Human Noise May Disturb Whales' "Love Songs"
By Bijal P. Trivedi
National Geographic Today
|June 19, 2002|
Whales belt out the loudest songs on Earththe slow, low ballads of
blue and fin whales can be heard for several thousand miles. Researchers
tracked down bellowing bassist fin whales in the Sea of Cortez, and
concluded that the songs were breeding displays to "serenade" females
because all the singers were male. The finding raises concerns that
rising levels of ocean noise caused by commercial vessels and military
sonar could interfere with these communications.
"These creatures sing for days at a time trying to get a simple message outI'm here, I'm available. Is anybody out there?" said Christopher Clark, co-author of the study and a bioacoustics researcher at Cornell University, which boasts one of the world's major centers for the study of whale sounds.
"The finding that only male fin whales are singing provides strong evidence that these long vocal sequences are courtship songs," said Roger Payne, President of the Ocean Alliance but best known for his co-discovery of humpback whale songs in the late 1960s. He was also one of the first to suggest that blue and fin whale songs could be heard across oceans.
The discovery makes a lot of sense because fin whales, like blue whales, do not have breeding grounds, said Payne. But they don't need them because they can locate each other with these long-distance calls.
The whales belt out their songs at a frequency of about 20 hertzjust below the range of human hearingand at an intensity equivalent to sitting in the front row of a rock concert.
Since the human contribution to ocean noise is also dominated by the low frequency sounds produced by shipping vessels, oil and gas exploration, and military activities, researchers fear the cacophony may disrupt or drown out the ocean banter of marine animals and could possibly damage their hearing.
Clark and his colleagues towed a hydrophonean underwater microphone originally developed by the Navy to look for submarinesbehind the research vessel to detect whale songs. The hydrophone fed into a converter box crafted by Clark to shift the whale songs to a higher pitch that humans could hear. A computer also analyzed the sounds and allowed the researchers to pinpoint the location of the individual making the noise.
Each note in the song lasts only a second and sounds like a "gentle burp," said Clark. Then there is a 14-second pause before the fin whale hits the next note. The entire song lasts about eight to ten minutes. Only when the composition is played at about 60 times its actual speed is the rhythm and pitch variation apparent. Blue whale songs can last up to twenty minutes with a two-minute interval between notes.
After locating a singing whale, Clark and his colleagues used a crossbow to get a sample of the whale's skin for genetic analysis. In each case there was no ambiguity that the whales they sampled were indeed the performers. In all nine cases the singers were male.
Taking a small biopsy sample for analysis is necessary because it is difficult to determine the sex of a fin whale unless it rolls on its stomachwhich it rarely does.
Clark's team also surveyed all the fin whales in the area and found there were equal numbers of males and femalesfurther supporting the idea that the singing was to attract females to the area. The research is published in the June 20th issue of the journal Nature.
While the Sea of Cortez, where the study took place, is relatively quiet, other waters, such as the Mediterranean sea, are polluted with the din of commercial vessels, ferries, and jet skis.
"In many places the oceans are filled with a generalized acoustic smog," said Clark. "Commercial shipping lanes around major ports are as noisy as the tarmac at Kennedy Airport."
But like people chatting in a crowded room, whales must have the ability to pick out signals from the rest of the noise, said Payne. The ocean is a very noisy place with the chatter of animals, the wind and storms, the grinding of the tides, and constant earthquakes.
Sonar initially generated concern when 16 rare and elusive beaked whales beached themselves in the Bahamas after the Navy used a mid-range sonar in March 2000. There is still no conclusive evidence whether the Navy's new low frequency sonar will cause problems for fin or blue whales.
"The frequency of the sonar is four octaves above the those used for fin whale communication, but we don't know whether it will be bothersome to the fin whales or other marine life," said Payne. The same is true for increases in commercial traffic. "We are faced with real genuine ignorance."
One study published in Nature in 2000 showed that low-frequency active sonar altered the singing behavior of humpback whales. Humpback songs were associated with reproduction but it is not clear whether the alterations would affect reproduction rates or were needed to compensate for the noise.
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