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 kg.
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 10m 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 have also been found in New South Wales waters.
Life history and behaviour
Dugongs may live for 70 years or more and are slow breeders. The female dugong does not begin breeding until she is 10-17 years old and only calves once every three to five years, providing seagrass and other conditions are suitable. This slow breeding rate means that dugongs are particularly susceptible to factors that threaten their survival.
Dugongs feed almost exclusively on seagrass, a flowering plant found in shallow water areas. An adult will eat about 30 kilograms of seagrass each day. As dugong 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 strike 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 or coral reefs pose the greatest threats.
Dugongs are also under threat from diminishing food sources. Seagrass meadows are being detrimentally affected by pollution (pollutants can include herbicide runoff, sewage, detergents, heavy metals, hypersaline water from desalination plants, and other waste products), algal blooms, high boat traffic and turbid waters. Today, dugongs need to rely on smaller seagrass meadows for food and habitat. When the seagrass habitat becomes unsuitable for foraging, dugong populations are displaced and placed under greater threat.
Other direct threats to dugongs include incidental mortality in gill fishing nets and shark meshing.
- The department monitors dugong mortality along the Queensland coast via StrandNet, the marine wildlife stranding and mortality database. StrandNet summarises the temporal and spatial distribution of injured, dying and dead marine wildlife in Queensland from records received by the department, the Great Barrier Reef Marine Park Authority, other government agencies, and those received directly from the public and rehabilitation facilities. The current Marine wildlife stranding and mortality database report for dugongs summarises dugong strandings and mortalities in Queensland reported during 2011. A total of 250 stranded or dead dugong (including ten unconfirmed reports) were recorded in 2011 and 90 (with five unconfirmed reports) in 2009. Marine wildlife stranding annual reports for dugong from 1998 onwards are available from the EHP Library catalogue.
- New legislation for the conservation and management of marine mammals has recently been released. This new legislation replaces the former Nature Conservation (Dugong) conservation Plan 1999 and Nature Conservation (Whales and Dolphins) Conservation Plan 1997, and brings those provisions into the Nature Conservation (Wildlife Management) Regulation 2006.
- Dugongs have important cultural and social values for Aboriginal and Torres Strait Islander people living in coastal areas. The department is working to provide a component of the Commonwealth funded Indigenous Turtle and Dugong Management Project. The project is responding to requests from Traditional Owner groups for training and support in compliance issues relevant to traditional hunting practices, development of sea country management plans and research and monitoring of sea country (in particular turtle and dugong populations and seagrass habitats).
What can you do to help this species?
- When boating, especially in shallow waters, 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. Such pollutants can affect the health of coastal mammals directly or indirectly through accumulation of poisonous substances in their food.
- Find out more about the new marine mammal legislation
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.