Shouting to be heard?
As the ocean gets louder, what happens to whales that communicate via sound? "They shout," according to a new study.
Susan Parks, an assistant professor of acoustics at Penn State, recorded sound on tags attached to North Atlantic right whales in the Bay of Fundy, Canada in 2001, 2002 and 2005. The tags, attached by suction cup, automatically released themselves after four hours.
Once recovered from the ocean surface, the tags showed that the amplitude of whale calls increased as the background got louder. Most of the noise came from ships, whose deep bellow overlaps the low-frequency vocalizations of the right whale.
Parks focused on the most common right whale sound, the rising-frequency upcall. "Behavioral studies show that the upcall is used when whales come together, but we're not sure whether they use it to say, 'Come on over here,' or just to say, 'I am here,'" says Parks.
Right whales are subject to serious study because they are scarce. In the 19th century, this whale was "right" for all the wrong reasons: high in fat, it lives in shallow water and floats after death. For all these reasons, the North Atlantic right whale became prime prey for whalers and nearly went extinct. About 400 North Atlantic right whales survive, Parks says. "They've had a lot of calves in the past six years, but in the past two weeks, two have died, in New Jersey and Maine. The recovery recommendations say we can't even afford to lose one a year."
Right whales are baleen whales that strain the ocean with a comb-like baleen to sieve out small animals called krill.
Right whale vocalizations
Can you hear me now?
It makes sense to shout in a loud environment, and this common-sense tactic appears not just in rock concerts, steel mills and airport runways, says Parks, who collaborated with scientists at Woods Hole Oceanographic Institution and Duke University. "We're showing this behavioral response in large baleen whales, but others have seen it in birds, primates, and killer and beluga whales; they all call louder in the presence of background noise."
Previous studies have documented changes in frequency or timing of whale calls in response to background noise, but "it's very difficult to measure sound level in free-ranging whales," Parks says. That measurement is what the tags made possible, she adds.
Making the case for whales
The Stellwagen Bank National Marine Sanctuary is a hotbed for commercial shipping and whales, including the endangered North Atlantic right whale. The whales are vulnerable to ships low-frequency noise, which interferes with their vocalizations. Sanctuary researchers counted 541 ships making 3,413 trips through the sanctuary during 2006, and concluded that large commercial vessels were indeed producing harmful noise. Tankers were the most damaging, causing twice as much "acoustic power" as cargo ships and more than 100 times as much as research ships.
The so-what? part
How could a louder ocean harm whales? Largely because they are social animals that communicate orally across long distances, and noise limits the effective range of that talk. At some point, the whales may tire of shouting, causing this communication -- and potentially whale society as a whole -- to collapse.
Parks says the main concern today is how noise will skew whale-monitoring efforts that rely on acoustic tracking. "The upcall is a contact call used by mothers to call their calves, and by adult males. Because everybody in the population uses this call, it is used extensively for monitoring right whales."
And with so much boat traffic, "it's getting harder to hear the whales," she says.
Noise may also change the quality, not just the volume, of the whale voices, she adds. "A lot of papers describe the sound that an animal makes by using a median value, and assume that's how it always sounds. We even have automated whale detectors that look for this exact signal [the upcall], but if whales change their sound when the background noise changes, the median signal won't be representative, and the detector will fail."
Terry Devitt, editor; S.V. Medaris, designer/illustrator; Jenny Seifert, project assistant; David Tenenbaum, feature writer; Amy Toburen, content development executive