Taxonomic Notes
All Bottlenose Dolphins around the world were previously recognized as Tursiops truncatus, but currently, the genus is considered to be composed of two species: T. truncatus (Common Bottlenose Dolphin) and T. aduncus (the smaller Indo-Pacific Bottlenose Dolphin) (Wang et al. 1999, 2000a,b). The Common Bottlenose Dolphin has a worldwide distribution in tropical and temperate latitudes but exhibits a strong ability to adapt to local conditions, a complex social structure and strong site fidelity which results in considerable habitat partitioning throughout its range. This, in turn, has created strong population differentiation accompanied, in some cases, by marked morphological differentiation. The taxonomy of Bottlenose Dolphins is confused due to this geographical variation, and it is very possible that additional species will be recognized in the future. Three subspecies are currently recognized by the Society for Marine Mammalogy's Committee on Taxonomy (2017) and a recent re-assessment of Tursiops taxonomy worldwide conducted by the International Whaling Commission confirmed their validity (IWC 2018). These subspecies are the Black Sea Bottlenose Dolphin (T. t. ponticus Barabash-Nikiforov, 1940) which differs morphologically and genetically from other forms including those in the nearby Mediterranean Sea (Barabash-Nikiforov 1960, Geptner et al. 1976, Natoli et al. 2005, Viaud-Martinez et al. 2008). The Lahille Bottlenose Dolphin (T. t. gephyreus) (Lahille, 1908), a larger form in the coastal waters of the western South Atlantic Ocean, is morphologically and genetically different from the offshore population in eastern South America (Costa et al. 2015, 2016; Fruet et al. 2011, 2015). The third subspecies is the nominate subspecies that includes the remaining Common Bottlenose Dolphins worldwide (T. t. truncatus (Montagu, 1821)). In the western North Atlantic, two forms, offshore and coastal, are distinguishable on the basis of morphology and ecological markers (Mead and Potter 1995) and have fixed genetic differences (Le Duc and Curry 1997, Hoelzel et al. 1998, Kingston et al. 2009, Rosel et al. 2009, Van Waerebeek et al. 2017a) and according to the recent IWC review the coastal population should be recognized as at least a different subspecies.
Taxon distribution as listed in assessment
The species occurs in the Gulf of Oman, but is apparently absent from the Arabian Gulf, reflecting a preference for deep, offshore water. Globally, this species is distributed through all tropical and temperate inshore, coastal, shelf, and oceanic waters (Hammond et al. 2012d).
