AUTHORS: Tammy M. Wilson, U.S. Geological Survey - Columbia Environmental Research Center Michael E Byrne, Department of Natural Resources, University of Missouri, Columbia Thomas W. Bonnot, Department of Natural Resources, University of Missouri, Columbia Robin D Calfee, U.S. Geological Survey - Columbia Environmental Research Center Matthew R Acre U.S. Geological Survey - Columbia Environmental Research Center
ABSTRACT: Grass carp (Ctenopharyngodon idella) are nonnative, herbivorous freshwater fish that represent an invasive, ecological threat in North American waters. They originate from eastern Asia, consume large amounts of aquatic vegetation, and establishment in novel waters can cause significant ecosystem changes. There is particular concern for grass carp establishment within the Lake Erie basin, where multi-jurisdictional grass carp removal efforts have been ongoing since 2017 to reduce Lake Erie's population and the chance of dispersal to the rest of the Great Lakes. However, effectiveness of removal efforts has yet to be quantified. Grass carp in Lake Erie are data-limited as catch numbers are < 100 per year. Therefore, we used multiple length-based stock assessment methods to evaluate if removal efforts were sufficient to reduce population size. We used a combination of length-based indicators (LBI), the length-based spawning potential ratio (LBSPR), and the length-based Bayesian biomass estimation (LBB) method to assess the stock. Although these length-based methods run on the assumption of a stock at equilibrium rather than a potentially growing population, by using multiple length-based methods to assess this stock, we worked to minimize biases that may have occurred. Preliminary results highlight the absence of immature removals and indicate that removal efforts may need to target smaller fish to collapse the population.
