ROME — The songs that whales and dolphins use to communicate, orient themselves and find mates are being drowned out by human-made noises in the world's oceans, U.N. officials and environmental groups said Wednesday.
That sound pollution — everything from increasing commercial shipping and seismic surveys to a new generation of military sonar — is not only confounding the mammals, it also is further threatening the survival of these endangered animals.
Studies show that these cetaceans, which once communicated over thousands of miles to forage and mate, are losing touch with each other, the experts said on the sidelines of a U.N. wildlife conference in Rome.
"Call it a cocktail-party effect," said Mark Simmonds, director of the Whale and Dolphin Conservation Society in Britain. "You have to speak louder and louder until no one can hear each other anymore."
An indirect source of noise pollution may also be coming from climate change, which is altering the chemistry of the oceans and making sound travel farther through seawater, the experts said.
Representatives of more than 100 governments are gathered in Rome for a meeting of the U.N.-backed Convention on the Conservation of Migratory Species of Wild Animals.
The agenda of the conference, which ends Friday, includes ways to increase protection for endangered species, including measures to mitigate underwater noise.
Environmental groups also are increasingly finding cases of beached whales and dolphins that can be linked to sound pollution, Simmonds said.
Marine mammals are turning up on the world's beaches with tissue damage similar to that found in divers suffering from decompression sickness. The condition, known as the bends, causes gas bubbles to form in the bloodstream upon surfacing too quickly.
Scientists say the use of military sonar or seismic testing may have scared the animals into diving and surfacing beyond their physical limits, Simmonds said.
Several species of cetaceans are already listed as endangered or critically endangered from other causes, including hunting, chemical pollution, collisions with boats and entanglements with fishing equipment. Though it is not yet known precisely how many animals are affected, sound pollution is increasingly being recognized as a serious factor, the experts said.
The sound of a seismic test, used to locate hydrocarbons beneath the seabed, can spread 1,800 miles under water, said Veronica Frank, an official with the International Fund for Animal Welfare.
A study by her group found that the blue whale, which used to communicate across entire oceans, has lost 90 percent of its range over the last 40 years.
Despite being the largest mammal ever to inhabit Earth, the endangered blue whale still holds mysteries for scientists.
"We don't even know where their breeding grounds are," Simmonds said. "But what's most important is that they need to know where they are."
Other research suggests that rising levels of carbon dioxide are increasing the acidity of the Earth's oceans, making sound travel farther through seawater.
The study by the Monterey Bay Aquarium Research Institute in the United States shows the changes may mean some sound frequencies are traveling 10 percent farther than a few centuries ago. That could increase to 70 percent by 2050 if greenhouse gases are not cut.
"This is a new, strange and unwanted development," Simmonds said. "It shows how the degradation of the environment is all linked."
However, governments seem ready to take action, said Nick Nutall, a spokesman for the U.N. Environment Program, which administers the convention being discussed in Rome. The conference is discussing a resolution that would oblige countries to reduce sound pollution, he said.
Measures suggested include rerouting shipping and installing quieter engines as well as cutting speed and banning tests and sonar use in areas known to be inhabited by the endangered animals.