Ocean Noise in the News
January 08, 2006
Scientists link sonar to some fatal whale beachings, though they aren't certain how the underwater sound causes trouble. Some suspect it can startle animals, making them surface so fast that they get the decompression illness known as the bends.
Environmentalists suspect that Navy sonar caused the rare beaching of three whale species in January 2005 on the Outer Banks. A federal National Marine Fisheries Service report expected as early as this month may or may not clear that up.
"There are so many hurdles to understanding the effects of sonar," said Andy Read, a Duke University marine mammal biologist based in Beaufort. "There are many questions we can't answer yet. The Navy can't answer them yet either."
The Navy acknowledges that some whales, very rarely, can be harmed by sonar. But on the basis of research and computer models, it concludes that a proposed sonar off North Carolina would bother, but not injure, a fraction of the marine mammals out there.
Protective steps would reduce that risk to almost nothing, the Navy says. The plan calls for posting trained scouts on ship decks to watch for animals and listening underwater for the animals. The Navy would decrease the strength of sonar signals when creatures get too close.
"We expect some behavioral reactions, whether it will be the animals turning away to leave the area or exhibiting some disturbance. We expect nothing more than that," said Aileen Smith, a Navy biologist and natural resources manager for the U.S. Fleet Forces Command in Virginia.
The Navy says it needs an Atlantic Ocean sonar range as a realistic training ground for sailors and pilots to detect a new generation of submarines. Powered by batteries and air-propulsion systems, the quiet vessels can sneak into coastal waters, unlike the deep-water subs the Navy chased during the Cold War.
A sonar system emits pulses of sound, which bounce off objects underwater. By analyzing the echoes, the Navy can detect and track what it cannot see. Sonar is a vital defense tool, but attention is growing to the technology's unintended consequences.
With a federal court suit, environmentalists in 2003 forced the Navy to limit use of its most powerful (low-frequency) sonar to a portion of the Pacific Ocean. This fall, environmentalists filed a second lawsuit, asking a federal court to also restrict the Navy's use of mid-frequency sonar, the kind envisioned for the training range off the North Carolina coast.
Mid-frequency sonar's primary use is to detect enemy submarines nearby - within 10 nautical miles. If the range is built, sailors and pilots aboard surface ships, aircraft and submarines would use it to test and refine their detection skills.
The loudest sonar on the range would produce pings reaching 235 underwater decibels. Scientists are still developing scales to describe underwater noise, but 235 underwater decibels is louder than the song of a humpback whale, which a nearby human listener can hear - and feel - underwater. Sonar pings are sustained for only a few seconds, however, while whale sounds go on for minutes, which makes the effect louder, scientists say.
The Navy evaluated potential sonar range sites off North Carolina, Virginia and Florida. But it has long favored a patch of ocean 47 miles offshore of the Marines' Camp Lejeune in Jacksonville. It's at the edge of the continental shelf and in the path of the warm-water Gulf Stream. Waters there teem with many types of fishes, sea turtles, dolphins and whales.
(Distributed by Scripps Howard News Service, http://www.shns.com.)