Name: Dugong (Dugong dugon)
Group: Marine Mammals.
Size: Length up to 3m, weight up to 570kg.
Diet: Seagrass community specialist.
Habitat: Coastal northern Australia from Shark Bay in Western Australia to Moreton Bay near Brisbane (all year), south to Port Stephens in NSW in summer.
Conservation status in Australia: Protected.
Superpower: Meet the only grass-munching mammal that spends all its life in the sea.
Why would a 400kg marine mammal with a face that only another dugong might love be considered as the origin of myths about mermaids and sirens? This link is usually attributed to the dugong’s pectoral mammary glands (which have been likened to human breasts) and long period of close calf dependency. But this link might be more about lust than likeness. There are stories about dugongs being used as surrogate females by fishermen at several places in their vast range, which extends through tropical and sub-tropical coastal and island waters from east Africa to Vanuatu.
But Australia is the dugong capital of the world. Our northern coastal waters support most of the world’s dugong population and are the most common marine mammals throughout most of this region. The Torres Strait region supports more dugongs than anywhere else.
Indigenous peoples have been hunting dugongs throughout their range for at least 4,000 years. The dugongs is a culturally significant species and features prominently in the art and stories of many coastal peoples, including Aboriginal and Torres Strait peoples across northern Australia. The coverings of the biblical Tabernacle and Ark of the Covenant are believed to have been made from dugong skin.
The dugong is the only member of the family Dugongidae and one of only four extant sirenians (seacows) – the other three species are manatees. Despite being in separate families, manatees and dugongs look remarkably alike. The most obvious difference is in the shape of the tail: manatees have a round tail like a beaver’s, while the tail of a dugong resembles that of a whale or a dolphin. The build of a manatee is more robust than that of a dugong, which looks like a manatee that goes to the gym! Dugongs look like a cross between a walrus and a dolphin without a dorsal fin.
From a biological perspective, the dugong is quite different to other marine mammals. It is the only herbivorous mammal that spends all its life in the sea. Manatees and dugongs are more closely related to elephants and hyraxes than other marine mammals.
The diving achievements of dugongs are modest, mostly reflecting the distributions of the seagrass communities on which they feed. Although dugongs mostly eat seagrass, they also target invertebrates at the high latitude limits to their range in winter and have been described as “closet omnivores”.
Dugongs perceive their aquatic environments largely through touch, hydrodynamic reception and hearing; vision and taste are also likely important to some degree. They have sparse sensory hairs all over their bodies that function like the lateral lines of fishes.
Dugongs are long-lived and slow-breeding. The oldest wild dugong that has been aged was more than 70 years old when she died. Dugongs generally have one calf every few years from a minimum age of around seven years. However, they suspend breeding when seagrass is in short supply after cyclones, floods or marine heatwaves.
The conservation status of the dugong is variable. It is listed as vulnerable to extinction at a global scale by IUCN and as endangered, critically endangered, or extinct in several of its more than 40 range countries. Fortunately, the dugong does not qualify for listing as threatened in Australia at a national scale. Nonetheless, they are protected as migratory and marine species. However, there is concern about the population in some regions, particularly the urban cost of the Great Barrier Reef.
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Helene Marsh, Emeritus Profess Environmental Science at James Cook University, leads a group that has been studying the conservation biology of dugongs since the 1970s and has advised the governments of 14 countries on their conservation.
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