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82 Dolphins Die in Mysterious Mass Stranding

Researchers don’t yet know what caused the animals to beach themselves.

Dozens of false killer whales have died under mysterious circumstances after stranding themselves on a remote shoreline in Florida’s Everglades National Park.

The U.S. National Oceanic and Atmospheric Administration (NOAA) Fisheries Service reports that 95 false killer whales stranded themselves at Hog Key, on Florida’s southwestern coast. Since the U.S. Coast Guard spotted the animals on Saturday, 82 of the animals have died. The Miami Herald reports that the stranding was the largest for false killer whales ever recorded in the state.

False killer whales are the fourth-largest members of Delphinidae—the family of aquatic mammals comprising dolphins—and can grow between 16 to 20 feet long. They look similar to killer whales but lack orcas’ distinctive white spots. While false killer whales have been spotted as far north as Alaska and western Canada, they are primarily found in the tropics. They are highly social, typically found in groups of 10 to 20 that comprise schools numbering in the hundreds.

The IUCN Red List—a globally recognized register that evaluates species’ risk of extinction—reports that data is too scant to assess the false killer whale’s conservation status. While populations in the waters around the main Hawaiian Islands have been declared endangered, the species does not have federal protections in Florida’s waters. Florida’s false killer whale population remains unknown, though as of 2004, researchers estimated that some 780 false killer whales lived in the northern Gulf of Mexico.

In an interview with the Miami Herald, Blair Mase, the coordinator of NOAA’s mammal stranding network, described the stranding as a rare occurrence. The last known stranding occurred in 1986, when three whales in a pod of 40 stranded themselves at Cedar Key, along Florida’s western coast. Six years before, 28 whales stranded off of Key West. And a January 1970 report from southeastern Florida describes a stranding that may have included 150 to 175 individuals, though researchers at the time could not confirm these estimates.

These numbers pale in comparison to the largest stranding on record, when 835 false killer whales beached themselves on Argentina’s shores in 1946.

The cause of the stranding remains unknown, though NOAA says that biologists will be analyzing samples taken from the dead animals in the coming months. It’s a tricky task: Of the 62 “unusual mortality events” tracked by NOAA since 1991, causes have been found for just 30, ranging from toxic algal blooms to run-ins with humans, such as collisions with shipping vessels.