DUGONG

The 'dugong' (''Dugong dugon'') is a large marine mammal which, together with the three species of manatee, is one of four extant members of the order Sirenia, the only fully-aquatic herbivorous mammals. 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. It is also the only sirenian in its range, which spans the waters of at least 37 countries throughout the Indo-Pacific, Marsh et al. 2002. Dugong : status reports and action plans for countries and territories. IUCN. though the majority of dugongs live in the northern waters of Australia between Shark Bay and Moreton Bay. Lawler et al. 2002. Dugongs in the Great Barrier Reef : Current State of Knowledge. CRC for The Great Barrier Reef World Heritage Area. In addition, the dugong is the only strictly-marine herbivorous mammal, as all species of manatee utilize fresh water to some degree.
Like all modern sirenians, the dugong has a fusiform body with no dorsal fin or hindlimbs, instead possessing paddle-like forelimbs used to maneuver itself. It is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth.Myers, P. 2002. Dugongidae. University of Michigan Museum of Zoology. Retrieved on 10 March 2007. The dugong is heavily dependent on seagrasses for subsistence and is thus restricted to the coastal habitats where they grow, with the largest dugong concentrations typically occurring in wide, shallow, protected areas such as bays, mangrove channels and the lee sides of large inshore islands. Its snout is sharply downturned, an adaptation for grazing and uprooting benthic seagrasses.
The dugong has been hunted for thousands of years, often for its meat and oil,Marsh, Helene. ''Fauna of Australia: Volume 1B Mammalia: Chapter 57 Dugongidae.'' CSIRO. ISBN 978-0-644-06056-1. although dugong hunting also has great cultural significance throughout its range. ''Species DUGONG.'' Conservation Management Institute. The dugong's current distribution is reduced and disjunct, and many populations are 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 based on the population involved. Despite being legally protected in many countries throughout their range, the main causes of population decline remain anthropogenic, and include hunting, habitat degradation, and fishing-related fatalities.Reeves et al. 2002. ''National Audubon Society Guide to Marine Mammals of the World''. Knopf. ISBN 0-375-41141-0. pp. 478-481 With its long lifespan and slow rate of reproduction, the dugong is especially vulnerable to these types of exploitation. In addition, dugongs are threatened by storms, parasites, and their natural predators, sharks, Killer Whales, and crocodiles.

Contents

Etymology and taxonomy

Anatomy and morphology

Distribution

Ecology and life history

Feeding

Migration

Importance to humans

Ancient interaction

In the Bible

Dugong in captivity

Conservation

See also

References

External links

Etymology and taxonomy

The dugong was first classified by Müller in 1776 as ''Trichechus dugon'',Dugong dugon. The Paleobiology Database. Retrieved on 22 July 2007. a member of the manatee genus previously defined by Linnaeus.Trichechus. The Paleobiology Database. Retrieved on 22 July 2007. It was later assigned as the type species of ''Dugong'' by LacépèdeDugong. The Paleobiology Database. Retrieved on 22 July 2007. and further classified within its own family by GrayDugongidae. The Paleobiology Database. Retrieved on 22 July 2007. and subfamily by Simpson.Dugonginae. The Paleobiology Database. Retrieved on 22 July 2007.
The word "dugong" derives from the Malay "duyung" meaning "lady of the sea".Winger, Jennifer. 2000. What's in a Name: Manatees and Dugongs. Smithsonian National Zoological Park. Retrieved on 22 July 2007. Other common local names include "sea cow", "sea pig" and "sea camel".

Anatomy and morphology

Dugong with attached remora (Lamen Island, Epi, Vanuatu).

The dugong's body is large and fusiform, with thick, smooth skin that is a pale cream color at birth but darkens dorsally and laterally to a brownish to dark grey color with age.^[1] The body is sparsely covered in short hair, a common feature among sirenians which may allow for tactile interpretation of their environment.^[2] The dugong has paddle-like forelimbs which aid in movement and feeding, while its fluked tail provides locomotion through vertical movement. The teats are located just behind the forelimbs, similar to their location in elephants. Like the Amazonian Manatee, the dugong lacks nails on its forelimbs.
Unlike the manatees, the dugong's teeth do not continually grow back via horizontal tooth replacement.Self-Sullivan, Caryn. Evolution of Sirenia. www.sirenian.org. Retrieved on 10 March 2007. The dugong has two incisors (tusks) which grow posteriorly until puberty, after which they first erupt in males. The female's tusks continue to grow posteriorly, sometimes erupting later in life after reaching the base of the premaxilla.Marsh, Helene. ''Fauna of Australia: Volume 1B Mammalia: Chapter 57 Dugongidae.'' CSIRO. ISBN 978-0-644-06056-1.
Like other sirenians, the dugong experiences pachyostosis, a condition in which the ribs and other long bones are unusually solid and contain little or no marrow. These heavy bones, which are among the densest in the animal kingdom,Waller et al. 1996. ''Sealife: A Complete Guide to the Marine Environment''. Smithsonian Institution. ISBN 1560986336. pp. 413-420 may act as a ballast to help keep sirenians suspended slightly below the water's surface.^[3]
Dugongs are generally smaller than manatees (with the exception of the Amazonian Manatee), reaching an average adult length of 2.7 metres (8.9 ft) and weight of 250 to 300 kilograms (550 to 660 lb). ''Dugong''. IFAW. Retrieved on 25 February 2007. An adult's length rarely exceeds 3 m, and females tend to be larger than males.

Distribution

Typical dugong Feeding area in Moreton Bay

Passage to the warmer sea around the southern tip of Moreton Island

Remaining populations of dugong are greatly reduced, although they once covered all of the tropical South Pacific and Indian Oceans. Their historic range is believed to correspond to that of certain seagrasses. Groups of 10,000 or more are present on the Great Barrier Reef of Australia, at Shark Bay, and in Torres Strait south of New Guinea. Before 1970, it is thought that large populations were also present in Mozambique and coastal Kenya, but these have dwindled. Palau also has a small population. On January 22, 2003, an individual was found (weight 300 kg, length 2 m) off the coast of Tanzania.
Moreton Bay in Brisbane, Australia is one of many homes to the dugong because it contains clean, clear water at the appropriate depth ranges, suitable food, and access to the sea for warmth. Although strong tidal currents affect the exact times and durations of each visit to the bay, the dugong return for protection from large sharks. This area is very important to the future of the dugong - it is a 200 km stretch of high density human habitation and recreation, with ease of access to study and learn how to best protect the remaining herds.
A small number of dugongs are also found in the Straits of Johor, (which separates Johor in Malaysia and Singapore), in the Philippine provinces of Palawan, Romblon, Guimaras, and Davao Oriental, and in the Red Sea in Egypt provinces Marsa Alam at Marsa Abu Dabbab.
The remaining dugongs in the Persian Gulf were reportedly further endangered by repeated U.S.-Iraq conflicts which resulted in large oil spills into the gulf. The current population of Persian Gulf dugongs is around 7500 ^[4], but their status is currently not well known.

Ecology and life history

Feeding

Dugongs are particular about their diets, with certain 'fields' of sea-grass cropped. Dugongs are referred to as 'sea cows' because their diet consists mainly of sea-grass. Unlike manatees, dugongs are exclusively benthic feeders. The muscular snouts of dugongs are more dramatically tapered than those of manatees. Their primary feeding mechanism is uprooting sea-grass by digging furrows in the sea-floor with their snouts. Dugongs in Moreton Bay, Australia are omnivorous since they choose to eat invertebrates such as polychaetes when the supply of their choice grasses decreases.^[5] They will also go to any fresh water sources for drinking. Without these fresh water sources, many would not survive. The amount of these fresh water sources, however, are beginning to decline. The dugong population is predicted to enter a steep decline. However, many scientists are working to prevent this potentially cataclysmic blow to the entire dugong population. Currently, this effort is proving futile, as the dugong population is not showing any increased population numbers.

Migration

During the winter, a few packs of dugongs will move to warmer places in the northern countries, such as bays and canals and others will also go to man built radiators for warmth. Dugongs also live in warmer waters of many other countries near the Equator.

Importance to humans

Ancient interaction

Ipoh's Gua Tambun - Dugong Neolithic Wall Painting

There is a 5000-year old wall painting of a dugong, apparently drawn by neolithic peoples, found in Tambun Cave of Ipoh city in the state of Perak, Malaysia. This was discovered by Lt.R.L Rawlings in 1959 while on a routine patrol in the area.
This dugong image together with some thirty other images were painted using haematite, a type of red colouring easily available in the area to ancestors of the Orang Asli living in and around Tambun.

In the Bible

The dugong is referred to in the Bible by the phrase "sea cow" in several places in Exodus (for example, 25:5 & 26:14) and in Numbers. Dugong hides were used in the construction of the Tabernacle.

Dugong in captivity

There are only 5 dugongs that are held in captivity in the world. Two are the featured attraction of Toba, Mie Toba Aquarium in Japan; the third, named Gracie, is at Underwater World, Sentosa Island, Singapore; and the last two are found in Sea World, Gold Coast, Queensland, Australia.

Conservation

Dugong are hunted for food throughout their wildlife range, usually for their meat and blubber. Also, the seagrass beds which the dugong depend on for food are threatened by eutrophication caused by agricultural and industrial runoff. Due to their shallow water feeding habits, dugong are frequently injured or killed by collisions with motor vessels. Because of their large size, they do not have many natural predators. These include sharks, killer whales, and saltwater crocodiles.
The US and Japanese government want to build a new base on a coral reef close to Henoko, in Nago prefecture, Okinawa. This plan has generated strong protests from Okinawans who are concerned that the local environment, home to the dugong, would be ruined.
Around the waters of Papua New Guinea, natives have been known for hunting dugongs. However, they also hunt dugong's predators, such as sharks.

See also

★ Evolution of sirenians

★ Dewgong

★ Dugong (Weebl's cartoon)

References

1. ADW: Dugong dugon: Information
2. Reep, R.L. et al (2002). "Tactile Hairs on the Postcranial Body in Florida Manatees: A Mammalian Lateral Line?". ''Brain, Behavior and Evolution'' '59', 141-154.
3. ADW: Sirenia: Information
4. [1]
5. Berta, Annalisa, James L. Sumich, Kit M. Kovacs: ''Marine Mammals: Evolutionary Biology'', Amesterdam: Elsevier. ISBN 0-12-088552-2

External links

★ Arkive ''(Dugong dugon)''

★ Roberto Sozzani ''The Dugong''

★ UNEP Dugong Action Plan

★ Sirenian International

★ Australian Museum Online ''Dugong Factsheet''

★ Dugong in Myanmar

★ Ph2otos.com - Dugong in Egypt