Since 1998, when the journal Nature published the first documented report linking mass strandings of whales with the use of sonar in military exercises, the public has increasingly come to understand that the sounds humans make in the sea can harm the creatures that live there. But while dramatic incidents involving military sonar have received extensive media attention, a much more widespread and potentially more insidious source of ocean noise has stayed below the radar: the huge cargo and tanker ships that haul ever-increasing loads of goods across the world’s oceans.

Over 90 percent of world trade is transported by ship. In one year, 2004, about 6.7 billion metric tons of cargo were hauled over a distance of about 4 million miles, according to the Round Table of International Shipping Associations. The noise from individual ships is not as loud as sonar or the seismic air guns used to explore for oil and gas, but the cumulative noise from cargo vessels pervades wide swaths of the oceans, particularly near shores, which is also where much marine life is concentrated. Because it also occupies the low-frequency bandwidth in which many whales and fish produce and perceive sounds, some scientists fear that vessel noise may be creating a diffuse aural “fog” that can mask crucial natural sounds--such as those that animals use to navigate, find food, communicate, or detect the approach of predators.

“I believe shipping is far and away the one [noise] source that has the potential to affect whole marine animal populations,” said Brandon Southall, director of the Ocean Acoustics Program of the National Oceanic and Atmospheric Administration (NOAA). “It’s an everyday, chronic source of noise in many places.”

A continuing increase in shipping noise is all but certain. The boom in global trade is driving demand for more and bigger ships; ports are being expanded in China, Korea, the U.S., and elsewhere, and new ones are being planned. New sea lanes are being considered along shorelines and also, as the polar ice melts, through sensitive Arctic marine habitats. In light of this expansion of ocean traffic, some people in government agencies, research institutions, and the shipping industry have begun to explore ways to quiet ship noise as soon as possible, rather than waiting for unquestioned evidence of a problem to emerge--something that could take decades, if not longer.