Vulnerability of Juvenile Bighead and Silver Carps to Predation by Largemouth Bass

The establishment of Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix throughout the Mississippi River basin potentially expands the prey base for native predators. A mechanistic understanding of interactions between nonnative prey and native predators is needed to assess the potential for predator regulation of Hypophthalmichthys carp populations and impacts on native predator assemblages. We conducted a series of experiments to quantify the selectivity and efficiency of Largemouth Bass Micropterus salmoides predation on juveniles of both of these Hypophthalmichthys species and behaviors that potentially influence this selectivity and efficiency. Selectivity was measured over 24 h in 2-m-diameter pools containing one of two prey assemblages consisting of three individuals from each of three species: (1) Bighead Carp with native littoral (Bluegill Lepomis macrochirus) and pelagic prey (Golden Shiner Notemigonus crysoleucas) or (2) Bighead Carp, Silver Carp, and a morphologically similar native prey (Gizzard Shad Dorosoma cepedianum). Foraging efficiency and predator-prey behaviors were quantified in 45-min trials in which Largemouth Bass foraged on 10 individuals of a single prey species inside a 750-L observation tank. All prey species were readily attacked and consumed by Largemouth Bass; Silver Carp were selected less often than Gizzard Shad, and Bighead Carp were selected at a higher rate than any of the other prey species. Of the species tested, Bighead Carp formed the tightest schools and were captured most efficiently by Largemouth Bass. Overall, Hypophthalmichthys carps were similar to native prey in their vulnerability to Largemouth Bass; therefore, factors affecting Hypophthalmichthys carp availability relative to native prey may shape postinvasion predator-prey interactions.