Preliminary Insights on the Habitat Use and Vertical Movements of the Pelagic Stingray (Pteroplatytrygon violacea) in the Western Mediterranean Sea

Abstract

Pelagic stingray (Pteroplatytrygon violacea) is the only species of stingray (Dasyatidae) that utilizes both pelagic and demersal habitats. It is the main bycatch species in pelagic longline fisheries targeting bluefin tuna (Thunnus thynnus) in the Gulf of Lions. In the Mediterranean Sea, their stock structure, behavioural ecology and movements are unknown. For the first time in the Mediterranean, 17 individuals (39–60 cm disc width) were tagged with pop-up satellite archival transmitting tags using a novel method of tag attachment to investigate horizontal and vertical movements. The tags were attached for between two and 60 days. Between the months of July and October, pelagic stingray occupied a temperature range of 12.5–26.6 °C, and a depth range extending from the surface to 480 m. Monthly trends in catch-per-unit-effort (CPUE) of pelagic stingray peaked in August and decreased by late autumn. Pelagic stingray may aggregate on the continental shelf during summer and move southwards in early autumn, and this movement pattern is considered in relation to the reproductive cycle and overwintering. At-vessel mortality was low, but there was varying evidence of post-release mortality, indicating the need for further work. Future work and options for bycatch mitigation are also discussed.