Sharks (superorder Selachimorpha) belong to a family of fish that have skeletons made of cartilage, a tissue more flexible and lighter than bone.

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Shark bodies are rounded and tapering at the ends. They breathe through a series of five to seven gill slits located on either side of their bodies.

All sharks have multiple rows of teeth, and while they lose teeth on a regular basis, new teeth continue to grow in and replace those they lose.

Shark ‘skin’ is made up of a series of scales that act as an outer skeleton for easy movement and for saving energy in the water. The upper side of a shark is generally dark to blend in with the water from above and their undersides are white or lighter colored, blends in with the lighter surface of the sea from below. This helps to camouflage them from predators and prey.

Sharks also have a very acute sense of smell that allows them to detect blood in the water from miles away.

Diet

Shark diet depends on the species, but most species of shark eat things like fish, crustaceans, mollusks, plankton, krill, marine mammals and other sharks. 

Population

It is difficult to estimate population numbers since there are many different species spanning a large geographic area. However, overall shark numbers are on the decline due to the many threats they face in the wild. 

Range

Sharks have adapted to living in a wide range of aquatic habitats at various temperatures. While some species inhabit shallow, coastal regions, others live in deep waters, ocean floors and the open ocean. Some species, like the bull shark, are even known to swim in both salt and fresh waters and deltas.

Behavior

Most sharks are especially active in the evening and night when they hunt. Some sharks migrate over great distances to both feed and breed. This can take them over entire ocean basins. While some shark species are solitary, others display social behavior at various levels. Hammerhead sharks, for instance, school during mating season around seamounts and islands.

Some shark species like the great white shark attack and surprise their prey, usually seals and sea lions, from below. Species that dwell on the ocean floor have developed the ability to bottom-feed. Others attack schooling fish in a feeding frenzy, while large sharks like the whale and basking sharks filter feed by swimming through the ocean with their mouths open wide and filtering large quantities of plankton and krill. 

Reproduction

Mating Season: Various times depending on the species.
Gestation: 2 months to 2 years depending on the species. Some species lay eggs, some have young covered by a thin membrane, and others give birth to live young.
Number of offspring: Depending on the species, could be 1-2 pups or more than 100 eggs or pups.
Soon after birth, sharks pups swim away to fend for themselves. They are born with fully-fledged sets of teeth and are able to take care of themselves.