A hawksbill turtle equipped with a satellite tag returns to an estuary in… (Alexander Gaos )
Scientists have made the surprise discovery that a population of critically endangered hawksbill turtles, thought to have been wiped out in the eastern Pacific from Mexico to Peru, has survived by occupying a novel habitat — mangrove estuaries — rather than coral reefs where they have been slaughtered for their exquisite shells.
The finding is particularly significant because it suggests a potentially unique evolutionary trajectory, said Alexander Gaos, lead author of a report being released Thursday in the online scientific journal Biology Letters.
"We now know there are about 500 adult female hawksbill turtles in at least four inland mangrove saltwater forests in El Salvador, Honduras, Nicaragua and Ecuador," Gaos said in an interview. "They are among the last remaining strongholds for this species. If these estuaries are destroyed by development of aquaculture and housing, the hawksbill turtle will disappear with them … that's more hawksbill turtles than anyone thought were left, but still very few."
Scientists are collaborating with coastal villages in the vicinity of the mangroves to "create community-based conservation programs," said Bryan Wallace, director of science and strategy for Conservation International's marine flagship species program. "All egg clutches are being relocated to hatcheries," he said.
Until now, Eretmochelys imbricata was believed to prefer open coasts and coral reefs in the Caribbean and Indo-Pacific regions. As recently as 2007, hawksbill turtles were considered nearly wiped out, based on research and scarce sightings.
To map the movements of the eastern Pacific's remnant turtle population, a team of scientists attached satellite transmitters to the backs of 12 adult females. Gaos said 83% of those turtles remained settled in the mangrove forests, contrary to the long-held notion that hawksbills are coral reef dwellers.
"These particular hawksbills spend the majority of their lives nesting and foraging in the mangroves," said Gaos, executive director of the nonprofit Eastern Pacific Hawksbill Initiative. "We still do not know why they adapted to this habitat, but we believe it may be due to a lack of coral reefs in the region."
Although adaptation has become a central concern of climate scientists because of global warming, there is no apparent connection between the habitat change and climate shifts, Gaos said.
"It is possible that global climate change could, at some point in the future, drive marine turtles into estuaries such as these," he said. "However, at this point, we do not believe that what we are seeing is a pattern that occurred over the past 20 to 30 years."
The findings support the results of a survey released last year showing that the largest known rookeries of the turtle, categorized as "critically endangered" by the International Union for the Conservation of Nature, are in El Salvador and Nicaragua.
The earliest reports of the hawksbill turtle date to diaries of 18th century pirates and missionaries who chronicled the growth of "tortoiseshell" industries in northwest Mexico.
Weighing about 100 pounds, with shells about 3 feet in diameter, hawksbill turtles have been killed by the millions for their shells, used to fashion folk art, eyeglasses, cigarette lighters and jewelry. Scientists believe the species is within several years of extinction. There is no accepted estimate of its worldwide population. It has been on the U.S. list of endangered species since 1975.
"We now have a new set of habitats to search for the species and fine-tune recovery efforts," Gaos said. "There's more hope now than ever for this rare and imperiled creature."