First eDNA evidence for the potential functional disappearance of the Endangered Maugean skate Zearaja maugeana in Bathurst Harbour, Australia

Detecting threatened species is vital for effective conservation but can be logistically challenging, especially in remote areas. Environmental DNA (eDNA) has emerged as a powerful, non-invasive, and cost-effective method for detecting rare marine species. The Maugean skate Zearaja maugeana is a micro-endemic and Endangered species, with only 2 known populations in the Bathurst and Macquarie Harbours, Western Tasmania, Australia. The species faces intense anthropogenic pressure in Macquarie Harbour and has not been recorded in Bathurst Harbour since 1992. We used eDNA sampling and video surveys to assess its presence in Bathurst Harbour. Water samples were collected from 26 sites during 2 surveys in November 2021 and February 2022. Five sites were also monitored using underwater video. DNA was extracted and analysed via qPCR using species-specific mitochondrial primers targeting NADH4 and COI gene regions. No sufficient concentrations of Z. maugeana DNA were detected to confirm presence via eDNA, although trace amounts were detected in the second survey. Video surveys also failed to detect individuals, feeding indentations, or preferred prey. These results suggest that Bathurst Harbour does not currently hold a population of Z. maugeana . Our findings highlight the need for urgent conservation action and continued research focused on the Macquarie Harbour Z. maugeana population. The protocol developed here may be useful when using eDNA to detect threatened marine or estuarine elasmobranch species in remote or challenging environments when results are crucial for guiding conservation actions.