When a pod of nearly 100 pilot whales stranded themselves last week on the shore of an Australian beach, it became the latest instance of a phenomenon that has long baffled marine biologists.

Wildlife officials in Western Australia made the decision to euthanize many members of the pod after rescue attempts were unsuccessful. By that time, half of the group had already perished on Cheynes Beach near Albany, in southern Western Australia.

Reports of beachings are sadly not uncommon, but experts struggle to explain why marine mammals strand themselves, either deliberately or inadvertently. What's more, with no proven explanation for why strandings occur, wildlife experts have little means to save the lives of species that do it, such as last week's long-finned pilot whales, a species that can grow up to 25 feet long and are identified by their black color and bulbous foreheads.

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“It’s such a strange and sad thing to watch a group of animals like that," said Andrew Read, a professor of Marine biology at Duke University who is also part of the Marine Mammal Commission. "They’re marvelous animals and I love being out in the water with them and it’s sad seeing them in such a difficult situation.”

How often do mammals beach themselves?

Thousands of stranded or beached marine animals in the U.S. are reported each year to the National Oceanic and Atmospheric Administration's stranding networks.

Under the 1992 Amendments to the Marine Mammal Protection Act, NOAA Fisheries was tasked as the lead agency to coordinate emergency responses to beached and distressed marine animals.

The organization maintains a national stranding database on every stranded marine mammal in the United States encountered by a network member. However, the database is not accessible to the public and USA TODAY's request for a data report on stranded long-finned pilot whales has not been completed as of Monday afternoon.

Experts say there is no evidence that whales or other marine mammals across the globe are beaching themselves more often. In fact, the behavior is a relatively commonplace one that Read said has been observed for centuries.

More likely, scientists say that awareness of the phenomenon may be growing, leading to more reports of beachings than before.

Sarah Sharp, an animal rescue veterinarian with the International Fund for Animal Welfare, shared that the organization's stranding numbers in Cape Cod for all marine mammals, including dolphins and seals, have increased in the past two decades. But she added that it is unclear if the rise is due to increased reporting or a true increase in number of stranded animals.

Earlier this month, 55 pilot whales died after rescuers found them washed ashore on a Scotland beach, the worst mass whale stranding in the area.

Australia itself has had multiple reports of mass whale beachings just within the past year.

Last September, 14 young sperm whales died in Australia after wildlife authorities found them beached on an island off the southeastern coast. The whales were found and photographed lying on their sides in the shallow water on the rocky shore of an island that is part of the state of Tasmania in the Bass Strait.

Days later, 230 pilot whales were stranded nearby on Tasmania's west coast on Ocean Beach in Macquarie Harbour.

But while global reports of beachings are capturing the world's attention, there remains no uniform international standard system for cataloguing beachings, said Randall Davis, a marine biologist at Texas A&M University.

“They're not necessarily becoming more frequent, but maybe we’re more aware of when they occur,” Davis shared.

Why do mammals beach themselves?

Theories abound for why mass beachings occur, but researchers don't have an exact answer to explain the phenomenon.

Pilot whales form tight social bonds that often last a lifetime, so experts say it's not inconceivable that if a member of the pod became ill and swam to the beach in distress, the other whales would follow. Another theory suggests that whales could beach themselves when noises in the water — some human-made —cause them to become disoriented, leading to navigational errors.

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Yet another explanation offered as the cause of beachings is that whales that become frightened of nearby predators flee in their panic to shallow waters.

"You’ll get all kinds of speculation,” Davis said. "But fundamentally, we don't know why they do it." 

Why did rescuers euthanize many of the whales?

Wildlife officials with the Parks and Wildlife Service of Western Australia expressed to reporters the difficulty of the decision to euthanize the pilot animals remaining last week on the beach.

The measure was a last resort, they said, taken only after attempts to coax the whales back to deep waters led them to strand themselves once again on the beach. In the burning sun, the surviving whales suffered, becoming overheated, their massive weight — the animals can weigh up to 6,600 pounds — crushing their organs.

Could any more have been done to save them from that fate? Many marine biologists and experts said, probably not.

“Once they come back, that’s probably a sign that you’re not going to be able to save them,” Read said. 

What can explain the strange huddling behavior observed in Australia?

Prior to stranding themselves on the Australian beach, video and photos showed the whales huddling together in shallow waters.

The unusual behavior puzzled some marine biologists, who struggle to explain what may have been behind it.

Davis posited that perhaps the display could be a form of socializing, given that the species is tactile and social in nature, while Read theorized that the whales could have been attempting to protect themselves from a predator.

Regardless, the strange behavior left Read and Davis baffled.

“My students and colleagues, none of us have ever seen anything like that, so it’s a very strange, unusual behavior to see the animals right on top of each other like that," Read said. "So seldom do we get an opportunity to see what happens before the animals show up on the beach. There was clearly something profoundly wrong with those animals.”

Because drone technology provided this crucial glimpse of previously unobserved bizarre behavior, Sharp suggested that more insights are ahead for researchers to glean from.

"It is likely these behaviors have occurred prior to strandings previously, but have not been documented in this way," Sharp said. "We still have a lot to learn about these animals."

Contributing: Associated Press

Eric Lagatta covers breaking and trending news for USA TODAY. Reach him at elagatta@gannett.com and follow him on Twitter @EricLagatta.

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