kinds of fishes survived the draining of Horseshoe Lake in the pools of the dredge ditch. The most important of these were the flier sunfish, the spotted sucker, and three species of forage fish — the live-bearing top minnow (Gambus/a), the golden shiner and the giz- zard shad. Fish Surveys Zoologists of the Natural History Survey have watched the course of events in Horseshoe Lake each year since it was rebuilt. In 1934, 1936, 1937 and 1938, a crew of men, outfitted with boats, nets and a miscellany of scientific equipment, caught, identi- fied, measured, weighed and took scales from large numbers of fish. This information has made it possi- ble to estimate the abundance of the important spe- cies in the lake, their rates of reproduction, rates of growth and death rates. The first three of these surveys were made by Mr. Francis D. Hunt, then field naturalist for the Natural History Survey. In order to make the fishing meth- ods for all years as uniform as possible, Mr. Hunt, who is now fish culturist for the Department of Con- servation, assisted in making the 1938 survey. Twenty-five kinds of fish were taken in hoop nets during these four surveys. Eleven of these kinds represent one percent or more of the total. A list of species and the numbers taken is shown in the accom- panying tabulation, along with average lengths for each year of the more abundant kinds. From year to year the same nets were used and set in about the same places in the lake. As these nets were one- inch mesh, the small fish, up to a size of about four inches in circumference, escaped. The same nets were used in the years 1932-1937 to catch fish for the population measurements in the lakes of the Illinois Valley. There it was found that in the warm weather of spring and sum- mer each net caught the fish from about one-tenth of an acre in one day. The total number of fish taken during these four surveys in Horseshoe Lake represents the catch from about 20 acres of water. This makes it possible to estimate within certain lim- its the total number of individuals in the lake of each of the more common species. Certain kinds of fish are caught in these nets much more readily than others. These differences in behavior have been taken into consideration in estimating the total num- bers shown in the tabulation. Estimates of Total Poundage At the present time it is estimated that Horseshoe Lake is supporting about 150 pounds per acre of bass, crappies and sunfish. The bullheads amount to an additional 65 pounds per acre. In addition to the above fish which may be taken readily on hook and line, there are probably about one-half million pounds of carp and buffalo, or about 200 pounds per acre. It appears that the total of all kinds of fish of edible sizes in the lake is about one million pounds or 400 pounds per acre. The 1937 Flood In late January and early February, 1937, the Ohio River flooded, covering a large part of several southern Illinois counties. The flood water backed up Bay Creek a few miles, cut across to Cache River, following its valley across the southern tip of the 6 8 10 TOTAL LENGTH state. Near Horseshoe Lake this water left the channel of the Cache to enter the Mississippi at Dog Tooth Bend. At the time of the flood it seemed likely that Horseshoe Lake might have lost a large part of its fish or that objectionable species might have moved in. The 1937 survey was made to determine Left. — The black crappie made up 37 percent of all fish taken in hoopnets by the four surveys. 1934-1938. A huge brood of black crappies was spawned in the spring of 1932 from breeding stock placed in the lake a few months earlier. This brood grew at a normal rate during its first two years, reaching an average total length of 6 inches by the spring of 1934. After that, growth was retarded by dwindling food supplies. These fish reached an average length of 8 inches by 1936 and since then have not grown at all. Moderate reductions in the numbers of this 1932 brood from year to year have not resulted in increased growth among the survivors because of increasing competition by the white crappies. The black crappie, more than any other fish, has been responsible for destroying the young, not only of its own kind, but also those of most other species in the lake. what changes the flood had made. We found no evi- dence that Horseshoe Lake had lost any of its fish. The only intruders were two spotted gars. Up to this time this species had not been taken in the lake, although it is present below the spillway. No sf)otted gars or other newcomers were caught in this spring's survey. If this flood had taken place in warm weather when fish are active, it seems certain that the fish population of Horseshoe would have been greatly disturbed and mixed up. Throughout the early part of the flood, the quieter waters were cov- ered with ice and at no time did the temperature rise more than a few degrees above freezing. It appears that the fish of Horseshoe and vicinity lay quietly while the fiood waters rose and went down again. Largemouth Black Bass Two of the diagrams show the essential facts about the largemouth bass in Horseshoe Lake. When the lake was visited in May of 1932, as many as a quart of Gambusia could be taken in a short haul with a minnow seine, together with bass fry about an inch long and large numbers of fry of the flier sunfish. The top minnows and the fry of the flier sunfish probablj- made up the bulk of the food of the bass that first year and were responsi- ble for their rapid growth. When the lake was visited in the summer of 1933 it was noted that the bass were growing very rapidly. The decline in the ", 8- I 2- t- o z UJ Largemouth Black Bass D Av OF All data (ill,Wis.nebr,La_) AV OF 328 FROM HORSESMOe LAKE ui 1st 2nd Jl Di D. D D D D 3rd 4TH 5th 6TH Tm 8tm 9th IOtm YEAR OF LIFE After Horseshoe Lake was rebuilt, food was at first abun- dant. The bass responded to this favorable condition more readily than other species and grew very rapidly. At an age of one year they were almost twice as long and weighed six times as much as the average yearling bass in the Mississippi Valley. Increasing competition by crappies re- duced growth in the bass to normal in their second year, then below normal, finally almost to zero. At the present time these bass are living on a subsistence basis. rate of growth and the reduction of the number of bass has resulted from competition and predation by the crappies, as well as from fishing. Hook-and- line fishing has apparently removed a larger percent- age of the bass than of the crappies. In June, 1934, a group of wardens under the direction of Chief In- spector Erio contacted 2,097 fishermen and enumera- ated their catch during the first three days of the first open season. Their catch included 2,544 bass, but only 74 crappies. This is because bass seem to bite better than crappies in summer. The growing scarcity of bass in this lake does not seem to be due to their failure to spawn or to lack of spawning places. The best way to reestablish the bass in satisfactory numbers would seem to be (1) to relieve them from competition and predation by taking out more crap- pies and (2) to plant bass too large to be swallowed by crappies. Crappies Crappies made up 46 percent of all the larger fish taken in the four surveys. The facts about their growth and numbers are shown in the accompanying diagrams. Of the very large carnivorous fishes, the white crappie is most numerous. It may be noted that the decline in abundance of bass has taken place at the same time as a corresponding increase in the number of white crappies. Within the past few years, larger crappies of both species have been caught or handled in Horseshoe Lake than in other Illinois waters in recent decades. A few of the very largest of these have been identi- fied as hybrids between the two species. The larg- est hybrid was 17.1 inches long and weighed 4.3 pounds. It was caught in March, 1936. Fishermen have noticed that large specimens of most kinds of fish are usually females. For example, 23 out of 27 of these large white crappies were fe- Below. — In the spring of 1932 the breeder bass previously placed in the lake spawned successfully. In the absence of many predators a large part of this brood survived. At the same time a large brood of crappies was also produced and survived. In succeeding years the bass spawned, but nearly all of the young have disappeared — probably eaten by the crappies. In each year since 1934, the number of legal-sized bass has been reduced to one-half or two-thirds of the number present the preceding year. The original 1932 brood still makes up over 90 percent of the bass population as shown by the 1936, 1937 and 1938 surveys. Largemouth Black Bass 1934 NO 1935 ^ ^M RELATIVE NUMBERS OF DIFFERENT SIZES OF WHITE CRAPPIES 12 14 IN Inches The white crappie, in contrast to the largemouth bass and the black crappie, produced a rather small brood in 1932 when the lake was new. Unlike these other species, it has produced moderate-sized broods each year which have es- caped destruction. This has resulted in a progressive increase in their numbers which is shown in the diagram below. White Crappie < O 5- 1937 I93S . ZZZZZZZZ 1934 NO Survey 1935 1936 1937 1936 —5- males. This does not mean that the female grows faster, but that the male dies off sooner. Bluegills and Other Sunfish The bluegill, more than any other species in the lake, has maintained a uniform population and a uniform size. It grows steadily and, apparently, re- I^roduces successfully year after year. The bluegill does not feed on other fishes extensively, probably because of its small mouth, and is in the position of a bystander in the struggle among the crappies and the bass. The flier sunfish multiplied rapidly during the first year and in 1934 constituted about onefifth of all fishes taken. Since then it has declined and has al- most disappeared. Only five were taken this year. A few other kinds of sunfishes and related species have been taken in small numbers each year. None of them shows any indication of reaching important numbers, with the possible exception of the yellow bass. Bullheads The black bullhead spawned very successfully in 1932. This brood reached an average length of 9 inches by 1934. Since that time they have been growing one-half inch per year. There is no evidence of the survival of any subsequent broods. In April, 1937, the black bullheads were all thin. They seemed to be "all head and tail." Their flesh was extremely soft and, on dressing, much of it pulled off with the skin. During the present spring most of them seemed to be in good condition although a few were still poor. The yellow bullhead also produced a large brood in 1932. Since then small broods have survived about every second year. The yellow bulheads also appeared to be starved in 1937, but not in 1938. A few were examined post mortem in 1937 but no evi- dence of disease or parasites was found. Bullheads are desirable food and it would seem a good thing to make better use of those in Horseshoe Lake. Forage Fish There appear to be about one -half million pounds of game fish and bullheads in Horseshoe Lake which feed almost entirely on fish. Experiments have shown that at moderate temperatures a largemouth bass must eat about one percent of its weight in fish per day in order merely to maintain its bodily proc- esses, without any increase in weight. Since there are about 200 days a year when the water of Horse- shoe Lake is warm, this means that one million pounds of forage fish are the minimal sustaining requirements for these fish. Growth of these game fish demands nourishment at the rate of 3 to 5 pounds of forage fish for each pound of new flesh added. Thus, it is not improbable that as much as two or three million pounds of small fish are con- sumed annually. The principal items which compose this enormous quantity of fish flesh are: (1) The young of larger fishes. (2) Both young and adults of a variety of min- nows and other small fishes, of which the golden shiner and the live -bearing top minnow have been of outstanding importance. (3) The gizzard shad. The gizzard shad, while not useful for human con- sumption, multiplies very rapidly and is an impwr- tant food for game fish in lakes. It has a further advantage in that it feeds upon the microscopic life in the water and does not compete for food with edi- ble species. From 1934 until 1937 the number of adult gizzard shad declined steadily, probably be- cause they were eaten by increasing numbers of crap- pies of large sizes. Now that the large-sized crap- pies are disappearing, the gizzard shad again shows an increase. Rough Fish The carp and buffalo which make up the bulk of rough fish in the lake now average about 5 pounds each. Each female carp of this size produces one- half million or more eggs. The young fish which develop from these eggs are an important food item of the game fish and tend to offset whatever com- petition the carp and buffalo offer in other respects. NOTE: — Reprinted in part from Illinois Conserva- tion, Summer. 1938. Cuts and type courtesy of Illinois Department of Conservation. (63389) —6— ■m