The herd of false killer whales, a kind of endangered, oversize dolphin, wormed its way into the narrow channels of Everglades National Park sometime over the weekend. The massive creatures, which can grow to 20 feet and 1,500 pounds, were soon trapped in the silty water, thick with mangrove roots. Scientists scrambled to help the stranded animals, but by yesterday, 81 of them were dead.

The die-off was the worst of its kind in Florida history for the mammals. And scientists say, for now, they have no idea why the animals all but committed mass suicide.

"Response teams continue to work trying to assess the scene after 95 false killer whales stranded along Hog Key in the Florida Everglades," according to NOAA Fisheries Service, which has coordinated the response. "The remote location makes it challenging for biologists to get to the scene."

False killer whales, as the name implies, are a close cousin to the more famous — and far better studied — orca. They're the fourth largest kind of dolphin, and they've been spotted in warm waters around the world.

It's not unheard of for the whales to breach and become stranded; hundreds were stranded in separate incidents in Australia, including one in 2005 when volunteers rescued most of the animals.

But the cases are rare — and none in Florida has been close to this size or this deadly. The last known stranding in Florida happened in 1986, when 40 of the creatures swam too close to Cedar Key and three ended up stuck.

This huge group of false killer whales was first spotted Saturday by the U.S. Coast Guard, which alerted NOAA. But the remote site — along the western edge of Everglades National Park, thick with strands of mangroves — made rescue attempts difficult. The scientists also had to contend with sharks in the area.

False killer whale stranding-area around scene in Everglades closed per the National Park Service-asking for no flyovers or boats for safety pic.twitter.com/XMHhTcsFMf — NOAA Fish Southeast (@NOAAFish_SERO) January 16, 2017

Rescuers Saturday were able to guide some of the dolphins to deeper water, and tried again Sunday. By Monday, 72 of the creatures had died, and scientists had to euthanize another nine that were too injured to survive.

95 false killer whales stranded off Hog Key, 81 dead, 1 seen alive, ~13 unaccounted for pic.twitter.com/rrltA7iVB6 — NOAA Fish Southeast (@NOAAFish_SERO) January 16, 2017

As for why such a large group could get trapped in the shallow, muddy flats of Everglades National Park, scientists have no answers at the moment. NOAA says tissue samples will be studied from the dead animals in the hopes of gleaning hints about what happened.

Perhaps the animals became disoriented or chased a food source too far into the park. There's certainly no reason to suspect that a deep animal instinct warned them of a coming global apocalypse, driving them to mass suicide first. No reason at all!

