After baby loggerhead turtles hatch, they wait until dark and then dart from their sandy nests to the open ocean. A decade or so later they return to spend their teenage years near those same beaches. What the turtles do and where they go in those juvenile years has been a mystery for decades. Marine biologists call the period the “lost years.”

Following the tiny turtles has proved to be difficult. Researchers tried attaching bulky radio tags, but the devices impeded the turtles' ability to move. The size of the tags shrank over time, yet the batteries remained stubbornly large. Then Kate Mansfield, a marine biologist at the University of Central Florida, got the idea to go solar.

She saw that other wildlife researchers were tracking birds with small solar panels. So her team decided to use similar tags with a matchbook-size panel, bringing the weight down to that of a couple of nickels. The researchers also figured out how to attach the tags securely without warping the turtles' shells, an idea that came from a team member's manicurist. She suggested acrylic lacquer as the base coat to hold silicone glue, which can grow with the turtles.

Mansfield's group tagged 17 turtles that ranged from three to nine months old. The scientists then plopped them—the biggest, seven inches long—off the coast of Florida and into the Gulf Stream, which is part of the North Atlantic Gyre, a system of currents that flows clockwise up the U.S. East Coast. Bryan Wallace, a marine biologist at Stratus Consulting and Duke University who was not involved in the work, said the study is likely to be remembered as a seminal paper in sea turtle biology. It was published in April in Proceedings of the Royal Society B.

“Based on long-standing hypotheses, we'd expect that the turtles would remain in the outer gyre currents and head toward the Azores,” an archipelago off Portugal, Mansfield says. As the team tracked subjects over a few months, however, it found the turtles did not stick to this itinerary. Many of them swam into the center of the gyre, where seaweed accumulates. The turtles forage in the seaweed and use it for shelter.

The turtles also traveled faster than predicted, reaching the waters off North Carolina within three weeks. At that speed, they could easily reach the Azores in less than a year. Although that timeline agrees with estimates based on passive drifting, the turtles take many side trips, which means their actual speed of locomotion is impressive.

Another surprise: the tags' temperature sensors consistently read several degrees higher than the turtles' local water temperature, which suggests that the seaweed mats keep these cold-blooded reptiles warm, an important condition for growth.