Endangered Turtle Makes Record 647-Day Journey
for National Geographic News
|January 24, 2008|
A leatherback sea turtle recently completed the longest recorded migration of any sea vertebrate: 12,774 miles (20,558 kilometers) across the Pacific Ocean.
The journey, tracked by satellite, provides the first record of a trans-Pacific migration by a leatherback.
The giant reptile began the trek in Indonesia's warm tropical waters in the summer of 2003.
Traversing the equatorial line, it encountered strong, swift currents before passing close to Hawaii's Kauai island.
Along the way, the turtle may have encountered swordfish, tuna, and other migrating leatherbacks returning after a successful foraging season off the North American coast.
Some of the turtle's dives sent it plunging into the cold darkness 3,300 feet (1,000 meters) below the ocean surface.
After 647 days of swimming, the animal finally reached the cool waters of the Pacific Northwest—where a feast of jellyfish awaited.
The turtle made this "epic journey spanning tropical and temperate waters of the Pacific just to eat jellyfish off Oregon," said Scott Benson of NOAA's Southwest Fisheries Science Center in Moss Landing, California.
Benson is a co-author of the study published recently in the journal Chelonian Conservation and Biology.
The leatherback sea turtle is the world's largest turtle. It can grow as long as six and a half feet (two meters) and weigh up to 2,000 pounds (900 kilograms).
Leatherbacks are also "patch feeders," eating only when food is abundant.
"Like large whales, their immense size allows them to store [food] reserves and travel great distances without eating regularly," Benson said.
"Although they are hatched at tropical beaches, they have unique adaptations for a reptile that enable them to tolerate cool, temperate waters."
Even so the estimated number of reproductive females has declined steeply in the past 25 years, and leatherbacks in the Pacific face extinction soon, according to Benson. The species is listed as critically endangered by the World Conservation Union (IUCN).
"Leatherback populations face threats from egg harvesting, fishery bycatch [unintentional marine life caught during fishing], ingestion of marine debris, and in some areas, direct harvest," he said.
"Most of the large nesting beaches in the western Pacific are now protected by the local people who share these beaches with the leatherbacks, [but] we must also ensure that foraging grounds—and the migratory routes that connect them to nesting beaches—are safe," Benson added.
(Related news: "Glow Sticks May Lure Sea Turtles to Death" [April 27, 2007].)
Tracking Every Move
Little had been known about the migratory routes of leatherbacks that nest in the western Pacific region, including some of the largest remaining nesting populations in Indonesia, Papua New Guinea, and the Solomon Islands.
Benson and his colleagues used satellite technology to track nine leatherback turtles from a previously unstudied population nesting on the beaches of Jamursba-Medi in the Indonesian province of Papua.
Transmitters were attached to nesting females using a backpack-like harness made of nylon webbing.
The transponders sent signals to satellites every two days, allowing the scientists to record diving behavior, sea temperatures, and high-resolution geographic positions.
While three animals traveled westward into the South China Sea, one turtle moved north to the Sea of Japan.
The remaining turtles traveled eastward, though only the one animal made it all the way across the Pacific Ocean.
"We had always assumed the leatherbacks occasionally spotted off California were from Mexico," said study co-author Peter Dutton, also with NOAA's Southwest Science Fisheries Service.
"Now we realize that conservation efforts need to be expanded across the ocean to the western Pacific breeding sites."
(Related news: "New Marine Conservation Area to Span Four Nations" [February 26, 2004].)
Satellite evidence suggests that the turtle with the longest transmission record (695 days) may have been captured at sea and brought on board a vessel.
Michael James, a leatherback turtle expert at Dalhousie University in Halifax, Canada, was not involved in the research.
"This work is particularly significant because you're dealing with a species that is highly imperiled," James said.
"A lot of work is focused on nesting beaches, and that's very important, but it's equally if not more important to figure out what the animals are doing the other 99.9 percent of the time—and that's really where tools [such as] satellite telemetry [are] key," he said.
"Unless you can identify where the animals are outside of the nesting season, you really don't know the sorts of impacts that may be affecting them."
"Leatherbacks are global mariners that don't recognize international boundaries," NOAA's Benson said.
"They transit through waters of multiple nations as well as international waters and can face threats from many human activities."
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