Ocean Noise and Marine Life

To human ears, the deep ocean may seem like a silent world, but it is in fact full of sound. Many marine animals, especially whales and dolphins, depend on sound far more than on sight, using it to find food, navigate, and communicate across great distances. In clear water, light fades within a few hundred meters, whereas sound can travel for many kilometers without growing weak. For these animals, then, hearing is not a minor sense but their （ 1 ） way of understanding the world around them.

Over the past century, however, the oceans have grown far noisier. The engines of cargo ships, the powerful sonar used by navies, and the equipment used to search for oil and gas beneath the seabed all add to a steady background of human-made noise. This noise can drown out the calls that animals use to find mates, stay together as a group, or warn one another of danger. （ 2 ） loud, unfamiliar sounds, some whales have been known to abandon important feeding grounds or to become separated from their young.

Reducing this problem may be more achievable than reducing many other forms of pollution. Unlike chemicals, noise leaves no lasting trace, so the ocean becomes quieter almost as soon as the source is switched off. Engineers have shown that redesigning ship propellers and simply asking vessels to slow down can cut underwater noise significantly, often at modest cost. （ 3 ） such measures, scientists hope, the seas can be made calmer for the many creatures that have always depended on them.