HOME

TheInfoList



OR:

The dugong (; ''Dugong dugon'') is a
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
. It is one of four living species of the order
Sirenia The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct ...
, which also includes three species of
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
s. It is the only living representative of the once-diverse family
Dugongidae Dugongidae is a family in the order of Sirenia. The family has one surviving species, the dugong (''Dugong dugon''), one recently extinct species, Steller's sea cow (''Hydrodamalis gigas''), and a number of extinct genera known from fossil r ...
; its closest modern relative, Steller's sea cow (''Hydrodamalis gigas''), was hunted to
extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
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 Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
. The dugong is largely dependent on
seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
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,
mangrove A mangrove is a shrub or tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...
channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austral ...
, the waters of large inshore islands and inter-reefal waters. The northern waters of Australia between Shark Bay and
Moreton Bay Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...
are believed to be the dugong's contemporary stronghold. Like all modern sirenians, the dugong has a fusiform body with no
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...
or
hind limb A hindlimb or back limb is one of the paired articulated appendages (limbs) attached on the caudal ( posterior) end of a terrestrial tetrapod vertebrate's torso.http://www.merriam-webster.com/medical/hind%20limb, Merriam Webster Dictionary-Hindli ...
s. The forelimbs 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 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 An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
. 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 lists the dugong as a species vulnerable to extinction, while the
Convention on International Trade in Endangered Species CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
limits or bans the trade of derived products. Despite 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 The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct ...
order of
placental mammals Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...
which comprises modern "sea cows" (
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
s as well as dugongs) and their extinct relatives. Sirenia are the only extant
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
s and the only group of herbivorous mammals to have become completely aquatic. Sirenians are thought to have a 50-million-year-old
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
record (early
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
-recent). They attained modest diversity during the Oligocene and
Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
, but subsequently declined as a result of climatic cooling, oceanographic changes, and human interference.


Etymology and taxonomy

The word "dugong" derives from the
Visayan Visayans ( Visayan: ''mga Bisaya''; ) or Visayan people are a Philippine ethnolinguistic group or metaethnicity native to the Visayas, the southernmost islands of Luzon and a significant portion of Mindanao. When taken as a single ethnic group ...
(probably Cebuano) '. The name was first adopted and popularized by the French naturalist
Georges-Louis Leclerc, Comte de Buffon Georges-Louis Leclerc, Comte de Buffon (; 7 September 1707 – 16 April 1788) was a French naturalist, mathematician, cosmologist, and encyclopédiste. His works influenced the next two generations of naturalists, including two prominent ...
, as "''dugon''" in ''Histoire Naturelle'' (1765), after descriptions of the animal from the island of
Leyte Leyte ( ) is an island in the Visayas group of islands in the Philippines. It is eighth-largest and sixth-most populous island in the Philippines, with a total population of 2,626,970 as of 2020 census. Since the accessibility of land has be ...
in the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
. The name ultimately derives from
Proto-Malayo-Polynesian Proto-Malayo-Polynesian (PMP) is the reconstructed ancestor of the Malayo-Polynesian languages, which is by far the largest branch (by current speakers) of the Austronesian language family. Proto-Malayo-Polynesian is ancestral to all Austronesi ...
*duyuŋ. Despite
common misconception Each entry on this list of common misconceptions is worded as a correction; the misconceptions themselves are implied rather than stated. These entries are concise summaries of the main subject articles, which can be consulted for more detail. ...
, the term does not come from Malay ''duyung'' and it does not mean "lady of the sea" (
Mermaid In folklore, a mermaid is an aquatic creature with the head and upper body of a female human and the tail of a fish. Mermaids appear in the folklore of many cultures worldwide, including Europe, Asia, and Africa. Mermaids are sometimes ass ...
). 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 Alfred A. Knopf, Inc. () is an American publishing house that was founded by Alfred A. Knopf Sr. and Blanche Knopf in 1915. Blanche and Alfred traveled abroad regularly and were known for publishing European, Asian, and Latin American writers in ...
. . pp. 478–481
It is known as the ''balguja'' by the
Wunambal The Wunambal (Unambal), also known as Wunambal Gaambera, Uunguu (referring to their lands), and other names, are an Aboriginal Australian people of the northern Kimberley region of Western Australia. People The Wunambal were, according to Norma ...
people of the
Mitchell Plateau Mitchell River National Park is a national park in the Kimberley region of Western Australia, northeast of Perth. The park adjoins the northern boundary of the Prince Regent National Park. The nearest towns are Derby, to the southwest, as wel ...
area in
the Kimberley The Kimberley is the northernmost of the nine regions of Western Australia. It is bordered on the west by the Indian Ocean, on the north by the Timor Sea, on the south by the Great Sandy and Tanami deserts in the region of the Pilbara, an ...
,
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
. ''Dugong dugon'' is the only extant species of the family
Dugongidae Dugongidae is a family in the order of Sirenia. The family has one surviving species, the dugong (''Dugong dugon''), one recently extinct species, Steller's sea cow (''Hydrodamalis gigas''), and a number of extinct genera known from fossil r ...
, and one of only four extant species of the
Sirenia The Sirenia (), commonly referred to as sea-cows or sirenians, are an order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The Sirenia currently comprise two distinct ...
order, the others forming the
manatee Manatees (family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living speci ...
family.Marsh, H. ''et al.'' (2002)
Dugong: status reports and action plans for countries and territories
IUCN.
It was first classified by Müller in 1776 as ''Trichechus dugon'', a member of the manatee genus previously defined by
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
. It was later assigned as the
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...
of ''Dugong'' by LacépèdeDugong
The Paleobiology Database. Retrieved on 22 July 2007.
and further classified within its own family by
Gray Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...
and subfamily by
Simpson Simpson most often refers to: * Simpson (name), a British surname *''The Simpsons'', an animated American sitcom **The Simpson family, central characters of the series ''The Simpsons'' Simpson may also refer to: Organizations Schools *Simpso ...
. Dugongs and other sirenians are not closely related to other
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their ...
s, being more related to
elephant Elephants are the largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members of the family Elephantidae ...
s. Dugongs and elephants share a monophyletic group with hyraxes and the
aardvark The aardvark ( ; ''Orycteropus afer'') is a medium-sized, burrowing, nocturnal mammal native to Africa. It is the only living species of the order Tubulidentata, although other prehistoric species and genera of Tubulidentata are known. Unlik ...
, one of the earliest offshoots of
eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...
ns. The fossil record shows sirenians appearing in the
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
, where they most likely lived in the
Tethys Ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...
. 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 Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
. 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. The results have suggested that the population of
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainlan ...
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 Timor is an island at the southern end of Maritime Southeast Asia, in the north of the Timor Sea. The island is divided between the sovereign states of East Timor on the eastern part and Indonesia on the western part. The Indonesian part, also ...
. One of the lineages stretches all the way from
Moreton Bay Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...
to
Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
, while the other only stretches from Moreton Bay to the
Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...
. 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 shape that tapers at both ends. It has thick, smooth skin that is a pale cream colour at birth, but darkens
dorsally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
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. 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 CD ...
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 Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...
. The dugong's tail flukes and flippers are similar to those of
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
s. 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 , mottoeng = "Arts, Knowledge, Truth" , former_names = Catholepistemiad, or University of Michigania (1817–1821) , budget = $10.3 billion (2021) , endowment = $17 billion (2021)As o ...
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 The auricle or auricula is the visible part of the ear that is outside the head. It is also called the pinna (Latin for "wing" or " fin", plural pinnae), a term that is used more in zoology. Structure The diagram shows the shape and location ...
, 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 sexes; the body structures are almost the same. A male's
testes A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
are not externally located, and the main difference between males and females is the location of the
genital A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...
aperture in relation to the umbilicus and the anus. The
lungs The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side ...
in a dugong are very long, extending almost as far as the
kidneys The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...
, which are also highly elongated in order to cope with the saltwater environment. If the dugong is wounded, its blood will
clot A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of cr ...
rapidly. The
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
of a dugong is unique. The skull is enlarged with sharply down-turned
premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
, which are stronger in males. The spine has between 57 and 60
vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
e. Unlike in manatees, the dugong's teeth do not continually grow back via horizontal tooth replacement. The dugong has two
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
s (
tusk Tusks are elongated, continuously growing front teeth that protrude well beyond the mouth of certain mammal species. They are most commonly canine teeth, as with pigs and walruses, or, in the case of elephants, elongated incisors. Tusks share ...
s) 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 premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
.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 Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiolog ...
of dugongs is , 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 Pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification (osteosclerosis), reducing inner ca ...
, 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 The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...
. . pp. 413–420
may act as a
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
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 India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
. 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. 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 Hydrocharitaceae is a flowering plant family including 16 known genera with a total of ca 135 known species (Christenhusz & Byng 2016), that including a number of species of aquatic plant, for instance the tape-grasses, the well known Canadian ...
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 The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...
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 Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Austral ...
and around windward and leeward, leeward 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
seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
es such as ''Halophila spinulosa'' 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 is home to the largest population, stretching from Shark Bay in Western Australia to
Moreton Bay Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...
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 The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an Australian territory in the central and central northern regions of Australia. The Northern Territory shares its borders with Western Aust ...
, with a population of over 20,000 in the gulf of Carpentaria 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, Queensland, 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 spills 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 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, 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 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 and Sea Cow Island 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, 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-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, particularly Gulf of Tonkin (Beibu Gulf), where efforts were made to protect it, including the establishment of :zh:广西合浦儒艮国家级自然保护区, 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 Royal Society Open Science concluded that dugongs were Functional extinction, 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 province, 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. 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, and very few dugongs are present in the Gulf of Thailand. 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. 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 (province), 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 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 The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
. Populations also exist around the Solomon Islands (archipelago), Solomon Islands archipelago and New Caledonia, 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 National Park, 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 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 Philippines, Philippine subspecies. Others postulate that the populations formed part of a super-population where migration between Ryukyu Islands, Ryukyu, Taiwan, and the Philippines was common.


Extinct Mediterranean population

It has been confirmed that dugongs once inhabited the water of the Mediterranean Sea, 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 change (general concept), climate changes. The Mediterranean is the region where the Dugongidae originated in the mid-late
Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
, 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 barb. A large number of infections and parasitic diseases affect dugongs. Detected pathogens include helminths, cryptosporidium, 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 animals, 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 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. 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.


Feeding

Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of
seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
. 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 A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...
, 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 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'', so as to maximize nutrient intake instead of bulk eating. Seagrasses of a lower seral community, 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, 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. 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, 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, Malaysia. This was discovered by Lieutenant R.L Rawlings in 1959 while on a routine patrol. Dugongs feature in Southeast Asian, especially Austronesian peoples, Austronesian, folklore. In languages like Ilokano language, Ilocano, Mapun language, Mapun, Yakan language, Yakan, Tausug language, Tausug, and Kadazandusun language, Kadazan Dusun of the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
and Sabah, the name for dugongs is a synonym for "mermaid". In Malay, 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 Cetacean stranding, 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 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; 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 Aboriginal Australians, 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 and the sea around Hainan Island. In Japan, 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 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 Birth, 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 CITES, 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 Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainlan ...
n 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 (Kenya), Wildlife Act 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. 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 India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
and Sri Lanka ban the hunting and selling of dugongs and their products. Japan 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 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 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 Gillnetting, 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.


Human activity

Despite being legally protected in many countries, the main causes of population decline remain anthropogenic 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. Modern farming practices and increased land clearing have also had an impact, and much of the coastline of dugong habitats are undergoing industrialization, 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 spills are a danger to dugongs in some areas, as is land reclamation. In Okinawa the small dugong population is threatened by United States military activity. Relocation of Marine Corps Air Station Futenma, Plans exist to build a military base close to the Henoko Bay, 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, detergents, Heavy metals, heavy metal, hypersaline water, herbicides, and other waste products all negatively affect seagrass meadows. Human activity such as mining, trawling, dredging, land reclamation, and boat propeller scarring also cause an increase in sedimentation which smothers
seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families (Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the or ...
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 cyclones 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 Ōmura Bay, Oura Bay area of Henoko Bay, 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 Surveying, 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 Australian aborigines, 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, after having been rescued from a fisherman's net and treated. The last one, a male, is kept at Sea Life Sydney Aquarium, 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

{{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