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Blinded by the Noise
23 February 2010 2:57 am
Credit: Wilma Passchier/Creative Commons
A new visualization reveals the dramatic impact of shipping traffic on Right Whales in New England
Before the invention of the Diesel engine, life was good for the Right Whales living off the coast of Boston. For thousands of years, the calls and songs they produced to keep track of each other over great distances were the only sounds probing the murky depths.
"The place in which these animals live is defined not only in terms of space, but in terms of sound - they live in an acoustic habitat," says Christopher Clark from Cornell University, who has been listening in on the whales to get a better understanding of how noise impacts their acoustic habitat. "Imagine living in a village where people can't see each other or where they're going. They have to rely on sounds and calls to keep track of each other and go about their lives."
Once a shire shrouded in peace and quiet, the Right Whales' village has since been drowning in the cacophony of cargo ships' and ocean liners' propellers that churn the waters.
Using an array of underwater listening devices installed on the sea floor, Clark and his research team have been able to record and monitor the sounds that define the Right Whales' acoustic seascape over long periods of time.
What the researchers found is alarming: Just like terrestrial habitats shrink in space, the whales' acoustic habitat is being destroyed.
"Each time a ship passes through the area, the acoustic habitat around the whales basically collapses," Clark says.
He has developed visualizations that show the impact over time and space. As long as no ship is in the area, only the whales' calls and counter-calls make up the acoustic seascape, as can be seen in the image: Like the soft twinkle of stars in a dark night sky, each spot marks the acoustic signature of a whale. As soon as a ship approaches, the 'night sky scene' turns into an exploding supernova, obliterating the light emitted by the stars and rendering them invisible in the process.
"The ship's noise bleaches out the whales' vocalizations," explains Clark, "robbing them of their acoustic habitat and essentially rendering them 'blind,' over and over again."
"Every day, five to six large ships move into and out of Boston, and their acoustic footprint can last for hours. As a result, the Right Whales trying to make a living off Boston are losing about 80 percent of their opportunities to keep in contact every day, day after day, month after month, year after year."
Although nobody knows for sure yet what the constant onslaught of noise does to the whales, whale researchers have found alarming indications of stress.
"Right whales are long-lived animals. When they were kids and teenagers, their world was normal," Clark says. "Acoustic habitat loss is a stressor and there are multiple stressors on a species."
His team has found that the whales often no longer bother answering calls from their peers. In this world of constant noise, they wouldn't be heard anyway.
"Their social network is constantly ripped apart," says Clark. "In one area, noise levels are now 105 decibel where they should be 75."
Other researchers from the Right Whale Consortium found that the animals show dramatic loss in vital body fat: In some individuals, the blubber layer is thinner than normal, hinting at the possibility that they no longer find enough food due to the noise.
Referring to the village metaphor, Clark says, "If you're one of the blind villagers but can't hear the dinner bell because of the deafening noise around you, you're going to go another night without food."
Moreover, the females give birth only every five years on average instead of every three.
Assembling the data from sound recordings taken in the field, Clark has developed a computer animation showing what happens when a ship passes through an area with Right Whales (follow link below to watch video).
Acoustic-space-loss_1-ship_Right-whale.mov (Video kindly provided by Christopher Clark)
The blue area shaped like a 'Hershey's Kiss' represents the 'communication space' for a calling right whale, in other words, its acoustic habitat at a given point in time. As the ship approaches, this area starts to shrink and is virtually obliterated when the vessel is closest to the whale.
"When the area in the animation goes black, it means that other whales cannot hear the calling animal," Clark explains. "They are now living in an urbanized, even industrialized, habitat and there is no rest for the weary."
"Keep in mind that Boston is not even a heavy shipping port," he adds. "What the whales are going through there is in fact happening all over the world."