Mysterious Ocean Sound Identified

By Larry O'Hanlon, Discovery News


Nov. 23, 2005—A mysterious underwater "boing" heard for 50 years by marine scientists and naval mariners in the North Pacific Ocean has finally been traced to breeding minke whales.

The discovery comes as a bit of a surprise, since it's usually not so hard to link a sound caught by hydrophones to a marine mammal.

That's because unlike fish, marine mammals have to come up for air and can be spotted on the surface.

"The common thinking was that it was being made by a large fish,” said Jay Barlow of the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, Calif.

Barlow was among the scientists onboard a research vessel near the Hawaiian Islands in 2002 that made the minke-boing connection.

A report on the discovery has just been published by Barlow and his colleague Shannon Rankin in the November issue of the Journal of the Acoustical Society.

"It sounds vaguely mechanical," Barlow said of the first interpretations of the minke's song. "I'm sure to sonar operators that struck fear."

But as it became clearer that the boing was both seasonal and regionally specific, the likelihood that it was being made by enemy submarines was ruled out.

As for marine biologists, they continued to wonder about the boing, but because it usually was heard in choppy areas with strong trade winds, spotting any undersea singers was next to impossible, Barlow explained.

But during the 2002 expedition, Barlow and his colleagues were ready with two hydrophones strung wide apart in tow behind their ship.

The hydrophones were linked to a computer onboard that immediately analyzed the small differences in the timing of sounds reaching each hydrophone to find out from which direction the sound was coming.

Although they were in the process of using the system to survey dolphins in the area, when they heard the mystery boing, they couldn't resist following it to discover its source. They chased the boing until a minke whale leaped right in front of them.

"Basically it was pretty obvious what was going on," said Barlow.

Jason Gedamke of the Australian Antarctic Division in Tasmania was pleased, but not particularly surprised, by the discovery.

A few years ago Gedamke discovered a related sound made by another sort of minke whale along the Great Barrier Reef, and suggested that the North Pacific boing was also made by minkes.

"We got a lot of resistance," said Gedamke. "It's great to get the confirmation."

As for why the migratory minke whales sing only for a few months each year, Gedamke has a suspicion.

Based on what's known about minke whales in Australian waters, as well as humpbacks and other whales, he suspects the singers are males and their the song has something to do with the mating process.

Knowing just who is singing is very important, said Gedamke, since it makes it feasible for biologists to use the sound to survey whale populations and see how healthy those populations are.

Minke whales are still being killed in large numbers by unregulated Japanese whaling operations, he said.