Assessment on accidentally captured silky shark post-release survival in the Indian Ocean tuna purse seine fishery

Satellite Archival tagging programs are key to evaluate post-release mortality of Endangered, Threatened, and Protected species that are caught incidentally in fishing operations. This work presents results of a tagging program conducted on purse seiners under ECHEBASTAR company, aimed at assessing post-release survival of silky sharks caught in association with tuna schools and released according to the Code of Good Practices. In two fishing trips carried out during 2020 and 2021, sixty silky sharks were tagged (28 and 32 silky sharks in the first and second trip, respectively) with 37 SPATs and 23 MiniPATs. A vitality index based on state and behavior at release was also assigned to all the sharks caught accidentally. The overall predicted silky shark survival was close to 40% based on vitality index derived from tagged sharks. Shark survivorship decreased as the fishing operation advanced and vitality index declined. This post-release survival estimate duplicates previous estimations obtained in purse seiners. The experience gained over time in the correct application of best practices and fauna release devices installed on-board (i.e., the bycatch conveyor belt) contribute to reducing shark mortality in the purse seiner fishery.