An 81-year-old boater was in critical condition yesterday after a stingray flopped onto his boat and stabbed him, leaving a foot-long barb in his chest, authorities said.

“It was a freak accident,” Lighthouse Point acting fire Chief David Donzella said. “It’s very odd that the thing jumped out of the water and stung him. We still can’t believe it.”

Fatal stingray attacks like the one that killed “Crocodile Hunter” Steve Irwin last month are rare, marine experts say. Rays reflexively deploy a sharp spine in their tails when frightened, but the venom coating the barb usually causes just a painful sting for humans.

James Bertakis of Lighthouse Point was on the water with his granddaughter and a friend Wednesday when the stingray flopped onto the boat and stung Mr. Bertakis. The women steered the boat to shore and called 911.

Surgeons were able to remove some of the barb, and Mr. Bertakis, who also suffered a collapsed lung, underwent surgery late Wednesday and early yesterday, the Miami Herald reported on its Web site.

A professor of marine biology and fisheries at the University of Miami, Ellen Pikitch, who has been studying stingrays for decades, said they are generally docile.

“Something like this is really, really extraordinarily rare,” she said. “Even when they are under duress, they don’t usually attack.”