Common Name: Indo-Pacific humpback dolphin
Humpback dolphins (Sousa sp.): Two genetic variations of humpback dolphins occur along the Indian coastline, the Indian Ocean humpback dolphin (Sousa plumbea) along the west coast and the Indo Pacific humpback dolphin (Sousa chinensis) by the east coast. As genetic studies provide newer results this might change further. We shall keep you updated!
The Indo Pacific humpback dolphin is a large cetacean with a slender beak and a slight melon on the forehead. It has rounded flippers. The small but prominent dorsal fin is placed on a small hump in the middle of the back. This platform for the fin is not as distinctive in the chinensis as it is in plumbea, and is almost absent in the animals in the South China Sea. There are marked keels above and below the tailstock. There is a distinct notch between the tail flukes, which are moderately concave along the rear edge.
The colour of the species is highly variable, but specimens off east India are light grey with predominantly pink pigmentation on the skin surface. Longitudinal blotches are found on the ventral side in larger specimens. The lower jaw may be cream coloured. Calves have a uniform pale cream colouration.
Size: Adults, Male Hump-backed Dolphins may be 3.2 m long, and females up to 2.5 m. They weigh up to 285 kg. Calves at birth, 90 cm long.
Appearance At Sea: Humpback dolphins surface to breathe in a very distinctive way. The beak emerges from the water first, and then the melon and hump. As it breathes, the animal cruises with the beak just on the water surface. Sometimes the head is lifted clear of the water and the hump and fin are clearly visible then. Finally the dolphin rolls, its head going down and the hump emerging more, before sliding out of view.
The usual social unit consists of a group of 2-20 who move together in an orderly fashion.
Indo-Pacific humpback dolphin (Sousa chinensis) from Orissa, east India, showing a small fin on a reduced hump and loss of pigmentation in adults. A robust body with pronounced beak, is a common coastal species in India. @ Dipani Sutaria
Humpback dolphins can heave themselves over mudbanks to get from one channel of water to another.
Found In: Indo-Pacific humpback dolphins are nearshore dolphins that use estuaries, river mouths and waters less than 20 m deep along the coast. They feed close to shore and in tidal creeks and estuaries and sometimes get stranded upstream.
Humpback dolphins generally feed on fish, molluscs and crustaceans.
World Distribution: Indo-Pacific humpback dolphins are distributed in the warm temperate and tropical coastal waters of the east Indian, Rameshwaram northwards till the coastal waters of the western Pacific Oceans.
Could Be Confused With: Indian Ocean humpback dolphins and with bottlenose dolphins.
Diagnostic Features: At sea, prominent dorsal fin placed on hump in the middle of the back; long, slender beak. Pink pigmentation and light coloured body.
Stranded Specimens: A dead adult can be easily identified by its hump and number of teeth. There may be 29 to 38 pairs of peg-like teeth in each jaw.