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.