Irrawaddy Dolphin

The Irrawaddy dolphin's colour is grey to dark slate blue, paler underneath, without a distinctive pattern. The dorsal fin is small and rounded behind the middle of the back. The forehead is high and rounded; the beak is lacking. The front of its snout is blunt. The flippers are broad and rounded. The finless porpoise (Neophocaena phocaenoides) is similar and has no back fin; the humpback dolphin (Sousa chinensis) is larger and has a longer beak and a larger dorsal fin.

It ranges in weight from 90 to 200 kg (200 to 440 lb) with a length of 2.3 m (7.5 ft) at full maturity. The maximum recorded length is 2.75 m (9.0 ft) of a male in Thailand.

The Irrawaddy dolphin is an oceanic dolphin that lives in brackish water near coasts, river mouths, and estuaries. It has established subpopulations in freshwater rivers, including the Ganges and the Mekong, as well as the Ayeyarwady River, from which it takes its name. Its range extends from the Bay of Bengal to New Guinea and the Philippines, although it does not appear to venture offshore. It is often seen in estuaries and bays of Borneo, with sightings from Sandakan in Sabah to most parts of Brunei and Sarawak, and another specimen was collected at Mahakam River in East Kalimantan. Its presence in Chinese, Taiwanese, and Hong Kong waters has been questioned, as the reported sightings have been considered unreliable.

Bangladesh: ~3,500 in coastal waters of the Bay of Bengal and 451 (VU) in the brackish Sundarbans mangrove forest

There are plenty of food items that this dolphin feeds upon. They include fish, crustaceans, and cephalopods. During foraging periods, herds of about 7 dolphins will circle around prey and trap their victim. These prey entrapments occur slightly below the water surface level.

Communication is carried out with clicks, creaks, and buzzes at a dominant frequency of about 60 kilohertz, which is thought to be used for echolocation. Bony fish (including catfish) and fish eggs, cephalopods (such as squid, octopus, and cuttlefish), and crustaceans are taken as food. Observations of captive animals indicate food may be taken into the mouth by suction. Irrawaddy dolphins are capable of squirting streams of water that can reach up to 1.5 metres (4 ft 11 in); this distinct behaviour has been known for herding fish into a general area for hunting. They do this sometimes while spyhopping and during feeding, apparently to expel water ingested during fish capture or possibly to herd fish. Some Irrawaddy dolphins kept in captivity have been trained to do spyhopping on command.

A female or male dolphin will attempt to pursue a mate for about a few minutes. They intertwine, facing their bellies together, and begin to copulate for 40 seconds. Once copulation has occurred, the dolphins will break away from each other and set off in different directions.

Irrawaddy dolphins have a mutualistic relationship of co-operative fishing with traditional fishers. Fishers in India recall when they would call out to the dolphins by tapping a wooden key, also known as a lahai kway, against the sides of their boats, asking the Irrawaddys to drive fish into their nets. In Burma, in the upper reaches of the Ayeyarwady River, Irrawaddy dolphins drive fish towards fishers using cast nets in response to acoustic signals from them. The fishermen attempt to gain the attention of the dolphins through various efforts such as using a cone-shaped wooden stick to drum the side of their canoes, striking their paddles to the surface of the water, jingling their nets, or making calls that sound turkey-like. A pod of dolphins that agrees to work alongside the fisherman will entrap a school of fish in a semicircle, guiding them towards the boat.