Turtles are washing up on shore in record numbers in Cape Cod.

As of this Tuesday, 396 turtles have been found stranded in Cape Cod Bay because the cold temperatures have immobilized them.

The previous high was 278 in 1999.

It’s called the “cold stun season” because once the water temperature drops to a certain level, the turtles become disoriented and can’t swim. The turtles include juvenile green sea turtles, loggerhead sea turtles and a few of the endangered Kemp’s Ridley turtles.

The stranding season usually runs from early November to late December or early January.

“It becomes a death sentence,” Molly Shuman-Goodier, a research technician with the Mass Audubon-Wellfleet Bay Wildlife Sanctuary, told the Star.

The turtles wash up on shore like driftwood.

Most are saved, but some die.

READ MORE: Massive dolphin stranding on Cape Cod puzzles experts

The reason for the record high is a bit of a mystery, but one thing is clear: This is mostly a good news story.

Conservationists say the record numbers show that the turtle population is growing, not falling as many had feared.

“It’s been a very good year for recovery,” said Shuman-Goodier. “The sooner they wash up the better. As it gets into December, fewer of them are alive.”

Shuman-Goodier is part of a rescue team, which includes stun patrols and volunteer beach walkers, who rush the turtles to the New England Aquarium’s Animal Care Center in Quincy.

The turtles nest in beaches in Florida and Mexico and come to the Cape Cod area to feed in the summer.

“This has always happened, but since they are endangered, it’s been a big effort,” Shuman-Goodier said. “We owe them a little help. Most of the turtles we got were alive. In the past, the numbers of survivors have been a lot lower.”

Shuman-Goodier says there are many reasons behind the surge in strandings this year:

Superstorm Sandy may have been a blessing because more turtles might have washed ashore earlier than usual when their bodies were warmer and their survival odds were better.

The Boston Harbor cleanup may have improved the food supply in the bay.

Loading... Loading... Loading... Loading... Loading... Loading...

There was good nesting four or five years ago and a lot of hatchlings survival.

• This year the fall water temperatures were several degrees higher than normal when they began washing up, leading to the belief there were more turtles in the area to begin with.

• Conservation efforts in the nesting beaches in Mexico and Florida have been stepped up to protect some of the endangered species.