Genetic variability and population structure of the thornback ray, Raja clavata, in north-east Atlantic and Mediterranean Sea

The overexploitation of the marine resources and the increasing fishing efforts, together with a non specialised fishery are anthropogenic factors that may allow to the population decline and local extinction of elasmobranch species. In the last few years, the monitoring of the marine fishery resources, once based only on studies of parameters, was enhanced by integrating genetic analysis with the traditional morphological and bio-ecological studies. Such a multidisciplinary approach may contribute significantly to the inventorying and to the conservation of biodiversity. The thornback ray Raja clavata is one of the most common species in the Mediterranean Sea and North-East Atlantic and has a high morphological variability, with several documented morphotypes. Its intraspecific variability was recently investigated using microsatellites nuclear markers which revealed a significant population structure in Southern England waters. We have investigated the population structure of Raja clavata in the Mediterranean and North East Atlantic throughout the genetic stock structure analysis of more than 200 individuals collected from different geographical areas: Celtic Sea and North Sea (North-East Atlantic), and Adriatic Sea, Tyrrenian Sea, coasts of Algeria and Turkey (Mediterranean Sea). The genetic variation of samples analysis was carried out through PCR amplification and sequencing of the hyper-variable region D-loop of the mitochondrial DNA. The statistical analysis of molecular variation showed a high polymorphism within and among geographical samples as well as significant genetic differences between samples of the Mediterranean and the Atlantic, except for the Turkish sample that unexpectedly showed an higher Dloop variability and genetic similarity with samples of the Celtic and North Seas