Fine-scale population structure of common bottlenose dolphins (Tursiops truncatus) in offshore and coastal waters of the US Gulf of Mexico

Patterns of dispersal and population structure of highly mobile marine fauna in the open ocean are not well understood. Much insight, however, can be gained from using common bottlenose dolphins (Tursiops truncatus), one of the most abundant marine mammals in the northern Gulf of Mexico (GOMx), as a model to better understand these aspects of the marine realm. Populations of common bottlenose dolphins in estuarine environments show evidence of strong population structure; however, whether this species similarly partitions the open ocean to the point that genetically differentiated populations are present is unknown. Such information is essential to accurately assess natural and anthropogenic impacts and is crucial for effective conservation and management. We used mitochondrial DNA control region sequence data, 19 microsatellite and 39 single nucleotide polymorphism loci to identify population structure of T. truncatus in coastal and offshore waters of the northern GOMx. Bayesian clustering and a multivariate method of discriminant analysis identified seven genetically distinct populations and levels of genetic differentiation were in line with other recognized populations of T. truncatus. The newly identified populations do not correspond to the currently delineated management stocks, suggesting revision may be necessary to establish accurate representation and effective management of the existing biological populations of T. truncatus in these waters. The finding of significant population structure in dolphins living in open-ocean waters augments the growing body of evidence indicating pelagic waters are not homogeneous even for highly mobile species.