ABC News' Darcy Bonfils reports:

Sharks are some of the most feared predators on the planet.

Last year, there were 53 attacks in the U.S. alone, and worldwide there were 80 unprovoked attacks, up from 78 the year before, according to the International Shark Attack File at the Florida Museum of Natural History.

This year, in the U.S. alone there have already been 18 - with two occurring last week in Hawaii.

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Paul de Gelder, a highly trained diver, was in the waters off the coast of Garden Island, Australia, when a 10-foot bull shark shredded his arm and leg in 2009.

"I can see the lip pulled back, I could see the gums and I could see these teeth all across my leg and over my wrist," he told the Discovery Channel's "I Escaped Jaws." "I hit him once and that did nothing. … That's when the pain really kicked in. … All I could do is flop around in the water while this monster was shaking me."

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Some experts say humans could be to blame for shark attacks because they have polluted the waters, overfished and taken away the food that sharks normally eat.

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To test the theory, a team of experts from Discovery Channel's "Shark Week" series show "Sharkpocalypse" took to the waters of the Bahamas with ABC News in search of the frightening creatures.

During an excursion into the Atlantic Ocean near Nassau, the researchers' boat was immediately surrounded by Caribbean reef sharks. Though normally shy around divers, the sharks have been known to get aggressive in the presence of food. As of 2008, there had been 27 reported Caribbean reef shark attacks on humans.

Another time, the "Sharkpocalypse" team tested the palate of a tiger shark with a buffet that included fish, pork, beef links, turkey and even a watermelon. A 14-foot tiger shark went straight for the barracuda, a fish typical of its diet. Next it went for the pig and then the turkey.

The day's lesson: Disrupt the shark's environment - take away their fish - and they'll feed on the next best thing. In another experiment, the researchers baited the sharks into a feeding frenzy and then sprayed a repellent that made them scatter in seconds.

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Gelder told "I Escaped Jaws" that every time he got in the water as a diver he saw sharks.

"Instantly, every single time," he said. "I was petrified."

His attack lasted just eight seconds but he lost a hand and leg that day.

"There was nothing [to be] salvaged. I just focused on getting to that safety boat. It was all I wanted to do," he told "I Escaped Jaws." "Someone was smiling on me that day."