10.14.2013

Marine Mammals: Dugongs

Marine Mammals: Dugongs
Shy and retiring, dugongs are marine mammals that spend their days feeding in the shallow waters of reefs and along coastlines in the Indian Ocean, the Indonesian archipelago, and the southwestern Pacific around the Philippines. Even though they resemble a cross between a seal and a walrus, dugongs are more closely related to elephants. The slow-moving mammals are easily identified by their triangular, whalelike tails, broad trunklike snouts, and long bodies, which reach 9 feet (2.7 m). Dugongs have a thick layer of blubber under their skin, a feature that gives them a round-shouldered look. Their mouths look like vertical slits on their upper jaws, and their flippers are small and paddle shaped.

Dugongs have unusually slow metabolic rates for mammals but function well in their warm water environments where they float and feed, expending very little energy. With very few predators and plenty of food, migration and other energetic types of behavior are not necessary. Most of their time is spent grazing on sea grass blades and digging up the grass roots, their favorite parts of the plants. Roots of sea grasses are rich in carbohydrates, but to reach these treats, the animals must dig around on the bottom of the reef, behavior that has earned them the nickname “sea pigs.” Equipped with very few teeth, a dugongs bites with a mobile disk at the end of its snout. The disk works like a rake, pulling in food and sending it back to the grinding plates in the mouth. The males also have tusks, enlarged incisors that project from below the upper lip.

Sexually mature between eight and 18 years, female dugongs give birth to one calf every three or four years. After a gestation period of 13 months, their cream-colored calves are born in shallow water. Mothers help the calves, measuring only 39.4 inches (100 cm), to the surface for their first breaths. A calf nurses for two years, always remaining close enough to its mother to touch her. During an average life span of 55 years, a female produces only five or six offspring.

Dugongs are so shy that not much is known about their social interactions. Attempts to observe their behavior disturb them and often kindle curiosity about the observers. Dugongs are spotted singly or in small groups of six to eight animals. Within a group there seems to be no leader or organized social structure.