Common Name: Irrawaddy Dolphin
Size comparison against an average human
Finless Porpoise range.
General Description: The Irrawaddy Dolphin resembles the Beluga or White Whale Delphinapteras leucas of Arctic waters, with its stout body, rounded head, well developed bulging eyes and distinct melon but no beak.
It is also similar in appearance to the Finless Porpoise Neophocaena phocaenoides, but is larger and has a dorsal fin. The dorsal fin is small and sickle-shaped with a rounded tip, and is placed well behind the midpoint of the body. Beyond this, a keel extends backwards on to the tail.
It has broad, long, paddle-like flippers. The mouthline is horizontal. There is a neck crease and the head can be freely moved. The colour of the animal is bluish grey - darker above, paling gradually to the belly
Size: Adults, Male Irrawaddy Dolphins grow to a length of 2.7 m, and females to 2.3 m. Weigh 90 to 150 kg. Calves at birth, 90 cm long.
Appearance At Sea: Irrawaddy Dolphins are usually seen alone or in small groups of 3 or 4, feeding or swimming together upstream or against the tide. Nothing is known of their social or reproductive behaviour except that calving apparently takes place in August off the Asian coast.
This species is quiet and inconspicuous, rising slowly to the surface so that only the rounded head protrudes, and then sinking quickly after blowing. This procedure is repeated 2-5 times at 10-second intervals, and is followed by a deeper dive which takes the dolphin out of view for up to 3 minutes.
Found In: Irrawaddy dolphins are usually found in coastal waters: rivers, estuaries, backwaters, brackish lagoons and mangrove creeks, not to be seen beyond one or two kilometres from the shore. However, it has also been reported to ‘travel in the open oceans’ in tropical regions. The Irrawaddy Dolphin feeds on the bottom in muddy water, catching fish and crustaceans.
Records from India:The following are the records of the Irrawaddy Dolphin Orcaella brevirostris from India:
|1866 [?]||Type skull, collected by Sir Walter Elliot at Vizagapatam, in
the British Museum (Natural History).
|De Silva, 1987|
|[?]||Record from Ganges river, 70–80 m upstream of the
Bay of Bengal.
|De Silva, 1987|
|19 November 1977||One live animal stranded on the Madras beach after a cyclone.||Miller, 1997|
|1915[?]||Large dead male specimen washed ashore on Kaladi Island,
|1985–1987||Decomposed body on Breakfast Island, and a dead female
specimen afloat in the northern sector of Chilka Lake,
apart from three live animal sightings.
|January–March 1987||One dead specimen washed ashore at Gahirmatha Beach,
Bhitarkanika Wildlife Sanctuary, Orissa.
|James et al., 1989|
It was estimated that there were no more than 20 Irrawaddy dolphins left in Chilka, where their population declined severely because of intense fishing activities. Fishermen of Sri Lanka also catch the Irrawaddy Dolphin as incidental by catch.
World Distribution: Irrawaddy Dolphins are found in the Ganges, Brahmaputra, Irrawaddy and Mekong rivers. This species is also known to be found in the tropical waters of the Indo-Pacific, from northern Australia and New Guinea through South-East Asia to the Bay of Bengal, which forms the western limit of its range.
Could Be Confused With: There is a possibility of confusion with the Finless Porpoise Neophocaena phocaenoides which also occurs in the same area and habitat.
|Snubfin Dolphin||Relatively large||The shade is more gray than blue.||Dorsal fin with rounded tip present|
|Finless Porpoise||Small||The shade is more blue than gray.||Dorsal fin absent|
Diagnostic Features: At sea, globose head and small snub fin.
Stranded specimens: The body shape is usually sufficient to identify the species. The Irrawaddy Dolphin has a distinctive skull. There are 12 to 20 pairs of teeth in the upper jaw and 12 to 18 teeth in each side of the lower jaw. The teeth are peg-like.