Noise Pollution Rising At Sea

Man-Made Din May Harm Marine Life

(AP) 
Researchers believe animals may use the ocean's natural "sound channels" to communicate over thousands of miles. The channel is created where dropping temperatures, which force sound waves downward, meet increasing water pressure, which forces sound waves upward. At a certain depth, the sound gets caught between the two opposing forces and bounds ahead with little resistance.

Researchers suspect that dumping a cacophony of new noise into this system isn't good. Southall said there's convincing evidence of a phenomenon called "masking," in which the increased ambient noise drowns out natural ocean communications.

Huge increases in commercial shipping have coincided with increased ocean noise. Between 1948 and 1998, the world shipping fleet has increased from 85 million tons worth of ship weight to 550 million tons, according to figures in a 2003 report "Ocean
Noise and Marine Mammals," published by the National Academies. Scientists say the background noise in the ocean has increased roughly 15 decibels in that time.

Joel Reynolds, director of the Marine Mammal Program at the Natural Resources Defense Council, said there's evidence marine mammals are changing their sound patterns or rates, which could show their normal communication has been disrupted.

Kathy Metcalf, director of Maritime Affairs at the Chamber of Shipping in America, said she concedes that increasing ocean noise caused by ships will at some point interfere with marine life. Metcalf advocates pre-emptive steps, such as installing quieter propellers in new ships, which would reduce noise and likely benefit the industry by increasing the efficiency with which ships move through water.

But retrofitting current ships to reduce noise would be extremely expensive, and the benefit is uncertain, she said.

"If somebody is going to signal we need to start absorbing these costs when we're not even sure there's a negative impact, that's where we're digging in our heels," she said. "There's a huge issue surrounding the validity of the science on this issue."

Southall acknowledges the mountain of work ahead to come up with real answers about ocean noise. To illustrate the difficulties of applying the science to ocean life, he points to the beluga whale, which flees from ship sounds in the high Arctic, but moves toward certain vessels in Alaska.

He added that sound is perceived by ocean animals so differently than land animals that it's almost like a different sense, making it hard to apply what we know about the effects of certain decibel levels to ocean life.

Still, Southall said he's optimistic that the emerging interest in the topic will lead to breakthroughs.

Reynolds said regulating ocean sound doesn't mean ending all its benefits, whether it's better national defense or the robust trade that comes with heavy shipping.

"We have to treat it like any other form of pollution," Reynolds said. "We have to regulate it to protect other things we care about."

Clark said uncertainties can't be an excuse to do nothing, because the damage might be done by the time the effects of noisy oceans are known.

"It's like global warming," he said. "We're going to get one chance."