Listen to the Sounds of Summer

Play to enjoy 45 sec. of the sounds of summer.
Your Flash Player Version is outdated. Please, upgrade Flash Player from here

Magnets Maps & Sex

The earth is surrounding by a magnetic field that affects the alignment of chemical elements such as iron in rocks, at the time they are produced by igneous activity. According to a new

hypothesis, this magnetic field also affects marine animals by helping them navigate the oceans and rivers.

Most biological explanations in animal behaviour centre around hunting for food or achieving a mate. Now this new 'magnetic imprint' hypothesis is put forward to explain the ability of adult fish and marine turtles to return to their place of birth to reproduce themselves. If the home birth place was good enough to produce them, then it must be good enough for their successful reproduction.

According to a recent scientific paper in the Proceedings of the National Academy of Sciences, newly born salmon and turtles are imprinted with the magnetic field of their birth area. They 'remember' this magnetic 'map' and use it when sexually mature to return to their birth place to attempt their own reproduction.
Professor Kenneth Lohmann (who has suggested this hypothesis) has used observations of turtle movements from their own studies between 2001 and 2004. His team has also suggested that this magnetic map or address is developed throughout the life of turtles to remember rich feeding places. Some turtles may not return to their birth place for many years, travelling thousands of miles to do so.

One difficulty with the hypothesis is that the magnetic field is constantly changing, even within the life of a turtle or salmon. However it is postulated that the change is not big enough for the animal to lose its way or be directed to an unsuitable area. On nearing their location other senses kick in to play. Salmon, for example use smell when moving closer to their spawning grounds.

Can this hypothesis be tested? Well it seems it's difficult to do so because of the high mortality rate among these animals. For example, only one is 4000 turtles reach sexual maturity; fewer salmon do, so which individuals do you follow from birth? A bit of a lottery for the scientist really.

However the hypothesis could achieve some support if it is used to successfully re-establish populations in either new areas or regions that have lost their once established populations.

Text: © Paul Whelan, 2008.