Dugong (Sea Cow)
The head of Dugong is remarkable for its expanded, trunk-like upper lip (elephants are considered to be their closest relatives). Unlike dolphins and other cetaceans they have two nostrils and no dorsal fin. They grow to about 3 m in length and to more than 400 kg in weight. Their main source of food is seagrass, although they sometimes supplement their diet with sea squirts that also live on the seagrass beds. At the turn of the century vast numbers of dugong were slaughtered for their much sought-after oil. By 1910 this industry had virtually collapsed due to the decimation of local populations. Dugong populations take a long time to recover because they have a very slow breeding rate and are vulnerable to loss of seagrass habitat. Moreton Bay is a stronghold with more than 700 individuals. Further north, in regions like Hervey Bay and Cooktown, dugong numbers have declined significantly in recent years possibly as a consequence to both natural and human-induced changes to the health and ecology of seagrass beds. Speed-boat traffic over seagrass beds also causes deaths due to boat and propellor strikes. There are few known natural predators of dugong, although sharks may take calves. Other threats include accidental entanglement and drowning in gill-nets.
There has been a recent serious decline in Dugong numbers in the Great Barrier Reef Marine Park between Cooktown and Hervey Bay. Between Dunk Island and Bundaberg numbers declined from around 3,500 in 1992 to around 1,700 by 1994. In Hervey Bay they declined from 2,200 in 1988 to 800 by 1994.
Although Dugongs are found in over 40 countries from eastern Africa to Vanuatu, the Australian population is the world's most significant from a long-term conservation perspective. Unlike many 'developing' countries where Dugongs occur, Australia has a relatively small human population that attaches high priority to issues of conservation. If Dugongs cannot be saved in the Great Barrier Reef Marine Park region, one of the few areas in the world where they protected, then it is doubtful that they will survive anywhere else.
James Cook University research has shown that the Dugong population of eastern Cape York north of Cooktown (10,000) is relatively stable. However, south of Dunk Island to Hervey Bay Dugong numbers have plummeted, probably as a result of accidental capture in set fish nets, hunting and habitat loss.
Set mesh nets have recently been banned in certain areas of critical Dugong habitat in the southern Great Barrier Reef Marine Park. Many Aboriginal Community Councils south of Cooktown have decided to suspend Dugong hunting. The Queensland Shark Protection Program has been reviewed to address the problem of Dugongs being caught in shark nets. Manage seagrass beds by preventing inflows of silt and herbicides from water catchments.
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