Early Round Goby (Neogobius melanostomus) Invasion Into Lake Michigan Tributaries and Competitive Interactions with Two Native Benthic Fishes.

The round goby is a prolific invasive species and is currently spreading into Great Lake tributary streams. There is a high potential for negative impacts on native benthic fishes in these stream habitats and the aim of this study is to assess the impacts of the round goby on two native darter species in particular (johnny darter and blackside darter). I review the history of round goby invasion in the Great Lakes and summarize hypotheses of the invasive characters of the round goby. Using game theory, I provide a G-function approach to understanding the outcomes of the round goby invasion in tributary streams. I conducted a field based laboratory study compare the fish communities in invaded and non-invaded reaches of two streams and found differences attributed to the CPUE of round gobies. CPUE of the johnny darter was different in invaded and non-invaded reaches, while it was not different for blackside darter. Stomach contents of the round goby and darters were analyzed and overlap was found between the invasive and native species. Finally, a laboratory experiment assessed the competitive behaviors of the round goby and the johnny darter and found that there were behavioral differences. The results for this study provide a baseline during the early invasion of two Lake Michigan tributaries and provide evidence of both exploitative and inference competition between the round goby and johnny darter. It is likely that these competitive interactions resulted in a realized niche shift of the johnny darter and there is a high likelihood that continued competition between the johnny darter and round goby will possibly result in a population decline of the johnny darter or even local extirpation