| Summary: | Maritime activities impact the natural migratory routes of marine organisms such as marine mammals and turtles. The coastal waters of Portugal are in the pathway of such routes for loggerhead turtles (Caretta caretta). While the local upwelling provides foraging grounds, there are no nesting beaches adjacent to the Iberian coast, offering an excellent opportunity to study the migration of the species. This study is the first report of the natal origins of loggerheads in the North-East Atlantic Ocean. We attempted to investigate the genetic diversity of 194 loggerhead turtles found stranded across the Portuguese coast and to assess the origin of individuals through many-to-one mixed-stock analysis. We successfully produced 16 haplotypes of 776 bp of mitochondrial DNA control region for 127 samples and detected a previously unknown haplotype. Comparison with baseline data from distinct nesting populations of the Mediterranean Sea, Cape Verde Islands and the North-West Atlantic Ocean revealed that most of the loggerheads originated in the North-West Atlantic and to a smaller degree in Cape Verde and the Mediterranean. In particular, the Gulf of Mexico in the North-West Atlantic yielded the largest part of the samples and specifically the Florida rookeries: Canaveral National Seashore, Melbourne Beach, Juno beach and Ft Lauderdale. Furthermore, this study highlights the important role of currents in the long journeys of turtles, since most of the contributing rookeries were along such currents. In conclusion, our results signify the need for conservation measurements like turtle excluder devices, tag tracking and fishing management in Portugal, where migratory species, like the loggerhead turtles, are vulnerable. As actividades marítimas têm um impacto significativo nas rotas migratórias de organismos marinhos, como cetáceos e tartarugas. As rotas da tartaruga-boba (Caretta caretta) cruzam as águas costeiras de Portugal cujo tráfego marítimo é muito elevado. A tartaruga-boba é uma das sete espécies de tartarugas ...
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