Comparison of concurrent trap-net and gill-net samples for black bullheads

Abstract

We compared concurrent trap-net (i.e., modified fyke net) and gill-net catches of black bullhead (Ameiurus melas) from 28 South Dakota water bodies sampled in 2000 or 2001. The length-frequency distribution of sampled black bullheads was significantly different (P = 0.0001) between gears, primarily because the trap nets commonly collected bullheads less than 150 mm total length, while such fish were collected in low numbers by the experimental gill nets. Size structure of stock-length (i.e., >150 mm) black bullheads was similar between gears, as evidenced by a correlation of proportional stock density values (P = 0.0001) with the y-intercept not different from 0 and the slope not different from 1. However, mean catch per unit effort (CPUE) of stock-length black bullheads in the two gears was not correlated (P = 0.10). Mean trap-net CPUE had a broad range (from near 0 to over 2,300 per net-night), while mean gill-net CPUE did not exceed 250/net-night, perhaps because of net saturation. Thus. both trap nets and experimental gill nets provided similar indices of population size structure, but the trap nets may provide a better index of relative abundance for black bullhead population monitoring.