How dolphins and porpoise use sound
Whales and dolphins (collectively called cetaceans) live in a world in which it is often difficult to see very far. Even in the clearest tropical water the visibility is less than a few hundred feet. Here in Cardigan Bay the visibility is usually not more than 30 feet. This means that cetaceans cannot rely on their vision to communicate or forage. Instead they use sound to explore their water world.
The dolphin can work out how far away the fish is from the time it takes the click that was sent out to return. The click returns when it bounces back of an object. If the dolphin keeps producing clicks and receiving the echos, it will get information back about the speed and direction that the fish is moving.
An echolocating dolphin can detect a 2.5cm object from 72 metres away! If the dolphin is far from the target it will produce clicks at a slow rate. The closer the dolphin gets to a target, the faster the clicks bounce back and the faster the dolphin sends out more clicks to detect the object the clicks are bouncing off.