The Dugong (Dugong dugon), also called baboy-dagat (pig of the sea) in Filipino, is the only surviving species belonging to the family Dugongidae. Also called the "sea cow," this gentle, slow-moving aquatic mammal feeds almost exclusively on the sea grasses in warm tropical and subtropical seas. This species is more closely related to elephants than to other marine mammals such as dolphins and whales.
The dugong is listed as endangered under the Endangered Species Act of the U.S. and as vulnerable on the IUCN Red List of Endangered Species.
Description
The dugong has a pale cream color at birth, which darkens to deep gray as it matures. It has a torpedo-shaped body with paddle-shaped forelimbs and a fluke-like tail for propulsion. The shape of its tail is one of the characteristics that helps to distinguish the dugong from other members of the Order Sirenia, as manatees (Family Trichechidae) have rounded tails. The dugong has thick skin sparsely covered by short coarse hairs. It has a rounded snout with a large muscular upper lip that hangs over a small mouth that opens downwards and is framed by stiff bristles on either side. It also has very heavy bones that help it to stay underwater to feed.
Adult dugongs are usually 2.4 to 2.7 meters long and weigh 230 to 360 kilograms. There is little or no difference between the appearance of males and females, although females may grow to be slightly larger than males and mature males may grow tusks which are used in social interactions.
The dugong has a low metabolism and tends to move relatively slowly, with an average swimming speed of 10 kilometers per hour, although it can double this speed if necessary. Unlike other marine mammals, it cannot hold its breath underwater for long periods of time, so dives last only from 1 to 3 minutes.
Habitat and Distribution
The dugong lives in shallow coastal waters of tropical seas, where sea grasses are abundant. It is seldom, if ever, found in freshwater. Dugongs are usually found in the coastal waters of the Indo-Pacific region, from the east coast of Africa to Vanuatu in the western Pacific, between latitudes of about 27° north and south of the Equator.
A report on dugongs made at the Third IUCN Conservation Congress held at Bangkok, Thailand in 2004 states that the dugong may have been present around almost all of the islands of the Philippines in the early 1900s. At present, occurrences of dugongs have been reported in Isabela and Quezon provinces, southern Mindoro and Palawan, Guimaras Strait and Panay Gulf, northeastern Mindanao, and southern Mindanao including the Sulu Archipelago and Sarangani Bay.
Reproduction
A dugong sexually matures at age 9 to 10 years or as late as 15 years. There are no specific breeding months; a female may come into heat anytime during the year. According to the University of Michigan website, while the length of time of a dugong’s pregnancy is unknown, though it is presumed to be about one year; while the EDGE website says it is 13 to 14 months. The female usually gives birth to a single calf; twin births are rare.
Newborn dugong calves are 100 to 120 centimeters long and weigh 20 to 35 kilograms. Calves are born in shallow water and surface almost immediately to take their first breath. They drink milk from their mothers for as long as a year and a half, although they may begin browsing on sea grass at 3 months after birth. Females mate and give birth only every 3 to 7 years. Dugongs are known to live at least 70 years in the wild.
Early sightings of dugongs by sailors are believed to have given rise to the legend of the mermaids. The name dugong itself comes from the Malayan "duyong" which means "mermaid".
The Steller's Sea Cow (Hydrodamalis gigas), the dugong's closest relative, was discovered on Bering Island in 1741. Due to reports of its excellent meat, it was hunted out of existence within 27 years. The last Steller's Sea Cow was reported killed in 1768.
The dugong has been hunted throughout its traditional range for its meat, hide, oil and bones. Its slow movement and inability to take long dives make it easy prey for hunters. Dugongs are also highly susceptible to being entangled in fishing nets or hit by boat propellers, which can lead to death or serious injury. Also, its slow reproductive rate means slow population growth, and a high mortality rate may hasten the decline of the species.
The Guimaras oil spill of August 11, 2006 damaged 24 square kilometers of the island ecosystem of Guimaras, including 12 hectares of sea grass beds, the feeding grounds of a small dugong population in the area, further impacting the species' chances of survival.
Administrative Order No. 55, Series of 1991, issued by the Secretary of the Philippine Department of Environment and Natural Resources, declares the dugong as a protected marine mammal of the Philippines and prohibits the killing of dugongs and the destruction of their habitats.