The Jadran's captain, Yitzhak Hermon, said that he stopped the boat less than a mile off the Sinai shore to let the passengers watch a group of dolphins cavorting nearby.

"Three people went into the water to swim with them," Hermon said. "When the two others came back, Richardson decided to stay in the water a bit.

"Suddenly we heard him scream. We thought it was a joke at first. Dolphins never attack humans. Then we saw him leap in the air and blood stained the water all around him. We understood that he was being attacked by sharks."

One of the crew sped to Richardson's aid in a rubber boat. When he reached him, he saw the injured man being circled by three dolphins, who leaped into the air, smacked the water with their tails and flippers, and placed themselves between Richardson and the sharks.

Oz Goffman, director of the Israel Marine Mammal Research and Assistance Center in Haifa, said that such behavior is known in cases where dolphins are protecting their young from sharks.

However, he said, he knew of no previous instance of dolphins defending humans against sharks. He said that a dolphin could kill a shark by ramming it.