New theory on how salmon find their way back to their Scottish birthplace

Every year, 20 million of them leave Scottish rivers and travel thousands of miles to Norway and Greenland to feed. Remarkably, they then return to Scotland, often to within 100 metres of where they were hatched, in a process that can take more than two years. How salmon complete such voyages across sea and ocean without getting lost has baffled scientists for generations. But a new theory proposes that the fish use the earth's magnetic field to locate their origins in Scottish rivers, according to press reports. Scientists believe that, in a process called "natal honing", salmon imprint the magnetic signature of their home once reaching adulthood. Kenneth Lohmann, professor of biology at the University of North Carolina in the United States, said: "Natal homing can be explained in terms of animals learning the unique magnetic signature of their home area early in life and then retaining that information." The Earth's magnetic field varies across the globe – each oceanic region has a different magnetic signature. Researchers believe that by remembering the unique "magnetic address" of their birthplace, fish may be able to distinguish that location from all others.