Comparison of Green and White Mesh Trammel Nets and Gill Nets to Assess the Fish Community in a Large River

Abstract

Standardized monitoring programs in great rivers need to identify and minimize the bias in the estimates of fish population characteristics to enable fishery managers to make informed decisions. We compared the effectiveness of green and white mesh in drifted trammel and anchored gill nets in capturing fish in the Missouri River from downstream of Fort Randall Dam, South Dakota, to the mouth of the river near St. Louis, Missouri. Sampling occurred from March to November 2006 and from April to May 2007. Paired green and white trammel net drifts (N = 383) caught 28 fish species from 12 families. Pairs of anchored gill nets set overnight (N = 193) caught 24 fish species from 12 families. Chi-square tests indicated that for most species there were no significant differences in occurrence between mesh colors in both the trammel and gill nets. However, occurrence was significantly higher in white mesh nets for goldeye Hiodon alosoides and blue sucker Cycleptus elongatus in trammel nets and for river carpsucker Carpiodes carpio and walleye Sander vitreus in gill nets. Despite turbidities in the Missouri River that ranged over two orders of magnitude, analysis of covariance indicated that water clarity had no significant effect on capture rates between green and white meshes. The majority of the variance in mean catch per unit effort (CPUE) of these species in both gears was spatial or temporal. In general, CPUE and precision were either similar or higher for white nets, making it unnecessary to dye nets green, which saves time and money. Because turbidity did not significantly affect catch rates between green and white mesh nets, the variations in CPUE can more confidently be attributed to localized changes in the actual relative abundance throughout the Missouri River.