New tags may help diagnose turtle losses

Up to 8 feet long and weighing in at 1,200 pounds or more, the leatherback is the world's largest turtle-and one of the most unusual. Because leatherbacks are endangered globally, conservationists are anxious to help protect these behemoths of the high seas.

 And a tiny, biodegradable screw may help.

 Earlier this month, Molly Lutcavage of the New England Aquarium in Boston affixed a small radio transmitter to the back of a female leatherback, just minutes after the turtle had laid a clutch of eggs on a beach in Culebra, Puerto Rico. Lutcavage anchored the pocket-pager-size device to the animal's shell, or carapace, with screws normally reserved for orthopedic surgery patients. She's hoping the transmitter-the smallest satellite tracking device ever used on a sea turtle-will remain in place for the better part of a year, sending signals whenever the leatherback surfaces.

 Wildlife biologists have long known the sites where adult females come ashore to lay eggs. However, "we have almost no data on leatherbacks in non-nesting areas," observes Samuel Sadove of Long Island University in Southampton, N.Y., and director of leatherback research in Culebra. "A whole portion of the leatherbacks' life cycle-probably the most significant portion-is spent feeding [at sea] or traveling to and from feeding areas," he says. The paths that the far-ranging, virtually warm-blooded animals take and the company they keep remain "huge unknowns."

 Meanwhile, the species is dying out. "To say that leatherbacks are disappearing at a staggering rate, especially within the last 7 to 10 years, is an understatement," Sadove maintains.

 If scientists could map the turtles' high-seas trek with long-lasting transmitters, they might learn where the animals are most vulnerable, helping regulators design programs to protect them effectively. Until now, the leatherbacks' unique shell has thwarted most long-term tagging efforts.

 While biologists can glue transmitters to the bony shells of other turtles, the oily, flexible skin that covers the thin, loosely fused, bony plates in a leatherback's carapace resists adhesives. Indeed, Lutcavage spent a semester with chemical engineering students at the Massachusetts Institute of Technology, having them test every glue they could find. The bottom line: "Nothing worked."

 Though some biologists have used bolts to attach transmitters to leatherback shells, the metal causes irritation. Eventually, the shell breaks around the bolt-dropping the transmitter and disfiguring the animal.

 The idea of trying biodegradable screws came from Anders G.J. Rhodin, an orthopedic surgeon in Lunenburg, Mass., who has made turtle biology his avocation. The leatherback supplies blood to the bone in its shell "in a way that's characteristic of mammals, but totally different from all other turtles," he says. So Rhodin suggested that Lutcavage take a mammalian approach, piercing the bone with roughly half-inch-long screws made of a synthetic polymer that slowly dissolves. She used screws provided by Instrument Makar of Okemos, Mich.

 Threaded through each screw is a nylon suture that ties on the $4,000 transmitter. "As the screws dissolve," Rhodin explains, "they are replaced by bone" that continues to anchor the sutures until they weaken and release the transmitter. Once unburdened, a turtle will swim away with an intact shell, he predicts.

 If this approach works, Lutcavage says, her goal will be to tag juveniles and males that are accidentally hauled in by fishing fleets at sea. Indeed, while other sea turtles that encounter fishing gear frequently drown when they get hooked or held underwater, leatherbacks more often survive encounters with fishermen because, as jellyfish feeders, they ignore the hook-ridden bait.