Population genetic structure of common bottlenose dolphins (Tursiops truncatus) in the Adriatic Sea and contiguous regions: Implications for international conservation

Habitat diversity plays a significant role in shaping the genetic structure of cetacean populations. However, the processes involved in defining the genetic differentiation of these highly mobile marine mammals are still largely unknown. Levels of genetic differentiation and dispersal patterns of common bottlenose dolphins (Tursiops truncatus) were assessed in the north-eastern Mediterranean Sea, with a focus on the Adriatic Sea. This is a region characterized by diverse marine ecosystems and high levels of human-induced habitat degradation. Although this species seems almost uniformly distributed throughout the Adriatic Basin, genetic evidence rejected the hypothesis of a single stock. Pairwise estimates of genetic differentiation at 12 microsatellite loci, and mitochondrial DNA (entire control region, 920bp), revealed diverse levels of genetic differentiation among five putative populations from the Tyrrhenian Sea to the Aegean Sea. A fine-scale genetic structure was recorded within the Adriatic Sea, where females appear to be the principal gene flow mediators. The assessment of recent migration rates indicates a relatively high level of gene flow from the North Adriatic towards adjacent areas. Indication of a fine-scale population structure across the Adriatic Sea is a factor to be carefully considered in the emerging marine management scenario set by the implementation of the EU Marine Strategy Framework Directive (2008/56/CE), particularly when it comes to assessing and managing direct mortality caused by human activities (e.g. fisheries or maritime traffic). A good knowledge of population structure at the basin level is also fundamental for the identification of potential Adriatic Special Areas of Conservation for the bottlenose dolphin under the Habitats Directive (Council Directive 92/43/EEC).