A young Western Australian man who stood on top of a whale carcass being devoured by great white sharks said it was a "stupid act" and he would not do it again.

Harrison Williams, 26, was filmed leaping into the water from a friend's boat and paddling a short distance to the dead whale before standing on top of the huge mammal on Saturday.

The Quinns Rock resident said he risked his life because one of his mates said "it would be pretty funny to surf the whale".

Mr Williams said the sharks in the water were "busy chomping on the whale" but once he climbed onto the blubbery corpse he immediately realised that it was a bad idea.

"Definitely it was a stupid act, didn't mean to disrespect anyone," he said.

"Mum thinks I’m an idiot, dad's not too proud either."