76 



Illinois Natlral History Survly Bulletin 



Vol. 27, Art. 2 



Studies on the effects of fish predators 

 were begun with the placing of six short- 

 nosed gars in a 1-acre pond containing 

 bass and bluegills; in this pond, bluegills 

 were constantly in a state of overpopula- 

 tion. Because the short-nosed gars were 

 unable to reproduce in the pond, their 

 numbers were easily controlled. From 

 this experiment, Durham (1955) expand- 

 ed the investigations of fish predation to 

 include about a dozen additional ponds 

 containing populations of stunted fish. 

 Using gars and cormorants as predators, 

 he was able to show improvement in 

 growth and size of fish and an improve- 

 ment in the survi\al rate of naturally 

 produced bass. 



Ten years of recording catches of fish- 

 ermen at Ridge Lake (Bennett 1954fl) 

 gave a yield figure of more than 11,000 

 largemouth bass following an original 

 stocking of 435 ; the fact that, in the last 

 6 years of the 10, 155,000 bluegills had 

 been removed following an original stock- 

 ing of 129 of these fish indicated that the 

 bluegills were not only more prolific but 

 showed a higher survival rate than the 

 bass. The annual hook-and-line yield of 

 bass varied between 10.9 and 30 pounds 

 per acre, although the lake was not con- 

 sidered a highly fertile one. During this 

 time the standing crop of bass varied be- 

 tween 30 and 50 pounds per acre. The 

 success of a bass spawn (and survival) 

 was negatively correlated with the num- 

 bers of yearling fish present in the lake, 

 particularly yearling bluegills. Young 

 bass surviving to post schooling fry stage 

 had about 1 chance in 35 of living to 

 reach a size of 7 to 10 inches; natural 

 mortality remained relatively high until 

 the fish reached an average weight of 

 0.75 pound; then it dropped to less than 

 5 per cent per year until fish reached 

 ages of 7 to 8 years, when the natural 

 death rate again became high. With the 

 s\stem followed at Ridge Lake of culling 

 the fish jvopulation at intervals of 2 years, 

 the average length of bass at the end of 

 the first growing season was 7.5 inches, 

 at the end of the second growing season 

 10.8 inches, and at the end of the third 

 13.0 inches. The single most important 

 fuuling at Ridge Lake was that a large 

 new year class of bass could be produced 

 at any spawning season by reducing the 



numbers of small bluegills in the lake 

 prior to the spawning period. This re- 

 duction could come about through arti- 

 ficial culling of the fish population, or, as 

 was later discovered, through concentrat- 

 ing the fish during the fall months pre- 

 ceding the bass spawning season by re- 

 leasing a large proportion of the water 

 from the lake and then allowing the lake 

 to refill over winter. Studies of the ef- 

 fects of these water releases, or draw- 

 downs, were begun in 1951 (Bennett 

 1954/') and they are still in progress. 

 Swingle tk Smith (1942), working on 

 fishes in Alabama ponds, built their man- 

 agement practices around a program of 

 pond fertilization ; they recommended 

 fertilization for ponds in other parts of 

 the country. In order to test the useful- 

 ness of fertilization as a pond manage- 

 ment technique in Illinois, Donald F. 

 Hansen began a testing program in ponds 

 located on the University of Illinois Ex- 

 perimental Farm near Dixon Springs in 

 southern Illinois, where soils are as poor 

 as any within the state. After 7 years of 

 fertilizing three ponds at various rates 

 with complete fertilizers and using three 

 other similar but unfertilized ponds for 

 controls, Hansen concluded that the im- 

 provement in fishing did not justify the 

 cost of the fertilizer, if fish were cropped 

 by hook-and-line. The unfertilized or con- 

 trol ponds furnished better bass fishing 

 than the fertilized ponds. Bluegills could 

 be caught at a more rapid rate in the 

 fertilized ponds, and the fish averaged 

 larger in size. In terms of extra fish flesh 

 produced by the fertilizer, the improved 

 fishing cost about $1.00 per pound of 

 fish. 



Tests on various combinations of fishes 

 in ponds have been going on for many 

 \ears (Bennett 1952). The combinations 

 used include largemouth bass-bluegill ; 

 largemouth bass-bluegill-waniiouth-black 

 bullhead ; largemouth bass-bluegill-war- 

 mouth-channel catfish ; largemouth bass- 

 golden shiner; largemouth bass— redear ; 

 largemouth bass-warmouth ; largemouth 

 bass-short-nosed gar; largemouth bass- 

 bluegill-short-nosed gar; smallmouth bass 

 alone ; and largemouth bass alone. No 

 combination appeared to be ideal, although 

 several combinations pro\ed to be as pro- 

 ductive of good fishing as the highly ad- 



