Dugong (Dugong dugon) Photo: C.J. Limpus
Common name: Dugong
Scientific name: Dugong dugon
Conservation status: Dugongs are listed as Vulnerable in Queensland (Nature Conservation Act 1992) and are listed as a Marine and Migratory species nationally (Environment Protection and Biodiversity Conservation Act 1999). It is ranked as a high priority under the Department of Environment and Heritage Protection (EHP) Back on Track species prioritisation framework.
The dugong is a large herbivorous marine mammal that has a long rotund body and a tail or fluke for propulsion. Adult dugongs can reach lengths of more than three metres and weigh up to 420 kilograms. Dugongs are easily distinguished from dolphins because they have no dorsal fin and a very distinctive head with paired nostrils on the tip of the snout.
Dugongs have relatively poor eyesight so rely on the sensitive bristles covering the upper lip of their large snouts to find and grasp seagrass. Cows and calves communicate by producing 'chirps'.
Habitat and distribution
Dugong density: Alana Grech and Helene Marsh, School of Earth and Environmental Sciences, James Cook University, Townsville Qld
Major concentrations of dugongs along the Queensland coast occur in wide, shallow, protected bays and mangrove channels, and in the inside edge of large inshore islands. These areas coincide with significant seagrass beds. They also use deep-water habitats. Large numbers have been sighted in water more than 10 metres deep in several areas including the Torres Strait, the northern Great Barrier Reef region, and Hervey Bay in southeast Queensland.
A large proportion of the world's dugong population is found in northern Australian waters from Moreton Bay in the east to Shark Bay in the west. Dugongs are also occasionally reported much further south in New South Wales.
Life history and behaviour
Dugongs may live for 70 years or more and are slow breeders. Female dugongs do not begin breeding until between seven and 17years old and calve once every three to six years, although this is variable between individuals and depends on environmental conditions.
Dugongs feed almost exclusively on seagrass, a flowering plant found in shallow water areas. An adult will eat about 7per cent of their body weight in seagrass each day. As dugongs feed, whole plants are uprooted leaving telltale tracks behind. They will also feed on macro-invertebrates such as sea squirts.
Known as 'cultivation grazers', dugongs feed in a way that promotes growth of Halophila ovalis - their preferred seagrass species. Pulling out the seagrass aerates the sea floor and increases the amount of organic matter in the area, thereby encouraging regrowth of the seagrass.
Dugongs are particularly vulnerable to boat strikes as they come to the surface to breathe, putting them directly in the path of boats and other watercraft. Boats travelling at speed or in shallow waters over seagrass beds pose the greatest threats.
Dugongs are also vulnerable to incidental capture in commercial fishing nets, entanglement in mesh used in the Queensland Shark Control Program, unsustainable hunting and disease.
A marked decline in the dugong population between Cooktown and Rockhampton has been associated with the cumulative effects of loss of foraging meadows, historical exploitation and other human activities. Seagrass meadows have been detrimentally affected by sediment discharge, habitat modification, pollution, cyclones and severe floods.
In contrast, Torres Straits supports one of the largest dugong populations in the world and sustainable hunting by indigenous peoples of Torres Straits and adjacent Papua New Guinea.
The dugong populations of southern Queensland (Hervey Bay and Moreton Bay) are also considered to be stable.
- The department monitors dugong mortality along the Queensland coast via StrandNet, the marine wildlife stranding and mortality database.
- Improving water quality on the Great Barrier Reef through the Reef Water Quality Protection Plan 2013.
- Protection of significant dugong habitat from incidental catch in commercial fisheries through Dugong Protection Areas and marine parks.
- Some protection from vessel collisions within marine parks is provided by ‘Go Slow’ areas.
Dugongs have important cultural and social values for Aboriginal and Torres Strait Islander people living in coastal areas. The recent Dugong Indigenous Management Project aimed at increasing the capacity of Traditional Owners to manage their sea country, and in particular the conservation and sustainable use of dugongs.
What can you do to help this species?
- When boating, especially in shallow waters, drive responsibly and be on the lookout for dugongs to avoid injuring them.
- Know where you need to go slow. Get the 'Go Slow' map defining turtle and dugong go slow areas or the Moreton Bay Marine Park User Guide. Always have the Maritime Safety Queensland Beacon to Beacon publication on board your vessel.
- Remember that rubbish you throw away or chemicals you discard may find their way into drainage systems that run into the ocean and harm dugongs or other marine wildlife.
- Report injured, sick, entangled, stranded or dead dugongs to the RSPCA hotline on 1300 ANIMAL (1300 264 625).
- Find out more about the recent marine mammal legislation
- Boat strike impact on turtles and dugong in Moreton Bay
- Dugongs in Moreton Bay
- Marine wildlife stranding
- Maps defining 'turtle and dugong go-slow areas' or the Moreton Bay Marine Park User Guide
- Department of Sustainability, Environment, Water, Population and Communities. 2012. Dugong dugon Dugong in the Species Profile and Threats Database.
- Meager, JJ, Limpus, CJ and Sumpton, W 2013. A review of the population dynamics of dugongs in southern Queensland: 1830-2012. Brisbane, Department of Environment and Heritage Protection, Queensland Government.