Of sounds and cetaceans: Quieting a noisy underwater world

Orcas, other porpoises and whales use sound to communicate with their pods. Oil and gas production might affect their ability to communicate.

Credit: 

iStockphoto.com/Dale Walsh

Marine mammals live in a world of sound. In the open ocean, whales and dolphins depend on sound waves, using echolocation to navigate, find food, attract mates and communicate. But their clicks and calls are not the only noises underwater: Oil and gas exploration, seafloor mapping, and ship and submarine navigation have increased dramatically over the past few decades, making the world’s oceans noisier than ever.

In recent years, a number of mass whale strandings linked to U.S. Navy sonar exercises have called attention to the potential side effects of artificial underwater noise on marine mammals. On March 15, 2000, 17 whales and dolphins from four species beached in the Bahamas after a Navy exercise involving an anti-submarine acoustical test. On July 3, 2004, several hundred melon-headed whales, normally a deepwater species, crowded into Hanalei Bay off the Hawaiian island of Kauai during a Navy sonar torpedo-tracking training exercise nearby. And on Jan. 15, 2005, 37 whales beached along North Carolina’s Outer Banks after a Navy sonar exercise off the coast.

Soon after the Outer Banks strandings, the National Resources Defense Council (NRDC) sued the U.S. Navy, calling for limited sonar use near whales and important marine mammal habitats. After several federal court rulings in favor of NRDC that emplaced six noise restrictions on marine activities, in October 2008, an appeal of the original case went all the way to the U.S. Supreme Court. In a split decision, the court ruled to overturn two of the restrictions but upheld four other rules that limit sound decibel levels, restrict sonar use in proximity to whales and ban exercises within 20 kilometers of the U.S. coastline.

But while the Navy’s use of sonar has caught the brunt of the sound controversy, it’s not the only source of human-made sound in the oceans. Noise from oil and gas exploration is also a significant contributor to the oceans’ sound budget.

In the aftermath of the 2005 strandings in North Carolina, Exxon Mobil mobilized eight other oil and gas companies to study the interactions of industry with marine life. Since then, the Exploration and Production Sound and Marine Life Joint Industry Program (JIP) has funded independent researchers who are trying to figure out everything from how whales process sound to how sonar-equipped ships can best avoid whales altogether. JIP’s stated goal is to fund acoustic and marine biology research to “systematically survey existing knowledge gaps about underwater sound and its effects on animals” — with the hope that human activities that use sound, seismic surveying and sonar in particular, can be further developed without harming the marine life that share the ocean.

Oil companies fund ocean science

Deepwater exploration is becoming a much more significant source of oil worldwide, with projects offshore of Angola, in the Gulf of Mexico, off the coast of Brazil, and in the Pacific Ocean near Australia, Indonesia and Malaysia. And with the United States letting the federal offshore drilling ban expire last year, offshore exploration may soon begin off the U.S. East and West coasts as well. All that exploration adds up to more noise underwater, which could disrupt whale behavior, especially along the marine mammal migration corridors that span both U.S. coasts. “If we can better understand how sound sources affect whales physically and behaviorally, we can begin to develop reasonable mitigation based on science, not just precaution,” says John Young, issue management coordinator of the Sound and the Marine Environment Issue Team for Exxon Mobil and executive committee chair of JIP.

JIP includes some of the world’s largest oil and gas exploration companies, including Exxon Mobil, Chevron, ConocoPhillips, Italy’s Eni and Norway’s Statoil. Now in its fifth year, JIP has evolved into a funding group that works with marine biologists to develop research projects related to the issues of sound and marine life. “JIP is an effort on the part of the oil and gas industry to step back and take a broader approach to investigating these very complex matters,” says Sue Moore, a marine biologist for NOAA’s Fisheries Science & Technology division in Seattle, Wash. “They are taking responsibility and for that, I applaud them,” she says.

JIP has broken down research interests into five categories: sound source characterization and propagation; physical effects on hearing; behavioral reactions to sound; mitigation; and research tools. Each research category has a committee of scientists, engineers and technical advisors, who are experts in the fields of sound and marine biology. Once a committee decides which issues within the five categories are most critical to study in the next year, it posts a request for specific project proposals on the JIP Web site and on Web sites for acoustical journals like Bioacoustics-L and Acoustics Today.

“On average we get anywhere from six to 20 proposals from scientists all over the world for a given project,” says Roger Gentry, a marine biologist with ProScience Consulting, LLC, an environmental consulting firm in Woburn, Mass., and senior advisor to JIP. Some projects, however, are so specific that only one or two people in the world are doing that kind of research. For example, only two research teams answered a call last year for project proposals to study the behavioral effects of seismic air gun noise on humpback whales, Gentry says. “Those controlled-exposure field experiments are like military operations, involving multiple ships,” he says. “There are just not very many people in the world who can do that.”

Once research teams submit their ideas, the proposals go to a peer review committee chaired by research scientists, who rank the proposals in terms of scientific merit. “The selection process is very similar to those used by the National Science Foundation and the Office of Naval Research, which is the largest source of funding for marine biology research in the world,” Gentry says. “It’s a necessary selection process to protect ourselves against the charge of tainted ‘tobacco science’ money.” Once a team’s proposal has been selected, JIP works out a budget for the project and finally, has the researchers sign a contract stipulating that the team publish their results in a peer-reviewed journal within two years of the project’s completion. The rigorous selection process and publishing requirements satisfy conflict of interest reservations anyone might have about oil and gas companies funding this type of research, Moore says.

Studies under way

Last October, the JIP partners greenlighted the program for another three years and chose the projects that will be funded this year. Priorities for 2010 include finishing a study on how sound from air guns travels underwater and developing better systems for detecting whales that might be nearby, Young says. Another major project will be a behavioral study on how humpback whales respond to air guns, which will take place in Australia over the next three years.

Air guns are a particularly thorny issue — so much so that JIP has already spent $7 million measuring their sound output in the ocean, according to Gentry. Air guns shoot low-frequency shock waves from an array towed behind a ship down into the water. These shock waves penetrate the seafloor and help locate pockets of oil, gas or mineral deposits. But to get the seismic profiles researchers need, the air guns release large quantities of highly compressed air at 15-second intervals. These guns can produce noise levels as high as 250 decibels, twice as loud as a jet engine and well over the 200-decibel threshold for permanent hearing damage in fish and whales.

Since 2005, researchers in Norway have been looking at how sound from air guns propagates through the water. To gauge how sound waves from air guns might affect whales or other marine life, researchers first need a better understanding of how sound actually travels underwater. Ideally, most of the energy produced by air guns is directed down toward the seafloor, but the seafloor’s bathymetry has a significant effect on how much sound energy escapes outward. “A big part of the air gun project is modeling how sound moves in different underwater terrains,” Gentry says. “The air gun arrays produce and propagate sound very differently depending on whether the environment is shallow water or deepwater, if the bottom is sloping or flat, and whether the seafloor is mud or rock.”

Another major focus of the 2010 program will be to modify existing technologies like hydrophones and radar to detect whales near a sound source like an air gun array — with the goal of avoiding whale-human interactions. “Right now the gold standard for detecting whales is to have somebody standing watch on the bridge of a boat looking out with big binoculars,” says James Eckman, a marine biologist at the Office of Naval Research in Arlington, Va. “But that method doesn’t work in bad weather or at night.” Fortunately, he says, the key to solving this problem might lie in already existing technology. “Most of these animals make noise, so just dropping a microphone in the water could work.” Radar, which is already required on all seagoing ships, could also be used to watch for large whales nearby, he says. The Supreme Court’s 2008 decision stated that sonar operations must cease if a whale or other marine mammal is spotted within two kilometers of a ship. “Right now seismic operations are shut down at night, when we can’t see the whales,” Young says. “Developing better ways to detect them would double our exploration efficiency at sea.”

Studying behavior: a whale of a challenge

Future projects will involve other lines of research as well. “Looking at JIP’s research categories, I agree that we need improvement in all five categories,” Moore says. “But I would emphasize the need for more behavioral studies more than anything.”

Efforts to better understand whale behavior, including how large whales respond to human-made sound, have often been hampered by logistics and funding. The upcoming humpback whale study in Australia will involve ships, equipment and funding from multiple sources, including JIP, the U.S. Minerals Management Service, Fisheries and Oceans Canada and the Australian Marine Mammal Centre. The field experiment will measure humpbacks’ behavioral responses to varying frequencies and volumes of sound produced from air guns, something that has never before been observed in a controlled research setting.

For all the attention the issue has gotten, the question of how sound affects whales and why human-made sources sometimes lead to strandings is not well-understood, Moore says. “This is an extremely complex issue,” she says. “And a lot of the pieces of this puzzle are still missing.”

For example, why human-made sounds sometimes cause whales to change their behavior and beach themselves remains a mystery. Such strandings don’t seem to be due to physical trauma. “None of the animals killed during the Navy sonar exercises showed acoustical trauma like blown out membranes or dislocation of the middle ear bones,” says Darlene Ketten, an acoustics specialist at the Woods Hole Oceanographic Institution in Massachusetts who has studied CT scans and performed necropsies on beached whales. “The sonar didn’t kill them. The cause of death was from stranding,” she says.

“There is a continuum of possible behavioral responses to sound,” she says. Some species seem to react to human-made sound just by moving away from the sound source, whereas others, like pilot whales and beaked whales, seem to panic and move close to land. The varied responses could be because of differences in stress-tolerance physiology between whale species, Ketten says. Beaked whales in particular may have a lower stress tolerance than other whales, similar to the way thoroughbred horses tend to be more high-strung than Clydesdales. “Some of the beached beaked whales had small hemorrhages in the fluid areas around the brain,” she says. “Again, that’s not a mortal injury, but it’s a marker for low stress tolerance that we see in horses, some species of birds and even some people.”

In addition to behavioral studies, Ketten would also like to see JIP fund more research on the physical effects of artificial sound on hearing. Conducting hearing tests on whales in the wild can be a challenge. For example, Gentry and his colleagues recently tried to capture a minke whale in Iceland to measure its hearing. The plan, he says, was to glue electrodes to the skin of the 9-meter-long whale to measure its brain’s response to sound, a similar technique to the methods used on human infants for hearing tests. But the whale moved too quickly for the researchers —“they didn’t even come close,” he says. The researchers could not get the electrodes on the whale, and thus the team came home with no data. Fortunately, several labs, including the University of Hawaii’s Institute of Marine Biology in Manoa, keep captive dolphins for hearing tests, which allows researchers to get around the sticky issue of catching the whales and dolphins in the wild.

Paul Nachtigall, a marine biologist at Hawaii’s Institute of Marine Biology, is applying for JIP funding to study whether false killer whales, a type of large dolphin, can amplify or dampen the volume of sounds they hear. Previous research indicates they can amplify their own echolocation clicks after they bounce off a distant object and come back. “It’s possible that some types of whales can turn the volume up and maybe even down on loud sounds,” Nachtigall says. That could have implications for mitigating sonar and seismic air gun use, he says. “If we can give them some warning of an impending blast, perhaps by ramping up the volume instead of starting off full force, they might be able to cover their ears, so to speak.”

In whale species that can’t be kept in captivity, Ketten suggests using computers to model their inner ear anatomy. “Modeling studies of the middle ear structures would give us an idea of just how sensitive these animals should be to sounds,” she says.

Such desktop studies make up the bulk of JIP funding, Gentry says. “Computer studies are the easiest to do and the cheapest,” he says. “Most of those studies cost less than $100,000, while lab and field studies easily go into the millions.” With such studies, researchers can get around many of the logistical problems of working in the open ocean. “The open ocean is a very difficult environment to work in,” Moore says. “Often weather dictates what you can do. It’s not unusual to only be able to work a few days in several weeks at sea.”

Sharing the sea

The challenges of studying marine mammals and determining how human actions affect them are not easy to overcome, but having a steady source of research funding will be important in the next few years as oil and gas exploration increases off U.S. coasts, especially in the Arctic, Moore says. “As sea ice recedes, I think funding from JIP will play a large role in galvanizing Arctic marine mammal research because of the interest in oil and gas development there,” she says. “Right now we know astonishingly little about where the whales are in the polar seas.”
As complex as the whales and sound issue is from a scientific standpoint, the solution may be as simple as staying out of whales’ way, Eckman says. “It may be as simple as enhancing our abilities to detect these animals in the ocean and then avoid them.” After all, 71 percent of the planet’s surface is ocean. It seems like there should be enough space for marine mammals to have some peace and quiet, even in an increasingly noisy underwater world.

Mary Caperton Morton
Thursday, March 18, 2010 - 12:00

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