By Friday morning, more than 150 short-finned pilot whales had been found lying on a beach in Western Australia.
News outlets report that some were pulled back out to sea by large cranes. The small whales can weigh between 907 to 5,443 kilograms. Fears that the carcasses were attracting sharks and a looming storm hindered rescue operations.
Most of the whales could not be saved.
Pictures and videos taken at the beach show a grim scene. Dozens of whales lay packed together in the surf.
Local wildlife authorities are taking physical samples from the dead whales to more closely examine why the stranding happened.
But the stranding, while mysterious for now, is not a rarity, says Nicola Hodgins from Whales and Dolphins Conservation, a marine mammal conservation group.
"This happens unfortunately many, many times," she says. Scientists have previously observed mass strandings off the coast of New Zealand, as well as other countries around the world.
The crux of why it happens en mass, she says, comes down to the fact that pilot whales are extremely social and close knit. They follow a matriarch and tend to form larger pods than other whale species, leading to larger strandings. (Learn about one of the largest strandings ever.)
"If one is sick, then the other whales don't want to leave their side," she notes. As a sick whale loses energy, it falls prey to the pull of waves and can sometimes drift ashore. "The other animals end up beaching as well because they don't want to leave them."
Until a necropsy can be performed, it's only possible to speculate if they followed a sick whale ashore.
Underwater noise is another theory Hodgins notes for why whales have beached in the past.
Sonic booms caused by seismic activity from oil and gas exploration or military sonar can be extremely loud, she notes. Pilot whales, like other whales and dolphins, use sound for critical communication, hunting, and navigation, so underwater noise leaves them especially vulnerable.
"[The sound] disorientates the animals," says Hodgins. "They end up trying to 'run away,' and the energy it takes to do that is potentially debilitating."
Other environmental influences have been found to cause mass strandings. Tsunamis can disrupt the whales' navigation, and toxic algal blooms have been responsible for disease-causing events that lead to mass die-off.
In some cases, a whale seeking prey could be stranded by accident, and other whales follow suite.
Pilot whales are known to have the largest stranding groups.
Last year, more than 600 were stranded in New Zealand, leading to about 400 casualties.