Blast from the Vast

What's the purpose of nature's most powerful sound?

By Shannon Brownlee|Wednesday, December 03, 2003
RELATED TAGS: UNUSUAL ORGANISMS, OCEAN

Leave aside, for a moment, the question of why Ted Cranford wanted to perform a CT scan on the head of a sperm whale and consider instead how he could pull it off. First, of course, he would need a dead whale, preferably a young one that had beached itself on the coast of California near his home. Then he would need a device big enough to scan a 600-pound head. And he would have to figure out how to keep the head preserved until he could set up the scanning machinery.

Finding a whale turned out to be the easy part. One fall day, a newly dead infant sperm whale conveniently appeared on San Gregorio Beach, just south of San Francisco. Cranford was attending a scientific meeting in Bristol, England, at the time, but two friends who are marine-mammal veterinarians knew what he was looking for. They drove up Highway 1 from Santa Cruz, 30 miles to the south, cut through several feet of blubber, muscle, and bone, and scooped up the head with a front-end loader borrowed from a nearby lumber company. Cranford’s friends dumped the head into the back of a pickup truck and drove it to the University of California at Santa Cruz’s Long Marine Laboratory, where they stashed it in a walk-in freezer. Then they sent him an urgent message to come home.

When Cranford began looking for funding to scan his whale head, several scientific agencies politely but firmly turned him down. The data would undoubtedly be of interest, they said, but the head of a sperm whale—even a baby sperm whale—simply could not be scanned. 

Courtesy of B. MØhl, M. Wahlberg, and P.T. Madsen, "The Monopulsed Nature of Sperm Whale Clicks," Journal of the Acoustical Society of America 114, vol. 2 (2003): 1143-1154. Printed with permission.

Image courtesy of Ted W. Cranford

Above left: A sperm whale’s click, recorded off the coast of Norway, is made up of a series of diminishing pulses that together last between 10 and 30 milliseconds. Above right: A colorized CT scan shows how such clicks, produced by the whale’s muscular “lips” (in blue, near the front), travel through the head and are amplified. The large spermaceti organ (in yellow, near the top), both magnifies and focuses the sounds, which bounce off the back of the skull (in white), then down and out the front of the head. Along the way, the whale’s clicks pass through the “junk”—lens-shaped pockets of fat (yellow stripes) that focus the sound down to an intense beam.

Cranford, however, is a man not easily parted from his ideas. He is also handsome, with a thatch of unruly reddish brown hair and a carefully trimmed graying beard. He has small, even teeth behind fleshy lips, one blue and one hazel eye, and a penchant for wearing sneakers, shorts, and vibrantly colored Hawaiian shirts, even at scientific meetings. Now a 47-year-old adjunct professor of biology at San Diego State University, he is known as Grizz, short for grizzly bear, to friends and close associates from his undergraduate and graduate student days in Santa Cruz. The nickname describes not so much his demeanor as his ursine size and his habit of greeting friends with bear hugs.

In graduate school Cranford first used high-tech medical imaging to probe the anatomy of a mammal—in that case a dolphin’s head. Since then he has made it his mission to find out how toothed whales and dolphins make their sounds. It is a nontrivial question, as scientists like to say, meaning the answer is both significant and hard to get. Toothed whales, a group that comprises sperm whales and killer whales along with another six dozen species of lesser whales, porpoises, and dolphins, can emit a bewildering cacophony of noises underwater. Drop a hydrophone over the side of a boat in the middle of a school and you will hear, depending upon the species, anything from birdlike trills to whistles, squeaks, squawks, oinks, blats, and Bronx cheers.

The sounds Cranford is most interested in, and has spent the last two decades trying to understand, are the rapid-fire clicks toothed whales use for echolocation. A single click comes as an instantaneous burst of energy that usually lasts less than 1/10,000 of a second yet contains an astonishing range of frequencies, or pitches, most of which are too high for humans to hear. These intense packets of sound emerge from the animal’s forehead as a focused beam, much like the light from a miner’s headlamp. Many dolphins and whales seem to be able to narrow or widen the beam at will by deforming a lump of fat in their forehead, known as the melon, the way a glass lens can shape a cone of light. The animals are able to shift the loudness of a single click in order to penetrate farther into the water in front of them. Some clicks are loud enough to temporarily deafen a person.

Sperm whales make the loudest sounds of all. One of their clicks, if heard in the open air, would be much louder than the sound of a jumbo jet taking off. “It’s the biggest and loudest damn biosonar source in the world,” Cranford says. Just imagine a crack that lasts 1/10,000 of a second but can be picked up by hydrophones—and heard by other sperm whales—at a distance of 15 miles or more.

How a flesh-and-blood animal can produce such a violent blast remains a mystery. Actually, almost everything about sperm whale anatomy is mysterious, because it is difficult to map body parts that are far bigger than the anatomist doing the mapping. The head of a big male sperm whale can be 25 feet long and take up a third of the animal’s length. Much of a sperm whale’s head is occupied by the spermaceti organ, a huge fibrous cask containing a milky, waxy material that was highly prized as a lubricant and lamp oil, and which to Nantucket whalers looked like nothing more than gallons and gallons of semen—hence the name. “I’ve never been able to figure out how they rationalized females having spermaceti too,” Cranford says.

To modern biologists, a structure as big and as odd as the spermaceti organ cries out for an evolutionary explanation, and marine mammalogists have argued for years over its function. Cranford subscribes to what marine mammalogists call the big bang theory, which argues, among other things, that a sperm whale’s head is a gigantic noisemaker. The spermaceti organ, according to this school of thought, helps amplify and focus the whale’s sonic emissions, which it uses to stun fast-swimming squid and fish long enough to gobble them up. The big bang theory has been difficult to demonstrate because no one knew the precise arrangement of parts inside a whale’s head. “When you cut into the animal you destroy the geometry, and it’s the geometry, the shape of tissues, and their consistency that are responsible for the sound beam,” Cranford says. He thought if he could find a way to scan a whale’s head, he could pin down the geometric relationships between its parts and decipher the purpose of the spermaceti organ.

First, though, there was the small matter of funding. Cranford’s adjunct professorship at San Diego State is unpaid unless he teaches or gets a grant through the university, and marine-mammal biology is not exactly a big priority for the National Science Foundation. Some years, Cranford has had to pay for his research out of his own pocket—or rather that of his wife, who is an invertebrate zoologist for the San Diego water department. The rest of the time, nearly all of his funding has come from the Office of Naval Research (ONR).

Images copyright © 1999 by Ted W. Cranford, all rights reserved.

Basso Profundo

A stereoscopic image of a sperm whale’s head reveals the inner workings that create its deafening sounds. To see a three-dimensional image, position your nose about a foot from the screen and slowly cross your eyes, focusing on the third image that will appear in the middle. The blue areas near the front are the “lips.” Air surrounding the skull (in white and lighter blue) reflects and amplifies the lips’ sounds like an acoustic shell behind a stage.

The Navy has very practical reasons for being interested in dolphin sounds. A blindfolded dolphin can detect an object three inches in diameter from a distance of 123 yards. That’s roughly equivalent to standing at one end of a football field and spotting a tangerine in the opposite end zone. More to the point for the Navy, a dolphin is a lot better at such tasks than the sonar dome on a submarine. Trained dolphins can pinpoint underwater mines from a distance of several hundred feet with almost 100 percent accuracy. Even the best submarine sonar domes, backed by a roomful of sophisticated computers that analyze the returning echoes, routinely miss mines. That’s not good enough, Cranford says: “It only takes one inexpensive little mine to blow a hole in a great big expensive ship full of sailors.”

Five years ago, the federal government gave a group of engineers several million dollars to begin developing an electronic dolphin—a self-propelled, mine-detecting underwater drone as perceptive as a cetacean. Such a device could be deployed from a ship to scan for mines even in shallow waters. If the drone found any, the ship could hightail it to safer waters without worrying about having to come back and pick up its drone. “We want to have something in a box that can do what the dolphins can do,” Bob Gisiner, the marine-mammal science program manager at ONR, told me. “They can find objects buried under the mud. We don’t have any sonar that can do that anywhere near as well.”

It turned out to be a hellishly difficult problem. Most of the Navy’s efforts were focused on signal processing, or detecting the echoes that come back from distant objects and computing where and what the objects are. “Everybody thought signal processing was sexy,” Gisiner said. Cranford’s research, by contrast, seemed to the engineers like a mere mechanical problem and not worth spending a lot of money on.

The engineers tried using piezoceramic elements, each of which emits only a single frequency or a very narrow band of frequencies. But a dolphin’s broadband click required a huge array of elements, and the prototypes failed to produce sounds of the right length, frequency, and duration. “In the end, they couldn’t make dolphin noises,” Gisiner said. “They just could not do it.”

 Even so, Gisiner has had to fight to keep Cranford’s funding going. Cranford says, “The only reason I’ve been able to stick with it is I’m really excited about the nuggets of discovery—that moment of finding something that nobody has found before. It’s like being a modern-day explorer. You’ve got to be a little abnormal to be willing to do absolutely anything to answer a question. Only 1 percent of the world’s population has a Ph.D. You are at the tip of the tail of a bell-shaped curve if you are willing to devote yourself to getting a Ph.D. in what amounts to a backwater of science.”

Cranford had no yearnings to be a scientist as a child. He grew up in a suburb of Los Angeles, the grandson of a dairy farmer who emigrated from Switzerland in 1919. He wears his grandfather’s gold ring. Cranford’s father was an elevator constructor. “He had to figure out how to maneuver an elevator into a little hole in the skeleton of a building,” Cranford says. “I’ve always wondered if I got my interest in understanding how things work from my dad. He was a mechanical engineer without the training.”

When Cranford enrolled in Long Beach Community College after finishing high school, no one in his family had ever gone past 12th grade. One day his zoology instructor told her students to propose a research project. “I wrote down, ‘I want to do my project on something bigger than a bread box,’” Cranford recalls. “I thought she was going to chew my butt. Instead she said, ‘Go to the Cabrillo Museum.’”

 

A prototype of Ted Cranford’s noisemaker, which the Navy had hoped to use to detect mines through echolocation. Modeled on dolphin physiology, the device is run by a compressor that forces air through surgical tubing and springy rubber parts. The latter replicate the two sets of muscular lips in a dolphin’s nasal passages. The resulting sound? Something like a Bronx cheer.

Photographs by Reuben Cox

The museum ran a whale-watching boat that plied the waters between Long Beach and the Channel Islands, searching for gray whales on their way from their feeding grounds in the Arctic to their calving shoals in Baja California Sur in Mexico. Cranford was hooked. After volunteering for the next six winters to lead whale-watching tours, he drove his Volkswagen bus up the coast and at the age of 24 enrolled as a junior at the University of California at Santa Cruz. There, the eminent marine mammalogist Kenneth Norris took him on as a graduate student. Norris set Cranford the task of figuring out how and exactly where dolphins make their sounds.

A few years before, Norris and another student had shown that dolphins make their sounds somewhere in their nasal passages, not in the larynx, as many marine mammalogists had assumed. Norris wanted Cranford to create a three-dimensional map of a dolphin’s head. He found Cranford a specimen and sent him off to do the rest. Cranford decided to cut thin slices of the frozen head with a diamond-studded wire saw, map the structures on each slice, and then use a computer to construct a three-dimensional image from the slices.

“The saw was a total failure,” Cranford said. He spent days dressed in foul-weather gear in a walk-in freezer at Sea World in San Diego. He tried to cut through the head, but the blubber and fat never froze completely, and the diamonds were repeatedly stripped from the expensive wires. To add to Cranford’s misery, the freezer was already occupied by a giant skua, a swan-size bird recently captured in the Antarctic. The oceanarium was holding the skua in isolation before introducing it to other animals in an exhibit. While Cranford wrestled with the saw, the bird attacked and vomited on him.

“It wasn’t that funny at the time,” he says. But in the end the saw didn’t matter. Before attempting to slice the dolphin head, Cranford had sweet-talked a radiologist at the University of California at San Francisco into letting him run it through the hospital’s CT scanner. “The idea was that I would scan the head first and then use the slices to interpret the scan,” he says. As it turned out, he didn’t need the slices, because the CT scans revealed two football-shaped lobes of fat contained within two sets of “lips”—tiny structures located in the nasal passage just below the blowhole. Cranford had found the dolphin’s sound sources.

Ten years later, when Cranford came into possession of a sperm whale’s head, he knew scanning it would require more elaborate measures. First, he found a CT scanner big enough at the Navy’s China Lake facility, a weapons testing and development station 200 miles northeast of Los Angeles. “It’s kind of a time warp that I was going to scan a whale there,” Cranford says. “The Navy’s marine-mammal program began at China Lake, and now I come full circle 40 years later.” The scanner, one of only two in the world at the time, was designed to probe solid-fuel rocket motors for cracks, holes, and other flaws.

Next Cranford had to find a way to keep the 600-pound head cold for the several days it would take to scan. He also had to hold the head steady, using materials that would not interfere with the X rays, were light enough to maneuver with muscle power and a forklift, and wouldn’t cost him and his wife their life’s savings.

His solution was propping the head inside a five-foot length of cardboard tube—the kind ordinarily used to cast concrete pillars for freeway overpasses. Cranford filled the space between the head and the tube with polyurethane foam. Within an hour it had hardened to a lightweight sarcophagus that both held the head in place and insulated it. Then Cranford loaded the whole contraption into a rented truck and drove all night from Santa Cruz to the desert.

An hour out of China Lake, huge raindrops pelted Cranford’s windshield, and the sky was split by lightning. “The storm zapped the computers that control the CT scanner, for only the second time in seven years,” he says. Cranford had to temporarily stash the head in the Navy’s freezer, which went down to –70 degrees Fahrenheit, cold enough to freeze even the fat and blubber. “By the time we were ready to scan, the head was solid,” he says. The giant CT scanner whirred and clicked eight hours a day for four days, building a picture of the inside of the little whale’s head, slice by slice. When Cranford put it all together, he had a three-dimensional image of one of the weirdest noses in the animal kingdom.

Photograph by Reuben Cox

Ted Cranford examines the skull and lower jaw of a beaked whale. Members of this family have recently been found stranded on beaches after seismic surveys and Navy sonar tests. Cranford is trying to figure out why.

On a late afternoon in October, Cranford slipped a CD into one of the three computers at his house in Serra Mesa, a suburb of San Diego. A colorized image appeared on-screen and slowly began to rotate. From the outside, a sperm whale head looks like a piece of gray clay that has been rolled into a short, fat sausage and then pinched to a slim ridge along its length on the bottom side. The animal’s lower jaw, which hangs under the ridge like an evolutionary afterthought, is even narrower—a flimsy structure only about three feet across at its widest point on a fully grown whale and studded with four-inch teeth. “Ken Norris used to say that a sperm whale’s head looks like it was designed by committee,” Cranford said.

But it’s the inside of the head that is truly bizarre. The blowhole, which lies at the front of the head slightly to the left of center, connects to a widened pocket at the front of the spermaceti organ. From this pocket, the left nasal passage loops around the left side of the spermaceti organ and goes directly to the lungs. The right passage begins at the same pocket and runs back between a pair of “lips” known as the museau de singe, French for “monkey muzzle.”

These lips are so tightly compressed—even in a dead whale—that if you thrust your hand through them they would cut off the circulation at your wrist. The right nasal passage continues from the museau to create a layer of air that stretches underneath the spermaceti organ and joins with a sac that covers the face of the skull before regaining its tubular shape and heading for the lungs. Beneath this convoluted arrangement lie lens-shaped chunks of fat, which whalers called junk because they are more difficult to retrieve than the contents of the spermaceti organ.

“If you think about it, this whole structure is really part of the animal’s nose,” Cranford said. He pointed to the parts of the nasal passage that form pockets around the front, bottom, and back of the spermaceti organ. “Those air surfaces are perfect sound mirrors,” Cranford said. “Ken Norris and some colleagues figured out that sperm whales might be making their clicks in the museau. I want them to be called phonic lips, even if it does anger the French. Anyway, the click travels backward from the lips through the spermaceti, which has the same sound-conduction properties as water. The sound bounces off the air sac at the back and then comes out through the junk.” With an index finger he traced the path of the sound from the back of the spermaceti organ, down through the chunks of fat, and out through the front of the animal’s nose. By the time the sound emerges, he said, it has been focused down to an intense beam no thicker than a telephone pole.

“Now, you have to ask yourself, why would they want to make these incredibly loud, focused sounds?” Cranford said. “Especially when the structure for making them, this spermaceti organ, is full of wax that is actually toxic to the animal and has to be sequestered in the cask and is so big it makes it pretty hard for the animal to maneuver. A sperm whale has this puny lower jaw, but it eats a huge variety of prey, from little bitty lantern fish about the size of a pocketknife to giant squid as long as a school bus. It simply can’t pay to chase down an individual jet-propelled squid or little lantern fish.”

Ken Norris thought that the whales use sound to stun their prey, an idea that would have sounded preposterous had several other outlandish theories of Norris’s not been proved right. Norris was one of the first to demonstrate that dolphins could echolocate and that they hear through their jaws. The first support for his big bang theory emerged in 1983, when Norris and Danish researcher Bertel MØhl performed a quick and dirty demonstration of the principle by setting off blasting caps in a pool of squid. A later experiment in MØhl’s lab more closely simulated the whale’s clicks and managed to stun 10 percent of the fish in a pool. A decade later, Cranford’s CT scan provided more evidence. The geometry inside the animal’s nose and the density of the various tissues make a perfect path for a very loud, focused sound.

Whale of a Noise

A sperm whale’s click is by far the loudest sound produced by any organism on the planet. The complex amplification system inside a whale’s head would produce nearly twice the decibels of a trumpeting elephant if both sounds were heard in the open air. But the acoustic properties of water magnify a whale click by another 60 decibels—potentially enough to stun vast quantities of fish and squid.

Cranford thinks evolution endowed sperm whales with a gigantic nose for another reason: sex. Big male sperm whales can advertise their size to females—and rivals—through the acoustic properties of their clicks. “When a sperm whale makes a click, some of the sound goes out the junk, but some of it bounces back and forth inside the spermaceti organ, going boing, boing, boing,” he said. With each reverberation, a slightly fainter miniclick is projected outward through the junk. The time between each of these miniclicks is determined by the length of the spermaceti organ: The longer the organ, the longer the interval between reverberations.

“It’s the acoustic equivalent of a peacock’s tail,” Cranford said. “Growing a big spermaceti organ costs a male a lot, metabolically. It takes a lot of energy to push that nose through the water. And there’s no way a smaller whale can cheat and produce clicks that have the acoustic properties of a bigger animal.” Cranford has one final piece of evidence for his theory: The spermaceti organ in males continues to grow, even after they reach maturity. In a female whale, or a young male, the spermaceti accounts for less than a quarter of the animal’s total length. It can take up as much as a third of the length of a big, mature male. “When it comes to sperm whale sex,” Cranford said, “size matters.”

Three years ago, the Office of Naval Research awarded Cranford a grant to build a low-tech dolphin noisemaker. Cranford, not surprisingly, thought this made perfect sense. “Dolphins and sperm whales make these sounds with the tissue in their noses, and it’s all in a streamlined package,” he says. “They did their research over several million years of evolution. They could save us a lot of development time.”

His team’s first step was to create a computer model of dolphin sound production. Next they crafted an actual device, made with a springy rubber that cures at room temperature and special material like that of an air bag. The rubber pieces approximate the parts of a dolphin’s noise-making anatomy. Compressed air passes through the parts and makes them vibrate, just like the air through the pursed phonic lips in a dolphin’s nose.

Unfortunately, the Office of Naval Research’s budget was recently slashed, and Cranford’s project was one of those that landed on the cutting-room floor. But he isn’t letting that stop him; there’s still too much to learn about how the animals produce their sound. “We aren’t getting perfect dolphin clicks yet,” he says, “but we’re too close to quit.”

Next Page
1 of 5
Comment on this article
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

ADVERTISEMENT
ADVERTISEMENT
Collapse bottom bar
DSCOctCover
+

Log in to your account

X
Email address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it emailed to you.

Not registered yet?

Register now for FREE. It takes only a few seconds to complete. Register now »