It was also discovered that whales in the North Atlantic Ocean seem to be moving together and coherently, even when they were far away from one another.

Why do whales move in such a way? What is impelling them forward? How do they communicate with each other, seemingly over thousands of miles of ocean?

For nearly nine years, Christopher Clark, a researcher from Cornell University of the United States, has been trying to answer these questions by listening to whale songs and calls in the North Atlantic using the navy's antisubmarine listening system.

The underwater microphones of SOSUS (Sound Surveillance System) can track singing blue whales, fin whales, humpback whales and minke whales.

A world linked by songs

There is a time delay in the water, and the response time for whales' communications is different from the time of human beings. Sounds are transmitted in the water at a speed of 1,450 meters per second.

This is four times faster than the transmission speed in the air. As a result, when whales communicate via songs, the responses come much quicker.

Because humans still know so litte about whale communications, Clark and his team decided to observe whale patterns of association and coordination.

Although the whales are spaced far apart, the SOSUS system provided a wealth of new data. Through weeklong soundings, Clark obtained thousands of acoustical tracks of singing whales from different species throughout the year.

"We now have evidence that they are communicating with each other over thousands of miles of ocean. Singing is part of their social system and community," Clark said.

Excellent singers by birth

Whale songs have a much bigger wavelength than human songs. The songs are very pleasant to the ears of whales born as bel canto singers.

Scientists have also discovered that whales sing new songs each year. New syllables appear constantly to replace old ones and the new syllables soon spread worldwide.

By using the tracking system, scientists have found that a whale in Hawaii sings a similar song to a whale in Bermuda. They also found that when a horde of whales return to their original territory after long-distance trips, they first sing old songs of the previous year and then new songs.

Information transfer via songs

Why do whales sing? Scientists think that they sing to locate their positions and to transfer information.

Whales will aim directly at a seamount that is 300 miles away, then once they reach it, change course and head to a new feature. It is as if they are slaloming from one geographic feature to the next. It means they must have acoustic memories much like our visual memories.

Whales communicate with each other via songs. To avoid sending information to their enemies, they use a unique low-frequency, which can only be heard by allies.

It is still unclear why whales make long-distance movements. What is influencing their movement and distribution? What are the ocean features whales are honing in on?

Threats on whales' habitat

Just as researchers gain new ways of understanding the linkages between whales and oceanographic features, what they hear is the rising tide of noise from an increasingly urbanizing marine environment - the collective noises from shipping traffic, oil and gas exploration and production, and recreational traffic. And every decade the amount of noise is doubling.

"Many whales have very traditional feeding grounds and their migratory routes occur along shallow coastlines, which are now some of the noisiest, most heavily impacted habitats," Clark explains.

"But often it is along these routes that the male songs are sent long distance to prospective females, who might not receive the message through the "ocean smog."

"If females can no longer hear the singing males, they lose breeding opportunities and choices. The ocean area over which a whale can communicate and listen today has shriveled down to a small fraction of what it was less than a century ago," said Clark.

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