Anthropogenic effects on shallow lentic systems of the Prairie Pothole Region (PPR), such as draining, pollution, climate change, and invasive species, are major threats to aquatic species, including crayfish. Crayfish are critical for freshwater food webs and act as habitat engineers through their diets and burrowing behavior. However, crayfish are declining, facing similar anthropogenic effects as the aquatic systems of the PPR. Nearly a third of crayfish species lack data critical for creating effective management plans;​ yet many regions lack historical data on crayfish distribution, habitat associations, and species status. There is a vital need to limit these knowledge gaps to protect native crayfish against threats, including the introduction of invasive crayfish. Invasive crayfish are a major factor in the decline of native crayfish as they out-compete native crayfish for food and shelter. As invasive crayfish expand their range, it is important to understand how they influence native crayfish and identify their habitat associations in novel environments to prevent the spread to other systems.

Rusty Crayfish (Faxonius rusticus) is an invasive species that has caused damage to ecosystems across the United States and Canada by disrupting aquatic food webs and outcompeting native crayfish. In 2018, Rusty Crayfish were found in Storm Lake, a shallow glacial lake in northwestern Iowa. Storm Lake is on the western front of the Rusty Crayfish invasion region and has undergone a variety of enhancement projects, making it a novel system for examining the habitat associations of Rusty Crayfish and native crayfish. We evaluated the habitat associations of Rusty and Virile crayfish (Faxonius virilis) within Storm Lake, focusing on habitat created or altered by enhancement projects, and explored the temporal variation in crayfish capture. We deployed 707 baited Gee’s minnow traps across three habitat regions based on water depth. We captured 112 crayfish;​ 65 Rusty Crayfish and 47 Virile Crayfish. Rusty Crayfish were strongly associated with cobble presence created by shoreline armoring, and Virile Crayfish were associated with macrophyte presence. Capture probability also varied by Julian day, with the highest capture probability for Rusty Crayfish in June and Virile Crayfish in August. Collectively, our results suggest niche partitioning could be occurring in Storm Lake as Rusty Crayfish outcompete Virile Crayfish for cobble habitat. Seasonal capture probabilities differed by species, which could be important to consider when sampling or monitoring Rusty Crayfish in other lentic systems of the PPR.

In addition to our sampling at Storm Lake, we wanted to address knowledge gaps on crayfish distribution, trapping efficiency, and habitat associations in other shallow lentic systems of the PPR in Iowa. We sampled 42 glacial lakes and wetlands using baited Gee’s minnow traps, capturing 780 crayfish (752 Calico Crayfish Faxonius immunis;​ 28 Virile Crayfish) at 25 sites. At each site, we collected waterbody-level environmental data on aquatic habitat, nearshore land cover, and fish community data. We used non-metric multidimensional scaling (NMDS) in conjunction with a multi-response permutation procedure (MRPP) to determine how habitat and fish communities are associated with crayfish presence. We also grouped sites using hierarchical clustering based on the waterbody-level environmental data. Finally, we used an 11-year crayfish dataset from Iowa’s multiple species inventory and monitoring (MSIM) program to explore how drought and Julian day influence crayfish capture probability using generalized linear mixedeffect models. Our results suggest Calico Crayfish presence was positively associated with shallow wetlands with emergent vegetation, silt substrate, and fewer fish species, while Virile Crayfish presence was positively associated with larger systems characterized by open water and various sport and non-sport fishes. Hierarchical clustering identified two groups of lentic systems:​ wetlands, where crayfish trapping efficiency was higher, and shallow lakes, where crayfish trapping efficiency was lower. Crayfish capture probability increased from 0.03 on Julian day 109, peaked at 0.10 on Julian day 198, and then declined to 0.02 by Julian day 289. These results provide new data on crayfish distributions, habitat use, and trapping efficiency that can help managers better monitor and manage crayfish populations in lentic habitats across the PPR, where distribution records are often sparse.