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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 Steller's sea cow (''Hydrodamalis gigas'') is an extinct sirenian described by Georg Wilhelm Steller in 1741. At that time, it was found only around the Commander Islands in the Bering Sea between Alaska and Russia; its range extended across ...
(''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 which support
seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...
s, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as
bays A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a narr ...
, mangrove channels, the waters of large
inshore A shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...
islands and inter-reefal waters. The northern waters of Australia between
Shark Bay Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
and Moreton Bay are believed to be the dugong's contemporary stronghold. Like all modern sirenians, the dugong has a
fusiform Fusiform means having a spindle-like shape that is wide in the middle and tapers at both ends. It is similar to the lemon-shape, but often implies a focal broadening of a structure that continues from one or both ends, such as an aneurysm on a b ...
body with no dorsal fin or hind limbs. The
forelimb A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial ( anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...
s or flippers are paddle-like. The dugong is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth. Its
snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
is sharply downturned, an adaptation for feeding in
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
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 Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
and oil. Traditional hunting still has great cultural significance in several countries in 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 The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
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 being legally protected in many countries, the main causes of population decline remain
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human im ...
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 Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...
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 The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
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 French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
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 common misconception, the term does not come from
Malay Malay may refer to: Languages * Malay language or Bahasa Melayu, a major Austronesian language spoken in Indonesia, Malaysia, Brunei and Singapore ** History of the Malay language, the Malay language from the 4th to the 14th century ** Indonesi ...
''duyung'' and it does not mean "lady of the sea" ( Mermaid). Other common local names include "sea cow", "sea pig" and "sea camel".Reeves, R. R. (2002). ''National Audubon Society Guide to Marine Mammals of the World''. Knopf. . pp. 478–481 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.Marsh, H. ''et al.'' (2002)
Dugong: status reports and action plans for countries and territories
IUCN.
It was first classified by
Müller Müller may refer to: * ''Die schöne Müllerin'' (1823) (sometimes referred to as ''Müllerlieder''; ''Müllerin'' is a female miller) is a song cycle with words by Wilhelm Müller and music by Franz Schubert * Doctor Müller, fictional character ...
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 Lacepede can refer to: * Bernard Germain de Lacépède (1756–1825), French naturalist and politician. * Lacepede Bay, a bay in South Australia. * Lacépède, Lot-et-Garonne, a ''commune'' in France * Lacepede Islands, a group of four islands in t ...
Dugong
The Paleobiology Database. Retrieved on 22 July 2007.
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 related to elephants. Dugongs and elephants share a
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
group with
hyrax Hyraxes (), also called dassies, are small, thickset, herbivorous mammals in the order Hyracoidea. Hyraxes are well-furred, rotund animals with short tails. Typically, they measure between long and weigh between . They are superficially simil ...
es and the aardvark, one of the earliest offshoots of eutherians. The fossil record shows sirenians appearing in the Eocene, where 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 Steller's sea cow (''Hydrodamalis gigas'') is an extinct sirenian described by Georg Wilhelm Steller in 1741. At that time, it was found only around the Commander Islands in the Bering Sea between Alaska and Russia; its range extended across ...
, 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 made on dugong populations using
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
. The results have suggested that the population of 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 all the way 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 boundaries between distinct groups.


Anatomy and morphology

The dugong's body is large with a
cylindrical A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an infini ...
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 Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
on the skin. The body is sparsely covered in short hair, a common feature among sirenians which may allow for
tactile Tactile may refer to: * Tactile, related to the sense of touch * Haptics (disambiguation) * Tactile (device), a text-to-braille translation device See also * Tangibility, in law * Somatosensory system, where sensations are processed * CD96 CD9 ...
interpretation of their environment. These hairs are most developed around the mouth, which has a large
horseshoe-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a bell-shaped curve has the shape of the vertical ...
upper lip forming a highly mobile muzzle. This muscular upper lip aids the dugong in foraging. The dugong's
tail fluke A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
s 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.Myers, P. (2002)
Dugongidae
University of Michigan Museum of Zoology. Retrieved on 10 March 2007.
A dugong's brain weighs a maximum of , 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 A teat is the projection from the mammary glands of mammals from which milk flows or is ejected for the purpose of feeding young. In many mammals the teat projects from the udder. The number of teats varies by mammalian species and often corr ...
, one located behind each flipper. There are few differences between 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 in relation to the umbilicus and the
anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...
. The lungs in a dugong are very long, extending almost as far as the kidneys, which are also highly elongated in order 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 sharply down-turned premaxilla, which are 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.Marsh, Helene
"Chapter 57: Dugongidae"
''Fauna of Australia'': Vol. 1B ''Mammalia''. CSIRO. .
The number of growth layer groups in a tusk indicates the age of a dugong, and the cheekteeth move forward with age. The full dental formula of dugongs is , meaning they have two incisors, three
premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...
s, 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,Waller, Geoffrey and Dando, Marc (1996). ''Sealife: A Complete Guide to the Marine Environment''. Smithsonian Institution. . pp. 413–420 may act as a ballast to help keep sirenians suspended slightly below the water's surface. 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 .Burnie D and Wilson DE (Eds.), ''Animal: The Definitive Visual Guide to the World's Wildlife''. DK Adult (2005), The largest individual recorded was long and weighed , and was found off the Saurashtra coast of west India. Females tend to be larger than males.


Distribution and habitat

Dugongs are found in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, along an estimated of coastline between 26° and 27° to the north and south of the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
. Their historic range is believed to correspond to that of seagrasses from the
Potamogetonaceae The Potamogetonaceae, commonly referred to as the pondweed family, is an aquatic family of monocotyledonous flowering plants. The roughly 110 known species are divided over six genera. The largest genus in the family by far is ''Potamogeton'', w ...
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 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, 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 waters around the coast 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 Windward () and leeward () are terms used to describe the direction of the wind. Windward is ''upwind'' from the point of reference, i.e. towards the direction from which the wind is coming; leeward is ''downwind'' from the point of reference ...
sides of large inshore islands, where seagrass beds are common. They are usually located at a depth of around , although in areas where the continental shelf remains shallow dugongs have been known to travel more than from the shore, descending to as far as , where deepwater seagrasses such as ''
Halophila spinulosa ''Halophila'' is a genus of seagrasses in the family ''Hydrocharitaceae'', the tape-grasses. It was described as a genus in 1806. The number of its contained species, and its own placement in the order Alismatales, has evolved. Description Th ...
'' are found. Special 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.


Australia

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
is home to the largest population, stretching from
Shark Bay Shark Bay (Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north of Perth, on the ...
in Western Australia to Moreton Bay in Queensland. The population of Shark Bay is thought to be stable with over 10,000 dugongs. Smaller populations exist up the coast, including one in Ashmore reef. Large numbers of dugongs live to the north of the Northern Territory, with a population of over 20,000 in the
gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
alone. A population of over 25,000 exists in the Torres Strait such as off Thursday Island, although there is significant migration between the strait and the waters of New Guinea. The Great Barrier Reef provides important feeding areas for the species; 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. Dugongs had been occasional visitors along the Gold Coast 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, and the current population is believed to range from 5,800 to 7,300. In the course of a study being carried out in 1986 and 1999 on the Persian Gulf, the largest reported group sighting was made of more than 600 individuals to the west of Qatar. However, recent studies revealed severe declines both in population size and distributions among the region. A 2017 study, for instance, found a nearly 25% drop in population since 1950. Reasons for this drastic population loss include illegal poaching,
oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...
s and net entanglement.


East Africa and South Asia

In the late 1960s, herds of up to 500 dugongs were observed off the coast of
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa: Due to the historical ...
and nearby islands. Current populations in this area are extremely small, numbering 50 and below, and it is thought likely they will become extinct. The eastern side of the Red Sea is home to large populations numbering in the hundreds, and similar populations are thought to exist on the western side. In the 1980s, it was estimated there could be as many as 4,000 dugongs in the Red Sea. Dugong populations in Madagascar are poorly studied, but due to widespread exploitation it is thought they may have severely declined, with few surviving individuals. 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 Bazaruto ( pt, Ilha do Bazaruto, from Ushurutswa, island of the mist) is a sandy island located approximately southeast of the mouth of the Save River, Mozambique (). It is the largest island in the Bazaruto Archipelago and in the Bazaruto Nati ...
, 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. The East Afircan population that is genetically distinct from those of the Red Sea and those off Madagascar. In Tanzania, observations have recently increased around the
Mafia Island Marine Park Mafia Island Marine Park is a protected marine nature reserve around Mafia Island, in the Indian Ocean southeast of Zanzibar Island. It is located in the Pwani Region jurisdiction of Tanzania. Impact on Marine Biodiversity Prior to the establis ...
where a hunt was intended by fishermen but failed in 2009.The Wiomsa magazine – People and Environment
/ref> In the Seychelles, dugongs had been regarded as extinct in 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 The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archi ...
and
Sea Cow Island Sea Cow Island, also known as Île Vache Marine, is a round 18 ha island on the Great Chagos Bank atoll of the Chagos Archipelago in the British Indian Ocean Territory. History It was named after the dugongs that were once abundant in th ...
was named after the species, although the species no longer occurs in the region. There are less 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
Laccadive Islands The Laccadive or Cannanore Islands are one of the three island subgroups in the Union Territory of Lakshadweep, India. It is the central subgroup of the Lakshadweep, separated from the Amindivi Islands subgroup roughly by the 11th parallel ...
, are presumed to be extinct. A population exists in the
Gulf of Mannar Marine National Park The Gulf of Mannar Marine National Park is a protected area of India consisting of 21 small islands (islets) and adjacent coral reefs in the Gulf of Mannar in the Indian Ocean. It lies 1 to 10 km away from the east coast of Tamil Nadu, Indi ...
and the
Palk Strait The Palk Strait ( ta, பாக்கு நீரிணை ''Pākku Nīriṇai'', si, පෝක් සමුද්‍ර සන්ධිය ''Pok Samudra Sandhiya'') is a strait between the Tamil Nadu state of India and the Jaffna Distric ...
between India and
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
, but it is seriously depleted. Recoveries of seagrass beds along former ranges of dugongs, such as the
Chilika Lake Chilika Lake is a brackish water lagoon, spread over the Puri, khordha and Ganjam districts of Odisha state on the east coast of India, at the mouth of the Daya River, flowing into the Bay of Bengal, covering an area of over . It is the bigge ...
have been confirmed in recent years, raising hopes for re-colorizations of the species. The population around the Andaman and Nicobar Islands are known only from a few records, and although the population was large during British rule, it is now believed to be small and scattered. Once distributed throughout the coastal belt in Sri Lanka, the dugong numbers have declined in last two decades.


Southern Pacific outside of Australia

A small population existed along the southern coast of
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
, particularly
Gulf of Tonkin The Gulf of Tonkin is a gulf at the northwestern portion of the South China Sea, located off the coasts of Tonkin (northern Vietnam) and South China. It has a total surface area of . It is defined in the west and northwest by the northern ...
(Beibu Gulf), where efforts were made to protect it, including the establishment of a seagrass sanctuary for dugong and other endangered marine fauna ranging in
Guangxi Guangxi (; ; Chinese postal romanization, alternately romanized as Kwanghsi; ; za, Gvangjsih, italics=yes), officially the Guangxi Zhuang Autonomous Region (GZAR), is an Autonomous regions of China, autonomous region of the People's Republic ...
. 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
Royal Society Open Science ''Royal Society Open Science'' is a peer-reviewed open access scientific journal published by the Royal Society since September 2014. Its launch was announced in February 2014. It covers all scientific fields and publishes all articles which are sc ...
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 Guangxi (; ; Chinese postal romanization, alternately romanized as Kwanghsi; ; za, Gvangjsih, italics=yes), officially the Guangxi Zhuang Autonomous Region (GZAR), is an Autonomous regions of China, autonomous region of the People's Republic ...
, 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 Phu Quoc Island and Con Dao Island, which hosted large populations in the past. Con Dao is now the only site in Vietnam where dugong are regularly seen, protected within the
Côn Đảo National Park Côn Đảo National Park () is a natural reserve area on Côn Đảo Island, in Bà Rịa–Vũng Tàu province in coastal southeastern Vietnam. The park includes a part of the island and the surrounding sea. The national park is characterized ...
. Nonetheless, dangerously low levels of attention to 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. On Phu Quoc, the first 'Dugong Festival' was held in 2014, aiming to raise awareness of these issues. In Thailand, the present distribution of dugongs is restricted to six provinces along the
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated from ...
, and very few dugongs are present in the
Gulf of Thailand The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet in the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula and the northern half of the Malay Peninsula. It is around in l ...
. The Gulf of Thailand was historically home to large number of the animals, but none have been sighted in the west of the gulf in recent years, and the remaining population in the east is thought to be very small and possibly declining. 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 The Malay Archipelago (Indonesian/Malay: , tgl, Kapuluang Malay) is the archipelago between mainland Indochina and Australia. It has also been called the " Malay world," "Nusantara", "East Indies", Indo-Australian Archipelago, Spices Archipe ...
. All the islands of the Philippines once provided habitats for sizeable herds of dugongs. They were common until the 1970s, when their numbers declined sharply due to accidental drownings in fishing gear and habitat destruction of seagrass meadows. Today, only isolated populations survive, most notably in the waters off the Calamian Islands in Palawan, Isabela in Luzon, Guimaras, and Mindanao. The dugong became the first marine animal protected by Philippine law, with harsh penalties for harming them. Recently, 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 Fast food is a type of mass-produced food designed for commercial resale, with a strong priority placed on speed of service. It is a commercial term, limited to food sold in a restaurant or store with frozen, preheated or precooked ingredien ...
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 clearly harming the coastal environment not only in Palawan but also across the islands of the Philippines. Populations also exist around the
Solomon Islands archipelago The Solomon Islands (archipelago) is an island group in the western South Pacific Ocean, north-east of Australia. The archipelago is in the Melanesian subregion and bioregion of Oceania and forms the eastern boundary of the Solomon Sea. The ...
and
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
, stretching to an easternmost population in Vanuatu. A highly isolated population lives around the islands of Palau. A single dugong lives at Cocos (Keeling) Islands although the animal is thought to be a vagrant.


Northern Pacific

Today, possibly the smallest and northernmost population of dugongs exists around the Ryukyu islands, and a population formerly existed off Taiwan. An endangered population of 50 or fewer dugongs, possibly as few as three individuals, survives 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 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 an 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 a research published in August 2022, the Zoological Society of London (ZSL) and the Chinese Academy of Sciences reported that the Dugong appears to be functionally extinct in Chinese coastal waters. 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 Kenting National Park (), commonly known as Kenting (), is a national park located on the Hengchun Peninsula of Pingtung County, Taiwan, covering Hengchun, Checheng, and Manzhou Townships. Established on 1 January 1984, it is Taiwan's oldest a ...
in the 1950s and 60s. There had been occasional records of vagrants at the Northern Mariana Islands prior to 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 were 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 An inland sea (also known as an epeiric sea or an epicontinental sea) is a continental body of water which is very large and is either completely surrounded by dry land or connected to an ocean by a river, strait, or "arm of the sea". An inland se ...
. 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 In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
. The Mediterranean is the region where the Dugongidae originated in the mid-late Eocene, along with Caribbean Sea.


Ecology and life history

Dugongs are long-lived, and the oldest recorded specimen reached age 73. They have few natural predators, although animals such as crocodiles, killer whales, and sharks pose a threat to the young, and a dugong has also been recorded to have died from trauma after being impaled by a
stingray Stingrays are a group of sea rays, which are cartilaginous fish related to sharks. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae ( ...
barb. A large number of infections and parasitic diseases affect dugongs. Detected pathogens include
helminth Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schi ...
s,
cryptosporidium ''Cryptosporidium'', sometimes informally called crypto, is a genus of apicomplexan parasitic alveolates that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (intestinal cryptosp ...
, different types of bacterial infections, and other unidentified parasites. 30% of dugong deaths in Queensland since 1996 are thought to be because of disease. Although they are
social animal Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies. Sociality is a survival response to evolutionary pressures. For example, when a mother wasp ...
s, they are usually solitary or found in pairs due to the inability of seagrass beds to support large populations. Gatherings of hundreds of dugongs sometimes happen, but they last only for a short time. Because they are shy, and do not approach humans, little is known about dugong behavior. They can go six minutes without breathing (though about two and a half minutes is more typical), and have been known to rest on their tail to breathe with their heads above water. They can dive to a maximum depth of ; they spend most of their lives no deeper than . Communication between individuals is through chirps, whistles, barks, and other sounds that echo underwater. Different sounds have been observed with different amplitudes and frequencies, implying different purposes. Visual communication is limited due to poor eyesight, and is mainly used for activities such as
lekking A lek is an aggregation of male animals gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners with which to mate. A lek can also indicate an avail ...
for courtship purposes. Mothers and calves are in almost constant physical contact, and calves have been known to reach out and touch their mothers with their flippers for reassurance. Dugongs are semi-nomadic, often traveling long distances in search of food, but staying within a certain range their entire life. Large numbers often move together from one area to another. It is thought that these movements are caused by changes in seagrass availability. Their memory allows them to return to specific points after long travels. Dugong movements mostly occur within a localized area of seagrass beds, and animals in the same region show individualistic patterns of movement. Daily movement is affected by the tides. In areas where there is a large tidal range, dugongs travel with the tide in order to access shallower feeding areas. In Moreton Bay, dugongs often travel between foraging grounds inside the bay and warmer oceanic waters. At higher latitudes dugongs make seasonal travels to reach warmer water during the winter. Occasionally individual dugongs make long-distance travels over many days, and can travel over deep ocean waters. One animal was seen as far south as
Sydney Sydney ( ) is the capital city of the state of New South Wales, and the most populous city in both Australia and Oceania. Located on Australia's east coast, the metropolis surrounds Sydney Harbour and extends about towards the Blue Mountain ...
. Although they are marine creatures, dugongs have been known to travel up creeks, and in one case a dugong was caught up a creek near
Cooktown Cooktown is a coastal town and locality in the Shire of Cook, Queensland, Australia. Cooktown is at the mouth of the Endeavour River, on Cape York Peninsula in Far North Queensland where James Cook beached his ship, the Endeavour, for repairs ...
.


Feeding

Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of seagrass. 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 Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
when seagrass is scarce. Although almost completely herbivorous, they will occasionally eat invertebrates such as jellyfish, sea squirts, and
shellfish Shellfish is a colloquial and fisheries term for exoskeleton-bearing aquatic invertebrates used as food, including various species of molluscs, crustaceans, and echinoderms. Although most kinds of shellfish are harvested from saltwater envir ...
. 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 on 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 is 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 ''Halodule'' is a genus of plants in the family Cymodoceaceae described as a genus in 1841. It is widespread on tropical and semi-tropical ocean shores of all continents except Europe and Antarctica. Species Hybridization has been reported in ...
'', so as 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 , and dugongs have been seen feeding as deep as . Dugongs are relatively slow-moving, swimming at around . When moving along the seabed to feed they walk on their pectoral fins. Dugong feeding may favor the subsequent growth 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.


Reproduction and parental care

A dugong reaches sexual maturity between the ages of eight and eighteen, older than in most other mammals. The way that females know how a male has reached sexual maturity is by the eruption of tusks in the male 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 life, 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 will establish a territory which females in estrus will visit. In these areas a male will try to impress the females while defending the area from other males, a practice known as
lekking A lek is an aggregation of male animals gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners with which to mate. A lek can also indicate an avail ...
. In other areas many males will attempt to mate with the same female, sometimes inflicting injuries to the female or each other. During this the female will have copulated with multiple males, who will have fought to mount her from below. This greatly increases the chances of conception. Females give birth after a 13- to 15-month
gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...
, 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 long and weigh around . Once born, they 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 will only leave its mother once it has matured. Calves in captivity have been observed sucking on their flippers as a way of asking to be fed.


Importance to humans

Dugongs have historically provided easy targets for hunters, who killed them for their meat, oil, skin, and bones. As the anthropologist A. Asbjørn Jøn has noted, they are often considered as the inspiration for mermaids, and people around the world developed cultures around dugong hunting. In some areas it remains an animal of great significance, and a growing ecotourism industry around dugongs has had an economic benefit in some countries. There is a 5,000-year-old wall painting of a dugong, apparently drawn by neolithic peoples, in Tambun Cave,
Ipoh , image_map = , map_caption = Location of Ipoh in Perak , pushpin_map = #Malaysia#Asia#Earth , pushpin_mapsize = 275px , pushpin_map_caption = Ipoh in Malaysia , coordinates ...
, Malaysia. This was discovered by Lieutenant R.L Rawlings in 1959 while on a routine patrol. Dugongs feature in Southeast Asian, especially
Austronesian Austronesian may refer to: *The Austronesian languages *The historical Austronesian peoples The Austronesian peoples, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples in Taiwan, Maritime Southeast Asia, M ...
, folklore. In languages like Ilocano, Mapun,
Yakan Yakan may refer to: * Yakan people, a community of the Philippines * Yakan language, a language of the Philippines * Cape Yakan, in Russia People with the name * Adly Yakan Pasha (1864–1933), Egyptian politician * Fathi Yakan (1933–2009), Le ...
, Tausug, and Kadazan Dusun of the Philippines and Sabah, the name for dugongs is a synonym for "mermaid". In
Malay Malay may refer to: Languages * Malay language or Bahasa Melayu, a major Austronesian language spoken in Indonesia, Malaysia, Brunei and Singapore ** History of the Malay language, the Malay language from the 4th to the 14th century ** Indonesi ...
, they are sometimes referred to as ''perempoen laut'' ("woman of the sea") or ''putri duyong'' ("dugong princess"), leading to the misconception that the word "dugong" itself means "lady of the sea". 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 corral A fish trap is a trap used for fishing. Fish traps include fishing weirs, lobster traps, and some fishing nets such as fyke nets. Traps are culturally almost universal and seem to have been independently invented many times. There are two mai ...
s in the Philippines, some parts of Sabah (Malaysia), and northern
Sulawesi Sulawesi (), also known as Celebes (), is an island in Indonesia. One of the four Greater Sunda Islands, and the world's eleventh-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Mindanao and the Sulu Ar ...
and the
Lesser Sunda Islands The Lesser Sunda Islands or nowadays known as Nusa Tenggara Islands ( id, Kepulauan Nusa Tenggara, formerly ) are an archipelago in Maritime Southeast Asia, north of Australia. Together with the Greater Sunda Islands to the west they make up t ...
(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 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 at killing dugongs, poaching remains a major problem. Dugongs are also widely hunted in Papua New Guinea, the Solomon Islands, Vanuatu, and
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
; 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. Dugong meat and oil have traditionally been some of the most valuable foods of Australian Aboriginals and Torres Strait Islanders. Some Aboriginals regard dugongs as part of their Aboriginality. Local fishermen in Southern China traditionally revered dugongs and regarded them as "miraculous fish". They believed it was bad luck to catch them and they were plentiful in the region prior to the 1960s. Beginning in the 1950s, a wave of immigrants from other regions that do not hold these beliefs resulted in dugongs being hunted for food and traditional Chinese medicine. This led to a steep decline in dugong populations in the
Gulf of Tonkin The Gulf of Tonkin is a gulf at the northwestern portion of the South China Sea, located off the coasts of Tonkin (northern Vietnam) and South China. It has a total surface area of . It is defined in the west and northwest by the northern ...
and the sea around Hainan Island. In
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
, dugongs were traditionally hunted in the Ryukyu Islands since prehistoric times. Carved ribs of dugongs in the shape of butterflies (a psychopomp) are found throughout Okinawa. They were commonly hunted throughout Japan up until around the 1970s. Dugongs have also played a role in legends in Kenya, and the animal is known there as the "Queen of the Sea". Body parts are used as food, medicine, and decorations. In the Gulf states, dugongs served not only as a source of food, but their tusks were used as sword handles. Dugong oil is important as a preservative and conditioner for wooden boats to people around the Gulf of Kutch in India, who also believe the meat to be an aphrodisiac. During the Renaissance and the
Baroque The Baroque (, ; ) is a style of architecture, music, dance, painting, sculpture, poetry, and other arts that flourished in Europe from the early 17th century until the 1750s. In the territories of the Spanish and Portuguese empires including t ...
eras, dugongs were often exhibited in wunderkammers. They were also presented as Fiji mermaids in sideshows.


Conservation

Dugong numbers have decreased in recent times. For a population to remain stable, 95 percent of adults must survive the span of one year. 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 area Important Marine Mammal Areas (IMMAs) were formulated by the joint International Union for Conservation of Nature (IUCN) Species Survival Commission / World Commission on Protected Areas, Marine Mammal Protected Areas Task Force (MMPATF) Global ...
s. 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 Wildlife refers to undomesticated animal species, but has come to include all organisms that grow or live wild in an area without being introduced by humans. Wildlife was also synonymous to game: those birds and mammals that were hunted for ...
for 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 The Mayotte Marine Natural Park () is a marine park surrounding Mayotte, a French overseas region. Mayotte is part of the Comoro Islands archipelago, which lies within the Mozambique Channel in the western Indian Ocean. Established in 2010, the p ...
. 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 Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
ban the hunting and selling of dugongs and their products.
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
has listed dugongs as endangered and has banned intentional kills 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 lists dugongs as a protected species; however, protection is not always enforced and souvenir products made from dugong parts can be openly found in markets in Bali. The dugong is a national animal of Papua New Guinea, which bans all except traditional hunting. Vanuatu and
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
ban 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 The ''Nature Conservation Act 1992'' is an act of the Parliament of Queensland, Australia, that, together with subordinate legislation, provides for the legislative protection of Queensland's threatened biota. As originally published, it prov ...
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 Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...
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.


Human activity

Despite being legally protected in many countries, the main causes of population decline remain
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human im ...
and include hunting, habitat degradation, and fishing-related fatalities. Entanglement in fishing nets has caused many deaths, although there are no precise statistics. Most issues with industrial fishing occur in deeper waters where dugong populations are low, with local fishing being the main risk in shallower waters. As dugongs cannot stay underwater for a very long period, they are highly prone to deaths due to entanglement. The use of shark nets has historically caused large numbers of deaths, and they have been eliminated in most areas and replaced with baited hooks. Hunting has historically been a problem too, although in most areas they are no longer hunted, with the exception of certain indigenous communities. In areas such as northern Australia, hunting remains the greatest impact on the dugong population. Vessel strikes have proved a problem for manatees, but the relevance of this to dugongs is unknown. Increasing boat traffic has increased danger, especially in shallow waters. Ecotourism has increased in some countries, although the effects remain undocumented. It has been seen to cause issues in areas such as Hainan due to
environmental degradation Environmental degradation is the deterioration of the environment (biophysical), environment through depletion of resources such as quality of air, water and soil; the destruction of ecosystems; habitat destruction; the extinction of wildlife; an ...
. Modern farming practices and increased land clearing have also had an impact, and much of the coastline of dugong habitats are undergoing
industrialization Industrialisation ( alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian society into an industrial society. This involves an extensive re-organisation of an econo ...
, with increasing human populations. Dugongs accumulate heavy metal ions in their tissues throughout their lives, more so than other marine mammals. The effects are unknown. While international cooperation to form a conservative unit has been undertaken, 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, the legislation does not exist to protect dugongs, and if it does it is not enforced.
Oil spill An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially the marine ecosystem, due to human activity, and is a form of pollution. The term is usually given to marine oil spills, where oil is released into th ...
s are a danger to dugongs in some areas, as is
land reclamation Land reclamation, usually known as reclamation, and also known as land fill (not to be confused with a waste landfill), is the process of creating new land from oceans, seas, riverbeds or lake beds. The land reclaimed is known as reclamati ...
. In Okinawa the small dugong population is threatened by United States military activity. Plans exist to build a military base close to the Henoko reef, and military activity also adds the threats of noise pollution, chemical pollution, soil erosion, and exposure to depleted uranium. The military base plans have been fought in US courts by some Okinawans, whose concerns include the impact on the local environment and dugong habitats. 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. Food shortages can be caused by many factors, such as a loss of habitat, death and decline in quality of seagrass, and a disturbance of feeding caused by human activity.
Sewage Sewage (or domestic sewage, domestic wastewater, municipal wastewater) is a type of wastewater that is produced by a community of people. It is typically transported through a sewer system. Sewage consists of wastewater discharged from residenc ...
,
detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more ...
s, heavy metal, hypersaline water,
herbicide Herbicides (, ), also commonly known as weedkillers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page fo ...
s, and other waste products all negatively affect seagrass meadows. Human activity such as mining, trawling,
dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing da ...
,
land reclamation Land reclamation, usually known as reclamation, and also known as land fill (not to be confused with a waste landfill), is the process of creating new land from oceans, seas, riverbeds or lake beds. The land reclaimed is known as reclamati ...
, and boat propeller scarring also cause an increase in sedimentation which smothers seagrass and prevents light from reaching it. This is the most significant negative factor affecting seagrass. '' Halophila ovalis''—one of the dugong's preferred species of seagrass—declines rapidly due to lack of light, dying completely after 30 days. Extreme weather such as
cyclone In meteorology, a cyclone () is a large air mass that rotates around a strong center of low atmospheric pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere as viewed from above (opposite to an anti ...
s and floods can destroy hundreds of square kilometres of seagrass meadows, as well as washing dugongs ashore. The recovery of seagrass meadows and the spread of seagrass into new areas, or areas where it has been destroyed, can take over a decade. Most measures for protection involve restricting activities such as trawling in areas containing seagrass meadows, with little to no action on pollutants originating from land. In some areas, water salinity is increased due to wastewater, and it is unknown how much salinity seagrass can withstand. Dugong habitat in the Oura Bay area of Henoko, Okinawa, Japan, is currently under threat from land reclamation conducted by Japanese Government in order to build a US Marine base in the area. 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. Capturing animals for research has caused only one or two deaths; dugongs are expensive to keep in captivity due to the long time mothers and calves spend together, and the inability to grow the seagrass that dugongs eat in an aquarium. Only one orphaned calf has ever been successfully kept in captivity. Worldwide, only three dugongs are held in captivity. A female from the Philippines lives at Toba Aquarium in Toba, Mie, Japan. A male also lived there until he died on 10 February 2011. The second resides in
Sea World Indonesia Sea World Ancol, also known as Sea World Jakarta or Sea World Indonesia, is a marine aquarium attraction in North Jakarta, Jakarta, Indonesia. It is part of the Ancol Dreamland complex, and consists of a main tank, a shark tank, and various oth ...
, 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 Underwater World, also known as Underwater World Singapore Pte Ltd, was an oceanarium located on the offshore Singaporean island of Sentosa. It was opened on 13 May 1991 and closed on 26 June 2016. History The oceanarium was developed by the ...
, was reported to have died in 2014 at the age of 19, from complications arising from an acute
digestive disorder Gastrointestinal diseases (abbrev. GI diseases or GI illnesses) refer to diseases involving the gastrointestinal tract, namely the oesophagus, stomach, small intestine, large intestine and rectum, and the accessory organs of digestion, the liver, g ...
.


References

{{Authority control Sirenians Marine fauna of East Africa Marine fauna of South Asia Marine fauna of Southeast Asia Marine fauna of Oceania Fauna of the Indian Ocean Vulnerable animals Vulnerable biota of Africa Vulnerable fauna of Asia Vulnerable fauna of Australia EDGE species Mammals described in 1776 Taxa named by Philipp Ludwig Statius Müller