Can We Use Environmental DNA to Detect Alligator Snapping Turtles (Macrochelys temminckii) at the Edge of Their Range?

Secretive aquatic animals are often particularly difficult to sample via traditional methodologies, especially when coupled with low population densities. Alligator snapping turtles (Macrochelys temminckii) are a fully aquatic chelonian endemic to the southeastern United States. At the northern extent of their range (i.e. Illinois and Indiana) this species is rarely encountered, and many records are chance encounters reported by citizen scientists. M. temminckii receive state-level protection throughout the bulk of their range and are currently under consideration for federal protection. As a consequence, documenting their occurrence across their range is a conservation imperative. Environmental DNA (eDNA) techniques detect DNA shed by animals into the environment to determine whether a species inhabits an area of interest. Due to their low detection probability at the edge of their range, eDNA may present a cost-effective method for M. temminckii surveys. We used an ongoing M. temminckii reintroduction in Illinois to test the efficacy of eDNA methods to determine detection limits using radio-telemetered individuals. Water samples were taken from known turtle locations, as well as random locations upstream and downstream from turtles. M. temminckii eDNA detections were positively correlated with turtle presence but showed limited downstream transport. Results from the Illinois methods-testing were applied to an eDNA survey of M. temminckii in two watersheds in Indiana, identifying locations with potential M. temminckii presence. Our results demonstrate that eDNA may be a viable means of detecting M. temminckii and could be utilized to better target areas to focus traditional sampling efforts.