WHERE DID ALL THE TURTLES GO?

by Louis E.V. Nevaer

(PNS) MERIDA, Mexico -- The Yucatan Peninsula, home to the largest hawksbill nesting population in the Atlantic, is witnessing a dramatic drop in the nesting population of the hawksbill sea turtle, one of the rarest marine turtles in the world. For more than a month now hundreds of female hawksbill turtles have been arriving to lay their eggs in thousands of nests around the thumb-shaped peninsula. But for unknown reasons, only about one-third of the nests will be laid by the endangered sea creature this year compared to the numbers a decade ago.

Almost two decades of conservation efforts -- which began in earnest in 1989 after Hurricane Gilbert, the strongest hurricane on record in the area -- are now confronting a series of puzzling challenges that suggest the emergence of global warming as a principal factor in declining sea turtle populations.

"After 1999, nesting populations of the hawksbill turtle plummeted dramatically," Wally Cuevas, a scientist at Pronatura, the largest conservation organization in the Yucatan, explained. "From a high of almost 6,000 hawksbill nests that year, we are now down to just over 2,000 nests."

Scientists puzzling over the collapse in the number of hawksbills returning to nest have advanced several theories. The first pitted the rights of Native peoples against environmental concerns: Scientists observed that Yucatan's hawksbill turtles traveled around the peninsula, some venturing east toward Cuba, but most clinging to the coast as they travel south to Belize, Honduras and Nicaragua. "Even though Nicaragua is a signatory nation to conventions that ban the hunting of sea turtles, they still hunt thousands of turtles in their waters," Wally Cuevas, the Pronatura scientist, said. "The Miskito people live along the eastern Caribbean shores of Nicaragua and they are are some of the sea turtle hunters."

But the plausibility that the Miskito people are hunting the sea turtles into extinction is discounted for two reasons. First, the Green Turtle also visits Nicaragua's Caribbean shores, and has not experienced a decline in the number of nests. Second, the economic lives of the Miskito have not changed during this decade, making it improbable that they are now able to hunt significantly more turtles than they were a decade ago.

Another theory centered on the observation that there was a gradual shift of nesting grounds from the southernmost area of the Gulf of Mexico, in Campeche Bay, to the northeastern end of the peninsula, near Holbox Island, where the Yucatan Peninsula is closest to Cuba. "Adult turtles tagged in the Yucatan were found to have traveled to the Florida Keys to feed," Blanca Gonzalez, a researcher at Pronatura, explained. "Over the course of their long lives" -- sea turtles can live longer than a century -- "perhaps there were natural cycles in their nesting habits over the decades."

These theories -- increased hunting of the turtles by Native people, or natural cycles in selection of feeding grounds -- have been superseded by data that document a warming of the Gulf Stream and currents in the Yucatan channel. In 2005, the natural upsurge that lifts nutrients from the ocean depths along the Yucatan channel was delayed when the ocean's temperature in the region rose one degree Celsius. "The warmer currents affected many species, including the habitats of the whale shark," Wally Cuevas reported. "It was an oceanographic phenomenon that was widely followed by scientists from around the world, and it was something no one can satisfactorily explain."

The increased ocean temperatures are believed to be killing off sponge populations on which sea turtles feed. "The seven species affected are a very small fraction of the 75 to 100 species seen on a dive, but they are some of the largest and most obvious sponges on the reefs," E. R. Gammill, an expert on coral reefs, is quoted as saying in a 2005 report on Reef.Sponge.com. "These diseases are lethal, and given the high percentages of individuals infected, this is a major event for these species."

Researchers now believe that abandoned breeding grounds and shifting sea turtle populations reflect the diminishment of suitable feeding grounds for the hawksbill turtles.

A clearer picture is emerging from data collected from the turtles themselves. In August 2007, 10 satellite transmitters were placed on post-nesting hawksbill turtles. Scientists wanted to understand where the inter-nesting and foraging areas frequented by the sea turtles were located, and how the migratory corridors used between nesting seasons were changing.

One of the hawksbill turtles outfitted with a deployed satellite transmitter named "Hach" was released off Holbox Island on August 2, 2007. Hach wandered off the island, where stable ocean temperatures have not diminished the feeding areas, for almost seven months. Then, on March 2, 2008, she embarked on a southward migration along the eastern coast of the Yucatan Peninsula, until she reached the waters off Belize on April 6, 2008, where she appeared to settle to forage. This slow meandering followed the coral reefs between Cozumel Island and Belize that are the world's largest reef system after Australia's Great Barrier Reef.

After reaching Belizean waters, all contact with Hach ended. Perhaps the transmitter malfunctioned or, perhaps, Hach has met her end.

What is clear, however, is that Hach's behavior is consistent with other hawksbills that are abandoning the foraging areas of Campeche Bay Sound, where sponges are dying off due to higher temperatures.

The pattern that has emerged this decade -- of abandoned breeding beaches along the warmer waters on the western shores of the Yucatan Peninsula and increased activity in the northeastern tip -- signals a significant short-term change that has not been satisfactorily explained. "It could be that several trends are coalescing, such as warmer waters, diminished foraging areas, bycatch in the region, disappearing sponges in specific areas, that explain the loss of two-thirds of the nests seen a mere decade ago," Ponatura's Wally Cueva explains. "Time will tell if climate is the ultimate culprit."

The fate of the hawksbill portends how conservation efforts in the Yucatan will evolve. Since 1989, more than 315,000 live hawksbill sea turtles hatchlings have been released back into the now warming oceans. Yucatan's exalted position as a global leader in protecting marine sea turtles would come to an end -- if the turtles fail to show up and nest.