Movement pathways and habitat use of blue sharks (Prionace glauca) in the Western Mediterranean Sea: Distribution in relation to environmental factors, reproductive biology, and conservation issues

The blue shark (Prionace glauca), a highly migratory and wide-ranging shark, has been classified as Critically Endangered in the Mediterranean Sea by the International Union for Conservation of Nature since 2016 due to overfishing. Surprisingly, basic information on its biology and ecology, essential for its conservation, remains unknown, and its regional stock has not been assessed. A multi-year large-scale telemetry tagging programme was implemented to fill these gaps. A total of 39 blue sharks were equipped with satellite tags in three areas of the Western Mediterranean, and their movements and home ranges were examined by sex and size class. Their distributions and habitat preferences across seasons were identified using satellite-based environmental data. Tagged sharks were capable of long-range movement between distant regions, but they did not move neither towards the Eastern Mediterranean basins nor the North Atlantic. We identified the Gulf of Lions as the mating, parturition and nursery grounds. We demonstrated that sharks can use the general geostrophic current system for large movements. Our results support the current stock boundary in the Mediterranean based on international conventional tagging programmes and genetic studies, but the absence of connectivity between the two Mediterranean basins and the North Atlantic basin suggests that they have distinct stocks. Our findings provide critical input for developing effective conservation and management plans for this cosmopolitan species. For the first time in the Mediterranean, this study provides insights into the movement patterns of blue sharks and their habitat preferences.