By Melissa Gaskill

Scientists have revealed that a mammoth effort to move thousands of turtle eggs from beaches around the Gulf of Mexico after the Deepwater Horizon oil spill may have saved almost 15,000 of the reptiles.

Between 25 June and 18 August, staff from the US Fish and Wildlife Service (FWS) moved more than 25,000 sea turtles eggs by road from northern beaches on the Gulf of Mexico to Kennedy Space Center on Florida's east coast. Throughout July, August and September, 14,676 hatchlings -- mostly loggerheads (Caretta caretta) -- were released into the Atlantic, says FWS biologist Sandy MacPherson.

Turtle hatchlings leave the beach of their birth to follow currents to mats of sargassum seaweed, remaining there a year or more, eating almost anything that passes by and breathing air at the surface. This behaviour made them particularly vulnerable to contact with, ingesting or breathing some of the millions of litres of oil floating in Gulf waters during peak nesting season. The risk prompted FWS officials to take action.

Trained individuals dug up eggs, placing them into hundreds of coolers prepared by Sea Turtle Conservancy, a charity based in Gainesville, Florida. Strapped into specially-made racks in private vehicles, the coolers were taken to a pick-up point, says executive director David Godfrey. FedEx vans with cushioned pallets, air-ride suspension and computer-monitored temperature control covered the remaining 500 miles to a 220 square-metre, air-conditioned warehouse at Kennedy.

Which way home?

Although officials deemed the project a success, it did generate controversy. Possible effects on survival rate concerned some biologists. The final hatching success rate was better than 50% (14,676 live hatches from 277 nests of avout 100 eggs each, or a potential 27,700) is roughly the same as that in the wild. But moving the eggs might have distressed or harmed the animals in unknown ways, says Robbin Trindell, a biological administrator at the Florida Fish and Wildlife Conservation Commission in Tallahassee. "We worked very carefully to construct the process to minimize possible impacts. But it was in and of itself an impact."

Biologists are also concerned about possible disruption of imprinting, the process that enables female turtles to return to nest on the beach where they hatched. Some think that imprinting occurs in the egg, others that it occurs as newly hatched turtles crawl towards the sea, and some believe that it may be a combination of the two. So it is unknown to which beaches turtles incubated primarily on northen Gulf beaches then released from beaches on the Atlantic Ocean will return.

Research1,2 suggests that imprinting relies at least in part on genetics. "I'm optimistic that letting the eggs incubate almost to the end, as the project did, means those turtles released on the east coast will ultimately will return to their natal beach," says Godfery.

An estimated 300 nests were left in place after officials determined in mid-August that the risk in the Gulf had greatly reduced, Trindell says. But data are not yet available on numbers of hatchlings from nests left in place.

Godfrey, who went offshore with project officials for that assessment, saw little sign of oil. "Most of the sargassum was drifting in from areas not exposed to oil, providing safe habitat for the turtles directly south of the nesting beaches," he says. "The question became whether we could still justify this massive relocation effort, which has risk despite all effort to avoid it. The project was the right thing to do, but it was right to stop when it did."