Leatherback turtles are the wandering type, undertaking far-flung ocean migrations of thousands of miles. What scientists who follow these long-lived creatures didn’t know, though, was just how many different routes they travel, and how far they journey before returning home. These are critical pieces of information for protecting the turtles, whose numbers are dropping. So Matthew Witt says he and his international team affixed trackers to the turtles and revealed the routes of their great sea voyages:
“What we’ve shown is that there are three clear migration routes as they head back to feeding grounds after breeding in Gabon, although the numbers adopting each strategy varied each year. We don’t know what influences that choice yet, but we do know these are truly remarkable journeys.” [The Guardian]
Gabon, in West Africa, is the home base for this largest breeding group of leatherbacks—it’s where they nest and lay their eggs. Witt’s team tracked 25 female turtles, all of whom followed one of those three general routes: out to the middle of the Atlantic and then back, down the African coast to the temperate South, or even all the way across the ocean to South America.
One female was tracked making a 7,563 kilometer (4,699 mile) journey traveling in a straight line across the South Atlantic from Africa to South America, said [Witt]. At a pace of 50 kilometers a day, that trip took about 150 days of consistent swimming, he said. [AP]
Over the course of about five years, these turtles swim out to these eating grounds, build up their strength, and then return to Gabon to mate. Because the turtles can live 50 years, this cycle repeats itself numerous times. But why do these females pick one of the three routes over the other two? Witt can’t say for sure, but perhaps they remember the path they took when they were young hatchlings and had to go with the ocean’s flow, and repeat that journey as adults.
The global population of leatherbacks is not known, although estimates based mainly on data from nesting sites suggest a decline of up to 80% between 1982 and 1996. In Malaysia, a site that had once supported 10,000 females contained just 37 in 1995. Conservation initiatives appear to have halted the decline in some sites. [BBC News]
Egg poaching has decimated some turtle populations around the world. That affects the Gabon turtles to a lesser degree because their hatching group is a national park. However, they are not free from the specter of fishing—particularly, finding themselves caught in fishing nets. That’s why scientists wanted to map out the turtle paths; it allows them to see the danger areas through which they swim.
Tracking technology has offered this new window to the travel routes of many animals that undertake globetrotting migrations. Here at 80beats we’ve previously covered the meanderings of humpback whales and tiny terns that fly 44,000 miles. If you want to read the full details about Witt’s turtle project, the study is presently available to read free at The Proceedings of the Royal Society B.
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Image: Wikimedia Commons (1896 illustration)