Dolphins of this highly variable species are characterized by robust bodies with long, well-defined beaks. In populations in the western Indian Ocean, the small dorsal fin sits on a hump, or ridge, in the middle of the animal’s back. In those in the eastern Indian and Pacific Oceans the ridge appears to be absent, or at least much less developed, and the dorsal fin is short and wide-based. In some areas, there also appear to be well-developed dorsal and ventral ridges on the tail stock, which are more exaggerated in males. The color pattern varies with age and area. In the western part of the range, light colored calves darken with age to become dark lead gray above and light gray below as adults. However, in the eastern Indian and Pacific oceans, dark calves lighten with age. In most areas of Southeast Asia and Australia, adults are pinkish white, often with spots and blotches. There are 27 to 39 sturdy teeth in each tooth row. Maximum known body lengths are 2.8 m (males) and 2.5 m (females), although unconfirmed reports of lengths up to 3.2 m have been reported. Weights of up to 280 kg have been recorded.
Can be Confused With
Humpback dolphins are most likely to be confused with bottlenose dolphins. Differences in dorsal fin shape (including presence of the hump on many humpback dolphins), head shape, and color can be used to distinguish between the two.
Indo-Pacific humpback dolphins are found from northern Australia and central China in the east, through the Indo-Malay Archipelago, and westward around the coastal rim of the Indian Ocean to southern Africa. They are inhabitants of tropical to warm temperate coastal waters and they often enter rivers, estuaries, and mangroves.
Ecology and Behavior
Indo-Pacific humpback dolphins are coastal and groups tend to be small, containing fewer than 10 individuals, although up to 30-40 have been seen together on occasion. Group structure has been studied using photo-identification techniques. At least off South Africa and in Hong Kong, fluidity in group structure is the rule.
Off South Africa, where the behavior of these dolphins has been most thoroughly studied, herds often patrol slowly parallel to shore and preferentially use sandy bays for resting and socializing, and rocky coastline and larger estuarine areas for foraging. They are moderately acrobatic, but only very rarely bowride. Groups in Hong Kong and in Australian waters often feed behind active trawlers.
Mating and calving occur all year, at least in South Africa and China, but there appear to be calving peaks in late spring to summer. Newborns appear to be around 1 m in length.
Feeding and Prey
Feeding is primarily on nearshore, estuarine, and reef fish. They also eat cephalopods in some areas, although crustaceans appear to be rare in the diet.
Threats and Status
Main threats include:
• Caught in fishing nets (such as gillnets and trawls) and in anti-shark nets off South Africa and Australia.
• Habitat loss
• Vessel strikes
• Pollution (organochlorines and trace metals have been found to be very high for several populations (such as those off South Africa and Hong Kong))
Currently, there is not much information on Indo-Pacific humpback dolphins, and they are currently listed as “Data Deficient” (IUCN) and “Not Listed” (ESA).
Jefferson, T.A. 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters. Wildlife Monographs 144:65 pp.
Jefferson, T.A. and L. Karczmarski. 2001. Sousa chinensis. Mammalian Species 655:1-9.
Karczmarski, L., V.G. Cockcroft, and A. McLachlan. 2000. Habitat use and preferences of Indo-Pacific humpback dolphins Sousa chinensis in Algoa Bay, South Africa. Marine Mammal Science 16:65-79.
Ross, G.J.B. 2002. Humpback dolphins Sousa chinensis, S. plumbea and S. teuszii. pp. 585-589 in W.F. Perrin, B. Würsig and J.G.M. Thewissen, eds. Encyclopedia of marine mammals. Academic Press.
Ross, G.J.B., G.E. Heinsohn, and V.G. Cockcroft. 1994. Humpback dolphins Sousa chinensis (Osbeck, 1765), Sousa plumbea (G. Cuvier, 1829) and Sousa teuszii (Kukenthal, 1892). pp. 23-42 in S.H. Ridgway and R. Harrison, eds. Handbook of marine mammals, Volume 5: The first book of dolphins. Academic Press.