Monitoring threatened species with environmental DNA and open ecological data: Local distribution and habitat preferences of scalloped hammerhead sharks (Sphyrna lewini)

Evidence-based environmental management is urgently required to enable progress towards global conservation commitments. To fill large-scale biodiversity knowledge gaps, governments, organisations and communities must adopt innovative ecological monitoring techniques. The emergence of environmental DNA (eDNA) survey methods, as well as the increased availability of in situ ocean observation and satellite remote sensing data, offers opportunities to overcome significant logistic and financial challenges previously associated with traditional biodiversity monitoring. Here, a 1.5 year-long eDNA survey reveals the spatial and temporal presence of ‘critically endangered’ scalloped hammerhead sharks (Sphyrna lewini) in Apra Harbor, Guam. The survey confirms the presence of S. lewini in the region, and shows eDNA detections are most frequent at the beginning of the dry season, in January. Combined analysis of eDNA results with open (freely available) ecological data identifies that S. lewini presence is associated with increases in water velocity, turbidity and wind direction, as well as decreases in temperature and wind speed. Additionally, the data indicate S. lewini are most frequent at sampling sites characterised by high turbidity, shallow depths, and large distances from the harbor entrance. Information on local distribution and habitat preferences generated here is fundamental to the establishment of management protocols that aim to minimise negative anthropogenic impacts on S. lewini in Apra Harbor. The work provides an example of contemporary marine monitoring for the efficient generation of biodiversity data; an approach that will enable informed management decisions and help to reduce the risk and rate of species extinctions throughout the next decade.