FORT PIERCE — Kiteboarder Stephen Schafer died from a loss of blood following an attack by a single, 8- to 9-foot shark this week off Hutchinson Island near Stuart, according to an autopsy and a shark expert who examined the body.

Dr. Linda O’Neil, associate medical examiner for the District 19 Medical Examiner’s Office at Indian River State College in Fort Pierce, said the autopsy she conducted Thursday afternoon revealed the cause of death was “exsanguination, or loss of blood, due to shark bites.”

George Burgess, the director of the Florida Program for Shark Research at the University of Florida who examined the bites Thursday night, said they were made by a species of requiem shark, a large family of mostly tropical sharks.

The family does not include great white sharks, Burgess said.

“Two of the likely possibilities are a bull shark or a tiger shark,” Burgess said, adding that a third possibility is a dusky shark.

Burgess said a close examination of bite mark photographs may determine which species is responsible: Tiger sharks have identical serrated teeth in both upper and lower jaws; bull and dusky sharks have serrated teeth above and puncturing teeth below.

Burgess said it will be 10 days or more before he might determine the species involved, and warned that the species is never determined in most cases.

Schafer, 38, of Stuart, was kiteboarding about a quarter mile off Stuart Beach when he was attacked.

O’Neil said Schafer suffered “two shark bites, one more serious than the other. The more serious was on the back of his right thigh. It was from 9 to 10 inches long and very deep. In fact, one of the teeth hit the bone.”

O’Neil said the femoral artery that runs through the thigh “gives off a lot of blood, and several of the branches off the femoral artery, all of them in the area of the bite, were severed.”

At the time of the autopsy, O’Neil said, “there wasn’t a lot of blood in his body. ... Stephen Schafer was a healthy young man, which means he had to lose a lot of blood to die, more than, say, an older or less healthy man.”

Schafer probably lost “more than 2,500 (cubic centimeters) of blood,” O’Neil said, which she compared to being “more than a 2-liter bottle of Coke.”

O’Neil said the second bite was “across the buttocks. The wound itself was really teeth marks, puncture bites. It didn’t tear any flesh away.”

Schafer also had a bite mark on his right hand that O’Neil said “appears to have occurred at the same time as the bite to the thigh. Apparently when the shark bit, (Schafer) put his hand down there to protect himself.”

Martin County lifeguard Daniel Lund reported seeing Schafer lying on his kiteboard late Wednesday afternoon and paddled out with a rescue board. Lund said Schafer told him he had been bitten by a shark.

Lund brought Schafer back to the beach, where rescue workers started CPR and took him to Martin Memorial Medical Center in Stuart. Schafer was pronounced dead at 4:41 p.m. Wednesday at the hospital.

O’Neil couldn’t say how much time passed between the attack and when Lund showed up to attempt to rescue Schafer.

“That would depend on whether (Schafer) put pressure on the wound to slow the bleeding,” she said, “and we just don’t know that.”

tyler.treadway@scripps.com

jim.kirley@scripps.com