Assessment of Lake Trout Refuge Effects on Fish Community Trends in Western Lake Superior

Aquatic Protected Areas (APAs) have been established for various ecological and socio-cultural purposes in the Laurentian Great Lakes, including encouragement of lake trout Salvelinus namaycush rehabilitation through creation of refuges protected from fishing mortality.  Controversy currently surrounds these refuges because previous research across the Great Lakes demonstrated conflicting results regarding refuge effectiveness, which is compounded by stakeholders in recreational, commercial, and tribal fishing sectors who resent associated harvest restrictions.  This controversy complicates policy decisions for management of lake trout in the Great Lakes, which historically is a high-priority species for rehabilitation because of its native status, ecological significance, and importance for the fishing industry.  Our research investigates the ecological significance of current lake trout refuges through assessment of the relative abundance of fish populations sampled inside versus outside these refuges.  Our assumption is that population abundance of species vulnerable to harvest will be higher within the immediate refuge vicinity than in surrounding areas without these no-take restrictions. To test our assumption, long-term fishery-independent survey data dating back to the early 1980s were compared after implementation of both the Gull Island Shoal and Devils Island Shoal refuges in the Apostle Islands Region of Lake Superior.  We evaluated the extent of potential refuge effects  through comparison of the changing trends in relative abundance of lake trout, lake whitefish Coregonus clupeaformis, and lake cisco Coregonus artedi at gillnet stations within and outside refuges.  Results to date indicate that trends in lake trout abundance increased at a marginally greater rate when calculated from stations sampled within the refuge versus outside over the time series.  However, while the overall trend in lake whitefish abundance increased over the entire time series, abundance inside the refuge remained significantly lower than in the surrounding vicinity.  This result poses interesting questions about the potential refuge effects on species other than lake trout and the potential for cascading trophic dynamics and top-down effects operating at different scales.  It is also possible that other factors, such as changes in fishing pressure in the area outside of refuge boundaries, might be exhibiting a more significant effect than the refuges on fish populations.  Improved understanding of the effects of these protected areas on critical populations is important to inform future fisheries management.  These developments may also help guide future research related to the use and location of APAs in the Great Lakes for protection and enhancement of Great Lakes fishes and their productivity.