Trophic status of a non-native crayfish in an oligotrophic lake: bottom-up view of a mixed warmwater and coldwater sport fishery food web

Abstract

Loffredo JR, Moore BC, Lee RW, Katz SL, Cross BK. 2019. Trophic status of a non-native crayfish in an oligotrophic lake: Bottom-up view of a mixed warmwater and coldwater sport fishery food web. Lake Reserv Manage. 35:396–414.Numerous studies in recent decades have observed variable trophic status for freshwater crayfish among endemic and exotic populations in lentic or lotic habitats. In this study, we used stable isotope analyses (SIA) to explore trophic status of an introduced population of northern crayfish (Faxonius virilis) in Buffalo Lake, Washington. Northern crayfish are an important prey item for introduced warmwater and coldwater fish species in this lentic system and may buffer competitive interactions between largemouth bass (Micropterus salmoides), rainbow trout (Oncorhynchus mykiss), and kokanee (Oncorhynchus nerka). In 2017, the δ13C and δ15N values of liver samples from 208 crayfish informed proportional diet estimates. Crayfish diets were comprised of 8 littoral sources and were examined for cannibalism, temporal, spatial, and ontogenetic trophic shifts. There was no significant spatial or temporal trophic shift detected in this crayfish population. Seasonal δ15N values among all crayfish size classes mirrored seasonal abundance shifts of littoral macroinvertebrates. A multiple-source stable isotope mixing model and relative trophic positions provided evidence for an ontogenetic trophic shift between juvenile and adult crayfish, from a generalist detritivore to a predatory diet dominated by Chironomidae and Ephemeroptera. The trophic status of Buffalo Lake crayfish may affect salmonid management goals if interspecific competition for food between crayfish and sport fish is biologically significant. Our research is an important first step to understanding crayfish trophic status in a lentic food web, and should inform fish stocking regimes and fishery regulations in management efforts to achieve long-term sustainability of this diverse fishery.