Repurposing Environmental DNA Samples to Verify the Distribution of Rocky Mountain Tailed Frogs in the Warm Springs Creek Basin, Montana

Abstract Rocky Mountain tailed frogs (Ascaphus montanus) were thought to exist exclusively in two tributaries of Warm Springs Creek watershed—Storm Lake Creek and Twin Lakes Creek, based on opportunistic observations of tailed frogs during fish sampling rather than formal basin-wide sampling for frogs. We used extant environmental DNA (eDNA) samples originally collected to delineate bull trout (Savelinus confluentus) occupancy to determine whether tailed frogs reside outside of their current known distribution in the Warm Springs Creek watershed. We were able to rapidly confirm tailed frog occupancy in these two tributaries of Warm Springs Creek watershed, and located tailed frogs throughout the mainstem of Warm Springs Creek where their presence was previously unknown. Repurposing eDNA samples provides a sensitive and extremely cost effective way to determine species distributions, because existing samples can continue to be retested for unrelated taxa without repeating field collections.