First long-term study of live observations of loggerhead and leatherback turtles in southern Portugal with relevance for conservation

Most of the information available on loggerhead turtles (Caretta caretta) and leatherback turtles (Dermochelys coriacea) for the southern coast of Portugal is based on stranding data, and to a less extent on telemetry data, with very little information derived from sightings of live animals. This work reports sightings data of loggerhead and leatherback turtles off the south coast of Portugal collected during dedicated surveys on board a research boat, from 2016 to 2022. The sightings data corrected for effort confirm the recurrent presence of loggerhead turtles in the study area, with a higher sightings rate in May and June. Conversely, leatherback turtles were only sporadically observed in some years. This study highlights the importance of the southern waters of Portugal for loggerhead turtles as a recurrent area used by individuals of this species, probably from different origins within the North Atlantic and the Mediterranean, in line with previous studies. The southern coast of Portugal, however, is heavily exploited by fisheries, and the main cause of death among sea turtles is bycatch. The results presented will therefore help inform future management measures aiming to reduce interactions with fisheries (e.g., limiting some fishing gears in the months with more sightings). Since the study area is probably used by loggerhead turtles from different Regional Management Units, the impacts of conservation measures imposed locally may also have beneficial effects at a regional scale.