Post-release mortality and behaviour of Carcharias taurus following release from SMART drumlines in an Australian bather protection program

Shark management programs have been implemented globally at various locations since the 1930s to protect beachgoers from human-shark interaction. Traditional shark management programs (e.g. shark nets and drumlines) aim to minimise these interactions by killing target species. However, they are not selective to the intended target species and often have significant bycatch of vulnerable species. As a result, non-lethal methods are being implemented with Shark-Management-Alert-in-Real-time (SMART) drumlines currently deployed as part of the New South Wales (NSW) shark management program off the east coast of Australia. This new technology can mitigate negative shark-human interactions while also providing real-time alerts to foster faster release times for captured target and non-target species. The grey nurse shark ( Carcharias taurus ) is a critically endangered species susceptible to capture as bycatch in shark management programs. This study quantified post-release mortality rates of C. taurus in the NSW shark management program and investigated the immediate and longer-term impacts of capture on horizontal and vertical movements following release from SMART drumlines. Between October 2022 and December 2023, 29 C. taurus were caught on SMART drumlines at seven locations in northern NSW and fitted with pop-up satellite archival tags set to a 150-day deployment period. There were no at-vessel mortalities and two post-release mortalities. Within the first 24 h following release, most sharks moved away from the coastline, spending most of this period in water temperatures between 19 and 20°C and water depths of < 40 m. Across the full deployment, sharks that survived exhibited normal migratory movements after 24 h post-release indicating reduced lethality of SMART drumlines on C. taurus compared to traditional methods. Our results suggest SMART drumlines provide an effective bather protection tool that enables rapid response times while improving post-release outcomes for non-target shark species.