Drowning in Sound

Sonar can kill whales. But could other noises be just as deadly

14 min read
Opening photo for this feature article.
Photo: Wayne Levin/Getty Images

It was a haunting sight. On a cold, gray day in January 2005, along a remote stretch of beach on North Carolina’s Outer Banks, dozens of pilot whales began to run themselves onto the sand. Eventually 34 of the jet-black, two-ton animals lay dead. The following day, three more whales—a newborn Minke whale and two dwarf sperm whales—washed up nearby.

Although whales can strand for various reasons, including sickness and disorientation, public speculation over the North Carolina stranding quickly zeroed in on a single culprit: military sonar. The U.S. Navy had been conducting a training exercise in the area around the time of the event, and an initial report by the National Marine Fisheries Service, which investigates strandings, listed sonar as a possible cause for the incident (the final report on the stranding was due out as this issue went to press). The Navy stated that the exercise took place about 100 kilometers from where the whales beached, too far to have had any effect. More than a year after the stranding, though, doubts still linger.

Not too long ago, the very idea that intense sound could do bodily harm to ocean creatures would have seemed bizarre, even to those who study marine mammals for a living. “If you had asked anyone 15 years ago, even 10 years, everybody would have said, ‘That’s a crazy idea,’” says Robert Gisiner, program manager for marine mammal science and technology at the Office of Naval Research (ONR), in Arlington, Va. Now Gisiner and other whale experts say they have no doubt there’s a link, at least between certain types of sonar systems and certain types of whales. In the last couple of years, the International Whaling Commission (IWC) and the Pentagon’s JASON scientific advisory panel—groups not necessarily known for their nature-friendly stances—have also noted with concern sonar’s harmful effects on cetaceans. “It’s been a journey of surprises,” Gisiner says.

Among the “surprises”: in 1996, 12 Cuvier’s beaked whales washed up along a 40-kilometer stretch of beach in western Greece, following a NATO training exercise in the Mediterranean Sea. Four years later, on the heels of a Navy exercise, four different species of whales stranded in the Bahamas. And in 2002, after a number of beaked whales stranded during a multinational naval exercise in the Canary Islands, necropsies found hemorrhaging around the animals’ ears and lungs and unusual gas bubbles in the blood and internal organs. Also anomalous about all three strandings was that they occurred over large areas and involved species that rarely strand in groups. By some counts, dozens of other whale strandings and an unknown number of whale deaths have been linked to military sonar [see photo, "Dead Calm”].

What’s less surprising, perhaps, is that the whales-versus-sonar controversy has spun into a public relations nightmare for the Navy. Environmental groups, most notably the Natural Resources Defense Council, in New York City, have taken the Navy to court, and letter and e-mail campaigns—not to mention the occasional stranding—ensure the issue is never out of the news for long.

The Navy, for its part, contends that it needs so-called active sonar to detect the latest generation of “quiet” submarines—diesel-powered machines that, when running on batteries, generate virtually no noise. Active sonar systems emit intense waves of acoustic energy into the water and then listen for the returning signals, and they are “the only way to detect diesel subs in certain situations,” says Capt. William Toti, the officer in charge of the Fleet Anti-Submarine Warfare Command, based in Norfolk, Va. Forty countries now have such subs, although the United States is more concerned about those that might acquire the vessels in the future, Toti says.

The sonar controversy has also focused attention on a broader issue: oceans everywhere are getting noisier because of commercial shipping, underwater oil and gas exploration, and other human activity, and scientists have no clear idea what harm these man-made noises pose to whales and other sea creatures. “The strandings are important because they raise the profile of noise,” says Sarah Dolman, science officer with the Chippenham, England­based Whale and Dolphin Conservation Society. “But they may be just the tip of the iceberg.”

“It’s difficult to appreciate how important sound is to cetaceans,” notes Dolman. Though they originally lived on land, over the last 40 million years whales, dolphins, and other cetaceans have evolved exquisitely sensitive ears, and they now rely on sound for virtually every activity: feeding, navigating, communicating, attracting mates. Using sound, for instance, some whales can detect small jellylike squid tens or even hundreds of meters away. Some scientists even speculate that whales use their songs to “visualize” the sea floor as they migrate across vast distances.

The oceans are noisy places to begin with. Wind, rain, surf, currents, and the animals themselves all contribute to the background noise; during the winter months, the calls of humpback whales raise the ambient noise level around Hawaii by 20 decibels or more.

But as human activity adds to the noise, it is casting an acoustic smog over vast areas [see photos, "Can You Hear Me Now?”]. Marine mammals can and do adapt to many kinds of man-made sound, but the rising tide of noise may be inhibiting the animals’ ability to feed, breed, and migrate, some whale experts say.

John Hildebrand, a professor at the Scripps Institution of Oceanography, in La Jolla, Calif., says comparisons of acoustic data from 40 years ago with more recent readings show that ambient ocean noise has risen about 3 decibels per decade; because decibels are logarithmic, that means the ambient noise intensity is doubling every 10 years. Although scientists who study ocean noise don’t like to point to a single noise source as being the worst for whales and possibly other marine life, they say that three sources seem most likely to pose the greatest threat: commercial shipping, air guns used for oil and gas exploration, and military sonar [see illustration, "Soundscape”]. All of these sources emit high-powered signals, typically above 180 dB, and they operate at the same low frequencies—below about 25 kilohertz—used by many whales [see sidebar, "How Much Sound Is Too Much?"].

On a foggy August morning, in his corner office overlooking an empty beach, Hildebrand runs through some sound samples. “This is an air gun,” he says. He’s plugged a subwoofer into his laptop, and the emerging sound (recorded about 1 km from the source) is impressive, how you’d imagine detonating a large firecracker in a swimming pool would sound: a deep, startling explosion. Oil and gas companies use air guns during seismic surveys. Typically, a surveying ship tows an air-gun array at a depth of up to 10 meters, firing shots of compressed air every few seconds; underwater microphones listen for reflected signals several kilometers away. By running the hydrophones’ output through digital signal processing software, seismic specialists get a picture of where oil and gas deposits might lie.

The air guns’ sound travels for thousands of kilometers. Researchers using an array of low-frequency hydrophones south of the Azores, for example, found that air-gun pulses, some originating more than 3000 km away, dominated their recordings, sometimes drowning out whale calls. They could even tell whether the air guns were located off the coast of Newfoundland or West Africa or Brazil. “At times in the summer, you can hear air guns going nearly continuously,” Hildebrand says. And as worldwide energy supplies grow tighter, companies are exploring more terrain than ever. The number of crews conducting offshore seismic surveys jumped more than 30 percent between February 2005 and February 2006, according to IHS Inc., an energy consulting company in Denver.

Next he plays a sample of a supertanker. The steady chugging comes mainly from the ships’ propellers and other machinery. There are currently more than 50 000 large cargo vessels, including 11 000 supertankers, crisscrossing the globe; much of the rise in ambient ocean noise comes from them. In areas with lots of ship traffic and therefore noise, whales have become louder, too. The songs of blue whales off the southern coast of California, for example, have risen several decibels in the last few decades, Hildebrand says.

Finally, the sound of a military sonar array. Like a fuzzy recording of modern music, it repetitively builds to a polytonal crescendo. Unlike passive sonar, active sonar arrays send out sweeps of focused sound. The sonar of chief concern operates at frequencies of 2 to 8 kHz—so-called midfrequency active sonar—with source levels well over 220 dB. Midfrequency sonar has been around since the 1960s and is now used by more than a dozen countries on at least 300 naval ships. A more recent invention is sonar operating at 100 to 1000 Hz, known as low-frequency active sonar. Low-frequency sonar remains largely experimental; the United States, the UK, China, Russia, France, and Italy are known to have deployed the technology. “The lower the frequency, the farther the waves propagate. The higher the frequency, the finer the granularity of information you’re getting,” explains the Navy’s Toti. “Low-frequency sonar is important for long-range detection, while midfrequency has a more refined detection capability.” He notes that the Navy’s use of active sonar has actually decreased over the last several decades, from more than 300 ships equipped with active sonar systems during the Vietnam War to about 200 today.

The Navy has acknowledged only four episodes where its sonar may have contributed to a whale stranding; the best documented of these is the Bahamas stranding in 2000. In that case, a Navy investigation concluded, a phenomenon known as a surface duct caused sound energy to be trapped near the ocean’s surface and to propagate farther than normal. The Navy did, however, modify how it uses midfrequency sonar following the incident. Among other things, personnel now listen for whale songs and clicks before activating the sonar pulses, and trained observers are on deck to look for whales surfacing.

Toti, an electrical engineer who specializes in underwater acoustics, remains unconvinced that sonar was to blame for many of the other strandings cited by the Navy’s critics. “I’ve reviewed several of these incidents, and from the positioning of the ships and what I know about the propagation of sonar, it’s inconceivable that the ship operations had anything to do with the stranding,” he says. “Marine mammals were stranding 10 000 years before sonar was invented, and they’ll be stranding 10 000 years after we’ve evolved to the point where we don’t need sonar anymore.”

Most whale experts, on the other hand, don’t have any doubts: sonar does kill whales. Two years ago, the IWC’s Scientific Committee, probably the world’s largest body of whale experts, met in Sorrento, Italy, to discuss sonar’s impact on whale populations. Andrew Read, a committee member and a professor of marine conservation biology at Duke University, in Durham, N.C., recalls that the committee went through its usual deliberations before issuing a report to its parent organization. “The committee says whatever it can agree on, which usually isn’t too much,” he says. But its eventual report did agree on this: the evidence linking midfrequency sonar to a series of whale strandings in recent years is “very convincing and appears overwhelming.”

A particular puzzle now is why beaked whales seem more susceptible to sonar than are other whales. A recent experiment on a captive beaked whale showed that while the animal could hear sounds in the 5 to 80 kHz range, its hearing was most sensitive in the upper half of that range, well above the levels used by midfrequency sonar. Not much more is known about these deep-diving whales, though they’re found throughout the world’s oceans. Some species of beaked whale are known only by skulls or carcasses that have washed ashore. “They’re really fascinating, but they haven’t gotten their 15 minutes yet,” says the ONR’s Gisiner. His office, which has an annual budget of about US $5 million, funds much of the basic research on marine mammal acoustics. Now, he says, learning more about beaked whales and why they react to sonar the way they do is the program’s top priority. “We’re getting a new window onto marine ecosystems just because we’re concerned about beaked whales.”

In the 2000 Bahamas stranding, some researchers have speculated that the intense sounds released gases throughout the whales’ bodies, much like decompression sickness, or “the bends,” that a human diver experiences from a too-rapid ascent. These gases in turn could lead to bleeding, disorientation, and the inability to navigate and echolocate. It’s possible the whales, startled or confused by the sonar, surfaced too rapidly; another theory is that the sound waves somehow directly caused the bubbles to form. “Whether it’s physiology, or behavior, or behavior that leads to a change in physiology, we don’t know yet,” Gisiner says.

Other types of whales also seem sensitive to sonar, though to differing degrees. In tests of the Navy’s low-frequency sonar in the late 1990s, for example, gray whales could be seen diverting around the source, while humpback whales sang louder and longer than normally. “We’re increasingly concerned about pygmy sperm whales and dwarf sperm whales—these guys are also very elusive, deep-diving animals,” says Dolman of the Whale and Dolphin Conservation Society. “And there have been a number of events involving the family of whales that includes orcas and melon-headed whales.” During a military exercise near Hawaii’s Hanalei Bay in 2004, Dolman says, about 200 melon-headed whales, which are usually found only in deep water, swam in close to shore; all the animals except one were eventually herded back out by rescuers.

Sonar may affect species other than whales, notes Duke’s Read. “We shouldn’t only be focused on beaked whales. How do fish and turtles respond to midfrequency sonars? We know virtually nothing about the effects of sonar on other components of the ecosystem,” Read says.

Despite the uncertainty, environmental groups say enough is known that it’s time to act. A year and a half ago, the Natural Resources Defense Council (NRDC) won a decisive court victory that forced the Navy to drastically scale back its testing of low-frequency active sonar; rather than deploy it across the Pacific Ocean, the Navy is now limited to areas along the eastern seaboard of Asia, around North Korea and China. Though some mass strandings have been reported in Taiwan since then, it’s been impossible to correlate those with the Navy’s sonar use, because the Navy doesn’t reveal where or when the system is operating, says Joel Reynolds, an NRDC senior attorney based in Santa Monica, Calif.

In late October, the NRDC again sued the Navy, this time over midfrequency active sonar—the technology implicated in the Bahamas and Canary Islands strandings. Among other things, the lawsuit demands that the Navy disclose when and where it will use its midfrequency sonar in testing and training exercises. “Right now, we don’t know until after the fact, when dead whales start showing up on shore,” says Reynolds.

With few exceptions, the NRDC says, the Navy has failed to follow rules set out under the Marine Mammal Protection Act of 1972. That law is quite specific: it states that anyone planning to engage in an activity that may harm protected animals first needs to get permission from the government. For the most part, the Navy hasn’t done so, Reynolds says.

To be sure, many people have found that getting such permission can be arduous. In testimony before a House subcommittee three years ago, Peter Worcester, a research oceanographer at Scripps, said one project he led spent nearly three years and more than half a million dollars to secure the requisite permits.

The NRDC lawsuit comes at an inopportune time for the Navy, which last fall announced plans to build a sonar training range off the southeastern coast of the United States. The range would cover about 1700 square kilometers; an array of hydrophones would be deployed on the seabed to record beacon signals given off by ships and submarines during training exercises. The Navy wants such a range primarily because the Atlantic fleet has no training range of its own, unlike fleets stationed on the West Coast or in Hawaii. The range would give sailors access to shallow coastal waters, where sonar is particularly tricky to use.

At present, the favored site for the range is off North Carolina, according to the Navy’s draft environmental impact statement, not far from the January 2005 stranding. Strandings of solitary whales and dolphins are common in the area, but mass strandings involving more than one species are rare events, notes Duke’s Read. The training ground would be “in my backyard,” he says, something he has mixed feelings about. “On the one hand, sometimes it’s good to concentrate these activities in one spot, so if there are environmental consequences, at least they’re localized,” he says. “But at the same time, the animals we study are here, and we’re particularly cognizant of the potential for adverse effects.”

At a series of public meetings to review the Navy’s plans, environmentalists, local fishermen, and charter-boat operators harshly criticized the plan. Among other things, they noted that the range is a rich one for whales and other marine life; the migratory path of the endangered North Atlantic right whale passes through the range. At the end of January, the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service, based in Silver Spring, Md., weighed in with its own objections, noting that the Navy hadn’t adequately addressed the range’s potential harm to whales. “The U.S. Navy is on the cutting edge of developing sonar technology,” says Reynolds. “There’s a lot of concern about making this area a center for acoustic development in the United States.”

Read says that of the sites the Navy is considering for its sonar range, the one in North Carolina is probably the least environmentally sensitive. Still, he says, “the Gulf Stream meanders through the range at some times of the year, and we know marine mammals like to aggregate along the edge of the stream. So there are certainly going to be animals out there, including beaked whales.” For that reason, he thinks the Navy needs to do more to mitigate any potential harm. Posting watchers on deck to look for whales isn’t terribly effective, he notes, because many of the animals spend less than 10 percent of their time at the surface. And simply listening for whale calls will miss any animals that happen to be silent at the time. “Unfortunately, we don’t really have much information about beaked whales, so it’s difficult to say what mitigation effects might be effective for them,” Read adds.

Reynolds says the NRDC is now considering legal action against other noise polluters. But with oil and gas companies, he says, it’s a harder sell, because they lack the kind of smoking-gun evidence seen with sonar. Only one stranding has ever been tied to air guns: in 2002, two Cuvier’s beaked whales beached in the Gulf of Mexico while a research ship was mapping the seafloor nearby, and the National Marine Fisheries Service eventually concluded that the evidence linking the stranding to the seismic survey was “inconclusive.” Making the case against commercial shipping may be harder still, because the industry is entirely unregulated when it comes to noise.

Still, the NRDC had some success about 10 years ago, when Exxon announced plans to do seismic testing off the coast of Santa Barbara, Calif.—and right along the migratory path of California gray whales. “We worked out a settlement with Exxon that, among other things, limited the time frame for testing, in order to avoid the whales’ migration,” Reynolds says.

It’s clear that the ocean is under siege from a lot of different sources

Several years later, though, Greenpeace, based in Amsterdam, Netherlands, tried to get the now-merged Exxon Mobil Corp. to halt seismic tests near Russia’s Sakhalin Island, just north of Japan. The area is a feeding ground for the Western Pacific gray whale, of which fewer than 100 remain. This time, the Irving, Texas­based company agreed only to temporarily pause its testing when whales were observed in the area. A company spokesperson quoted in a Bloomberg News story said that “there have been no documented injuries to marine mammals from using these air guns.”

Oil and gas companies are subject to the same laws as the Navy, Reynolds points out, and in theory, they’re required to get permits to conduct their seismic surveys. But the Minerals Management Service, in Washington, D.C., which oversees offshore exploration, has been lax about policing the fuel industry, he says. Seismic surveys in the Gulf of Mexico and Alaska often go on without authorization. “They haven’t even asked [the oil and gas companies] to do environmental impact statements,” Reynolds says.

But even if every U.S. polluter were to agree to reduce its output, that still wouldn’t eliminate the problem, he adds. Ocean noise “is a classic example of an international problem. Sound travels enormous distances and affects many countries. We need to develop an international solution,” says Reynolds.

Success in crafting such an international policy toward human-created noise seems remote at this point. Similar exercises have ended badly. Two years ago, the U.S. Marine Mammal Commission, a federal agency charged with overseeing government policy regarding marine mammals, convened an advisory committee to assess current thinking on ocean noise. The 28-member group, which included representatives from the oil and gas industry, the Navy, academia, and environmental groups, could never agree on what should be done about the problem or even how serious it is. Instead of issuing a report outlining the consensus of the group, the committee eventually decided to issue a report consisting largely of individual statements from members. The report, released in February, is posted on the commission’s Web site, https://www.mmc.gov.

The European Parliament, in Strasbourg, France, meanwhile, overwhelmingly agreed to a resolution that called on its members, as well as the North Atlantic Treaty Organization and other international bodies, to adopt moratoriums on the use of high-intensity sonar. It’s the first time any popularly elected body has addressed the issue so directly, but the resolution is nonbinding. So far, only Spain has cut back its use of midfrequency sonar, and only in a 50-km perimeter around the Canary Islands.

Time may be running out. Whales and other marine life face an ever-growing list of threats, including overfishing and water pollution. At a gathering of the Marine Mammal Commission in Anchorage, Alaska, last September, much of the discussion centered on climate change and the disturbing effects the warming of the polar caps is already having on marine life. Among the most troubling developments is that, for several months of the year, an ice-free passage now stretches across the North Pole, from Asia to Europe. If current trends continue, researchers say, the passage will be ice-free year-round by 2080. Commercial shipping and oil and gas exploration won’t be far behind. Animals unaccustomed to human traffic will now have to deal with this new encroachment, even as they cope with the receding ice, shifting food supplies, and changing water chemistry.

“It’s clear that the ocean is under siege from a lot of different sources, and they act synergistically to stress every living thing in the ocean,” says Reynolds. Tackling noise is just one piece, but it’s critical. “We can begin to regulate man-made noise today, or we can ignore it until the impact becomes irreversible.”

To Probe Further

The National Research Council has issued four scientific reports that look at anthropogenic sound and marine mammals, available on the National Academies Press Web site, https://fermat.nap.edu. The most recent, “Marine Mammal Populations and Ocean Noise,” was released last year.

The Natural Resources Defense Council’s “Sounding the Depths II” (https://www.nrdc.org) and the Whale and Dolphin Conservation Society’s “Oceans of Noise” (https://www.wdcs.org) provide overviews on the sources of underwater anthropogenic noise and the risks they may pose to marine mammals.

The U.S. Navy’s Whales and Sonar Web site, https://www.whalesandsonar.navy.mil, lays out the Navy’s case for the necessity of sonar.

Discovery of Sound in the Sea, https://www.dosits.org, has sound samples and explanations of ocean acoustics for a lay audience.


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