Indus River Dolphin: Special Biological Features

The Blind Dolphin

	© WWF
Did you know? People who live by the Indus River call the dolphin "susu" (an Urdu word) after the sound it makes - a sneeze-like breathing sound.

The Indus River dolphin is functionally blind having evolved without a crystalline lens or well-developed light-sensitive organ.

A deep fold just above the dolphin's mouth is the remnant of what might once have been eyes down the evolution line.

However, this is not a disadvantage but an adaptation to living in the silt-laden turbid waters of the Indus where eyes are virtually useless, as very little light penetrates below the surface of the murky water.

Echolocation: How does the dolphin sonar work?
Dolphins (and other toothed whales) can produce high-pitched clicks. These sound pulses are emitted into the water through the 'melon' at the front of the dolphin's head. When these clicks hit an object, some of the sound echoes back to the "sender".

By listening to the echo and interpreting the time it took the echo to come back, the dolphin senses the distance of the object. (That's why sonar is also called echolocation). One click often results in a number of weaker echoes.

This gives the dolphin some information about the structure and size of the object. By moving its head (thereby aiming the clicks at other parts of the object) the dolphin can get more information on other aspects of the object.

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