Evaluation of Trophic Niche Overlap between Native Fishes and Young-of-the-Year Common Carp

Abstract

Common carp Cyprinus carpio is a ubiquitous invasive species that commonly imposes negative effects on aquatic ecosystems. However, research evaluating the effects of carp on native fishes is limited. Carp are highly fecund and larvae and juveniles can be abundant. If age-0 carp use similar prey resources as native fishes, they may compete if food becomes limited. We used traditional diet analysis for samples during Jul. and Aug. 2008 in Brant Lake. Stable isotopes were used for samples collected during Aug. and Sep. 2009 in Brant Lake and Lake Sinai to examine prey resource use by age-0 carp and four native fishes: bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, yellow perch Perca flavescens, and orangespotted sunfish Lepomis humilis. Age-0 carp were generally as or more abundant than native fishes. In Jul. Daphnia dominated the diets of all fishes sampled, resulting in high (>60%) dietary overlap ranging from 87–98%. In Aug. Daphnia density in Brant Lake declined and dominant diet prey types shifted for carp (to Trichoptera and Daphnia), yellow perch (to Amphipoda), and the three Centrarchids (to Cyclops and Diaptomus). This diet shift resulted in lower diet overlap between Centrarchids and either carp (<40%) or yellow perch (3–16%) but high diet overlap within Centrarchids (67–97%). Stable isotope analysis further indicated greater resource overlap when most fishes relied on zooplankton and lesser overlap as fishes shifted to benthic prey. Our results suggest that resource competition between age-0 carp and native fishes is most likely to occur during early summer if Daphnia availability becomes limited but becomes less likely as dominant prey in diets increasingly diverge among fish species over time.