Dugongs

Dugongs are in trouble throughout the Great Barrier Reef World Heritage Area. Numbers have dramatically declined along the urban coast and without urgent and effective action, dugongs are at high risk of disappearing from the region.

Much of the information about dugongs in the Great Barrier Reef World Heritage Area comes from research conducted over the past 30 years by Professor Helene Marsh and her colleagues and students at James Cook University and from the local knowledge of Indigenous people and fishers. The contributions of these people in acquiring and providing this information are gratefully acknowledged.

Facts About dugongs

Order: Sirenia Genus: Dugong Species: Dugong 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 seagrass, which form meadows in sheltered coastal waters. As dugongs feed, whole plants are uprooted and a telltale feeding trail is left.

Relatives

Dugongs are more closely related to elephants than to other 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).

Distribution

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 and Moreton Bay in Queensland.

The known range of the dugong: (From: Marsh et al., 2002, 'Dugong Status Report and Actions Plans for Countries and Territories

Life in the sea

A dugong surfacing for air over a shallow tropical seagrass habitat. Note the twin nostrils that are raised up above the water

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 all other mammals, dugongs must surface to breathe. However, unlike other marine mammals such as some whales and dolphins, dugongs cannot hold their breath under water for very long. It is generally for only a few minutes, especially if they are swimming fast.

A dugong herd viewed from a blimp-mounted camera

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. Their 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.

Life history

Dugong list history