The Irrawaddy Dolphin (Orcaella brevirostris) is a species of dolphin found near coasts and in estuaries in parts of south-east Asia.
Taxonomy:
The Irrawaddy Dolphin was identified by Owen in 1866 and is the only species
in its genus. It is similar to the beluga in appearance. It has sometimes
been listed in either a family containing just itself and in Monodontidae
and Delphinapteridae. Nowadays there is widespread agreement to list it in
the Delphinidae family
Genetically the Irrawaddy Dolphin is closely related to the Orca. The species name brevirostris comes from the Latin meaning short-beaked.
Physical description:
This species has a large melon and a blunt, rounded head. Its beak is indistinct.
The dorsal fin is short, blunt and triangular. It is located about two-thirds
of the way along the back. The flippers are long and broad. It is lightly
coloured all over - slightly more white on the underside than the back. It
appears whiter than it actually is when set against the background of a muddy
river.
Length is about 1 m at birth and 2.3 m at full maturity. Birth weight is about 10 kg. Adult weight exceeds 130 kg. Lifespan is about 30 years.
The Irrawaddy Dolphin is a slow swimmer. It surfaces in a rolling fashion and lifts its tail fluke clear of the water for a deep dive only. Irrawaddy Dolphins spit streams of water from their mouths whilst spyhopping. Dolphins of the species kept in captivity have been trained to do this on demand.
Population and distribution:
Although sometimes called the Irrawaddy River Dolphin, it is not a true river
dolphin but an oceanic dolphin that lives near coasts and enters rivers, including
the Ganges and the Mekong as well as the Irrawaddy from which it takes its
name. Its range extends from the Bay of Bengal to New Guinea and northern
Australia.
Human interaction:
On account of their coastal nature Irrawaddy Dolphins are more susceptible
to interference than other river dolphins. The most direct threat is the capturing
of Irrawaddys for their oil. As an endangered species, they are legally protected
from hunting, however, enforcement may be poor along tens of thousands of
miles of coast line. Entanglements in gillnets and deaths injury due to explosives
used in fishing are common in Vietnam and Thailand. All along its distribution
population and other habitat degradation worries conservationists. Human influence
such as nets crossing river channels restrict movement and isolate populations,
causing them to decline. The population in India's Chilka Lake, which has
suffered from entanglement in fisher's gill nets and drag nets, is believed
to have dwindled to as few as 50 individuals.
Irrawaddys are also taken to perform in aquariums. Though this practice is less common than it used to be, it still has a significant local impact.
The IUCN lists several populations, including those in the Mahakam River and Malampaya Sound, as critically endangered.
References:
National Audobon Society Guide to Marine Mammals of the World
Encyclopedia of Marine Mammals
Whales, Dolphins and Porpoises, Mark Carwardine.