A sharks senses have evolved with sharks to become an effective and efficient means of survival. It is interesting to note that because sharks have no other predator but man, they are not equipped with some of the defensive mechanisms of other sea creatures.
A sharks senses work in unison to make it an efficient predator that can sense injured animals and fish from several miles away. Experiments have been done on some shark's to get an idea of how the senses of a shark work together with interesting results. When a shark's nose is stopped up it has significant difficulty hunting, even though the sense of smell is not the primary sense. The entire body of a shark plays an important role in the effectiveness of the senses and it's ability to hunt and survive.
Depending on whether the shark is a surface feeder or a bottom feeder, their eyesight may be very good, or poor. Many sharks have eyesight that are ten times more sensitive to light than a human. They can see objects and prey from 70-100 feet away. Studies done on Lemon Sharks revealed that they could detect color and preferred bright shiny colors and objects.
Two highly developed senses are hearing and smell. In tests on sharks in captivity, one drop of blood could be detected in 2,000 gallons of water. In the ocean sharks can smell blood from many miles. In addition, many sharks are attracted to the scent of chemicals in the gut and can be found at sewage outfalls. Another interesting feature of a sharks sense of smell is their ability to smell directionally. When a smell enters their nostrils, the scent enters the nostril first that is in the direction of the scent. Their hearing is received, unfiltered directly from the hole in their head to the inner ear. Sounds with a very low frequency are heard easily from as much a . 6 miles away.
The really interesting senses are those that are not shared with humans. There are thousands of tiny electroreceptor ampules around the head of a shark called Ampullae of Lorenzine that detect electromagnetic fields from other animals. Sharks have the greatest electrical sensitivity of any animal. All animals, including humans, give off an electromagnetic field. When they are injured or hurt, their the intensity of the field changes minutely. A shark picks up this slight change in the electromagnetic field and, when combined with the indicators of the other senses, heads directly for the injured animal from several miles away.
Another unique sense is the Lateral Line on the shark. The tubes run on either side of the body and have a lot of resemblance to ear canals. There are tiny, sensitive hairs in the canals that response to any vibration in the water up to ten feet away. When an animal or human is splashing in the water or disabled, the frequency can be as low as 25-50Hz and the Lateral Line will detect the vibrations and direct the shark to the location.
When all of the sharks senses are combined they create a perfect method for a fish that spends most of its life hunting for prey that is hiding or moving in a vast ocean.
Sharks senses has long fascinated Pam Golding while watching sharks along the Eastern Seaboard of Southern Africa.
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