Species:

Indo-Pacific Humpback Dolphin

Indian Ocean Bottlenose Dolphin

Irrawaddy Dolphin

Finless Porpoise

Dugong

 

 

 

Dugong (Dugong dugon)

Description

The dugong is a member of the order Sirenia and a cousin of the manatee. They are slightly smaller than the manatee, growing to about 3m in length (420kg). The tail shape is the main physical difference between the two species, with the manatee tail being “paddle” shaped and the dugong fin-like.

Dugongs are grey-brown in colour with a paler underside. They have a broad, flat muzzle with two nostrils on the top of the snout and there is no dorsal fin. Adult dugongs may develop tusks (which are absent in all the manatee species) and look a little like a cross between a dolphin and a walrus. They often have lots of scars on their backs, which remain un-pigmented, making them look white compared to the rest of the back. Dugongs have two mammary glands under the “armpit”, which resemble human breasts and may explain the link between legends of mermaids and dugongs.

Distribution:

The dugong has a wide range covering 37 different countries. They are widely distributed in the Indian and Pacific Oceans, being found along the southeast coast of Africa and west coast of Madagascar, north to the Arabian peninsula, east to India, Thailand, Indonesia, Papua-New Guinea, the Philippines and as far north as Japan.

Distribution of the dugong Reproduced from Marsh et al 2002.

Dugongs frequent coastal waters, with major concentrations occurring in shallow protected bays, mangrove channels and inshore islands where there are large seagrass beds. They have also been observed in offshore waters but in areas where the continental shelf is shallow and protected (Marsh, 2002).

 

Behaviour:

Dugongs are quite different from manatees and are actually more closely related to the extinct Steller's sea cow than to any living species of manatee. Unlike the manatee, Dugongs are never found in fresh water, spending all their time in salt water where they feed on sea grasses. They are very discrete when surfacing, with often only their nostrils appearing above the surface. This combined with their slow movements make them very difficult to spot in the wild.

When feeding, they often uproot the whole plant, leaving long bare furrows in the seagrass bed. They prefer “weedy” or “pioneer” species of seagrass, especially species in the genera of Halophila and Halodule (Marsh, 2002). These are high in nutrients but low in fibre and therefore easily digested. Dugong feeding is thought to affect both the species composition and nutrient quality of a seagrass bed, and if dugongs become extinct in a particular area, the seagrass meadows are likely to deteriorate (Marsh, 2002).

Dugong may live to be greater than 70 years old in the wild, but are threatened by habitat degradation and other environmental impacts. These mammals can stay underwater for six minutes before surfacing. They sometimes breathe by "standing" on their tail with their heads above water. Dugongs spend much of their time alone or in pairs, though they are sometimes seen gathered in large herds of a hundred animals. Little is known about the herd structure of dugongs and the mother/calf pairing in the only definite long-lasting social unit.