This is the third year that Blanco, an Argentine graduate student at Dexler University in Philadelphia, Pennsylvania, has spent the November-to-March leatherback nesting season at Playa Grande.
She and her colleagues cataloged up to 80 females and about 400 nests this season.
That number is up from 58 turtles that came ashore during the 2006-to-2007 season, but fewer than the 108 that were seen in the 2005-to-2006 season.
Leatherbacks do not nest every year, so the reptiles' cycle of nesting populations repeat about every three years.
The overall number of turtles nesting at Playa Grande, however, is down dramatically from the 1980s, experts say.
"There used to be more than a thousand turtles on the beach every night, but now we see at most four to five turtles [a] night," Blanco said.
Twenty years ago, the poaching of turtle eggs—considered a delicacy in much of Central America—was so rampant that every egg was taken during Playa Grande's nesting season.
"We're now seeing the results of that poaching 20 years ago," Blanco said.
Poaching was eliminated after Playa Grande became part of the Las Baulas National Park in 1991.
Since then, the beach has been under strict surveillance by park officials and nonprofit groups.
"This national park fulfills an important function to protect one of the species—the leatherback turtle—that is in critical danger of extinction," said Rotney Piedra, the park's director.
Young leatherbacks face bleak prospects even without human threats.
Leatherbacks lay about 70 eggs in a one-time process that takes up to two hours. Afterward they return to the sea and take no further part in the care of their offspring.
Only a few of the eggs produce hatchlings. Once they break out of their shells at night, the babies must survive a dangerous crawl to the water, with crabs, seagulls, and hawks snagging many along the way.
Researchers don't know much about what happens to the surviving hatchlings after they enter the ocean, but it's believed that only a few in every thousand survive to become adults.
At least 800 hatchlings have been born at Playa Grande since November 2007.
Eggs found below the high-tide line or at risk of being trampled by beachgoers are taken by conservationists to an enclosed nursery set up on the beach.
Recently Blanco showed a visitor three hatchlings that had come out of the nursery that morning. She kept them in cool shade inside a shed at the group's compound.
"As soon as it gets dark again, we will release them onto the dry sand and let them crawl into the water," she said, carefully handling a tiny turtle, its front flippers sticking to her latex gloves.
Many of the beaches where turtles once nested are now lined with hotels and resorts.
The reptiles are disoriented by lights and noise, which prevents them from finding their way back into the sea.
Tamarindo, a popular tourist town next to Playa Grande, once had an important nesting beach, but no turtles have been seen there in more than 15 years, experts say.
"Lighting, sand mining, and pollution caused by coastal development are all seriously damaging not only to sea-turtle nesting beaches but also the overall environment," said Alec Hutchinson, director of nesting-beach projects for PRETOMA, a Costa Rican sea-turtle advocacy group.
Las Baulas National Park, where Playa Grande is located, has a zone measuring 410 feet (125 meters) from the high-tide line that must be protected from any development.
Under a new law, Costa Rica's government has ordered the expropriation of an undisclosed number of properties that are located inside the no-building zone on land totaling 113 acres (46 hectares).
The government plans to pay about U.S. $500 million in compensation to landowners, mostly Europeans and U.S. citizens—some of whom have resisted the decision.
The process has been bogged down for several years, but in late February, Costa Rican President Óscar Arias finally signed six of the expropriation decrees in a move that environmentalists call a victory.
"We must save every single nest, and this can only be attained by preserving their natural nesting habitat from human alterations," said Randall Arauz, PRETOMA's president.
"The more pristine the environment, the better it is for the turtles."
However, protecting the beaches alone will not ensure the survival of the leatherbacks, conservationists say.
In fact the animals' biggest threat may be longlines, where they can get caught in hooks intended for other marine life and drown.
"By saving only the beaches, we will make sure the longliners catch the leatherbacks," Arauz said.
(Related: "Reopening Hawaii Fishery May Harm Sea Turtles, Experts Say" [April 1, 2004].)
He advocates creating more marine protected areas and temporary longline fishing closures in areas where sea turtles are common.
Different types of hooks are being developed that may reduce sea turtle catch, but the new designs could increase the catch of other endangered species, such as sharks.
"Relying on hook designs alone is not going to benefit sea turtles or other organisms unless coupled with an efficient reduction of fishing effort and training of fishermen, so that they learn how to release turtles from fishing gear," Arauz said.
Hutchinson, PROTEMA's nesting director, said more conservation work needs to be done.
"To successfully mitigate threats to sea turtles and other marine life," he said, "it is necessary to look at the big picture and create a holistic approach to conservation that protects turtles both in the water and on the beach."
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