Disruption of magnetic orientation in hatchling loggerhead sea turtles by pulsed magnetic fields

William P. Irwin, Kenneth J. Lohmann

Loggerhead sea turtles (Caretta caretta) derive both directional and positional information from the Earth's magnetic field, but the mechanism underlying magnetic field detection in turtles has not been determined. One hypothesis is that crystals of biogenic, single-domain magnetite provide the physical basis of the magnetic sense. As a first step toward determining if magnetite is involved in sea turtle magnetoreception, hatchling loggerheads were exposed to pulsed magnetic fields (40 mT, 4 ms rise time) capable of altering the magnetic dipole moment of biogenic magnetite crystals. A control group of turtles was treated identically but not exposed to the pulsed fields. Both groups of turtles subsequently oriented toward a light source, implying that the pulsed fields did not disrupt the motivation to swim or the ability to maintain a consistent heading. However, when swimming in darkness under conditions in which turtles normally orient magnetically, control turtles oriented significantly toward the offshore migratory direction while those that were exposed to the magnetic pulses did not. These results are consistent with the hypothesis that at least part of the sea turtle magnetoreception system is based on magnetite. In principle, a magnetite-based magnetoreception system might be involved in detecting directional information, positional information, or both.