390 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 3 



Table 14. — Average calculated total lengths in inches of 98 black crappies collected with 

 hoopnets from Onized Lake, August 29-31, 1938. 



Brood 



1935... 

 1937... 

 Total. . . 

 Average . 



'■.35 



9.00 



11.38 



fish many times (Beckman 1941; Ben- 

 nett, Thompson & Parr 1940; and oth- 

 ers). It lasts until natural reproduction 

 supplies a sufficient number of individuals 

 to cause severe competition for food. In 

 the case of Onized Lake, in which the in- 

 creased growth rate observed in the 1940 

 collections did not persist, it must be 

 assumed that, as the population of crappies 

 was not being replaced adequately by natu- 

 ral reproduction, some other species (pos- 

 sibly young bluegills or warmouth bass) 

 offered sufficient competition to the young 

 crappies to reduce their first year growth 

 rate to about that of the 1937 brood. 



A few growth studies made on the black 

 crappie supply some information on the 

 yearly length increment of this fish in 

 waters of other states. Eschmeyer & 

 Jones (1941) include the black crappie 

 in their study of the growth of game fish 

 in Norris Reservoir, and Schoffman 

 ( 1940) gives data on black crappie growth 

 in Reelfoot Lake. Material from these 

 sources, along with calculated lengths 

 of black crappies from Onized Lake, 1940 

 collection, has been used in the drafting of 

 fig. 5. The growth curve for Norris Res- 

 ervoir is based on age group III of the 

 1940 collection, which, with the exception 



10 



8 



(0 



u 



X 



u 



z 



I 

 I- 

 o 



z 



UJ 



4 



-1 

 < 



I- 



O 2 



YEARS 



OF 



LIFE 



Fig- 4. — Average rate of growth of black crappies taken from Onized Lake as shown by 

 1938, 1940 and 1941 collections. Crappies spawned in 1939 (1940 collection) showed unusually 

 rapid first year growth. 



