The dugong (Dugong dugon) is the only living species in the mammalian family Dugongidae and one of only four species in its order, Sirenia. It inhabits shallow marine waters from East Africa to Vanuatu, from the Philippines down to Australia. Dugongs grow up to thirteen feet (4 m.) long, and weigh between 500 and 2,000 pounds (225-900 kg). Their smooth skin can be brown or grey, and it is covered approximately every inch with short sensory bristles. They have small eyes and a round oral disk that is densely covered with more stiff sensory bristles. They do vocalize, but unlike whales and dophins (the only other fully aquatic marine mammals), they do not utilize echolocation. Dugongs are similar in overall appearance to other sirenian species (the manatees). Differences include more caudal location of their nostrils on their snout than manatee nostrils and their tails are fluke-like, as opposed to the round tail seen in manatees.
Dugongs are herbivores. Sea grasses are consumed preferentially, but they will also eat some algae. Dugongs have molars that continue to grow throughout life. This may be beneficial to counteract the dentally abrasive effects of the silica that naturally occurs within the plants of their diet. Dugongs are strictly marine and therefore do not require fresh water, though they will drink it if it is provided.
Multiple anthropogenic activities, including hunting, watercraft collisions, fishing gear entanglement, and habitat loss and degradation have had negative impacts on the dugong. Natural occurrences, including extreme weather phenomena such as cyclones and predation by sharks and orca whales, also cause mortalities. Dugongs reproduce slowly, and provide a great deal of maternal investment; the calf suckles for at least 18 months. These factors make dugongs slow to rebound from population declines. The IUCN Red List of Threatened Species lists dugongs as Vulnerable to extinction.
(Lanyon et al. 2006; Marsh 1988, 2008; Marsh et al. 1978; Marsh et al. 2001; Marsh et al. 2002)
Dugongs reproduce slowly and experience substantial hunting pressure in portions of their range.
Le Dugong a une silhouette plus fusiforme que le Lamantin. Sa tête est massive, latéralement compressée et son museau porte des lèvres très développées entourées de vibrisses sensorielles courtes et nombreuses. Les narines sont situées à l’avant supérieur de la tête. Les yeux sont petits mais visibles, sombres avec un cercle orbitaire pâle. Les nageoires pectorales sont ovales, en forme de pagaie, maintenues contre le corps lorsqu’ils nagent et dépourvues de griffe. Sa nageoire caudale ressemble à celle des cétacés : elle a deux lobes distincts et une encoche médiane nette. Sa peau est lisse et recouverte de poils courts et soyeux. Sa pigmentation est grisâtre sur le dessus et blanchâtre en dessous. Sa formulaire dentaire change avec l’âge, ainsi il compte : I2/3, C /2, P0/0, M12/12 pour les juvéniles et I2/3, C /2, P 0/0, M 2-3/2-3 pour les adultes. Il ressemble au Lamantin.
Prudent, il passe une grande partie de la journée caché et attend la nuit pour se nourrir dans les eaux moins profondes. Sociable, le Dugong forme des petits groupes de 6 individus généralement. La maturité sexuelle est atteinte à l’âge de 9-10 ans. La période de reproduction peut s’étaler toute l’année avec cependant un pic entre juin et septembre. Les mâles se livrent à de violents combats avant de pouvoir se reproduire. Les femelles mettent bas, tous les 2,5-7 ans, après une gestation de 12 à 15 mois, d’un nouveau-né de 1-1,5 mètre de long et pesant environ 20 à 35 kg. Le jeune est allaité pendant 14 à 18 mois, période durant laquelle il apprend à localiser les sites d’alimentation et d’hivernage. Au cours de sa vie, une femelle peut donner naissance à 5-6 petits. Il peut vivre jusqu’à 30 ans bien qu’un spécimen ait été retrouvé âgé de 76 ans. Herbivore, le Dugong se nourrit principalement de zostères (Halodule sp. et Halophila sp.) dont il apprécie particulièrement les rhizomes. Les espèces les plus consommées sont en général moins fibreuses, plus riches en nitrogène et plus digestes.
Le Dugong est le seul mammifère herbivore qui soit strictement marin. Il fréquente généralement les eaux côtières tropicales et subtropicales. Il se retrouve dans les baies, les mangroves et à proximité des récifs coralliens. Ces zones se caractérisent en général par la présence de lits de phanérogames. Ils utilisent des habitats différents en fonction des activités. Ainsi, les bancs de sable et les estuaires sont des sites de mises bas, les prédateurs étant moins présents, tandis que les eaux plus profondes peuvent être utilisées comme refuge en hiver.
KISZKA J., VELY M., BERTRAND N., BREYSSE O., WICKEL J. & MALECK-BERTRAND N. 2003. Le Dugong (Dugong dugon, Müller 1776) autour de l’île de Mayotte (Océan Indien occidental) : bilan récent des connaissances acquises et préconisations pour sa conservation. 32p.
MARSH H., PENROSE H., EROS C. & HUGUES J. 2002. Dugong Status Report and Action Plans for Countries and Territories. Report Series. Early Warning and Assessment, United Nations Environment Program UNEP/DEWA/RS.02-1.
SHIRIHAI H. 2007. Guide des mammifères marins du monde. Toutes les espèces décrites et illustrées. Les Guides du naturaliste. Delachaux et Niestlé, Paris, 385p.
Dugongs are large sirenians found in coastal marine areas of the Pacific Ocean and the Red Sea, along coastal eastern Africa, India, the Malay Peninsula, and to Australia and New Guinea. They can get up to 900 kg in size and are herbivorous, feeding on sea grasses, macroalgae, and occasional invertebrates.
Dugongs (Dugong dugon), also known as sea cows, have a broad but fragmented range, encompassing tropical waters from East Africa to Vanuatu, about 26 degrees both north and south of the equator. This range spans at least 48 countries and about 140,000 km of tropical coastline. The largest population of sea cows is found in the northern waters of Australia between Shark Bay (Western Australia) and Moreton Bay (Queensland). The second largest population is found in the Arabian Gulf. Dugongs are not considered migratory but are known to travel great distances within their range in order to find food.
Biogeographic Regions: oriental (Native ); ethiopian (Native ); australian (Native ); indian ocean (Native )
Distribution in Egypt
East Africa to southern Japan, including U.S.A. (Trust Territories)
Dugongs are large, solid mammals with short, paddle-like front flippers and a tail with a straight or concave perimeter that is used as a propeller. Their tail differentiates them from manatees, the tail of which is paddle-shaped. Dugong fins resemble those of dolphins, but unlike dolphins, dugongs lack a dorsal fin. Females have mammary glands under the fins from which their calves suckle. Adult dugongs weigh from 230 to 400 kg and can range from 2.4 to 4 m in length. Their thick skin is brownish-grey, and its color can vary when algae grows on it. Tusks are present in all dugongs, but they are usually only visible through the skin in mature males, whose tusks are prominent, and in old females. Their tusks are projections of the incisor teeth. There are no other external physical differences between sexes, as they are monomorphic. Their ears have no flaps or lobes but are nonetheless very sensitive. Dugongs are suspected to have high auditory accuity to compensate for poor eye sight. Their snout is rather large, rounded over and ends in a cleft. This cleft is a muscular lip that hangs over the down-turned mouth and aids the dugong in its foraging of sea grass. Dugongs have a down-tipped jaw which accommodates the enlarged incisors. Sensory bristles that cover their upper lip assist in locating food. Bristles also cover the dugong’s body. Paired nostrils, used in ventilation when the dugong surfaces every few minutes, are located on top of the head. Valves keep them shut during dives.
The only other species known in the family Dugongidae is Hydrodamalis gigas (Steller’s sea cow), hunted to extinction in 1767, just 36 years after their discovery. They were similar in appearance and color to dugongs but were substantially larger, with a body length of 7 to 10 m and weight between 4,500 and 5,900 kg.
Range mass: 230 to 400 kg.
Range length: 2.4 to 4 m.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike; ornamentation
Madagascar Mangroves Habitat
The endangered Malagasy sacred ibis (Threskiornis bernieri), is found in the Madagascar mangroves ecoregion as well as certain other western coastal Madagascar habitat and the Seychelles. These Madagascar mangroves shelter highly diverse mollusk and crustacean communities, while capturing sediment that threatens coral reefs and seagrass beds. Although up to nine mangrove tree species have been recorded, most of the Madagascar mangrove stands contain six species in four families: Rhizophoracae (Rhizopora mucronata, Bruguiera gymnorrhiza and Ceriops tagal), Avicenniaceae (Avicennia marina), Sonneratiaceae (Sonneratia alba) and Combretaceae (Lumnitzera racemosa).
Some ot the other notable avian associates of the Madagascar mangroves are: the Madagascar Heron (Ardea humbloti, VU), Madagascar Teal (Anas bernieri, EN), Madagascar plover (Charadrius thoracicus, VU), and Madagascar fish eagle (Haliaeetus vociferoides, CR). The Malagasy kingfisher (Alcedo vintsioides) is also thought to occur in these mangroves. This habitat is important for migratory bird species, such as Common ringed plover (Charadrius hiaticula), Crab plover (Dromas ardeola), Gray plover (Charadrius squatarola), African spoonbill (Platalea alba) and Great White Egret (Egretta alba).
A number of mammalian taxa are found in the ecoregion, chiefly lemurs, tenrecs and bats. The sole terrestrial apex mammalian predator of the ecoregion is the Malagasy civet (Fossa fossana), a Madagascar endemic.
Tenrecs occurring in the ecoregion are: Large-eared tenrec (Geogale aurita), the tiniest extant tenrec; Greater hedgehog tenrec found in the Madagascar mangroves, an insectivorous mammal; Lesser hedgehog tenrec (Echinops telfairi); and Tailless tenrec (Tenrec ecaudatus). Each of these tenrecs is endemic to Madagascar, save for the Tailless tenrec, which is also found on Comoros and a few other islands in the region.
Primates found in the Madagascar consist of several lemur species: the Endangered Verreaux's sifaka (Propithecus verreauxi), endemic to western and southwestern Madagascar; the Vulnerable Black lemur (Eulemur macaco); the Vulnerable Red-fronted lemur (Eulemur rufus); the Vulnerable Sambirano Bamboo Lemur (Hapalemur occidentalis); the Endangered Coquerel's Mouse-lemur (Microcebus coquereli), a Madagascar endemic; the Vulnerable Decken's sifaka (Propithecus deckenii), a western Madagascar endemic; Sambirano Woolly Lemur (Avahi unicolor), a northwestern Madagascar endemic; Pale-forked crown lemur (Phaner pallescens), endemic to western Madagascar; Fat-tailed dwarf lemur (Cheirogaleus medius); and Grey mouse lemur (Microcebus murinus).
Bats occurring here are the Near Threatened Malagasy rousette (Rousettus madagascariensis), a cave rooster capable of navigating the airspace of rather dense intact forest; Vulnerable Madagascan fruit bat (Eidolon dupreanum); Near Threatened Commerson's roundleaf bat (Hipposideros commersonii); Near threatened long-fingered bat (Miniopterus schreibersi); Rufous trident bat (Triaenops rufus); Malagasy giant mastiff bat (Otomops madagascariensis), a Madagascar endemic; Malagasy White-bellied Free-tailed Bat (Mops leucostigma), endemic to Madagascar and the Comoros islands of Anjouan and Moheli; Malagasy slit-faced bat (Nycteris madagascariensis), a narrow endemic to the Irodo River Valley in northern Madagascar; Mauritian tomb bat (Taphozous mauritianus); Trouessart's trident bat (Triaenops furculus), endemic to Madagascar and the outer Seychelles atolls; Manavi Long-fingered Bat (Miniopterus manavi), endemic to Madagascar and Comoros; Grandidier's Free-tailed Bat (Chaerephon leucogaster); Robust yellow bat (Scotophilus robustus); Malagasy mouse-eared bat (Suncus madagascariensis); and Malagasy serotine (Neoromicia matroka). Flying foxes found in the ecoregion are: Madagascan flying fox (Pteropus rufus), an important seed disperser who mates whilst hanging upside down.
Other mammals found in the ecoregion are the Madagascan pygmy shrew (Suncus madagascariensis); The only Rodentia member in the ecoregion is the Dormouse tufted-tailed rat (Eliurus myoxinus).
There are a limited number of reptilian taxa found in the Madagascar mangroves: Snake-eyed skink (Cryptoblepharus boutonii); and aquatic apex predator Nile crocodile (Crocodylus niloticus). Some sea turtles, primarily green turtle (Chelonia mydas, EN) and Hawksbill turtle (Eretmochelys imbricata, CR), nest along the western coast within the Madagascar mangroves. The declining species Dugong (Dugong dugong, VU) is also found in the mangroves.
There is only one amphibian species present in the Madagascar mangroves: Mascarene ridged frog (Ptychadena mascareniensis).
There is particularly high diversity among the fish populations in the Madagascar mangroves,the families of which include: Mugelidae, Serranidae, Carangidae, Gerridae, Hemiramphidae, Plectrorhynchidae and Elopidae. The neighboring coral reefs that are associated with the mangroves have also been noted for extremely high fish diversity.
- C.MIchael Hogan & World Wildlife Fund. 2015. Madagascar mangroves. Encyclopedia of Earth. National Council for Science and Environment. Washington DC
- Hughes, R.H. & Hughes, J.S. 1992. A Directory of African Wetlands. UUCN, Gland Switzerland and Cambridge UK/UNEP, Nairobi, Kenya/WCMC, Cambridge, UK. ISBN: 2880329493
Unlike their mostly freshwater cousins, manatees, dugongs are primarily marine mammals. Dugongs generally inhabit shallow waters, remaining at depths of around 10 m, although they occasionally dive to depths of 39 m to feed. These shallow areas are typically located in protected bays, wide mangrove channels and in sheltered areas of inshore islands. Seagrass beds consisting of phanerogamous seagrasses, their primary source of nourishment, coincide with these optimal habitats. Dugongs, however, are also observed in deeper water where the continental shelf is broad, neritic and sheltered. Dugongs use different habitats for different activities. For example, tidal sandbanks and estuaries that are quite shallow, are potential areas suitable for calving. Another example of specialized habitats are lekking areas, which are only used during mating season.
In a study off the coast of Australia, near Darwin, a pair of dugongs was captured in and tracked frequenting rocky reef habitats. Aerial surveys also showed that most dugongs in that region were found associated with a rocky reef. Because habitats of this kind have relatively low spatial coverage, dugongs actively select them. However, it is not known why dugongs frequently seem to forage in these areas, as there is no seagrasses on these reefs and they are not known algae consumers.
Range depth: 0 to 39 m.
Average depth: 10 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: coastal
Other Habitat Features: estuarine
Habitat and Ecology
Water temperature and chemistry ranges based on 17 samples.
Depth range (m): 0 - 0
Temperature range (°C): 26.555 - 28.645
Nitrate (umol/L): 0.016 - 0.422
Salinity (PPS): 34.445 - 35.083
Oxygen (ml/l): 4.539 - 4.709
Phosphate (umol/l): 0.114 - 0.270
Silicate (umol/l): 0.900 - 6.969
Temperature range (°C): 26.555 - 28.645
Nitrate (umol/L): 0.016 - 0.422
Salinity (PPS): 34.445 - 35.083
Oxygen (ml/l): 4.539 - 4.709
Phosphate (umol/l): 0.114 - 0.270
Silicate (umol/l): 0.900 - 6.969
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.
Dugongs are primary consumers and the only completely herbivorous marine mammals. They consume seagrass, particularly of the families Potamogetonaceae and Hydrocharitaceae in the genera Halophila and Halodule. They prefer seagrasses that are low in fiber, high in available nitrogen, and are easily digestible for better nutrient absorption. Their long intestine aids the digestion of seagrass. They also have a low metabolism. When seagrass is scarce, dugongs also eat marine algae. They are speculated to supplement their diet with invertebrates such as polychaete worms, shellfish and sea squirts which live in seagrasses.
Dugongs use their flexible upper lip to rip up entire seagrass plants. If the entire plant cannot be uprooted, they rip off leaves. Their grazing leaves distinctive furrows in the seagrass beds that can be detected from the surface. To be supported properly by their environment for a year, dugongs require a territory with approximately 0.4 ha of seagrass. This area varies with individual and the extent of their movement, the amount of seagrass detected on the sea floor compared to what it actually ingested, the yearly productivities of seagrass, and the rates of re-growth of seagrass.
Animal Foods: aquatic or marine worms; other marine invertebrates
Plant Foods: algae; macroalgae
Primary Diet: herbivore (Folivore , Eats sap or other plant foods)
Dugon adalah konsumen primer dan mamalia laut benar-benar herbivora. Mereka mengkonsumsi lamun, terutama dari keluarga dan Potamogetonaceae Hydrocharitaceae di Halophila marga dan Halodule. Mereka lebih memilih lamun yang rendah serat, tinggi dalam nitrogen yang tersedia, dan mudah dicerna untuk penyerapan nutrisi yang lebih baik. Usus panjang mereka membantu pencernaan lamun. Mereka juga memiliki metabolisme rendah. Ketika padang lamun langka, dugong juga makan ganggang laut. Mereka berspekulasi untuk melengkapi diet mereka dengan invertebrata seperti menyemprotkan polychaete cacing, kerang dan laut yang hidup di lamun.
Dugong menggunakan bibir fleksibel atas mereka untuk merobek-robek seluruh tanaman lamun. Jika seluruh lamun tidak bisa tercabut, mereka akan merobek daun. Sebagai herbivora mereka meninggalkan khas alur-alur di padang lamun yang dapat dideteksi dari permukaan. Harus didukung dengan baik oleh lingkungan mereka selama setahun, duyung membutuhkan suatu wilayah dengan sekitar 0,4 hektar padang lamun. Daerah ini bervariasi dengan individu dan sejauh mana gerakan mereka, jumlah lamun terdeteksi di dasar laut dibandingkan dengan apa yang sebenarnya dicerna, produktivitas tahunan padang lamun, dan tingkat pertumbuhan kembali dari padang lamun. Makanan Hewan: air atau cacing laut; invertebrata laut lainnya. Makanan: ganggang; makroalga dengan diet primer: herbivora (Folivore, Santapan getah atau makanan nabati lainnya).
Intensive grazing of dugongs on seagrass has numerous effects on the ecosystem, both directly on the seagrass and indirectly on other organisms that live in or feed on seagrass. Their grazing contributes to nutrient cycling and energy flow as they stir up sediment. Their fecal matter also acts as a fertilizer, which helps seagrass to more quickly reestablish. However, in the short term, intense grazing reduces habitats and nurseries for important commercial fish species and other invertebrates which live in seagrass.
Ecosystem Impact: biodegradation
Dugongs have very few natural predators. Their massive size, tough skin, dense bone structure, and rapidly clotting blood may aid defenses. Sharks, crocodiles, and killer whales, however, feed on juvenile dugongs. Additionally, dugongs are often killed by humans. The are hunted by some ethnic tribes in Australia and Malaysia, caught in gill and mesh nets set by fishers, struck by boats and ships, and are losing habitat and resources due to anthropogenic activities.
- Sharks Selachimorpha
- crocodiles Crocodyloidea
- killer whales Orcinus orca
- humans Homo sapiens
Life History and Behavior
Dugongs are very social creatures, occurring in mother and calf pairs to herds of 200 individuals. Communication is therefore vital among individuals in this species. The two primary methods of communication this species uses are sound and vision. Much like dolphins, dugongs use chirps, whistles, barks and other sounds that echo underwater in order to communicate. Each sound has its own amplitude and frequency that characterizes the signal, which implies a possible purpose. For example, “chirp-squeaks” have frequencies between 3 and 18 kHz and last for about 60 ms. These "chirp-squeaks" were observed in dugongs foraging on the sea floor for vegetation and when patrolling territories. Barks are used in aggressive behavior and trills in movements that seem to be displays. In order to hear the ranges of sound, dugongs have developed exceptional hearing, which they use more than their sight.
Visual communication is a useful source of communication when dugongs are in close contact. During breeding season, males perform lekking behavior, a physical display in a specific location to draw in females with which to mate. The vision of dugongs, however, is quite poor and they rely on other senses to create a mental map of their surroundings. Dugongs also utilize their sense of smell. They have an elementary olfactory system that allows them to sense chemicals in their environment to a certain degree. This can be used to detect other dugongs, or most likely, for foraging. They can smell aquatic plants and can therefore determine where the next feeding ground should be or where to proceed on their feeding furrow.
Touch is another sense that dugongs use in order to communicate. They have sensatory bristles all over their body, including many on their lip, which help detect vibrations from their surrounds. This allows dugongs to forage more efficiently as they can sense the seagrass against their bristles. This is particularly useful as it complements their poor eyesight. Mothers and calves also engage in physical communication, such as nose touching or nuzzling that strengthens their relationship. Mothers are almost always in physical contact with their calf, the calf either swimming beneath the mother by the fin or riding on top of her. Calve may even on occasion reach out a fin to touch their mother to gain reassurance.
Communication Channels: visual ; tactile ; acoustic
Other Communication Modes: vibrations
Perception Channels: visual ; tactile ; acoustic ; ultrasound ; vibrations ; chemical
Dugongs have lifespans of 70 years or more in the wild, which is estimated by counting the growth layers that make up a dugong’s tusks. However, they are prone to a extensive array of parasites and diseases, some of which are infectious. Dugongs are difficult to keep in captivity due to their specialized diet, which is expensive to provide as the specific type of seagrasses cannot be grown in captivity. Calves are rarely seen in captivity because they suckle for about 18 months after birth. Only one orphaned calf has ever been successfully introduced into captivity in Australia.
Status: wild: 70 years.
Status: wild: 70.0 years.
Status: captivity: 10.0 years.
Status: wild: 55.0 years.
Status: wild: 55.0 years.
Lifespan, longevity, and ageing
The mating behavior of dugongs varies slightly with location. For example, in a mating herd in Moreton Bay, off the coast of Queensland, males take part in aggressive competitions for females in oestrous. In comparison, dugongs in South Cove in Western Australia display a mating behavior similar to lekking. A lek refers to a traditional area where male dugongs gather during mating season to participate in competitive activities and displays that attract females. As these lekking areas lack resources necessary to females, they are drawn to the area only to view the males' displays. Male dugongs defend their territories, and they change their behavioral displays to attract females. After attracting females, male dugongs proceed through several phases in order to copulate. The “following phase” occurs when groups of males follow a single female, attempting to mate with her. The “fighting phase” occurs after, consisting of splashing, tail thrashing, rolls and body lunges. This can be violent, as witnessed by scars observed on the body of females and on competing males from their protruding tusks. The “mounting phase” occurs when a single male mounts a female from underneath, while more males continue to vie for that position. Hence, the female is mounted several times with the competing males, almost guaranteeing conception. Dugongs are thus polyandrous.
Mating System: polyandrous
Female dugongs reach sexual maturity at 6 years of age and may have their first calf between the ages of 6 and 17. Males reach sexual maturity between 6 and 12 years of age. Because breeding occurs year-round, males are always waiting for a female in oestrous. The reproductive rate of dugongs is very low, and they only produce one calf every 2.5 to 7 years depending on location. This may be due to the long gestation period, which is between 13 and 14 months. At birth, calves are about 30 kg in weight, 1.2 m in length, and very vulnerable to predators. Calves nurse for 18 months or longer, during which time they do not stray far from their mother, often riding on their mother's back. Despite the fact that dugong calves can eat seagrasses almost immediately after birth, the suckling period allows them to grow at a much faster rate. Calves mature between 6 and 9 years of age for both genders.n. Once mature, they leave their mothers and seek out potential mates.
Breeding interval: Females dugongs breed every 2.5 to 7 years.
Breeding season: Dugongs mate year round.
Average number of offspring: 1.
Range gestation period: 13 to 15 months.
Range weaning age: 14 to 18 months.
Average time to independence: 7 years.
Range age at sexual or reproductive maturity (female): 6 to 17 years.
Range age at sexual or reproductive maturity (male): 6 to 12 years.
Key Reproductive Features: year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; viviparous
Average birth mass: 27500 g.
Average number of offspring: 1.
Females dugongs invest considerable time and energy in raising calves and are the primary caregivers of their young. Mothers and calfs form a bond which is strengthened throughout the long suckling period of the calf, which is up to 18 months, as well as physical touches that occur during swimming and nursing. Each female spends about 6 years with their calf. During the first 1.5 years, mothers nurse their calf and demonstrate how to feed on seagrasses. The next 4.5 years, or until the calf reaches maturity, are spent feeding together and bonding. In their early years, calves do not travel far from their mother as they are easy prey for sharks, killer whales and crocodiles.
Parental Investment: precocial ; female parental care ; pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); extended period of juvenile learning
Molecular Biology and Genetics
Barcode data: Dugong dugon
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Dugong dugon
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1
Dugongs are listed as a vulnerable on the IUCN Red List, endangered on the US Federal list, and is on Appendix I on CITES. This threatened status is primarily due to human hunting and activities. Dugongs are inadvertently trapped in fish and shark nets and die due to lack of oxygen. They also get struck by boats and ships. Additionally, pollution into the oceans from surrounding land kills seagrass beds and may also negatively influence dugongs directly. Dugongs are also hunted for their meat, oil and other valuable commodities as previously mentioned.
Populations of dugongs are unable to rebound in part because of their very low reproduction rate. If all female dugongs in the population bred at their full potential, the maximum rate the population could increase is 5%. This rate is low even despite their long lifespan and low natural mortality rate from lack of predators.
Some protected sites for dugongs have been established, particularly off the coast of Australia. These areas contain seagrass beds and optimal environments for dugongs, such as shallow water and areas in which to calve. Reports have been made assessing what each country in the dugong range should carry out to preserve and rehabilitate these gentle creatures.
US Federal List: endangered
CITES: appendix i
IUCN Red List of Threatened Species: vulnerable
IUCN Red List Assessment
Red List Category
Red List Criteria
The only reference site is the urban coast of Queensland where the most robust quantitative data on population trends are available and a 40 year time series of catch rates in nets set for bather protection indicates that the CPUE in 1999 was only 3% of that in 1962 (Marsh et al. 2005). This CPUE is considered an index of dugong decline in the region from all causes during this period. This decline and modern aerial survey estimates of dugong abundance were used to backcast the population in the region in the early 1960s (which would be expected to have been lower than that at the time of European settlement as a cottage commercial industry for dugong oil had existed at several locations along this coast since the 1850s. The extrapolation suggested that the region supported 72,000 (95% CI 31,000, 165,000) dugongs in the early 1960s compared with an estimated 4,220 (95% CI 2,360, 8,360) dugongs in the mid 1990s. The seagrass habitat in the region is currently insufficient to support 72,000 dugongs, a result which suggests that the habitat had also declined (unlikely) or that the shark net CPUE has overestimated the decline (see Marsh et al. 2005). If the magnitude of this decline was robust and typical of the entire range of the dugong, the dugong would qualify for being classified as Critically Endangered at a global scale.
As summarized in Table 2.1, the major causes of the dugong’s decline along the urban coast of Queensland are still present in most of the dugong’s range as follows: gill netting 87-99%, subsistence hunting 85-98%, human settlement 82-85%, agricultural pollution 80-89%. The magnitude of these threats is likely to be greater in most other parts of the dugong’s range than in Queensland. The Queensland coast supports a low human population density relative to most other parts of the dugong’s range and has a well developed system of marine parks and pro-active management. There is also anecdotal evidence that the area of occupancy of the dugong has declined in many parts of its range, especially along the coasts of east African and India where anecdotal evidence suggests that it is at high risk of extinction.
Even in the regions where we have classified the status of the dugong as stable, this classification is unconfirmed. Much of the northern Western Australian and some of the Northern Territory coast has never been surveyed for dugongs and there are no accurate estimates of the Indigenous harvest. The sustainability of this harvest must be questioned as it has been shown to be unsustainable by population modeling in remote parts of Queensland and Torres Strait (Heinsohn et al. 2004, Marsh et al. 2004).
Genetic information on dugong stocks is limited. Recent work based on mitochondrial DNA and microsatellite markers (Brenda McDonald, unpublished data) indicates that the Australian dugong population is not panmictic. There is clear evidence of two maternal lineages, which have a geographical basis apparently reflecting the existence of the Torres Strait land bridge between Australia and PNG, despite the flooding of this land bridge some six thousand years ago. The Australian dugong population still has a fair degree of genetic diversity indicating that recent losses are not yet reflected in the genetic makeup of the population. There is some evidence of gene flow between dugongs in Australia and Eastern Indonesia.
To date, there has been little effective management intervention to reduce anthropogenic impacts on the dugong, apart from legislative protection which is almost ubiquitous throughout its range. Management plans have been developed for some 22-24% of the range (mainly in Australia) but are in place in only 18-22% of the range. The dugong is protected by marine protected areas in 22-23% of its range (again mostly in Australia) (see Table 1.3 in attached PDF).
Because of the uncertainty associated with the assessment of the status of the dugong both on the Queensland coast based on the CPUE data (Marsh et al. 2005) and the rest of its range, we suggest that the classification should remain as Vulnerable A2bcd.
Follow the link below to see the tables referred to in the text.
- 2006Vulnerable(IUCN 2006)
- 1994Vulnerable(Groombridge 1994)
- 1990Vulnerable(IUCN 1990)
- 1988Vulnerable(IUCN Conservation Monitoring Centre 1988)
- 1986Vulnerable(IUCN Conservation Monitoring Centre 1986)
- 1982Vulnerable(Thornback and Jenkins 1982)
Date Listed: 12/02/1970
Lead Region: Foreign (Region 10)
Where Listed: except Palau
Date Listed: 12/02/1970
Lead Region: Foreign (Region 10)
Where Listed: in Palau
Population location: Entire, except Palau
Listing status: E
Population location: Palau
Listing status: E
For most current information and documents related to the conservation status and management of Dugong dugon , see its USFWS Species Profile
Status in Egypt
Numbers low or very low, but unknown whether there is a sustainable population in Egypt.
Relevance to Humans and Ecosystems
There are no known adverse effects of dugongs on humans.
Dugongs are economically valuable while alive as a form of ecotourism. Activities such as dugong-watching cruises in Australia and swimming with dugongs in the Philippines and Vanuatu help local economies. Dugongs are also hunted for a variety of reasons. In Malaysia, dugongs are eaten opportunistically when incidentally caught in fishing nets or traps and when incidentally or purposely caught when fish bombing, a method of fishing which involves throwing a bomb into the water. Dugongs killed in these circumstances are usually consumed locally or sold to neighboring islands for a good price, as the meat is considered a delicacy. One dugong apparently sold for $105 USD, which could stimulate local economy. In Australia, some native people regard hunting the dugong an integral part of their traditions. Humans eat their meat and use their oil. Dugong tusks are also used as a treatment for a variety of ailments including asthma, back pain, and shock. Tusks are also made into amulets and, in powdered form, mixed to make a drink. Smoking pipes can be carved from the tusks and the emitted smoke is said to have medicinal properties. Dugongs provide a thriving trade between villages and islands, although trafficking dugong parts is illegal.
Positive Impacts: food ; body parts are source of valuable material; ecotourism ; source of medicine or drug
The dugong (//, //; Dugong dugon) is a medium-sized marine mammal. It is one of four living species of the order Sirenia, which also includes three species of manatees. It is the only living representative of the once-diverse family Dugongidae; its closest modern relative, Steller's sea cow (Hydrodamalis gigas), was hunted to extinction in the 18th century. The dugong is the only strictly marine herbivorous mammal, as all species of manatee use fresh water to some degree.
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 meadows, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as bays, mangrove channels, the waters of large inshore islands and inter-reefal waters. The northern waters of Australia between Shark Bay and Moreton Bay are believed to be the dugong's contemporary stronghold.
Like all modern sirenians, the dugong has a fusiform body with no dorsal fin or hind limbs. The forelimbs or flippers are paddle-like . The dugong is easily 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. 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 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 degradtion and hunting. With its long lifespan of 70 years or more, and slow rate of reproduction, the dugong is especially vulnerable to extinction.
- 1 Etymology and taxonomy
- 2 Anatomy and morphology
- 3 Distribution and habitat
- 4 Ecology and life history
- 5 Importance to humans
- 6 Conservation
- 7 Gallery
- 8 References
- 9 External links
Etymology and taxonomy
The word "dugong" derives from the Tagalog term dugong which was in turn adopted from the Malay duyung, both meaning "lady of the sea". Other common local names include "sea cow", "sea pig" and "sea camel".
Dugong dugon is the only extant species of the family Dugongidae, and one of only four extant species of the Sirenia order, the others forming the manatee family. It was first classified by Müller in 1776 as Trichechus dugon, a member of the manatee genus previously defined by Linnaeus. It was later assigned as the type species of Dugong by Lacépède and further classified within its own family by Gray and subfamily by Simpson.
Dugongs and other sirenians are not closely related to other marine mammals, being more related to elephants. Dugongs and elephants share a monophyletic group with hyraxes and the aardvark, one of the earliest offshoots of eutherians. The fossil record shows sirenians appearing in the Eocene, 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, 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. 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.
There are claims mentioning that several subspecies such as in Okinawan waters exist either historically or presently.
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 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 interpretation of their environment. These hairs are most developed around the mouth, which has a large horseshoe shaped upper lip forming a highly mobile muzzle. This muscular upper lip aids the dugong in foraging.
The dugong's tail flukes and flippers are similar to those of dolphins. These flukes are raised up and down in long strokes to move the animal forward, and can be twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing. The dugong lacks nails on its flippers, which are only 15% of a dugong's body length. The tail has deep notches.
A dugong's brain weighs a maximum of 300 g (11 oz), about 0.1% of the animal's body weight. With very small eyes, dugongs have limited vision, but acute hearing within narrow sound thresholds. Their ears, which lack pinna, 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 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 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 wounded, a dugong's 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. 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 126.96.36.199, meaning they have two incisors, three premolars, and three molars on each side of their upper jaw, and three incisors, one canine, three premolars, and three molars on each side of their lower jaw. Like other sirenians, the dugong experiences pachyostosis, a condition in which the ribs and other long bones are unusually solid and contain little or no marrow. These heavy bones, which are among the densest in the animal kingdom, may act as a ballast to help keep sirenians suspended slightly below the water's surface.
An adult's length rarely exceeds 3 metres (9.8 ft). An individual this long is expected to weigh around 420 kilograms (926 lb). Weight in adults is typically more than 250 kilograms (551 lb) and less than 900 kilograms (1,984 lb). The largest individual recorded was 4.06 metres (13.32 ft) long and weighed 1,016 kilograms (2,240 lb), and was found off the Saurashtra coast of west India. Females tend to be larger than males.
Distribution and habitat
Dugongs are found in warm coastal waters from the western Pacific Ocean to the eastern coast of Africa, along an estimated 140,000 kilometres (86,992 mi) of coastline between 26° and 27° degrees to the north and south of the equator. Their historic range is believed to correspond to that of seagrasses from the Potamogetonaceae and Hydrocharitaceae families. The full size of the former range is unknown, although it is believed that the current populations represent the historical limits of the range, which is highly fractured. The dugong is the only strictly-marine herbivorous mammal, as all species of manatee utilise fresh water to some degree. 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 per cent 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. Large numbers also exist in wide and shallow mangrove channels and around leeward sides of large inshore islands, where seagrass beds are common. They are usually located at a depth of around 10 m (33 ft), although in areas where the continental shelf remains shallow dugongs have been known to travel more than 10 kilometres (6 mi) from the shore, descending to as far as 37 metres (121 ft), where deepwater seagrasses 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, minimising the risk of predation. Deep waters may provide a thermal refuge from cooler waters closer to the shore during winter.
The Middle-East and Africa
Populations of dugongs exist in the water of 37 countries and territories. 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 the home of 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. 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 be around 7,500. In Mozambique, most of local populations remaining are rather very small where the largest (about 120 individuals) occur at Bazaruto Island, but they have become rare in historical habitats such as in Maputo Bay and on Inhaca Island.
Northern Indian Ocean
A highly isolated breeding population exists in the Marine National Park, Gulf of Kutch, the only population remaining in western India. It is 1,500 kilometres (932 mi) from the population in the Persian Gulf, and 1,700 kilometres (1,056 mi) from the nearest population in India. Former populations in this area, centred 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. Dugongs are also found in the Andaman and Nicobar Islands and is the state animal of this territory. Once distributed throughout the coastal belt in Sri Lanka, the dugong number declined in last two decades due to heavy hunting by the fishermen. Now only the north-eastern coastal belt is home for the rest of dugong population around Sri Lanka.
It is listed as an endangered species on the southern coast of Pakistan.
Continental China, Vietnam, and Cambodia
A very small remnant population still exists today along the coast from Guangdong, Leizhou Peninsula, and Hainan Island, to the Gulf of Tonkin. Today, dugongs off southern China are centred on Hainan Province, excluding the west coast of the island of Hainan. The Chinese government has funded a sanctuary for dugong and mangrove conservation ranging from Hepu County to Shankou in Guanxi, also aiming to secure local Chinese White Dolphins. 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 had been hosts to large numbers in the past. On Phu Quoc, the first 'Dugong Festival' was held in 2014, and there have been several land-based observations on Côn Đảo in recent years as well. The Côn Đảo National Park in Vũng Tàu has been declared as a suitable site to observe them. Nonetheless, dangerously low levels of awarenesses for 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.
Japan, Taiwan, and the Philippines
Today, possibly the smallest and northernmost population of dugongs exists around the Nansei Shoto islands, and a population formerly existed off Taiwan. An endangered population of 50 or fewer dugongs, possibly as few as only three individuals, survives. around Okinawa.
Historically, the Yaeyama Islands held the largest concentration of dugongs, with more than 300 individuals. On Aragusuku Island, large quantities of skulls are preserved at an utaki that outsiders are strictly forbidden to enter. Amami Oshima was the northernmost edge of the historic range, where a single animal was confirmed in the 2000s, over 40 years after the last previous records. A vagrant strayed into port near Ushibuka, Kumamoto, and died due to poor health. Dugongs in these areas were literally wiped out by historical hunts as payments to the Ryukyu Kingdom and devastating mass illegal hunts and fisheries used dynamite to destroy whole coral systems after the World Wars. There have been two theories about the biological origins of this population. One is that these stocks had been isolated and were an endemic Philippine subspecies. This, however, is contrary to the idea of "the only method to restore the Okinawan population is to wait until vagrants from the Philippines stray into and re-colonize the areas".[clarification needed] The other is that one super-population constantly migrates or mixes throughout the range of the Ryukyu Archipelago, Taiwan, and the Philippines.
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 with the largest population vicinity to Palawan. All the islands of the Philippines are believed to have once provided habitats for dugongs, which were common until the 1970s. Taiwanese populations seem to be almost extinct, although remnant individuals may visit areas with rich seagrass beds such as Dongsha Atoll.
It is unclear whether populations in these areas once consisted a super-population or underwent constant mixing. There are occasional records of vagrants at the Northern Mariana Islands as well.
South Asia and South Pacific
The Gulf of Thailand also used to have a large population, but they have not recently been sighted in the west of the gulf, and the population in the east is thought to be very small. 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. Populations exists around the Solomon Islands archipelago and New Caledonia, stretching to a westernmost population in Vanuatu. A highly isolated population lives around the islands of Palau.
Australia is home to the largest population, stretching from Shark Bay 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 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.
Extinct Mediterranean population
It has been confirmed that dugongs once inhabited the water of the Mediterranean possibly until after the rise of civilizations along the inland sea. This population possibly shared ancestry with the Red Sea population, and the Mediterranean population had never been large due to geographical factors and climate changes. The Mediterranean is the region where the Dugongidae originated in the mid-late Eocene, along with 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 behaviour. 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 39 metres (128 ft); they spend most of their lives no deeper than 10 metres (33 ft). 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 travelling 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 localised 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 15 kilometres (9.3 mi) up a creek near Cooktown.
Dugongs, along with other sirenians, are referred to as "sea cows" because their diet consists mainly of sea-grass. When eating they ingest the whole plant, including the roots, although when this is impossible they will feed on just the leaves. A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass is scarce. Although almost completely herbivorous, they will occasionally eat invertebrates such as jellyfish, sea squirts, and shellfish. Dugongs in Moreton Bay, Australia, are omnivorous, feeding on invertebrates such as polychaetes or marine algae when the supply of their choice grasses decreases. In other southern areas of both western and eastern Australia, there is evidence that dugongs actively seek out large invertebrates. This does not apply to dugongs in tropical areas, in which faecal evidence indicates that invertebrates are not eaten.
Most dugongs do not feed from 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 fibre, high in nitrogen, and easily digestible. In the Great Barrier Reef, dugongs feed on low-fibre high-nitrogen seagrass such as Halophila and Halodule, 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 specialised diet. There is evidence that dugongs actively alter seagrass species compositions at local levels. Dugongs may search out deeper seagrass. Feeding trails have been observed as deep as 33 metres (108 ft), and dugongs have been seen feeding as deep as 37 metres (121 ft). Dugongs are relatively slow moving, swimming at around 10 kilometres per hour (6.2 mph). When moving along the seabed to feed they walk on their pectoral fins.
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 heat 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 13–15 month gestation, usually to just one calf. Birth occurs in very shallow water, with occasions known where the mothers were almost on the shore. As soon as the young is born the mother pushes it to the surface to take a breath. Newborns are already 1.2 metres (4 ft) long and weigh around 30 kilograms (66 lb). 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.
Importance to humans
Dugongs have historically provided easy targets for hunters, who killed them for their meat, oil, skin, and bones. 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 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. During the Renaissance and the Baroque eras, dugongs were often exhibited in wunderkammers. They were also presented as Fiji mermaids in sideshows.
Dugong meat and oil have traditionally been some of the most valuable foods of Australian aborigines and Torres Strait Islanders. Some aborigines regard dugongs as part of their Aboriginality. 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 to people in India, and its meat is believed to be an aphrodisiac. Dugong ribs were used to make carvings in Japan. In Southern China dugongs were traditionally regarded as a "miraculous fish", and it was bad luck to catch them. A wave of immigration beginning at the end of the 1950s resulted in dugongs being hunted for food. In the Philippines dugongs are thought to bring bad luck, and parts of them are used to ward against evil spirits. In areas of Thailand it is believed that the dugong's tears form a powerful love potion, while in parts of Indonesia they are considered reincarnations of women. In Papua New Guinea they are seen as a symbol of strength.
Dugong numbers have decreased in recent times. For a population to remain stable, 95 per cent 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. 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 for endangered species. Mozambique has had legislation to protect dugongs since 1955, but this has not been effectively enforced. 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. India 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 is 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. 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.
In Viet Nam, an illegal network targeting dugongs had been detected and was shut down in 2012.
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 effects remain undocumented. It has been seen to cause issues in areas such as Hainan due to environmental degradation. Modern farming practise and increased land clearing have also had an impact, and much of the coastline of dugong habitats is undergoing industrialisation, 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. Socio-political needs are an impediment to dugong conservation in many developing countries. The shallow waters are often used as a source of food and income, problems exacerbated by aid used to improve fishing. In many countries, legislation does not exist to protect dugongs, and if it does it is not enforced.
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. 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.
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 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 and prevents light from reaching it. This is the most significant negative factor affecting seagrass.
One of the dugong's preferred species of seagrass, Halophila ovalis, 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.
Current imminent threat to the habitat is the case of Oura bay area in Henoko, Okinawa, Japan, where a small population of dugong inhabit. Despite it being the northern limit of Dugong, their habitat is about to be destroyed by land reclamation conducted by Japanese Government in order to build a US Marine base in the ocean. In August 2014, preliminary drilling surveys are being conducted in the grazing habitat. It is expected to seriously damage the dugong population's habitat, leading them into local extinction.
Capture and captivity
The Australian state of Queensland has sixteen dugong protection parks, and some preservation zones have been established where even aborigines 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 five dugongs are held in captivity. A female from the Philippines lives at Toba Aquarium in Toba, Mie, Japan. A male also lived there until it died on 10 February 2011. Another is at Underwater World, Singapore, due to its mother being killed when it was a calf. A third resides in Sea World Indonesia, after having been rescued from a fisherman's net and treated. The last two, a male and a female, are kept at Sydney Aquarium, where they have resided since they were juveniles.
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