Cetaceans—mammals of the sea, a group including whales, dolphins, and porpoises—have auditory systems similar to man, though much more sensitive. Because of poor visibility conditions underwater, hearing is much more important than seeing. Hearing, interpreting, and acting on auditory information is an oceanic matter of life and death.
In water, the velocity of sound is 4.3 times greater than in air. Sounds are intensified, and marine mammals today are being increasingly stressed by noise pollution in the sea. The sources are many: shipping, oil and gas development, seismic surveys, marine construction, and military operations. Each of those noise sources is increasing, further intensifying their damage to life in the sea.