Sept. 11, 2001, brought peace to few in the world -- except whales.
In the panic following the attacks, global commerce ground to a stop, quieting tankers and container ships in berths across North America. The pause reached the Gulf of Maine, a haven for North Atlantic right whales, one of the most endangered whale species.
Typically, the whales' songs are backbeated by the cavitation of ship propellers. For a few days in September, though, the beat faded.
Scientists from the New England Aquarium were out monitoring the gulf's whales on Sept. 11, as they have since the 1980s. And while it took years to realize it, acoustic and biological records taken in that stillness are the first to show that the persistent racket thrown off by commercial shipping may cause chronic stress in whales.
"It's hard to make people realize, off our shores, how noisy it is," said Rosalind Rolland, a veterinarian at the aquarium and the lead author on a study, published today in the Proceedings of the Royal Society B, documenting the whale's stress.
Like attempts to use grounded airliners to study contrails, the report is one of a few studies that have used Sept. 11's suspension of the typical to delve into everyday phenomena. Given its ad hoc nature, the study is by no means definite, but it may serve as a wake-up call to researchers and industry that maritime shipping, through its sheer size, may be causing chronic pain to some of nature's most charismatic creatures.
"It is a incredibly interesting study that was very opportunistic," said Dan Costa, a biologist at the University of California, Santa Cruz, and an expert on marine mammal adaptation who was not affiliated with the study. "The results are quite something and really speak to the issue of the effect of human activities on whales. However, all of this is tempered by the fact that it was 9/11 that made it possible."
It is a critical advance beyond past small-scale studies, added Lindy Weilgart, a whale researcher at Dalhousie University who was also unassociated with the study.
"Up to this point, most noise-effect studies were just based on very short-term changes in behavior of a few individuals, which didn't really mean much in terms of affecting the health of the overall population," Weilgart said. "Ultimately, [that's] what we care most about."
For the two days following Sept. 11, overall noise in the Bay of Fundy, home to the Right Whale Conservation Area, dropped by 6 decibels with most of that decrease coming from a steep fall in low-frequency ship noise. During this relative calm, the stress hormones expressed by sampled whales in the bay fell in a way unseen again for four years after the attacks, suggesting the whales may suffer from chronic stress, the researchers found.
As it is for humans, this stress can be an incredible burden for whales, Rolland said.
"It's the chronicity of the stress that's the problem," she said. "When you have the constant secretion of these stress hormones, it can influence reproduction. ... If you're constantly under stress, there's a lot of wear and tear."
Rolland is upfront in noting that the number of whales sampled in the days after Sept. 11 -- nine total -- is small. (In addition, the acoustic recordings are relatively short, but backed by data on ship traffic.) Her team wrestled with the data but found that it remained robust even when accounting for the random swings seen in the whales' hormones. Still, the study is far from ideal, and Rolland won't call it conclusive.
"We can't repeat the experiment," she said, "which is obviously what you'd like to do."
Despite its limits, the study gives support to a rising body of knowledge showing that human noise in the ocean can cause difficulties and, in some cases, trauma for a host of sea creatures. It is a din major ocean operators are taking seriously, including the Office of Naval Research, which has helped fund Rolland's work and is now supporting a marine stress lab at the New England Aquarium.
This noise has many sources. Most prominently, there are the sharp, loud echoes produced by sonar and seismic surveying for oil and gas, which have gained broad notice in recent years. But gliding beneath these spikes has been an ever-growing baseline of the growling, long-lasting acoustic waves caused by the enormous propellers of commercial shipping.
The sheer amount of shipping has caused an appreciable increase, worldwide, in the ocean's ambient noise at the low frequencies used by many whales for their songs -- a staggering change, scientists say, and one comparable with our ability to increase global levels of carbon dioxide, if far less studied. By some estimates, shipping noise has doubled every decade.
"In the ocean's very quietest moments, blue whales singing off the Grand Banks of Canada can sometimes be heard more than 1,500 miles away off the coast of Puerto Rico," wrote Christopher Clark, director of the Bioacoustics Research Program at Cornell University and a pioneer in marine noise pollution, in an editorial last month. "But on most days," he added, "that distance is a mere 50 to 100 miles.
Like all baleen whales -- the group of comb-mouthed krill eaters that includes the blue and humpback whales -- right whales have long evolved the ability to live in the wind-driven noise that dominates the sea's higher frequencies. The whales instead prefer long-range, low frequencies to call over many miles. Until sailors came around, these low frequencies were their undisturbed telegraphic domain, used to find mates and food.
But while researchers have hypothesized that the low-frequency sounds from large-scale shipping, especially in heavily trafficked routes, could block baleen song and cause the whales harm, it has been a difficult question to study. Fifty-ton whales are not the easiest test subjects, Rolland said, and more often than not, researchers have had to rely on small visual and audio studies of the mammals' behavior.
This work has found whales adapting in different ways to background noise: They have moved their habitats. They've made more energetic calls and shifted their frequencies. They've sung longer and repeated themselves more often. They've waited until the noise went away -- if, indeed, it does. But ultimately, these studies are inconclusive on whether the health and life of the whale is permanently changed, Weilgart said.
Rolland helped the field move past this behavioral work in the late 1990s, pioneering studies of the right whales' most available biological material -- their feces.
Case for action?
Working in Fundy, and at times aided at sea by trained scent dogs, Rolland found that she could analyze the oily scat left by right whales for critical reproductive and adrenal hormones. The techniques were already well developed for primates, and by the mid-2000s her team had shown that it could detect elevated stress hormones from whales caught in fishing nets.
As Rolland's team refined this analysis, she continued, year after year, to collect scat samples in the late summer and early fall. During the 2001 campaign, Susan Parks, then a doctoral student at the Woods Hole Oceanographic Institution and a co-author of the study, was independently studying the calls of the bay's right whales. More often than not, these calls echoed through a jumble of motors and propellers.
On Sept. 12 and 13, though, the whales' calls came in crystal clear.
At the time, however, Rolland was not working on noise pollution, and she did not make the connection between her hormone research and Parks' recordings until late 2009, while preparing for a naval workshop on marine mammal stress. She had years of data on stress levels in the bay, and it quickly became apparent that she had a signal in the noise.
Since it is impossible to halt maritime traffic for science, it will be difficult to create a controlled experiment to further test the whales' sensitivity. Ideally, Rolland would study southern right whales near Antarctica, home to far less shipping, to get a sense of how much noise is needed to elevate stress hormones. But there is no money for it, she said.
Despite limited evidence, Weilgart feels there is a compelling case for pre-emptive action.
"We should be doing a better job of separating endangered whales from noise sources -- or also, in this case, the risk of collisions with ships," she said. "Making ships quieter, through quieting the noise from their propellers and engines mainly, should be a priority, and may even help the shipping company's bottom line."
Indeed, the whales' possible sensitivity could be one of those rare win-win environmental causes. The U.N.'s International Maritime Organization is already exploring how to decrease the noise caused by large propellers, and these noise reductions tend to go hand in hand with increasing the propellers' efficiency. In an era of high fuel costs, it may not be the most difficult upgrade to sell to shipping giants.
Limiting noise won't alone conserve the whales, Rolland added. She suspects it is only one reason North Atlantic right whales have taken so long to rebound since the end of whaling. (Their numbers are still under 500.) The whales live in an almost urban environment, she said. They deal with ships. The get caught in nets. The swim through water redolent with human waste.
"They're tough animals to be surviving at all," she said.
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