MONTEREY, Calif. — Scientists were documenting stranded sea turtles on California's beaches nearly 40 years ago when they noticed that leatherbacks — massive sea turtles that date to the time of the dinosaurs — were among those washing up on shore. It was strange because the nearest known population of the giants was several thousand miles away in the waters of Central and South America.
Their mysterious presence led researchers to a startling discovery. A subset of leatherbacks that hatches on beaches in Indonesia, Papua New Guinea, Vanuatu and the Solomon Islands were migrating 7,000 miles across the Pacific Ocean to the cold waters off the U.S. West Coast, where they gorged on jellyfish before swimming back. The epic journey stunned scientists.
"There are birds that go farther, but they fly. There's a whale shark that might swim a little further, but it doesn't have to come up for air. This animal is actually pushing water all the way across the Pacific Ocean," said Scott Benson, an ecologist with the National Oceanic and Atmospheric Administration's fisheries service in Monterey, who has studied the turtles for decades. "It's just a majestic animal."
But now, just as scientists are beginning to fully understand the amazing odyssey, the turtles are disappearing — and fast.
In less than 30 years, the number of western Pacific leatherbacks in the foraging population off of California plummeted 80% and a recent study co-authored by Benson shows a 5.6% annual decline — almost identical to the decline documented thousands of miles away on nesting beaches. About 1,400 adult females were counted on western Pacific nesting beaches, down from tens of thousands of turtles a few decades ago, and there are as few as 50 foraging off California, Benson said.
If nothing changes, scientists say, the leatherbacks — creatures that can weigh half as much as a compact car and have 4-foot-long flippers — could be gone from the U.S. West Coast within three decades, a demise brought on by indiscriminate international fishing, the decimation of nesting grounds and climate change.
"The turtles were there and we finally started paying attention," said Jim Harvey, director of San Jose State University's Moss Landing Marine Laboratories at San Jose State University and the study's co-author. "We got into looking at the story just as the story was ending."
The study provides critical, but devastating, new population information that doesn't bode well for the leatherbacks, said Daniel Pauly, a fisheries professor at the University of British Columbia and an international expert on reducing commercial fishing's impact on marine ecosystems.
"If you find the decline in one place, that might have a number of causes, but if you find the same estimate of decline in two places that indicates something much more serious," said Pauly, who was not involved in the study. "They are really in big trouble."
NOAA launched an aggressive initiative to save them in 2015 and will now release an updated action plan this month to inspire greater international cooperation in reducing the number of eggs pillaged on beaches and the number of Pacific leatherbacks entangled in commercial fishing gear.
The leatherbacks have likely been foraging off the U.S. West Coast for millennia. There are six other distinct leatherback populations scattered around the world but none of them complete such a long migration. As many as 60% of the leatherback turtles that hatch in the western Pacific Ocean make the trip to California — and scientists aren't sure why some do and others don't. Some go farther north, to waters off Oregon and even Washington state.
All the world's leatherbacks are under pressure, but the subset that migrates for months across the vastness of the Pacific faces unique threats that are particularly difficult for conservationists to counter. Leatherbacks in the eastern Pacific, which nest in Mexico and Costa Rica, are also experiencing a population crash from a sharp reduction in nesting beaches.
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