Biodiversity monitoring for biocredits: a case study comparing acoustic, eDNA, and traditional methods

Abstract New environmental policy reforms and a growing demand for nature repair products such as biodiversity credits (biocredits) have increased the need for low-cost, scalable and reliable biodiversity monitoring techniques. We compare the financial costs, time commitments, and data outputs of various biodiversity survey methods using a case study in a temperate agricultural landscape in southeast Australia. We conducted in-person aural and visual surveys, camera trapping, eDNA sampling, and automated species detection from passive acoustic monitoring (PAM). All techniques exhibited relative strengths and weaknesses. PAM was limited to vocalising taxa with developed detection models (i.e., birds and amphibians), yet they recorded ~ 70 times more detections than other techniques, detecting over ten more species per site on average than any other method. It also had the lowest cost per species over five or more repeat campaigns. In-person surveys produced intermediate detection levels across most taxa, but they were the most time-consuming method. eDNA sampling was the quickest method and was the only one to account for invertebrate species, yet the costs grew rapidly with multiple campaigns. We provide a decision-support tool to help conservation managers select the most suitable techniques for biodiversity monitoring. Our data shows that modern methods such as eDNA and PAM can provide cost- and time-effective solutions to monitor most taxa. To support a growing market and promote high-quality biocredit schemes, future efforts must prioritize reducing monitoring costs and improving the detection efficiency of technological solutions across a broader range of taxa.