The dugong (; Dugong dugon) is a marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow (Hydrodamalis gigas), was hunted to extinction in the 18th century.

The dugong is the only sirenian in its range, which spans the waters of some 40 countries and territories throughout the Indo-West Pacific. The dugong is largely dependent on seagrass communities for subsistence and is thus restricted to the coastal habitats that support seagrass meadows, with the largest dugong concentrations typically occurring in wide, shallow, protected areas, such as bays, mangrove channels, the waters of large inshore islands, and inter-reefal waters. The northern waters of Australia between Shark Bay and Moreton Bay are believed to be the dugong's contemporary stronghold.

Like all modern sirenians, the dugong has a fusiform body with no dorsal fin or hind limbs. The forelimbs or flippers are paddle-like. The dugong is easily distinguishable from the manatees by its fluked, dolphin-like tail; it also possesses a unique skull and teeth. Its snout is sharply downturned, an adaptation for feeding in benthic seagrass communities. The molar teeth are simple and peg-like, unlike the more elaborate molar dentition of manatees.

The dugong has been hunted for thousands of years for its meat and oil. Traditional hunting still has great cultural significance in several parts of its modern range, particularly northern Australia and the Pacific Islands. The dugong's current distribution is fragmented, and many populations are believed to be close to extinction. The IUCN lists the dugong as a species vulnerable to extinction, while the Convention on International Trade in Endangered Species limits or bans the trade of derived products. Despite it being legally protected in many countries, the main causes of population decline remain anthropogenic and include fishing-related fatalities, habitat degradation, and hunting. With its long lifespan of 70 years or more and slow rate of reproduction, the dugong is especially vulnerable to extinction.

Evolution

Dugongs are part of the Sirenia order of placental mammals which comprises modern "sea cows" (manatees as well as dugongs) and their extinct relatives. Sirenia are the only extant herbivorous marine mammals and the only group of herbivorous mammals to have become completely aquatic. Sirenians are thought to have a 50-million-year-old fossil record (early Eocene-recent). They attained modest diversity during the Oligocene and Miocene but subsequently declined as a result of climatic cooling, oceanographic changes, and human interference.

Etymology and taxonomy

The word "dugong" derives from the Visayan (probably Cebuano) '. The name was first adopted and popularized by the French naturalist Georges-Louis Leclerc, Comte de Buffon, as "dugon" in Histoire Naturelle (1765), after descriptions of the animal from the island of Leyte in the Philippines. The name ultimately derives from Proto-Malayo-Polynesian *duyuŋ. Despite a common misconception, the term does not come from Malay ' and it does not mean "lady of the sea" (mermaid).

Other common local names include "sea cow", "sea pig", and "sea camel". It is known as the balguja by the Wunambal people of the Mitchell Plateau area in the Kimberley, Western Australia.

Dugong dugon is the only extant species of the family Dugongidae, and one of only four extant species of the Sirenia order, the others forming the manatee family. It was first classified by Müller in 1776 as Trichechus dugon, a member of the manatee genus previously defined by Linnaeus. It was later assigned as the type species of Dugong by Lacépède and further classified within its own family by Gray and subfamily by Simpson.

An adult's length rarely exceeds . An individual this long is expected to weigh around . Weight in adults is typically more than and less than . The largest individual recorded was long and weighed , Females tend to be larger than males. These hairs are most developed around the mouth, which has a large horseshoe-shaped upper lip forming a highly mobile muzzle. and flippers are similar to those of dolphins. These flukes are raised up and down in long strokes to move the animal forward and can be twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing.

A dugong's brain weighs a maximum of , about 0.1% of the animal's body weight. dugongs have limited vision, but acute hearing within narrow sound thresholds. Their ears, which lack pinnae, are located on the sides of their head. The nostrils are located on top of the head and can be closed using valves. The lungs in a dugong are very long, extending almost as far as the kidneys, which are also highly elongated to cope with the saltwater environment. The dugong has two incisors (tusks) which emerge in males during puberty. The female's tusks continue to grow without emerging during puberty, sometimes erupting later in life after reaching the base of the premaxilla. The number of growth layer groups in a tusk indicates the age of a dugong, may act as a ballast to help keep sirenians suspended slightly below the water's surface.

Distribution and habitat

thumb|left|alt=Dugong on its side stirring up sand|Dugong on the sea floor at [[Marsa Alam, Egypt]]

Dugongs are found in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, between 26° and 27° to the north and south of the equator. Today, populations of dugongs are found in the waters of 37 countries and territories. and large numbers are also found in wide and shallow mangrove channels and around leeward sides of large inshore islands, where seagrass beds are common. this reef area houses a stable population of around 10,000, although the population concentration has shifted over time. Large bays facing north on the Queensland coast provide significant habitats for dugong, with the southernmost of these being Hervey Bay and Moreton Bay. where a re-establishment of a local population through range expansions has started recently.

Persian Gulf

The Persian Gulf has the second-largest dugong population in the world, inhabiting most of the southern coast, A 2017 study found a nearly 25% drop in population since 1950. Reasons for this drastic population loss include illegal poaching, oil spills, and net entanglement. The resident population around Mayotte is thought to number just 10 individuals. In Mozambique, most of the remaining local populations are very small and the largest (about 120 individuals) occurs at Bazaruto Island, but they have become rare in historical habitats such as in Maputo Bay and on Inhaca Island. The Bazaruto Island population is possibly the last long-term viable population in East Africa, with only some of its core territory lying within protected waters. In Tanzania, observations have recently increased around the Mafia Island Marine Park where a hunt was intended by fishermen but failed in 2009. In the Seychelles, dugongs had been regarded as extinct in the 18th century until a small number was discovered around the Aldabra Atoll. This population may belong to a different group than that distributed among the inner isles. Dugongs once thrived among the Chagos Archipelago and Sea Cow Island was named after the species, although the species no longer occurs in the region.

There are fewer than 250 individuals scattered throughout Indian waters. A highly isolated breeding population exists in the Marine National Park, Gulf of Kutch, the only remaining population in western India. It is from the population in the Persian Gulf, and from the nearest population in India. Former populations in this area, centered on the Maldives and the Lakshadweep, are presumed to be extinct. A population exists in the Gulf of Mannar Marine National Park and the Palk Strait between India and Sri Lanka, but it is seriously depleted. Recoveries of seagrass beds along former ranges of dugongs, such as the Chilika Lake have been confirmed in recent years, raising hopes for re-colonizations of the species. The population around the Andaman and Nicobar Islands is known only from a few records, and although the population was large during British rule, it is now believed to be small and scattered. including the establishment of a seagrass sanctuary for dugong and other endangered marine fauna ranging in Guangxi. Despite these efforts, numbers continued to decrease, and in 2007 it was reported that no more dugong could be found on the west coast of the island of Hainan. Historically, dugongs were also present in the southern parts of the Yellow Sea. The last confirmed record of dugongs in Chinese waters was documented in 2008. In August 2022, an article published on the Royal Society Open Science concluded that dugongs were functionally extinct in China, which was based on a large-scale interview survey conducted across four southern Chinese maritime provinces (Hainan, Guangxi, Guangdong, and Fujian) in the summer of 2019.

In Vietnam, dugongs have been restricted mostly to the provinces of Kiên Giang and Bà Rịa–Vũng Tàu, including Phú Quốc Island and Côn Đảo Island, which hosted large populations in the past. Côn Đảo is now the only site in Vietnam where dugongs are regularly seen, protected within the Côn Đảo National Park. Nonetheless, dangerously low levels of attention to the conservation of marine organisms in Vietnam and Cambodia may result in increased intentional or unintentional catches, and illegal trade is a potential danger for local dugongs.

In Thailand, the present distribution of dugongs is restricted to six provinces along the Andaman Sea, and very few dugongs are present in the Gulf of Thailand. The Gulf of Thailand was historically home to a large number of animals, but none have been sighted in the west of the gulf in recent years, Dugongs are believed to exist in the Straits of Johor in very small numbers. The waters around Borneo support a small population, with more scattered throughout the Malay Archipelago. Recently, the local marine trash problem in the archipelago remained unabated and became the biggest threat to the already dwindling population of dugongs in the country. Litters of plastic waste (single-use sachets, plastic bottles, fast food to-go containers, etc.) and other non-biodegradable materials abound in the coastal areas. As these materials may be mistaken as food by dugongs, these may lead to death due to plastic ingestion. Overpopulation and lack of education of all coastal fisherfolk in the Philippines regarding marine trash are harming the coastal environment not only in Palawan but also across the islands of the Philippines. The first documented sighting in Sarangani Bay occurred in July 2024.

Populations also exist around the Solomon Islands and New Caledonia, stretching to an easternmost population in Vanuatu. A highly isolated population lives around the islands of Palau.

Northern Pacific

Today, possibly the smallest and northernmost population of dugongs exists around the Ryukyu islands, and a population formerly existed off Taiwan. around Okinawa. New sightings of a cow and calf have been reported in 2017, indicating a possible breeding had occurred in these waters. A single individual was recorded at Amami Ōshima, at the northernmost edge of the dugong's historic range, more than 40 years after the last previous recorded sighting. A vagrant strayed into a port near Ushibuka, Kumamoto, and died due to poor health. Historically, the Yaeyama Islands held a large concentration of dugongs, with more than 300 individuals. On the Aragusuku Islands, large quantities of skulls are preserved at a utaki that outsiders are strictly forbidden to enter. Dugong populations in these areas were reduced by historical hunts as payments to the Ryukyu Kingdom, before being wiped out because of large-scale illegal hunting and fishing using destructive methods such as dynamite fishing after the Second World War.

In March 2025, a fisherman accidentally caught a dugong in his nets at Fenniaolin in Yilin County in northeast Taiwan, which he released back into the sea. This was the first sighting of a live dugong in Taiwan waters in 88 years.

Populations around Taiwan appear to be almost extinct, although remnant individuals may visit areas with rich seagrass beds such as Dongsha Atoll. Some of the last reported sightings were made in Kenting National Park in the 1950s and 60s. There had been occasional records of vagrants at the Northern Mariana Islands before 1985. It is unknown how much mixing there was between these populations historically. Some theorize that populations existed independently, for example, that the Okinawan population was isolated members derived from the migration of a Philippine subspecies. Others postulate that the populations formed part of a super-population, where migration between Ryukyu, Taiwan, and the Philippines was common.

Extinct Mediterranean population

It has been confirmed that dugongs once inhabited the water of the Mediterranean possibly until after the rise of civilizations along the inland sea. This population possibly shared ancestry with the Red Sea population, and the Mediterranean population had never been large due to geographical factors and climate changes. The Mediterranean is the region where the Dugongidae originated in the mid-late Eocene, along with the Caribbean Sea.

Ecology and life history

thumb|left|alt=A large dugong swimming towards the right with a smaller dugong half its size hugging its back, both in very shallow water with the surface and seabed just above and below them respectively|A mother and calf in shallow water

Dugongs are long-lived, and the oldest recorded specimen reached age 73. and have been known to rest on their tails to breathe with their heads above water.]]

thumb|Dugong with juvenile golden trevally, [[Neil Island, Ritchie's Archipelago]]

Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of seagrass, particularly the genera Halophila and Halodule. or marine algae when the supply of their choice grasses decreases. In other southern areas of both western and eastern Australia, there is evidence that dugongs actively seek out large invertebrates. This does not apply to dugongs in tropical areas, in which fecal evidence indicates that invertebrates are not eaten. When moving along the seabed to feed, they walk on their pectoral fins. Species such as Zosteria capricorni are more dominant in established seagrass beds, but grow slowly, while Halophilia and Halodule grow quickly in the open space left by dugong feeding. Females know that a male has reached sexual maturity by the eruption of the male's tusks, since tusks erupt in males when testosterone levels reach a high enough level. The age when a female first gives birth is disputed, with some studies placing the age between ten and seventeen years while others place it as early as six years. and people around the world developed cultures around dugong hunting. In some areas, it remains an animal of great significance,

Dugongs feature in Southeast Asian, especially Austronesian, folklore. In languages like Ilocano, Mapun, Yakan, Tausug, and Kadazan Dusun of the Philippines and Sabah, the name for dugongs is a synonym for "mermaid". A common belief found in the Philippines, Malaysia, Indonesia, and Thailand is that dugongs were originally human or part-human (usually women), and that they cry when they are butchered or beached. Because of this, it is considered bad luck if a dugong is killed or accidentally dies in nets or fish corrals in the Philippines, some parts of Sabah (Malaysia), and northern Sulawesi and the Lesser Sunda Islands (Indonesia). Dugongs are predominantly not traditionally hunted for food in these regions and they remained plentiful until around the 1970s.

Conversely, dugong "tears" are considered aphrodisiacs in other parts of Indonesia, Singapore, Malaysia, Brunei, Thailand, Vietnam, and Cambodia. Dugong meat is considered a luxury food and is also believed to have aphrodisiac properties. They are actively hunted in these regions, in some places to near-extinction.

In Palau, dugongs were traditionally hunted with heavy spears from canoes. Although it is illegal and there is widespread disapproval of killing dugongs, poaching remains a major problem. Dugongs are also widely hunted in Papua New Guinea, the Solomon Islands, Vanuatu, and New Caledonia; where their meat and ornaments made from bones and tusks are highly prized in feasts and traditional rituals. However, hunting dugongs is considered taboo in some areas of Vanuatu.

Conservation

thumb|Dugong on a 2005 [[Indonesia|Indonesian postage stamp]]

Dugong numbers have decreased in recent times. For a population to remain stable, the mortality of adults cannot exceed 5% annually. The estimated percentage of females humans can kill without depleting the population is 1–2%. India and Sri Lanka ban the hunting and selling of dugongs and their products. Japan has listed dugongs as endangered and has banned intentional killing and harassment. Hunting, catching, and harassment are banned by the People's Republic of China. The first marine mammal to be protected in the Philippines was the dugong, although monitoring this is difficult. Palau has legislated to protect dugongs, although this is not well enforced and poaching persists. Protection is not always enforced and souvenir products made from dugong parts can be openly found in markets in Bali. Traditional dugong hunters continued to hunt for many years, and some have struggled to find alternative incomes after ceasing. In Vietnam, an illegal network targeting dugongs had been detected and was shut down in 2012. socio-political needs are an impediment to dugong conservation in many developing countries. The shallow waters are often used as a source of food and income, problems exacerbated by aid used to improve fishing. In many countries, legislation does not exist to protect dugongs, and if it does it is not enforced. It was later revealed that the government of Japan was hiding evidence of the negative effects of ship lanes and human activities on dugongs observed during surveys carried out off Henoko reef. One of the three individuals has not been observed since June 2015, corresponding to the start of the excavation operations.

Environmental degradation

If dugongs do not get enough to eat, they may calve later and produce fewer young. In August 2014, preliminary drilling surveys were conducted around the seagrass beds there. The construction is expected to seriously damage the dugong population's habitat, possibly leading to local extinction.

Capture and captivity

The Australian state of Queensland has sixteen dugong protection parks, and some preservation zones have been established where even Aboriginal Peoples are not allowed to hunt. The second resides in Sea World Indonesia, after having been rescued from a fisherman's net and treated. The last one, a male, is kept at Sydney Aquarium, where he has resided since he was a juvenile. Sydney Aquarium had a second dugong for many years, until she died in 2018.

Gracie, a captive dugong at Underwater World, Singapore, was reported to have died in 2014 at the age of 19, from complications arising from an acute digestive disorder.

References

  • Dugong - britannica.com