Shark Bay is home to one of the largest and most stable populations of dugong in the world. The huge shallow seagrass meadows of Shark Bay provide an ideal habitat for these marine mammals.
The dugong is related to the manatee, of which there are three species. Sadly another close relative, the Steller's sea cow, became extinct in the 1700s due to hunting by humans.
There are other populations of dugong in Australia, notably along the Queensland coast from Townsville north into the Torres Strait.
The dugong inhabits the waters of around 40 countries in the Indo-West Pacific region.
The three species of manatee all depend on fresh water to some extent so the dugong is the only member of the order Sirenia to be a fully marine mammal.
A mature dugong can weigh as much as 400 kilograms and measure three metres in length. They are usually a mid-greyish colour but some are lighter and almost pinkish.
Although it was thought that the dugong was herbivorous, feeding only on seagrasses, they have been observed eating sea pens (feather like relatives of corals) and a type of mollusc that lives under the sand on the sea floor. It is thought that their need to eat foods other than seagrass stems from them being unable to get rhizome rich tropical seagrass to eat during the winter months. They seem to be supplementing the lack of their normal diet with animal protein.
The name 'dugong' seems to come from a language (or languages) around the Indian Ocean and means 'sea pig'.
Unlike the manatee with its round paddle like tail, the dugong has a tail similar to whales. They have a short trunk-like snout that assists them with rooting up seagrass and they have a number of unusual adaptations that make life for a mostly herbivorous marine animal possible.
Their large intestine is 30 metres long and accounts for much of their bulk. Their lungs are large and extend along the upper wall of their body cavity and as far down as their kidneys. While the lungs assist with buoyancy, they also need to spend a lot of time on the sea floor and their bones are especially heavy. This gives them a neutral or slightly negative buoyancy.
The population in Shark Bay is estimated to be around 10,000. This represents close to ten percent of the total world population.
Shark Bay is a sub-tropical area and the usual habitat of dugong is tropical. In the Shark Bay area they seem to have movement patterns that allow them to follow the warmer water.
Dugong are long lived creatures with females attaining and age of 70 years or more. They only begin to breed from 12 to 17 years old and may only have a calf once every 3 to 7 years. This slow rate of reproduction makes them vulnerable to exploitation and they are now a protected species but not quite fully protected.
Calves stay with their mothers for up to 18 months and despite being able to eat seagrass from just two weeks old, they may continue to suckle for much of the time they remain with their mothers. When in danger the calves will take up a position above the mother's back.
Dugongs do not congregate in herds. Males are thought to be solitary but will gather in 'dancing grounds' to attract females.
The Aboriginal people of Australia have traditionally hunted the dugong and are still allowed to do so, including in the World Haritage listed Shark Bay area. This has been responsible for lower dugong numbers in some areas, especially in Queensland. Aboriginal hunting involves spearing the dugong and using an attached rope to drag the animal through the water with a boat to drown it. It is claimed that it can take up to two hours for the animal to die.
Dugongs are gentle and inquisitive animals and we do not believe that this cruel parcatise should be allowed to continue. While we do recognise that cultural practices are important, where they inflict unnecessary pain and suffering they should be abandoned to the past. Cruelty in the name of culture should never be acceptable.
Europeans began hunting dugong in Australian waters in the 1850s. In commercial operations the dugong were netted, brought to the surface and shot.
Oil extracted from dugong flesh was even used during World War One to ease the suffering of gas attack victims.
Other threats to dugongs include loss of seagrass habitat and boat strikes. When boating in areas inhabited by dugongs you need to post a bow watch and travel at lower speeds. Dugongs are slow and despite their excellent hearing, they cannot move out of the way of boats travelling faster than ten knots. Animal threats to dugongs include large sharks, saltwater crocodiles and killer whales. Apart from their large size, dugongs are virtually defenceless.
While dugongs are usually shy and will flee from noisy boats, they will often approach boats with the engine switched off and investigate.
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