The study solves one of the mysteries of marine science — how whales are able to migrate across thousands of miles of ocean with great accuracy. It also suggests that they may be more intelligent than had been realised because the ability to create and interpret such maps would need powerful brains.
The new insights came after scientists were granted access to a network of undersea microphones installed across the north Atlantic by the US navy to listen out for enemy Soviet submarines. The research was carried out in Cornwall where the US navy has one of its listening bases.
From the base at St Mawgan the researchers retuned the underwater microphone system to listen in to the songs of hundreds of blue, fin, humpback and minke whales scattered across the ocean. Once they had identified the animals they used the system to plot their positions and movements across the north Atlantic.
Christopher Clark, director of the bioacoustics research programme at Cornell University, New York, who led the work in Cornwall, said that after the animals sang they would wait and listen for the echoes to return. The noises emitted were so powerful they could traverse hundreds of miles of ocean before bouncing off a geological feature and returning to the whales that had made them more than 20 minutes later.
“Whales will aim directly at a seamount that is 300 miles away, then once they reach it, they change course and head to a new feature. It is as if they were slaloming from one geographic feature to the next. They appear to have acoustic memories analogous to our visual memories,” said Clark.
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During the research Clark obtained thousands of acoustical tracks of singing whales for different species throughout the year. The recordings confirmed that whales were also using their songs to talk to one other, again often over vast distances.
Clark told a meeting in Washington of the American Association for the Advancement of Science: “We now have the ability fully to evaluate where they are and how long they sing for. We have evidence that they are communicating over thousands of miles of ocean. Singing is also part of their social system and community.”
The US navy system is so sophisticated Clark was able to move a cursor around a screen and listen in on different areas of the Atlantic to find whales.
When he found one he could fix its location and observe it interacting with animals hundreds of miles away. Clark listened in to one “whale conversation” where a creature off Bermuda appeared to be communicating with another off Newfoundland.
One important conclusion was that whales must perceive their world on a much larger scale than humans — feeling themselves as travelling “with” companions who might be hundreds of miles away and determining their position in relation to distant continents and land masses rather than nearby features. But besides the sound of whales singing, Clark also picked up more disturbing sounds — the roar made by human activities such as shipping traffic, oil and gas exploration, and recreational traffic.
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Comparison with past research suggests that such noises are doubling in intensity every decade — and that it may be deafening whales.
It is already well known that loud underwater noises such as those used by naval sonars or oil prospecting equipment can destroy a whale’s ability to navigate, often resulting in mass strandings. Clark believes that such sound pollution may already have shrivelled the distances over which whales can communicate and find mates.
A separate study published this weekend shows that this new threat to whales comes at a crucial time with their populations are at an all-time low because of past human whaling activity.
The study, by Steve Palumbi of Stanford University, attempted to work out how many whales there were before whaling started. He looked at the amount of variation in the DNA of whale meat bought in a Japanese market. The amount of variation in certain types of DNA is known to reflect the size of past populations. He found that the modern populations of most species number less than a tenth of what they once were.
“Some people argue that modern whale populations are recovering and that we can start hunting whales once again but the DNA tells a different story: a past with an ocean that was teeming with whales and from which most have been wiped out,” he said.