User:Wrasse
From Wikipedia, the free encyclopedia
 |
||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 |
||||||||||||||||
|
|
||||||||||||||||
| Scientific classification | ||||||||||||||||
|
||||||||||||||||
|
|
||||||||||||||||
| Dugong dugon (Müller, 1776) |
||||||||||||||||
 Natural range of D. dugon.
|
The dugong (Dugong dugon) is the only living species of the family Dugongidae (following the 18th century extinction of Steller's Sea Cow) and together with the three species of manatee forms the aquatic mammalian order Sirenia. It is the only sirenian in its range, which spans the shallow waters of at least 37 countries and territories in the Indo-Pacific;[2] however, the majority of dugongs live in the northern waters of Australia between Shark Bay and Moreton Bay.[3]
Like all sirenians, the dugong has a fusiform body with paddle-like forelimbs and no dorsal fin or hindlimbs. It is easily distinguished from the manatees by its fluked, dolphin-like tail, but also possesses a unique skull and teeth.[4]
The IUCN lists the dugong as a species vulnerable to extinction. The primary causes for population declines are anthropogenic, and include hunting, habitat degradation, and fishing-related fatalities.[5] With its long lifespan and slow rate of reproduction, the dugong is especially vulnerable to these types of exploitation.[2] In addition, dugongs are threatened by storms, parasites, and their natural predators, sharks and Killer Whales.[5]
Contents |
[edit] Anatomy and Morphology
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 (551 to 661 lb).[6]
The dugong grows two incisors (tusks) which are largest in males, and unlike the manatees, its teeth do not continually grow back via horizontal tooth replacement.[7]
[edit] Distribution
The dugong's historic range is believed to correspond to that of certain seagrasses,[2] which the dugong is specialized towards.
Remaining populations of dugong are greatly reduced, although they once covered all of the tropical South Pacific and Indian Oceans.[citation needed] 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 200km 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 near Egypt.
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 [8], but their status is currently not well known.
[edit] Ecology and Life History
While all sirenians are herbivores, manatees use fresh water freely, making the dugong the only strictly-marine herbivorous mammal.[2]
[edit] 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. 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.
[edit] Migration
During the winter, a few packs of dugongs will move to warmer places in the northern countries, such as bays and canals and other will also go to man built radiators for warmth. Dugongs also live in warmer waters of many other countries near the Equator.
[edit] Importance to Humans
[edit] Ancient interaction
There is a 5000 years 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.
[edit] Dugong in captivity
There are only three dugong held in captivity in the world, two are the featured attraction of Toba, Mie Toba Aquarium in Japan; and the other, named Gracie, is at Underwater World, Sentosa Island, Singapore.
[edit] 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. They only have large ones such as 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.[citation needed]
Around the waters of Papua New Guinea, natives have been known for hunting dugongs. However, they also hunt dugong's predators, such as sharks.
[edit] Evolutionary history
[edit] Etymology and taxonomic history
The name dugong originated from the Malay language duyung meaning lady of the sea or mermaid.
[edit] References
- ^ Marsh (2006). Dugong dugon. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Database entry includes a lengthy justification of why this species is vulnerable
- ^ a b c d Marsh et al. 2002. Dugong : status reports and action plans for countries and territories. IUCN.
- ^ Lawler et al. 2002. Dugongs in the Great Barrier Reef : Current State of Knowledge. CRC for The Great Barrier Reef World Heritage Area. p.2
- ^ Myers, P. 2002. Dugongidae. University of Michigan Museum of Zoology. Retrieved on 10 March 2007.
- ^ a b Reeves et al. 2002. National Audubon Society Guide to Marine Mammals of the World. Knopf. ISBN 0-375-41141-0. p.481
- ^ Dugong. IFAW. Retrieved on 25 February 2007.
- ^ Self-Sullivan, Caryn. Evolution of Sirenia. www.sirenian.org. Retrieved on 10 March 2007.
- ^ [1]
[edit] External links
