Dugong (Dugong dugon)
What does it look like?
With its paddle-like flippers, fluked tail and portly body – measuring 3 m long and weighing up to 450 kg – the dugong resembles an overweight dolphin. However, it is actually more closely related to the elephant! Its elongated snout faces downwards and has an enormous, bristly mobile upper lip, used to strip seagrass leaves or snuffle up rhizomes from the sea floor. Adult males and some females even have short tusks. Special valves keep the nostrils closed while underwater, where the dugong can remain submerged for up to six minutes. Its heavy skeleton helps it stay on the bottom while feeding. But because its seagrass diet is hard to digest, the dugong has an extraordinary large intestine. It’s as thick as a fire hose and stretches some 30 m long!
Where does it live?
The dugong is found in warm, shallow waters between 26º north and south of the Equator, from east Africa to Vanuatu. But about the world’s most significant population – 10,000 to 12,000 animals, or 10% of the species – lives in Shark Bay. The bay’s protected waters and plentiful seagrass meadows
are perfect for the dugong, the world’s only marine mammal herbivore. It feeds almost exclusively on seagrass – up to 50 kg (wet weight) per day! However, it does occasionally snack on molluscs and crustaceans. As it feeds it stirs up plumes of sand, leaving meandering trails that can be seen from the air.
The location of dugongs in Shark Bay varies during the year, depending on water temperature and the abundance of specific seagrass species. In winter they take refuge in warmer waters off Dirk Hartog Island
and Bernier and Dorre Islands
; in summer they gather to feed on nutritious seagrasses in the Gladstone Special Purpose Zone in the eastern bay, and at the southern end of Henri Freycinet Harbour. An award-winning research
team from Shark Bay’s Aboriginal community has discovered much about the dugong’s behaviour in the region.
How does it breed?
Dugongs have a similar lifespan to humans, living up to 70 years. The female has her first young, called a calf, between 12–17 years of age. Only one calf is born per pregnancy, which lasts up to 14 months, and pregnancy occurs every three to seven years. A newborn calf is pale brown, just over 1 m long and weighs up to 35 kg! It can swim as soon as it is born, although it needs a little help from its mother to go to the surface to breathe. The calf starts eating seagrass while still very young, but continues to drink its mother’s milk until it is 18 months old. It may stay with its mother for two years or more, swimming just above her back and communicating with bird-like chirps, squeaks and trills.
Any threats to its survival?
The dugong is considered globally vulnerable to extinction
. Sharks and killer whales eat dugongs but the worst threats are pollution and coastal development, which destroy seagrass beds, as well as boat traffic, entanglement in fishing nets, and hunting. In Shark Bay, the biggest threat to the dugong is boat strike. Although the dugong has good eyesight and excellent hearing, and can swim at 20 kph over short distances, its average speed is 10 kph – even slower when it is feeding. Please travel slowly when boating over seagrass beds, to avoid injuring or even killing dugongs. If you come across a herd of dugongs, cut the boat’s engine and enjoy the privilege of a close encounter with this rare and gentle animal.
For more information about Western Australian wildlife check out the WA Museum Fauna Base
to download a printable PDF of this fact sheet.