Turtle Trekkers: Atlantic leatherbacks scatter widely

Satellite surveillance of leatherback turtles in the Atlantic Ocean is posing tricky new questions for conservationists.

The data, the first of their kind to be published, reveal that these highly endangered turtles range widely over the Atlantic instead of sticking to “turtle corridors,” says Jean-Yves Georges of the National Center for Scientific Research in Strasbourg, France. That’s disappointing for conservationists, he says, because satellite monitoring of Pacific turtles in the 1990s revealed a well-defined migration corridor that helped focus conservation efforts. There’s no such luck in the Atlantic, Georges and his colleagues report in the June 3 Nature.

Another turtle-tracking paper in the same issue of Nature highlights a second complication. The leatherbacks dive mostly to the depths targeted by long fishing lines that hook commercially prized fish such as tuna, report Graeme Hays of the University of Wales in Swansea and his colleagues.

Leatherbacks are the biggest of the marine turtles, sometimes growing to a length of 6 feet. When a leatherback egg hatches on a beach, the little turtle works its way to the surf and paddles out to sea. What happens next has remained mostly unknown. Mating apparently takes place at sea, since scientists see only female adults on land, when they make forays onto beaches to lay eggs, says Georges. No one knows how long the turtles live, but speculation runs as high as 80 to 100 years.

The species as a whole is declining, says Georges. In 1982, rough estimates of nesting females worldwide reached 115,000. By 1995, the number had dropped to 34,500. The Atlantic population is the biggest remaining one and therefore represents the best hope for sustaining the species, he says.

Georges, Sandra Ferraroli, and their colleagues fitted small backpack transmitters onto 31 female Atlantic leatherbacks on beaches of French Guiana and Suriname. The team then followed the animals’ movements for up to 16 months. The turtles fanned out to the north and to the east, and several looped around the mid-Atlantic.

The same travel pattern showed up in the paths of the nine turtles that Hays and his colleagues tracked to study diving depth.

The difference between Atlantic- and Pacific-movement patterns in turtles probably stems from the differences in the food-rich zones where warm and cold currents clash, comments Frank Paladino of Indiana Purdue University at Fort Wayne. He welcomes the new studies as “important” for biologists trying to work out ways to keep commercial fisheries from inadvertently killing endangered sea turtles.