Shelter, respiration rates, and prey consumption as factors contributing to displacement of mottled sculpin (Cottus bairdi) by round goby (Apollonia melanostomus) in Great Lakes nearshore areas

Great Lakes mottled sculpin (Cottus bairdi) populations appear to be declining in response to round goby (Apollonia melanostomus ) invasion of nearshore areas. I conducted several laboratory experiments to evaluate the potential mechanisms and consequences of this native fish displacement. First, I evaluated the respiration rates of these two species as a function of shelter availability. Respiration rates were not significantly different between shelter and non shelter treatments for both species. In addition, respiration rates were not significantly different when the species were compared by size regardless of treatment. Large mottled sculpin and round goby respiration rates were significantly greater than smaller fish of the same species. I also conducted maximum consumption trials using amphipods as prey items. Surprisingly, mottled sculpin consumed significantly greater numbers of amphipods than round goby. The larger fish consumed more amphipods than the smaller fish. Mottled sculpin and round goby biology and ecology overlap making them competitors in the nearshore areas of the Great Lakes. The results of this study suggest that round goby have the potential to cause ecosystem-wide bioenergetic changes because although respiration rates are the same as the mottled sculpin at similar sizes, round goby can grow larger and occur in greater numbers, thereby generating greater metabolic demands compared to the native mottled sculpin.