Sharks Exploring Ambient Electric and Earth’s Magnetic Fields

The electric fields the sharks and rays are presented with are primarily DC fields, but the ampullae of Lorenzini are sensitive to low-frequency AC fields and not to DC fields. For the sharks to distinguish between the different kinds of electric fields, they must make the proper movements to convert the DC stimuli into the low-frequency AC range of the ampullary sense organs. These movements include the swerving motions during steady swimming, as well as acceleration and deceleration as the animals move through the water. During steady travel, the signal received from turning left and right in the ambient electric field is inherently of an AC nature, independent of the forward speed. The movements are part of the animals’ normal behavior and allow the animals’ ampullae of Lorenzini to detect the field in the low-frequency AC range. When a shark travels in a horizontal plane it can unambiguously discriminate between the ambient electric field and the electric field giving the animal its magnetic compass heading. The author explains the differences between his electromagnetic orientation model and an alternative magnetic orientation model. He also addresses whether the sensory data are processed in the time-domain or frequency domain.