ON CAPE COD BAY, Mass. - A spotter bangs three times on the boat's cabin roof, signaling the captain to cut the throttle — now.

Inthe foggy gray of Cape Cod Bay, the reason for the abrupt stop soonbecomes apparent: The research vessel is surrounded by rare NorthAtlantic right whales, their glossy black heads bobbing just above thesurface as they feed on plankton slicks.

Shipstrikes are the top human-related cause of death for these mammals,which are in danger even from this vessel, a slow-moving research boatcalled the Shearwater. But new technology could soon help safeguard the whales by using sound, not sight, to track the creatures' movements.

"We're listening to their chatter," whaleexpert Christopher Clark said aboard the Shearwater, referring to thegrunts and groans whales use to communicate. "They can't keep theirmouths shut."

Inthe past, tracking whales often depended on inefficient aerial surveys,which were limited by weather and how often the whales surfaced.

Nowresearchers listen for the whales using 13 underwater microphonesattached to buoys off the coast of New England. Eventually, scientistshope to follow their movements closely enough so boats can slow downand post lookouts.

"Theslower the ships go, the lower the risk of killing a whale with aship," said Clark, director of the bioacoustics research program at theCornell Lab of Ornithology, and the project's lead scientist.

Hearing, not seeing whale

Kathy Metcalf ofthe Chamber of Shipping of America said shippers would welcome alistening system because they are currently being asked to reduce theirspeed despite uncertainties about where the whales actually are.

"We've been saying all along that if we can get real-time information, we want to avoid them," Metcalf said.

The right whale was hunted nearly toextinction in the late 18th century, and the death of even one in theestimated population of 350 to 400 is a setback. Since 1986, at least32 right whales have been killed by ships.

Theslow-moving whale is oblivious to its surroundings while feeding and isfrequently at risk while migrating up and down the East Coast throughbusy shipping lanes and waters laced with fishing gear in which it canget tangled.

Clark got the idea after a chat in 2001 withfellow whale researcher Moira Brown, who wondered if they could recordthe whales in Cape Cod Bay and then match the sounds with whatscientists were seeing.

Clarkwas shocked to hear the tape loaded with calls even when no one knewwhales were present. He started recording more frequently in largerareas and discovered the whales were always around, even when theplanes spotted nothing.

Clark believes whales use the calls, similarto a grunting "moo" or a high-pitched "whoo," to communicate who theyare, where they are and where to find food. Sound moves much moreefficiently in water than air, and the animals can easily talk overseveral miles on a calm day.

Engineersat the Woods Hole Oceanographic Institution developed a thumb-sizedunderwater microphone attached to a buoy to listen for the whales.

Tenof the 13 buoys installed so far are in the shipping lane that runs toBoston through Stellwagen Bank, an underwater plateau at the mouth ofMassachusetts Bay. Each can detect a whale within a five-mile radius.

Computers on the buoys separate the whalecalls from other ocean noise, collect that data and periodicallytransmit the information to the Cornell lab, where researchers cancontact navigators or call Clark's cell phone with their findings.

"I get this little beep all the time, that says, 'You've got whales,'" he said.

Whenthe system is complete, it will send the whales' whereabouts bysatellite to Cornell. From there, the information can be sent to aradio transmitter and broadcast to vessels.

Shipsoperated by Excelerate Energy and Neptune LNG, both shippers of naturalgas, must brake to 10 knots in whale areas under the terms of theirfederal license. Other ship slowdowns are voluntary.

Stop the ship! Horny female ahead

Aproposed regulation under review by the White House would require allships to slow to 10 knots if whales are in the area. Clark thinks thatis a reasonable limit, but shippers object to the mandate for safetyand economic reasons.

Containership lines, they say, operate on tight schedules, so slowing down meansadding time to a trip and risking higher costs and lost customers.

Metcalf,of the Chamber of Shipping, said reducing speeds to 10 knots can alsoreduce maneuverability. Her group is pushing for a provision to allowships to increase speeds in whale areas if needed to safely navigate.

"There's no doubt that anybody on a ship, given sufficient room to doit, would take all the avoidance behaviors in the world" to prevent astrike, she said.

On the Shearwater's recent trip, whales couldbe seen surfacing amid whitecaps as a team sampled the reddish gooeyplankton so researchers could study the whale's food source. Knowingmore about the whales' feeding habits could eventually help scientistsforecast where the animals appear.

Meanwhile, Clark retrieved a malfunctioning listening buoy and repaired it.

Everythingon the boat stopped when a female right whale who had apparently sentout a mating call rolled on her back and waved her flank as severalsuitors rushed to accept the invitation.

Itwas a hopeful sign, but Charles Mayo of Provincetown's Center for Coastal Studies cautioned that the species remains on the edge of extinction, despite the sightings of as many as 80 right whales around Cape Cod Bay in the past month.