Large-Shark Hunting Habits Exposed by Crittercam

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In some places, tiger sharks may be the only species to eat large prey like turtles, dugongs, and dolphins. Their teeth, which cut in both directions, are like razor blades, perfectly evolved for cutting through turtle shells and bone.

However, they may be considered somewhat lazy. "They are not a super-fast and maneuverable shark," Heithaus said. "They really do rely on surprise to catch things."

Since 1997, Heithaus has used the Crittercam to study tiger sharks in Shark Bay on the West Coast of Australia. The technology has helped the researchers establish the critical role that tiger sharks play there.

"Tiger sharks may influence where dugongs spend their time, and since dugongs are major grazers of sea grass, that could influence how the sea grass beds are structured, and because sea grass beds provide the foundation for whole ecosystems, that might affect where juvenile fish can be, which may in turn influence where turtles can be," Heithaus said. "You see how the effects go through the whole ecosystem."

The Crittercams show the sharks spending most of their time on shallow sea grass beds, where they find most of their prey. Heithaus and his team have also been able to show that tiger sharks cause dolphins to abandon shallow sea grass beds, their best feeding grounds. The dolphins will rather not eat much, but be safe, than risk becoming shark food.

"The Crittercam also showed us how the tiger sharks kind of bounce through the water," he said. "They swim along the surface, drop to the bottom, and then swim up to the surface again. This is probably a strategy to surprise animals that are close to the surface."

Body Slam

Now, Heithaus and his team, including his wife Linda, a marine biologist, are using Crittercam to study two kinds of sharks in Florida waters: bull sharks and hammerheads.

"We're taking our first tentative steps," Heithaus said. "We're still trying to figure out how to work with these sharks and what information we can get from the Crittercam. It's far too early to draw any conclusions, except to say that the technology works well on both those species."

The bull shark is relatively small. It may grow to be nine feet long. A pregnant female may hit 500 pounds (227 kilograms), small compared to a 2000-pound (910-kilogram) white shark. But they're one of the few species of sharks that will go after potential prey of the same size. Heithaus calls the bull shark "the pit bull of the sea."

"They're one of the top predators in the Florida waters," he said. "I've seen footage of them body-slam boats when they get annoyed."

The bull sharks are also special because they can survive in fresh waters. Some have swum 4,000 kilometers (2,500 miles) up the Amazon River in South America. One stray bull shark was even found in the Mississippi River all the way up to Illinois.

Meanwhile, the hammerhead sharks, with their bizarre head shaped like a hammer, have confounded scientists for years. Why on Earth would the shark have a head like that?

"It's probably evolved for a number of reasons," said Heithaus. "It will increase their maneuverability, and it also helps their sensory capabilities."

The hammerheads can use their heads to pin their prey to the bottom of the sea while they eat it. Their favorite foods are rays and other sharks.

But hammerhead sharks are very susceptible to overfishing. Populations in the Atlantic Ocean may have dropped as much as 90 percent in some places.

"They're one of the hardest species of shark I've worked with, because they're so fragile," said Heithaus. "In general, we should be concerned about the future of our oceans. Some hammerheads are among the shark species we should be most worried about."

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