New records of the non-native virile crayfish Faxonius virilis (Hagen, 1870) from the upper Snake River drainage and northern Bonneville Basin of the western United States

The virile crayfish Faxonius virilis (Hagen, 1870) is a widespread non- native species across North America, and may be an emerging invasive species globally. We report new records for F. virilis from the upper Snake River drainage and northern Bonneville Basin of the western United States. We sampled 162 sites for crayfish during the summers of 2016 and 2017, detecting F. virilis at 22 of these sites, which ranged from small streams to wadeable rivers, as well as artificial reservoirs and a large natural lake (Bear Lake, Idaho and Utah). We also report the first records for F. virilis from the large, mainstem Snake River. However, we did not find F. virilis in the Snake River headwaters of western Wyoming, and detections of this species were few in the Snake River drainage below Shoshone Falls in south central Idaho. We also found no F. virilis in eastern Oregon. The widespread distribution of F. virilis in the upper Snake River drainage and northern Bonneville Basin may be a conservation concern for native crayfishes in this region, specifically the pilose crayfish Pacifastacus gambelii (Girard, 1852) and the Snake River pilose crayfish Pacifastacus connectens (Faxon, 1914). We recommend that research is undertaken to address ecological interactions of non-native F. virilis with native species, communities, and ecosystems in the western United States, and that education, outreach, and regulatory options be pursued to further limit the introduction and spread of this species.