 Dugongs (Dugon~ dugon) are mammals and have a life span of 70 years or more, similar to our own.
Females do not have their first calf until they are at least ten and sometimes up to 17 years old. They bear only one calf at a time after a pregnancy lasting about a year, and suckle the calf for 18 months or more. The calves never venture far from their mothers and often ride on their backs.
Females produce calves only once every three to five years, so adult survival must be very high. This means that at least 95% of adults alive at the beginning of a year must still be alive twelve months later for population numbers to be sustained.
The age of a dugong is estimated by counting growth layers in its tusks (like measuring tree rings) which erupt after puberty in males and in a small proportion of older females. Groups of males follow a female dugong in oestrous (or “on heat”) and many mate with her, inflicting scars on the female’s back, and on each other.
There are only four living types of sea cow: three are manatee species (Trichechidae) found in the Atlantic region and one dugong (Dugongidae) found in Australian tropical and subtropical waters. The other modern clugonid, the seven- metre long Stellar’s Sea Cow was exterminated by sealers in the North Pacific in the late 18th century. Dugongs are classified ar, Sirenia, or Sea Cows, and their nearest terrestrial relative is the elephant.
Adult dugongs grow to three metres long and weigh up to 400 kg, Newborns are about 1.2 metres long and weigh up to 30 kg. Dugongs are believed to see about as well as a diver wearing a face mask and seem to have acute hearing. Their eyes, and ears which have no flaps or lobes, are on each side of the head. Their paired nostrils are on the top of the head and have valve-like devices that prevent water entering when they dive. Dugongs surface for air for a few seconds, every few minutes.
Dugongs appear to have a good memory of place, as satellite tracking shows them returning hundreds of kilometres to specific spots. Because like humans, they live for a long time, they must have few natural predators but they are prey to sharks, crocodiles and killer whales as young animals. If their mothers die, it is almost impossible to rescue the young, as we can with some other wildlife, because calves suckle for so long and their seagrass diet cannot be grown in captivity. Orphaned calves have not so far been successfully rehabilitated in Australia because of their complex nutritional requirements.
They have flippers and tails that resemble those of dolphins, but they lack a dorsal fin. Unlike dolphins which can be recognised from individual physical characteristics, individual dugongs are difficult to distinguish although most are marked by scars delivered by the tusks of other dugongs. They can move over very large areas, which they travel alone or with their calves in search of food.
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