The majority of a 470-strong pod of pilot whales found stranded off Australia's remote southern coast has died, officials said on Wednesday, as rescuers struggled in freezing waters and fading light to free those still alive.

The group, which is the biggest beaching in the country's modern history, were first spotted a wide sandbank during an aerial reconnaissance of rugged Macquarie Harbour in Tasmania state on Monday.

After two days of a difficult and dangerous rescue attempt, state marine scientists said at least 380 of the long-finned pilot whales had died.

Also read:&nbsp;<a href="http://13.235.153.162/world/rescuers-race-against-time-to-save-180-stranded-whales-in-australia-329357" hreflang="en">Rescuers' race against time to save 180 stranded whales in Australia</a>

By late Wednesday, around fifty of the mammals were freed but experts said there was a high likelihood they would return as many did during the rescue attempt a day earlier, creating an exhausting loop for rescuers who cannot work through the night.

The outlook for the remaining 30 stranded and still alive pilot whales, a species of oceanic dolphin that grow to 7 metres (23 ft) long and can weigh up to 3 tonnes, was bleak.

"As time goes on, they do become fatigued and their chance of survival reduces," Nic Deka, Parks and Wildlife Service incident controller said. "We do expect to rescue more but increasingly our focus is what do with the carcasses."

In Pics:&nbsp;<a href="https://www.wionews.com/photos/australia-rescues-25-whales-in-one-of-its-worst-beaching-events-329456" hreflang="en">Australia rescues 25 whales in one of its worst beaching events</a>

The refloating process involves as many as four or five people per whale wading waist-deep in freezing water, attaching slings to the animals so they can be guided out of the harbour by a boat.

The stranding, about 200 kms (120 miles) northwest of the state capital Hobart, is the biggest on record in modern Australia and one of the largest in the world, drawing attention to a natural phenomenon that remains a mystery to scientists.

"It's certainly a major event and of great concern when we potentially lose that many whales out of a stranding event," said Peter Harrison, a professor at the Southern Cross University Whale Research Group.

"Quite often we only get to really see them when there are bad outcomes, such as this stranding event. We absolutely need some more investment in research to understand these whales in Australian waters."

In 1996, 320 pilot whales washed up on the coast of Western Australia, in what was then reported to be the country's biggest mass stranding. About 600 pilot whales beached in nearby New Zealand in 2017.

The majority of a 470-strong pod of pilot whales found stranded off Australia's remote southern coast has died, officials said on Wednesday, as rescuers struggled in freezing waters and fading light to free those still alive.

The majority of a 470-strong pod of pilot whales found stranded off Australia's remote southern coast has died, officials said on Wednesday, as rescuers struggled in freezing waters and fading light to free those still alive. The group, which is the biggest beaching in the country's modern history, were first spotted a wide sandbank during an aerial reconnaissance of rugged Macquarie Harbour in Tasmania state on Monday. After two days of a difficult and dangerous rescue attempt, state marine scientists said at least 380 of the long-finned pilot whales had died. Also read: Rescuers' race against time to save 180 stranded whales in Australia By late Wednesday, around fifty of the mammals were freed but experts said there was a high likelihood they would return as many did during the rescue attempt a day earlier, creating an exhausting loop for rescuers who cannot work through the night. The outlook for the remaining 30 stranded and still alive pilot whales, a species of oceanic dolphin that grow to 7 metres (23 ft) long and can weigh up to 3 tonnes, was bleak. "As time goes on, they do become fatigued and their chance of survival reduces," Nic Deka, Parks and Wildlife Service incident controller said. "We do expect to rescue more but increasingly our focus is what do with the carcasses." In Pics: Australia rescues 25 whales in one of its worst beaching events The refloating process involves as many as four or five people per whale wading waist-deep in freezing water, attaching slings to the animals so they can be guided out of the harbour by a boat. The stranding, about 200 kms (120 miles) northwest of the state capital Hobart, is the biggest on record in modern Australia and one of the largest in the world, drawing attention to a natural phenomenon that remains a mystery to scientists. "It's certainly a major event and of great concern when we potentially lose that many whales out of a stranding event," said Peter Harrison, a professor at the Southern Cross University Whale Research Group. "Quite often we only get to really see them when there are bad outcomes, such as this stranding event. We absolutely need some more investment in research to understand these whales in Australian waters." In 1996, 320 pilot whales washed up on the coast of Western Australia, in what was then reported to be the country's biggest mass stranding. About 600 pilot whales beached in nearby New Zealand in 2017.

Australia says majority of 470-strong beached whale pod has died

Scientists have long known that some beaked <a href="http://www.wionews.com/world/sharp-rise-in-whale-dolphin-stranding-deaths-in-india-91">whales beach themselves and die in agony</a> after exposure to naval sonar, and now they know why: the giant sea mammals suffer decompression sickness, just like scuba divers.

At first blush, the explanation laid out Wednesday by 21 experts in the Royal Society journal Proceedings B seems implausible.

Millions of years of evolution have turned whales into perfectly calibrated diving machines that plunge kilometres (miles) below the surface for hours at a stretch, foraging for food in the inky depths.

The heart rate slows, blood flow is restricted, oxygen is conserved.&nbsp;

So how could the ocean's most accomplished deep-sea diver wind up with nitrogen bubbles poisoning its veins, like a scuba novice rising too quickly to the surface?

Short answer: beaked whales — especially one species known as Cuvier's — get really, really scared.

"In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern," lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas de Gran Canaria, Spain, told AFP.

"The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen," she added. "It's like an adrenalin shot."

One type of sonar in particular throws these whales off balance.

'Atypical' mass strandings 
Developed in the 1950s to detect submarines, mid-frequency active sonar (MFAS) is used today in naval patrols and exercises, especially by the United States and its NATO allies.

Starting around 1960, ships began emitting underwater signals in a range of about 5 kilohertz (kHz).

That is when the mass beaching of beaked whales, especially in the Mediterranean, began.

Between 1960 and 2004, 121 of these so-called "atypical" mass strandings took place, with at least 40 closely linked in time and place with naval activities.

These were not individual strandings of old or sick animals, nor en masse strandings such the one last November in New Zealand, when more than 200 pilot whales beached themselves together.

Rather, a handful or more beaked whales would wash ashore within a day or two, and no more than few dozen kilometres apart. &nbsp; &nbsp;&nbsp;

The most deadly episode, in 2002, saw 14 stranded over a 36-hour period in the Canary Islands during a NATO naval exercise.

"Within a few hours of the sonar being deployed, the animals started showing up on the beach," Bernaldo de Quiros said.

Outwardly, the whales showed no signs of disease or damage: they had normal body weight, and no skin lesions or infections.

Internally, it was another story. Nitrogen gas bubbles filled the veins, and their brains were ravaged by haemorrhaging.

Autopsies also revealed damage to other organs, as well as to the spinal cord and central nervous system.

Canary Island moratorium 
As with altitude sickness, reactions -- in humans, and probably in whales -- to nitrogen bubbles in the blood vary in type and intensity.

A 2003 study in Nature on the possible link between sonar and whale deaths led to Spain banning such naval exercises around the Canary Islands in 2004.

"Up until then, the Canaries were a hotspot for this kind of 'atypical' strandings," said Bernaldo de Quiros. "Since the moratorium, none have occurred."

The authors called for similar bans to be extended to other regions where at-risk whales are known to congregate.

The Cuvier's grows up to seven metres (23 feet) and dines mainly on deep-water squid and fish. Its upwardly turned mouth gives the impression of a permanent smile.

The whale is listed as "vulnerable" on the IUCN Red List of endangered species, and is thought to have a global population of 5,000 to 7,000.&nbsp;

Other threats include ship strikes, ocean pollution and shifting habitats caused by climate change.

Scientists have long known that some beaked whales beach themselves and die in agony after exposure to naval sonar, and now they know why: the giant sea mammals suffer decompression sickness, just like scuba divers.

Scientists have long known that some beaked whales beach themselves and die in agony after exposure to naval sonar, and now they know why: the giant sea mammals suffer decompression sickness, just like scuba divers. At first blush, the explanation laid out Wednesday by 21 experts in the Royal Society journal Proceedings B seems implausible. Millions of years of evolution have turned whales into perfectly calibrated diving machines that plunge kilometres (miles) below the surface for hours at a stretch, foraging for food in the inky depths. The heart rate slows, blood flow is restricted, oxygen is conserved. So how could the ocean's most accomplished deep-sea diver wind up with nitrogen bubbles poisoning its veins, like a scuba novice rising too quickly to the surface? Short answer: beaked whales — especially one species known as Cuvier's — get really, really scared. "In the presence of sonar they are stressed and swim vigorously away from the sound source, changing their diving pattern," lead author Yara Bernaldo de Quiros, a researcher at the Institute of Animal Health at the University of Las Palmas de Gran Canaria, Spain, told AFP. "The stress response, in other words, overrides the diving response, which makes the animals accumulate nitrogen," she added. "It's like an adrenalin shot." One type of sonar in particular throws these whales off balance. 'Atypical' mass strandings Developed in the 1950s to detect submarines, mid-frequency active sonar (MFAS) is used today in naval patrols and exercises, especially by the United States and its NATO allies. Starting around 1960, ships began emitting underwater signals in a range of about 5 kilohertz (kHz). That is when the mass beaching of beaked whales, especially in the Mediterranean, began. Between 1960 and 2004, 121 of these so-called "atypical" mass strandings took place, with at least 40 closely linked in time and place with naval activities. These were not individual strandings of old or sick animals, nor en masse strandings such the one last November in New Zealand, when more than 200 pilot whales beached themselves together. Rather, a handful or more beaked whales would wash ashore within a day or two, and no more than few dozen kilometres apart. The most deadly episode, in 2002, saw 14 stranded over a 36-hour period in the Canary Islands during a NATO naval exercise. "Within a few hours of the sonar being deployed, the animals started showing up on the beach," Bernaldo de Quiros said. Outwardly, the whales showed no signs of disease or damage: they had normal body weight, and no skin lesions or infections. Internally, it was another story. Nitrogen gas bubbles filled the veins, and their brains were ravaged by haemorrhaging. Autopsies also revealed damage to other organs, as well as to the spinal cord and central nervous system. Canary Island moratorium As with altitude sickness, reactions -- in humans, and probably in whales -- to nitrogen bubbles in the blood vary in type and intensity. A 2003 study in Nature on the possible link between sonar and whale deaths led to Spain banning such naval exercises around the Canary Islands in 2004. "Up until then, the Canaries were a hotspot for this kind of 'atypical' strandings," said Bernaldo de Quiros. "Since the moratorium, none have occurred." The authors called for similar bans to be extended to other regions where at-risk whales are known to congregate. The Cuvier's grows up to seven metres (23 feet) and dines mainly on deep-water squid and fish. Its upwardly turned mouth gives the impression of a permanent smile. The whale is listed as "vulnerable" on the IUCN Red List of endangered species, and is thought to have a global population of 5,000 to 7,000. Other threats include ship strikes, ocean pollution and shifting habitats caused by climate change.

Why do whales commit suicide? Answer may be sonar

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Australia says majority of 470-strong beached whale pod has died

Why do whales commit suicide? Answer may be sonar