Irrawaddy Dolphin - Habitat and Subpopulations

Habitat and Subpopulations

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 subpopulations 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.

It is often seen in estuaries and bays in Borneo Island, with sightings from Sandakan in Sabah, Malaysia, to most parts of Brunei and Sarawak, Malaysia. A specimen was collected at Mahakam River in East Kalimantan.

No range-wide survey has been conducted for this vulnerable species; however, the worldwide population appears to be over 7,000, with over 90% occurring in Bangladesh. Populations outside Bangladesh and India are classified as critically endangered. Known subpopulations of Irrawaddy dolphins are found in eight places, listed here in order of population, including conservation status.

1. Bangladesh; 5,832 (VU) in coastal waters of the Bay of Bengal and 451 (VU) in the brackish Sundarbans mangrove forest
2. India; 138 (VU) in the brackish water Chilka Lake
3. Laos and Cambodia; 78-91 (CR) in a 190 km (118.1 mi) freshwater stretch of the Mekong River
4. Indonesia; (CR), in a 420 km (261.0 mi) stretch of the freshwater Mahakam River
5. Philippines; about 42 (CR) in the brackish inner Malampaya Sound. Researchers are studying the recent discovery of 30-40 dolphins sighted in the waters of Bago City and Pulupandan town in the province of Negros Occidental, in Western Visayas
6. Burma; about 58-72 (CR) in a 370 km (229.9 mi) freshwater stretch of the Ayeyarwady River
7. Thailand: less than 50 (CR) in the brackish Songkhla Lake.