What is electroreception, and how do sharks use it to their advantage?

Sharks are naturally built for hunting. These agile ocean predators possess a unique sense called electroreception, which enables them to detect prey with pinpoint precision. While other members of the elasmobranch family, like rays and skates, also share this ability, sharks have the most refined version of electroreception.

Shark Image Collection

Electroreception refers to the ability to sense electrical currents. But how is electricity relevant to sharks in their underwater environment? Any movement, including the slightest muscle twitch, produces small electrical currents. This concept is similar to how electrocardiogram machines in hospitals monitor the electricity generated by our heartbeats.

While open air doesn’t conduct electricity away from our bodies, salt water does, which is beneficial for sharks. Salt water contains sodium and chlorine ions, which are charged particles that have gained or lost electrons. These ions separate and move freely in water, allowing electricity to flow.

This can be likened to the way batteries operate. A battery functions as an electrochemical cell that separates positively and negatively charged ions. When connected, these opposite charges attract, causing the positive and negative ions to flow toward each other and exchange electrons to stabilize.

A similar process occurs when living cells interact with salt water. Since fish cells have a different charge compared to the surrounding saltwater, this interaction generates a small voltage, much like a battery. Sharks can detect the slightest fluctuations in this electrical current, down to one-billionth of a volt [source: Fields]. If two AA batteries were placed 1,000 miles (1,600 kilometers) apart, a shark could sense if one had run out of power [source: Viegas].

How are sharks able to do this? Learn about the part of a shark’s body responsible for regulating this extraordinary internal navigation system on the next page.

Electroreception for Hunting and Navigating

The source of sharks' electroreception abilities is located around their snouts and lower jaws. If you examine a shark's face closely, you'll notice tiny dots near its mouth that resemble large blackheads. The number of these dots varies with the shark's level of activity. More active species have over 1,500 of these dots, while more sedentary ones have only a few hundred [source: Parker].

These dots are actually pores known as ampullae de Lorenzini. Each pore is filled with an electrically conductive jelly, and the base of each ampullae contains hair-like cells called cilia. When electrical currents pass through the jelly, they stimulate the cilia. This is similar to how cilia in human ears respond to sound waves by alerting the brain. In sharks, the cilia detect changes in nearby electrical currents, triggering the release of neurotransmitters in the shark's brain, signaling the presence of something alive nearby.

The ampullae de Lorenzini are a key component of the shark's lateral line. The lateral line is a sensory organ found in many fish and amphibians that runs along their sides from gills to tail. This long, hollow tube opens out into the skin at perforated scales. It allows sharks to sense changes in water displacement, pressure, and direction.

When combined with sharks' other senses, the lateral line and electroreception make sharks exceptional hunters. Since two-thirds of a shark's brain is dedicated to its sense of smell, it can track prey even in the darkest waters [source: Parker]. Electroreception activates when the shark is about 3 feet (1 meter) away from its target, helping guide its jaws for a precise, final strike [source: PBS]. To protect themselves, great white sharks roll their eyes back into their heads during the last part of the attack, allowing electroreception to take over their navigation [source: Dingerkus].

Experiments testing sharks' electroreception abilities have shown that these creatures will indeed make last-minute feeding decisions based on electrical signals. For instance, when presented with both dead fish and an electrically charged rod, a shark will initially swim toward the fish but change course at the last second to head toward the metal rod instead [source: Fields]. Researchers hope to use this information to create a shark deterrent that tricks their electroreception system.

The power of electroreception also explains why sharks may continue attacking a human victim even if someone else is attempting a rescue. Rather than being distracted by the rescuer, sharks are repeatedly drawn back to the original victim due to the salt released from blood in the water [source: Viegas]. The increased salt concentration amplifies the electrical field around the victim, keeping the shark focused on them.

Given sharks' remarkable ability to detect electrical changes, scientists are also exploring whether electroreception plays a role in their navigation. One theory suggests that the Earth's magnetic fields may interact with saltwater to generate electrical currents, which sharks could follow during their long migrations [source: Parker].