The Dugong

Dugongs, or sea cows as they are sometimes called, are marine animals which can grow to about three metres in length and weigh as much as 400 kilograms. They are the only marine mammals in Australia that live mainly on plants. The name sea cow refers to the fact that they graze on the seagrasses, which form meadows in sheltered coastal waters. As dugongs feed, whole plants are uprooted and a telltale-feeding trail is left.

Dugongs are more closely related to elephants than to marine mammals such as whales and dolphins, but their closest living aquatic relatives are the manatees. Manatees are aquatic mammals that live in freshwater rivers and coastal waters of West Africa, the Caribbean, South America and the southern United States (Florida). Another close relative was Steller's sea cow, previously found in the northern Pacific. It was hunted to extinction in the 1700s by sealers for its meat. It grew almost three times as long as the dugong and fed on large algae (kelp).

Dugongs inhabit shallow, tropical waters throughout the Indo-Pacific region. Most of the world's population of dugongs is now found in northern Australian waters between Shark Bay in Western Australia ( over 10,000) and Moreton Bay in Queensland. Dugongs lived in the shallow waters of at least 37 countries and territories around the world. Throughout their range which runs from east Africa to Vanuatu between about 26° north and south of the Equator, Dugongs have already disappeared from some places including the waters off Mauritius, western Sri Lanka, the Maldives, Japan's Sakishima Shoto Islands, Hong Kong's Pearl River estuary, several islands in the Philippines and parts of Cambodia and Vietnam.

Dugongs Life at sea

Dugongs swim using their whale-like fluked tail and they use their front flippers for balance and turning. Their movements are often slow and graceful. Early explorers and sailors believed that they were mermaids because of their streamlined bodies and the large teats at the base of their flippers.

They have a rounded head with small eyes and a large snout. The nostrils are at the top of the snout and, like mammals, dugongs must surface to breathe. However, unlike other aquatic mammals such as some whales, dolphins and porpoises, dugongs cannot hold their breath under water for very long. It is generally for only a few minutes, especially if they are swimming fast.

Dugongs have poor eyesight but acute hearing. They find and grasp seagrass with the aid of coarse, sensitive bristles, which cover the upper lip of their large and fleshy snout. Small tusks can be seen in adult males and some old females. During the mating season, male dugongs use their tusks to fight each other.

Dugongs are slow-moving and have little protection against predators. Being large animals, however, only large sharks, Saltwater Crocodiles and Killer Whales are a danger to them. Young Dugongs hide behind their mothers when in danger.

Dugongs are protected, except where traditionally hunted by Aboriginal people. In Australia, Dugongs are accidentally drowned in fish and shark nets. Seagrass meadows can be destroyed by dredging and smothered by soil washed into the sea during heavy storms and cyclones. Under the Environment Protection and Biodiversity Act 1999 they are listed marine and migratory species. They are listed on Appendix 1 of the Conservation of International Trade in Endangered Species of which Australia is a signatory.

Dugongs life history is made of finely balanced population parameters. They can live up to 70yrs but normally die younger. The females reproductive period is 6-17yrs and the males 4-16yrs the gestaion period is between 13-15mts and the female will only have one calf and the calf will stay with the mother anything up to 7yrs depending on female or male. The rate of breeding is around 5% per year but the mortality rates is also 5% per year.

The slow breeding rate and long life span mean that dugongs are particularly susceptible to factors that threaten their survival. Throughout their worldwide range they are threatened by human impacts, particularly on their habitat.