But then what? How do the surviving little turtles manage to swim great distances and sometimes buck contrary currents?
The most comprehensive perspective to date on precisely how young loggerheads navigate their transoceanic migration was published in two complementary papers produced by a research team led by Kenneth J. Lohmann, a marine biologist at the University of North Carolina at Chapel Hill, according to the National Science Foundation, which supported the research.
“Young turtles probably rely on a strategy of smart swimming to optimize their energy use during migrations,” Lohmann said. “The new results tell us that a surprisingly small amount of directional swimming in just the right places has a profound effect on the migratory paths that turtles follow and on whether they reach habitats favorable for survival.” He was quoted by the National Science Foundation, which added:
The team’s most recent paper argues that young loggerheads, which begin their migrations as tiny two-inch-long hatchlings, likely advance along their open-sea route through a combination of strategic swimming interspersed with passive drifting on favorable ocean currents. By swimming only in places where they are in danger of being carried off course and drifting passively in other areas where ocean currents move in the same direction that the turtles want to go, young loggerheads can migrate long distances on limited energy stores.
Lohmann studied turtles that were hatched in Florida. He speculated in another paper that the young turtles follow an inherited magnetic map that provides them with direction.
Only one in 4,000 turtle hatchlings survive to return to the Florida beaches. Those who do spend much of their time in the relative safety of the deep ocean where they travel in great circles until they are large enough to return to the shallow coastal waters, the research said.
Loggerhead turtles mainly are restricted to Costa Rica’s Caribbean’s beaches. Lohmann said that since each population of turtles has its own inherited magnetic map, turtles from one population could not be moved to replace a deleted population in another area.
Scientists studied these metal maps under laboratory conditions where they could control the magnetic field to which the turtles were subjected.
“The results also indicate that turtles obtain both latitude and longitude-like information from the oceanic magnetic field,” said David Stephens, a program director, quoted by the National Science Foundation. “They may thereby obtain much richer spatial representations from magnetic fields than do humans with their compasses.”
Lohmann also said that the typical practice of surrounding turtle nesting sites with wire mesh fences for protection might distort the ability of the hatchlings to navigate, the foundation added.