When Bleakney began asking around, though, he learned that fishermen saw leatherbacks swimming in the waters off Maritime Canada regularly enough to call late summer "turtle season." The conclusion was inescapable, he wrote in 1965. "Evidently there is an annual invasion of our cool Atlantic coastal waters by turtles of tropical origin." Their southern roots were obvious from the few dead turtles he examined. One had a twig from a tropical mangrove tree stuck in its eye; others carried warm-water barnacles. Yet the leatherbacks were surviving, even flourishing, at temperatures that would kill other sea turtles. Stranger still was what he found inside them: Their huge stomachs contained masses of chewed-up jellyfish, stinging tentacles and all, and their gullets were lined with three-inch spines, angled inward to hold in all that slippery prey.
Bleakney eventually moved on to other studies—sea slugs were a special passion of his—but he never stopped marveling at the great beasts he had encountered on the fishing piers of Nova Scotia. "It was mind-boggling," he recalled in a recent interview with Canadian conservationists. "A reptile of that size, that lives in ice water, that can thrive on jellyfish." Almost 50 years later, scientists are still astonished at the leatherback's physical prowess, though today wonder is alloyed with a more modern sentiment: fear that even before we fully understand the leatherback and its epic life story, our own activities may be driving it to extinction.
Over the past 25 years, researchers counting the leatherbacks that crawl out to nest on tropical and subtropical beaches have sounded the alarm as the numbers plummeted: from tens or even hundreds of thousands of turtles on the Pacific beaches of Mexico and Central America to a few hundred today; from thousands in Malaysia to a handful. The International Union for the Conservation of Nature lists leatherbacks as critically endangered, and to list the many ways they die is to despair: tangled and drowned in fishing gear, choked on drifting plastic bags, struck by ships, slaughtered for meat, doomed even before they can hatch when nests are dug up and the eggs sold as food or aphrodisiacs. The leatherback lineage goes back a hundred million years—"it was on the beaches when T. rex was the primary predator," says Scott Eckert of the Wider Caribbean Sea Turtle Conservation Network at Duke University. Now, in some parts of its range, it is at the end of the line.
Spend time with researchers like Eckert, though, and you'll begin to see this turtle as a survivor. The leatherback can dive nearly a mile, swim across oceans, and keep itself warm in water close to freezing. It survives on a diet that few other creatures can stomach. And, most important, it keeps its options open. Other sea turtles are faithful to specific nesting beaches and feeding grounds, which makes them especially vulnerable as human pressures increase. But the leatherback can be more of an opportunist, exploiting favorable conditions—undeveloped nesting beaches, rich blooms of jellyfish—as it finds them. "These turtles treat the entire ocean as their pond," says Jeanette Wyneken, a biologist at Florida Atlantic University. The result is that, in some regions, leatherback populations are actually on the rise.