Dugongs are very large sea mammals, sometimes called “sea cows.” They have been familiar to humans for centuries, particularly because, for some reason, these ungainly creatures gave rise to the mermaid myths of the past.
Adult dugongs, both male and female, range in size from 8 to 13 feet (2.4 to 4 meters). They weigh between 500 and 1,100 pounds (230 to 500 kilograms) and have a big roll of fat around their bodies. Dugongs are gray or rusty brown in color; their young, called calves, are born a creamy beige and then darken as they grow.
Although dugongs breathe air into their lungs like land mammals, they live in the ocean and never come onto land. They are able to stay underwater for up to about six minutes at a time, but their dives usually last only one to three minutes before they come up for air.
They have nostrils near the top of their long snouts on a large lip that can reach up to the water’s surface to make breathing easier. Dugongs have a broad flat tail with a notch at its center and paddle-shaped flippers. They flap their tails in an up-and-down motion to propel them through the water, steering and balancing with their flippers.
Dugongs are herbivores (plant eaters) who graze on sea grasses on the ocean floors in warm shallow waters. Although their eyesight is poor, they have bristles on the lips of their snouts that help them find the grasses they eat. They spend a good deal of their time grazing.
Dugongs are social animals. At one time they were known to travel in large herds of several hundred or even thousands of animals. Since their numbers have declined, they usually travel in herds of about six animals.
Not much is known about this shy species, but evidence suggests that lasting bonds form between mated dugongs and also that there are distinct family groups within the larger herd. Aggressive behavior is not normal. Dugongs make whistling sounds among themselves that communicate fear; calves make a bleating sound. Mating takes place throughout the year.
Females give birth to one offspring at a time, and they generally give birth only once every three to seven years. A newborn calf is delivered in shallow water, and is able to swim immediately to the surface for air. The offspring will stay with the mother for about a year.
Sexual maturity occurs at about 10 years of age or later. Dugongs in the wild can live to be up to 70 years old. Because they live a long time and breed at a slow rate, they cannot recover quickly from population declines and they are thus more threatened by them.
Habitat and current distribution
Pacific and Indian Oceans within a very wide range, but the populations within this range are scattered.
Currently there are populations of dugong in waters around Australia, New Guinea, Sri Lanka, Indonesia, the Pacific Islands, the Persian Gulf, the Red Sea, and off the coast of east Africa. The number of dugong worldwide was estimated at the end of the 1990s at approximately 100,000. Australia has the largest population. Many areas report significant declines in the population.
History and conservation measures
The dugong is reported in the literature of the ancient world: it was seen in Greece, in Egypt, and in the Mediterranean, but there have not been dugong in those areas for centuries. Dugong populations have disappeared from their former habitats off several island groups in the Indian Ocean. They are declining around Guam and along the mainland coast of eastern Asia.
A very serious decline has occurred along the coasts of India, southwestern Asia, Africa, and Madagascar. The Torres Strait off Australia, where the dugong has always been abundant, has also lost significant numbers due to overhunting.
Aboriginal and Torres Strait Islanders, indigenous (native) people of Australia for whom the animal is a traditional food, are exempt from laws against hunting dugong, and kill an estimated 750 animals a year.
Dugongs have natural enemies, but their biggest threat comes from humans and is largely due to hunting. Dugong meat is said to taste like tender veal. Dugong hide has been used to make good-quality leather.
There is also a strong market for dugong oil, bones, and teeth. Dugongs are still legally hunted in some parts of their range. Humans also kill the dugong by accident.
Coastal areas in which the dugong have lived are increasingly being used for residential, recreational, and agricultural purposes. Shark nets set up around beaches to protect swimmers from predators trap and kill dugongs regularly. Gill nets used by fisherman also trap the dugong.
Increasing boat traffic has taken a toll. Pollution has resulted in the loss of sea grass beds essential to their survival. Other enemies to the dugong are sharks and some other sea predators. Hurricanes at sea sometimes strand dugongs.
In Australia dugongs are protected and there are a number of programs in progress to restore the sea grass beds and protect the natural habitat of the dugong. Net fishing has been banned in dugong areas, and fishermen have been required to take a course on endangered species in order to stop unnecessary accidents.
Many of Australia’s indigenous communities have agreed to stop hunting the animal and are educating their populations about dugong management. At beaches, alternatives to shark nets are being used to protect swimmers without endangering dugong. Further research about the species is underway. Worldwide, protection of the dugong and its habitat is inconsistent.