Distribution, density, and habitat associations of the narrowly endemic coldwater crayfish (faxonius eupunctus) in the Eleven Point River drainage, Arkansas and Missouri, U.S.

North America harbors an exceptionally high number of rare or narrowly distributed crayfishes, and many of these species are threatened with displacement by a variety of biological, chemical, and physical factors. Detailed distributional and ecological data are lacking for many North American crayfishes, making the assignment of appropriate conservation protection designations difficult. A better understanding of the distribution, population densities, and habitat associations of rare and narrowly distributed crayfishes is therefore warranted to most effectively protect and manage these species. The purpose of this research was to assess the distribution and local population densities of the narrowly endemic Coldwater Crayfish (Faxonius eupunctus) in the Eleven Point River drainage, Arkansas and Missouri, U.S. My principle objectives were to: (1) assess the distribution of F. eupunctus within the Eleven Point River drainage to further evaluate its potential use of tributary streams; (2) estimate local F. eupunctus population densities to determine where the species is most abundant; and (3) investigate physical habitat variables relating to, and potentially influencing, local F. eupunctus densities. I used multiple sampling approaches, including environmental DNA sampling, to assess the distribution, density, and habitat of F. eupunctus throughout the Eleven Point River drainage. Faxonius eupunctus occurred primarily in the main stem Eleven Point River but was detected in a downstream reach of one of its largest tributary streams. Faxonius eupunctus site densities were highest in the middle reaches of the species’ range in the main stem Eleven Point River, and my analyses showed that F. eupunctus density was strongly related to current velocity, in-stream temperature, and streambed substrate size. Results from this study corroborate evidence from previous research in supporting that F. eupunctus is restricted to large streams within its range. Further, I present new evidence that F. eupunctus is most abundant in the middle reaches of its range in the main stem Eleven Point River, and I discuss a variety of local-scale physical habitat variables potentially influencing this noteworthy spatial abundance pattern. I also present support for the use of environmental DNA for the detection of rare lotic-dwelling crayfish species, although I highlight potential limitations of eDNA applications in lotic environments