| dc.description.abstract | Many invasive species have established in the Laurentian Great Lakes basin and have caused substantial impacts to native species and the lacustrine ecosystems within the basin. The establishment of Round Goby (Neogobius melamostomus) in the Great Lakes and its subsequent effects on native species have been well documented. However, after its secondary invasion into tributaries of the Great Lakes, there is limited study of how Round Goby has affected the native fishes within these ecosystems. Therefore, the overall objective of this research was to increase understanding of how Round Goby has affected the relative abundance, diversity, and resource use of native fishes in tributary ecosystems of the Great Lakes.
The catch per unit area (CPUA) of Round Goby in both the Ausable River (a tributary of Lake Huron) and Big Otter Creek (a tributary of Lake Erie) was highest in the downstream reaches located closest to lake habitats, but CPUA rapidly decreased upstream from each lake and approached zero after 18 and 14 river km upstream in the Ausable River and Big Otter Creek, respectively. A negative relationship between the CPUA of Round Goby and several darter species was detected along the tributaries, with moderately negative association between Round Goby and Rainbow Darter (Etheostoma caeruleum) in the Ausable River and Johnny Darter (Etheostoma nigrum) and overall Percidae species in Big Otter Creek. The negative relationship between the CPUA of Round Goby and these darter species was found over greater spatial scales than reported in previous studies of Round Goby in Great Lakes tributaries and highlights how impacts from Round Goby likely vary both temporally and spatially.
To better understand resource use by Round Goby, stable isotope values of Round Goby in Big Otter Creek were compared to values of Round Goby from around the Great Lakes. Round Goby displayed high niche plasticity across the Great Lakes basin, but were generally more depleted in δ13C in Big Otter Creek than in Great Lakes populations. Additionally, the resource use of benthic and benthopelagic fishes was compared between sites where Round Goby was present and absent in Big Otter Creek to determine whether Round Goby may have altered trophic relationships. Benthopelagic species appeared to shift their resource use in the presence of Round Goby, whereas significant resource overlap was evident between benthic species (including Blackside Darter (Percina maculata) and White Sucker (Catostomus commersonii)) and Round Goby. The effects of niche compression on benthic species were reflected by reduced mean fish condition, which benthopelagic species appeared to have avoided due to the larger isotopic niche shift away from that of Round Goby. Round Goby was also associated with reduced relative abundance of native fishes, suggesting a resource-based competitive effect. Collectively, results show that Round Goby has affected the ecological resource use of native fish communities in a Great Lakes tributary and that benthic species (and those unable to shift their resource use) are likely most susceptible to competition pressure from Round Goby. | en |
