It is easy to see why overfishing can devastate shark populations. The deep sea holds many species in surprising forms and about which relatively little is known. The eyes in these deep water sharks are often emerald green and adapted to perceive the luminescence of other animals that also dwell where sunlight never reaches. All sharks can be considered flesh eaters although a few feed like baleen whales, filtering the water for plankton and small fish. The degree of specialization in feeding is indicated by the shape and size of a shark's teeth.
Sharks teeth are in parallel rows and tooth loss and replacement is continuous throughout life.
Studies by Mote scientists have shown that, on average, small nurse sharks will, one tooth at a time, replace an entire front row of teeth every ten days or so in summer and every one to two months in winter when they are feeding less and their metabolism slows down. Despite their reputation, sharks seldom bite people, although the bite of even a small shark can be serious with loss of flesh and heavy bleeding. Most attacks are believed to result from a case of mistaken identity as when a swimmer is among fish upon which a shark is feeding, or when the shark believes it is repelling an intruder, or when a person bumps into, steps on or otherwise molests a shark. Large pelagic sharks like the oceanic whitetip shark, the mako, the blue, and the white shark, all of which sometimes feed on large prey, have been implicated in fatal shark attacks. For swimmers in the Gulf of Mexico, the potentially most dangerous sharks are the tiger shark, the hammerheads, the lemon shark and the aggressive bull shark that will enter brackish water and sometimes even fresh water.