A rorqual - a species of baleen whale - refloated off the western French coast on Tuesday has returned to shallow water and is once again in difficulty.This as a pod of about 230 pilot whales was found stranded on the rugged west coast of Tasmania on Wednesday.

Australian wildlife officials say only half of the stranded mammals appeared to be alive.

Aerial images show dozens of whales strewn at the waterline on a long beach near Macquarie Harbour.

Locals covered survivors with blankets and doused them with buckets of water in an effort to keep them alive. Other whales nearby tried to struggle back towards deeper water, and yet other lay dead.

"It appears about half of the animals are alive," said a statement from Tasmania's Department of Natural Resources and Environment.

Officials said marine conservation experts and staff with whale rescue gear were en route to the scene.

They will try to refloat animals strong enough to survive and also tow the carcasses out to sea, to avoid attracting sharks to the area.

Two years ago, Macquarie Harbour was the scene of the country's largest-ever mass stranding, involving almost 500 pilot whales.

More than 300 pilot whales died during that stranding, despite the efforts of dozens of volunteers who toiled for days in Tasmania's freezing waters to free them.

Strandings remain a tragic mystery

The cause of mass strandings is still not fully understood.

Scientists have suggested they could be caused by groups of animals going off track after feeding too close to shore.

Pilot whales - which can grow to more than six metres long - - are highly sociable and can follow podmates who stray into danger.

That sometimes occurs when old, sick or injured animals swim ashore and other pod members follow, trying to respond to the trapped whale's distress signals.

Other researchers believe gently sloping beaches like those found in Tasmania confuse the whales' sonar making them think they are in open waters.

The news of the stranding came just hours after a dozen young male sperm whales were reported dead in a separate incident on King Island -- between Tasmania and the Australian mainland.

The young whales' deaths may be a case of "misadventure", wildlife biologist Kris Carlyon from the state government conservation agency told the local Mercury newspaper.

"The most common reason for stranding events is misadventure, they might have been foraging close to shore, there might have been food and possibly they were caught on a low tide," Carlyon said.

"That's the theory at the moment."

Saved whale back in danger in Brittany

An individual from another whale species, the rorqual, was refloated by volunteers on Tuesday in Finisterre in western France.

According to the ONG Sea Shepherd, that creature is once again in difficulty, having returned to shallow water where it risks running aground near the town of Douarnenez.

Earlier this year, a beluga whale died after becoming trapped in the River Seine, which runs through Paris to the Atlantic coast.

Originally published on RFI