First detection of critically endangered scalloped hammerhead sharks (Sphyrna lewini) in Guam, Micronesia, in five decades using environmental DNA

• Novel eDNA survey for detecting critically endangered scalloped hammerhead sharks. Enables the first detection of hammerheads in Guam since 1971. A single-day sampling effort outperforms five decades visual surveys. The method is non-invasive, cost-effective, and user friendly. Survey application allows rapid data generation science-based conservation. Among sharks, ( Sphyrna lewini ) have undergone steepest population declines worldwide. Due to their high susceptibility exploitation, species now classified as ‘critically endangered’, most threatened category listed by International Union Conservation Nature. There an urgent need on distribution S. inform design implementation effective conservation management strategies, mitigate risk global extinction. Environmental DNA (eDNA) emerging a powerful monitor geographic distribution, trends, habitat usage rare species. In comparison traditional methods, methods offer lower cost, higher rates, are non-invasive. At present, there no targeted assay existing assess either fisheries-dependent, leading bias, or costly laborious, impracticality regions low unknown abundance. Here we present optimised workflow presence using apply these successfully detect sharks Guam, western Pacific Ocean, where has not been scientifically reported 1970s. was achieved from effort, demonstrating efficacy technique workflow. If implemented, developed here will enable information Pacific, likely globally, assist accurate placement no-take reserves best species’ recovery.