Beached on Cape

But the sea turtle's rescuers, including a volunteer who plucked it from the churning surf in Brewster, weren't ready to give up hope. If it shows signs of life, the turtle will be transported to a marine mammal intensive care unit at the New England Aquarium today, complete with intravenous drips and volunteers to hold its chin out of the water so it can breathe.

"We'll give it until tomorrow," sanctuary director Bob Prescott said yesterday. "We've seen them come back before."

The huge, incapacitated turtle represents one of the great natural mysteries of Cape Cod Bay: Why are sea turtles trapped here when cold weather comes? Why have more been washing up on beaches in recent years?

So far, 83 cold-stunned sea turtles have been stranded on Cape Cod beaches since late October, most of them dinner-plate-sized Kemp's ridleys, considered the most endangered sea turtle in the world. A few are green turtles or larger loggerheads.

The turtles, almost all under 6 years old, are immobilized by cold waters that on Wednesday dipped to 28 degrees near shore in Orleans. Unable to paddle their flippers or even to feed, they are at the mercy of ocean currents and wash up on shore when a strong wind blows, as it has in recent weeks.

Volunteers walk the Cape's beaches every high tide, every day in the late fall and early winter, searching for dark mounds that can signal a chilled turtle. On Wednesday morning on Skaket Beach in Orleans, Prescott battled fierce winds and icy sea foam that hid any sign of turtles from view.

The loggerhead found in Brewster by volunteer Mary Myers was in an area where ice had not yet formed. At the sanctuary, it was gently placed next to two Kemp's ridleys scooped up Tuesday morning by volunteers in Truro.

The ridleys were a sorry sight, with flippers spread out like paralyzed arms. By Wednesday late morning, Prescott officially declared them dead; rigor mortis had set in.

Yesterday, another Kemp's ridley was brought in, frozen solid, and unless the weather warms, searchers don't believe they'll find any more alive.

Before the 1970s, reports of turtles washing up on Cape beaches were rare. Scientists believed that the handful of turtles they found, particularly the Kemp's ridleys, were "lost waifs" that got caught in the Gulf Stream.

But since the 1970s, when Prescott began organizing volunteers to walk the beaches, the numbers have steadily risen, hitting an all-time high of 281 strandings in 1999. Numbers have dipped slightly since then, but still remain high.

"The consistency that we are seeing them here means they are not lost waifs, but are actually foraging" for food, said Kara Dodge, Northeast stranding assistant coordinator for the National Marine Fisheries Service.

One theory why the turtles are stranded at the Cape is that they are lured by warm temperatures, but then don't know how to escape when temperatures plunge.

A reason that more Kemp's ridleys may be washing up on Cape Cod in the fall is that their numbers are increasing. The creatures are known to nest in only one place -- Rancho Nuevo, Mexico -- and better protection of those areas and a reduction in the accidental catch of ridleys by shrimp trawlers have meant an uptick in their population, from just a few thousand several years ago to about 6,500 now.

"There are a lot of theories, but we don't understand exactly why they remain beyond summer," Dodge said.

As Prescott and his staff carefully monitored the loggerhead at the sanctuary Wednesday afternoon and evening, the New England Aquarium was bustling, as workers and volunteers monitored 34 turtles from the Cape, almost all Kemp's ridleys. The turtles must be warmed slowly, about 5 degrees per day, or they could die from tissue damage.

Most of the turtles brought to the aquarium survive, though many have broken flippers, shell fractures, or other problems that require months of rehabilitation.

Beth Daley can be reached at Bdaley@globe.com.