May, 1945 



Bennett: Overfishing, Onized Lake 



389 



Black crappies taken in hoopnets from Onized Lake in 1940. These crappies were li 

 and 21 years old. 



Scales and total length measurements 

 from crappies taken from hoopnet collec- 

 tions in 1938 and 1940, and from 21 of 

 the 22 fish taken in the final census, were 

 used in calculating the lengths shown in 

 tables 14, 15 and 16. 



The lengths of black crappies collected 

 from Onized Lake are plotted in fig. 4. 

 No crappies older than four summers are 

 known to have been taken from the lake 

 during this study. Calculated lengths of 

 the 1938 and 1941 crappie collections 

 showed relatively slow growth rates for 

 the first year, and a marked increase dur- 

 ing the second growing season. The 1940 

 collection included 226 crappies in their 

 second summer of life (1939 brood) that 

 averaged 4.02 inches for calculated first 

 year growth, or about a half more than 

 the first year lengths for the other collec- 

 tions. Most of the fish of the 1940 collec- 

 tion were spawned in the year of the great- 

 icst hook-and-line yield, and their rapid 

 Igrowth may have been related to an abun- 

 jdant food supply resulting from the re- 

 moval of many fish. Growth stimulation 

 caused by an increased amount of avail- 

 able food brought about by one of several 

 possible situations has been observed in 



Table 13. — Age-length frequencies of the 22 

 black crappies collected from Onized Lake in 

 the census of June 24-28, 194L The census 

 was made about V/i months after the spawn- 

 ing season, and the lengths shown for each age 

 include the growth increment for the early 

 part of the 1941 season. 



