FIDEL CASTRO MAY go to hell for the things he has done, but if he gets into heaven it might be for what he hasn't done—what has not been despoiled, destroyed, polluted, or paved. After that ear-busting visit to María la Gorda, I had taken my rental car even farther west, out the last, long, pot-holed road in Cuba, to the westernmost point in the West Indies, Cabo San Antonio. Here was one of the Caribbean's last refuges for a true dinosaur, Chelonia mydas, the oceangoing green turtle.

The land was flat, scrubby, and bitter, and only tiny iguanas—"shore puppies" in Cuban parlance—moved through the brush. After hours of searching, I spotted not a turtle but a lean, sunburned Cuban in a tight swimsuit and a cowboy hat. He ambled up from the beach, as surprised to see anyone here as I was.

Rolando Díaz is a 42-year-old wildlife technician; the government deploys researchers like him and students from the University of Havana to camp out in 15-day stints guarding eight beaches where the green turtles breed. He showed me his camp: a Eureka tent in the sea grapes, an AM radio, and a cistern for water. "Here we are trying to save turtles," Rolando said, "so my grandchildren can see them. We've seen as many as 130 turtles on this little beach, but there aren't many this year. Something is wrong. Normally they are here by now."

The biggest threat, he said, was not development or predators but ordinary Cubans. Once, when technicians missed a single 15-day stint, hungry locals ate about 70 turtles. "We come here from Havana and tell people, ‘Don't eat turtles, they are almost gone,' " Rolando explained. "And they say, ‘So are we.' The majority here live on turtles. It is hard to do conservation in a poor country. It's hard to be an ecologist in Cuba." His salary was 350 pesos a month, or $13. His own brother, head of the turtle program, had gone to a conference in Greece and never come home.

I stood the beach vigil all that long night with Rolando. The females come ashore most nights in the summer, dragging their dinosaur carapaces to the tree line and scooping out huge bunkers to bury a hundred or more eggs. One mother had come up last night, and Rolando showed me her four-foot-wide path through the sand, and the stick he used to mark the new nest. Aside from humans, dogs, feral pigs, gulls, rats, and even crabs would root up the eggs.

At 1:30 A.M., the night clouded over, hiding the moon. The turtles preferred this total darkness, but it made every rock in the surf look like a carapace, and clouds of mosquitoes emerged to torture me. Before retiring, Rolando warned me not to lie down, but I did, and I discovered why: The sand was infested with jejere, mites that bit me until blood ran down my ankles. From 2:30 to 3:30 I tried napping on a smooth driftwood plank, then awoke with a yelp when a red crab bit my toe.

Rolando emerged from his tent again, and we sat listening to the waves break. He had the eloquence of a man who has been waiting for a conversation for 15 days. The ocean was "my friend the sea. It is beautiful above and below. That's my world, the beautiful sea. If I could be reborn, I'd be a fish, a whale, even a shark. I love them all."

"How much would tourists pay for that?" Rolando asked. "To have a crab touch their toe? Fifty dollars? Everyone wants nature. They could come here and see turtles and live in tents …"

After a while he went back into the Eureka, but I stayed, walking the empty beach, hours without light, traffic, people, boats, or anything but the sea and its mysteries, above and below.

I never saw a turtle. At 5:15 A.M., when the first crack of purple appeared in the east, I went to my little rental car, twisted across the front seat, and went to sleep.

Everything will be better tomorrow.