Irrawaddy dolphins are similar to the Beluga in appearance, though most closely related to the Orca. They have a large melon and a blunt, rounded head, and the 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. Adult weight exceeds 130 kg (287 lb) and length is 2.3 m (8 ft) m at full maturity. Maximum length is 2.75 m (9 ft) of a male.
Monday, September 27, 2010
Naming for Irrawaddy Dolphin
A young / baby of a Irrawaddy dolphin is called a 'calf or pup'. The females are called 'cow' and males 'bull'. A Irrawaddy dolphin group is called a 'team, school, pod, herd, alliance (male) or party (female)'.
What are the main threats to Irrawaddy Dolphin?
Unexploited but vulnerable
Although the Irrawaddy dolphin is not directly exploited, it is exposed to incidental mortality in fisheries (e.g., gillnets in Australia and in Malampaya, explosives), the principal cause of depletion. Habitat degradation due to development of dams, deforestation and mining also continue to undermine the species to a lesser extent.The small population of the Mahakam River (Indonesian Borneo) and possibly that of the Ayeyarwady River (Myanmar) are also live-captured for display purposes.
Threat of Irrawaddy Dolphin
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 fishers are sympathetic to the dolphins plight, it is difficult for them to abandon their traditional means of livelihood.
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
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. 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.
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
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.
Irrawaddy Dolphins' History
The Irrawaddy Dolphin was first described by Sir Richard Owen in 1866 based on a specimen found in 1852, in the harbour of Visakhapatnam on the east coast of India. 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.
Overall grey to dark slate blue, paler underneath. No distinctive pattern. Dorsal fin small and rounded behind middle of back. Forehead high and rounded; beak lacking. Broad rounded flippers. The similar species that can be found in Borneo is the Finless Porpoise, Neophocaena phocaenoides, is similar and has no back fin: the Humpback Dolphin, Sausa chinensis, is larger, has longer beak and larger dorsal fin.
The several common names for Orcaella brevirostris (Latin) include: English: Irrawaddy dolphin, Local Chilika dialect: Baslnyya Magar or Bhuasuni Magar (oil yielding dolphin), Oriya: Khem and Khera], French: Orcelle, Spanish: Delfín del Irrawaddy, German: Irrawadi Delphin, Burmese: Labai, Indonesia: Pesut, Malay: Lumbalumba, Khmer: ផ្សោត Ph’sout , Lao: Pha’ka and Filipino: Lampasut. In Thai, one of its names is pla loma hua bat, because its rounded head is thought to resemble the shape of a Buddhist monk's bowl, a hua bat.
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.
Overall grey to dark slate blue, paler underneath. No distinctive pattern. Dorsal fin small and rounded behind middle of back. Forehead high and rounded; beak lacking. Broad rounded flippers. The similar species that can be found in Borneo is the Finless Porpoise, Neophocaena phocaenoides, is similar and has no back fin: the Humpback Dolphin, Sausa chinensis, is larger, has longer beak and larger dorsal fin.
The several common names for Orcaella brevirostris (Latin) include: English: Irrawaddy dolphin, Local Chilika dialect: Baslnyya Magar or Bhuasuni Magar (oil yielding dolphin), Oriya: Khem and Khera], French: Orcelle, Spanish: Delfín del Irrawaddy, German: Irrawadi Delphin, Burmese: Labai, Indonesia: Pesut, Malay: Lumbalumba, Khmer: ផ្សោត Ph’sout , Lao: Pha’ka and Filipino: Lampasut. In Thai, one of its names is pla loma hua bat, because its rounded head is thought to resemble the shape of a Buddhist monk's bowl, a hua bat.
Irrawaddy Dolphins' 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.[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.
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 fishers 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.
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.[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.
Reproduction of Irrawaddy Dolphin
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