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.
estimate the number
of living shark species at more than 350. More than
42 species of sharks live off the North Carolina
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.
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.