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Most sea creatures. from whales and dolphins to fish . sharks, shrimps and possibly even anemones respond to sound, and many can produce it. They use it to hunt and to hide, find mates and food, form and guide shoals, navigate 'blind', send messages and transmit warnings, establish territories, warn off competitors, stun prey, deceive predators, and sense changes in water and conditions.
Marine animals click bones and grind teeth; use drum-tight bladders and special sonic organs to chirp, grunt, and boom: belch gases; and vibrate special organs. Far from the 'silent deep', the oceans are a raucous babel.
Into this age-long tumult, in the blink of an evolutionary eye, has entered a new thunder: the throb of mighty engines as 46,220 large vessels plough the world's shipping lanes. Scientists say that background noise in the ocean has increased rough ly by 15 decibels in the past 50 years. It may not sound like much in overall terms; but it is enough, according to many marine biologists, to mask the normal sounds of ocean life going about its business. At its most intense, some even say noise causes whales to become disoriented, dolphins to develop 'the bends'. fish to go deaf, flee their breeding grounds or fail to form shoals - enough to disrupt the basic biology of two thirds of the planet.
'Undersea noise pollution is like the death of a thousand cuts', says Sylvia Earle, chief scientist of the US National Oceanic and Atmospheric Administration. 'Each sound in itself may not be a matter of critical concern, but taken all together. the noise from shipping. seismic surveys, and military activity is creating a totally different environment than existed even 50 years ago. That high level of noise is bound to have a hard, sweeping impact on life in the sea.