May, 1945 



Bennett: Overfishing^ Onized Lake 



383 



Table 8. — Fish of desirable sizes* in Onized Lake at the time of the final census, June 24-28, 194L 



Species 



Per Cent of 

 Number Total Number of 



Named Species 



Weight, 

 Pounds 



Per Cent of 



Total Weight of 



Named Species 



Largemouth bass 47 



Black crappie 7 



Bluegill 325 



Warmouth bass 13 



Green sunfish 9 



Yellow bass 4 



Black bullhead 2 



Yellow bullhead 36 



Carp 1 



Golden shiner 37 



Total 481 



17.1 



31,8 



5.0 



0.8 



3.7 



100.0 



100.0 



10.4 



100.0 



41.1 



5.2 



101.8 



2.2 



55.6 



2.3 



1.6 



3.1 



2.8 



10.7 



12.0 



4.2 



196.3 



93.6 



68.3 



23.9 



8.0 



24.6 



100.0 



100.0 



28.9 



100.0 



58.5 



44.4 



♦Arbitrarily set at 10 inches for largemouth bass, 8 inches for black crappies, 7 inches for yellow bass, bullheads 

 and golden shiners, and 6 inches for bluegills, warmouth bass and green sunfish. 



tive numbers of fishes of desirable* sizes 

 then remaining in the lake; (3) the indi- 

 vidual ability of various species present 

 to withstand overfishing; and (4) the 

 effect of overfishing on the growth rates 

 of all species. 



A careful census was made during the 

 period of June 24 to 28, inclusive, and 

 data on a small number of dead fish found 

 after June 28 were tabulated by Austin 

 Vincent and John Conrad of the Owens- 

 Illinois Glass Company. Table 7 lists 

 the kinds of fish collected and gives details 

 as to numbers and weights. The lake 

 contained a total population of 9,171 fish 

 weighing 442.17 pounds, or, on the basis 

 of an acre, 4,586 fish weighing 221.09 

 pounds. It is of interest to note that the 

 1939 yield in pounds per acre was greater 

 than the weight of all fish per acre at the 

 itime of the complete census in 1941. All 

 I species of fish that were taken in the creel 

 census were present in the final census. In 

 addition, there were one carp, one common 

 sucker and one blunt-nosed minnow; these 

 i probably represented escaped bait. Fish- 

 ermen were allowed to use "minnows" in 

 fishing, but were asked to deposit them 

 [with the caretaker after fishing, rather 

 than release them in the lake. 



Of the 9,171 fish collected in the final 

 census, 481 or 5.2 per cent were of desir- 

 able sizes. However, these fish represented 

 44.4 of the weight of all fish. Listed in 



♦Desirable size is arbitrarily set as at least 10 inches 

 for largemouth bass, 8 inches for black crappies, 7 inches 

 r yellow bass, bullheads and golden shiners and 6 

 "dies for bluegills, warmouth bass and green sunfish. 



table 8 are the number and weight of the 

 fish of desirable sizes of each species; also, 

 the percentage of each species, by weight 

 and by number, in the desirable size class. 

 All the yellow bass were of desirable size. 

 On the other hand, only 5.0 per cent of all 

 bluegills present were of desirable size ; 

 their weight was 23.9 per cent of the 

 weight of all bluegills. The number of 

 bluegills of desirable size, 325, was much 

 larger than that of any other species ; also 

 the bluegills of all sizes were more numer- 

 ous than fish of other species. Although 

 only 17.1 per cent of the largemouth bass 

 were of legal size, the weight of these fish 

 was 93.6 per cent of the total weight of 

 all largemouth bass. 



Eflfects of Overfishing 



No fish population analysis may be con- 

 sidered complete unless the age composi- 

 tion of that population is known. In fishes, 

 where the pattern of growth may vary a 

 great deal with the amount of available 

 food, the length of the growing season, 

 and the potential size and age for a selected 

 species, the scale method of age determina- 

 tion and its corollary, the calculation of 

 growth from scale measurements, is inval- 

 uable. 



Samples of scales were taken from many 

 fish collected in the final, or poison, cen- 

 sus of 1941. Because the accuracy of 

 growth calculations depends, among a 

 number of other factors, upon the accu- 

 racy of length measurements, fish badly 



