50.
Dugong
(Dugong dugon)
VU
Overview
Dugongs are more closely related to elephants than to marine mammals such as whales and dolphins. They are sometimes referred to as “sea cows” in reference to the fact that they feed almost exclusively on sea grass. Dugongs have long been associated with myths and legends - the Ark of the Covenant was reputedly protected by dugong hide, and early sightings of the species by lonely sailors are believed to have led to the legend of the mermaids. Although commercial hunting of dugongs is now banned, the species may still be at risk from traditional hunting and the destruction of sea grass beds by human activities.
Urgent Conservation Actions
Creation of additional protected areas, identification of main threats and measures to minimise human impact on the species.
Distribution
Found throughout the Indo-Pacific region, from the east coast of Africa to Vanuatu in the western Pacific.
Associated Blog Posts
1st Aug 11
This ever smiling creature may have once inspired mermaid myths. Dugongs are surprisingly more closely related to elephants than to other marine mammals such...  Read

Media from ARKive
ARKive image - Adult female dugong with calf
ARKive video - Dugong - overview
ARKive video - Dugong swimming to water's surface to breathe
ARKive image - Adult female dugong swimming with calf
ARKive video - Dugongs swimming
ARKive image - Dugong feeding
ARKive image - Dugong swimming
ARKive video - Dugong herd swimming
ARKive image - Dugong
ARKive video - Dugong herd swimming with calf
ARKive video - Dugong feeding
ARKive image - Dugong, eye detail
ARKive image - Lower mouth of dugong, showing large bristly hairs
ARKive video - Large herd of Dugong feeding
ARKive image - Dugong surfacing to breathe
ARKive image - Dugong coming to surface to breath
ARKive image - Dugong scratching back
ARKive image - Dugong with remoras
ARKive image - Dugong attempting to dislodge remoras by twisting body
ARKive image - Dugong opening mouth, possibly an aggressive display
Evolutionary Distinctiveness
Order: Sirenia
Family: Dugongidae
Dugongs are more closely related to elephants than to marine mammals such as whales and dolphins. They belong to an ancient radiation of African mammals known as the Afrotheria. This superorder includes seven groups of animals thought to have shared a common ancestor around 100 million years ago. These animals have little superficial resemblance to each other. Together with the sirenians and elephants, this group also includes the aardvark, hyraxes, sengis (or elephant-shrews), golden moles and tenrecs.

Sirenians are conventionally divided into four families: two, the Prorastomidae and the Protosirenidae, are extinct and known only from the Eocene, while the Dugongidae (dugongs, including Steller’s sea cow) and Trichechidae (manatees) survive today.

The fossil record of the Sirenia extends over 50 million years. The sirenians are thought to have branched off from the Proboscidea (elephants) during the Palaeocene, and quickly dispersed to the New World. The earliest known representative of the group was a pig-sized prorastomid from Jamaica from the early Eocene. This four-legged animal could walk on land, but probably spent much of its time in water. It had an extremely dense skeleton, which acted like ballast to keep the animal submerged in shallow waters. By the middle Eocene, protosirenid sea cows were abundant in North America, Europe and Asia. While the early sirenians had narrow snouts that suggested selective browsing, the muzzles had by this time broadened and became more downturned to ‘mow’ the carpets of seagrass on the ocean floor. The Dugongidae first appeared in the mid-late Eocene of the Mediterranean region. It was among these forms that the loss of the functional hind limbs took place. The manatees (Trichechidae) are the dugong’s closest living relatives. They are thought to have diverged from the Dugongidae at some time between the late Eocene and mid Oligocene.

Until a few hundred years ago the dugong’s closest relative was Steller’s sea cow (Hydrodamalis gigas), which formerly occurred around the Commander Islands in the northern Pacific. It was hunted to extinction within 27 years of its discovery in the eighteenth century. It grew almost three times as long as the dugong and fed on large algae (kelp).
Description
Size: 
Total length: 240-270 cm
Weight: 230-360 kg
Dugongs are large, torpedo-shaped marine mammals that have paddle-like forelimbs and a fluke-like tail used for propulsion. Their tough skin is usually a dull brownish-grey colour above and lighter below. The skin is thick and relatively smooth, and is sparsely covered with short, coarse hairs. The species has a distinctive rounded snout, with a large, muscular upper lip that hangs over the small, downwardly-opening mouth. There are stiff bristles on either side of the mouth. There is little sexual dimorphism, although females may grow to a larger average size than do males. Mature males grow tusks that are used in social interactions. Tusks are occasionally also present in older females. Dugongs and manatees are the only herbivorous marine mammals living today. They can be easily distinguished by their tail morphology, which is fluked and whale-like in the dugong and more rounded in the manatee.
Ecology
Dugongs are also called “sea cows” in reference to the fact that they feed almost exclusively on sea grass. Marine algae may also be eaten, although this is believed to occur only when sea grass is scarce. Long distance migration is unknown, although some individuals have been recorded swimming up to 600 km at certain times of year. Activity patterns are thought to be determined by tidal movements, with animals resting in areas of deeper water until it is possible to move towards the shore to feed in the shallow sea grass beds. Most feeding takes place at depths of 1-5 m. Dugongs have a low metabolism and tend to move relatively slowly. The average swimming speed is around 10 km per hour. Unlike most other marine mammals they cannot hold their breaths for long periods of time; most dives last around 1-3 minutes. There are historical reports of dugongs gathering in herds numbering thousands of individuals. Although they are less abundant today, they are still occasionally seen in groups of a hundred or more when food is plentiful. More often they are seen alone or in pairs. Breeding appears to occur throughout the year, with peak months for births varying geographically. The gestation period is around 13-14 months, after which time females give birth to a single calf (twins are rare). Newborns are 100-120 cm long and weigh 20-35 kg. They are born in shallow water and surface almost immediately to take their first breath. The calves begin to graze within three months of birth, although lactation commonly lasts a further 11-15 months. Sexual maturity attained by both males and females as early as 6 years but may be delayed until 17 years. The interbirth interval varies, but is generally thought to be around 3-7 years. Due to their large size, dugongs have very few natural predators (other than sharks). They have been known to live for more than 70 years in the wild.
Habitat
Occurs in the shallow coastal waters of tropical seas, where there is an abundance of sea grass. It is also regularly observed in deeper offshore waters in areas where the continental shelf is wide, shallow and protected. The species is more strictly marine than manatees and is seldom found in freshwater.
Distribution
Relict populations of the species survive in coastal waters throughout the Indo-Pacific region, from the east coast of Africa to Vanuatu in the western Pacific, between latitudes of about 27° north and south of the Equator. Today, most dugongs are found in northern Australian waters between Shark Bay in Western Australia and Moreton Bay in Queensland.
Population Estimate
The total number in Australian waters may exceed 80,000 and is probably more than half the world’s total. The second largest distribution, around 7,000 individuals, is in the Persian Gulf.
Population Trend
Although it is difficult to monitor dugong populations, anecdotal evidence indicates that numbers are declining in most parts of its range.
Status
Classified as Vulnerable (VU A2bcd) on the 2010 IUCN Red List of Threatened Species.
Threats
The species has been traditionally hunted throughout much of its range for its meat, hide, oil and bones. Although commercial hunting is now banned, dugong products from indirect takes are still highly valued, and traditional hunting of the species by the indigenous peoples of Australia and the western islands of the Torres Strait continues. The species’ large size, slow swimming speed and dependence on coastal habitats make them easy targets for hunters. Researchers fear that due to other factors this traditional harvesting of the species is no longer sustainable. Habitat loss and degradation is thought to be a major threat. High levels of human population growth and rapid rates of industrialisation are occurring throughout much of the dugong’s range. Sea grass ecosystems are very sensitive to human activity and may be destroyed directly by mining or trawling, or lost as a result of dredging, land clearing and land reclamation. These activities cause increases in sedimentation and turbidity, which blocks out light and smothers the plants. Accidental entanglement in gill or mesh nets or traps set by fishermen is an indirect cause of dugong mortality. Since dugongs cannot hold their breath for long periods of time, many drown as a result of entanglement in these nets. Factors such as pollution, vessel strikes and disease may also threaten dugong populations, although their effect has yet to be quantified. The species’ life history makes it particularly vulnerable to these threats. Dugongs are long-lived with a low reproductive rate, long generation time, and a high investment in each offspring. Even under ideal conditions, simulations have predicted that dugong numbers will not rise by more than about 5% per year. A slight reduction in adult survivorship can cause a population to crash.
Conservation Underway
The species is listed on Appendix I of the Conservation of International Trade in Endangered Species (CITES), and on Appendix II of the Convention on Migratory Species (the CMS or Bonn Convention). Dugongs are found within the Great Barrier Reef World Heritage Area, and in 1997 a system of 16 Dugong Protection Areas was established here to protect key populations and sea grass beds. Indigenous communities in Australia and the Torres Strait islands are working with the Australian government to improve the sustainability of the indigenous harvest of dugongs. This has led to a voluntary cessation of hunting in some areas. There is ongoing research into the distribution and behaviour of the species.
Projects

The conservation and management of many marine mammal populations relies on accurate and precise estimates of their abundance and distribution using aerial surveys. We aim to test whether Unmanned Aerial Vehicles (UAVs) can replace manned aircraft to (1) reduce costs, (2) reduced human risk, (3) deliver superior data on detection, location, abundance and identification of marine mammal species. This project aims to (1) develop and test technology and techniques for UAV surveys and (2) conduct and compare traditional manned and UAV surveys of dugongs and humpback whales to test the viability of UAV surveys.

This project encompasses dugong research and conservation efforts across the island nations of Comoros, Madagascar and Mauritius in the western Indian Ocean.

We are working with partners to trial innovative means of sustaining community-based conservation initiatives through providing access to health, education and microfinance in return for  conservation actions.

This project works with the University of the Philippines, Western Palawan University, fishers associations, local government, community groups and tour and dive operators to research and conserve dugongs in Palawan, their last stronghold in the country.

Conservation Proposed
Habitat conservation is a critical issue since dugongs delay breeding when they do not have enough food. The most urgent task is to determine the distribution and relative abundance of dugongs in each part of its range. A 2002 dugong action plan recommends that areas that still support significant areas of dugongs should be identified and protected, and that conservationists should work with local people to identify the major causes of dugong mortality and minimise human impacts on the species. Ideally this should be done in the context of comprehensive plans for coastal zone management, perhaps using the dugong as a flagship species.
Associated EDGE Community members

Anouk has been carrying out cetaceans surveys since 1985

Amanda is a marine biologist

Patricia is the Director of C3 and leads the organisation's dugong research.

Links
Sirenews
This is the newsletter for the IUCN/SSC Sirenia Specialist Group highlighting conservation efforts for this species.
References
ARKive. (Jan 2006).

Marsh, H. 2008.Dugong dugon. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. www.iucnredlist.org. Downloaded on 14 November 2010.

Domning, D. P. 1999. Fossils Explained 24: Sirenians (seacows). Geology Today. Mar-Apr: 75-79.

Marsh, H. (Compiler). 2002. Dugong Status Report and Action Plans for Countries and Territories. UNEP/DEWA/RS.02-1.

Nowak, R.M. 1999. Walker's Mammals of the World. Sixth edition. The Johns Hopkins University Press, Baltimore and London.

Distribution map based on data provided by the IUCN Global Mammal Assessment

if you can provide new information to update this species account or to correct any errors, please email us at info@edgeofexistence.org


Forum comments
  1. Anonymous
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    was this page peer-viewed?

    Posted 5 years ago #

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