According to a new scientific study, loggerhead turtles that nest on beaches with similar magnetic fields turn out to genetically similar to one another – a process identified as “isolation by navigation”.

Loggerhead turtles hatch in the south-eastern USA, where the research was carried out, and migrate solo across the Atlantic before eventually making the return trip.

Because of their “geomagnetic imprinting”, their intention is to return to nest at the beach they left behind – but they can be misled into ending up at a different site far away if it has a similar magnetic field.

Magnetic fields at any point on Earth can be defined in terms of both their intensity and their inclination angle to the planet’s surface, and these two factors can be detected by turtles and certain other animals.

Human intervention, such as seafront construction or laying power-lines on the seabed, can alter the magnetic-field signatures used by the turtles for navigation.

Biologists Kenneth Lohmann and J Roger Brothers of the University of North Carolina at Chapel Hill investigated their hypothesis of isolation by navigation by analysing DNA samples from 834 nesting female turtles across 20 different locations on the south-eastern US coast.

The nesting sites included some on both the east and west coasts of Florida that had similar magnetic fields.

The authors believe that their findings could be relevant not only to the conservation of turtles but of other long-distance migratory animals that use magnetic positional information for navigation, such as sharks or salmon.

The study is published in Current Biology.

Divernet - The Biggest Online Resource for Scuba Divers