Origins and impacts of ghost fishing gear entanglement on loggerhead sea turtles in the Western Mediterranean Sea

Loggerhead sea turtles (Caretta caretta) face multiple anthropogenic threats, including entanglement in abandoned, lost, or discarded fishing gear (ALDFG). Using a unique 28-year dataset (1993-2020) of sea turtle stranding records from the Balearic Sea (Western Mediterranean, n = 1,057), we aim to (i) evaluate long-term trends in strandings and entanglement events, (ii) identify the debris responsible for entanglement, and (iii) investigate the potential origin of ghost fishing gear through the integration of stranding records and Lagrangian backtracking simulations. Overall strandings increased over time, with seasonal peaks in summer and autumn. Entanglement-related cases escalated from 2018 onwards, peaking at 47 in 2020. Although entanglement presented low short-term mortality (19.1%) in comparison to other casualties, it caused severe injuries, including partial or complete loss of flippers in 16.8% of cases. In-depth analyses of entangling debris from 2014–2020 revealed that fishing-related items, particularly from fish aggregating devices (FADs), accounted for most identified cases (35.8%). Lagrangian backtracking simulations provide indications of the origin of ghost FADs. Basin-scale simulations suggest that ghost fishing gear observed across the Western Mediterranean Sea may derive from multiple countries, highlighting its transboundary nature. By applying Lagrangian backtracking simulations to ghost fishing gear observations and entanglement records, this study provides new insights into the potential origin and connectivity of ghost FADs in the Western Mediterranean Sea. These findings identify ghost FADs as a regionally significant threat to loggerhead turtles, with both immediate and long-term ecological consequences. Our study underscores the need for coordinated international management, targeted mitigation measures, and sustainable fishing practices to reduce ALDFG inputs and protect vulnerable marine megafauna in the Mediterranean Sea.