Comparative fecundity of the imperiled crayfish Faxonius quadruncus creaser and invasive crayfish Faxonius hylas (FAXON) in the St. Francis River drainage of Missouri, USA

Knowledge of crayfish species' life history traits is vital to their conservation and management. Fecundity is one trait that is a likely indicator of extinction risk and potential invasiveness. Fecundity-related data are lacking for the imperiled St. Francis River crayfish (Faxonius quadruncus) that is declining in the presence of the invasive woodland crayfish (Faxonius hylas). We sampled ovigerous females in three populations each of F. quadruncus and invasive F. hylas in Missouri (USA) Ozarks streams during April 2014 to compare fecundity and egg size between the two species. Differences in fecundity-related traits existed among populations of F. quadruncus, but no differences existed between the species. Results for both species were well within the ranges reported for other Faxonius species, but likely reflect small sample sizes rather than the entirety of each species. We also investigated the utility of field versus laboratory fecundity measures and found that field egg counts on live females varied among observers and also underestimated laboratory counts by an average of 22%. We provide a linear equation that can serve as a correction adjustment for field pleopodal fecundity estimates on live females to avoid specimen sacrifice during future monitoring of these species.