Aboriginal knowledge and artwork has not only informed us of their shared history with dugongs but also much of our scientific dugong knowledge. The dugong, or dugong dugon, is the only living member of the Dugongidae family, and is closely related to the manatees of the Trichechidae family, both of these family's belong to the order of Sirenia and are closely related to elephants. Dugongs can live up to 70 years. They have a fluke like tail which helps it move through the water at speeds of up to 18km/hr and flippers to steer whilst swimming. These act as forelegs as the browses the seagrass meadows on the coastline floor with its bristly lips ideally suited for grazing. Unfortunately its specific feeding behaviour, big body and slow speed make it an easy and desirable target for hunters and its need to surface regularly to breathe makes it vulnerable to boat strikes.
Yanuwa people’s names for the parts of a dugong
Source: Smyth (2006).).
Another risk for the dugong population is their slow reproductive rate. Females can start mating at around 6 years but sometimes delay breeding until they are 17 depending on food availability. After conception the females gestate for about 13-15 months, giving birth usually to a single live calf who suckles for a further 14-18months. The mother will not breed again for another 2.5-7 years.
Whilst all these threats are significant, possibly the greatest is the dugongs dependency on sea-grass, lying along shallow coastline waters, as a primary and singular food source. With populations spread across 48 countries from East Africa to Australia and over 140km of coastline the population is only considered to be stable in remote regions of the Northern Territory and Western Australia. Dugong populations along the Queensland Coastline, although once considered stable, are now declining rapidly - most likely due to its reduced habitat.
The Dugong Ecosystem
Source: Carruthers,
Dennision,
Longstaff,
Waycott,
Abal, et al. (2002).
Source: Carruthers,
Dennision,
Longstaff,
Waycott,
Abal, et al. (2002).
Within Moreton Bay the water quality has become so poor that some sub-regions, such a Bramble Bay, which used to contain a dense distribution of sea-grass, is now unable to consistently support any. Human activity and its inevitable pollution, such as urban storm-water drain run-off, agricultural chemical and sedimentary run-off, numerous sewage treatment plants effluent, and increased water turbulence from boating, have reduced the water and soil quality to the point where insufficient sunlight and poor soil nutrient composition make sea-grass growth impossible. The disappearance of this valuable food source from the Bay and the habitat these sea-grass meadows provide will not only affect dugong populations but also many other valuable marine species.
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