Study: Sharks Bite With Upper Jaws

Here's a question you're not likely to ask when you feel that sudden pain in your leg while spending a day in the surf:

How, exactly, does a shark manipulate its jaw so that it can easily rip out a hunk of flesh?

But Cheryl Wilga wanted to know, which is a bit odd since the Aleut Indian grew up in Alaska where concerns over fish are of a more practical nature, like how to catch the elusive king salmon.

Wilga became obsessed with sharks after moving from Kodiak, Alaska, to the University of South Florida in Tampa, where pioneering research was underway to try to decipher just how these mythical creatures function in the water.

Humans More Likely to Nip

It's a big issue in Florida, which leads the world each year in shark attacks on humans. According to the International Shark Attack File maintained by the Florida Museum of Natural History, there were 34 unprovoked shark attacks in Florida's waters last year, contributing to a record number of 79 such attacks worldwide.

Ten of the attacks resulted in fatalities, one of which was in Florida.

But as shark lovers will quickly point out, the chances of getting attacked by a shark are really quite low. You're a thousand times more likely to get bitten by a dog than a shark, according to George H. Burgess, who is director of the International Shark Attack File, a clearing house for all things related to sharks.

In fact, you're 100 times more likely to get bitten by another human than a shark, Burgess says, and much more likely to be killed by lightning.

None of that is likely to ease our fears of being gobbled down by a wild shark, which undoubtedly adds to our fascination with these creatures of the deep.

"Anytime you mention a shark it draws a lot of attention," says Wilga, who recently conducted postdoctoral research on sharks at Harvard University before joining the biology faculty of the University of Rhode Island. She says that's largely because of the fear of shark attacks, but she insists most people think the study of sharks is "cool."

But it's not easy.

"Sharks are a pain in the neck to work with," she says. "They have to have a lot of tender loving care."

Many species cannot survive in captivity, even for a little while, and those that do require a big tank, and lots of clean water, and there's the little problem of "you always know they can potentially remove parts of your body," Wilga says.

Her research has led to a better understanding of two key areas — how the shark's jaw functions, and how the fish maintains its buoyancy in the water. Both areas have yielded some surprises, but it took a marriage of physics, engineering and biology to find them.

Because of the difficulty of keeping sharks in the lab, Wilga's research has been focused on smaller sharks that pose no real threat to humans, including the spiny dogfish, sandbar and bamboo sharks. It is thought that many characteristics of these species are shared by all sharks.

Upper Jaw Clamp

At the University of South Florida, Wilga worked with Philip Motta, a biologist who moved shark research beyond the realm of studying cadavers and trying to figure out how they function.

It was while working with Motta that she made her first breakthrough. Many experts had through that sharks bit their prey by maneuvering their lower jaw, like humans, but that turned out not to be the case.

Bamboo sharks were photographed in the lab with a high-speed camera that produces 500 images every second. Tiny electrodes, about the size of a human hair, were inserted into the muscles of the shark's jaw to record every movement of the muscle. The two sets of data were later combined to see which muscles moved while the shark was gobbling down its lunch.

The evidence revealed that when a shark eats, its upper jaw extends out from the head, then the fish bites, then the upper jaw retracts under the head. Think of it as a conveyor belt pulling flesh into the mouth.

Once that question had been answered, Wilga turned to another area that is poorly understood: How the shark, which is not naturally buoyant, manages to swim.

The old theory was that "sharks swim like airplanes fly," using their pectoral fins to provide lift, just as an airplane uses its wings for the same purpose.

That, however, turns out to be dead wrong.

It is the shark's body, not its fins, that provide the lift, the research shows, but how Wilga found that out is as interesting as the conclusion itself.

Even if you study it in a glass tank, you can't really see how the fish gets its lift, because water is clear and such things as stream lines and vortexes are invisible.

So Wilga borrowed from the field of engineering.

"Its called digital particle image velocimetry," she says, and it's a system that allows her to determine just what the shark is doing to maintain its buoyancy by revealing the effect the fish is having on the water. In other words, she can actually see the way the water moves as the fish swims through it.

"Its really cool," she says.

Swimming in Beaded Water

Tiny glass beads, so small they can pass through the shark's gills without bothering the fish, were dumped into the tank. Each bead is coated with silver.

Then, a low powered laser that puts out a flat beam like a sheet of paper shines up through the tank. As the fish swims, the beads flow through the water, depending on how the fish maneuvers, and the beads reflect the movement of the water.

That data is recorded on a high-speed video camera, providing a complete record of the shark-water interaction. What it revealed, she says, is that the shark uses its tail fins to push it through the water, but it uses the shape of its body — not its fins — to provide the lift.

This breakthrough in shark aerodynamics is so new it's not even in the textbooks yet. None of this data is likely to ease the fear of sharks. But if you get hit, at least now you'll have a better idea of what's going on.

Enjoy the summer.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.