A West Australian man has sheepishly confessed his mum and dad think he is an idiot for swimming out to a floating whale carcass and clambering aboard as dozens of sharks were eating it.

Harrison Williams, of Perth, got the idea after the dead humpback had been floating between Fremantle and Rottnest Island for several days. Video footage shows him leaping in the sea, swimming to the 12-metre carcass and climbing aboard – despite the presence of several tiger sharks and a Great White which were all in a feeding frenzy as they feasted on the corpse.

Mr Williams, an extreme sports enthusiast, has admitted to TV network Seven News he acted on the spur of the moment without really considering the consequences.

"At first I couldn't get a grip and I ended up using my chin to drag myself up," he said. "I was out on a boat with the boys and one of them said it would be pretty funny if I surfed a whale so I just did it. He [the shark] was too busy chomping on the whale so it wasn't too bad."

Williams admits his parents thought he was an idiot for swimming out to the dead whale. Facebook/ Harrison Williams

Asked if he'd do such a reckless act again Mr Harrison said: "I've done it, I don't need to do it again. It was definitely a stupid act, but I didn't mean any disrespect to anyone. Mum thinks I'm an idiot, and dad isn't too proud either."

Western Australia has one of the world's highest rates of shark attacks and on Twitter Mr Williams was the butt of some Mickey-taking, with suggestions he could receive a Darwin Award – nominated to people who do stupid or risky things which should remove them from the gene pool.

One tweet read: "Only in Australia would a guy be sitting on a carcass in the ocean whilst sharks are feeding on it…"

However, Williams had his defenders. Another tweet read: "If I came across a floating whale I'd probably have a sit on it too. There's a box to tick."

Sharks can smell a drop of blood from up to a quarter of a mile away and swimmers are advised not to even enter the water when there is blood around. Department of Fisheries regional manager Tony Cappelluti said Williams's actions were irresponsible.

"It is very risky to enter the water around that type of large food source because even if you can't see sharks it's highly likely the carcass is attracting them from a long way away," said Cappelluti. "Irrespective of some type of adrenaline rush or whatever you're trying to get out of performing that type of act, it's highly risky."