Dugongs

Dugongs (Dugong dugon) are marine mammals, which are commonly known as sea cows. Australia is home to most of the world’s dugongs. They live in northern waters between Shark Bay in Western Australia and Moreton Bay in Queensland. One of the reasons for nominating the Great Barrier Reef as a World Heritage Area in 1981 was its importance as a feeding ground for large populations of dugongs.

Dugongs can grow to three metres, can weigh up to 400 kg and live for at least 70 years. They have ears and eyes on the side of the head and, although they do not see very well, are believed to have acute hearing. Sensitive bristles covering their upper lip are used to find and grasp seagrass. They generally surface to breathe after only a few minutes underwater, breathing through nostrils on the top of the head. Their flippers and tails resemble those of dolphins but they lack a dorsal fin.

Females can have their first calf from six years of age. They produce a calf only once every 2.5–5 years after a gestation period of about 14 months. Calves are about 1.2 m long and weigh about 30 kg. They suckle for at least 18 months and often ride above their mothers’ backs.

Dugongs feed mainly on seagrass but can also eat invertebrates such as polychaete worms, sea squirts and shellfish. In the GBR, they feed mainly on seagrasses, which they graze mostly in shallow waters less than 10 metres deep.

Dugongs can move large distances, travelling alone or with their calves in search of food. Aerial surveys show large fluctuations in dugong numbers over long stretches of coastline due to movements of large numbers of the population.

Aerial surveys indicate that the dugong population in the northern GBR/Torres Strait region is substantial (>20,000 individuals). In the southern GBR, numbers are smaller and have been declining since the 1980s.

While fishing has been blamed for dugong loss, other events, such as extreme weather, hunting, modern farming practices, increasing boat traffic and land clearing which causes a change in the composition of river run-off, all have an influence.

Most of the dugongs and their habitat on the urban coasts of Queensland are in marine parks. As well, 16 dugong protection areas have been established along the Queensland coast. Gill and mesh net fishing is restricted in these areas.

The Torres Strait Islanders and coastal Aborigines of northern Australia have an important connection with dugongs. Traditionally, dugong meat and oil are important food sources. Hunting can be carried out in the GBR Marine Park except in preservation zones. However, since the decline in dugong numbers in the southern GBR, some traditional owners have decided to suspend dugong harvesting.

The aerial surveys of the northern GBR and Torres Strait since the mid 1980s have not shown a significant decline in dugong numbers, despite concern about the sustainability of the traditional harvest. Community-based management, working with Traditional Owners and commercial fishers to develop appropriate management arrangements will ensure dugong numbers are maintained at a healthy and sustainable level.