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==Conservation==
==Conservation==
Entanglements in fishnets and and habitat degradation worries conservationists. As an [[threatened species]], they are legally protected from hunting; however, enforcement may be poor along tens of thousands of miles of coast line.<ref name="IUCN"/><!--expand this section-->
Entanglements in fishnets and and habitat degradation worries conservationists. As an [[threatened species]], they are legally protected from hunting; however, enforcement may be poor along tens of thousands of miles of coast line.<ref name="IUCN"/>

In 2004, the Convention on International Trade in Endangered Species of Wild Fauna and Flora [[CITES]] transferred the Irrawaddy dolphin from [[CITES#Appendix_II|Appendix II]] to [[CITES#Appendix_I|Appendix I]], which forbids all commercial trade in species that are threatened with extinction.<ref name="CITES">{{cite news|url=http://www.cites.org/eng/news/press/2004/041014_cop13final.shtml|title=CITES takes action to promote sustainable wildlife|last=CITES|date=2004-10-14|work=Press Release|publisher= Convention on International Trade in Endangered Species of Wild Fauna and Flora|accessdate=2008-12-29}}</ref><!--expand this section-->
==References==
==References==
{{reflist}}
{{reflist}}

Revision as of 10:34, 29 December 2008

Irrawaddy Dolphin
Size comparison against an average human
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Cetacea
Family:
Delphinidae
Genus:
Orcaella
Species:
O. brevirostris
Binomial name
Orcaella brevirostris
Owen in Gray, 1866[1]
Orcaella genus range map
See: Irrawaddy Dolphin
Geographic Range Map

The Irrawaddy Dolphin (Orcaella brevirostris) is a euryhaline species of dolphin found in discontinuous sub-populations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia.

Etymology and Taxonomic History

The Irrawaddy Dolphin was first described by Sir Richard Owen in 1866 based on a specimen found in 1852, in the harbour of Vishakhapatnum on the east coast of India.[2]It is one of two species in its genus. It has sometimes been listed variously in a family containing just itself and in Monodontidae and in Delphinapteridae. There is now widespread agreement to list it in the Delphinidae family.

Genetically the Irrawaddy Dolphin is closely related to the Orca. The species name brevirostris comes from the Latin meaning short-beaked. In 2005, genetic analysis showed that the Australian Snubfin Dolphin found at the coast of northern Australia forms a second species in the Orcaella genus.

The several common names for Orcaella brevirostris (Latin) include: English: Irrawaddy dolphin, Local Chilika dialect: Baslnyya Magaror Bhuasuni Magar (oil yielding dolphin), Oriya: Khem and Khera

[2], French: Orcelle, Spanish: Delfín del Irrawaddy, German: Irrawadi Delphin, Burmese: Labai, Indonesia: Pesut, Malay: Lumbalumba, Khmer: Ph’sout, Lao: Pha’ka and Filipino: Lampasut.[3] In Thai, one of its names is pía loma hooa baht, because its rounded head is thought to resemble the shape of a Buddhist monk's bowl, a hooa baht.[4]

Description

Irrawaddy dolphins are similar to the Beluga in appearance, though most closely related to the Orca. This species has a large melon and a blunt, rounded head. Its beak is indistinct. The dorsal fin, located about two-thirds posterior along the back, is short, blunt and triangular. The flippers are long and broad. It is lightly coloured all over, but slightly more white on the underside than the back. Adult weight exceeds Template:Kg to lb kg and length is Template:M to ft m at full maturity. Maximum recorded length is Template:M to ft of a male from Thailand.[4]

Reproduction

These Dolphins are thought to reach sexual maturity at 7 to 9 yrs. In the Northern Hemisphere, mating is reported from December to June. Its gestation period is 14 months, giving birth to a single calf every 2 to 3 years. Length is about Template:M to ft1 m at birth. Birth weight is about Template:Kg to lb kg. Weaning is after two years. Lifespan is about 30 years.

Behavior

Irrawaddy dolphins communicate with clicks, creaks and buzzes at a dominant frequency of about 60 kilohertz which is thought to be used for echolocation. Bony fish and fish eggs, cephalopods, and crustaceans are taken as food. Observations of captive animals indicate that food may be taken into the mouth by suction. Irrawaddy Dolphins sometimes spit streams of water, sometimes while spyhopping, during feeding, apparently to expel water ingested during fish capture or possibly to herd fish. Some Irrawaddy Dolphins kept in captivity have been trained to do spyhopping on command. The Irrawaddy Dolphin is a slow swimmer, but swimming speed of 20-25 km/hour was reported when dolphins were being chased in a boat.

It surfaces in a rolling fashion and lifts its tail fluke clear of the water only for a deep dive. Deep dive times range from 70—150 seconds to 12min. When 277 group dives were timed (time of dis-appearance of last dolphin in group to emergence of first dolphinin the group) in Laos, mean duration was 115.3 s with a range of 19 s to 7.18 min.[4] They make only occasional low leaps and never bow-ride. Groups of fewer than 6 individuals are most common, but sometimes up to 15 dolphins are seen together. [5] [6]

Interspecific competition has been observed when Orcaella was forced inshore and excluded by more specialised dolphins. It is also reported that when captive Humpback Dolphins (Sonsa chinensis) and Irrawaddy Dolphins were held together, the Irrawaddy Dolphins were frequently chased and confined to a small portion of the tank by the dominant Humpbacks. In Chilika Lake, local fishermen say that when Irrawaddy Dolphins and Bottlenose Dolphins meet in the outer channel, the former get frightened and are forced to return toward the lake.[2]

Habitat and sub-populations

Irrawaddy Dolphin on Mekong River at Kratié, Cambodia

Although sometimes called the Irrawaddy River Dolphin, it is not a true river dolphin but an oceanic dolphin that lives in brackish water near coasts, river mouths and in estuaries. It has established sub-populations in freshwater rivers, including the Ganges and the Mekong as well as the Irrawaddy River from which it takes its name. Its range extends from the Bay of Bengal to New Guinea and the Philippines.

No range-wide survey has been conducted for this vulnerable specie, however it appears that the worldwide population is over 7,000, with over 90% occurring in Bangladesh. Populations outside Bangladesh and India are classified as critically endangered. Known sub-populations of Irrawaddy Dolphins are found in eight places, listed here in order of population, including conservation status.

Chilka Lake, India, habitat of Irrawaddy Dolphins
  1. Bangladesh; 5,832 (VU) in coastal waters of the Bay of Bengal[7]
  2. and 451 (VU) in the brackish Sundarbans mangrove forest[8]
  3. India; 138 (VU) in the brackish water Chilika Lake[9]
  4. Laos and Cambodia; 114-152 (CR) in a 190 km (118.1 mi) freshwater stretch of the Mekong River
  5. Indonesia; (CR), in a 420 km (261.0 mi) stretch of the freshwater Mahakam River
  6. Philippines; about 77 (CR) in the brackish inner Malampaya Sound
  7. Myanmar; about 58-72 (CR) in a 370 km (229.9 mi) freshwater stretch of the Ayeyarwady River
  8. Thailand: less than 50 (CR) in the brackish Songkhla Lake.[10]

Interaction with Humans

Irrawaddy dolphins have a seemingly mutualistic relationship of co-operative fishing with traditional fishermen. Fishermen in India recall when they would call out to the dolphins, to drive fish into their nets. [11] In Myanmar, in the upper reaches of the Ayeyawady River, Irrawaddy dolphins drive fish towards fisherman using cast nets in response to acoustic signals from them. In return, the Dolphins are rewarded with some of the fishermens by-catch.[12] Historically, Irrawaddy River fishermen claimed that particular dolphins were associated with individual fishing villages and chased fishes into their nets. A 1879 report indicates that legal claims were frequently brought into native courts by fishermen to recover a share of the fish from the nets of a rival fisherman which the plaintiffs dolphin was claimed to have helped fill.[4]

Threats

Fishermen with fishnets in Bangladesh

Irrawaddy Dolphins are more susceptible to human conflict than most other dolphins who live farther out in the ocean. Drowning in gillnets is the main threat to Irrawaddy dolphins throughout their range. The majority of reported dolphin deaths in all subpopulations is due to accidental capture and drowning in gillnets and dragnets, and in the Philippines, bottom-set crabnets. In Myanmar, electrofishing and gold mining are also a serious and continuing threat. Though most fishermen are sympathetic to the dolphins plight, it is difficult for them to abandon their traditional means of livelihood.[10]

In several Asian countries, Irrawaddys have been captured and trained to perform in public aquariums. The charismatic appearance and unique behaviors of Irrawaddy dolphins, including spitting water, spyhopping and fluke-slapping, make them very popular for shows in dolphinariums. The commercial motivation for using this dolphin species is high because it can live in freshwater tanks and the high cost of marine aquarium systems is avoided. The region within and nearby the species’ range has developed economically and theme parks, casinos and other entertainment venues that include dolphin shows has increased. In 2002 there were more than 80 dolphinariums in at least nine Asian countries[13]

Collateral deaths of dolphins due to blast fishing were once common in Vietnam and Thailand. In the past, the most direct threat was the killing of Irrawaddys for their oil.

The IUCN lists five of the seven subpopulations as critically endangered, primarily due to drowning in fish nets.[10] For example, the Malampaya population was first discovered and described in 1986, at the time consisting of 77 individuals. Due to anthropogenic activities, this number dwindled to 47 dolphins in 2007.[14]

Conservation

Entanglements in fishnets and and habitat degradation worries conservationists. As an threatened species, they are legally protected from hunting; however, enforcement may be poor along tens of thousands of miles of coast line.[10]

In 2004, the Convention on International Trade in Endangered Species of Wild Fauna and Flora CITES transferred the Irrawaddy dolphin from Appendix II to Appendix I, which forbids all commercial trade in species that are threatened with extinction.[15]

References

  1. ^ "Orcaella brevirostris (Owen in Gray, 1866)". ITIS Report. Integrated Taxonomic Information System. pp. Taxonomic Serial No.: 180471. Retrieved 2008-12-27.
  2. ^ a b c Sinha, R.K. (May–Aug 2004). "THE IRRAWADDY DOLPHINS ORCAELLA OF CHILIKA LAGOON, INDIA'". Journal of the Bombay Natural History Society. 101 ((2)). Mumbai, India: online edition: Environmental Information System (ENVIS), Annamalai University, Centre of Advanced Study in Marine Biology, Parangipettai - 608 502, Tamil Nadu, India: 244–251.{{cite journal}}: CS1 maint: date format (link)
  3. ^ "PROPOSAL FOR INCLUSION OF SPECIES ON THE APPENDICES OF THE CONVENTION ON THE CONSERVATION OF MIGRATORY SPECIES OF WILD ANIMALS" (PDF). PROPOSALS. ENEP/CMS. 2008-8-27. Retrieved 2008-12-26. {{cite web}}: Check date values in: |date= (help)
  4. ^ a b c d Stacey, Pam J. (1999-5-5). "Orcaella brevirostris" (PDF). Mammalian Species (616). American Society of Mammalogists: 1–8. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ "Irrawaddy dolphin (Orcaella brevirostris)". Arkive. Wildscreen. 2008. Retrieved 2008-12-26.
  6. ^ Culik, Boris; Kiel, Germany (2000). "Orcaella brevirostris (Gray, 1866)". REVIEW ON SMALL CETACEANSDistribution, Behaviour, Migration and Threats. UNEP/CMS Convention on Migratory Species. Retrieved 2008-12-26.{{cite web}}: CS1 maint: multiple names: authors list (link)
  7. ^ "Large population of endangered dolphins found in Bangladesh". Times of India, Flora and Fauna. 2008 Bennett Coleman & Co. Ltd. 2008-10-11. Retrieved 2008-12-29.
  8. ^ SMITH, Brian D. (2006,). "Abundance of irrawaddy dolphins (Orcaella brevirostris) and ganges river dolphins (Platanista Gangetica gangetica) estimated using concurrent counts made by independent teams in waterways of the sundarbans mangrove forest in Bangladesh". Marine mammal science, Society for Marine Mammalogy. vol. 22 (no3). Oxford, UK: Blackwell: pp. 527-547. ISSN 0824-0469. {{cite journal}}: |issue= has extra text (help); |pages= has extra text (help); |volume= has extra text (help); Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)CS1 maint: extra punctuation (link)
  9. ^ Das, Subrat (2008-2-28). "Dolphins better off in Chilika - Survey reveals dip in death toll of Irrawaddy School". The Telegraph. Calcutta. pp. Front page. Retrieved 2008-12-25. {{cite news}}: Check date values in: |date= (help)
  10. ^ a b c d Template:IUCN2006
  11. ^ D’Lima, Coralie (2008). "Dolphin-human interactions, Chilika" (PDF). Project summary. Whale and Dolphin Conservation Society. Retrieved 2008-12-21.
  12. ^ Tun, Tint (2008). "Castnet Fishing with the Help of Irrawaddy Dolphins". Irrawaddy Dolphin. Yangon, Myanmar. Retrieved 2008-12-25.
  13. ^ Vertefeuille, Jan (2004-10-8). "Irrawaddy Dolphins Gain Trade Protection Under CITES; WWF Urges Countries to Stop All Live Captures". Press release. World Wildlife Fund. Retrieved 2008-12-29. {{cite news}}: Check date values in: |date= (help)
  14. ^ Yan, Gregg (2007-03-08). "Rare Palawan dolphins now down to 47 - WWF". Section A. Philippine Daily Inquirer. pp. 1, 6. Retrieved 2007-03-10. {{cite news}}: Check date values in: |date= (help)
  15. ^ CITES (2004-10-14). "CITES takes action to promote sustainable wildlife". Press Release. Convention on International Trade in Endangered Species of Wild Fauna and Flora. Retrieved 2008-12-29.


Bibliography

  • National Audubon Society Guide to Marine Mammals of the World ISBN 0-375-41141-0
  • Encyclopedia of Marine Mammals ISBN 0-12-551340-2
  • Whales, Dolphins and Porpoises, Mark Carwardine, ISBN 0-7513-2781-6

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Irrawaddy_dolphin&oldid=260650889"