Killer Whales Strain to "Talk" Over Ship Noise?

Christine Dell'Amore in Friday Harbor, Washington
National Geographic News
September 10, 2009

Killer whales raise their voices to be heard over boat noise, and the effort may be wearing the whales out as they try to find food amid dwindling numbers of salmon, new research says.

The killer whales of Puget Sound make more calls and clicks while foraging than while traveling, suggesting that such mealtime conservations are key to coordinating hunts, the work reveals. (See a Puget Sound map.)

Several types of vessels, from small whale-watching boats to large cruise ships, also traverse the coastal waters off Washington State and neighboring British Columbia, Canada.

"[The killer whales'] call exchange is incredibly important … and vessel noises have the potential to mask these calls," said research leader Marla Holt of Seattle's Northwest Fisheries Science Center, which is run by the National Oceanic and Atmospheric Administration (NOAA).

Holt and colleagues' previous research had shown that some killer whales make louder calls to be heard over vessel rumblings—just as people raise their voices to talk over the din of a cocktail party.

Now the researchers think the cacophony could be causing the region's killer whales to use up more energy during hunts, even as their preferred prey, chinook salmon, are on the decline.

Killer Whales' Mysterious Drop

In Puget Sound a small group of killer whales known as the Southern Residents has been found to be particularly well-suited to eating salmon—even down to the whales' tooth size.

These animals don't eat seals or other mammals, as do the transient killer whales that migrate through the sound.

In the mid- to late 1990s the Southern Resident population mysteriously shrank by nearly 20 percent, from 97 to 88 animals. Today there are 85 individuals.

In 2005 the federal government listed the population as endangered under the U.S. Endangered Species Act.

No one knows for sure, but the cause was likely a combination of fewer salmon, exposure to toxic contaminants, and vessel noise, according to Lynne Barre of NOAA's National Marine Fisheries Service Northwest Regional Office.

Continued on Next Page >>




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