Dugong

• 1. Introduction

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  In March 2025, a fisherman at Fenniaolin in Yilin County, northeast Taiwan, hauled in his nets and found a dugong caught inside. He released it back into the sea. It was the first live dugong seen in Taiwan's waters in 88 years. The dugong is a marine mammal that lives on underwater grass, and its story is full of absences like the one that sighting briefly ended. Who is this animal, and why do biologists link it to elephants rather than to whales or seals? How does a plant eater spend its whole life in salt water? And why is a creature that can live 70 years or more fading from coastlines across the Indo-West Pacific?

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• 2. Origins and Names

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  The order Sirenia, which holds dugongs and manatees, has a fossil record about 50 million years long, beginning in the early Eocene. Its members are the only plant-eating mammals that ever became fully aquatic. They are also the only plant-eating marine mammals alive today. Sirenians reached modest diversity in the Oligocene and Miocene, then dwindled as the climate cooled, ocean conditions shifted and people interfered.

  Despite its home in the sea, the dugong is not close kin to other marine mammals. Its nearer relatives are elephants. Sirenians, elephants, hyraxes and the aardvark form one group, among the earliest branches of the eutherian mammals. The earliest sirenians most likely lived in the Tethys Ocean. The two living sirenian families diverged in the mid-Eocene. Later, in the Miocene, dugongs and their closest relative, Steller's sea cow, split from a shared ancestor. Hunters wiped out Steller's sea cow in the 18th century. No fossils of any other dugong-family member are known, which leaves Dugong dugon as the only living species in its family and one of just four living sirenians. The other three are manatees.

  The word dugong comes from the Visayan dugung, probably the Cebuano form. The French naturalist Georges-Louis Leclerc, Comte de Buffon, popularised it as dugon in his Histoire Naturelle in 1765. He worked from descriptions of an animal on the island of Leyte in the Philippines. A common story says the word comes from the Malay duyung and means lady of the sea, or mermaid. That is a misconception. The word traces back to a Proto-Malayo-Polynesian root instead.

  Other names include sea cow, sea pig and sea camel. The Wunambal people of the Mitchell Plateau area in the Kimberley, Western Australia, call the animal balguja. In 1776 the scientist Müller first classified it as Trichechus dugon, placing it in the manatee genus that Linnaeus had defined. Lacépède later made it the type species of the genus Dugong. Gray then gave it a family of its own, and Simpson a subfamily.

  Studies of mitochondrial DNA have since mapped how dugong populations relate to one another. Southeast Asian dugongs form a distinct population. Australia has two separate maternal lineages, and one of them also includes dugongs from Africa and Arabia. Only limited genetic mixing has occurred between Southeast Asia and Australia, mostly around Timor.

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• 3. Built for Seagrass

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  A dugong three metres long, about the most an adult usually reaches, weighs roughly 420 kilograms. Adults typically fall between 250 and 900 kilograms, and females tend to be larger than males. The largest ever recorded was found off the Saurashtra coast of west India. It measured 4.06 metres and weighed 1016 kilograms.

  The body is cylindrical and tapers at both ends, wrapped in thick, smooth skin. Newborns are pale cream. With age the back and sides darken to brownish or dark grey, and algae growing on the skin can shift the colour again.

  The tail is the quickest way to tell a dugong from a manatee. It has flukes like a dolphin's, with deep notches. The animal raises and lowers them in long strokes to move forward and twists them to turn. The paddle-like flippers have no nails and measure only 15 percent of the body length. They help with turning and slowing.

  Feeding shaped the head. The snout bends sharply downward, an adaptation for grazing on the seabed. A large, horseshoe-shaped upper lip forms a muscular and highly mobile muzzle. Short hairs cover the body sparsely but grow most thickly around the mouth, and they may let the animal read its surroundings by touch.

  The skeleton is unusually heavy. Dugongs show pachyostosis, in which the ribs and other long bones are solid and hold little or no marrow. These bones rank among the densest in the animal kingdom. They may act as ballast, holding the animal just below the water's surface.

  The brain weighs at most 300 grams, about 0.1 percent of body weight. The eyes are very small and vision is limited, but hearing is acute within narrow sound thresholds. The ears have no external flaps. The nostrils sit on top of the head and close with valves. The lungs are very long, reaching almost as far as the kidneys. The kidneys are elongated too, which helps with life in salt water. If a dugong is wounded, its blood clots rapidly.

  The teeth are just as distinctive. The molars are simple and peg-like, and unlike manatees, dugongs do not keep replacing teeth horizontally. Two incisors form tusks, which emerge in males at puberty. In females the tusks keep growing without emerging, and sometimes break through later in life. Counting the growth layer groups inside a tusk reveals the animal's age.

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• 4. Gardeners of the Seabed

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  Seagrasses of the genera Halophila and Halodule make up most of a dugong's diet, which is why it shares the nickname sea cow with manatees. A dugong usually swallows the whole plant, roots included, and falls back on the leaves only when it cannot pull up the rest. It uses its mobile upper lip to dig plants out, leaving furrows in the sand. Then it shakes each plant to knock off the sand before eating. Sometimes it gathers a pile of plants in one spot first.

  Because its eyesight is poor, the dugong often finds edible plants by smell. It also feels its way along with its long, sensitive bristles. When it moves along the seabed to feed, it walks on its pectoral fins. Otherwise it is slow, cruising at around 10 kilometres per hour.

  Dugongs are choosy. Most do not feed in lush meadows but where the seagrass is sparse. The grasses they eat most are low in fibre, high in nitrogen and easy to digest. In the Great Barrier Reef they take Halophila and Halodule to maximise nutrients rather than bulk. They prefer seagrass at an early stage of growth, in areas not yet fully vegetated.

  They are almost entirely plant eaters, yet not quite. Dugongs occasionally eat jellyfish, sea squirts and shellfish. In Moreton Bay, Australia, they turn to invertebrates such as polychaetes, or to marine algae, when their preferred grasses thin out. In other southern parts of Australia, both west and east, they actively seek out large invertebrates. Fecal evidence shows that tropical dugongs do not eat invertebrates.

  The feeding changes the meadow itself. Zosteria capricorni dominates established seagrass beds but grows slowly. Halophila and Halodule grow quickly in the open space a feeding dugong leaves behind. This habit, called cultivation grazing, favours the fast-growing, nutrient-rich grasses that dugongs prefer. Cycles of grazing at different meadows may also supply them with more young, less fibrous plants. Feeding trails have been found as deep as 33 metres.

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• 5. Slow Lives

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  The oldest dugong on record reached the age of 73. Adults have few natural predators, though crocodiles, killer whales and sharks threaten the young. One dugong is recorded as dying from trauma after being impaled by a stingray barb. Disease is a bigger killer. Infections and parasites, including helminths, cryptosporidium and several bacterial infections, affect the species, and an estimated 30 percent of dugong deaths in Queensland since 1996 are thought to come from disease.

  Dugongs are social animals, yet they are usually alone or in pairs, because seagrass beds cannot feed large groups. Gatherings of hundreds do happen, but they last only briefly. Shy and wary of people, they remain poorly understood. A dugong can hold its breath for six minutes, though about two and a half is more typical. Some have been seen resting on their tails with their heads above water. They talk with chirps, whistles and barks that echo underwater. Mothers and calves stay in almost constant contact, and calves reach out with a flipper to touch their mothers for reassurance.

  The animals are semi-nomadic. They travel long distances for food but stay within a range for life, and their memory lets them return to particular places. Their movements seem to follow changes in seagrass. Tides shape the day, since in areas with a large tidal range dugongs ride the tide to reach shallow feeding grounds. In Moreton Bay they move between foraging grounds inside the bay and warmer oceanic waters. One individual was seen as far south as Sydney. Another was caught 15 kilometres up a creek near Cooktown.

  A dugong reaches sexual maturity between the ages of eight and eighteen, later than most mammals. Females can tell when a male is mature because his tusks erupt once testosterone levels are high enough. Courtship varies by place. In some populations males hold territories that receptive females visit, a practice called lekking. In others, several males chase one female and fight to mount her from below, sometimes injuring her or each other.

  Gestation lasts 13 to 15 months and usually produces a single calf, born in very shallow water. Sometimes the mother is almost on the shore. She pushes the newborn to the surface for its first breath. The calf is already 1.2 metres long and weighs about 30 kilograms. It nurses for 14-18 months while starting to eat seagrass soon after birth. Estimates for the gap between births range from 2.4 to 7 years. That slow pace leaves little room for loss, a point that matters once nets and hunting enter the picture.

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• 6. Scattered Waters

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  Along an estimated 140,000 kilometres of coastline, dugongs live in warm waters from the western Pacific to the eastern coast of Africa. They favour wide, shallow, protected bays, mangrove channels and the sheltered sides of large inshore islands, where seagrass grows. They are the only strictly marine plant-eating mammal, since every manatee species uses fresh water to some degree. They usually stay at around 10 metres depth. Shallow water serves as a calving site with less risk from predators, while deeper water may offer warmth in winter. Survey data are poor, but a worldwide decline of 20 percent over the last 90 years is thought likely. They have vanished from Hong Kong, Mauritius and Taiwan.

  Australia holds the largest population, stretching from Shark Bay in Western Australia to Moreton Bay in Queensland. Shark Bay has over 10,000 dugongs and seems stable. The Gulf of Carpentaria holds over 20,000, and the Torres Strait over 25,000, with much movement between the strait and New Guinea. The Great Barrier Reef shelters about 10,000. On the Gold Coast, a local population has recently started to re-establish itself.

  The Persian Gulf has the world's second-largest population, estimated at 5,800 to 7,300. Surveys carried out between 1986 and 1999 found a single group of more than 600 animals west of Qatar. A 2017 study found a drop of nearly 25 percent since 1950, blamed on poaching, oil spills and net entanglement.

  East Africa tells a harsher story. In the late 1960s, herds of up to 500 were seen off its coast. Today numbers there are 50 or below. The resident group around Mayotte may be only 10 animals. The largest in Mozambique, about 120 at Bazaruto Island, may be the last long-term viable population in East Africa. In the Seychelles, dugongs were thought extinct in the 18th century until a few turned up around the Aldabra Atoll. Sea Cow Island in the Chagos Archipelago keeps their name, though they no longer live there.

  Indian waters hold fewer than 250. A highly isolated breeding group in the Gulf of Kutch is the last in western India, 1500 kilometres from the Persian Gulf population. Former populations around the Maldives and Lakshadweep are presumed extinct.

  China's story is a recent one. In 2007, no dugong could be found on the west coast of Hainan. The last confirmed record in Chinese waters came in 2008. An article in Royal Society Open Science in August 2022, based on interviews across four southern provinces in 2019, concluded the animal was functionally extinct there. In the Philippines, herds were common until the 1970s. The dugong became the first marine animal protected by Philippine law. Vietnam's dugongs now appear regularly only at Côn Đảo.

  The far north of the range is even thinner. Around Okinawa survive 50 or fewer dugongs, possibly as few as three, though a cow and calf were reported in 2017. The Yaeyama Islands once held more than 300. Dugongs were also once found in the Mediterranean, possibly until after civilizations rose along that sea. On the Aragusuku Islands, large numbers of dugong skulls are kept at a sacred site, called a utaki, that outsiders are strictly forbidden to enter.

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• 7. Mermaids and Sea Country

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  In Tambun Cave, near Ipoh in Malaysia, a wall painting of a dugong is about 5,000 years old, apparently drawn by Neolithic peoples. Lieutenant R.L. Rawlings found it in 1959 while on a routine patrol. Hunters have long killed dugongs for meat, oil, skin and bones. The anthropologist A. Asbjørn Jøn has noted that people often consider the animal the inspiration for mermaids, and cultures around the world grew up around hunting it.

  The mermaid link is built into language. In Ilocano, Mapun, Yakan, Tausug and Kadazan Dusun, the word for dugong doubles as the word for mermaid. In Malay, it is sometimes called perempuan laut, meaning woman of the sea, or putri duyong, meaning mermaid princess. Across the Philippines, Malaysia, Indonesia and Thailand, a common belief holds that dugongs were once human, usually women, and that they cry when butchered or beached. Because of this, killing one by accident is bad luck in the Philippines, parts of Sabah, northern Sulawesi and the Lesser Sunda Islands.

  Elsewhere the tears carry the opposite meaning. In parts of Indonesia, Singapore, Malaysia, Brunei, Thailand, Vietnam and Cambodia, dugong tears are considered aphrodisiacs. The meat is a luxury food, believed to have the same property, and hunting there has driven some populations toward extinction. In Palau, hunters traditionally threw heavy spears from canoes. In Papua New Guinea, the Solomon Islands, Vanuatu and New Caledonia, meat and ornaments made from bones and tusks are prized at feasts and rituals, though hunting is taboo in some parts of Vanuatu.

  Southern China offers a stark contrast. Local fishermen revered dugongs as miraculous fish and thought catching one brought bad luck, and the animals were plentiful before the 1960s. From the 1950s, immigrants who did not share these beliefs hunted them for food and traditional Chinese medicine, and numbers in the Gulf of Tonkin and around Hainan collapsed. In Okinawa, ribs of dugongs are carved into butterflies, a symbol of a guide for souls of the dead. Japanese hunters took dugongs until around the 1970s. In Kenya the animal is called the Queen of the Sea. In the Gulf states, tusks were turned into sword handles. Around the Gulf of Kutch in India, dugong oil is used to preserve and condition wooden boats.

  For Australian Aboriginal peoples and Torres Strait Islanders, dugong meat and oil are among the most valuable foods, and some Aboriginal people regard the dugong as part of their Aboriginality. Dugongs belong to sea-country, a living network of relationships linking people, animals and coastal environments. Management programs in the Torres Strait and northern Queensland now combine traditional ecological knowledge with scientific monitoring and co-management.

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• 8. Under Pressure

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  For a dugong population to stay stable, adult deaths cannot exceed 5 percent a year. The share of females that people can kill without causing decline is only 1-2 percent. Even in the best conditions, a population is unlikely to grow by more than 5 percent a year. The last major worldwide study, in 2002, concluded that the dugong was declining and possibly extinct in a third of its range. Its status was unknown in another half. The IUCN Red List classes it as vulnerable, and the Convention on International Trade in Endangered Species restricts or bans trade in its products.

  Nets are a leading danger. Because dugongs cannot stay under water for long, entangled animals drown. Shark nets once killed large numbers and have mostly been replaced with baited hooks. In northern Australia, hunting has the greatest effect on the population. Heavy metals build up in dugong tissue over a lifetime, more than in other marine mammals, though the effects are unknown.

  Habitat loss may matter even more. Sedimentation from mining, trawling, dredging, land reclamation and boat propeller scarring smothers seagrass and blocks light, and it is the most significant negative factor. Halophila ovalis, a preferred species, dies completely after 30 days without light. Cyclones and floods can destroy hundreds of square kilometres of meadow, and recovery can take over a decade. In the Philippines, plastic waste that dugongs may mistake for food has become the biggest threat to the dwindling population.

  Okinawa shows how politics and habitat collide. Plans for a United States military base near the Henoko reef involve land reclamation in Oura Bay, with preliminary drilling surveys around the seagrass beds in August 2014. Of the three individuals known there, one has not been seen since June 2015, when excavation began. Okinawans have challenged the plans in United States courts. It later emerged that the government of Japan had hidden survey evidence of harm from ship lanes and human activity.

  Laws vary widely. Mozambique has protected dugongs since 1955, but enforcement is weak. Indonesia listed them as protected in 1999 and began a conservation plan in 2018, yet souvenirs made from dugong parts are openly sold in Bali. The dugong is a national animal of Papua New Guinea, which bans all but traditional hunting. The United Arab Emirates has banned all hunting and drift net fishing. In northern Queensland, the World Wide Fund for Nature bought gillnet licences to reduce fishing pressure. Queensland has sixteen dugong protection parks, and in Vietnam an illegal network targeting dugongs was shut down in 2012.

  Captivity is not an escape. Dugongs are costly to keep because mothers and calves stay together so long, and aquariums cannot grow the seagrass they eat. Only one orphaned calf has ever been successfully kept. A male at Toba Aquarium in Japan died on the 10th of February 2011. Gracie, at Underwater World in Singapore, died in 2014 at the age of 19 from a digestive disorder. Meanwhile, seagrass beds have recovered in recent years at Chilika Lake in India, a former dugong range, raising hopes that dugongs may one day return.

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