How to identify a shark on a biting rampage.

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Dec. 10 2010 7:05 PM

I'd Know Those Teeth Marks Anywhere

How to identify a shark on a biting rampage.

Shark. Click image to expand.
"Does this look like the shark that bit you?"

Shark attacks in the Egyptian resort town Sharm el-Sheikh have left four swimmers injured and one dead in the past week. American scientists say they have positively identified two shark-suspects so far. But how do marine biologists figure out whodunit?

Julia  Felsenthal Julia Felsenthal

Julia Felsenthal is an assistant at Slate.

In this case, with photographic evidence. Experts think they've determined that the same oceanic white tip shark was responsible for two of the attacks because photographs taken prior to and during both attacks reveal an animal with matching bodily markings. There's no way to track the shark down, but scientists do have a clear idea of what it looks like and could presumably identify it if they happened upon it. As for two of the other three attacks, the experts guess they might have been perpetrated by the same mako shark because the attacks occurred within five minutes and 10 yards of each other, and the bite patterns on the victims were similar. They don't actually know which particular mako shark is responsible.

The case of the oceanic white tip in Egypt  is highly unusual: Generally experts are left grasping at straws and can do no more than figure out the species of the attacker and not the appearance of the individual shark. Since photographic evidence is rare, experts fall back on eyewitness reports (detailing the shark's size, color, and markings)—which are notoriously unreliable. People who end up in close proximity to a shark tend to greatly overestimate the animal's size. To make matters worse, 85 percent of people attacked by sharks never see the shark that bit them.

Examination of the bite wound itself can be more useful, because shark teeth differ widely from species to species. From the diameter of the bite, scientists may be able to suss out the shark's size. The way that the victim's flesh is torn surrounding the points of incision can indicate the motion the shark used while biting; some sharks, particularly smaller ones, have the flexibility to vigorously shake their heads while attacking. Examining the bite marks, as well as the places where shark teeth scraped on human bone, can reveal whether the teeth had smooth or serrated edges.

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Of course, if scientists can get their hands on part of the actual tooth, that's even more revealing—a sort of bingo moment in establishing what species of shark inflicted the bite. And in fact, it's not uncommon for a shark's teeth to break off mid-bite; sharks are cartilaginous creatures, and their teeth aren't rooted in bone like humans' are. (A shark jaw is like a conveyor belt of teeth; when the tooth in front breaks off in a seal or a surfboard or a human, there's another tooth right behind it to take its place.)

If scientists manage to identify the species of shark responsible for the attack, there is actually very little they can do with that information, besides to enter it into a database such as the International Shark Attack File, which tracks shark-attack trends for scientific purposes. Knowing what the shark looks like—as in Egypt—hardly changes the situation. Sharks are transient creatures, and they're unlikely to stick around the same beach for long. 

Though historically the response to shark attacks has been martial—fishermen go out and try to capture or kill sharks in the area, in hopes of preventing another attack—scientists nowadays consider that sort of witch hunt a fool's errand that only promotes a false sense of safety. In most cases, how could fishermen possibly know that they've caught the right shark or that the shark they've caught is more likely to attack than any other shark? Scientists suggest focusing not on shark behavior, which we don't understand very well, but on human behavior, which we do. A more enlightened response is to close the beaches for a few days following the attack and to educate beachgoers on ocean safety. Besides, the myth of the rogue, man-eating shark has gone out of fashion.  Even Peter Benchley, the author of the book Jaws, admitted late in life that he had done a disservice to sharks in portraying them as monstrous villains.

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Explainer thanks Chris Lowe of the California State University Long Beach Shark Lab, George Burgess, curator of the International Shark Attack File, and John McKosker of the California Academy of Sciences.

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