Catch, bycatch, and mitigation options for endangered sharks in data poor fisheries: a case study on pelagic thresher sharks (Alopias pelagicus) in the eastern Indian Ocean

Context Endangered pelagic thresher sharks (Alopias pelagicus) are facing high fishing pressure in many countries. As the world’s largest shark fishing nation, with particularly high catch rates of thresher sharks, the impact of Indonesian fisheries has become a global priority for thresher shark conservation. Therefore, baseline data is needed to inform management and implement international agreements. Aims This research provides data and management recommendations for data-poor targeted shark fishing in Western Indonesia, where thresher sharks are regularly caught. Methods Daily landings data was recorded from June 2019 to December 2020 in Southwest Aceh and analysed to explore catch patterns, risk factors for thresher sharks, and potential mitigation options. Key results Twenty-five wooden vessels of <30 gross tonnage target sharks in the Indian Ocean. We recorded a total of 109 pelagic thresher individuals during the study period, with a female-skewed sex ratio (1 female:0.39 male). Almost all pelagic threshers were caught by the bottom longline. Conclusions Based on this data, we offer some potential management measures to reduce fisheries impacts on pelagic thresher sharks by applying a simple mitigation hierarchy framework. Implications These results provide fisheries management recommendations, including effort limits and gear modifications.