Department of Parks adn Wildlife

What is a dugong? The dugong (Dugong dugon) is a fascinating marine mammal that can grow up to three metres long, weigh over 400 kilograms and live for more than 70 years. It is often referred to as a 'sea cow' as it is the only marine mammal that is a herbivore (plant eater) and lives almost entirely on seagrass. The dugong is more closely related to elephants than it is to dolphins or whales.

What do they look like? Dugongs have a rotund body shape and are light brown, while the young calves are pale brown. They have a flattened fluked tail (like a dolphin) but (unlike dolphins) have no fin on their upper back. They also have paddle-like flippers and a distinctive head shape. Their mouths are large, and the upper lip is covered with bristles which are used to find and nibble seagrass. Their nostrils are near the front of the head, which enables them to breathe with most of their body beneath the surface. The dugong's ears and eyes are on the side of its head.

Vision courtesy of MIRG Australia ( Office Productions

Graphic : Location Map of the Dugongs in Western Australia Where do they live? Australian dugongs live in the shallow warm waters of northern Australia, ranging from Shark Bay Marine Park in Western Australia around the north to Moreton Bay in Queensland. It is believed that there are 80,000 dugongs in Australian waters and Shark Bay Marine Park has the largest population of dugongs in the world with more than 10,000 living in the bay. Most of the important dugong habitats in Western Australia are protected in marine parks, marine reserves or proposed marine parks. As well as Shark Bay Marine Park, dugongs are also common in Ningaloo Marine Park, Montebello Islands Marine Park, Barrow Island Marine Park, the proposed Dampier Archipelago Marine Park and Lalang-garram / Camden Sound Marine Park.

What they eat and how: They feed on seagrass, usually in quite shallow water 1-5 metres deep, but are known to feed on seagrass at depths of over 20 metres. Dugongs use their flippers to ‘walk' along the seabed as they graze on seagrasses and can dig up an entire seagrass plant including the roots and shake their heads to get all the sand off their food. They eat approximately 50 kilograms of seagrass each day.

Threats: Their natural predators include sharks, crocodiles and killer whales. People, however, are the main threat to dugongs. Being slow moving, they are often victims of boat strikes and are occasionally seriously injured by propellers. In many parts of the world people hunt them for food and in Australia they are a traditional food for Aboriginal people.

Behaviour: Dugongs live in small groups called herds and communicate with chirp-squeaks, trills and barks. Their movement over an area can be followed by the sand cloud they make as they move along the seafloor. Their movements are slow and graceful. The average swimming speed is 10 kilometres per hour, but over short bursts they are capable of swimming up to 22 kilometres per hour. Dugongs stay submerged from 30 seconds to over six minutes, depending on their activity, and dives typically last 1-3 minutes. Unlike other marine mammals, dugongs cannot hold their breath under water for very long.

Breeding and caring for young: Dugongs are usually able to reproduce by the age of nine or 10 years, though sometimes not until as late as 15 years. A female dugong gives birth to only one calf every 3-7 years and the pregnancy lasts for 12-14 months. To keep the newborn calf safe from sharks, the female moves to shallow water when she is ready to give birth. The estimated size of a newborn is slightly more than a metre in length and between 20-35 kilograms in weight. Mothers nurse their young for up to 18 months and the calf may stay with its mum for up to two years. It suckles milk from the mother's teats and there is one teat under each flipper. Dugongs do not mate for life and male dugongs do not help to rear the young.

Conservation status: Dugongs are an officially protected species worldwide. In Australian waters dugongs are regarded as vulnerable under Commonwealth legislation.

How you can protect the dugong: As dugongs are slow moving, boaties need to ‘go slow for those below', especially over seagrass beds, shallow areas and in channels where dugongs, turtles and other marine wildlife feed.