GULF SHORES, Ala. — Each summer, a ritual millions of years old unfolds on this beach. A 300-pound loggerhead turtle drags herself out of the water for the first time since her birth, probably on the same beach, 18 years ago.

Under the moonlight, she kicks a 2-foot-deep hole into the sand, drops in a gleaming heap of eggs, covers it and then lumbers back out to sea. Two months later, 100 or more tiny turtles will scratch their way up through the sand, glimpse the shine of the moon and stars on the water that serves as some kind of celestial GPS, and head for the sea.

But the five remaining species of sea turtles that inhabit the Gulf of Mexico are facing not just a threat to that ritual, but even to their survival.

More than 350 turtles have been found dead or foundering along the Gulf Coast since the April 20 BP oil well blowout, a number wildlife biologists find alarming. At least 62 turtles have been found covered in oil. Rescuers in Gulfport, Miss., on Thursday were called to collect 20 turtle carcasses, the highest daily number they have ever recorded. Researchers say there is no way of knowing how many more turtles have perished at sea.

"Before, we didn't deal much with dead turtles. The calls we'd get were few and far between," said Tim Hoffland, director of animal care at the Institute for Marine Mammal Studies in Gulfport.

"But since this oil spill, it's just gone berserk. I'm getting calls from my people saying they can't even walk a quarter-mile on the beach without running into dead turtles. It's crazy."

The turtle deaths pose a complex forensics mystery for scientists, many of whom say they are not ready to blame it all on the oil spill. Many of the stranded turtles, for example — five times the number seen in recent years — have been caught by fishing hooks. Toxicology tests will try to determine whether a toxic algae bloom may have killed some of the animals.

"What we're doing is a CSI for sea turtles," said Michael Ziccardi, director of the Oiled Wildlife Care Network at University of California, Davis, who has been working in the field to help diagnose the deaths. "We're taking all of that information and pursuing the clues to try to see why these animals are dying."