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Shark Attacks Shark in Dramatic Video

A deadly encounter between a tiger shark and a hammerhead was recorded in the Gulf of Mexico.

Watch: An epic battle wages off the coast of Louisiana, between a tiger shark and a hammerhead.

A college student on a fishing trip in the Gulf of Mexico caught dramatic footage of a big tiger shark repeatedly attacking a hammerhead on a fishing line.

Shot on July 17, the video shows a hammerhead shark struggling on the line. Then, a tiger shark cruises in and bites the hammerhead.

The attack went on for several minutes, until the tiger shark "grabbed the hammerhead around its head, broke the line, and then dragged him straight down," says Ryan Willsea, who made the video with his brother Aaron, and whose line caught the hammerhead.

"It was an incredible thing to see and catch on film," he says.

Willsea spent three days fishing in the Gulf during a vacation to the area, using baitfish and hoping to catch tuna. He and his fellow anglers tried their luck about 30 to 40 miles (about 50 to 60 kilometers) off of Venice, Louisiana.

"When we got the hit, we first thought it was a another big tuna," says Willsea, who had caught two other tuna earlier that day. "But then we saw it was a hammerhead."

The crew "played" the big fish for five to ten minutes before the tiger shark appeared, first as a dark shadow in the water, Willsea says. (See where The Shallows got sharks wrong.)

Sharks Being Sharks

That big fish was undoubtedly a tiger shark (Galeocerdo cuvier), says George Burgess, who leads the shark research program at the Florida Museum of Natural History.

Tiger sharks, which live in warm waters around the world, are "expert at taking advantage of situations when a potential prey item is compromised," says Burgess. "And nothing makes an animal more compromised than having a hook in its mouth and being pulled to a boat."

Tiger sharks routinely go for other sharks, especially when they are wounded. In fact, the reputation of sharks as "the garbage eaters of the sea, which will go after everything," is largely based on the species, Burgess says. Large and powerful, the tiger shark is one of a handful of species that most commonly bites people.

Watch: Tiger sharks, swimming with an awesome predator.

The hammerhead was most likely a scalloped hammerhead (Sphyrma lewini), which is common in the Gulf, says Burgess. Tiger sharks usually leave them alone when they are healthy but hunt them opportunistically when they are injured. (See how shark species size up.)

Willsea estimates the hammerhead was seven to eight feet (a little over two meters) long, and the tiger shark even bigger, likely weighing over 1,000 pounds (450 kilograms). There's not enough reference to say that with confidence, however, Burgess warns. Tiger sharks are known to reach a length of 18 feet (5 and a half meters).

Both sharks were likely attracted to the area by the oil platform that can be seen in the distance in the video. Such structures function like artificial reefs, attracting corals, barnacles, and other stationary organisms on their surfaces. Those animals, in turn, attract small fish. Larger fish, like tuna and sharks, then show up to eat the small fish.

What's more, hooking a fish can lead to a lot of movement and splashing.

"All that activity is highly provocative to sharks," Burgess says. "No doubt the tiger shark was attracted to that."

Burgess adds "it's a little ironic to see one shark eating another, but it's not unusual."

Perhaps even more ironic, hammerheads often steal other fish from the lines of fishermen when they get a chance. (Learn about the mysterious shark attacks on sea otters.)

Watch: World's Deadliest: Hammerheads

Sharks in Decline

Sharks have been declining around the world, thanks to overfishing for their fins and accidental entrapment as "bycatch" in gear meant to snare other species, such as shrimp or tuna. Hammerheads are particularly vulnerable because they tend to asphyxiate quickly if they get trapped in gear. They need to keep moving steadily to draw enough water over their gills to breathe.

Despite the threats against them, sharks have been recovering slowly in U.S. waters—where they enjoy rigorous protections—and in sanctuaries around the world. In Louisiana waters, it is legal to catch hammerheads throughout the year except from April 1 to June 30. Recreational fishing boats are permitted to take one shark per trip. (See a bobcat drag a shark out of the water.)

But seeing the two sharks battle in the water "was a once-in-a-lifetime experience," Willsea says.

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