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Fishery independent gill net surveys provide valuable demographic information for population assessment and resource management, but relative to net construction, the effects of ancillary species, and environmental variables on focal species catch rates are poorly understood. In response, we conducted comparative deployments with three unique, inter-agency, survey gill nets used to assess walleye Sander vitreus in Lake Erie. We used an information-theoretic approach with Akaike’s second-order information criterion (AICc) to evaluate linear mixed models of walleye catch as a function of net type (multifilament and two types of monofilament netting), mesh size (categorical), Secchi depth, temperature, water depth, catch of ancillary species, and interactions among selected variables. The model with the greatest weight of evidence showed that walleye catches were positively associated with potential prey and intra-guild predators and negatively associated with water depth and temperature. In addition, the multifilament net had higher average walleye catches than either of the two monofilament nets. Results from this study both help inform decisions about proposed gear changes to stock assessment surveys in Lake Erie, and advance our understanding of how multispecies associations explain variation in gill net catches. Of broader interest to fishery-independent gill net studies, effects of abiotic variables and ancillary species on focal specie’s catch rates were small in comparison with net characteristics of mesh size or twine type.

Patterns in abundance, growth, and condition of lake whitefish (Coregonus clupeaformis) from Lake Erie were compared with those from Lake Ontario. Discontinuous assessment data were available from 1972 to 2003 for each lake to describe abundance, growth, and condition, while a seasonally intensive field program was undertaken in 2003 to describe diet, energy density, and gonadosomatic index (GSI). Through time, abundance declined more in Lake Ontario than in Lake Erie. Length-at-age (growth) and condition both declined significantly in Lake Ontario but did not change in Lake Erie. Diet analysis revealed chironomids, dreissenid mussels and sphaeriids made up the bulk of lake whitefish diet in Lake Erie. Diet in Lake Ontario exhibited more seasonal variability with amphipods and gastropods comprising the bulk of the spring and fall diets, and dreissenid mussels dominating summer diets. Lake whitefish energy density (J/g wet mass) was significantly higher in Lake Erie than in Lake Ontario, increasin...