382 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 3 



ported to a breeding pond below the lake 

 dam. 



The hoopnet catches for the two seasons 

 are shown in table 6. Although the total 

 catch in number of fish was larger in 1940 

 than in 1938, the total weight of the catch 

 was less; the number per net-day was 3.37 

 times as great in 1938 as in 1940. Only 

 two species of fish, black crappies and blue- 

 gills, were numerous enough in these 

 catches for comparison. Both of these 

 species readily enter the nets. In 1938, 

 crappies were caught at the rate of 23.78 

 per net-day, while in 1940 the catch was 



The evidence of a reduced population 

 of fish of desirable sizes in 1940 is not as 

 strong from a comparison of the rate of 

 catch of hoopnets, as from the anglers' 

 records, but both census methods indicate 

 a striking reduction in the numbers of 

 these fish. 



Analysis of the Population 



On June 24, after Onized Lake had 

 been fished for 3 months in the 1941 sea- 

 son, the fish remaining in the lake were 

 poisoned with the object of making a 



Table 7. — Census of all fish in Onized Lake, area 2 acres, June 24-28, 1941. 



Fish Species 



Largemouth bass .... 

 Total 



Black crappie 



Bluegill 



Warmouth bass 



Green sunfish 



Yellow bass 



Total 



Yellow bullhead 



Black bullhead 



Total 



Carp 



Common sucker 



Total 



Golden shiner 



Blunt-nosed minnow. 

 Total 



Grand total 



Average per acre 



only 6.50 per net-day. In blue-gills the 

 reduction in numbers was not so marked, 

 as the 1938 catch was at the rate of 6.00 

 per net-day and the 1940 catch 2.75 per 

 net-day. The reduction in weights of 

 these two species from 1938 to 1940, as 

 shown by the catch per net-day, was even 

 greater than the reduction in numbers. 



detailed study of a population supposedly 

 depleted by overfishing. This study was 

 designed to give answers to a number of 

 questions ; namely, ( 1 ) the weight of fish 

 present in the lake, in pounds per acre, 

 after the removal of a 1939 crop of 349.95 

 pounds per acre and a 1940 crop of 142.52 

 pounds per acre; (2) the actual and rela- 



