Irrawaddy Dolphin

The irrawaddy dolphin (Orcaella brevirostris) is a species of dolphin found in sea coasts in estuaries and rivers. The irrawaddy dolphin has a striking resemblance to the beluga whale even though it’s more related to the orca.

It has a large melon and a blunt, rounded head, and the beak is indistinct. The dorsal fin, located about two-thirds posterior along the back, is short, blunt, and triangular. The flippers are long and broad. It is lightly colored all over, but slightly more white on the underside than the back. Unlike any other dolphin, the Irrawaddy’s u-shaped blowhole is placed on the left of the midline and opens towards the front of the dolphin. Their short beaks appear very different than those of other dolphins, and their mouths are known for having 12-19 peg-like teeth on each side of their jaws. Irrawaddys can range from 90kg to 200kg and the length is 2.3m at full maturity. The Irrawaddy dolphins’ color is grey to dark slate blue, paler underneath, with no distinctive pattern. The dorsal fin is small and rounded behind the middle of the back and it has a forehead that is high and rounded.

Irrawaddy dolphins have a seemingly mutualistic relationship of co-operative fishing with traditional fishers. According to Wikipedia, “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 grasp the attention of the dolphins through various efforts such as using a cone-shaped wood stick to drum the side of their canoe, striking their paddles to the surface of the water, jingling their nets, or making calls that sound turkey-like. A herd of dolphins, who agree to work alongside the fisherman, will entrap a school of fish in a semi-circle, guiding them towards the boat. In return, the dolphins are rewarded with some of the fishers’ bycatch Historically, Irrawaddy River fishers claimed particular dolphins were associated with individual fishing villages and chased fish into their nets. An 1879 report indicated legal claims were frequently brought into native courts by fishers to recover a share of the fish from the nets of a rival fisher which the plaintiff’s dolphin was claimed to have helped fill.”

 

 

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