These pores detect weak electrical impulses produced by prey and by the earth's magnetic field. Scientists believe sharks use this sense like a radar to target prey, and as a compass to travel long distances in the open ocean. There are over 350 species of sharks in the oceans of the world. Sharks live all over, from the cold polar waters to the warm tropical seas. Unfortunately the average person is more likely to drown than to even SEE a shark, let alone be attacked by one.
Many sharks are small, and eat fish, shellfish, and clams.
The most dangerous sharks, such as the great whites and tiger sharks, hunt in shallow coastal waters. They may sometimes confuse human swimmers with seals or porpoises, their natural prey. The midwater shark and the pygmy ribbontail catshark the two smallest sharks, at around 9 inches long. Their skeleton is made up entirely of cartaliage, the same material that makes up the soft part of our noses. Sharks arose about 350 million years ago and have remained virtually unchanged for the past 70 million years.