Movement, habitat use, and survival of juvenile grass carp in an Appalachian reservoir

Abstract

Grass carp Ctenopharyngodon idella have been widely introduced in aquatic ecosystems to combat outbreaks of problem aquatic plants. However, the extent to which introduced carp stray from intended habitats and ecosystems is frequently unevaluated. Grass carp were stocked into a temperate riverine and montane reservoir (Claytor Lake, VA USA) to control a rapidly spreading Hydrilla verticillata infestation. Fish introductions sparked concern that grass carp might exit the reservoir and impact adjacent river ecosystems and native plants. We conducted a 2-y telemetry study concurrent with annual grass carp stockings in Claytor Lake to investigate migration potential, habitat use, and annual survival of recently introduced grass carp. We radio-tagged 34 and 45 juvenile grass carp in 2011 and 2012, respectively. In both years, grass carp movements were highest during the first month post-stocking and declined dramatically thereafter, presumably due to carp settling in areas with high hydrilla biomass. Only 3% of radio-tagged grass carp exited the reservoir upriver over the study period. Statistical modeling indicated grass carp movements were driven largely by temperature, while other climatic (e.g., wind speed and barometric pressure) and habitat variables (depth, vegetation coverage) were occasionally also important. Year-1 survival of grass carp was 44% for the 2011 cohort, and 25% for the 2012 cohort. Even though young grass carp did not express an inclination for out-reservoir migrations during the study, these patterns may change as fish approach sexual maturity, hydrilla coverage declines, and divergent climate variations occur. We recommend managers continue monitoring grass carp movements alongside changes to the spatial and temporal dynamics of hydrilla in the reservoir over time.