Diet and foraging of Round Goby (Neogobius melanostomus) in a contaminated Harbour

Anthropogenic pollution and the introduction of damaging invasive species are two factors that commonly contribute to freshwater ecosystem degradation. Although Hamilton Harbour (ON, Canada) is a well-studied ecosystem, the diet, trophic position, and foraging behaviour of the invasive Round Goby (Neogobius melanostomus) in this highly impacted ecosystem was not well understood. In this study, we compared Round Goby digestive tract content, foraging behaviour, and stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope values of this benthic fish from sites of low and high sediment contamination (metals, PAHs, and PCBs) in Hamilton Harbour. We also assessed prey availability by conducting sediment invertebrate abundance analyses at these sites. Regardless of site, chironomids, cladocerans, copepods and dreissenids were the most common food items found in Round Goby digestive tracts, and females always had heavier gut contents compared to males. There was no effect of site contamination on species richness in the gut samples or species richness and abundance in sediment samples. However, fish from the high contamination site consumed fewer prey items, had lower gut fullness scores, and fed at a lower trophic level based on lower δ¹³C and δ¹⁵N. Our results suggest that Round Goby living in contaminated areas are feeding less than Round Goby from areas of lower contamination, and that these diet differences do not reflect differences in prey availability. Fish from the high contamination site also typically moved slower while foraging, but this slower movement did not translate into less food being consumed in this laboratory foraging experiment. Taken together, these results provide an analysis of the main prey items of Round Goby in Hamilton Harbour, and demonstrate how polluted environments can impact diet, prey availability, and feeding behaviour of an introduced fish species.