Sousa chinensis, Indo-Pacific Hump-Backed Dolphin [+]

Kingdom Animalia Phylum Chordata Class Mammalia Order Cetacea Family Delphinidae Genus Sousa species: Sousa chinensis [+ITIS +WoRMS]

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Description & Behavior

The Indo-Pacific hump-backed dolphin, Sousa chinensis (Osbeck, 1765), aka the Chinese white dolphin or Pacific humpback dolphin is characterized by its stocky body and long, well-defined beak. It is named for its dorsal fin that, in most populations, sits on a hump that is more pronounced in males. Some Indo-Pacific hump-backed dolphins do not have the hump or it is not as prominent. Some also have distinctive ridges along the tail stock, particularly males. Males reach a maximum of 3.2 m in length, females 2.5 m and adults weigh up to 284 kg. This species varies in color by age and region. Some are light in color when they are born, darkening to a dark gray on the dorsal side, light gray on the ventral side. In the western Indian Ocean and off the coast of China calves are born with dark coloring that lightens with age to a pink-tinted white color with spotted patterns. Indo-Pacific hump-backed dolphins near Malaysia and northern Australia, however, are nearly white. This species has 29-38 peg-like teeth in the upper and lower jaw.

The Indo-Pacific hump-backed dolphin travels in groups of <10, although some groups have contained up to 30 animals. Some schools observed off the coast of South Africa appeared stable. Also in South Africa, schools of Indo-Pacific hump-backed dolphins appear to prefer sandy bays for resting and socializing and open rocky coastline for foraging. These dolphins are moderately acrobatic slow swimmers (average 4.8 kph)and are rarely seen bow riding. In spite of their slow swim speed, Indo-Pacific hump-backed dolphins have been known to chase off or kill sharks.

Indo-Pacific hump-backed dolphins are physically very similar to Atlantic hump-backed dolphins in spite of their geographic separation.

World Range & Habitat

The Indo-Pacific hump-backed dolphin, Sousa chinensis, is found in tropical and temperate coastal waters of the Indian and Pacific Oceans from northern Australia and southern China in the east, through Indonesia, and around the coastal rim of the Indian Ocean to southern Africa. They are known to enter rivers, estuaries, and mangroves, particularly the latter. They prefer shallow waters <20 m in depth with warm temperatures between 15-36°C.

» GBIF occurrence data in Google Earth [Tips] | Ocean Biogeographic Information System (OBIS) (World Distribution) [about]

Feeding Behavior (Ecology)

Indo-Pacific hump-backed dolphins feed near the shore on estuarine and reef fish, mollusks, and crustaceans. They tend to hunt in small groups using echolocation to find food, although they have been observed hunting individually. They hunt as a group, however the feed singly. This dolphin is considered a gregarious species, but they are also known to be aggressive, particularly when feeding.

Life History

The Indo-Pacific hump-backed dolphin, Sousa chinensis, appears to breed year round and calves are generally born during summer months between December-February. Mating behaviors are thought to include chasing in circles at higher speeds, swimming on one side while waving a flipper in the air, and somersaulting.

Conservation Status/Additional Comments

Some Indo-Pacific hump-backed dolphins, particularly in the northwest Indian Ocean, have been hunted for human consumption and oil. Entanglement in fishing gear and being caught as bycatch pose a threat throughout the range. These dolphins are also caught in anti-shark gillnets off southeast Africa and eastern Australia, which may pose a threat to the sustainability of this species in South Africa. Mortality off South Africa has been implicated as a population threat there. Mangrove degradation due to coastal development may also pose a threat to this species as mangroves are an important part of their habitat.