Print PageSpecies invasions are considered a major driver of global ecological change, and the magnitude of an invader’s impact on a system is correlated with its abundance. Round gobies (Neogobius melanosomus) were discovered in the Great Lakes in the early 1990s, have since had negative impacts on native fish populations, and are now expanding into tributaries of the Great Lakes. To learn more about their impacts on native fishes in streams, we conducted an in-stream mesocosm experiment across a gradient of round goby density: 0/m2 (density before invasion), 2.7/m2 (density at study site), and 10.7/m2 (density of Great Lakes coastal habitats and several tributaries). Each treatment had an equal density of native fishes, including common shiners, creek chubs, white suckers, and johnny darters. Each individual was weighed before and after the experiment so fish growth could be measured.
Results/Conclusions
Our results showed that when compared to the control (density of 0 round gobies/ m2), a low goby treatment (density of 2.7 round gobies/ m2) led to weight loss in native fishes. Relative to the low-goby treatment, a high goby treatment (density of 10.7 round gobies/ m2) led to weight gain in native fishes and weight loss in round gobies. These results show a parabolic relationship between round goby abundance and native fish growth. This suggests that round gobies do have a negative effect on native fishes in streams, which decreases when round gobies achieve Great Lakes density. This study indicates that when round gobies attain a sufficient density, an increase in intraspecific competition causes a decrease in interspecific competition – this may illustrate a density-dependent mechanism of upstream expansion.
