Evaluating monitoring options for conservation: comparing traditional and environmental DNA tools for a critically endangered mammal.

While conservation management has made tremendous strides to date, deciding where, when and how to invest limited monitoring budgets is a central concern for impactful decision-making. New analytical tools, such as environmental DNA (eDNA), are now facilitating broader biodiversity monitoring at unprecedented scales, in part, due to time, and presumably cost, of methodological efficiency. Genetic approaches vary from conventional PCR (cPCR; species presence), to metabarcoding (community structure), and qPCR (relative DNA abundance, detection sensitivity). Knowing when to employ these techniques over traditional protocols could enable practitioners to make more informed choices concerning data collection. Using 12 species-specific primers designed for cPCR, eDNA analysis of the Yangtze finless porpoise (YFP; Neophocaena asiaeorientalis asiaeorientalis), a critically endangered aquatic mammal within the Yangtze River, we validated and optimized these primers for use in qPCR. We tested repeatability and sensitivity to detect YFP eDNA and subsequently compared the cost of traditional (visual and capture) sampling to eDNA tools. Our results suggest cPCR as the least expensive sampling option but the lack of PCR sensitivity suggests it may not be the most robust method for this taxon, predominately useful as a supplementary tool or with large expected populations. Alternatively, qPCR remained less expensive than traditional surveys, representing a highly repeatable and sensitive method for this behaviorally elusive species. Cost comparisons of surveying practices have scarcely been discussed; however, given budgetary constraints particularly for developing countries with limited local oversight but high endemism, we encourage managers to carefully consider the trade-offs among accuracy, cost, coverage, and speed for biodiversity monitoring.