Do native predators feed on non-native prey? The case of round goby in a fluvial piscivorous fish assemblage

Abstract We evaluated whether or not the invasive round goby ( Neogobius melanostomus ) represents an important prey source for seven native fish predators in Lake St. Pierre (St. Lawrence River, Canada). The frequency of occurrence of round goby in the stomach contents of brown bullhead ( Ameiurus nebulosus ) and channel catfish ( Ictalurus punctatus ) was very low ( Perca flavescens ) and 65% (sauger; Sander canadensis ). Several competing models linking the probability of occurrence of round goby in stomach contents to variables related to space, physical habitat, biotic interactions and predator size were tested for the five species feeding on round goby. Results indicated that space variables influenced round goby occurrence in stomachs for all species. In addition, physical habitat variables had an influence for sauger and walleye ( Sander vitreus ); biotic variables had an influence for yellow perch, walleye and sauger; and size had an influence for northern pike ( Esox lucius ), smallmouth bass ( Micropterus dolomieu ) and walleye. These results are discussed in light of known biological features of the round goby and native predators studied here and have important implications in terms of understanding round goby invasion success in the Great Lakes–St. Lawrence system.