An important issue for the protection of rare and threatened species is to obtain efficient large-scale population size estimates to comply with legal statutes. However, assessment and monitoring of species of concern are challenged by costs, logistics and negative impacts on target populations. Evidence is growing that environmental DNA (eDNA) can provide information not only on species presence/absence, but also on species abundance. However, this new data collection approach is challenged by uncertainty related to false positives and false negatives, as well as environmental effects on eDNA quantity. This, in turn, has been slowing down the integration of eDNA analysis within management and conservation strategies. We tested a large-scale eDNA monitoring survey to track both amphibians and reptiles, the two taxonomic groups of species with the highest proportion of declining species. The efficiency of eDNA to detect and quantify amphibian and reptile populations in seven lakes and five rivers using multiple and species-specific primers was compared to a standardized visual survey and an occupancy distribution model.
Results/Conclusions
Our results empirically support the effectiveness of eDNA metabarcoding to inform about local herpetological distributions. The only inconsistency on the 34 species was the detection of the Northern Watersnake (Nerodia sipedon) outside of its known distribution range. First considered as a false positive result, an observation of this species by a landowner was then reported in the same river section where the water samples were collected. The latter was particularly relevant given that this species is likely to be designated threatened or vulnerable by provincial government in the near future. Moreover, detection rates provided similar results to standardized visual surveys currently used to develop conservation strategies for the wood turtle, a species protected against illegal collection and trade in most of its distribution range in North America. Our results provide an empirical demonstration of the effectiveness of the eDNA method to evaluate both species distribution and effective semi-quantitative tool, provided that assay calibration and standardization is performed. Integrating eDNA within policy decisions will clearly rely on the rigor with which eDNA will be used and interpreted. With improved methodology and standards, eDNA will continue improving in reliability and also in credibility with conservation planners. We therefore conclude by discussing the successes and limitations of the eDNA method for management and conservation purposes.