Assessment of environmental DNA for detecting and monitoring translocated North American beaver

There is growing interest in working with beavers (Castor canadensis and Castor fiber) to restore and maintain ecosystem function, improve hydrologic conditions and build climate resiliency in freshwater ecosystems. Beaver translocation into historically occupied but degraded systems has been increasingly applied as a restoration practice over the last two decades. Knowledge of beaver distributions on the landscape is critical to understanding where and when beaver translocations may be effective. However, current understanding of beaver occupancy and translocation success is limited by uncertainty, subjectivity and inefficiency associated with available monitoring methods. We evaluated the efficacy and spatial inference associated with environmental DNA (eDNA) techniques for detecting beaver presence in natural wetland and stream systems in the Cascade mountains of Washington State. We conducted eDNA sampling paired with radio-tracking of translocated beavers at four relocation sites from October 2020 through October 2022 to elucidate spatial patterns of site use, eDNA detection probability and eDNA quantity. We found that eDNA techniques detected beaver rapidly over long distances - up to 2.9 km from known locations within the first week after release - and reliably detected beavers when they were upstream, with positive detections in 92.4% of downstream eDNA samples collected 1-3 months after release. We also found that eDNA quantity decreased with increasing distance from beaver and increased with the amount of upstream beaver activity. Our study suggests that eDNA is a sensitive tool for monitoring translocated beaver and can provide spatial information on beaver location and site use within a stream system. Hence, eDNA methods could be a valuable tool for rapid inventory and assessment of beaver occupancy and our findings highlight important implications for using eDNA to monitor other semi-aquatic mammal species that share similar life histories.