The Indo-Pacific humpback dolphin has a typically streamlined body and a long slender beak(5). Populations differ in both shape and colour, with those in the west of the range possessing a 'double-step' dorsal fin with a fatty hump upon which the dorsal fin sits (6). Although usually dark grey on their back and lighter underneath, white and pink variations are also known; the most famous of these are the 'pink dolphins' of Hong Kong bay (2). The humpback dolphin has an unusual diving posture, first lifting its beak out of the water and arching its back, and then pausing before dipping below the surface or flipping its tail to dive (2). Given the wide morphological differences, there is some disagreement as to whether the Indo-Pacific humpback dolphin does in fact represent four different species: Sousa plumbea, Sousa lentiginosa, Sousa chinensis and Sousaborneensis respectively (5).
Little is known about the behaviour of the Indo-Pacific humpback dolphin, but small groups of around three to seven individuals are most commonly seen (5). These are slow-swimming dolphins, typically travelling at around 4.8 kilometres per hour (5). Despite this sluggishness, many aerial displays are seen; including breaching, when the dolphin leaps out of the water, lob tailing (slapping the surface of the water with the tail) and spyhopping, when the dolphin raises its head vertically out of the water and then sinks below the surface quietly (6). These dolphins feed primarily on reef-associated and estuarine fish (9). Individuals may be aggressive and this appears to affect dominance rank within the group (5).
Indo-Pacific humpback dolphins are at risk from factors that also threaten all other cetaceans, such as entanglement in fishing nets, pollution and the depletion of fish stocks worldwide (6). These coastal dolphins are also threatened by boat traffic, a factor that is especially pertinent in Hong Kong where this dolphin's habitat is also the busiest harbour in the world. In South Africa, shark nets may be an important cause of mortality but more data on this potential threat is required (8).
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