What is Considered to be a Shark's "Sixth" Sense?

13 October 1997

In addition to the five senses that humans possess, sharks also receive sensory input through electroreception, the ability to sense weak electric fields. Sharks not only sense these fields, they rely on them to locate prey and, perhaps, navigate through the ocean.   Sharks have the greatest sensitivity of any known marine animal to electric fields.

Scientists estimate the number of living shark species at more than 350. More than 42 species of sharks live off the North Carolina coast of which 28 are common.

This specialized system of gel-filled pores, called the ampullae of Lorenzini, allows the shark to detect the small electrical signals that all animals, including human beings, emit. This sense works best at close range and enables the shark to pinpoint an animal it may not even see in dark water. A shark also uses this sense to position its head and mouth when moving in for final attack.

Sharks are unable to distinguish between natural signals and those produced by artificial objects such as metal and wire. This may explain why sharks sometimes attack boats, docks, and steel cages.

The shark's "sixth" sense, along with their other specialized senses, makes them among the most efficient predators on earth. Sharks have one of the keenest senses of smell of any animal. They can scent from great distances and their sensitivity to smell seems to increase the longer they have been without food. In fact, scent detection comprises almost 70% of a shark's brain activity.

Sharks also have well-developed inner ears that enable them to hear sounds more than a half mile away. They are particularly sensitive to irregular, low-frequency sounds, precisely the kinds of sounds made by fish that are injured and swimming erratically.

A shark's sense of touch is stimulated by direct contact or water movement. A special system called a lateral line, a narrow strip of sensory cells that runs along the sides of the body, allows them to detect changes in water pressure and pick up vibrations in the water.

Contrary to popular belief, sharks have excellent vision. Like humans but unlike most fish, they can open and close their pupils in response to varying amounts of light. In fact, their eyes are ten times more sensitive to light than human eyes.

Surprisingly, sharks do taste their food and some species seem to prefer certain foods to others. Their mouth and throat are lined with taste buds. If these taste buds are not satisfied, sharks will reject the food after tasting.

The shark's sensory system, one of the most sophisticated in the animal world, has earned it the nickname, "the perfect predator." However, experts consider only half a dozen species to be dangerous. Most are shy and harmless, avoiding people and other large animals when possible.