Irrawaddy Dolphin
Orcella brevirostris
Lifespan:
~30 years
IUCN:
Endangered in coastal waters, freshwater regions critically endangered
Distribution
Throughout South East Asia in sheltered coastal waters eg. estuaries, mangroves and deltas
5 isolated freshwater populations: Myanmar, Borneo, Lao and Cambodia (Mekong), India, Thailand
Whilst not described as a river dolphin, there are isolated freshwater populations hundreds of miles from the coastline
Description
Max size: adult males up to 280cm (130kg), newborns up to 100cm (10kg)
Beakless with blunt-rounded heads
Flexible necks leaving obvious neck creases and a straight mouth line with movable lips giving the appearance of a smile
Slate-grey colour with a paler underside producing a bipartite pattern
Behaviour and Ecology
Usually seen travelling in groups of 2-3 but occasionally reach up to 15 individuals
Diet consists of fish, shrimp and cephalopods hunted in shallow water
Very social but not very active at surface; can occasionally be seen low breaching
Spit water to potentially confuse fish during hunting
Myanmar population fish cooperatively with local fishermen by herding fish towards the boat - dolphins pick off the weaker individuals and those that are trapped around the outskirts of the net before the fishermen retrieve their nets
Main Threats
Habitat Loss
Damming affects the freshwater populations as they become isolated and confined to smaller areas which means reduced hunting opportunity.
They are now restricted to 40% of their original range.
Coastal populations are also affected by dams as they reduce the flow into estuaries and mangroves
Bycatch
Arguably the biggest threat to Irrawaddy dolphins as they get entangled in small scale gillnets - this has always been the biggest reason for premature death and is increasing every year
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Captivity
Irrawaddy dolphins are attractive to aquaria as they are relatively easy to catch using small fishing boats.
Individuals have been taken from Cambodia, Myanmar, Indonesia, Vietnam and Thailand in the past.
A ban on international commercial trade (CITES) came into effect in 2004 which stopped the capture of wild specimens of Irrawaddy dolphins.
Pollution
Industrial and domestic waste enters the rivers resulting in high levels of water contaminants in both freshwater and coastal habitats.
Six populations have been recorded to have skin abnormalities likely associated with high levels of water pollution.
Fun facts
Named after the Ayeyarwady River in Myanmar, formerly known as the Irrawaddy River when Myanmar was Burma; in the Sundarbans mangrove forest Irrawaddy Dolphins occupy the same habitat of ganges river dolphins
Coastal Cambodian populations occupy the same space as Indo-pacific humpback dolphin and Indo-pacific finless porpoiseLaotian and
Cambodian folklore suggests Irrawaddy Dolphins to be reincarnations of their ancestors
West Kalimantan people share stories of Irrawaddy Dolphins being naughty children that stole rice from the shaman, but they burnt their mouths and jumped into the river to cool down but transformed into Irrawaddy Dolphins
