Shark
Selachimorpha
Animal Type: Cartilaginous fish
Habitat: Oceans worldwide
Diet: Mostly carnivorous
Skeleton: Cartilage instead of bone
Species: More than 500 known species
About Sharks
Sharks are a large and diverse group of fish found throughout the world's oceans. They have existed for hundreds of millions of years and appeared long before dinosaurs walked on land.
Sharks come in many different shapes and sizes. Some are small enough to fit in your hands, while the enormous whale shark can grow longer than a school bus.
Although sharks are fish, their skeletons are not made from bone. Instead, they are made primarily from cartilage, the same flexible material found in parts of the human nose and ears.
Shark Senses
Sharks have highly developed senses that help them locate prey and navigate through the ocean.
They can detect movement, smell chemicals in the water, and sense vibrations through a system called the lateral line.
Sharks also possess special sensory organs called the ampullae of Lorenzini. These tiny pores allow them to detect weak electrical fields produced by living animals.
Sharks continually replace their teeth throughout their lives. Many species have several rows of teeth, and when one is lost, another can gradually move forward to take its place.
The Sunlight Zone
Many familiar sharks spend much of their time in the Sunlight Zone, also known as the Epipelagic Zone. This layer stretches from the ocean's surface to about 200 meters (656 feet) deep.
Sunlight reaches this part of the ocean, allowing phytoplankton, algae, and marine plants to carry out photosynthesis. Because so much food originates here, the Sunlight Zone supports enormous numbers of marine animals.
Sharks in these waters may hunt fish, squid, rays, sea turtles, and other animals depending on the shark species.
Not every shark remains near the surface. Some species regularly travel into much deeper water, and deep-sea sharks can spend most of their lives far below the Sunlight Zone.
What Do Sharks Eat?
Shark diets vary greatly. Many species are predators that eat fish, squid, crustaceans, marine mammals, or other sharks.
However, not every shark hunts large prey. Whale sharks and basking sharks are filter feeders. They swim through the water collecting tiny organisms such as plankton instead of hunting large animals.
Shark Teeth
Different sharks have teeth suited to different diets. Sharks that catch fish may have narrow, pointed teeth that help grip slippery prey.
Sharks that attack larger animals may have broad, serrated teeth designed for cutting, while some bottom-dwelling species have flatter teeth for crushing crabs and shellfish.
Because shark teeth are constantly shed and replaced, a single shark may produce thousands of teeth during its lifetime.
How Do Sharks Breathe?
Sharks breathe using gills. Water passes across the gills, where oxygen dissolved in the water enters the shark's bloodstream.
Some sharks need to keep swimming so water continues flowing over their gills, but many species are able to actively pump water across their gills while resting.
Different Types of Sharks
There are more than 500 known shark species. Some well-known examples include great white sharks, tiger sharks, hammerhead sharks, bull sharks, mako sharks, nurse sharks, whale sharks, and thresher sharks.
Their lifestyles can be extremely different. Some live around coral reefs, some cross the open ocean, some remain near the seafloor, and others inhabit deep, dark waters.
Where Are Sharks Found?
Sharks live in oceans throughout the world, from warm tropical reefs to cold polar waters.
A few species, including bull sharks, are even capable of entering freshwater rivers. Because the shark group is so diverse, sharks can be found in an enormous variety of marine habitats.
Why Sharks Are Important
Sharks are important members of marine ecosystems. Predatory sharks can help regulate the populations and behavior of other animals in the food web.
Many shark populations face threats from fishing, accidental capture, habitat changes, and the demand for shark products. Protecting sharks can also help protect the larger ocean ecosystems they inhabit.