Post-release survival of loggerhead sea turtles bycaught in demersal trawls in overwintering habitats of the Adriatic Sea

Abstract

Fishery-related mortality is a major anthropogenic threat to marine megafauna, and gear-specific estimates are essential for effective conservation management of populations. We assessed cryptic post-release survival of loggerhead turtles (Caretta caretta) incidentally captured in a Croatian demersal-trawl fishery operating in overwintering habitats of the northern Adriatic Sea at depths of 45–84 m, with a mean tow duration of 390 ± 43 min. Ten individuals with a mean carapace length of 57.2 ± 9.4 cm were equipped with Argos-linked platform transmitter terminals with a pressure sensor and released after regaining activity following 15–90 min of on-board recovery. We inferred individual fate (dead/alive) from transmission continuity, movement trajectories, location-class composition and submergence records. Nine animals provided telemetry data and exhibited biologically plausible movements and repeated diving beyond the 15-day post-release threshold period, with total tracking durations of 94–512 days. Apparent survival was conservatively estimated at 90% (9/10; exact 95% confidence interval 55.5–99.7%), suggesting the conservation value of this on-board recovery procedure for the reduction of delayed mortality of sea turtles in demersal trawl fisheries.