European stranding networks as a tool for monitoring marine mammal populations (Part II): assessing their utility to monitor bycatch mortality
ICES Journal of Marine Science
9 jul 2026
English
An extensive survey of 45 European stranding networks shows that stranded marine mammals provide valuable data on bycatch mortality, identifying affected species, temporal and spatial trends, and implicated fisheries, including artisanal and illegal operations. Despite wide data collection, limitations such as inconsistent necropsy practices, variable expertise, uneven regional coverage, and funding constraints reduce the reliability and comparability of bycatch assessments. Networks frequently diagnose bycatch using external and internal indicators, but methods and certainty vary. Respondents highlight significant bycatch impacts on species including common dolphins, harbour porpoises, and seals, with notable regional hotspots such as the Bay of Biscay and Iberian waters. Recommendations include harmonized protocols, expanded necropsy capacity, improved data reporting, standardized uncertainty assessment, expanded carcass tagging for drift modelling, and stronger collaboration with fishers. Improved coordination and funding are deemed essential for integrating stranding-derived bycatch data into European bycatch assessment and management frameworks.