Sea turtles can navigate themselves around the world with their own equivalent of the global positioning system (GPS), scientists believe after new research.
Turtles are able to navigate across thousands of kilometres of open ocean relying on the Earth’s magnetic fields. Scientists have wanted to know how turtles make vast Atlantic journeys, returning to specific feeding sites with pinpoint accuracy.
According to a recent report in the journal Nature, tests show that the turtles can locate their position from subtle variations in the Earth’s magnetic field.
The turtles’ navigation aid is the equivalent of the GPS (global positioning system), but instead of relying on satellites in space, it depends on magnetism.
Researchers in the United States built a cube-shaped magnetic coil device almost the height of a two-storey house. The coil was used to reproduce the magnetic fields that lie in different areas along the southeastern coast of the United States.
A tank of water in the centre of the coil allowed the scientists to expose turtles to various magnetic fields while noting the direction they swam in.
Juvenile green turtles were captured from their feeding grounds near Melbourne Beach, Florida, and tethered to a tracking device in the tank.
Turtles exposed to a magnetic field simulating the one found 337 kilometres north of the test site pointed themselves southwards.
Those exposed to a field mimicking the one existing 337 kilometres south of the site swam north. In each case, the turtles swam in the direction that would have taken them home had they been at the place where each magnetic field was found.
Dr Ken Lohmann, one of the investigators from the University of North Carolina at Chapel Hill, said: ”These results imply that turtles have a kind of magnetic map. In other words, they can figure out where they are relative to home using magnetic field information.
”This is a far more complex use of the field than just having a magnetic compass that gives direction.”
Last year Dr Lohmann and his marine biologist wife Catherine showed that spiny lobsters possess a similar map sense based on magnetism.
Previously many experts had assumed that complex navigational fields required a sophisticated brain and nervous system, which are lacking in lobsters and other invertebrates.
Dr Lohmann said: ”The picture that is emerging is that magnetic positioning systems are real, and the fact that they exist in both lobsters and sea turtles suggests that they may be widespread among animals.”
Future studies will look at precisely how the magnetic map is organiSed and what components of the field the turtles detect, he said.
The green turtle is an endangered species and all turtles tested were released back into the sea unharmed. – Sapa-DPA