Dugong

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...

Dugongs are found in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, along an estimated 140,000 kilometres (87,000 mi) of coastline between 26° and 27° to the north and south of the equator. Their historic range is believed to correspond to that of seagrasses from the Potamogetonaceae and Hydrocharitaceae families. The full size of the former range is unknown, although it is believed that the current populations represent the historical limits of the range, which is highly fractured. Their distributions during warmer periods of the Holocene might have been broader than today. Today, populations of dugongs are found in the waters of 37 countries and territories. Recorded numbers of dugongs are generally believed to be lower than actual numbers, due to a lack of accurate surveys. Despite this uncertainty, the dugong population is thought to be shrinking, with a worldwide decline of 20 percent in the last 90 years. They have disappeared from the waters of Hong Kong, Mauritius, and Taiwan, as well as parts of Cambodia, Japan, the Philippines, and Vietnam. Further disappearances are likely. Dugongs are generally found in warm coastal waters with large numbers concentrated in wide and shallow protected bays. The dugong is the only strictly marine herbivorous mammal, as all species of manatee utilise fresh water to some degree. Nonetheless, they can tolerate the brackish waters found in coastal wetlands, 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. They are usually located at a depth of around 10 m (33 ft), although in areas where the continental shelf remains shallow, dugongs have been known to travel more than ten kilometres (6 mi) from the shore, descending to as far as 37 metres (121 ft), where deepwater seagrasses such as Halophila spinulosa are found. Specific habitats are used for different activities. It has been observed that shallow waters are used as sites for calving, minimizing the risk of predation. Deep waters may provide a thermal refuge from cooler waters closer to the shore during winter.

Timor-Leste

Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of seagrass, particularly the genera Halophila and Halodule. When eating they ingest the whole plant, including the roots, although when this is impossible they will feed on just the leaves. A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass is scarce. Although almost completely herbivorous, they will occasionally eat invertebrates, such as jellyfish, sea squirts, and shellfish. Dugongs in Moreton Bay, Australia, are omnivorous, feeding on invertebrates such as polychaetes 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. Most dugongs do not feed in lush areas, but where the seagrass is more sparse. Additional factors such as protein concentration and regenerative ability also affect the value of a seagrass bed. The chemical structure and composition of the seagrass are important, and the grass species most often eaten are low in fiber, high in nitrogen, and easily digestible. In the Great Barrier Reef, dugongs feed on low-fiber high-nitrogen seagrass such as Halophila and Halodule, to maximize nutrient intake instead of bulk eating. Seagrasses of a lower seral are preferred, where the area has not fully vegetated. Only certain seagrass meadows are suitable for dugong consumption, due to the dugong's highly specialized diet. There is evidence that dugongs actively alter seagrass species compositions at local levels. Dugongs may search out deeper seagrass. Feeding trails have been observed as deep as 33 metres (108 ft), and dugongs have been seen feeding as deep as 37 metres (121 ft). Dugongs are relatively slow-moving, swimming at around 10 km/h (3 m/s). When moving along the seabed to feed, they walk on their pectoral fins. Dugong feeding may favor the subsequent growth of low-fibre, high-nitrogen seagrasses such as Halophilia and Halodule. 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. This behavior is known as cultivation grazing and favors the rapidly growing, higher nutrient seagrasses that dugongs prefer. Dugongs may also prefer to feed on younger, less fibrous strands of seagrasses, and cycles of cultivation feeding at different seagrass meadows may provide them with a greater number of younger plants. Due to their poor eyesight, dugongs often use smell to locate edible plants. They also have a strong tactile sense and feel their surroundings with their long sensitive bristles. They will dig up an entire plant and then shake it to remove the sand before eating it. They have been known to collect a pile of plants in one area before eating them. The flexible and muscular upper lip is used to dig out the plants. This leaves furrows in the sand in their path.

longest observed 73 years.

A dugong reaches sexual maturity between the ages of eight and eighteen, older than in most other mammals. 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. There is evidence that male dugongs lose fertility at older ages. Despite the longevity of the dugong, which may live for 50 years or more, females give birth only a few times during their lives and invest considerable parental care in their young. The time between births is unclear, with estimates ranging from 2.4 to 7 years. Mating behaviour varies between populations located in different areas. In some populations, males establish a territory that females in estrus then visit. In these areas, the male attempts to impress females while defending the area from other males, a practice known as lekking. In other areas many males attempt to mate with the same female, sometimes inflicting injuries on the female or each other. During this event, the female copulates with multiple males, who fight to mount her from below. This greatly increases the chances of conception. Females give birth after a 13- to 15-month gestation, usually to just one calf. Birth occurs in very shallow water, with occasions known where the mothers were almost on the shore. As soon as the young is born the mother pushes it to the surface to take a breath. Newborns are already 1.2 metres (4 ft) long and weigh around 30 kilograms (65 lb). Once born, calves stay close to their mothers, possibly to make swimming easier. The calf nurses for 14–18 months, although it begins to eat seagrasses soon after birth. A calf leaves its mother only after it has matured.

The dugong's body is large with a cylindrical shape that tapers at both ends. It has thick, smooth skin that is a pale cream colour at birth but darkens dorsally and laterally to brownish-to-dark-grey with age. The colour of a dugong can change due to the growth of algae on the skin. An adult's length rarely exceeds 3 metres (10 ft). An individual this long is expected to weigh around 420 kilograms (930 lb). Weight in adults is typically more than 250 kilograms (550 lb) and less than 900 kilograms (1,980 lb). The largest individual recorded was 4.06 metres (13 ft 4 in) long and weighed 1,016 kilograms (2,240 lb), and was found off the Saurashtra coast of west India. Females tend to be larger than males. The body is sparsely covered in short hair, a common feature among sirenians which may allow for tactile interpretation of their environment. These hairs are most developed around the mouth, which has a large horseshoe-shaped upper lip forming a highly mobile muzzle. This muscular upper lip aids the dugong in foraging. The dugong's tail flukes 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. The dugong lacks nails on its flippers, which are only 15% of a dugong's body length. The tail has deep notches. A dugong's brain weighs a maximum of 300 g (11 oz), about 0.1% of the animal's body weight. With very small eyes, 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. Dugongs have two teats, one located behind each flipper. There are few differences between the sexes; the body structures are almost the same. A male's testes are not externally located, and the main difference between males and females is the location of the genital aperture to the umbilicus and the anus. 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. If the dugong is wounded, its blood will clot rapidly. The skull of a dugong is unique. The skull is enlarged with a sharply down-turned premaxilla, which is stronger in males. The spine has between 57 and 60 vertebrae. Unlike in manatees, the dugong's teeth do not continually grow back via horizontal tooth replacement. 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, and the cheek teeth move forward with age. The full dental formula of dugongs is 2.0.3.33.1.3.3, meaning they have two incisors, three premolars, and three molars on each side of their upper jaw, and three incisors, one canine, three premolars, and three molars on each side of their lower jaw. Like other sirenians, the dugong experiences pachyostosis, a condition in which the ribs and other long bones are unusually solid and contain little or no marrow. These heavy bones, which are among the densest in the animal kingdom, may act as a ballast to help keep sirenians suspended slightly below the water's surface.

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.

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%. This number is reduced in areas where calving is minimal due to food shortages. Even in the best conditions, a population is unlikely to increase more than 5% a year, leaving dugongs vulnerable to over-exploitation. The fact that they live in shallow waters puts them under great pressure from human activity. Research on dugongs and the effects of human activity on them has been limited, mostly taking place in Australia. In many countries, dugong numbers have never been surveyed. As such, trends are uncertain, with more data needed for comprehensive management. The only data stretching back far enough to mention population trends comes from the urban coast of Queensland, Australia. The last major worldwide study, made in 2002, concluded that the dugong was declining and possibly extinct in a third of its range, with unknown status in another half. The IUCN Red List lists the dugong as vulnerable, and the Convention on International Trade in Endangered Species of Wild Fauna and Flora regulates and in some areas has banned international trade. Most dugong habitats fall within proposed important marine mammal areas. Regional cooperation is important due to the widespread distribution of the animal, and in 1998 there was strong support for Southeast Asian cooperation to protect dugongs. Kenya has passed legislation banning the hunting of dugongs and restricting trawling, but the dugong is not yet listed under Kenya's Wildlife Act as an endangered species. Mozambique has had legislation to protect dugongs since 1955, but this has not been effectively enforced. France has a National Action Plan covering the species, implemented within the Mayotte Marine Natural Park. Many marine parks have been established on the African coast of the Red Sea, and the Egyptian Gulf of Aqaba is fully protected. The United Arab Emirates has banned all hunting of dugongs within its waters, as has Bahrain. The UAE has additionally banned drift net fishing, and has declared an intention to restore coastal ecosystems dugongs rely on. 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. Indonesia listed dugongs as a protected species in 1999, and in 2018 the Fisheries Ministry began implementing a conservation plan. 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. The dugong is a national animal of Papua New Guinea, which bans all except traditional hunting. Vanuatu and New Caledonia ban the hunting of dugongs. Dugongs are protected throughout Australia, although the rules vary by state; in some areas, indigenous hunting is allowed. Dugongs are listed under the Nature Conservation Act in the Australian state of Queensland as vulnerable. Most currently live in established marine parks, where boats must travel at a restricted speed and mesh net fishing is restricted. The World Wide Fund for Nature has purchased gillnet licences in northern Queensland to reduce the impact of fishing. In Vietnam, an illegal network targeting dugongs had been detected and was shut down in 2012. Potential hunts along Tanzanian coasts by fishermen have raised concerns as well.

The word "dugong" derives from the Visayan (probably Cebuano) dugung. 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 duyung 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. Dugongs and other sirenians are not closely related to other marine mammals, being more closely related to elephants. Sirenians and elephants share a monophyletic group with hyraxes and the aardvark, one of the earliest offshoots of eutherians. The fossil record shows sirenians appearing in the Eocene, when they most likely lived in the Tethys Ocean. The two extant families of sirenians are thought to have diverged in the mid-Eocene, after which the dugongs and their closest relative, the Steller's sea cow, split off from a common ancestor in the Miocene. The Steller's sea cow became extinct in the 18th century. No fossils exist of other members of the Dugongidae. Molecular studies have been conducted on dugong populations using mitochondrial DNA. The results have suggested that the population in Southeast Asia is distinct from the others. Australia has two distinct maternal lineages, one of which also contains the dugongs from Africa and Arabia. Limited genetic mixing has taken place between those in Southeast Asia and those in Australia, mostly around Timor. One of the lineages stretches from Moreton Bay to Western Australia, while the other only stretches from Moreton Bay to the Northern Territory. There is not yet sufficient genetic data to make clear the boundaries between distinct groups.