Habitat-Mediated Impact of Round Goby in Tributaries

Round goby (Neogobius melanostomus) are currently invading Great Lakes tributaries; however, their impacts on native fish communities in tributaries to date appears to be less severe than in the Great Lakes proper. In tributaries, higher overall water velocity may form an effective barrier to the upstream movement of round goby, which cannot sustain high swimming speeds. On some Great Lakes tributaries, dams may impede round goby range expansion; however, when round goby arrive upstream of dams, the slower water velocity in reservoirs may provide a refuge for this typically lentic species that facilitates its establishment and further spread. As average water velocity increases upstream of the reservoir, we hypothesize that the competitive advantage of round goby over native benthic species (e.g., logperch Percina caprodes) that has been previously observed will shift in favour of natives that are adapted to higher water velocities. These species overlap in the Grand River (southern Ontario).  Here, we test variation in the magnitude of round goby impact on native benthic fish in relation to local variables (including water velocity and distance upstream from high-abundance round goby source populations) by developing theoretical path models and comparing them with field data.