In living organisms, almost all atoms and molecules hold some sort of electrical charge. When molecules interact with other molecules, these electrical charges also interact (Kalmijn et al, 2002). Some organisms, such as electric rays and eels, are able to create powerful electric charges that can be used as defense mechanisms. All organisms, including humans, emit weak electrical charges as a result of the physiological processes taking place within them. Because aquatic animals have different charges than the surrounding water, and the movement of the gills relies heavily on electrical charges, aquatic animals inadvertently emit an electrical field into the surrounding water. These fields, depending on their strength, can be detected by other organisms, including predators. Sharks and rays have the most sensitive electrosensory systems and can respond to electrical gradients of less than five nanovolts per centimeter (Bastian, 1994). The heads of sharks are covered with thousands of pores which make up the ampullae of Lorenzini. In blacktip reef sharks (C. limbatus), it was found that they have an average of 2,224 pores on their head. The hammerhead (S. lewini) was found to have on average 3,067 pores (Kajiura, 2001). These pores allow sharks to detect and process the electrical charges in the surrounding water. The ampullae will be discussed in more detail on the following page.
It is hypothesized that sharks use their electrosensory system, the ampullae of Lorenzini, to detect electric fields emitted by other fish and then use these charges to determine the location of their prey. It was later determined that sharks use these charges to locate possible pray, but do not know what the organism is until they are within visual range of their target (Kalmijn et al, 2002). As sharks swim through an electrical field, they use the changes in the strength of the field to determine the location of the fish or other animal that is emitting the field.
Pores of the ampullae of Lorenzini in a porbeagle shark. Picture used with permission from Dr. Steven Campana. http://www.marinebiodiversity.ca/shark/english/images/por%20ampullae.jpg
|STRUCTURE OF THE AMPULLAE|
|THE FUNCTION OF THE GEL IN THE AMPULLAE|
|THE COMPASS SENSE|
|NEURO-ECOLOGY AND PERIPHERAL MORPHOLOGY|
|ELECTRICAL SHARK DETERRENTS|