May, 1945 



Bennett: Overfishing^ Onized Lake 



387 



Table 12. — Average calculated total lengths in inches of 81 largemouth bass collected from 

 Onized Lake in the census of June 24-28, 194L 



Brood 



Number 



OF 



Fish 



Average Calculated Length by 

 Years of Life 



1936 8 1.68 



1937 7 4.81 



1938 7 3.93 



1939 17 4.07 



1940 42 3.07 



Total 81 



Average 3 .37 



9.40 

 10.32 

 10.83 

 11.15 



10.58 



13.21 

 14.04 

 14.90 



14.01 



16.24 

 16.75 



18.56 



16.48 18.56 



body of water contained a bass popula- 

 tion that comprised 13.2 per cent of the 

 weight of all fish present. 



In comparing the growth curves of 

 largemouth bass in these two lakes, fig. 2, 

 it is of interest to note that bass growth 

 in Onized Lake was relatively poor dur- 

 ing the first summer, but rapid in subse- 

 quent growing seasons, and that the 

 Onized Lake fish reached legal length 

 when almost a year younger than those of 

 Sportsmen's Lake. Slow first season 

 growth is also indicated for Onized Lake 

 in fig. 3, where the growth curve of bass 

 in this Illinois lake is shown with that of 

 618 bass from Wisconsin and 30 from 

 Louisiana (Bennett 1937). The first sea- 



son growth of bass in Onized Lake was 

 less than the growth of the Louisiana bass 

 and about equal to that of the Wisconsin 

 bass. The Illinois fish exceeded the Wis- 

 consin fish in size after the first year and 

 approached the Louisiana bass in size in 

 the second and third years of life, falling 

 short of the southern fish during the fourth 

 and fifth years. The explanation of poor 

 first year growth seems to relate to severe 

 competition among young fish of all species 

 in Onized Lake. The continually large 

 catch of adult fish reduced predation on 

 the young to the extent that an entire 

 growing season was required to decimate 

 their numbers. Meanwhile, because of 

 food competition among these young fish, 



2 

 YEARS 



4 

 OF 



6 

 FE 



8 



Fig. 2. — Average rate of growth of largemouth bass taken from Onized Lake in the 1941 

 census, and from Sportsmen's Lake (old gravel pit) near Lincoln, Illinois. 



