Little migrants: Assessment of stranded loggerhead turtles (Caretta caretta) source populations found in the north-east Atlantic

Maritime activities affect the migratory routes of marine organisms, including loggerhead turtles (Caretta caretta). The coastal waters of mainland Portugal lie along these routes, providing foraging grounds but lacking nesting beaches, making them ideal for studying turtle migration. This study presents the first assessment of the natal origins of loggerheads in the North-East Atlantic. We analysed the genetic diversity of 127 stranded loggerhead turtles along the Portuguese coast, sequencing the mitochondrial DNA control region (776 bp). Sixteen haplotypes were identified, including a previously unknown one. Mixed-stock analysis revealed that loggerhead turtles stranded in Portuguese mainland coastal waters appear to originate predominantly from the Western Atlantic, with possible contributions from other regions including Cape Verde and the Eastern Mediterranean, though the latter remains uncertain. The primary sources were Florida rookeries, particularly Canaveral National Seashore, Melbourne Beach, Juno Beach, and Ft. Lauderdale. Our findings underscore the role of oceanic circulation patterns in shaping migration routes, as turtles predominantly followed major currents across the Atlantic. The predominance of juveniles among stranded individuals in areas with known high fishing pressure indicates that Portuguese waters may pose significant anthropogenic risks for this life stage. This study highlights the vulnerability of juvenile loggerheads in Portuguese waters and underscores the need for conservation strategies, including bycatch mitigation and fisheries management. Further ecological studies, such as tag tracking, are essential to understanding migratory patterns and improving conservation efforts in this critical migratory corridor.