S.C.U.B.A. Diving

February 27, 2006 — By Tara Godvin, Associated Press

HONOLULU — Rain falling on the surface of the ocean can be heard more than a mile deep, and at some frequencies it's louder than passing ships, according to oceanographer Jeff Nystuen.

Nystuen, of the Applied Physics Laboratory at the University of Washington, is one among scientists studying how sound travels through the ocean, to better understand how loud, man-made noises might affect marine creatures.

"We don't really know what is too loud underwater, and we need to know what the baseline is," Nystuen said.

Loud underwater noises, particularly U.S. Navy sonar, have long been blamed by environmentalists for the fatal beachings of whales.

The Natural Resources Defense Council and other plaintiffs alleged in a federal lawsuit last fall that the Navy's mid-frequency sonar used for detecting enemy submarines disturbs and sometimes kills whales and dolphins.

The Navy settled a similar lawsuit three years ago by agreeing to limit its peacetime use of experimental low-frequency sonar.

To find out what sounds sea creatures are exposed to, Nystuen moored microphones at spots around the world, from the Mediterranean to the South China Sea, to collect a year's worth of sound. He spoke Thursday during the biannual ocean sciences meeting of the American Geophysical Union.

Building up his inventory of sounds since 1999, Nystuen is looking for long-term patterns of relative loudness.

His findings show that among higher pitched sounds, rain is the loudest, far louder than passing ships. Among lower-pitched sounds, shipping is the loudest sound, followed by rain.

Nystuen's recordings haven't yet been able to account for the creatures' behavior in response to noise.

"If you came to see me in Seattle and said, 'I want to see some killer whales,' I would take you to Haro Strait, which is the noisiest environment that I've ever made measurements in," he said. Haro Strait lies between the U.S. and Canada near Victoria.

Nystuen said his listening devices could be used to make sure animals aren't nearby before setting off a blast or testing sonar.

The U.S. Army Corps of Engineers spent three years figuring out how best not to harm protected species during a project completed this summer at the port of Miami that required the agency to blast solid rock out of the harbor, said Terri Jordan, a biologist with the corps.

Before triggering any explosion, a 4,000-foot perimeter was searched by helicopter and boat for signs of any animals, including porpoises, manatees and sea turtles.

If any animal wandered within about 2,500 feet of the blast site, the project stopped until the animal left. The width of the perimeter was calculated by doubling the distance usually used to protect Navy divers from bomb blasts.

Five minutes prior to the main explosion, a smaller "fish scare" blast was set off to scatter any fish in the area.

During the 40-day project, workers logged 186 animals and only one possible reaction -- a dolphin that jumped out of the water during a blast.

As shipping traffic increases, ports will need to expand their capacity and often will need to remove underwater rock, Jordan said -- and that will mean blasting.

"So we think this is where we'll be going in the future unless new construction techniques become available," she said.

Source: http://www.enn.com/today.html?id=9960