Passive and Active Modes of Electro-orientation

This chapter describes the behavioral evidence of electric and magnetic orientation in sharks and rays and explains the physical principles of passive and active modes of orientation. The author explains in detail how the physical characteristics of the animals’ sensory system are affected by these fields and clarifies which fields the animals are presented with. The sharks can discriminate between the electric fields informing them about their drift in ocean streams and the electric fields informing them about the magnetic compass heading. Further, the author explains the biological structure of the ampullae as high-resistance voltage detectors over the surface of the animal’s snout and therefore provides a comprehensive view of the electromagnetic environment and how the animals perceive and react to this environment. Appendices to this chapter describe the definition of the symbols, the mathematical concepts of forces and gradients, concepts of potential difference, voltage, divergence, and curl, and a detailed analysis of a technical example. Also included is an axiom of an electric field inside and in the vicinity of a resistive sphere.