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Planet Earth

Killing Whales with Sound

Darlene Ketten's fascination with how whales hear has swept her into a storm of controversy

By Max Aguilera Hellweg and Susan McCarthyApril 1, 2002 6:00 AM


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This is one of Darlene Ketten's more comfortable field dissections: The sun is out, there's a pleasant breeze, only one vulture looms overhead, and the whale doesn't stink.

It's a small male sperm whale, only a year or two old—maybe 16 feet long if it were all here. Conveniently, only the head remains, at most a ton of blubber, skin, and bones resting on a wooden pallet. "You can lift it with a forklift! I love it," says Ketten, a biologist who studies the hearing of whales. Because this whale has been kept frozen, it is the freshest sperm whale she has cut into in years, and she can't help contrasting it with her last sperm whale dissection in 1999, on New Year's. She was at a party, "in velvet minidress and three-inch heels," when she got the call—a whale had beached and died on Nantucket Island. She dropped everything and got on an airplane. The whale stank horribly. She and her team dissected the ears and returned to the airport. On the way home everyone smelled so bad they were put on another plane by themselves, Ketten recalls.

Her subject this day had stranded on a beach in the Gulf of Mexico months earlier. Bathers poured water on him and covered him with their towels, but he was too sick to return to the sea, too big for any wildlife rehabilitation center. To end his misery, he had to be killed. Because his peripheral veins had collapsed, it proved impossible to inject a mortal dose of sedative. Finally, a veterinarian administered a local anesthetic, cut an artery, and let the whale quietly bleed out into the shallow water. Then the vet and a team from the National Park Service cut off his head, packed it in 150 bags of ice bought at a minimart, and trucked it to a walk-in freezer.

Now that head is surrounded by 15 scientists at the boat launch of the National Marine Fisheries Service Center in Fort Walton Beach, Florida. The researchers hope to solve a few of the mysteries of sperm whale anatomy. Wanda Jones, a Fisheries Service biologist, had the task of thawing the head—for three days. She's hoping that was enough.


Darlene Ketten (in blue shirt) dissects out the left eye of this sperm whale for a colleague while others work on the brain and the nose.

Ketten begins by recording every possible dimension of the left side of the whale's head and jaw: position and size of the outer ear, size of the eye, distance between the center of the outer ear and the center of the eye, size of the blowhole, length of the jaw. As she finishes, the others join in the attack.

Ketten cuts through layers of blubber and muscle, searching for the tympano-periotic bulla, a bone complex that houses the middle and inner ear. She shows a dry specimen, smaller than her fist, taken from a whale that stranded in 1964. It may be hollow, but it is extraordinarily heavy. Ear bones of cetaceans—whales, dolphins, and porpoises—are the densest bones in the world, protecting delicate inner-ear tissues from damage and the tremendous pressure of dives. Sperm whales are thought to dive as much as a mile below the surface in search of squid and other prey.

The biologists wear a combination of medical and nautical gear, including surgical scrubs and rubber boots. They are piratical as they get into the flensing spirit. "Where are our butcher knives? Our big knives—where are they?" inquires Ketten, adding, "The art of flensing hasn't changed much over the past 100 years."

Blubber is surprisingly attractive: a spotless milk-white layer, inches thick, beneath the whale's deep, rich black skin. Beneath the blubber, Ketten finds jaw fats, creamy in color, far softer. When she tentatively identifies the shape of the casing that holds the fats, she says: "It's so cool! It's a sort of ovoid lobe of fat—if my theory is correct—that runs along the jaw, conducting sound waves." She describes the lobes as shaped like a pair of rabbit's ears, one on each side of the jaw.

As dusk falls, she reaches the ligaments behind the bulla and calls for a flashlight. Cutting it loose, she holds it up for all to admire before injecting it with formalin to preserve the cochlear structures inside. "It's a rock that has really delicate membranes in it," she says.

On the second day, the biologists tip the head over with a forklift so they can work on the other side. Ketten injects methylene blue dye into the outer ear, a slit about a third of an inch wide and shaped like a sound hole on a violin. The dye travels less than two inches before it hits an obstruction, possibly a lump of wax and dead tissue similar to those Ketten has seen in other whales. The canal may be a blind pouch, a useless relic of the whale's ancestry as a land animal. Ketten says she will examine it "slowly, tediously, carefully" in the laboratory to figure out whether it has any function.

Next, she saws out a block of tissue that contains the middle and inner ear so it can be put through a CT scanner, membranes intact. When the block finally comes loose, she peers into the space behind the ear and points out the enormous auditory nerve that passes through a hole in the skull from the brain to the ear. The nerve is big not only because whales are big; it is big because hearing is a whale's most important sense.

Cetaceans descended from land animals 50 million to 60 million years ago. Gradually losing their legs, they evolved into ocean dwellers in a dim world where sound serves them better than light. As a result, their hearing developed far beyond ours, while their eyesight deteriorated—some river dolphin species have no functional lenses in their eyes and can register little except light and darkness. While humans have 38 optic nerves for every auditory nerve, the sperm-whale ratio is one-to-one. Instead of relying on eyesight, sperm whales use sound—to keep track of one another, announce the discovery of food, and cry in distress. Many cetaceans also use sound to echolocate. By uttering high-pitched sounds and listening to how the sounds bounce back to them, they can navigate lightless waters, find prey, and detect objects with phenomenal precision. The changes in the cetacean ear, head, and brain that have heightened this sense are a triumph of adaptation.

Nevertheless, whales also display vulnerabilities that humans are just beginning to understand: Sometimes they leave the water and strand themselves on a beach, where, more often than not, they die. Researchers know that strandings occur because an animal is ill, injured, or old. They are now worried that more and more of the injuries are caused by human behavior. The noise made by freighters in crowded shipping lanes, by underwater drilling and explosions, and by sonar devices used to hunt for submarines may be damaging whales' ears.

Darlene Ketten never wanted to spend her days holding press conferences or giving interviews about marine mammal politics. With a joint appointment at Woods Hole Oceanographic Institution and Harvard Medical School, she studies the anatomy of cetaceans. Among researchers, already a cautious lot, she is legendary for her meticulous collection of data. She would be quick to point out that supporting hypotheses is inherently slow, cumulative, and incremental work. In her field there's a paucity of data about whales and dolphins to draw on because, she points out, "You have to wait for a volunteer." As a consequence, "It takes me millennia to get things out because I won't publish on a specimen number of one."

The data she has gathered so far from those limited sources have been maximized by a breakthrough she made in 1980, when she was studying for a doctorate at Johns Hopkins. Confronted by her first whale ear blocks, chunks of tissue similar to that cut from the sperm whale in Fort Walton Beach, she couldn't decide where to slice. So she visited the radiology department to ask if an X ray might locate the ear. They suggested a CT scan instead. The density of whale bones created problems, but eventually Ketten perfected a technology that worked, transforming the study of whale anatomy and even human cochlear implantation. (See "The Ketten Connection Between Whales and People," below.) The advantage of CT scans is that researchers can manipulate them endlessly to produce cross sections at different points and from different angles. Material of different densities can be removed from the image to show only bone, only muscle, or only fat.

In the scans, Ketten was able to see structures and fine details of the whale ear that had never been observed before. Because cetaceans have evolved so that their outer ears do little if any work, researchers had suggested that jaw fats receive sounds. Ketten was the one who put forth convincing evidence that the soft fat shaped like a rabbit's ear in a whale's head will pick up sound waves as the mammal moves through water and carry the waves to the middle and inner ear. "This particular type of fat has an acoustic impedance that's similar to seawater," she says, referring to cetaceans affectionately as "acoustic fatheads."

While the structure of cetaceans' middle and inner ear is similar to that of land mammals, including humans, Ketten has found differences that allow whales and dolphins to hear higher frequencies than they otherwise might, improving their ability to echolocate. She has determined that cetaceans can hear much higher and lower frequencies than humans because they have evolved a bigger range of widths and stiffnesses in the basilar membrane in the cochlea of their inner ears.

Ketten also discovered that cetacean ears fall into three anatomic groups based on their lives in the water: "The frequencies they hear tell you something about what's important to them in their environment."

For example, odontocetes—toothed whales and dolphins—come in two flavors. Type I odontocetes hear upper-range ultrasonics, peaking above 100 kilohertz, about 80 kilohertz higher than human ears can hear. These animals include species such as the Amazon dolphin, which navigates in narrow spaces and clouded waters. Type II, the lower-range ultrasonic odontocetes, peak below 80 kilohertz. They are creatures of the coast and the open sea, needing lower frequencies to echolocate over longer distances in the search for, say, herring. There's something of a trade-off involved: Higher frequencies give precise images in echolocation; lower frequencies travel much farther but miss very small objects. Over the years Ketten has demonstrated that more than a dozen species that weren't previously known to echolocate have the capacity.

Ketten calls a third group Type M, for mysticetes, animals such as baleen whales that feed in the open sea on huge schools of krill and small fish. Their hearing and vocalizations are the least well known because they live far out at sea and tend to strand less often. The structure of their ears indicates they're adapted to using low frequencies, peaking between 10 hertz and 35 kilohertz, and apparently don't use echolocation. How they find their food without it isn't known. There is evidence suggesting that their lowest calls can be detected thousands of miles away, across the basin of an ocean.

So little is known about so many species of whales and dolphins that Ketten becomes frustrated when she is pressured by environmentalists and government agencies to give definite answers. She grumbles that "marine mammalogy is a field in which the plural of anecdote is data." And although she is eager to study the blocks of tissue she cut from the Fort Walton Beach sperm whale, she has had to put much of that work on hold to focus on the most demanding, high-profile case she has ever undertaken: 16 whales that beached in the Bahamas two years ago.

Most were beaked whales, and they stranded in the Providence Channels in the northern Bahamas. At the time, the U.S. Navy was testing tactical mid-frequency sonar in the area. Six of the whales died. Ten were pushed back to sea and may have survived. The deaths—and the possibility that sonar was responsible for them—triggered a controversy that is still unsettled.


Despite an assault by researchers on this young sperm whale's frozen head, no one is certain why the animal stranded. He was neither thin nor injured, but he had been separated from his mother and his herd.

Sonar is simply man-made echolocation. Researchers often use the terms dolphin sonar or bat sonar as a shorthand for echolocation. Humans use sonar to navigate, fish, hunt for shipwrecks, and detect quiet modern submarines. There is little doubt that if sonar is intense enough, it can harm any living thing in its path. Some researchers speculate that some dolphins and whales use intense blasts of sound to blast fish or squid into insensibility. The Navy's sonar during the test reached 235 decibels at the source—underwater decibels are calibrated on a different scale from airborne decibels. At 180 decibels (underwater), human lung tissue begins to bruise.

Sent to investigate by the National Marine Fisheries Service, Ketten found hemorrhages in the ears and in the acoustic fats of five beaked whales she examined. Although pressured, Ketten refused to jump to conclusions at a press conference because she hadn't finished her analysis and hadn't yet seen the data on when and where the sonar had been active. "I'm still not ready to say the Navy did it," she told reporters.

She emphasized that injuries to the ears of the whales did not kill them, although those injuries presumably caused them to strand. "They didn't die from the damage to their ears," she says. "They died from being on the beach for hours and hours." She did conclude that the injuries were consistent with acoustic or impulse trauma and contributed to an interim report put out jointly by the Navy, the Fisheries Service, and the National Oceanic and Atmospheric Administration last year. The report concluded that the tactical sonar was the "most plausible" source of the injuries to the whales' ears. The report recommended research to prevent incidents in the future, including identifying beaked-whale habitats and learning what sounds they make and use—precisely the sort of work Ketten wishes she had more time to do.

Determining whether any sea creature's death is caused by humans is an enormously difficult task. Ketten points out that she doesn't even have a database of what normal whale ears look like. Nobody is certain yet whether man-made noise is harming cetaceans, but researchers are trying to figure out which noises might be worse than others, how they do damage, and how the damage can be mitigated. Ketten says so much attention is being paid to the sonar threat that the far more widespread issue of ship noise has been neglected. Shipping lanes around the world are crisscrossed by enormous tankers broadcasting low-frequency noise that may be harming whales every day. She compares the problem of ship noise for whales to industrial noise for humans. Not only do many people work in harmful levels of industrial noise but countless people flock to rock concerts so loud they cause permanent and significant hearing loss. She wonders if dolphins seen bow riding near ships are doing something similarly foolish.

While some sounds may cause physical harm, there may be others that cause more subtle damage. "If you're an animal and you're breeding," says Ketten, "and somebody does the equivalent of scratching their nails on a blackboard, it may have an impact on your breeding." Noise pollution may also mask signals animals need to hear. If cetaceans can't communicate over long distances because a smog of sound intervenes, they might not be able to locate mates.

Ketten says solutions will not come easily: "Everyone wants a literal sound bite: 'This is safe.'" There may not be frequencies that are safe for all animals. "What's safe for a dolphin may not be safe for a seal," she says. "It's important to do this testing, and it's important to mitigate. I think sailors are a precious commodity just like marine mammals." If there is a balance to be struck between whales and people, one of the two will have to learn a lot more about the other first.

The Ketten Connection Between Whales and PeopleIn 1986, when Darlene Ketten was working at Harvard, she happened to overhear a conversation about cochlear implants in a hallway. "They were saying, 'Well, we can't get good scans because of the metal implant,' and I said, 'Yes, you can.'"

Much of a cochlear implant is made of platinum, a dense element that plays havoc with scans. As dense as platinum is, it's not much denser than cetacean ear bones, which had been a problem Ketten had to overcome in her scans. Soon she began consulting with implant teams at Harvard's Massachusetts Eye and Ear Infirmary and at the Washington University School of Medicine in St. Louis.

Cochlear implants restore partial hearing for some people who are profoundly deaf but whose auditory nerves are intact. The implant is an array of electrodes that functions in place of the cochlea. After the array is surgically placed in the inner ear, it is connected to an external device that does the listening the outer and middle ear ordinarily do, turning sound waves into electrical impulses and transmitting them to the electrodes, which then stimulate auditory neurons.

Inner-ear anatomy varies significantly from person to person, so surgeons must decide in each case where to place the implant, how to avoid damaging nearby features such as the facial nerve, and even which ear to operate on. Positioning the implant correctly is critical. With her ability to read scans involving dense material and visualize complex three-dimensional structures, Ketten was able to help surgeons decide before surgery where electrodes should be placed, and where, after surgery, they finally landed, so that audiologists could figure out which sound frequencies to assign to each electrode in the array.

This work continues to unfold: A recent study by Ketten and her colleague Margaret Skinner, a research audiologist at Washington University, showed that the farther into the cochlea the electrode array is implanted, the better the patient's ability to recognize spoken words.

Ketten's work on humans has also contributed to her cetacean research. "A lot of my work on marine mammals is in pathology, postmortem work," she says, "and that's something I learned in my work with human patients: to look at diseases or describe traumas using scans." — S. M.


A discussion of the adaptation of seals to their marine environment can be found at

A good description of cochlear implants appears at

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