Relatives

A dugong surfacing for air over a shallow tropical seagrass habitat. Note the twin nostrils that are raised up above the water

Dugongs are more closely related to elephants than to other marine mammals such as whales and dolphins, but their closest living aquatic relatives are the manatees. Manatees are aquatic mammals that live in freshwater rivers and coastal waters of West Africa, the Caribbean, South America and the southern United States (Florida). Another close relative was Steller’s sea cow, previously found in the northern Pacific. It was hunted to extinction in the 1700s by sealers for its meat. It grew almost three times as long as the dugong and fed on large algae (kelp).

Life in the sea

Dugongs swim using their whale-like fluked tail and they use their front flippers for balance and turning. Their movements are often slow and graceful. Early explorers and sailors believed that they were mermaids because of their streamlined bodies and the large teats at the base of the flippers of the female dugongs.

A dugong herd viewed from a blimp-mounted camera

They have a rounded head with small eyes and a large snout. The nostrils are at the top of the snout and are valvular, allowing them to be closed when diving to keep the water out.  As with all other marine mammals, dugongs must surface to breathe. However, unlike other marine mammals such as some whales and dolphins, dugongs cannot hold their breath under water for very long. Dives generally last for only a few minutes, especially if they are swimming fast.

Dugongs have poor eyesight but acute hearing. They find and grasp seagrass with the aid of coarse, sensitive bristles that cover the upper lip of their large and fleshy snout. Small tusks can be seen in adult males and some old females. During the mating season, male dugongs use their tusks to fight each other. Their slow breeding rate and long life span mean that dugongs are particularly susceptible to factors that threaten their survival. Throughout their worldwide range they are threatened by human impacts, particularly by the effects of habitat degradation.

Life history