This is a rush transcript from "On the Record ," April 25, 2008. This copy may not be in its final form and may be updated.

GRETA VAN SUSTEREN, HOST: Joining us live is Dr. Pete Klimley. He is a professor of marine biology at UC Davis and a shark behaviorist. Pete, you know, we hear these things, and you know, they're so tragic. And none of us know much about sharks. Is it unusual that a shark would attack a human?

PETER KLIMLEY, SHARK BEHAVIORIST: Well, it is -- you know, sharks generally feed on seals and sea lions. And it's generally when a person is in the wrong place, near a seal colony, is when they're attacked. But then again, these sharks, they migrate between seal colonies. And if you happen to be in the wrong place at the wrong time, and this is a female that's swimming south to give birth -- they give birth at the islands off, like, San Clemente. And it sees you and it's hungry. And what they generally see -- they don't see anything really well at the surface. It's just a kind of a moving object. They dash up and they seize it.

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VAN SUSTEREN: When you say that feeding -- so it's not -- it wouldn't be aggressive but for the fact that it's hungry? In other words, a shark wouldn't just merely attack you unless it wanted to feed?

KLIMLEY: Well, there are also other attacks that are defensive. Just like a cat bares its teeth and arches its back and erects its fur to act really large, if you approach a shark really close and very quickly, it will show this display, where it pulls its fins down and moves its jaws out and it shows you what it can inflict an injury with.

But with only three sharks -- the bull shark, the tiger shark and the white shark -- it's -- it has to do with feeding. Now, with the white shark, I've always believed that the white sharks, they select their prey based on fat. And humans really are not fatty, but seals are. Seals have half their body weight in fat, and that has twice the energy of muscle. So in a sense, they're little power bars. They're almost like a -- not like a powerball that a -- powerball that a hiker might use, but a large Milky Way or Snickers that a soldier might use going into battle. These are really - - seals are very nutritious.

Now, this swimmer, you know, was very lean, at the surface, in a group of people. The shark -- the white sharks are really misnamed by being called white sharks, they're dark because they match the sea floor and can't be seen -- dashed to the surface, grabbed him and probably realized that it wasn't a seal -- it wasn't soft like a seal would be -- and spit him out because a big shark like that could take a person under and take a prey under much bigger than that person and consume it.

VAN SUSTEREN: You mentioned tiger, bull and white shark. Which is the -- I mean, which is the biggest of those three?

KLIMLEY: Well, the white shark is the largest of all of them. The tiger shark gets a little smaller. White sharks, you know, have been known to get almost 20 feet. One time I was working out of a zodiac, and I moved from the zodiac over to another boat, and a shark came up and bit the zodiac and sank it. And we -- you can take the bite width and you can use an equation to relate length of the bite width and tell just how large that shark was. And it was a large shark. It was close to 20 feet in length. And this could be done with the wounds of a person, too.

VAN SUSTEREN: Well, it's a terrible tragedy, certainly, for this man and his family. Pete, thank you.

KLIMLEY: Thank you.

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