In the letter, he wrote that he had been sitting on his surfboard board when he felt a hit on his left side.
"It was like being hit by a truck,” he wrote. "It bit me around my back, buttock and elbow, and took a chunk out of my board.”
He "got a glimpse of the shark as it let go and disappeared," after which he paddled back to the beach still holding his board.
The beach has now been closed, and members of the public have been asked to avoid the area.