Advocates for the protection of whales have long argued that they are stressed by underwater noise from ships. Now researchers say that an ocean experiment that was unfolding during the 9/11 attacks offers evidence that such claims may have merit, at least as far as North Atlantic right whales are concerned.

In the immediate aftermath of the attacks, governments halted commercial transportation in much of the world — including the Bay of Fundy, the principal summer feeding ground of the whales and the shipping route to Saint John, New Brunswick, a busy port.

The whales, like other baleen whales, communicate with acoustic signals at low frequency, the range of many noises from ships. Researchers have long known that whales move off, reduce their own calls and otherwise respond to ship noise. One reason is that the noise is stressful for them, the new research suggests.

The scientists, led by whale experts at the New England Aquarium in Boston, were in the bay in September 2001 collecting samples of whale feces as part of their long-running research efforts. Feces are a rich source of information about the animals; among other things, hormones detected in the feces can tell scientists whether a whale is male or female, sexually mature or pregnant, and offer other clues about overall health, including the creature’s stress levels.



When the noise levels fell, the researchers recorded reduced fecal levels of glucocorticoids, metabolites of stress-related homones. Other research on land animals has linked the substances to stressors like snowmobiles and road traffic, the scientists say.

In their study, published in a recent issue of Proceedings of the Royal Society B, the researchers note that chronic elevation of stress hormones can stunt growth, inhibit the body’s immune system and cause other problems.

The researchers acknowledged that their study has a few limitations. Weather-wise, September is not the best time to collect fecal samples, they write, and the experimental conditions are “non-repeatable.”

The biggest threats to North Atlantic right whales from humans are getting struck by ships or entangled in fishing gear, incidents that have declined in recent years. Still, the fate of the species is hardly secure.

Acoustic pollution presents “less visible but pervasive disturbance to these coastal-dwelling whales,” the researchers wrote.

An earlier version of this post misidentified the province in which Saint John, on the north shore of the Bay of Fundy, is located. It is in New Brunswick, not Newfoundland.