A 20-metre whale carcass that had washed up on a reef off Rottnest Island's main ferry jetty has been towed out to sea.
Several large sharks had been seen feeding on the whale, after it was spotted about 100 metres offshore from the holiday destination near the Thomson Bay ferry jetty on Tuesday morning.
Dozens of people gathered on the jetty to watch as sharks could be seen rising out of the water and thrashing about as they tore flesh from the huge animal.
Graeme Meinema, the shark response manager for the Department of Primary Industries and Regional Development, said the carcass was very fresh so they were able to attach a tow line to it before taking it out to the back of the Rottnest trench.
"We just basically [ran] a loop around the bottom of the tail," Mr Meinema said.
He said the loop was attached to the vessel, which towed the carcass into the channel where it would be picked up by a patrol boat.
Popular beaches to re-open
Rangers were forced to close popular swimming spots at Thomson Bay, Pinky Beach, the Basin and Longreach Bay.
They will re-open on Wednesday.
It was not clear how the animal died, but Mr Meinema said it was either a pygmy blue whale or blue whale.
"Being spring, a lot of the animals are coming down from the northern waters, with calves," he said.
"A lot of those animals will give birth and some of them don't survive.
"Essentially they pass away at sea and that's when they become an issue for us and a meal for the sharks."
Initial reports were that four tiger sharks were feeding on the carcass, but fisheries officers reported 15-17 tiger sharks, with no sightings of white sharks.
"We're very fortunate the carcass was very fresh, so the residue that remains in the water should be well and truly gone by tomorrow," he said.
But he urged people to remain careful.
Ferry services to Rottnest have not been interrupted but skippers have been asked to take care to avoid the whale.
