Noise Pollution Rising At Sea

Man-Made Din May Harm Marine Life

(AP)  The ocean was flat and the winter darkness over Cape Cod Bay was unbroken by ship lights. But below the bay's surface, Christopher Clark found things weren't as serene as they seemed.

The bay is saturated with sound.

"It's just a great, big amphitheater," said Clark, a Cornell bioacoustics scientist who monitored the bay with underwater listening devices.

The sound carrying through the bay that evening was part of an ever louder man-made din that's filling the world's oceans, and some say harming marine life.

High profile whale beachings have been linked to sonar blasts and sparked fierce public debate over the military's use of sound in national defense. But a broader concern for scientists is rising levels of ocean background noise, much of it generated by commercial shipping, and whether it interferes with the way the entire sea has operated for eons.

Based on volume of traffic alone, scientists know the North Atlantic and North Pacific oceans, which are the busiest, are also the noisiest, Clark said. The area around Indonesia is heavy too with shipping traffic.

Hearing is the primary sense for marine life, which uses sound for navigation and communication. Some scientists believe the spreading "acoustic smog" is essentially blinding marine life, affecting feeding, breeding and other crucial activities.

"Their world is just being collapsed," Clark said. "They rely so heavily on sound. They can't see anything."

Despite concerns, evidence is scant of the real effects of sound.

Even with new technology, ocean animals are hard to track, and drawing conclusions about how sound influences their behavior is difficult. No system exists to monitor ocean sounds worldwide, and the data that's collected is often taken from a small number of
sites that measure only certain frequencies. Underwater sound also seems to affect different animals in completely different ways.

Businesses and the military are unlikely to make major changes before more is known.

Brandon Southall, an acoustics researcher at the National Oceanic & Atmospheric Administration, said better research is urgently needed.

"People are inherently tied to the ocean for food, for cures to diseases, for weather," he said. "We're figuring out things are more interconnected than we ever could have originally envisioned."

Sound, which is created when molecules collide, carries farther and five times faster in water than air because of water's density. Since molecules in water are spaced closer together, they lose less energy before colliding with other molecules and sound is transferred more quickly and efficiently.

Through the ages, marine animals have learned to take advantage of the ocean's natural sound stages. Whales, for instance, talk about basic things like where the best food or breeding is. They even seem to compete to produce the most intricate songs.