Irrawaddy dolphin

Orcaella brevirostris
Maximum length: 
  • Male: 2.75m
  • Female: 2.3m
  • Calf: 1m
Maximum weight: 
  • Male: 130 kg's
  • Female: Unknown
  • Calf: 10 kg's
Diet: 
  • Fish
  • Cephalopods
Estimated population: 
Unknown
IUCN Listing: 
VU (All Riverine populations are classified as CR; Ayeyarwady, Mekong and Mahakam River, Malampaya Sound and Songkhla Lake)
CITES Appendix: 
I
CMS Appendix: 
I, II
Classification: 

The Irrawaddy dolphin is closely related to the Australian snubfin dolphin, and the two were only recently recognised as distinct species. As well as marine populations, there are five distinct freshwater populations of Irrawaddy dolphin; Mahakham, Ayeyarwady and Mekong Rivers, Songkhla Lake and Malampaya Sound. The relatively small size of the Irrawaddy dolphin, its mobile ‘expressive' head and its ability to spit water when instructed have unfortunately made this species popular in captivity in recent years. Its preference for coastal and estuarine habitats has also put it at risk from development which in some areas has caused serious fragmentation of populations.

Appearance: 

The Irrawaddy dolphin is robust with a round melon, no beak, and a mouthline that angles up, giving it a smiling appearance. It has a long flexible neck, allowing it to turn its head from side to side, a distinct neck crease, and a small triangular dorsal fin with a blunt tip. The flippers are large and spatulate, with curved leading edges and rounded tips. The Irrawaddy dolphin has a uniform dark blue-grey to medium grey or pale blue colouration, with a paler underside. Some individuals are lighter all over, giving them the appearance of a small beluga, only one with a dorsal fin. In the field it is most likely to be confused with the finless porpoise (or even sometimes the dugong) but the porpoise is much smaller and lacks a dorsal fin (as does the dugong).

Behaviour: 

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 have been seen spitting water from their mouths in the wild, and this behaviour is thought to help them hunt by confusing schools of fish. 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. Irrawaddy dolphins are known to cooperate with fishermen in both the Ayeyarwady and Mekong Rivers by driving fish into the waiting nets.

Distribution: 

The Irrawaddy dolphin is distributed across the coastal Indian Ocean from India to Indonesia. It prefers deep pools of large rivers, sheltered inshore marine waters with substantial freshwater inputs, like mangrove swamps and lagoons, and partially isolated brackish or freshwater bodies. They are never found more than a few miles offshore and individuals have been found more than 1,300km upstream, with some spending their entire lives in fresh water. These habitats bring the Irrawaddy dolphin into close contact with many human activities and the construction of dams has significantly reduced the natural range of the freshwater populations. Irrawaddy dolphins are principally threatened by incidental mortality in gillnets and other fisheries gear, although prey depletion, habitat alteration and pollution from agrochemicals are all believed to be taking a toll. The IUCN listed the Irrawaddy dolphin as Vulnerable in 2008, although the five aforementioned freshwater populations, are listed as Critically Endangered.

Distribution map: