Up from the Sand: In French Guiana, Giant Leatherback Turtles Emerge from the Surf in an Ancient Ritual of Life
Gilbertas, Bernadette, International Wildlife
Enormous and all aglow, the moon slowly makes its appearance at the oceanside Indian village of Yalimapo in French Guiana. Dividing the shadowy darkness, it spotlights wave crests, leaving the troughs unlit. In this mottled surf, an indistinguishable bulge of water forms, disappears, then swirls closer. Suddenly, a gigantic and shiny mass raises itself onto the shore. The leatherback sea turtle has arrived.
For 27 years each night in late spring, scientists have watched these endangered reptiles descend on the beach at Yalimapo on the northern shoulder of South America. They will lay their eggs in the sand, and a mysterious cycle of life will begin again, but not before a gauntlet of perils has conspired to make this great ocean beast a symbol of troubled seas.
Of the eight sea turtle species, the leatherback is the largest. Individuals average about 440 kilograms (970 lbs.), and their soft backs -- which consist not of shell but of an assembly of small, very fine bony plates supporting a layer of dense, skin-covered fat -- can reach up to 1.9 meters (6.2 ft.) in length.
Little is known about the leatherback's life at sea, except that it visits all the world's oceans, lives at great depths and feeds primarily on jellyfish. Leatherbacks affixed with radio beacons have dived up to 1,000 meters (3,280 ft.). They can swim thousands of kilometers in a few weeks, resurfacing every four minutes to breathe, and have been tracked in cold waters from Newfoundland south to the southern Chilean coast. Analysis of stomach content in beached individuals shows that in addition to jellyfish, their diet is composed of fish, various invertebrates and crustaceans.
The turtles mate in their home sea. Then, from March to July in the Northern Hemisphere and from November to February in the Southern Hemisphere, the females come ashore to lay their eggs. Close to 160 nesting sites are catalogued around the world -- from Gabon in Africa to Mexico in Central America, with less significant sites in Southeast Asia where human predators have long ravaged nesting populations. Hattes Beach at Yalimapo is now the species' most important nest-building site.
Once a female exits the choppy waves here, she heads for dry ground above the tidal mark. After sweeping sand vigorously on the chosen nesting site with her front feet, she is then all but motionless. Only the back feet, curved like two spoons, move back and forth alternately to dig a hole.
The pitlike nest, relatively elaborate, can reach up to 80 centimeters (2.5 ft.) deep and includes an incubation chamber at the bottom. Masking the entrance of the pit with her foot to hide her activity, the female lays about 60 to 70 white eggs, round and fat like billiard balls, dropping two or three at a time. Then come 30 more eggs, sterile and smaller in size. Their role is not yet clearly established, but they could be for protection of the fertile eggs or to supply moisture.
With laying complete, the female fills up the hole and presses down the sand. For another half hour, she methodically sweeps the nest to hide the entrance. Finally, after almost two hours have passed on the moonlit beach, she returns to the sea. In about 10 days, she will come back to lay another 100 eggs nearby. Altogether, she will do this seven or eight times in a season.
After 50 to 90 days of incubation, the eggs are ready to hatch. The gender of the turtles depends on the warmth of the sand and the incubation temperature. Below 29.5 degrees Celsius (85.1 F), the eggs become males, above this, females. After the first little turtle tears the membrane of its egg using a beak on the end of its snout, the other newborns begin to hatch, abandoning their eggs in unison. …