Spatio-temporal changes in littoral fish community structure along the St. Lawrence River (Québec, Canada) following round goby (Neogobius melanostomus) invasion

The round goby (Neogobius melanostomus), a small Ponto-Caspian bottom-dwelling fish species, was first observed in the St. Lawrence River in 1997. After twenty years, it is now considered as one of the most successful invaders of the St. Lawrence River. Despite the elevated abundances observed throughout the river, little is known about its impacts on the littoral/mid-shore fish community. In this study, we used a large dataset obtained from an annual standardized fish survey held in the St. Lawrence River to analyze the impacts of round goby on littoral native fish community and native predator assemblages within five distinct segments of the river characterized by different round goby abundances. Throughout the system, the round goby negatively impacted the abundances of tessellated darter (Etheostoma olmstedi) likely as a consequence of competitive exclusion. In contrast, the small pelagic/demersal brook silverside (Labidesthes sicculus) and emerald shiner (Notropis atherinoides) increased in abundance. Indirect food web effects, such as predation pressure relaxation, are suspected. Native predator abundances exhibited contrasting trends in the different sectors analyzed, with the exception of smallmouth bass (Micropterus dolomieu) abundances that increased in all fluvial lakes. We hypothesize that trophic relationships between littoral fish and native predators are influencing the outcomes of the round goby invasion of the St. Lawrence River