Stress hormones in North Atlantic right whales fell during a lull in shipping activity following the September 11, 2001 attacks on the World Trade Center and Pentagon. The finding suggests that ship noise may do more than annoy the marine mammals.
Observations in the wild have already shown that noisy ships can change whale behavior. Engines and propellers give off low-frequency sounds that carry well underwater and overlap with the frequencies whales use to chitchat. To be heard in a din, the social animals increase the volume, pitch or length of their calls. Often they turn away from sudden sounds or avoid loud waters altogether.
“This is the first evidence that whales have a physiological response to noise,” says veterinarian Rosalind Rolland of the New England Aquarium in Boston. Her team’s findings appear online February 8 in Proceedings of the Royal Society B: Biological Sciences.
To see if these responses to noise stem from anxiety, Rolland’s team began measuring stress hormones in the feces of North Atlantic right whales in Canada’s Bay of Fundy in 2001. During the summer, these endangered whales feed and breed next to busy shipping lanes in this narrow body of water.
The attacks of September 11 interrupted this experiment. With fewer large ships moving in and out, the bay suddenly quieted, especially in the low frequencies thought to bother whales.
This relative peace seems to have relaxed the whales, says Rolland. Stress hormones in her team’s 2001 samples were lower in the months after September 11 than in the months before. No similar decline was seen in four subsequent years of monitoring, suggesting that other factors in the environment weren’t to blame.
“This is what many of us had been looking for,” says Christopher Clark, director of Cornell Laboratory of Ornithology’s Bioacoustics Research Program in Ithaca, N.Y.
Yet this unplanned experiment wasn’t ideal: It relied on only four days of sound recordings before and after 9/11 and a small number of excrement samples.
“I am not really sure [this paper] shows what is claimed,” says Ian Boyd, a marine biologist at the University of St. Andrews in Scotland.
Boyd and his colleagues have proposed a way to put the results to the test. They suggest that portions of the world’s oceans be deliberately quieted for brief periods, perhaps by temporarily rerouting shipping traffic. Such planned experiments could help scientists pin down how the rising tide of underwater noise is affecting one of the ocean’s most charismatic creatures.
