This site is indebted to the writings of Lyall Watson (amongst others), for his amazing and well-researched book Whales of the World, illustrated by Tom Ritchie.

INDOPACIFIC HUMPBACK DOLPHIN Sousa chinensis

Description Small; length averages 2 m (6.5 ft) for both sexes, with a possible maximum of 3.1 m (over 10ft); calves are 90 cm (35 inches) at birth. Weight averages 85 kg (187Ib), with a maximum of 139 kg (306 lb); calves are about 25 kg (55 lb) at birth.
The shape is almost as variable as the colour. Calves have a classic dolphin form, much like that of the Bottlenose Dolphin (Tursiops truncatus 76), but as they mature, fatty tissue accumulates on the back, forming a narrow longitudinal hump. This intrudes between the back and the unchanged dorsal fin which is perched incongruously on top. Males and some females also develop large keels above and below the tailstock.
The beak is long and cylindrical, there is a slight melon and the flippers are short and rounded. The dorsal fin is roughly triangular, curving backwards in calves, but becoming softer and more rounded later. In older individuals with prominent humps the fin is often so flexible that it flaps at the tip. Indo Humpback dolphin

The colour ranges from deep lead grey to ivory white, in a variety of patterns from unmarked to heavily spotted. Calves of all forms are uniform pale cream. In the South China Sea many dolphins keep this colour into maturity. In the Bay of Bengal and sometimes across the Arabian Sea to the coast of East Africa adults also remain light coloured, but develop a pattern of yellow, pink, grey and ruddy spots or freckles, mainly on their backs. Across the entire range certain adults seem to become completely dark, leaving a light area only on the belly, but when these dolphins age they acquire white blazes on the tip of the beak and on the ends of the flippers and fin. Scars are often prominent. All Humpback Dolphins breathe in a most distinctive way, which makes identification simple.

The over­riding impression is of slow, measured movement. First the rodlike beak breaks water, followed by the melon and the hump. Then, while the dolphin blows, it cruises horizontally for a moment with the long beak just resting on the surface, but sometimes with the whole head lifted completely clear of the water, when the large hump and relatively small fin are clearly visible. Finally it ducks the head down, rolls the hump a little higher and slides from view. When undisturbed this deliberate pattern may be repeated several times, with the dolphin remaining at the surface for 3-5 seconds over each breath. At the end of a sequence the dolphin bends the hump at an acute angle, arching the back very steeply, and shows the entire tail as it dives almost vertically, disappearing for a period of 1-5 minutes.

Humpback Dolphins behaving in this way will allow a diverto get about 20m close to them, but any attempt to get closer invariably leads to their diving, dashing off underwater in all directions and reappearing at the surface some distance away. Sometimes, before fleeing, one of the group will sit up vertically in the water with its whole head exposed. These dolphins are apparently neither afraid of, nor attracted to, larger boats, never bow riding, but sometimes swimming about beneath an anchored vessel.

Indopacific Humpback Dolphins often associate with Bottlenose Dolphins (Tursiops truncatus 76) in shallow water, small groups apparently integrating fairly easily with larger schools of Bottlenoses. We have also seen them feeding together with Spinner Dolphins (Sti'11l'l/a longirostris 70) just outside fringing reefs off the East African coast. Humpback Dolphins feed exclu¬sively in shallow water, often in mangrove swamps, on a wide assortment of fish, molluscs and crustaceans, generally after dark. The usual social unit is a group of 2-20 (average 8 or 9), who move together in an orderly way. Young tend to be more playful, leaping into the air and twisting for no apparent reason. Sometimes a mother and nursing calf are found on their own and, occasionally, a solitary adult, usually a male, can be seen.

Courtship begins with one of a pair (we presume the male) floating on his side and beating rhythmically on the water with his exposed flipper. He follows this up by swimming alongside the female, rocking in the water as he goes. There ensues a flurry of chasing, leaping, rubbing, fluke stroking, inverted swimming, biting and clasping; ending with copula¬tion, which takes place belly-to-belly with both partners standing vertically in the water.
Graham Saayman of the University of Cape Town reports a spectacular display, seen on the coast of South Africa, in which the dolphins swim upside down, burst out of the water still inverted, turn a full back somersault and re-enter, right side up but facing in the opposite direction.

Newborn calves have been seen in March and April north of the equator, but nothing else is known about periods of gestation or lactation.

Indopacific Humpback Dolphins produce directional clicks and creaks with a frequency of up to 25 kHz, clearly involved in echolocation. They also make a high-pitched whistle which, in groups of animals, sometimes builds up into a harmonic scream that seems to have a signal function.

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