An unusual scene unfolded in Florida Bay over the weekend: Eight spinner dolphins were found nearly lifeless on shallow muddy flats, far from home.
Marine biologists are still trying to understand how the dolphins wound up near Little Rabbit Key in steamy water miles from their deepwater hunting grounds in the Gulf of Mexico. But they suspect powerful Hurricane Hermine played a part when it pushed up from the Caribbean. Despite frantic rescue efforts by volunteers who rushed to the remote area after angler reports, all eight perished. The dead could also be part of a larger stranding.
They were literally seizing on the boat.
Art Cooper, director of operations for Dolphins Plus Marine Mammal Responder
“They were literally seizing on the boat,” said Art Cooper, director of operations for the nonprofit Dolphins Plus Marine Mammal Responder group. “They actually got worse as we went.”
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Known for flying, twisting leaps that entertain cruise ship passengers, pointy-nosed spinner dolphins typically inhabit offshore waters in the Gulf, where the population is estimated to be between 7,000 to 12,000 from South Florida to Texas. The dolphins also live in waters around the U.S. Virgin Islands and Puerto Rico, but it’s more likely that the stranded dolphins came from the Gulf, where they have come under increasing stress since the BP Deepwater Horizon oil spill in 2010. Between 2010 and 2014, 933 whales, dolphins and porpoises were found dead in an unprecedented die-off.
Biologists are conducting necropsies to look for other causes for the stranding. But so far the main culprit seems to be the massive, meandering hurricane that began slowly creeping through the Florida Straits Aug. 28.
When storms roll in, they can churn up water that disorients sea life, particularly spinner dolphins that hunt in water 300 to 900 feet deep, said Jill Richardson, a marine ecosystems scientist at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. Big waves and turbulence in the water can also force them to swim harder and burn up more energy.
They’re going to get disoriented and they have to swim harder, which uses up more energy and then they get pushed somewhere where they have no idea where they are.
Jill Richardson, marine ecosystems researcher at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science
“They’re going to get disoriented and they have to swim harder, which uses up more energy and then they get pushed somewhere where they have no idea where they are,” she said.
That somewhere was the sweeping, shallow bay, pockmarked with basins that at low tide empty out, make navigating treacherous and provide none of the fish spinners eat. A local fisherman first spotted four of the dolphins Saturday morning and called park officials, Cooper said. Cooper contacted him to make sure he wasn’t mistaking the stranding with bottle-nosed dolphins that regularly feed around flats.
“He said I’ve been out here since I was ten and I know what shoal feeding is,” Cooper said, saying that the angler insisted, “These don’t look like dolphins out here. They’re literally throwing themselves onto the flats.”
By the time his crew arrived, the dolphins were stranded on separate banks with mud so deep Cooper sank to his knees. Using floats, he and his team swam to the gaunt dolphins, got them onto the floats and swam back to their rescue boat. They were about to leave when another angler spotted a fifth dolphin. After retrieving it, they moved the dolphins to a bigger boat with vet staff, gave them IV fluids and drew blood. The call was made to euthanize three that were clearly suffering. Two were stable enough to be sent to SeaWorld in Orlando, Cooper said, where they arrived just after midnight. Both died the next day.
Sunday morning another call came. This time a spinner was swimming freely, but far off course near Conch Key off Marathon. The crew raced out and guided the dolphin back out to sea. Late Sunday, a third call came that more dolphins were spotted again near Little Rabbit Key. But there wasn’t enough daylight left for the crew to make the 30-mile trip out and back, Cooper said.
The next morning, the team returned and found three more emaciated dolphins. All were badly dehydrated and sunburned. None were well enough to survive, so Cooper said vets again made the difficult call to euthanize them.
So far no other dolphins, which swim in both small herds and in numbers by the thousands, have been spotted. But Richardson said the deaths could be part of a larger stranding.
“You get areas of the bay that are impossible to access,” she said. “So I don’t think we’d know for sure unless they did an aerial survey.”
Follow Jenny Staletovich on Twitter @jenstaletovich