Magnetic fields clue to migration
Updated on 02 December 2008
One of nature's greatest mysteries could be about to be solved after scientists revealed a new theory on how salmon find their way home.
Salmon and some species of sea turtle migrate vast distances back to the places in which they hatched in order to reproduce. But how they actually complete such difficult voyages across seemingly empty, featureless expanses of ocean without getting lost has baffled scientists for generations.
Some species of sea turtle migrate thousands of miles across entire oceans back to their birthplaces after leaving more than 10 years earlier. And after hatching in rivers, salmon travel hundreds of miles out to sea before returning home to spawn years later.
But now a new study proposes that salmon and sea turtles use the Earth's magnetic field to learn and then remember an imprint of their home address. The magnetic field varies significantly across the globe with each region having its own distinct magnetic pattern or signature.
Marine biologists on the study propose that once turtles and salmon reach adulthood they use the magnetic field and the imprinted magnetic memory of their birthplace, learnt in infancy, to navigate home in a process called natal homing.
Kenneth Lohmann, professor of biology at the University of North Carolina, US, said: "What we are proposing is that 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 theory, if proved, could prove a huge boost to conservation efforts as it will enable environmentalists to pinpoint vulnerable parts of migration routes.
Salmon and sea turtles often bypass suitable breeding grounds on their huge journeys in favour of the places they were born. Scientists on the study propose that the animals behave in this manner due to previous breeding success at that site.
Professor Lohmann explained: "For animals that require highly specific environmental conditions to reproduce, assessing the suitability of an unfamiliar area can be difficult and risky.
"In effect these animals seem to have hit on a strategy that if a natal site was good enough for them, then it will be good enough for their offspring." The theory is revealed in the journal Proceedings of the National Academy of Sciences.
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