Whale-watcher boats may be making so much noise that killer whales off the coast of Washington have to change their calls to communicate over the racket.
Recordings made during the past 3 years, after a boom in whale watching in Washington State, show that killer whales lengthen a characteristic call by about 15 percent when boats cluster around them, reports Andrew D. Foote of the University of Durham in England.
Recordings from earlier eras, when there were fewer whale watchers, showed no link between call length and the presence of boats, say Foote and his colleagues in the April 29 Nature. They suggest that boats following the whales may not interfere with animal communication until some critical number of churning engines makes the noise just too loud.
That change “is certainly a red flag,” contends coauthor Rus Hoelzel, also of Durham. “Maybe we ought to think about fewer boats.”
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People naturally adjust their voices to make themselves understood over background noise, and research suggests that animals do the same. Humpback whales lengthen their calls during playback of low-frequency active sonar, and in the July 17, 2003 Nature, researchers in the Netherlands reported that city birds near heavy traffic tend to sing at higher pitches (SN: 7/19/03, p. 37: City Song: Birds sing higher near urban traffic).
The killer whale–research team analyzed recordings from three pods, or maternally related whale groups. In these pods, which live off the Washington coast, “everybody seems to stay home with Mum,” says Hoelzel. “There are males we saw born 30 years ago, and they’re still there.”
Each pod has its own distinctive primary call, which accounts for more than half the vocalizations and may coordinate foraging. Foote describes the three pods’ calls, respectively, as sounding like a train whistle, a kitten mewing, and a slide whistle. The researchers compared the length of these calls, with and without boats present, in recordings from 1977 to 1981, 1989 to 1992, and 2001 to 2003.
The only difference in call length turned up in the last period. During the 1990s, the average number of vessels clustering around a pod of whales increased roughly fivefold, and it now averages about 22. This whale population has been declining since 1996, but biologists aren’t sure why.
“One thing I want to make clear is that I think whale watching is a good thing,” says Hoelzel. It just may need tighter regulation, he explains.
Roger Gentry, who directs acoustics studies of marine mammals for the U.S. National Oceanographic and Atmospheric Administration, says he certainly finds it plausible that killer whales would compensate for underwater clamor. However, the meaning for the whales of the increase in call length isn’t yet clear. “We have to keep watching,” he says.