Dugongs have a slow reproductive rate. A female will raise only one calf every three to five years. Any threats to dugong can endanger the population. Experts consider that the decline in dugong numbers is due to unsustainable mortality from human-related causes such as habitat loss, commercial mesh nets (fishing nets), shark nets set for bather protection, and hunting. Hunting appears to have been sustainable in earlier years at levels higher than today. The additional recent causes of dugong decline have now made hunting unsustainable. Dugongs have become entangled and drowned in certain types of mesh nets in the Great Barrier Reef World Heritage Area. Dugongs can only hold their breath for a maximum of eight minutes, and will drown quickly once entangled in a net. These nets are those often described as mesh nets (floating or set mesh nets) and are used by some commercial fishers. Shark nets (nets set to catch sharks near bathing areas) have been responsible for the death of 541 dugongs in the Great Barrier Reef since the early 1960s Dugongs depend on access to healthy seagrass meadows to survive, as do commercial and recreational fishers, as seagrass beds are also important habitats for prawns and many commercial fish species. The dumping of dredge wastes and the discharge of silt from coastal rivers reduces the amount of light available to seagrass communities, thereby limiting their growth. The clearing of land and a variety of other agricultural activities in river catchments can increase the amount of silt washing into the sea, particularly after heavy rains. Trawling by commercial fishing vessels and pollution from urban run-off or ships can also damage seagrass meadows. The actual or potential loss of the dugong's seagrass feeding habitat is potentially the most significant issue for the long-term survival prospects of dugongs in the southern Great Barrier Reef. Dugongs are important in maintaining the health of seagrass meadows. Seagrass loss was considered a major cause of death of dugongs in Hervey Bay in 1992 following a flood. Boating and shipping also create hazards for dugongs. Dugongs may be killed or injured when struck by any part of a vessel and may also be scared away from their feeding areas by vessel traffic. In some circumstances, stress is suspected of contributing to illness in dugongs. Dugong deaths occur in unknown but probably significant numbers from illegal fish netting and illegal hunting. Illegal activities which degrade dugong habitat can also have an indirect effect on their survival.
Rarely seen, the dugong can live for 70 years and grow to three meters in length and weighs 400 kilograms. Dugongs are found from the Arabian States of the Red Sea to the Pacific Coast of Australia and the Solomon Islands. Their range includes waters of 43 different countries, and extends from eastern Africa to Vanuatu and between twenty-seven degrees north and south of the equator. However, many dugong populations are relict or extinct. Australia is the last stronghold for the dugongs where most of the world's dugongs are found, between Shark Bay in Western Australia and across the north to Moreton Bay in Queensland.. However, dugong numbers are also on the decline in the southern Great Barrier Reef and Hervey Bay areas. Of the 80,000 or so dugongs in Australia, about 12,000 occur in the Great Barrier Reef World Heritage Area. Dugong meat is an important source of protein for remote indigenous communities. A large dugong contains many kilograms of meat. In more settled regions dugongs still have an economic value to indigenous communities as a food source, in addition to the cultural value of hunting and distributing the meat.
Dugong numbers have declined significantly since 1986-87 in the southern region of the Great Barrier Reef World Heritage Area and the species is facing the threat of disappearing from the area. The decline was discovered through aerial surveys, which covered 39 000 square kilometres of the inshore waters of the southern Marine Park, in 1986-87, 1992 and 1994, and have detected a population decline from an estimated 3480 animals (+/- 460) to 1682 (+/- 240) within eight years. It has been estimated that the dugong population can only cope with loss from human-caused mortality of less than 1-2% per year.