Factors Affecting Walleye Catch in Short-Term Gill-Net Sets in a Large Minnesota Lake

Abstract

Gill nets are a versatile fish sampling gear used for many species and habitats; however, their usefulness may be limited by selectivity patterns and reliance on fish movement, which can be influenced by several factors. We evaluated the effect of net length, time of day, sampling date, surface water temperature, soak time, water depth, and location on the number, length, and initial mortality of walleyes Sander vitreus caught in short-term (mean, 38.8 min; range, 10–200 min) gill nets set in Mille Lacs Lake, Minnesota. The number of walleyes caught was best described by a generalized additive model (GAM) that contained all seven covariates and explained 35% of the variation in catch. The length of walleyes caught was best described by a GAM that contained time of day, sampling date, soak time, and sampling location as covariates and explained 11% of the variation in fish length. The initial mortality of walleyes was best described by a GAM that included surface water temperature and soak time as covariates. Walleye catches were higher from dusk to dawn than at other times, with peak catches occurring around 0500 and 2100 hours, demonstrating the diel activity patterns of walleyes. Catches also increased with surface water temperature and soak time. However, the initial mortality of walleyes also increased with surface water temperature and soak time, with the largest increase in initial mortality at soak times longer than 60 min. Investigators can use these results to assist in designing and planning short-term gill-netting efforts to maximize the catch and minimize the mortality of walleyes.

Received June 23, 2010; accepted October 22, 2010

ACKNOWLEDGMENTS

We thank the many MNDNR field staff for assistance with the fieldwork and Daniel Isermann for encouraging pursuit of this analysis. Michael Hansen, the Associate Editor, and three anonymous reviewers provided helpful comments that improved the manuscript. Charles Anderson, Melissa Drake, Donald Pereira, and Rodney Pierce provided valuable reviews of an earlier version of this manuscript. Andrew Williquett provided assistance with creating Figure 1. The study was funded in part by the Federal Aid in Sport Fish Restoration (Dingell–Johnson) Program, D-J Project F29-R, Minnesota.