Increased sample size provides novel insights into population structure of Mediterranean loggerhead sea turtles

The loggerhead sea turtle (Caretta caretta), has the widest distribution among sea turtle species in the Mediterranean, requiring regional and international collaborations in addition to local efforts to better inform conservation actions. Molecular techniques are powerful tools for the assessment of population dynamics at large scales, especially in determining the connectivity among different nesting and foraging sites, and genetic diversity. In this study, a large sample was collected synchronously in the nesting areas located in the north, south and eastern Mediterranean. Recently confirmed nesting sites from Albania and other nesting sites represented by lower sample sizes were also included in order to better assess the genetic composition of the region's rookeries. Samples from 698 individuals were collected and the longer (815 bp) mtDNA D-loop fragment of these samples was sequenced. We recorded 15 haplotypes, three of which were novel. In addition, our results show that some haplotypes considered of Atlantic origin, have a wider dispersal in the Mediterranean than previously thought, albeit with low levels of representation. Our results contribute to determining the likely origin of haplotypes that were previously only recorded from foraging sites. They highlight the utility of broad-scale sampling, with increased sample sizes and the longer mtDNA sequence to determine genetic diversity and connectivity. This study also demonstrates the importance of continued monitoring for the contribution of Atlantic-origin haplotypes to the Mediterranean population and the effects of climate change on the resident Mediterranean population, which is expected to expand its geographical range for reproduction. This work is important for, mixed stock analyses (MSA) that seek to determine the natal regions of stranded or accidentally caught sea turtles and those purposefully obtained from foraging sites. In doing so biogeographic linkages between areas of the Mediterranean can be elucidated for conservation purposes.