Response of Native and Naturalized Fish to Salmonid Cage Culture Farms in Northern Lake Huron, Canada

Abstract

AbstractCage culture of salmonids has expanded into the northern Great Lakes in recent decades, but the effects of this industry on native and naturalized freshwater fish communities have yet to be fully explored. We compared the relative abundance, community composition, and stable isotope composition of wild fish and selected macroinvertebrates between cage and reference sites in the Manitoulin Island region of northern Lake Huron to test the proposition that cage culture operations have altered their distributions and trophic ecologies. Catch per unit effort was higher at cage sites than at reference sites for both small‐ and large‐bodied fishes, but not for crayfish. Species composition varied significantly between cage and reference sites for the small‐fish assemblage but not for the large‐fish assemblage. The stable isotope ratios (δ13C, δ15N, and δ34S) of dreissenid mussels, crayfish (family Cambaridae), and four species of small‐bodied fish did not differ greatly between the cage and reference sites, suggesting that the direct consumption of farm waste is limited. However, the overlap in isotopic signatures between farm waste and wild biota was considerable. Salmonid cage farms in northern Lake Huron are an attractant to many species of wild fish, but it is not clear how the waste from these farms enters the local food web.