More than 50 pilot whales died after stranding themselves on a beach in Western Australia, but authorities said Wednesday they were "optimistic" that the other 45 whales in the pod could survive.

The pod of almost 100 long-finned pilot whales was spotted in shallow water off Cheynes Beach, about 400 kilometres (250 miles) southeast of Perth on Tuesday.

Fifty-one of them died overnight, despite the efforts of volunteers and staff from the state's Parks and Wildlife Service.

Late on Wednesday afternoon, incident controller Peter Hartley said the surviving whales were being monitored and, once they have been assessed as being strong enough, they would be released.

Volunteers in kayaks will help to herd them past the rocky part of the coast and out into deeper water, he added.

"We're optimistic -- we've got to be optimistic in this game," he said.

"It's highly stressful for all the people here -- volunteers and staff -- and you've got to have something to hold onto."

A spokesperson said the Parks and Wildlife Service had been "overwhelmed with hundreds of offers of help" but that it had enough volunteers and the public should "stay away" from the beach "for safety reasons".

"The priority focus of the Incident Management Team is to ensure the safety of staff and volunteers and the welfare of the whales," they said.

"The response zone has a range of hazards, including large, distressed and potentially sick whales, sharks, waves, heavy machinery and vessels."

Mass strandings of pilot whales are not uncommon in Australia and New Zealand.

Last October, around 500 pilot whales died when they beached on the remote Chatham Islands in New Zealand.

Scientists do not fully understand why mass strandings occur, but pilot whales -- which can grow to more than six metres (20 feet) long -- are highly sociable, so they may follow pod-mates who stray into danger.

Bec Wellard, a marine mammal scientist at Project Orca, said the reasons for whale strandings were still not known.

"We still don't know why -- if we did, we could perhaps do more to prevent it," she told AFP.

"But with pilot whales, they frequently strand en masse -- an individual might be ill or in trouble and the rest of the pod follows them -- that can lead them to strand."

She said that, because of the pilot whales' "strong family bonds", it was important to try to re-float them together.

But she added that, if the surviving whales' health is compromised, an assessment needs to be made as to whether efforts to refloat them "could just be prolonging their suffering". 

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