GULF OF THE FARALLONES NATIONAL MARINE SANCTUARY — As the 45-foot-white catamaran "Kitty Kat" bobbed in the ocean near the Farallon Islands last month, Jackie Dragon dropped a hydrophone overboard to capture the underwater sounds of an oil tanker gliding by a mile to the south.

To those watching it from the catamaran, the 900-foot, black-and-white tanker cruised in majestic silence out to sea through the marine sanctuary, due west of the Golden Gate Bridge.

But a speaker attached to the waterproof microphone soon broke the silence, as it transmitted the underwater racket caused by the tanker's propeller. To Dragon, the rhythmic churning resembles the sound of a freight train.

"Now you really hear it," Dragon told a group of ecotourists and researchers on the Aug. 15 trip. The expedition was the first trip this year for the Vessel Watch project, which began in 2008 and is run by Pacific Environment in San Francisco.

"It gets really obnoxious," said Dragon, head of the marine sanctuaries campaign for the group.

Vessel Watch is the only effort thus far to monitor underwater noise from large ships passing through the nearby sanctuary, and it's among just a handful of such endeavors worldwide.

The San Francisco group runs the program to gather data and cultivate public awareness about the toll of ship traffic noise on imperiled marine animals, many of which rely on sound for survival. With 100,000 large commercial vessels now crisscrossing the world's oceans, according to an estimate from the Chamber of Shipping of America, there's little escape from the noise generated by the ships' propellers.

"We get to turn it off," added Ingrid Overgard, an ocean noise expert volunteering for the trip. "They have to live with this 24 hours a day, seven days a week."

And the number of large oceangoing vessels is expected to double or even triple by 2030.

"That is pretty much a given," said Kathy Metcalf, a former deck officer on oil tankers and director of maritime affairs for the Chamber of Shipping of America.

Scientists only have scratched the surface of knowledge on the effects of human-caused noise on marine animals, in part due to the difficulty inherent in ocean research. One oft-cited 2006 study, however, reported that underwater ship noise doubled every decade off the Southern California coast since the Navy took measurements in the 1960s, rising 10 to 12 decibels during that time.

In an unlucky coincidence, the low-frequency sound generated by ships falls in the same range used by whales to communicate, and it's capable of traveling hundreds of miles through water without diminishing.

Hearing a problem

Many marine animals rely on their hearing to live in the murky or pitch-black waters that make up much of the ocean. In that dark realm, hearing reigns as the chief sense.

But when human-caused noise is added to the mix, the animals' own attempts at communication may be masked. It can also interfere with their efforts to locate prey, detect predators and can cause them the abandon prime feeding or breeding habitat.

In a 2005 report from the Natural Resources Defense Council, called "Sounding the Depths II," the organization described ship noise pollution as "death from a thousands cuts," especially for already-threatened species.

The report also describes harm caused by underwater sonar used for military purposes or for oil exploration, which experts from the International Whaling Commission and the Navy agree is linked to mass strandings of whales.

But a number of scientists think the cumulative effects of chronic noise pollution from merchant vessels could pose an even greater threat to marine mammals than the intermittent blasts from sonar.

It's a newly emerging issue, and an initial challenge is raising awareness about it within the international shipping industry, according to Metcalf, with the shipping association.

She only learned of it after receiving an invitation to a 2004 conference run by the National Oceanic and Atmospheric Administration, called "Shipping Noise and Marine Mammals." It was the first scientific symposium on the topic.

Since then, she has become something of a change agent, pushing for naval designers to incorporate "noise quieting" technologies into new ships, primarily with new propeller and hull designs.

"A lot of people, when a new issue comes up, say, 'I don't see proof that it's a problem yet, so let's just pretend like it doesn't exist,'"‰" Metcalf said. "We took a different tack on that. We said, 'You know what, if it's an issue, let's get in on the ground floor and talk about it.'"‰"

Curing sounds' fury

Most undersea sound generated by ships comes from their propellers. As the blades turn, they create thousands of tiny bubbles, a process called "cavitation." The sound of these bubbles bursting is the main source of ship noise pollution. Ship engines are a distant secondary contributor, she said.

And cavitation means wasted energy. "Cavitation and propellers equal inefficiency," Metcalf said.

Environmental groups also support improved ship design as a critical step toward reducing shipping noise. But a 2008 report from the International Fund for Animal Welfare, called "Ocean Noise: Turn it Down," also advocates for the more immediate remedy of rerouting commercial vessels around sensitive habitat when whales and other imperiled animals are present, and slowing down ships when entering those areas.

"The magic number is 10 knots," said Dragon, with Pacific Environment. "If ships were traveling slower, they'd be cleaner, they'd be quieter and they would be safer," she said, alluding to ship strikes, which in 2007 killed four blue whales in shipping lanes off Santa Barbara.

But Dragon also acknowledged the issue is a "nonstarter" with the shipping industry, at least as a voluntary measure.

Metcalf concurred. Slowing down ships from cruising speeds of 25 knots would lead to more ships on the ocean, because it would delay arrival times for in-demand products, she said. And a sanctuary speed limit would add many hours to voyages, piling on costs. The restrictions would be onerous for large vessels traveling along coastlines, Metcalf added, which are replete with sensitive marine habitat.

Remedies in water

Retrofitting existing ships with propellers that create less cavitation is also proposed as near-term remedy. Metcalf said that's possible for some ships, but existing hull shapes make it "virtually impossible" for many others.

A 10-knot limit when whales are present took effect this year for liquefied natural gas carriers at Stellwagen Bank National Marine Sanctuary in Massachusetts, and its adjacent waters. Another restriction took effect in 2008 on the Eastern Seaboard, requiring the slowdown of all large ships during the season that federally endangered right whales congregate.

Metcalf said the economic effect of the seasonal slowdown on the shipping industry "was huge."

The federal regulations were enacted to protect the whales from death and injury by ship strikes, which have increased in recent decades on the East Coast. But they have the ancillary effect of reducing ship noise, said Leila Hatch, an ecologist who runs the underwater acoustics program at the Stellwagen marine sanctuary.

Scientists at Stellwagen are overseeing a new underwater acoustic array that's adding data to scarce research on the issue. "We're probably the farthest along in the world looking at shipping noise and whale behavior," Hatch said.

A small, vital program

Seeing a similar system of acoustic arrays established at the marine sanctuary surrounding the Farallon Islands is a "dream" for Carol Keiper, the naturalist on board the catamaran.

Between excitedly pointing out porpoises, seabirds, and gray, humpback and blue whales for passengers, Keiper said, "They have all this amazing technology set up at Stellwagen."

For now, the small Vessel Watch program is the only research on the topic for the Gulf of Farallones sanctuary, which is particularly rich in marine life. It relies on the tourists joining the trip donning the hat of "citizen scientist."

During the seven-hour journey, they can help monitor the presence of whales in a shipping lane and take photos of any breaching animals. The data is shared with scientists studying whales off the coast of California, and recordings of underwater ship noise are sent to a researcher at Scripps Institution of Oceanography.

For details on the Vessel Watch program, which runs through November, go to www.pacificenvironment.org.