Sharks are amazing creatures. They have roamed the Earth’s seas since nearly the beginning of time. Their size, power, and great, toothy jaws fill us with both fear and fascination. Sharks have few natural predators allowing them to roam the earths oceans with relative ease. There are over 500 types of sharks ranging in size from a few centimeters to more than 15 meters. They are found in all seas and are common to depths of 2,000 meters (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive and be found in both seawater and freshwater.
They are “cartilaginous fish” meaning that the structure of the animal’s body is formed of cartilage, instead of bone. Unlike the fins of bony fishes, the fins of cartilaginous fishes cannot change shape or fold alongside their body. Even though they don’t have a bony skeleton like many other fish, they are still categorized with other vertebrates in the Phylum Chordata, Subphylum Vertebrata, and Class Elasmobranchii. This class is made up of about 1,000 species of sharks, skates and rays. They have five to seven gill slits and rigid dorsal fins, for which they are famous. And though they kill only a few people each year, media coverage and movie portrayals of attacks have marked sharks as voracious killing machines. Our fears—and appetites—fuel an industry that hunts more than 100 million sharks each year and threatens to purge these vital predators from the oceans.