Ирравади дельфині: сипаттамасы және өмір салты

Species of mammal

The Irrawaddy dolphin (Orcaella brevirostris) is a euryhaline species of oceanic dolphin found in scattered subpopulations near sea coasts and in estuaries and rivers in parts of the Bay of Bengal and Southeast Asia. It closely resembles the Australian snubfin dolphin (of the same genus, Orcaella), which was not described as a separate species until 2005. It has a slate blue to a slate gray color. Although found in much of the riverine and marine zones of South and Southeast Asia, the only concentrated lagoon populations are found in Chilika Lake in Odisha, India and Songkhla Lake in southern Thailand.

One of the earliest recorded descriptions of the Irrawaddy dolphin was 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 the Monodontidae and Delphinapteridae. Widespread agreement now exists to list it in the family Delphinidae.

The species' name brevirostris is from the Latin meaning short beaked.

The Irrawaddy dolphin's colour is grey to dark slate blue, paler underneath, without a distinctive pattern. The dorsal fin is small and rounded behind the middle of the back. The forehead is high and rounded; the beak is lacking. The front of its snout is blunt. The flippers are broad and rounded. The finless porpoise (Neophocaena phocaenoides) is similar and has no back fin; the humpback dolphin (Sousa chinensis) is larger, and has a longer beak and a larger dorsal fin. Maximum recorded length is of a male in Thailand. The Irrawaddy dolphin is similar to the beluga in appearance, though most closely related to the killer whale. It has a large melon and a blunt, rounded head, and the beak is indistinct. Its dorsal fin, located about two thirds posterior along the back, is short, blunt, and triangular. These dolphins are usually two toned, with the back and sides being gray to bluish gray and the belly lighter. They do this sometimes while spyhopping and 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 speeds of were reported when dolphins were being chased in a boat. In a year, females can sometimes swim as fast as average of 45 km, males can swim up to average of 100 km. Most Irrawaddy dolphins are shy of boats, not known to bow ride, and generally dive when alarmed. They are relatively slow moving but can sometimes be seen spyhopping and rolling to one side while waving a flipper and occasionally breaching. They are generally found in groups of 2 3 animals, though sometimes as many as 25 individuals have been known to congregate in deep pools. Groups of fewer than six individuals are most common, but sometimes up to 15 dolphins are seen together. Traveling and staying in groups not only enables Irrawaddy dolphins to hunt, but it also creates and maintains social bonds and allows copulation to occur. 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 30 to 150 seconds to 12 minutes. When 277 group dives were timed (time of disappearance of the last dolphin in the group to the emergence of the first dolphin in the group) in Laos, mean duration was 115.3  seconds with a range of 19  seconds to 7.18  minutes.

Irrawaddy dolphins have a mutualistic relationship of co operative fishing with traditional fishers. Fishers in India recall when they would call out to the dolphins, by tapping a wooden key also known as a lahai kway, against the sides of their boats, asking the Irrawaddys to drive fish into their nets. In Burma, in the upper reaches of the Ayeyarwady River, Irrawaddy dolphins drive fish towards fishers using cast nets in response to acoustic signals from them. The fishermen attempt to gain the attention of the dolphins through various efforts such as using a cone shaped wooden stick to drum the side of their canoes, striking their paddles to the surface of the water, jingling their nets, or making calls that sound turkey like. A pod of dolphins that agrees to work alongside the fisherman will entrap a school of fish in a semicircle, guiding them towards the boat. In return, the dolphins are rewarded with some of the fishers' bycatch. Historically, Irrawaddy River fishers claimed particular dolphins were associated with individual fishing villages and chased fish into their nets. An 1879 report indicated legal claims were frequently brought into native courts by fishers to recover a share of the fish from the nets of a rival fisher that the plaintiff's dolphin was claimed to have helped fill.

Irrawaddy dolphins are more susceptible to human conflict than most other dolphins that live farther out in the ocean. Drowning in gillnets is the main threat to them throughout their range. Between 1995 and 2001, 38 deaths were reported and 74% died as a result of entanglement in gillnets with large mesh sizes. 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 Burma, electrofishing, gold mining, and dam building are also serious and continuing threats. Though most fishers are sympathetic to the dolphins' plight, abandoning their traditional livelihood is difficult for them. In Laos, a dam across the Mekong River is planned. This could threaten the existence of the endangered Irrawaddy dolphins in downstream Cambodia. Laos's government decision is to forge the dam upstream of the core habitat of the Irrawaddy dolphins. This could precipitate the extinction of this specific species in the Mekong River. The dam builders' proposal is to use explosives to dig out the tons of rock. This will create strong sound waves that could possibly kill the Irrawaddy dolphins due to their highly sensitive hearing structures. In several Asian countries, Irrawaddy dolphins have been captured and trained to perform in public aquaria. Their charismatic appearance and unique behaviors, including spitting water, spyhopping, and fluke slapping, make them very popular for shows in dolphinaria. 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 near the species' range has developed economically; theme parks, casinos, and other entertainment venues that include dolphin shows have 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 killing them for their oil. The IUCN lists five of the seven subpopulations as endangered, primarily due to drowning in fish nets. In the Mahakam River in Borneo, 73% of dolphin deaths are related to entanglement in gillnets, due to heavy fishing and boat traffic.

The Irrawaddy dolphins in Asia are increasingly threatened by tourist activity, such as large numbers of boats circulating the areas in which they live. The development of tours and boats has put a large strain on the dolphins.

Cutaneous nodules were found present in various vulnerable populations of Irrawaddy dolphins. A more precise estimate of the affected dolphins is six populations. Although the definite fate of this emergent disease is unknown, the species is at risk.

The Irrawaddy dolphin's proximity to developing communities makes the effort for conservation difficult. Entanglement in fishnets and degradation of habitats are the main threats to Irrawaddy dolphins. Conservation efforts are being made at international and national levels to alleviate these threats.

Portions of Irrawaddy dolphin habitat in the Sundarbans mangrove forest of Bangladesh are included within of three wildlife sanctuaries, which are part of the Sunderbans World Heritage Site. The Wildlife Conservation Society is working with the Bangladesh Ministry of Environment and Forests to create protected areas for the 6000 remaining dolphins

Irrawaddy dolphins are fully protected as an endangered species under Cambodian fishery law. In 2005, The World Wide Fund For Nature (WWF) established the Cambodian Mekong Dolphin Conservation Project with support from government and local communities. The aim is to support the survival of the remaining population through targeted conservation activities, research, and education. In January 2012, the Cambodian Fisheries Administration, the Commission for Conservation and Development of Mekong River Dolphin Eco tourism Zone, and WWF signed the Kratie Declaration on the Conservation of the Mekong River Irrawaddy Dolphin, an agreement binding them to work together, and setting out a roadmap for dolphin conservation in the Mekong River. On 24 August 2012, the Cambodian government announced that stretch of the Mekong River from eastern Kratie province to the border with Laos has been stated as limit fishing zone which uses floating houses, fishing cages and gill nets are disallowed, but simple fishing is allowed. This area is patrolled by a network of river guards, specifically to protect dolphins. Between January and February 2006, a dozen Irrawaddy dolphins were found dead. The discovery of 10 new baby dolphins on the coast of Cambodia was a relief and gave hope that the endangered Irrawaddy dolphins would make a comeback in population. Since the endangerment was evident, 66 guards have been posted on the coast of Cambodia to protect these dolphins, and only two deaths have been reported since these efforts. To make more efforts to keep these animals from going extinct, the use of fishing nets on the coast of Cambodia is banned, as well.

The Irrawaddy dolphin (under the common name of snubfin dolphin, with the scientific name misspelled as Oreaella brevezastris) is included the Indian Wildlife Protection Act, Schedule I, which bans their killing, transport and sale of products.

A conservation program, entitled Conservation Foundation for the Protection of Rare Aquatic Species of Indonesia, focused on protecting the Irrawaddy dolphin population and their habitat, the Mahakam River. The program not only educates and surveys the public, but also monitors the dolphin population and their habitat. A prime example of this is the establishment of patrols in several villages.

Some major concern for the population in the Mekong River has arisen due to numerous threats. In the 1970s, many Irrawaddy dolphins were slaughtered for oil, and soon after, intensive fishing practices with explosives and gillnets began. As of now, the dolphins are protected in Cambodia and Laos Democratic Republic. Now, both explosive fishing and use of gillnets is restricted in many of the Irrawaddy dolphin's habitats. The Si Phan Don Wetlands Project has successfully encouraged river communities to set aside conservation zones and establish laws to regulate how and when fish are caught. In April, after a 200 kg Irrawaddy dolphin was found dead on the coast of Laos, the death toll for Irrawaddy dolphins is now five in 2015. Usually, Irrawaddy dolphins are found dead with bruises and scars on their body, being killed by illegal poaching, but this Irrawaddy dolphin was found dead because of old age. She is the oldest and largest Irrawaddy dolphin researchers have discovered. The dolphin was in length and most likely in her late 20s.

Myanmar's Department of Fisheries took charge in December 2005, and instituted a protected region in a segment of the Ayeyarwady River between Mingun and Kyaukmyaung and created multiple provisions, as well.

In 2000, Malampaya Sound was proclaimed a protected seascape. This is the lowest possible prioritization given to a protected area. In 2007, the Coral Triangle Initiative, a new multilateral partnership to help safeguard the marine and coastal resources of the Coral Triangle, including the Irrawaddy dolphin subpopulation in Malampaya Sound, was launched. In 2006, a new population was discovered in Guimaras island in the Visayas. In 2015, another new population was discovered in Bago in Negros Occidental, part of Negros island in the Visayas.

In 2002, the Marine and Coastal Resources Department was assigned to protect rare aquatic animals such as dolphins, whales, and turtles in Thai territorial waters. To protect the dolphins, patrol vessels ensure boats stay at least away from dolphins and no chasing of or running through schools of dolphins occurs. Many fishermen on the Bang Pakong River, Prachinburi Province, have been persuaded by authorities to stop shrimp fishing in a certain area and 30 to 40 fishing boats have been modified so they can offer dolphin sightseeing tours. A total of 65 Irrawaddi dolphins has been found dead along the coast of Trat Province in the past three years. The local fishing industry is blamed for the deaths of the dolphins. In January 2013, over a dozen dead Irrawaddy dolphins were found on the coast of Thailand. These dolphins were said to be dead because of a lack of oxygen. Dolphins are mammals, and unlike other animals that live in the sea, they must come to the surface for air. Many of the dolphins are found dead in the water, and others were washed ashore, said to have been dead for a few days. Also, in the first week of February 2013, as many as four Irrawaddy dolphins were found dead. The Natural Resources and Environment Ministry is studying artificial breeding options in 2022 to try to save the last herd of Irrawaddy dolphins in Songkhla Lake, which is on the verge of extinction after only 14 were found in the most recent survey. They also intend to list dolphins as a protected species, Thailand's highest level of animal protection.

In 2008, the Department of Forestry and Sarawak Forestry Cooperative in Sarawak established a protected area for Irrawaddy dolphins in Santubong and Damai (Kuching Wetland).