SCIENTISTS may have solved one of the most intriguing puzzles in marine biology - how sea creatures navigate across thousands of miles of ocean with pinpoint accuracy.

They have found evidence that sea turtles and salmon can read the “magnetic map” of their native area and imprint it into their memories.

Many other species, such as whales and sharks, may use similar techniques to navigate the seas. They can also read and remember variations in the earth’s magnetic field.

“In some oceanic regions rocks rich in magnetic minerals produce local magnetic anomalies,” said Kenneth Lohmann, professor of biology at the University of North Carolina, Chapel Hill.

These have often been viewed as potential problems for magnetically sensitive species but an interesting possibility is that anomalies might also serve as useful markers.

Scientists have long known that the earth’s magnetic field shows slight variations and that each ocean has a different magnetic signature. But they were uncertain whether marine animals could detect them.

Salmon have long been thought to find the rivers of their birth by “smelling” the water through their gills, but scientists have recently realised that this could only ever work over relatively short distances. Another possibility is hydrodynamics – patterns of water movement generated by currents and waves as they interact with each other, the shoreline and the ocean bed.

Now Lohmann and others are beginning to show that many sea creatures deploy all three methods, but magnetic navigation is the most important over long distances.

Lohmann chose to work with sea turtles and salmon because both species migrate over long distances and periods of time but always seem to remember how to get home.

In one set of experiments, Lohmann showed baby turtles already had an inbuilt magnetic map to help guide them in their first migrations across the Atlantic.

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