Hearing
Low-frequency sounds can travel great distances underwater, so a shark's auditory system could be the first sense to pick up an interesting target.
Rapid, irregularly-pulsed sounds at low frequencies (below 600 hertz) similar to those made by injured prey or a group of spawning fish can alert a hunter such as a bull shark from over 1.6 km (1 mile) away.
Vibration Sensors
At 100 m (330 ft), a shark's lateral line system kicks in. This row of fluid-filled sensory canals on either side of its body responds to pressure changes and movements, so a shark can almost feel the presence and location of something moving in the water--a kind of 'touch-at-a-distance.'
Smell
At a distance of 0.5 km (1/3 mile), a shark can smell blood in the water and follow a trail back to the source. It can detect one part of fish extract in 25 million parts of seawater, the equivalent of ten drops of blood in an average-sized municipal swimming pool. Scents travel a long way on ocean currents, enabling sharks to detect food from long distances.
Electrical Sensors
The most extraordinary sensory system is one that detects electricity. In the snouts of most sharks are small, jelly-filled pits, known as the 'Ampullae of Lorenzini'. In each pit is a sensor that detects minute electrical fields associated with contracting muscles, such as those in a pumping heart. The system is remarkably sensitive. A shark is able to detect muscular activities in its prey, even if the target is hiding under the sand or gravel of the sea bed.
The great white shark uses its electrical sense not for locating prey but in the moment just before contact. In order to protect its eyes from the claws or teeth of seals and sea lions, it swivels them back into special sockets and is momentarily blind. The electrical field generated by the seal's muscles guides the shark the last few centimetres to its target.
Sight
At 25m (82 ft) in relatively clear water, a shark can spot movements.
They can see even in very dim light. Like domestic cats, they have a tapetum lucidum - a layer of shiny plates behind the retina at the back of the eye that reflects light back onto the retina's light sensitive cells. It ensures that the maximum amount of available light falls on the retina, enabling the animal to see almost in the dark.
Using this, a shark is able to rise rapidly from the dimly-lit depths into the bright light of surface waters without being blinded. Not all sharks have this screening, deep-sea sharks have a tapetum but no melanoblasts, an adaptation to a world of inky darkness where the only light is often from bioluminescent fish and other marine creatures.
Updated 2012
Low-frequency sounds can travel great distances underwater, so a shark's auditory system could be the first sense to pick up an interesting target.
Rapid, irregularly-pulsed sounds at low frequencies (below 600 hertz) similar to those made by injured prey or a group of spawning fish can alert a hunter such as a bull shark from over 1.6 km (1 mile) away.
Vibration Sensors
At 100 m (330 ft), a shark's lateral line system kicks in. This row of fluid-filled sensory canals on either side of its body responds to pressure changes and movements, so a shark can almost feel the presence and location of something moving in the water--a kind of 'touch-at-a-distance.'
Smell
At a distance of 0.5 km (1/3 mile), a shark can smell blood in the water and follow a trail back to the source. It can detect one part of fish extract in 25 million parts of seawater, the equivalent of ten drops of blood in an average-sized municipal swimming pool. Scents travel a long way on ocean currents, enabling sharks to detect food from long distances.
Electrical Sensors
The most extraordinary sensory system is one that detects electricity. In the snouts of most sharks are small, jelly-filled pits, known as the 'Ampullae of Lorenzini'. In each pit is a sensor that detects minute electrical fields associated with contracting muscles, such as those in a pumping heart. The system is remarkably sensitive. A shark is able to detect muscular activities in its prey, even if the target is hiding under the sand or gravel of the sea bed.
The great white shark uses its electrical sense not for locating prey but in the moment just before contact. In order to protect its eyes from the claws or teeth of seals and sea lions, it swivels them back into special sockets and is momentarily blind. The electrical field generated by the seal's muscles guides the shark the last few centimetres to its target.
Sight
At 25m (82 ft) in relatively clear water, a shark can spot movements.
They can see even in very dim light. Like domestic cats, they have a tapetum lucidum - a layer of shiny plates behind the retina at the back of the eye that reflects light back onto the retina's light sensitive cells. It ensures that the maximum amount of available light falls on the retina, enabling the animal to see almost in the dark.
Using this, a shark is able to rise rapidly from the dimly-lit depths into the bright light of surface waters without being blinded. Not all sharks have this screening, deep-sea sharks have a tapetum but no melanoblasts, an adaptation to a world of inky darkness where the only light is often from bioluminescent fish and other marine creatures.
Updated 2012
