They are fast, illusive and live in concealing medium, water. The ideal shark for research is the lemon shark, since it is coastal, spends a lot of its time near the surface and is not too aggressive. A few facts that researchers do know about sharks if that they sit at the top of the ocean's food chain which means most of the more than 350 species of sharks have few natural predators besides humans. Sharks bodies are not consisted of bone but rather cartilage for extra flexibility. Sharks interestingly enough have what most people would call a sixth sense because they are able to sense electrical and magnetic fields, which help them detect prey and orient themselves in correspondence with the earth's magnetic fields.
Most species grow slowly and mature very late.
Sharks range in the danger that they pose to humans from none at all to rather dangerous and life threatening. A few harmless sharks are the Wobbegong shark, Epaulette shark, the Horned shark and the Blind shark. Fairly common sharks are the Silvertip Reef sharks, the Sandbar shark and the Grey Nurse shark. The more dangerous sharks are the Bullshark, the Tiger shark, the Great White and the Oceanic Whitetip shark. The sharks that can really do some harm to human are the ones with large triangular shaped teeth with serrated edges.