Post-release survivorship studies on common thresher sharks (Alopias vulpinus) captured in the southern California recreational fishery
The common thresher shark (Alopias vulpinus) is the focus of a popular southern California recreational fishery that targets individuals using multiple fishing gears and techniques. Despite increasing trends in the use of catch and release techniques in the recreational fishery for thresher sharks, a comprehensive estimate of post-release survival is not available for all modes of capture. This study focused on assessing post-release survival in two modes of capture routinely observed in the southern California recreational fishery: (1) sharks that are caught using caudal-based angling techniques and unintentionally released with trailing gear left embedded and (2) sharks that are caught and released using mouth-based angling techniques. Post-release survivorship was assessed using pop-up satellite archival tags programed for 10- and 90-day deployments, with the former used for mouth-caught sharks and the latter for individuals with trailing gear. Post-release survivorship estimates for the trailing gear studies were based on data from nine common thresher sharks (111-175 cm FL) while the mouth-based experiments utilized data from an additional seven sharks (125-187 cm fork length, FL). For the trailing gear studies, six sharks died within 5 days after release, one died after 81 days, and two sharks survived the deployment period for an overall survivorship rate of 22%. All seven mouth-hooked common thresher sharks survived the acute (∼10 days) effects of capture (100% survivorship). These results suggest that in the southern California recreational thresher shark fishery, caudal-based angling techniques, which often result in trailing gear left embedded in the shark, can negatively affect post-release survivorship. This work also reveals that mouth-based angling techniques can, when performed properly, result in high survivorship of released sharks.