The Dugong (Dugong dugon), commonly known as the sea cow, is a sea grass-dependant marine mammal of tropical and subtropical coastal waters, with high genetic biodiversity value. It is the sole member of the genus Dugong, which is the only extant member of the Family Dugongidae. The Dugongidae share the Order Sirenia with three species of manatee found in the Atlantic regiopn. The dugong's genes are more distinctive than those of most species, which usually have genera and Family-level relatives. The dugong is also one of a suite of large, long-lived marine vertebrates, inclusing turtles and inshore cetaceans, which are under pressure from human activities. Dugong conservation therefore represents the opportunity - and responsibility - to contribute significantly to the conservation of ocean biodiversity.

Currently dugongs are classified as vulnerable to extinction under the 2009 World Conservation Union (IUCN) Red List of Threatened Species. This classification describes taxons that face a high risk of extinction in the wild in the medium-term future.

Ecological Importance of Dugongs

The dugong has a large range which spans at least 48 countries and territories over an estimated 140,000km of coastline which includes tropical and subtropical coastal and inland waters from East Africa to Vanuatu to Japan. UNEP published the Dugong Status Report and Action Plans for Countries and Territories in 2002. It states that "throughout much of its range, the Dugong is represented by relict populations separated by large areas where its numbers have been greatly reduced or it is already extirpated. The dugong is still present at the historical limits of its global range, although there is evidence of a reduction in its area of occupancy within its range. In most parts of its range, the anecdotal evidence suggests that dugong numbers are declining". Dugongs have already disappeared from some places including Mauritius, the Maldives, Japan's Sakishima Chains. Hong Kong's Pearl River Estuary, several islands in the Philippines, Cambodia and Vietnam. Remaining major populations have been reported in Australia, the Middle East region including the Gulf and parts of the Red Sea, the northern and eastern coasts of East Africa, Indonesia and the Pacific islands.

Generally dugongs are found in coastal waters. Major concentrations tend to occur in wide shallow protected bays, wide shallow mangrove channels and in the lee of large inshore islands where seagrass beds occur. However, dugongs are also observed in deeper waters further offshore where the continental shelf is wide, shallow and protected. This distribution corresponds with that of deepwater seagrasses. There is evidence that dugongs use specialised habitats for various activities such as calving and mating. The life history attributes of dugongs are likely to vary across the range of habitat types.

The dugong is a seagrass specialist, uprooting whole plants when they are accessible, but feeding only on leaves when the whole plant cannot be uprooted. The highly specialised dietary requirements of the dugong imply that only certain seagrass meadows may be suitable as dugong habitat. It has been suggested that grazing activity by dugongs alters the species composition of seagrass communities at a local scale to favour their dietary requirements. Thus areas that support sizeable numbers of dugongs may have the capacity to provide better, "quality" food than areas that support few or no dugongs and rely only on natural turnover rates for recycling and redistribution of nutrients.

Vulnerable to Threats

Dugongs are long-lived – up to 70 years – and are slow to mature and breed. Females have their first calf when they are between six and 17 years old and then produce calves only once every 2,5–5 years. The female will usually only bear one calf after a pregnancy which lasts about 14 months. The age of first reproduction and calving intervals may lengthen as a result of food shortages. The dugong’s low reproductive rate means that a very high proportion (more than 95%) of adult animals have to survive each year for a dugong population to be maintained. Population simulations indicate that even with the most optimistic combinations of life-history parameters (e.g. low natural mortality and no human-induced mortality) a dugong population is unlikely to increase by more than 5% per year. Thus the dugong’s life history makes it particularly vulnerable to rapidly increasing human pressures.

Dugongs are vulnerable to human-related influences due to their life history and their dependence on seagrasses that are restricted to coastal habitats, and which are often under increased pressure from human activities. The rate of population change is most sensitive to changes in adult survival. Even a slight reduction in adult survival as a result of habitat loss, disease, hunting, or incidental drowning in nets, can cause a chronic decline in a dugong population. Given the extensive distribution of the dugong, there are a range of threats, some of which are unique to particular regions and some which span its entire range.

Concerted Action Needed

Conservation and management of dugong populations through domestic policy may be afforded through initiatives such as formally declaring dugong protection areas, regulation and enforcement of activities within these areas, prohibition of direct take (except possibly for traditional purposes), and the implementation of a rigorous and effective environmental impact assessment process in areas of significance.

Managing adverse impacts on dugongs throughout their vast and often remote range presents a challenge, which will require a pro-active and comprehensive approach. Ultimately conservation initiatives would seek to conserve dugongs across both their historic and current range. Such a systematic and co-coordinated approach will benefit not only dugong populations but also the ecological integrity of the marine environment.