Mark Watkins, who was cruising with his father 50 km away from the port city of Bunbury, posted a picture of the weird find on Facebook.
Taking a closer look, the Australians found out that the strange huge orb was a whale carcass. The bloated corpse was due to gas being emitted as the animal's internal organs and stomach contents decomposed.
"We realized it was a dead whale when we felt the smell," Mark said.
When the fishermen were leaving, sharks bit through the whale's thick skin, and the gas was released outside.
"Decomposing whale is one of the worst smells in the world," marine biologist Andrew David Thaler told National Geographic. If sharks do not manage to bite through a dead whale's skin, its bloated body can float in the sea for a very long time until it sinks. The breakdown of a dead whale can take up to 30 years, the specialist added.
