utilized as efficiently as they will be when the lake contains fish of a greater range of 

 sizes and ages. There is a tendency to underfish small lakes In Illinois and to protect 

 young fish from all kind of fish predators. Under these conditions, large, dominant 

 broods of fish appear at 3- to 5-3rear Intervals, tending to make hook-and-llne fishing 

 Irregular. When these lakes are fished intensively, the broods of young produced each 

 jrear grow rapidly and the success of fishing is more nearly uniform. 



It has been suggested by Ellis (1937) and others that impounded waters decline in 

 fertility with increasing age. Measurements of fish yields and carrying capacity of old 

 artificial lakes do not support this view. As newly constructed lakes are usually stocked 

 with a small nvanber of breeders of desirable kinds, lack of crowding makes possible good 

 fishing for the first few years. Later, excessive multiplication of these fish produces 

 stunted, slow-growing broods not attractive to hook-and-llne fishermen. In addition, the 

 introduction of undesirable kinds through careless stocking, or by escaped bait, tends to 

 encovirage the production of a large undesirable population which competes with desirable 

 kinds for food. In lakes with mixed populations, intensive fishing for certain kinds, 

 such as bass, bluegllls and other species which take the hook, tends to relieve the com- 

 petition on the less desirable kinds and causes them, rather than the desirable kinds, to 

 increase. Furthermore, the undesirables are usually fish such as carp, buffalos, suckers, 

 bullheads and gizzard shad, which roll the bottom muds and Interfere with the feeding and 

 biting of those kinds, such as bass, crapples, bluegllls and other sunfishes, which depend 

 on their sense of sight. In such cases, additional stocking does not improve fishing but 

 merely aggravates the condition of overcrowding. 



The ordinary evidence used to support the claim of a loss of fertility would have 

 been borne out by the history of Fork Lake, where success of fishing declined to a very 

 low point over a period of years. When poison was applied and a census made, the lake's 

 carrying capacity for fish was found to be very high, but the fish population consisted 

 of stunted hook-and-llne species and undesirables. After these were replaced with small 

 numbers of desirable fish, the lake again produced good fishing. Fishing in Horseshoe 

 Lake was greatly Improved in much the same manner. (Thompson & Bennett 1938; and Ellis 

 1937, disciassion). 



Small percentages of fish of desirable sizes and evidence of slow growth are often 

 misinterpreted in making recommendations for fish management. Too often. Improved spawn- 

 ing facilities, greater length limits and other restrictions have been applied to correct 

 such conditions. To us It appears that the remedy is the exact opposite — to restrict re- 

 production and to thin the population so that growth rates will be increased and more fish 

 reach attractive sizes. 



SUMMARY 



1. In 1939, after Fork Lake had been stocked in 1938 with 270 adult bluegllls and 

 1,440 largemouth bass fry, 1,289 fish weighing 223.4 pounds were removed. This cropping 

 was done at monthly intervals at the rate of about 25 pounds of fish per month. The total 

 yield for 1939 was at the rate of 162 pounds of fish per acre. 



2. The lake also produced about 99 pounds of turtles, 1.6 pounds of bullfrogs and 

 14 muskrats. On the 60 acres of land immediately surrounding Fork Lake, 49 quail and 134 

 rabbits were killed by huntere. 



3. Previous to the elimination of the old population and the restocking in 1938, 

 only 1.8 per cent of the fish of Fork Lake were of desirable sizes. During 1939, 39.2 per 

 cent of all fish taken with inchnuesh hoopnets or hook and line were of desirable sizes 

 (see tables 3 and 4). At the end of the season this percentage was much higher. 



4. A few bass reached legal length at the age of 13 to 14 months. Yearling bluegllls 

 taken from the lake in September, October and November averaged more than 6 Inches in 

 length. The breeder bluegllls grew rapidly in 1938, but slowly In 1939. 



5. The index of condition was high In bluegllls until the onset of the spawning 

 period, when it dropped. A slight improvement in condition appeared in late August and 

 September, followed by a drop in October and November. Bass were of average plumpness 

 when compared with those of other Illinois waters, and did not vary much tltroughout the 

 year. 



6. Many fish from Fork Lake were heavily parasitized. This condition did not seem 

 to affect their growth. 



7. Some of the yearling bluegllls had formed annull on their scales before April 18, 

 and all of them had formed annull by the end of May. Most breeder bluegllls began annulus 

 formation later than the yearlings and did not complete this formation until October. 

 Annulus formation in bass extended from mid April to late September. A second or false 

 annulus appeared in many fish. Thirty-eight per cent of the yearling bass and 24 per cent 



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