What is a Shark?

Mary McMahon
Mary McMahon

Sharks are a group of carnivorous ocean going fish with 368 different species in a total of 30 families. Some species of shark, such as the great white, are infamous among humans because they have been involved in attacks resulting in severe injury and sometimes death. In general, however, sharks are shy fish, who will not attack unless provoked.

Great white sharks are one of the few species that have attacked humans.
Great white sharks are one of the few species that have attacked humans.

Sharks have been around since prehistoric times, with fossils indicating that sharks have maintained their basic shape and evolutionary adaptations for millions of years. The fish is simple, efficient, and relatively intelligent, with evidence suggesting that sharks can acquire skills on par with many land animals. Some sharks are endangered due to heavy human trade in their fins, including many of the large species of shark.

Scientists have failed to keep a great white shark captive long enough to conduct extensive research on the famed predator.
Scientists have failed to keep a great white shark captive long enough to conduct extensive research on the famed predator.

Sharks range in size from the pygmy shark, which is seven inches (18 centimeters) long, to the whale shark, which can reach 50 feet (15 meters) in length. Most sharks have gray upper bodies and pale lower bodies for camouflage purposes. Sharks have several other characteristics which distinguish them from most fish, beginning with their skeleton, which is formed from cartilage rather than bone. This makes sharks stronger and more flexible that many fish species.

Sharks also have rough, sand-papery skin which can be quite painful to the touch. In addition, shark teeth will grow back if dislodged, guaranteeing the fish a formidable life-long dentition. Many sharks have slightly serrated teeth as well. Sharks have multiple gills on each side, with some species having as many as eight, while most range between five and six.

Most sharks have streamlined bodies designed for moving efficiently through the water. Many species have a projecting dorsal fin, and all have split caudal or rear fins. The shark can move very rapidly in search of prey, and depending on the size of the fish, sharks eat small food, plankton, shellfish, and crustaceans.

Sharks can be found all over the world, inhabiting temperate waters as well as tropical, with some species favoring shallow water. Shallow water species can pose a risk to humans, as the sharks will feel threatened by swimmers, surfers, and the like, and may attack if they feel cornered, or if they mistake the human for prey. Swimmers should avoid areas known to harbor sharks, as well as being aware of their environment. If attacked, biologists recommend that victims fight back in every way possible.

Shark meat is consumed by many cultures, although the rising levels of mercury found in shark meat make this consumption inadvisable. The fins of the shark are highly prized, leading to a global threat to shark species.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@ Parmnparsley- I took the submarine tour on Maui and saw a group of reef sharks. They were darting and swarming around in the water near the edge of the reef. I was glad that I was on the dry side of the glass.


@ Malena- A shiver is one word used to describe a group of sharks. Groupings of sharks can also be referred to as a gam, pod, school, herd or a few others that I can't think of at the moment. It can be a somewhat frightening and awe inspiring thing to see a large school of sharks.

I have only seen a school of sharks once, and it was a school of hammerhead passing below our boat near the reefs of Hawaii's big island. All I could make out were the silhouettes of about 15 or 20 hammerheads against the ocean bottom. They swam probably 30 feet below us. We were fishing for octopus, but after seeing that we stuck to the boat and moved on to the next spot. I know that they would have likely left us alone, but it is still a little nerve wracking to be in the water when there are that many sharks swimming the area. It was a cool sight though.


A group of sharks is called a shiver.

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