Sharks

Sharks have the same five senses of sight, hearing, smell, taste, and touch that humans have. Moreover, some of these senses are more acute in sharks. Sharks also have an additional sense; they can detect weak electric fields in the water.

Sharks are known to possess a complex visual system, and can even see color. A problem for sharks is that, if they are in deep or murky water, the light level is very low. Several features of the shark eye make it well-suited to vision in dim light. Unlike most fish, sharks have a pupil that can adjust to the amount of light in the environment. Also, shark eyes have high numbers of the structures that actually detect light (the rods), so that even in low light an image is formed. Finally, sharks have a special reflective membrane (the tapetum lucidum) at the back of the eye, which enhances their vision in low light even further. Cats have a similar membrane in their eyes, which is why their eyes seem to reflect light in the dark. The membrane, for both cats and sharks, helps them see in dim light.

Two tiny pores on the top of the sharks head lead to their inner ears. The inner ear contains organs for detecting sound waves in the water, as well as three special canals that help the animal orient in the water. The sound receptors are very sensitive, especially to irregular and low-frequency (20-300 Hz) sounds. These are the types of noises a wounded prey animal would be likely to make. The distance at which a shark can hear a sound depends on the intensity of the sound at its source: a vigorous disturbance or a loud underwater noise will produce sound waves that travel further in the water than those produced by a smaller disturbance.

A shark's nostrils are two pores on the front of its snout. As the shark swims forward, water passes through the nostrils and chemicals in the water are detected as odors. The nose is used only for detecting odors, not for breathing. Some sharks can detect as little as five drops of fish extract in a swimming pool of water. Sharks can easily use their sense of smell to detect and home in on prey, by swimming in the direction of the increasing scent.

Evidence suggests that sharks can taste their food, and that they have preferred prey. Small taste buds line the mouth and throat of sharks, and they seem to reject foods based on their taste. Some scientists argue that the reason most shark attacks on humans involve only one bite is that the animal realizes, after biting, that the person does not taste the same as the prey expected.

Sharks have two types of touch sense. One is the ability to sense when an object touches their body. The second is the ability to detect an object by the movements of the water it causes. This is similar to how you might detect where a fan is located in a room, because you can feel the movement of the air on your skin. Sharks and other fish have a specialized, very sensitive receptor system for detecting these types of water movements. This sensory system involves a series of tiny, shallow canals and pits running beneath the surface of the skin, known as the lateral line and the pit organs. The movement of water against the canals and pits is detected in receptor organs, and this information is used to "visualize" the presence of nearby organisms and objects.

All organisms in sea water generate a weak electric field around them, like an invisible halo. Small pits in the skin of sharks end in receptors that can detect extremely low-voltage electric fields in the water. Sharks use this sense to locate their prey at close range. Some sharks can even find their prey under sand and mud.