Mysterious underwater noise is likely a whale mating call

Loren Coleman lcolema1 at maine.rr.com
Thu Jan 2 06:10:26 EST 2003


http://www.signonsandiego.com/news/science/20021227-9999_2m27whales.html

Mysterious underwater noise is likely a whale mating call
        
San Diego-based researchers uncover source of sonar puzzle


By Terry Rodgers 
UNION-TRIBUNE STAFF WRITER

December 27, 2002 

The mystery of an underwater noise that for years confounded Navy sonar
operators in the North Pacific Ocean has been solved by a San Diego-based
research team. 

The perplexing sound ­ similar to the sound of an electric razor ­ has been
identified as a call produced by minke whales, said Jay Barlow of the
Southwest Fisheries Science Center in La Jolla.

"The military was very interested in learning what the sound was, even
though they knew it was not a threat," said Barlow, a scientist with the
National Oceanographic and Atmospheric Administration, which operates the
research center. 

For decades, sonar operators in the North Pacific had heard the mechanical
twang, which scientists speculated was from a marine mammal or large fish.

Scientists aboard the David Starr Jordan, a NOAA research vessel from San
Diego, made the discovery during a 41/2-month expedition this fall to
identify and count marine mammals near the Hawaiian Islands.

On two occasions when the distinctive sonar "boing" was picked up by a
hydrophone the ship was towing, observers on deck saw a minke whale
surfacing, Barlow said.

Most likely the sounds are mating calls produced by male minke whales, he
said. 

"By identifying the source of the 'boing,' we also found the previously
undiscovered breeding area of the North Pacific minke whale," he said. "All
this time they were hiding in the typically rough waters of winter in the
central North Pacific."

The expedition was significant because it was the first to thoroughly
document the distribution of marine mammals within the 200-mile U.S.
Exclusive Economic Zone around the Hawaiian Islands, he said.

The McArthur, a NOAA research vessel based in Seattle, also participated in
the expedition. 

"Previous studies were done by scientists using small watercraft that rarely
traveled more than 10 miles from the islands," Barlow said. "What they saw
in the past was just the tip of the iceberg."

During the expedition, trained spotters used 25-power binoculars capable of
spotting whale spouts up to six miles away.

Barlow said his research team was surprised by the high numbers of sperm
whales it encountered in the North Pacific, which he compared to a desert
because of its relative scarcity of plankton and other marine life necessary
to support a diverse food chain.

The area also had surprisingly few dolphins compared with the prolific
numbers along the California coast, he said.

"Although much is known about the familiar humpback whale, which is common
around the main Hawaiian islands in winter, and the spinner dolphins that
rest in coves there, almost nothing was known about the many species that
are found farther offshore," Barlow said.

The data gathered from the expedition will provide a baseline and allow
scientists to detect any significant changes in marine mammal populations.

"We're especially interested in the potential for human harm to the
species," Barlow said.

(The minke whale call recorded by the David Starr Jordan can be heard on the
Web at http://www.whaleacoustics.com/audiofish.asp) 

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