The shores of Cape Cod, Massachusetts, have seen a spike in the number of debilitated and dead sea turtles, with more than 200 washing up in the past several days.
"Cold-stunning," as rescuers call it, happens when the tropical reptiles are trapped in cold water and — because they're ectothermic, or reliant on external heat for their bodies to function — their systems begin to shut down.
Unable to swim, they can be pushed along by strong winds to the shore or to shallower waters, where they can literally freeze to death.
"It was like they were flash-frozen, flippers in all weird positions like they were swimming," Robert Prescott, director of Massachusetts Audubon Society's Wellfleet Bay Wildlife Sanctuary, told the Cape Cod Times.
Prescott told CNN that of the more than 200 turtles found off Cape Cod this week, 173 had died and 54 survived. Many were juvenile Kemp's ridley turtles, the most endangered sea turtles in the world, the sanctuary said in a statement. Other species were found as well, including a nearly 300-pound loggerhead.
Jenette Kerr, spokesperson for the Wellfleet Bay Wildlife Sanctuary, told the Cape Cod Times that on Wednesday, 87 turtles were found, mostly alive. On Thanksgiving, 82 had washed ashore, all but one of which died — a spike that Kerr attributed to "drastic change in the weather overnight."
Overall, more than 400 cold-stunned turtles have turned up in the area this year. Some of this week's survivors have been transported to the New England Aquarium's Animal Care Facility for rehabilitation.
Scientists say that the naturally migratory turtles are heading farther north as climate change warms the planet's oceans. Some are now summering in the Cape Cod Bay, where they become trapped "by the Cape's hook-shaped geography," the sanctuary said.
Blocked from migrating down to warmer waters, the turtles are left vulnerable to volatile weather, like this week's cold snap and gale-force winds.
"Sea turtles are moving further north along our coast ... as waters are warming and they are expanding their ranges," biologist Wallace J. Nichols told NBC News. "When we get these quick swings from warm to cooler, the turtles that haven't made it south definitely get into trouble."
"Stranding season" typically lasts from about Thanksgiving to Christmas, the sanctuary said. This year's numbers have already passed what's typical for a year, Prescott said — and the total might climb to 1,000 sea turtles before the end of December.
In the last four decades, cold-stunned sea turtles have been on the rise, peaking with more than 1,200 animals in 2014, according to the sanctuary.
"The reasons for the phenomenon aren't clear, but much warmer waters in the Gulf of Maine and increased nesting productivity for some sea turtle species may be two factors," the sanctuary said in its statement.