Variation in external morphology of resident bottlenose dolphins (Tursiops truncatus) in Bahia San Antonio, Patagonia, Argentina.

Two geographic variations of bottlenose dolphins were described in Argentina (Bastida & Rodriguez, 2003); bottlenose dolphins characterized by their triangular dorsal fin shape (coast of the province of Buenos Aires), and bottlenose dolphins characterized by their falcate dorsal fin shape (coast of the province of Chubut). It was stated that `their clear difference would indicate that both geographic forms are isolated¿ (Bastida & Rodriguez, 2003 p.137).
A photo-identification study carried out in Bahía San Antonio (BSA), North Patagonia Argentina, showed a similar variation in external morphology among year-round resident bottlenose dolphins. Out of the 15 bottlenose dolphins considered year-round resident in the bay (Vermeulen & Cammareri, 2009), three are clearly distinguishable by a more falcate dorsal fin, a darker coloration and a notably shorter beak. These individuals, with one associated calf, were first identified in September 2008 and could be re-identified in the study area up to 13 days over all the different seasons. On all occasions, they were re-identified in close association with each other and on 10 occasions in close association with triangular dorsal fin shaped bottlenose dolphins. Behavioural observations made during these associations indicated that these mixed dolphin groups were 18% of their time feeding, 18% socialising, 17% slowly travelling and resting, 16% travelling in medium and fast speed and 7% milling (n=380 min). Although both forms show variations in external morphology, the extent to which this phenotypic variation is genetically correlated remains unknown. A clear insight on the differentiation between these regional forms might have important conservation implications for this species in Argentina.