By Jenny Staletovich

Miami Herald

MIAMI — By the time rescuers returned to a mass stranding of false killer whales on the remote coast of Southwest Florida early Sunday, most had died overnight, their corpses now drawing aggressive, and hungry, bull and tiger sharks.

With waters too dangerous to enter and chances of survival unlikely, the team turned their attention to unraveling what caused the mysterious deaths, now the largest stranding on record in the state.

On Tuesday, Erin Fougeres, the program administrator for the National Oceanic and Atmospheric Administration’s Southeast stranding network, said rescue teams completed full necropsies on six of the whales, performed partial dissections on others and collected tissue samples from nearly all of the 82 whales that have died. Another 13 remain missing.

In the upcoming weeks, pathologists will look at blubber, skin and tissue from the whales’ organs to try to understand what drove so many into the brown, turbid waters near Hog Key and just north of Lostmans River, a location about as remote and wild as any left in the state.

“There’s a lot of different factors that could potentially cause it,” said Fougeres, listing changes in tide or unusual weather, water conditions such as red tide, or military sonar exercises blamed for killing beaked whales. The strong social bond shared by the whales could also be their undoing: healthy whales often follow the sick. Of all the different species, false killer whales also hold the record for the largest whale stranding ever, Fougeres said.

The Gulf of Mexico is routinely plagued with red tide outbreaks, with moderate to high amounts detected just this month far to the north. Over the last week, the state also began investigating a mysterious string of pelican deaths, leading U.S. Rep. Charlie Crist to ask the Environmental Protection Agency to test waters for toxicity in a letter Tuesday. Fougeres said it was unlikely the deaths are related.

False killer whales are well known in Hawaii, where the deep ocean water they inhabit runs close to shore and a local population routinely entertains fishermen and visitors with spiraling acrobatics. What is largely known about the species — among the largest members of the dolphin family — comes from studies done on the herd. So many were getting caught on longlines set for swordfish and tuna in waters near the islands that they were added to the endangered species list in 2012.

But in Florida, they remain an enigma, air-breathing mammals that live miles offshore in the Gulf of Mexico, where they dive nearly 900 feet in search of tuna, octupuses and other deep-sea marine life to eat. The last time the Gulf whales were surveyed in the 1990s and early 2000s, fishery experts put their numbers between about 700 and a thousand. But today that information is considered too outdated to be valid, so government assessments list the herd as “unknown.”

After a caller alerted the Florida Fish and Wildlife Conservation Commission dispatch Saturday, the U.S. Coast Guard headed out to confirm the beaching. By 1 p.m., a team of FWC law enforcement agents had reached the scene and found dozens of sick whales, Fougeres said. Members of the FWC stranding team based in Port Charlotte hurried after them. But it wasn’t until 3 p.m., with staff from the Mote Marine Laboratory in Sarasota also on scene, that teams had the manpower necessary to coordinate efforts, made even more difficult by the lack of cellphone service.

“Once they had a critical mass of responders, they made efforts to lure the whales out,” she said.

Two calves were rounded up, loaded onto stretchers and carried alongside boats to draw the whales from the shallow muddy waters, where many had squeezed between the thickets of mangrove roots. Between six and 10 whales followed the boaters to deeper water, but rescuers had to abandon efforts when it became too dark to navigate, Fougeres said. By the time they returned early Sunday, many of the whales had died overnight. Large tiger and bull sharks had also started feeding on the bodies, making it too dangerous for rescuers to get in the water to help the remaining whales. Of the 95 originally reported, 72 died on their own. Another nine were euthanized by rescuers. The last remaining whale found alive was euthanized Monday afternoon, Fougeres said.

While the whales typically swim in pods of about 10 to 20, when it comes to strandings, they tend to die en masse. No one is really sure why, Fougeres said.

“We don’t know enough about this particular whale behavior, but they could form temporary groups,” she said, or what scientists call a “fission-fusion society.” For some activities, like eating, they split up. For other activities, like sleeping, they come together. A beaching could be part of the highly social herd’s fission.

Given the scene, she said it was unlikely that the missing 13 whales have survived.

“They didn’t look like they were in great shape,” she said. “I don’t think anyone was particularly optimistic about them making it all … across the Continental Shelf and back into deep water.”