Resilience in the line: insights on post-release survival from long-term monitoring and satellite tagging of blue sharks (Prionace glauca) in the Southern Adriatic Sea

The bycatch of pelagic sharks in Mediterranean longline fisheries remains a critical conservation issue with potential cascading effects on pelagic ecosystems. This study is the first to provide an integrated assessment of blue shark (Prionace glauca) bycatch and post-release survival in the southern Adriatic Sea, combining multi-year fishery monitoring, fisher cooperation, and satellite telemetry. From 2019 to 2024, data were collected through on-board observation, landing-site monitoring, and fisher logbooks, ensuring representative spatial and temporal coverage of the swordfish longline fleet. Catch rates remained stable, but landings declined after 2021, suggesting greater compliance with no-retention measures and increased awareness among fishers. A total of 45 blue sharks were equipped with pop-up satellite tags, which yielded an estimated post-release survival rate of 77%. The majority of mortalities occurred within the first four days. Survival was strongly influenced by capture condition and body size, indicating the higher resilience of adult individuals. A Random Forest model identified soak time as the main determinant of capture condition, followed by environmental variables such as sea-surface temperature, chlorophyll-a, and dissolved oxygen. Integrating capture-condition frequencies with telemetry data enabled us to estimate that approximately 68% of incidentally captured sharks could survive if released promptly. These findings underscore the ecological importance of reducing blue shark mortality in the Mediterranean, where the species, classified as Critically Endangered, plays a key role as an apex mesopredator. The study demonstrates that empirically guided catch-and-release, supported by fisher cooperation and adaptive management, can enhance ecological resilience and stakeholder engagement in pelagic ecosystems.