Dr. Michael Moore, U.S. Geological Survey, Iowa Cooperative Fish and Wildlife Research Unit
Dr. Michael Weber, Iowa State University
ABSTRACT: Crayfish play an important ecological role in freshwater systems, as they are pivotal in freshwater food webs, acting as important consumers and prey resources and as ecosystem engineers. Despite their importance, crayfish populations are declining globally, due to anthropogenic land use changes and competition from introduced species. This decline has raised concerns about crayfish populations in Iowa, especially in the heavy altered prairie pothole region. Thus, our objectives are to determine the environmental variables associated with occupancy of crayfish across the prairie pothole region of Iowa, as well as assess the variables affecting crayfish detection probability to aid in future sampling and monitoring efforts. We sampled 25 wetlands and 19 natural lakes using baited minnow traps, and collected trap-level habitat data that we hypothesized would explain the variation in detection probability among traps including dissolved oxygen, pH, water temperature, dominant substrate, and presence of cobble and macrophytes. Additionally, we recorded lake-scale data such as waterbody type, mean depth, percentage of macrophyte, and fish stocking effort that we hypothesized would explain variation in occupancy probability among waterbodies. Of our 1195 traps, 110 traps captured Calico Crayfish (Faxonius immunis) across 19 sites and 25 traps captured Virile Crayfish (Faxonius virilis) across 9 sites. There were distinct habitat differences between the two species, with all F. immunis being found in wetlands and all but three F. virilis being found in natural lakes. Our data suggest that occupancy of these crayfish is low, but is strongly associated with water body type and that detection probability is also low. However, detection probability increases when traps are located near cobble habitats for F. virilis and macrophytes for F. immunis. This emphasizes the importance of managing these species separately, but also providing diversity of habitat types across the prairie pothole region for crayfish diversity to thrive.
