Hundreds of pilot whales have died in a mass stranding in southern Australia despite efforts to save them, with rescuers racing Wednesday to free a few dozen survivors.

Another 200 long-finned pilot whales were discovered Wednesday in Macquarie Harbour, on the rugged and sparsely populated west coast of Tasmania, taking to 470 the number that have become stuck this week.

About 270 pilot whales were found Monday, sparking a major effort to free the giant mammals from a sandbar only accessible by boat.

Parks and Wildlife Service manager Nic Deka said most of the second pod, which was discovered early Wednesday morning by an aerial surveillance crew, were believed to be dead.

"We have a boat that's arrived on site a short while ago, so they've assessed one group -- the smaller group which is in one bay -- and all of those whales are dead," he told AFP.

"They're currently going around to the second bay where the bigger group is."

The rescue crew of 60 conservationists, skilled volunteers and local fish farm workers are now concentrating their efforts on the survivors from the first pod, which are partially submerged.

"The best assessment that we've got from this morning is that somewhere between 50 and 70 whales are potentially still alive," Deka said.

"So they're the animals that we're focusing our efforts on."

Rescuers spent Tuesday wading in the cold shallows to free about 25 creatures, using boats fitted with special slings to guide them back to the open ocean.

"They're focused on the job -- it's demanding work, some of them are up to their chest in cold water so we're trying to rotate the crews," Deka said.

"Its very draining physically. It's also draining emotionally."

The discovery of another 200 whales makes the mass stranding the largest recorded in Tasmania, an island state off mainland Australia's south coast.

They were found between seven and 10 kilometres (four-six miles) from the first group, with the distance and tannin-stained waters meaning rescuers did not spot them sooner.

Officials have now expanded their search area to see if more whales are stuck nearby.

Some of the whales rescued Tuesday re-stranded overnight in line with predictions by whale behaviour experts, but Deka remained upbeat about the rescue mission as several more were freed Wednesday.

"The good news is the majority of whales that were rescued are still out in deep water and swimming," he told reporters in the nearby town of Strahan.

"They haven't stranded. So we've been more successful than not."

The causes of mass strandings remain unknown -- even to scientists who have been studying the phenomenon for decades.

However, some researchers have suggested the highly sociable pilot whales may have gone off track after feeding close to the shoreline or by following one or two whales that strayed.

Tasmanian environment department marine biologist Kris Carlyon said it was a "natural event" with strandings of the species occurring regularly throughout history in both southern Australian and neighbouring New Zealand.

"We do step in and respond in these situations, but as far as being able to prevent these occurring in the future, there's really little that we can do," he said.

Carlyon said animal welfare issues were a major reason authorities and conservationists intervened in mass strandings, along with public expectations and the ability to learn more about a species.

Key questions about mass whale strandings
Sydney (AFP) Sept 22, 2020 - About 270 pilot whales were discovered stranded in an Australian harbour this week, sparking a major rescue mission.

Here is a Q&A on the phenomenon:

Why do the whales get stranded?

The reasons whales and dolphins strand are not fully understood but theories include sickness, navigational error, the presence of predators and extreme weather.

High-frequency sonar has also been blamed. The use of anti-submarine sonars was suspected of causing the mass beaching of whales in 2002 in the Canaries after a NATO exercise.

When a single whale or dolphin is found washed up on a beach, it is usually because of illness, according to Mike Double, the head of the Tasmania-based Australian Marine Mammal Centre.

In the Tasmania case, one or two pilot whales may have headed for shore after becoming sick, with the highly sociable pod following, or they could have been chasing their deep-water prey and strayed too close to the coast, Double said.

Is this common?

Sadly, yes. While the Tasmania stranding is one of the biggest recorded in the region, the southern reaches of Australia regularly see mass whale beachings.

In 2017, more than 600 of the creatures beached themselves in neighbouring New Zealand, with rescuers managing to save about 400.

Both areas are known "hotspots" for whale strandings, with recorded incidents dating back to the 1800s in New Zealand, according to Karen Stockin, an expert in marine mammals at the country's Massey University.

Mass whale strandings also regularly occur in other parts of the world.

In April 2015, about 150 melon-headed whales were discovered washed up on a stretch of beach in Japan. More than 300 whales were found on a remote Patagonian inlet in southern Chile later the same year.

One of the largest known mass beachings in the last century was of false killer whales in October 1946, when an estimated 835 of them were stranded near Argentina.

Can the whales be saved?

Usually, specialised equipment is brought in to return stranded whales from beaches to the ocean.

But in the Tasmanian case, the surviving whales are stuck on two sandbars in the harbour and can only be reached by boat -- meaning rescuers have to jump into the chilly shallows and help manoeuvre the creatures into deeper water.

Using slings attached to boats, the whales are being guided into the water then out of the harbour into open ocean -- a method that has so far saved at least 25 whales.

Stockin said "at least a portion are likely to turn tail and re-beach" after being refloated, presenting an ongoing challenge for rescuers.

Survival rates ultimately depend on how long the whales have spent out of the water, she said.

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Rescuers race to save 180 stranded whales in Australia
Sydney (AFP) Sept 22, 2020
Rescuers faced a race against time to save nearly 200 whales stuck in a remote Australian harbour on Tuesday, hoping to prevent the toll of 90 dead from rising further after managing to free "a small number" of the stranded mammals. Scientists said two large pods of long-finned pilot whales became stuck on sandbars in Macquarie Harbour, on Tasmania's rugged and sparsely populated west coast. Images from the scene showed a shallow body of water, thick with scores of the large slick-black mammals ... read more