Facts From the Shark Cage: Special Senses of the Great White Shark

The words, "special senses," typically call to mind comic book superheroes and cheesy television psychics - very rarely does one immediately think of sharks. Nonetheless, sharks (such as the great white) are among many animals on the planet with fascinating sensory capabilities beyond those familiar to humans. In addition to sight, taste, touch, and an extremely strong sense of smell, great white sharks have two other sensory receptor systems: mechanoreception and electroreception.

Mechanoreception is a sensory system by which an animal detects the energy changes from varying pressures and movements in the environment. Sharks can sense the wave disturbances made by other animals and objects in the water from quite a distance, greatly aiding them in finding prey. The erratic thrashings of a wounded seal or fish are like the loud PA-system announcements we all remember from grade school, calling everyone to the cafeteria for lunch! Sharks are quickly aware of new objects introduced in the surrounding water, such as boats or shark diving cages, and often come to investigate. Scientists also believe that sharks use mechanoreception to navigate, sensing the direction and movement of changing currents.

Anyone who sees a photo of a great white shark (or is lucky enough to safely see one in person!) is able to notice the ridge that runs lengthwise along both sides, from the gills to the tail fin. This is called the "lateral line." Like eyes and noses are to the senses of sight and smell, the lateral line is largely responsible for the shark's mechanoreception abilities.

Great whites can not only sense movement in the water, but also minute electrical impulses. This type of sensory system is called electroreception. Easily visible on the underside of the shark's snout are a sprinkling of pores called the ampullae of Lorenzini. Named after the Italian researcher who first commented on them in 1678, these pores resemble numerous blackheads or a 5 o'clock shadow. Each pore is filled with conductive gel and sensory cells, giving the great white the ability to detect the weak electrical signals given off by all living organisms. The small amount of energy generated by the heartbeats and muscle contractions of other animals are easily picked up by the ampullae of Lorenzini. Certain metals, when introduced into seawater, give off an electrical signal that is picked up by sharks. Researchers, fisherman, and those who dive with sharks have noticed that great whites occasionally bump or bite metal parts of their boat to investigate these new electric impulse sources. Responsible researchers and great white cage divers build their cages out of metals with very little electrical ion reaction to seawater.

Extensive study of the great white's "special senses" has not been possible thus far, due to our inability to keep one in captivity for the length of time necessary for comprehensive observation and testing. One juvenile white shark, kept for 3 days in the San Francisco Steinhardt Aquarium in 1980, showed sensitivity to a tiny section of her aquarium with a miniscule electrical differential of 0.125 millivolt. From this and other calculations, marine biologists estimate that the great white shark can detect the electrical equivalent of a D-cell flashlight battery at a distance of almost 1,000 miles away!