Al Brennaka shows where a shark bit his arm during an interview in Pompano Beach, Fla. Brennaka lost half his arm at age 19 after being attacked by a shark while surfing off Daytona Beach. Despite his injury, Brennaka is one of more than a dozen attack survivors who have become shark advocates, trying to educate the public about sharks' declining populations and their importance to ocean ecosystems.

Kent Bonde shows where he was attacked by a shark during an interview in Key Biscayne, Fla. A shark ripped off his calf muscle while he was spearfishing in the Bahamas in 2001. Bonde is now a shark advocate.

Kent Bonde, left, and Mike Beach, pictured here in Key Biscayne, Fla., are survivors of shark attacks, and are now shark advocates.

Patrick Thornton shows some of the scars from a shark attack in late June on the North Carolina coast. Thornton cautions other swimmers that he didn’t see the shark’s fin until after it first bit him.

Patrick Thornton shows more scars from the wounds he received in a shark attack in lJune on the North Carolina.