Sharks possess a sensory ability known as electroreception, allowing them to perceive weak electrical fields in their environment. This sense provides them with a perception of the world different from human experience. It enables these marine predators to interact with their surroundings in ways beyond the five common senses, helping them navigate and locate food within the ocean’s depths.
The Ampullae of Lorenzini
The specialized organs responsible for a shark’s electroreception are called the Ampullae of Lorenzini. These structures appear as small pores on the shark’s skin, concentrated around the head and snout. Each pore connects to a jelly-filled canal that extends inward, ending in a cluster of sensory cells. These ampullae are highly sensitive electroreceptors, forming a network across the shark’s face. The sensory cells within these ampullae are directly connected to nerve fibers, which transmit signals to the shark’s brain for interpretation.
How Sharks Sense Electric Fields
Sharks detect electric fields using the properties of the highly conductive jelly filling the ampullary canals. When an external electric field is present, it creates a voltage difference between the pore opening on the skin’s surface and the base of the sensory cells located deeper within the ampulla. This voltage difference triggers an influx of calcium ions, initiating a nerve impulse that is sent to the shark’s brain for processing. Sharks can detect incredibly faint electrical signals, which is roughly equivalent to the electric field produced by a common AA battery if its terminals were separated by over 1,000 miles. This sensitivity allows them to perceive the subtle bioelectric fields generated by muscle contractions or heartbeats of prey, even those concealed from view.
Why Electroreception is Vital for Sharks
Electroreception plays an important role in a shark’s survival, offering several advantages. A primary application is the detection of hidden or camouflaged prey. Sharks can locate prey buried beneath sand or obscured by murky waters by sensing the faint electrical fields produced by their muscle movements, even when other senses are limited. This ability allows them to pinpoint organisms like flatfish or stingrays.
This sensory capability also assists in navigation by allowing sharks to detect the Earth’s geomagnetic fields. These subtle electrical currents, generated by the movement of ocean currents through the Earth’s magnetic field, can serve as navigational cues during long-distance migrations. While less understood, electroreception may also facilitate social interactions among sharks, aiding in recognizing conspecifics or interpreting behavioral signals. Furthermore, the detection of larger, approaching electrical fields could provide an early warning system for avoiding potential predators.
Electroreception in Other Animals
While prominently associated with sharks, electroreception is not exclusive to them. Many other aquatic and semi-aquatic animals also possess this sensory ability. Rays, closely related to sharks, employ Ampullae of Lorenzini to locate prey buried in the seafloor. Freshwater paddlefish use specialized electroreceptors on their elongated snouts to detect the weak electrical fields generated by zooplankton, their primary food source.
The platypus has electroreceptors on its bill, which it uses to locate prey like shrimp and insect larvae while foraging underwater. Some amphibians, such as salamanders, and certain fish groups, including electric fish, also exhibit electroreception. Electric fish, such as electric eels and knifefish, not only detect electric fields but also generate their own, using them for navigation, communication, and stunning prey.
References
1. “Sharks’ Electric Sense: The Ampullae of Lorenzini.” PBS, www.pbs.org/wgbh/nova/sharks/sense.html.