The Undersea World of Sound

Snorts, dicks, whistles, groans tune in to the long-distance language of the ocean.

The vast oceans of the world are dark, deep and mysterious places where eyesight counts for little as soon as you venture very far beneath the surface.

For humans, who live in a world dominated by visual stimuli, to exist in such conditions would be impossible. But for whales and dolphins that live in the ocean or, in the case of a few species, muddy rivers and estuaries, the darkness is unimportant. What is crucial to them is sound.

Sound is an efficient way to transmit and sense information, especially as it travels five times faster through water than through air. If humans shout to someone, it is unlikely that they will be heard a kilometer away. But if a whale 'shouts' in an ocean channel, another whale may hear it tens, if not hundreds of kilometers away.

Whales and dolphins use sound in two ways: for communication and for echolocation. Dolphins, porpoises and toothed whales communicate through a wide variety of high-frequency sounds - pure tone whistles, pulsed squeals, screams or barks –generally at frequencies of 5OOHz to 20kHz (where a hertz is a cycle per second and a kilohertz a thousand).

But as well as using sounds to communicate, toothed whales and dolphins also rely on echolocation to learn about their immediate environment, including prey that might be lurking nearby. They produce intense short broad-band pulses of sound in the ultrasonic range of between 0.25 and 220 kHz. These clicks are brief – typically less than one millisecond long – but they are repeated many times each second.