Effects of a Non-Native Salmonid Removal on Native Fishes in a Lake Superior Coldwater Tributary

In order to investigate the ecological impacts of non-native salmonid fishes (Oncorhynchus spp.) on native brook trout (Salvelinus fontinalis) of conservation concern, a physical removal of steelhead trout and coho salmon occurred during 2008-2010 in Sevenmile Creek in the upper peninsula of Michigan. During 2011 reinvasion was monitored. Over the project, 3138 steelhead and 2177 coho salmon were removed. Brook trout CPUE modestly increased at the end of the removal. Brook trout habitat use shifted to more fish in lower reaches of the experimental river. Condition and movement patterns were also assessed. YOY and age 1 salmonid diet overlap was slightly higher within species, with the most interspecific overlap occurring within size/age classes and in June. Following removal, non-native salmonids quickly rebounded. This study demonstrates that non-native salmonids do generate potentially negative impacts on native fishes in the upper peninsula of Michigan, but that the interactions between these species are likely complex across time and space and may be poorly reflected in population abundance.  Managers seeking to conserve or rehabilitate native fishes in the region should consider the potential effects of non-native, socially valuable salmonids and consider logistically feasible management strategies to deal with the impacts of these fishes.