392 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 3 



of age group II of the 1939 collection, 

 shows the largest first-year growth. 

 Schoffman's data are based on the average 

 actual lengths of fish on which ages were 

 determined. Points at the extremities of 

 the Norris Reservoir and the Onized Lake 

 curves represent average actual lengths of 

 fish at the time of capture. As shown in 

 fig. 5, the growth curve of the black crap- 

 pies from Onized Lake lies between the 

 other two, indicating that the Onized Lake 

 fish grew faster than those of Reelfoot, 

 hut less rapidly than those of Norris Res- 

 ervoir. 



The excessive cropping of Onized Lake 

 resulted in an unusually rapid rate of 

 growth of black crappies. Schoffman 

 (1940) in his study of Reelfoot Lake 

 black crappies suggests that the minimum 

 legal length of crappies in Tennessee be 

 increased from 8 to 9 inches, in order to 

 give them greater protection and "since 

 the greatest weight per length is reached 

 in the 8th summer." An assumption of 

 this kind is not valid, because fish growth, 

 within limits, is a reflection of food 

 abundance. 



Bluegill 



Lepomis macrochirus Rafinesque 



Bluegills apparently thrive under con- 

 ditions of intensive fishing. Not only did 

 this species make up 60.9 per cent of the 



number and 48.1 per cent of the weight of 

 all fish taken bv fishermen from Onized 

 Lake, 1938-1941, table 5, but, in the final 

 fish census, bluegills represented 71.4 per 

 cent of all fish present, and their weight 

 was 52.7 per cent of the weight of all fish. 

 As recorded in the creel census, the aver- 

 age weight of 2,433 bluegills caught was 

 0.23 pound, table 5 ; a fish of this weight 

 has a length of slightly more than 6 inches. 

 The largest bluegill recorded by the custo- 

 dian weighed approximately 1 pound. 

 Bluegills caught and recorded in the creel 

 census of 1939 averaged larger, weighing 

 0.25 pound each, than in succeeding years; 

 in 1940, the average weight was 0.21 

 pound and, in 1941, 0.18 pound, table 5. 

 Table 17 gives the age-length frequencies 

 of the bluegills taken in the 1941 census. 

 As many of these fish were not accurately 

 aged or measured, but sorted into age 

 groups on the basis of their size range, 

 this table is an estimate of the actual age- 

 length distribution of the population. No 

 fish in the collections were much more 

 than 3 years (in fourth summer) of age. 

 As in similar tables for other species, 

 the number recorded for 1941 brood blue- 

 gills does not represent the actual number 

 in the lake at the time of poisoning. The 

 1941 brood probably exceeded the 1940 

 brood in number of individuals. The 

 number of individuals of desirable sizes 

 listed in table 8 represents an accurate 



Table 17. — Age-length frequencies of the 6,545 bluegills collected from Onized Lake in 

 the census of June 24-28, 1941. The census was made about II/2 months after the spawning sea- 

 son, and the lengths shown for each age include the growth increment for the early part of the' 

 1941 season. 



2 55 



i 145 



3 36 



1 



2 



4 



2 



5 



1 



2 



6 Desirable Size 



2 



7 



1 



2 



Total 236 



11 

 11 



36 

 25 

 83 



\ 



