Spatial and seasonal variability in the diet of round goby (Neogobius melanostomus): stable isotopes indicate that stomach contents overestimate the importance of dreissenids

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Our results provide new information that diet, carbon source and trophic position of an invasive fish species, round goby ( Neogobius melanostomus ), varies seasonally, spatially and with body size in littoral habitats of Lake Ontario. Based on stomach contents and stable isotopes, round goby fed at a higher trophic position in the cooler, less productive Kingston Basin relative to the Bay of Quinte. Bay of Quinte round goby were more reliant on terrestrial carbon, whereas littoral carbon dominated in the Kingston Basin. Although stomach contents suggested dreissenids were the dominant prey item of round goby, stable isotope mixing models estimated that dreissenids were never >39% and 11% of the diet in Bay of Quinte and Kingston Basin, respectively. Stable isotopes indicated amphipods, chironomids and cladocerans were the most important prey, and were at times common items in stomach contents, but this varied with site, season and year. Given their high abundance, the impact of round gobies on the benthic biodiversity of the Great Lakes may be more significant than indicated by stomach content analysis alone.