Linking reproduction and recruitment: Identifying demographic bottlenecks limiting the spread of Bighead Carp and Silver Carp in the Ohio River

Objective Reproduction and recruitment represent distinct demographic processes that may independently limit establishment and spread of an invasive species. We evaluated reproduction and recruitment success of Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in the Ohio River basin across multiple spatial and temporal scales to identify potential demographic bottlenecks. Methods We assessed detection/nondetection data on Bighead Carp and Silver Carp eggs/larvae and young of the year (age 0) to provide information on these species’ reproduction and recruitment, respectively. Data were assessed at reach-level (i.e., pool) and site-level spatial scales and at annual and intra-annual temporal scales throughout the Ohio River basin, relating patterns of egg/larval and young-of-the-year occurrence to adult relative abundance, hydrologic conditions, and nursery habitat availability. Results Estimated occurrence of Bighead Carp eggs/larvae and young of the year was inconsistent throughout the study area, suggesting limited establishment success in the Ohio River. Silver Carp egg/larval persistence probability was primarily associated with adult densities rather than variation in flow or temperature, and eggs were estimated to occur across a large portion of the basin. However, Silver Carp young-of-the-year occurrence appeared to be spatially restricted. Annual pool and intra-annual site young-of-the-year persistence probability was correlated with the availability of nursery habitat at both scales. Young of the year were consistently detected at only one location, a floodplain lake (Hovey Lake) in the John T. Myers pool, indicating the presence of a potential localized source population in this location. Conclusions Silver Carp eggs/larvae were detected across much of the invaded portion of the Ohio River, suggesting that reproduction is widespread. However, young-of-the-year occurrence was most strongly associated with nursery habitat. In the Ohio River, the lack of widespread nursery habitat may be limiting the recruitment success of young-of-the-year Silver Carp into the population, potentially creating a demographic bottleneck that constrains their spread in this basin.