Invasion of Virile Crayfish Faxonius virilis (Hagen 1870) in the Lower Henrys Fork Drainage, Idaho

Abstract The invasive virile crayfish Faxonius virilis (Hagen 1870) has recently been documented in the upper Snake River drainage of Idaho, but its distribution is poorly known. Our objective was to determine the presence and distribution of F. virilis in the Henrys Fork drainage of the Snake River. Sampling was conducted during summer and autumn 2018 at 30 sites located in Henrys Fork River drainage, including the major tributaries Teton River, North Fork Teton River, South Fork Teton River, and Moody Creek. We used baited minnow traps and kick nets to determine presence of F. virilis. Absence was only reported if we unsuccessfully captured F. virilis using kick nets because this technique is more effective. Faxonius virilis was detected in all five streams. We did not detect F. virilis at sites at the upstream extent of sampling. This pattern suggests that F. virilis are invading the drainage in an upstream direction. Presence of species of conservation concern (e.g., Yellowstone cutthroat trout [Oncorhynchus clarkii bouvieri Jordan and Gilbert 1883], bluehead sucker [Catostomus discobolus Cope 1871], and western pearlshell [Margaritifera falcata Gould 1850]) warrant additional research to determine the effect of F. virilis on these species.