Andrew Eddy, 30, was on a private boat with his wife, Margot Dukes-Eddy and her family at the time of the shark attack Sunday morning at Sombrero Reef, according to the Monroe County Sheriff's Office.
Eddy, of Atlanta, had just slid into the water when a large shark latched onto his shoulder.
"Dukes saw the shark's dorsal fin and then blood filling the water. Dukes, without hesitation, dove into the water and pulled Eddy to the safety of the boat," Deputy Christopher Aguanno wrote in his report.
The Miami Herald reported that Dukes managed to avoid injury during the rescue, but deputies described Eddy's shark bite wound as severe. Medics were waiting for them when they reached the beach in Marathon. Eddy was then flown to Ryder Trauma Center at Miami's Jackson Memorial Hospital, where a spokeswoman said the family requested privacy.
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Several other snorkelers from other boats were already in the water when the attack happened, the deputy wrote. He said other boaters told deputies they had seen a bull shark in the area that morning, which they estimated to be as much as 9 feet (2.7 meters) long.
George Burgess, who retired as director of the University of Florida's International Shark Attack File, agreed that it was likely a bull shark that bit Eddy.
The file has recorded 17 unprovoked shark bites since 1882 in Monroe County. For comparison, Volusia County in northern Florida has had 312, earning the area the designation of "the shark bite capital of the world."
That's because the Keys lack the waves that make Volusia County's beaches popular with swimmers and surfers, Burgess said. In the Keys, people tend to spend their time in the water snorkeling, scuba diving and hanging around sandbars, activities that are less likely to attract sharks.