Long-Term Impacts of the Invasive Round Goby Neogobius melanostomus on Fish Community Diversity and Diets in the St. Clair River, Michigan

Abstract

Round gobies (Neogobius melanostomus) were first documented within the St. Clair River in 1990, and subsequently impacted native benthic fishes, including sculpins and darters, through direct predation and competition for space and prey. In order to identify long-term impacts on fish species associated with the round goby invasion in the St. Clair River, Michigan, I compared fish community composition and diet overlap between round goby and native species in 1994 with similar data from 2011. All fish were collected by trawls (3-, 5-, 7-, 9-, 11-m depths) and seines (1 m) in May, July, and September 2011, and compared to similar data collected in May, June, and September 1994. Catch-per-unit effort (CPUE) for rainbow darter (Etheostoma caeruleum) and round goby significantly decreased in the nearshore zone between 1994 and 2011. In the offshore zone, relative abundance of northern madtom (Noturus stigmosus) decreased significantly between 1994 and 2011, while round goby relative abundance both increased and decreased, depending on month. CPUE of channel darter (Percina copelandi), johnny darter (Etheostoma nigrum), mottled sculpin (Cottus bardii), and round goby also significantly decreased in the offshore zone between 1994 and 2011. There was significant diet overlap between round gobies and native rainbow darter in 1994, suggesting diet overlap and competition for food contributed to rainbow darter population declines in the St. Clair River from 1994 to 2011. However, significant diet overlap was also found in both years between round goby and other native species that did not decline from 1994 to 2011. In 2011, round gobies showed significant diet overlap with rock bass (Ambloplites rupestris) in the nearshore zone, and significant overlap with logperch (Percina caprodes) and trout-perch (Percopsis omiscomaycus) in the offshore zone. In 1994, reliance on zebra mussels (Dreissena polymorpha) by adult round goby prevented frequent significant diet overlap from occurring between large round gobies and native species that could not consume zebra mussels, but in 2011, round gobies, logperch, and trout-perch all consumed quagga mussels (Dreissena bugensis). These results suggest that differential foraging strategies allowed some native fish to forage without competition from round goby, and that the negative impacts of the round goby invasion and establishment on fish species diversity within the St. Clair River may be isolated to a few species, and due to competition for other resources, such as space. Establishment of the round goby within Great Lakes tributaries, nearshore environments, and more recently the Mississippi River basin will likely have differing impacts on native fish communities based on the pre-existing communities, other environmental stressors, and foraging habits of native fishes.