An integrated approach for assessing the survival of discarded sandbar sharks, Carcharhinus plumbeus, captured in scientific longlines

Abstract

The sandbar shark (Carcharhinus plumbeus) has a global distribution and is caught by commercial fishers and recreational anglers. Aims. To assess the stress physiology, release condition, and post-release survival of sandbar sharks caught in longline surveys conducted in Western Australia. Methods. Post-release survival of sandbar sharks caught in longlining surveys was assessed using an integrated approach that combined the use of hook-timers, qualitative release conditions, satellite-tagging, and blood physiology. Key results. Of 57 individuals examined, there was 100% post-capture survival after a maximum of 4 h on the hook. Most of these animals (88%) displayed a strong release condition, exhibiting minimal behavioural impairment. All 13 satellite-tagged individuals survived 30 days post-capture. Sharks dived up to 307 m deep and showed cyclical depth movement patterns, with some individuals moving through the water column both day and night, whereas others moved almost exclusively at night. The concentration of blood metabolites did not significantly change with time-on-hook. Conclusion. Post-capture and post-release survival of 100% after up to 4 h on hooks suggested that the use of longlines for surveying sandbar shark abundance had no deleterious effects on captured sharks. Implication. This will support future stock assessments of sharks by quantifying the survival rates in the methods used for long-term monitoring of sandbar shark populations.