Fish community changes in Shoal Lake, Canada, following the overexploitation of walleye (Sander vitreus) (2015 MSc)

Overexploitation of a single target species often results in fish community changes. Commercial and recreational overexploitation of walleye (Sander vitreus) in Shoal Lake, Ontario, in the early 1980s resulted in a ban on walleye fishing. In this study, we summarize potential changes in the catch-per-unit-effort of large-bodied fishes (abundance and biomass in gill nets) and small-bodied fishes (abundance in shoreline seines) for most years in the period 1979-2001. Through our analysis of gill net data, we found that the collapse of walleye was followed by increases in the abundance and biomass of yellow perch (Perca flavescens), cisco (Coregous artedi), and white sucker (Catostomus commersoni). Lake whitefish (Coregonus clupeaformis) also increased following the collapse, but this pattern was confounded by reduction in the lake whitefish commercial harvest. We found no evidence that the collapse of walleye benefited potential competitors (e.g. northern pike, Esox lucius). The collapse also resulted in semi-annual alternations between minnow (Pimaphales spp.) and a combination of yellow perch and shiners (Notropis spp.). Overall, our results are consistent with the general literature showing that the overexploitation of a top predator affects the broader community and with the walleye literature showing that these community shifts tend to reflect a top-down, trophic cascade that stems more from predator-prey relationships than from competitive relationships. Our case study provides important insight into the structure and function of aquatic food webs and the trophic ecology of top predators.

Thao C, T Mosindy, PA Venturelli (2016) Fish community changes in Shoal Lake, Canada, following the overexploitation of walleye (Sander vitreus). Journal of Freshwater Ecology 31:443-450