ST. PETERSBURG, Fla. (AP) _ A mangled human hand found in the belly of a shark can't be identified through fingerprints, according to authorities, who know of no recent shark attacks in the area.

Three University of South Florida graduate students doing research found the adult-sized, partially digested hand in one of their specimens.

A digital watch was still attached but not working.

St. Petersburg police speculate the hand had been in the 5-foot black-tip shark's stomach no more than a day when it was found Saturday, Sgt. Charles San Marco said. He said sharks digest their food rapidly.

There have been no recent reports of shark attacks, said Debbie Poulkrabek, police communications supervisor.

The hand has been taken to the Pinellas County Medical Examiner's office for study, but cannot be identified through fingerprints because it was partially decomposed, police said.

The students who found the hand in the freshly caught shark declined to talk about their discovery, but a St. Petersburg man fishing nearby with his sons saw it when they stopped their boat next to the researchers' to offer help.

''We thought maybe there was a snake or an eel in the boat the way the one fellow was jumping around,'' said John L. Irvin.

''It was in a plastic bag, and they showed it to us,'' said John M. Irvin, 26, of Miramar. ''It looked like a person's hand that had been mangled up pretty good.''

A shark researcher said black-tip sharks are common in waters off Florida. They are not known to be vicious and can swim great distances quickly, said Kristie Killam, a University of South Florida graduate student.

The shark was caught three miles southwest of Bay Vista Park off Pinellas Point in Tampa Bay.