Of all the devastation in the Gulf of Mexico caused by the Deepwater Horizon blowout, no one single species is being directly affected as much as the critically endangered Kemp’s ridley sea turtle. Only 8,000 adult females nested in 2009, and the adult males are thought to be even fewer. Those that remain have been hit hard. Most of the surviving juveniles inhabit the waters 20 to 30 miles from shore, feeding and growing in the same currents and gyres that collected the bulk of the four million barrels spewed by the now capped well. There were confirmed reports of ridleys being burned alive in the pools of corralled, concentrated oil that BP had been burning off during the spill.

Almost every gravid female ridley lays her eggs on a single beach in Tamaulipas, Mexico, coming ashore in a unique mass-nesting event known as the arribada—the arrival. Kemp’s cousins in the Pacific, the Olive ridleys, also do this, but the other five sea-turtle species (and a small percentage of ridleys) are solitary nesters and don’t always return to the same place. The arribadas happen at Rancho Nuevo—a beach 900 miles southwest from the blowout. It’s only 200 miles south of Brownsville, Texas. Not a bad drive, only I’m told it’s too dangerous because three warring factions of narcotrafficantes—the Gulf cartel, the Zetas (former hit men of the cartel), and a local mafia called La Maña—have been having shoot-outs along it. Instead, I fly to Tampico, the sleepy port where the opening scene of The Treasure of the Sierra Madre was filmed, which is 60 miles south of Rancho Nuevo. (Not that Tampico is immune to the violence; the week before I arrive, the naked bodies of five policemen were found hanging from one of its bridges, I am told by a fellow gringo who narrowly escaped being shaken down at one of the narcos’ impromptu roadblocks right in the city.) I’m met at the airport by two people from the federal agency that manages Mexico’s protected areas, and they whisk me to the nearby Hampton Inn for the night.

In the morning we are driven to the Rancho Nuevo beach reserve by its director Dr. Gloria Tavera. Its 20 miles of wild white sand are patrolled three times a day by guards on A.T.V.’s, and 20 times a day or more during nesting season. Dr. Tavera tells me that the arribadas are over, but that the white ping-pong-ball-size eggs, having incubated for 45 days, are starting to hatch.

Sure enough, at five a.m. on the second morning, we jump onto four-wheelers and bomb down to the South Corral, four miles from the camp, where dozens of the 800 nests from the June 3 arribada are erupting with hatchlings, about 90 per nest. The babies are three inches long and look like black rubber-toy turtles. They crawl down to the surf and, as soon as they hit the water, their angled forelimbs begin to flap wildly. Then they’re pulled into the breaking waves by the undertow and are off, on their own, into the great unknown. Guided by pure instinct, fueled by the remaining yoke in their waterproof belly sacs, they will swim straight out for five days or so until they hit the mats of sargassum, a golden-brown, free-floating marine algae (these lines of sargassum are often only 20 or 30 feet wide, but can extend for miles, and offer cover and food for the hatchlings). We don’t know how many hatchlings will survive to adulthood, but the most common ballpark estimate is only one in a thousand. Many will be picked off by sharks, many other species of fish, dolphins, and sea birds. Everything wants to eat them. But many more than usual will die when the clockwise currents of the Gulf carry the turtles directly up into the area contaminated by the Deepwater Horizon spill. “The internal damage from the hydrocarbons to the organs of the ridleys could make them unable to reproduce,” Dr. Tavera tells me. “That would mean extinction. But nobody knows.”