Bulletin 15 - November 1981: Dugong (Dugong Dugon)

Dugong (Dugong Dugon)

The dugong is a large mammal inhabiting silty inlets offshore from Abu Dhabi. Their presence is known mainly from the deal animals caught in fishing nets between December and March and which end up outside the fish souk. Specimens up to eight feet in length have been recorded.

Little is known about dugongs for they are shy, retiring animals, but they have been described extensively because the dugong is the creature most frequently associated with mermaid mythology. They are unusual in the animal kingdom in being underwater grazers and are therefore herbivores. Virtually all other marine mammals are carnivores. Dugongs feed almost exclusively on certain sea grasses, flowering plants that live in warm shallow water where there is plenty of light but minimal wave action. They strip submarine foliage or dig up rhizomes, curiously without raising sediment from the sea bed. Any grit or sand that does get into the food is carefully washed away before being eaten.

The dugong has a close relative in the manatee, but differs fundamentally in the shape of its tail. It possesses crescent-shaped flukes which are horizontal to the line of the body, giving the appearance of a cross between a large seal and a small whale.

Their diet provides a clue to ancestry. The abrasive plant food wears down the teeth, which are then replaced from behind. The only other group in which this occurs is that containing elephants. About 50- to 60-million years ago it seems as if both dugong and elephant had a common ancestor. The fossil record also reveals that dugongs and their relatives were once more widely distributed throughout the world.

For the past century or so, they have been confined to the Indo-Pacific oceans, ranging from the east coast of Africa, Red Sea, Arabian Gulf, the coasts of India, Sri Lanka, and New Guinea to Australia. The dugong was brought almost to the point of extinction and is still on the 'Danger list" because of activities of its main predator -- man.

Although virtually defenseless, dugongs do not seem to be threatened by sharks, killer whales or giant estuarine crocodiles that frequent some dugong habitats. With protection in some areas, the dugong is making a slow comeback. The position of dugongs around Abu Dhabi is uncertain, as no scientific surveys have been carried out. With coastal dredging and new shipping channels, the shallows normally inhabited by dugongs are being disturbed. Any sightings of live or dead specimens will be of interest.

Little is known of their reproductive activity. Dugong cows give birth to a single calf every three years. The young animal stays with its mother for about a year, and does not mature fully until it is between eight and fourteen years old. All being well, its life expectancy is about 60 years.

Evidence from the Umm an Nar excavations of the 1960s suggests that dugongs might have been much more numerous locally some 4000 years ago. The middens beside the settlement site are full of dugong bones and even now it is easy to recognize the heavy tusk-like teeth amid the refuse of bird-bones and potsherds. The archaeological evidence points to dugong constituting a major part of local man's diet in those far-off days.

(See Dugongs by Professor Colin Bertram in Bulletin No. 1.)