Irrawaddy dolphin  (Orcaella brevirostris)

The Irrawaddy dolphin is classified as Vulnerable (VU) on the IUCN Red List (1) and is listed on Appendix I of CITES (3). Geographically isolated populations in the Ayeyarwady River (Myanmar), Mahakam River (Indonesia), Malampaya Sound (Philippines), Mekong River (Lao PDR, Cambodia and Vietnam) and Songkhla Lake (India) are classified as Critically Endangered on the IUCN Red List (1).

A particularly distinctive dolphin, the Irrawaddy has a rounded head with no beak and a flexible neck, causing visible creases behind the head (2). Although most closely related to the orca (4), the Irrawaddy dolphin is similar in body form to the beluga whale, but darker in colour, with a pale to dark grey back and a light underside. The dorsal fin is small, triangular and rounded, and the flippers are long and broad (2).

The Irrawaddy dolphin has a patchy distribution in the shallow, coastal waters of the Indo-Pacific from the Philippines to northeastern India. Freshwater subpopulations occur in three river systems: the Mahakam of Indonesia, the Ayeyarwady (previously Irrawaddy) of Burma, and the Mekong of Laos, Cambodia and Viet Nam. It is also found in completely or partially isolated brackish water bodies such as Chika Lake in India and Songkhla Lake in Thailand (1).

Inhabits coastal, brackish and freshwaters of the tropical and sub-tropical Indo-Pacific (2).

Believed to be reincarnated humans by some of the people of Laos (2), Irrawaddy dolphins are less active than many other dolphins with only the uppermost dorsal surface of the animal becomes visible during a slow rolling dive; they make only occasional low leaps and never bow-ride. Feeding together in groups of usually less than six, but as many as 15 (5), the Irrawaddy dolphin can dive for up to 12 minutes to feed on bony fish, crustaceans, cephalopods and fish eggs. Irrawaddy dolphins are known to spit water to herd fish, and have even been reported to stun large fish with a blow from the lower jaw, only to play with them before casting them aside (2). In some areas of Asia, fishermen consider the Irrawaddy dolphin to be a competitor for fish, but in other areas the fishermen attract them to the boat and encourage them to drive fish into the nets where the dolphins also benefit by preying on fish whose movements are confused by the nets and those that are momentarily trapped around the edges or in the mud (6). Irrawaddy dolphins communicate with clicks, creaks and buzzes (7) at a dominant frequency of about 60 kilohertz which is thought to be used for echolocation (8).

Little is known about the reproductive biology of the Irrawaddy dolphin, but it is thought to breed between April and June in the Mahakam River, and gestation is estimated at 14 months and weaning after two years (2).

This dolphin species is known to carry out daily migrations from the Semayang Lake in eastern Borneo to the Mahakam River, returning to the lake in the evening. In Indonesia, Irrawaddy dolphins move into tributaries at high water and into the main river during low water (4).

The major threat to the Irrawaddy dolphin is incidental entanglement in gillnets (5) (9), but it is not believed to be at risk of imminent extinction (2). In the Ayeyarwady River it is also at risk from electrocution and prey depletion from electric fishing (10). Other issues affecting this dolphin include increasing pollution, construction of dams and the build-up of silt and sedimentation following severe erosion (2). Fishing with explosives also results in dolphin casualties (4). Most live captures are for the oceanarium trade in Asia (4), and hunting of this species is rare, occurring only in parts of India to harvest oil for the treatment of rheumatism (2).

Very few provisions have been made to conserve the dolphins or their habitat. The Irrawaddy dolphin is protected by law in Laos, Vietnam and Cambodia. Direct taking of cetaceans is prohibited in Bangladesh, India, Laos, Malaysia, Myanmar and Thailand. (9). In December 2005, the Department of Fisheries in Myanmar established a protected area for Irrawaddy dolphins along a 74 kilometre segment of the Ayeyarwady River. Protective measures in the area include requiring fishermen to immediately release dolphins if found alive and entangled in their nets, and prohibiting the trade and catching or killing of dolphins and the use of electricity fishing and gill nets that obstruct the water-course, are more than 300 feet long, or spaced less than 600 feet apart (11). The problem of live captures for the aquarium trade has largely been solved by the uplisting of the species to Appendix I of the Convention on International Trade in Endangered Species (CITES) which prohibits international trade. Some captive breeding of this species has been successful (2).

View information on this species at the UNEP World Conservation Monitoring Centre.

To learn more about a Whitley Award-winning conservation project for this species, click here.

For further information on the conservation of the Irrawaddy dolphin see:

• Whale and Dolphin Conservation Society (WDCS):
  www.wdcs.org