One of the surviving Cape Cod Bay turtles. New England Aquarium Weak, immobile, and close to death, the turtles wash limply on to the sand. The wind and waves draw them up to the shore, where their cold bodies — incapacitated by the frigid, late-autumn ocean — will lie prone on the beach, unable to move or defend themselves.

Here, they can do nothing but await rescue.

Each week since mid-November, staff members and volunteers from the Massachusetts Audubon Society's Wellfleet Bay Wildlife Sanctuary in South Wellfleet, Mass., have diligently patrolled the shoreline, both day and night, searching for these stranded sea turtles, which have washed up on the shore in droves this year — a mysterious event that has left wildlife experts scratching their heads.

Every year, a few sea turtles — usually 200 at most, in recent years — linger a little too long in Cape Cod Bay after the rest of their brethren have drifted back out to sea in search of warmer waters. These turtles somehow miss their cue to leave and end up staying behind as the waters cool.

As the autumn draws to a close, temperatures start to drop in the bay, and the turtles eventually become so cold that they're unable to move. The natural movement of the ocean, helped by the wind, pushes these stiffened turtles up onto the beaches. So, wildlife experts in the area devote time each season to gathering up the stranded turtles and nursing them back to health.

But the annual turtle stranding jumped this year — approximately 1,200 "cold-stunned" sea turtles have landed on the Massachusetts shore already, most of these critically endangered Kemp's ridley sea turtles. It's an overwhelming number, and one that wildlife experts have been hard-pressed to explain.

"I am hearing a lot of theories, but the reality of the situation is we really don't know — nobody knows," said Connie Merigo, stranding program manager at the New England Aquarium.

Volunteers preparing to rescue a turtle from the beach. Courtesy of Massachusetts Audubon Society - Wellfleet Bay Wildlife Sanctuary

The rescue effort

This cold-stunned turtle was discovered at night. Courtesy of Massachusetts Audubon Society - Wellfleet Bay Wildlife Sanctuary More than 150 volunteers have turned out this season to help Audubon staff members with the rescue effort. Since November, they've been going out several times a week to look for stranded turtles, depending on the wind.

Wind speed and direction is a big indicator of how many turtles will wash up in a given day, said Bob Prescott, director of the Wellfleet Bay Wildlife Sanctuary. The highest numbers tend to come in when the wind blows from the west and blows above 15 miles per hour. So far, the record has been 198 turtles in a single day.

Weaker winds or winds blowing from the east might only bring in a few turtles in a day — but Prescott said there's almost always at least one coming in every day.

A possible explanation

Almost all of the turtles are between two and three years old, which is the case every year. So some experts have speculated that the Kemp's ridley sea turtle experienced an unexpected population explosion a few years ago, Prescott said. This year's large numbers of stranded turtles could just be because there are a lot more turtles out there.

These sea turtles would have been born in 2011 or 2012 in the Gulf of Mexico, where Kemp's ridley turtles go to lay their eggs. Most baby sea turtles will stay around the Gulf of Mexico, but every year a few venture slowly up the East Coast — by the time they make it to Massachusetts, they're already about two years old.

This is why all the turtles that wash up on the shore are around the same age — it's the only time in their lives they'll make it that far north, Prescott said. Turtles that don't get trapped in the cold waters start making their way back south at the end of the summer.

At the end of the day, though, more research is needed to understand exactly what's been going on this year in Cape Cod Bay.

Care and treatment

What the experts do know is that these turtles need lots of care, and fast. Cold-stunned turtles are entirely helpless by the time they wash up on shore, having lost their ability to swim or move around. Many of them stop eating as the water temperature drops, so they're often malnourished, and they're highly susceptible to pneumonia. In any given year, up to 50 percent of them might die, Prescott said.

A cold-stunned sea turtle receiving care at the New England Aquarium's animal care center. New England Aquarium Once a turtle is rescued, Wellfleet staff members weigh it, measure it, and keep its temperature constant until it can be transported to the New England Aquarium's animal care center in Quincy, Mass. for further treatment. So far this season, the aquarium has treated more than 700 turtles. Hundreds of others have died, some surviving for a few hours after reaching the beach, and others washing up already dead.

At the care center, staff members are responsible for raising the turtle's temperature back to normal — but very slowly. "We raise their temperature by 5 degrees a day until they're back up to normal reptile temperature," Merigo said. "We could be doing serious damage at a cellular level if we just try to increase them over 24 hours."

Staff members keeping an eye on rescued sea turtles at the New England Aquarium's animal care center. New England Aquarium Once they're stable enough, the turtles can move to other care facilities, like animal hospitals and aquariums, up and down the East Coast. These partners are a vital part of the turtle rescue effort.

"We have an excellent vet staff and rescue team, but this number of sick patients has just exceeded our resources," Merigo said. "It's really comforting to know there's such a fantastic and strong network ready to help us out."

Eventually, the healthy turtles will be released back into the wild.

What now?

According to the International Union for Conservation of Nature (IUCN), the Kemp's ridley sea turtle is a critically endangered species — in fact, it's been endangered since the 1980s. Prescott says this year's event doesn't necessarily spell trouble for the species, but it will be hard to say for years yet.

The turtles don't reach maturity and begin reproducing until they're about 10 years old, so it will take at least eight more years for this year's Cape Cod survivors to produce a new generation. That generation could be smaller than normal if it turns out this year's cold-stunning event took out a significant number of Kemp's ridleys. But Prescott said this kind of population challenge "could be easily overcome by three or four really big successful hatch years next year or the year after."

For now, wildlife experts in the Cape Cod area are prepared to keep up the turtle rescue for a little while longer. The last of the turtles are often gone by this late in the season, but Merigo, from the New England Aquarium, said a few more stragglers could still come in over the next few weeks.