(Müller, 1776) - Dugong
Distinctive Characteristics
The dugong is unique among living sirenians in having whale-like flukes with a median notch, instead of the rounded tails of manatees. In general, dugongs are more streamlined and cetacean-like than manatees. The area in front of the flukes is laterally compressed into a peduncle. The paddle-shaped flippers have no nails. There is a downward deflection to the muzzle, which ends in a “rostral disk” with short, dense bristles. The nostrils are valve-like and are situated on the top of the animal's snout. The skin is generally smooth (not wrinkled, although there are folds) and is sprinkled with short hairs.
Adults are slate grey on the back, slightly lighter on the belly. Calves are a pale cream colour.
The dental formula is I 2/3, C 0/1, PM 3/3, M 3/3 (the 6 molars and premolars are reduced to 2 or 3 in older animals). The lower incisors and canines, and the inner pair of upper incisors, are vestigial.
Can be confused with
This is the only sirenian in the Indo-Pacific. There is some possibility of confusion with the finless porpoise, but the single blowhole of the porpoise and the double nostrils of the dugong will allow them to be easily distinguished.
Size
Maximum known size for dugongs is about 3.3 m and at least 400 kg (a specimen reported to be 4.06 m and 1016 kg is considered to be an error). At birth, dugongs are between 1 and 1.5 m long and weigh about 20 kg.
Geographical Distribution
Dugongs are widely distributed in the Indo-Pacific region in coastal tropical and subtropical waters. They also occur in inshore waters, in bays and channels. The range is discontinuous: from southeast Africa north to the Red Sea; in the Persian Gulf; along western India to Sri Lanka; and throughout Indonesia and the Pacific islands, to the Ryukyu Islands in the north and the central coasts of Australia in the south.
Biology and Behaviour
Dugongs occur mostly in small groups of up to 6 individuals. Herds as large as several hundred animals periodically form, although not as often as in the past. Dives up to 8 minutes have been recorded.
There is some reproductive activity throughout most of the year, with calving peaks in June to September in at least some parts of the range. Not much is known about reproductive behaviour in the dugong, but groups of males seem to compete to mate with a single estrus female. The gestation period is about 13 to 14 months, and a single calf is born.
The food of dugongs consists of various types of bottom vegetation, primarily seagrasses. Feeding trails in seagrass beds can be seen in dugong feeding areas exposed by the tides.
Exploitation
There is subsistance and commercial hunting of dugongs in many areas. Destruction of seagrass beds and pollution also pose a threat to this species. They have been extirpated in some parts of their range; in others, they are still abundant.
IUCN Status
Vulnerable.