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Whales and other marine mammals, fish, and even some invertebrates depend on sound, which travels much farther in water than light does. The animals use sound to find food and mates, to avoid predators, and to communicate. They face a growing problem: Man-made noise is drowning them out.
“For many of these animals it’s as if they live in cities,” says marine scientist Brandon Southall, former director of the National Oceanic and Atmospheric Administration’s (NOAA) ocean acoustics program.
Two years ago the problem made it to the U.S. Supreme Court, in a case that might have been called U.S. Navy v. Whales. The Court’s decision protected the right of naval vessels to test submarine-hunting sonar systems, whose intense sound pulses have been linked to several mass whale strandings.
But the Navy is not the lone villain. Oil company ships towing arrays of air guns fire round-the-clock fusillades loud enough to locate oil buried under the seafloor – and also to be heard hundreds of miles away. Undersea construction operations drive piles into the seafloor and blast holes in it with explosives.
And most of the rising tide of noise – a hundredfold increase since 1960, in many areas – is created simply by the dramatic growth in shipping traffic. “Shipping noise is always there,” Southall says. “It doesn’t have to be lethal to be problematic over time.” The problem is getting steadily worse for another reason. As we’re making more noise, we’re also making the ocean better at transmitting it. Seawater is absorbing less sound as carbon dioxide from fossil-fuel burning seeps into the ocean and acidifies it.
Noise drives many species of whales, dolphins, and other marine animals to change their behavior markedly – their calling, foraging, and migration patterns – even when it’s not enough to drive them onto a beach. Cod and haddock in the Barents Sea have been found to flee the area when air guns start firing, drastically reducing fish catches for days. Large baleen whales are of special concern. They communicate over vast distances in the same frequencies, around the lowest C on a piano, that ship propellers and engines generate. On most days, says Christopher W. Clark, director of the bioacoustics research program at Cornell University, the area over which whales in coastal waters can hear one another shrinks to only 10 to 20 percent of its natural extent.
Clark studies endangered northern right whales, whose habitat includes busy shipping lanes for the port of Boston. In 2007 he and his colleagues deployed a network of seafloor recorders and automated listening buoys in Massachusetts Bay. From three years of continuous recordings, they then compiled a complete underwater “noise budget.” Color animations of the data show the calls of right whales getting all but obliterated as ships pass.
“The whales’ social network is constantly being ripped and reformed,” Clark says. Unable to communicate, individual whales have trouble finding each other and spend more time on their own.
The 10 listening buoys now bobbing in Massachusetts Bay could actually help the animals. The researchers are sharing their real-time data on whale locations, transmitted from the buoys via satellite, with tanker captains, who can then slow down their ships or alter course to avoid whales. It’s a small note of hope in the din. “Science can only help in so many ways,” Clark says. “Then we have to decide whether the animals are important to us.”