AUTHORS: Anna Raney, University of Missouri and Florida Fish and Wildlife Conservation Commission; Jacob Westhoff, U.S. Geological Survey, Missouri Cooperative Fish and Wildlife Research Unit, School of Natural Resources
ABSTRACT: Crayfish invasions are among the top global threats to native crayfish populations. In Missouri, cross-basin introductions have impacted multiple endemic species. The Saint Francis River crayfish (Faxonius quadruncus) and Big Creek crayfish (F. peruncus), endemic to the upper Saint Francis River (USFR) drainage in Missouri, are currently under threat of extinction due to introductions of Woodland Crayfish (F. hylas) from nearby drainages. Previous research has documented reduced abundances and range reductions for both native species in reaches invaded by Woodland Crayfish. However, the entire ranges of the native species have not been systematically sampled prior to this study, and past survey data documenting the invasion are over 15 years old. Management agencies need updated information to create an informed recovery plan for the two threatened species. Using a stratified random sampling design, we conducted a basin-wide distribution survey at 96 sites across the USFR drainage in 2022-2023. We incorporated presence-absence data from this survey with coarse-scale environmental variables into random forest, boosted regression, and spatial stream network models to create species distribution models for the two endemic species and the invasive Woodland Crayfish population. Additionally, we used targeted, intensive sampling to locate the leading edges of invasion in six streams. During these efforts, we discovered and mapped additional invasions in two major tributaries to the USFR drainage and documented a 1.4 km range expansion upstream from the 2009 leading edge in Orr Hollow Creek. The Woodland Crayfish is now present in most major tributaries on the left side of the basin as well as multiple locations in the mainstem river. Despite these range expansions, small impoundments at multiple locations appeared to harbor refuge populations of endemic crayfish based on survey data. Results from this study can be used to identify refugia for native species and locate barriers to further invasion.
