There were dramatic scenes in the ocean off Rottnest on Saturday when a man jumped off his boat and clambered onto the carcass of a humpback whale with at least five sharks nearby.
Tony Capelutti, from the Department of Fisheries Shark Response Unit, said there were a number of shark sightings and warnings throughout the day.
"Around lunchtime one of the reports stated that four tiger sharks and a white shark were feeding on the carcass of a humpback whale four nautical miles east of Rottnest," he said.
A number of people in boats were in the vicinity watching the sharks feed when suddenly a man jumped out of his boat into the water and swam over the to carcass and climbed onto it.
"We are assuming that when he did that the sharks were still in the vicinity," Mr Capelutti said.
The man sat on the carcass for a short time before men in another boat went over to him and took him off the carcass and delivered him back to his own boat.
"I don't know why he did that but if it was for some kind of adrenaline rush it was very unwise," Mr Capelutti said..
"He has not committed any offence as far as the Fisheries Act is concerned but it is a risky situation and risky behaviour."
The incident was filmed by a TV crew in the 7 News helicopter.
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