Difference between revisions of "Dugong" - New World Encyclopedia

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==References==
 
==References==
 
<ref name="ADW">{{cite web | last =Fox | first =David L. | authorlink =David L. Fox | title =ADW: Dugong dugon: Information | work =Animal Diversity Web | publisher =University of Michigan Museum of Zoology | date =1999 | url =http://animaldiversity.ummz.umich.edu/site/accounts/information/Dugong_dugon.html | accessdate = 2007-04-29 }}</ref>  
 
<ref name="ADW">{{cite web | last =Fox | first =David L. | authorlink =David L. Fox | title =ADW: Dugong dugon: Information | work =Animal Diversity Web | publisher =University of Michigan Museum of Zoology | date =1999 | url =http://animaldiversity.ummz.umich.edu/site/accounts/information/Dugong_dugon.html | accessdate = 2007-04-29 }}</ref>  
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* Grzimek
  
 
International Fund for Animal Welfare. 2008. .<ref name=IFAW> [http://www.ifaw.org/ifaw_asia_pacific/save_animals/other/dugong.php ''Dugong'']. [[International Fund for Animal Welfare (IFAW)|IFAW]]. Retrieved on 25 February 2007.</ref>  
 
International Fund for Animal Welfare. 2008. .<ref name=IFAW> [http://www.ifaw.org/ifaw_asia_pacific/save_animals/other/dugong.php ''Dugong'']. [[International Fund for Animal Welfare (IFAW)|IFAW]]. Retrieved on 25 February 2007.</ref>  

Revision as of 02:56, 13 November 2008

Dugong[1]
Fossil range: Early Eocene–Recent
Dugong Marsa Alam.jpg
Conservation status
Status iucn3.1 VU.svg
Vulnerable

(IUCN) [2]

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Sirenia
Family: Dugongidae
Gray, 1821
Subfamily: Dugonginae
Simpson, 1932
Genus: Dugong
Lacépède, 1799
Species: D. dugon
Binomial name
Dugong dugon
(Müller, 1776)
Natural range of D. dugon.
Natural range of D. dugon.

Dugong is the common name for a large, herbivorous, fully aquatic marine mammal, Dugong dugon, characterized by gray-colored, nearly hairless skin, paddle-like forelimbs, no hind limbs, a fluke-like (forked) tail, and tusks. The dugong is 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 found the Indo-Pacific from eastern Africa to southeast Asia.

Dugons are part of the order Sirenia along with manatees, both of which are sometimes know as "sea cows." The dugong is the only strictly-marine herbivorous mammal, as all species of manatee utilize freshwater to some degree, and other taxons of marine mammals consume prey to at least some extent. The dugong is heavily dependent on seagrasses for subsistence.

he dugong has been hunted for thousands of years, often for its meat and oil (Marsh 1989), although dugong hunting also has great cultural significance throughout its range.[3] The dugong's current distribution is reduced and disjunct, and many populations are close to extinction.[4] 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.[5] With its long lifespan of 70 years or more[citation needed], and slow rate of reproduction, the dugong is especially vulnerable to these types of exploitation.[4] In addition, dugongs are threatened by storms, parasites, and their natural predators, sharks, killer whales, and crocodiles.[5]

Overview and description

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

The dugong is a large marine mammal which, together with the manatees, is one of four living species of the order Sirenia. Sirenians are one of four groups of marine mammals, the others being cetaceans (whales, dolphins, and porpoises), sea otters, and pinnipeds (walruses, earless seals, and eared seals). The sirenians and cetaceans are completely aquatic, while pinnipeds spend considerable time on land, including giving birth and raising their young, and sea otters can mate and raise their young entirely at sea. Sirenia is thought to have evolved from four-legged land mammals over 60 million years ago, with the closest living relatives being the Proboscidea (elephants) and Hyracoidea (hyraxes) (Domning 1994).

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. The main visual difference between manatees and dugongs are the tails. A manatee tail is paddle-shaped, while a dugong tail is forked, similar in shape to that of a whale of dolphin. The paddle-like forelimbs aid in movement and feeding, while its fluked tail provides locomotion through vertical movement. The dugong also possesses a unique skull and teeth (Myers 2002).

The dugong has thick, smooth skin that is a pale cream color at birth but darkens dorsally and laterally to a brownish to dark gray color with age (Fox 1999). The body is sparsely covered in short hair, a common feature among sirenians, which may allow for tactile interpretation of their environment (Reep et al. 2002). 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 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 1989). The full dental formula of dugongs is:

2.0.3.3
3.1.3.3

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), may act as a ballast to help keep sirenians suspended slightly below the water's surface (Myers 2000).

Dugongs are generally smaller than manatees (with the exception of the Amazonian manatee), reaching an average adult length of 2.7 meterss (8.9 feet]]) and a weight of 250 to 300 kilograms (550 to 660 pounds]) (IFAW 2008). An adult's length rarely exceeds 3 meters, and females tend to be larger than males (Marsh 1989). The largest known dugong was an exceptional female landed off the Saurashtra coast of west India, measuring 4.03 meters (13.3 feet) and weighing 1,018 kilograms (2,240 pounds) (Wood 1983).

The word "dugong" derives from the Tagalog term dugong, which was in turn adopted from the Malay duyung, both meaning "lady of the sea" (Winger 2000). Other common local names include "sea cow," "sea pig," and "sea camel" (Reeves et al. 2002).

Distribution

File:DugongAreaMoretonBay.jpg
Typical dugong Feeding area in Moreton Bay
Dugong on the sea floor at Marsa Alam, Egypt

The dugong is the only sirenian in its range, which spans the waters of at least 37 countries throughout the Indo-Pacific, from Africa to the Philippines and the South China and East China Seas, where sea grasses are found (Marsh et al. 2002; Grzimek et al. 2004). However, the majority of dugongs live in the northern waters of Australia between Shark Bay and Moreton Bay (Lawler et al. 2002). Manatees are found in both freshwater and marine environments in parts of the Americas and Africa.

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.[4] Its snout is sharply downturned, an adaptation for grazing and uprooting benthic seagrasses.

Remaining populations of dugong are greatly reduced, although they once covered all of the tropical South Pacific and Indian Oceans.[citation needed] Their historic range is believed to correspond to that of certain seagrasses.[4] 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.[citation needed]

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, Arabian Sea along Pakistan, 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 [6], but their status is currently not well known.

An endangered population of 50 or fewer dugongs survives around Okinawa.[7]

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 seafloor 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.[8] 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, is 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 herds of dugongs will move to warmer places in the northern countries, such as bays and canals.[citation needed] Dugongs also live in warmer waters of many other countries near the equator.

Reproduction

Dugong mother and offspring from East Timor

Gestation in the Dugong lasts around 13 months, and results in the birth of a single young. The calf is not fully weaned for a further two years, and does not become sexually mature until the age of 8-18, longer than in most other mammals. As a result, despite the longevity of the Dugong, which may live for fifty years or more, females give birth only a few times during their life, and invest considerable parental care in their young.[9]

Etymology and taxonomy

The dugong was first classified by Müller in 1776 as Trichechus dugon,[10] a member of the manatee genus previously defined by Linnaeus.[11] It was later assigned as the type species of Dugong by Lacépède[12] and further classified within its own family by Gray[13] and subfamily by Simpson.[14]

Importance to humans

Ancient interaction

File:Ipoh-tambuncave-dugong.jpg
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.

When seen from above, the top half of a dugong or manatee can appear like that of a human woman[citation needed]. Coupled with the tail fin, this produced an image of what mariners often mistook for an aquatic human—probably the origin of the mermaid myth.

During the Renaissance and the Baroque eras, dugongs were often exhibited in wunderkammers. They were also presented as Fiji mermaids in sideshows.

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 may have been used in the construction of the Tabernacle, if dugong is an accurate translation of the biblical animal tachash.

Dugong in captivity

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

Conservation

Dugong are hunted for food throughout their wildlife range, usually for their meat and blubber. [citation needed] 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 U.S. and Japanese government want to build a new military 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.[citation needed] Greenpeace stepped-up its campaign protesting the Okinawa base expansion in the summer of 2007, as authorities recommenced their airbase development plans [15].

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)

Notes

  1. J. Shoshani, "Dugong," In D. E. Wilson, and D. M. Reeder, eds., Mammal Species of the World, 3rd edition (Johns Hopkins University Press 2005). ISBN 0801882214.
  2. H. Marsh, "Dugong dugon," 2008 IUCN Red List of Threatened Species (IUCN 2008). Retrieved on November 12, 2008. Database entry includes a lengthy justification of why this species is vulnerable Database entry includes a lengthy justification of why this species is vulnerable
  3. Species DUGONG. Conservation Management Institute.
  4. 4.0 4.1 4.2 4.3 Cite error: Invalid <ref> tag; no text was provided for refs named IUCNpdf
  5. 5.0 5.1 Reeves et al. 2002. National Audubon Society Guide to Marine Mammals of the World. Knopf. ISBN 0-375-41141-0. pp. 478-481
  6. Case Study
  7. Galvin, Peter. Saving the Okinawa dugong. Center for Biological Diversity web site. Center for Biological Diversity. Retrieved 2008-05-15.
  8. Berta, Annalisa, James L. Sumich, Kit M. Kovacs: Marine Mammals: Evolutionary Biology, Amesterdam: Elsevier. ISBN 0-12-088552-2
  9. Anderson, Paul K. (1984). in Macdonald, D.: The Encyclopedia of Mammals. New York: Facts on File, 298-299. ISBN 0-87196-871-1. 
  10. Dugong dugon. The Paleobiology Database. Retrieved on 22 July 2007.
  11. Trichechus. The Paleobiology Database. Retrieved on 22 July 2007.
  12. Dugong. The Paleobiology Database. Retrieved on 22 July 2007.
  13. Dugongidae. The Paleobiology Database. Retrieved on 22 July 2007.
  14. Dugonginae. The Paleobiology Database. Retrieved on 22 July 2007.
  15. Take Action: Save the dugongs | Greenpeace International

References
ISBN links support NWE through referral fees

[1]


  • Grzimek

International Fund for Animal Welfare. 2008. .[2]


[3]

H. Marsh, "Dugong dugon," 2008 IUCN Red List of Threatened Species (IUCN 2008). Retrieved on November 12, 2008.

[4]

Marsh, H. 1989. .Cite error: Closing </ref> missing for <ref> tag


[5]

[6]

[7]


J. Shoshani, "Dugong," In D. E. Wilson, and D. M. Reeder, eds., Mammal Species of the World, 3rd edition (Johns Hopkins University Press 2005). ISBN 0801882214.</ref>

[8]

[9]

[10]

External links

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  1. Fox, David L. (1999). ADW: Dugong dugon: Information. Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved 2007-04-29.
  2. Dugong. IFAW. Retrieved on 25 February 2007.
  3. Lawler et al. 2002. Dugongs in the Great Barrier Reef : Current State of Knowledge. CRC for The Great Barrier Reef World Heritage Area.
  4. Marsh et al. 2002. Dugong : status reports and action plans for countries and territories. IUCN.
  5. Myers, Phil (2000). ADW: Sirenia: Information. Animal Diversity Web. University of Michigan Museum of Zoology. Retrieved 2007-05-13.
  6. 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.
  7. Self-Sullivan, Caryn. 2007 Evolution of Sirenia. www.sirenian.org. Retrieved on 10 March 2007.
  8. Waller et al. 1996. Sealife: A Complete Guide to the Marine Environment. Smithsonian Institution. ISBN 1560986336. pp. 413-420
  9. Winger, Jennifer. 2000. What's in a Name: Manatees and Dugongs. Smithsonian National Zoological Park. Retrieved on 22 July 2007.
  10. Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc (1983), ISBN 978-0851122359