OnEarthBy OSHA GRAY DAVIDSON, OnEarth magazine

The Kemp's ridley sea turtle, one of the great success stories in marine conservation, is among the creatures most threatened by the Deepwater Horizon oil platform spill on the Gulf Coast.

Biologists sometimes call Kemp's ridley "the Gulf's sea turtle" because it typically spends its entire life in the Gulf of Mexico. All other species tend to roam in and out of the Caribbean. Just a century ago, this smallest of all sea turtle species was relatively common. In 1947, as many as 40,000 females came ashore on a single day to the turtle's major nesting beach in northeastern Mexico.

Their eggs were considered an aphrodisiac and were gobbled up by the tens of thousands in Mexico. Adult ridleys were accidentally caught by U.S. and Mexican shrimp trawlers and drowned. By 1985, biologists counted a total of just 702 ridley nests left on the coast. The marine reptile was going extinct.

But the little turtles made a big turnaround, says Dr. Donna Shaver, chief of sea turtle science at Padre Island National Seashore in Texas.

"It's taken a lot of work by a lot of people," Shaver said this week. "But over the years, the number of Kemp's ridley nests on the Texas coast has grown exponentially."

In 2005, there were 50 nests in Texas, most of them on Padre Island. By the next year, that number had doubled. Last year, Shaver recorded nearly 200 nests on Lone Star beaches. In Mexico, still the primary nesting site, biologists found 20,000 nests in 2009.

Then came the April 20 explosion on BP's offshore rig, which left 11 workers presumed dead and caused what now appears to be the largest-ever release of oil into U.S. waters, eclipsing even the 1989 Exxon Valdez disaster — a flow that continues with no end in sight.

Effects of the spill and other factors

"At this point, I can't say if any turtles have died due to oil from the rig explosion," says Andre Landry, Jr., a turtle expert at Texas A&M. "That doesn't mean they haven't. And it certainly does not mean that they won't."

Landry directs his college's sea turtle and fisheries ecology research laboratory. When I reached him yesterday, Landry was still on the water, returning from a nesting patrol north of Galveston Island. He hasn't spotted any ridley nests yet this year, but the season, which generally starts in early April, is just beginning. It was delayed by a record cold snap this winter. Although Landry didn't find any nests yesterday, he recovered two young ridleys — both dead.

"We've had a rash of deaths here in Texas — 30, probably approaching 40 turtles by now," he says. Most have been ridleys, but all sea turtle species are listed as endangered or threatened. It's impossible to say what's causing the spike, which began several days before the oil spill. The number of strandings — when sea turtles come ashore sick, injured, tangled in fishing gear, or dead — varies from year to year.

Both Landry and Shaver are concerned about the oil gusher's impact on the ridley's chances of survival in the coming years. No one knows how much oil will leak before the well is capped. The direction and speed of the drifting oil changes with the wind and weather. Even if most nesting beaches are spared a direct hit by large amounts of oil, Kemp's ridleys aren't necessarily safe. Although they tend to stay within the Gulf, ridleys migrate from their nesting beaches to distant foraging grounds. Many of the turtles native to Padre Island, and even some that nest in Mexico, feed in the shallow waters near shore, from Texas across the Gulf coast to the Florida Panhandle. Those are the areas most likely to be hit hard by the oil spill.

"One of their favorite foraging spots is immediately west of the Mississippi River," says Landry. "If we have a wind or current change, we may see them fouled."

Danger lies on the surface of the water

Oil in the water column (below the surface) isn't much danger to the turtles. Unlike fish that get their oxygen from water, sea turtles breathe air. The danger comes when they surface to breathe. If they happen to surface in an oil slick, turtles are liable to swallow or inhale oil, which could be fatal.

Landry focuses on another potentially more damaging problem caused by the oil: the destruction of the ecosystem. "Kemp's ridleys eat crustaceans, primarily blue crabs," he says. "If the oil contaminates the habitat that sustains the crabs, that will almost certainly affect the turtle's ability to survive."

Another threat could also last for years. Ridleys don't reach sexual maturity for at least a decade. During their first several years after hatching, young turtles drift on mats of seaweed that form in the gulf. The same combination of forces that forms these clumps also channels oil. Young turtles can easily get caught in the sticky mat of seaweed and oil and drown. (These same floating habitats are already dangerous for young turtles because of the enormous amounts of plastic garbage they contain. In a recent Florida study, 100 percent of small loggerhead turtles found on these mats had ingested plastic.)

Despite all the new threats posed by the oil disaster, the Park Service's Donna Shaver tries to remain optimistic about the species she has championed for three decades. After all, she was there when Kemp's ridley sea turtles were nearly wiped out in the mid-1980s. That gives her hope that they can continue to be survivors, even under the worst of circumstances.

But no one knows if those hopes are justified — and it will be years before we get an answer.

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Editor's note: OnEarth correspondent Osha Gray Davidson is the author of the book Fire in the Turtle House, which tracks a mysterious disease threatening the survival of sea turtles worldwide.

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