As expected, the turtles all headed north with the Gulf Stream, then most turned eastward around Cape Hatteras in North Carolina… The turtles weren’t single-mindedly heading toward the Azores, but looping around in small eddies and trying to avoid the coldest water. They also spent almost all of their time on the surface, and Mansfield suspects that this is to help stay warm.
It’s a familiar scene: baby sea turtles scampering down the beach just after they hatch. Some are eaten by birds, others by fish near the shore. As for the newborns who do survive the first few hours of frenzy, what are they up to once they’re in the ocean? Do they take breaks from riding the waves by floating idly in the sun?
So little is know about this oceanic stage -- which lasts at least 1 to 2 years -- that scientists call it the “lost years.” Over the decades, researchers have pieced together their natural history through various means: from ship observations and current patterns to brick-sized satellite tag and isotopes from tissue. They’ve created computer simulations of the journey, Science explains, and it goes something like this: Once off the continental shelf, the turtles eventually end up in a current, called the North Atlantic subtropical gyre, before returning to their birthplaces on the east coast of the U.S.
Now the technology is finally small enough. Katherine Mansfield from the University of Central Florida and colleagues remotely tracked young loggerheads (Caretta caretta) in the Atlantic Ocean using solar-powered satellite transmitters the size of smartphones. Using solar cells reduces bulk and weight due to batteries.
They collected 17 hatchlings (barely over an inch in diameter) from beaches in southeastern Florida and raised them until they were 3.5 to 9 months old. By then their shells were up to 7 inches long and big enough to have transmitters glued on. Then they were released them from a boat about 11 miles offshore.
The transmitters survived between 27 and 220 days, during which some turtles roamed as far as 2,700 miles to the Azores, most of the way to Portugal. Science describes:
Seven turtles made their way into the Sargasso Sea, inside the gyre. There they hung out in floating mats of sargassum, a type of seaweed, where they dined on crustaceans while staying hidden from predators. The dark plants also absorb heat from the sun. Temperature measurements from the transmitters on the shells were typically 4 to 6 degrees Celsius warmer than sea surface temperatures, study coauthor Warren Porter of the University of Wisconsin–Madison says in a news release.
Using buckets of sargassum and turtle models, the researchers showed experimentally how tangles of seaweed soak up energy from the sun, and that turtles can snuggle up in that heat to supercharge their growth. “Typically, if you have a 10-degree increase in your body temperature, your metabolic rate runs twice as fast,” Porter explains. “If you’ve got about half that, like the turtles do, you’re getting a 50 percent increase in your growth rate.”
The work was published in Proceedings of the Royal Society B this week.
Image: Jim Abernethy, NMFS permit 1551 via UW-Madison News