Haplotype and biometric patterns in loggerhead turtles from the Adriatic foraging ground

The Adriatic Sea is an important foraging area for the loggerhead turtle Caretta caretta. Due to the increase of anthropogenic impacts, a growing number of individuals are captured as by-catch, found stranded or drifting at sea. Turtles mortality within the Adriatic Sea can affect Mediterranean populations, increasing the risk of losing genetic diversity. Biometric data on 93 loggerheads from three Adriatic areas (northwestern, northeastern and southern Adriatic) and patterns of sequence polymorphism of the mtDNA Control Region long fragment were used to investigate the sizes/age distribution of the collected individuals and to assess their geographic origins by using a Bayesian Mixed Stock Analysis (MSA). The biometric data revealed that collected turtles belonged to a wide range of sizes, although juveniles and subadults were the most abundant classes. Five haplotypes were detected. Two are endemic of Mediterranean rookeries and one is a rare haplotype found once in a Floridian rookery and in two Mediterranean nests. The other two haplotypes were found both in Atlantic and Mediterranean populations. The Mixed Stock Analysis revealed the presence of individuals from Greek and Turkish rookeries, this latter group was found in the southern Adriatic. Individuals from Libya and Cyprus rookeries were also found in the Adriatic stock. Current patterns, juvenile natal homing and imprinting of ontogenetic habitats could be potential drivers of the stock composition in the three Adriatic areas. Variations of turtle migration patterns, recruitment and mortality may drive differential contributions of rookeries to the foraging grounds. In this study, a substructuring within the Adriatic basin is hypothesized, consisting of differential distribution of stocks among three areas. However, these results might be biased by the uneven sample size among areas. Further studies with consistent sample sizes are recommended to quantify potential genetic differentiation within the Adriatic Sea. Nevertheless, present results recommend preservation action to be taken both at the nesting sites and in the foraging grounds were genetically isolated Caretta caretta populations, originating from different Mediterranean rookeries, mix together.