Sharks for Kids

A shark is a type of fish. It lives in water, breathes through gills, has fins, and has a backbone.

There are more than 500 different kinds of sharks. They come in an amazing variety of shapes and sizes. Some are small enough to fit in your hand.

The enormous Whale Shark can grow longer than a school bus.

Some sharks are fast swimmers that travel through the open ocean, while others spend much of their time close to the seafloor.

What Makes a Shark a Fish?

• Sharks breathe through gills.
  Water passes over a shark’s gills. The gills take oxygen from the water. Sharks do not have to come to the surface to breathe air the way whales and dolphins do.
• Sharks have fins.
  A shark’s fins help it move and control its body in the water. Different fins help with swimming, steering, turning, and balance.
• Sharks have a backbone.
  Sharks are vertebrates, which means they have a backbone. Their backbone is made of cartilage instead of bone.
• The body temperature of most sharks is like the water around them. When the water gets warmer or colder, their bodies do too. A few sharks, including some mako and white sharks, can keep parts of their bodies warmer than the water.

How Are Sharks Different Than Most Fish?

• Sharks have dermal denticles.
  A shark’s skin is covered with tiny, tooth-like scales called dermal denticles. They make the skin feel rough and help water flow smoothly over the shark’s body.
• Sharks continually replace their teeth.
  Many sharks grow new teeth throughout their lives. When a tooth is lost, another can move forward to replace it. Different sharks have different kinds of teeth depending on what they eat.
• Sharks do not have swim bladders.
  Many bony fish have a gas-filled organ called a swim bladder. It helps them control their position in the water. Sharks do not have one. Instead, their large, oily liver helps them stay buoyant. Their fins also help control their movement.

Caribbean Reef Sharks

Great White Shark

Sharks come in many different shapes and sizes. They do not all look the same. Different sharks have adapted to different habitats and ways of finding food.

A typical fast-swimming shark has a smooth, streamlined body. It has a pointed or rounded snout, fins, and a strong tail. This body shape helps the shark move easily through the water.

But not every shark looks like this. Angel sharks have flat bodies that help them rest on the seafloor. Hammerhead sharks have wide heads shaped like hammers. Sawsharks have long snouts lined with tooth-like structures. Wobbegongs have flat bodies, patterns, and skin flaps that help them hide on the seafloor.

 Why Do Sharks Have Fins?

Sharks use different fins for different jobs. The tail fin, or caudal fin, provides much of the power for swimming. Pectoral fins on the sides help with lift and control. Dorsal fins on the back help keep the shark from rolling.

Fins can also tell us something about how a shark lives. Fast-swimming sharks may have long or stiff fins that help them travel. Sharks that live near the bottom may have broad fins. These fins can help them move and rest near the seafloor.

Why Do Sharks Have So Many Different Teeth?

A shark’s teeth match the way it eats. Sharks that catch fish may have narrow, pointed teeth for holding slippery prey. Sharks that bite larger animals may have broad, sharp-edged teeth for cutting. Sharks that eat hard-shelled animals may have flatter teeth for crushing.

Whale Sharks and Basking Sharks are different. They are filter feeders that collect tiny organisms from the water. They do not need large cutting teeth to eat.

Scientists use classification to organize living things into groups. Sharks belong to a scientific group called a class, which is divided into smaller groups called orders. Living sharks are divided into 9 orders. In the classification system, order comes after class and before family.

Shark-like fishes appeared hundreds of millions of years ago, long before the first dinosaurs walked on land.

The earliest sharks did not look exactly like the sharks swimming in the ocean today. Over millions of years, different shark groups appeared, changed, and disappeared. Some ancient sharks had body shapes, teeth, or spines that would look very unusual to us now.

Studying shark fossils can be difficult because a shark’s skeleton is made mostly of cartilage. Cartilage usually breaks down after an animal dies instead of becoming a fossil. Shark teeth are much harder, so they are among the most common shark fossils scientists find.

Teeth can reveal a lot. Their shape can help scientists identify different kinds of ancient sharks and sometimes give clues about what those sharks ate.

Sharks also survived several major extinction events that changed life on Earth. The sharks living today are the result of this very long history of change and survival.

Sharks live in waters around the world. Some are coastal sharks that live near land, while others are ocean sharks that live farther out at sea. A few sharks can even live in freshwater rivers.

Sharks also live in many different habitats. A habitat is the place where an animal lives and finds what it needs to survive.

Coastal Waters

Coastal waters include areas near beaches, bays, islands, and shorelines. These waters often have plenty of food. Some young sharks also use sheltered coastal areas as safe places to grow.

Coral Reefs

Coral reefs are busy habitats filled with fish and other animals. Sharks may hunt around the reef, rest in sheltered areas, or swim along its edges.

Mangroves and Seagrass Meadows

Mangroves and seagrass meadows grow in shallow coastal waters. They provide food and shelter for many animals. Some young sharks use these protected habitats while they grow.

Open Ocean

The open ocean stretches far beyond the coast. Sharks that live here may travel enormous distances searching for food, mates, or suitable water conditions.

Deep Sea

The deep sea is cold, dark, and under great pressure. Sharks that live here have special adaptations that help them survive in this difficult environment.

Sharks do much more than swim around looking for food. They rest, travel, avoid danger, find mates, and respond to what is happening around them.

Different sharks behave in different ways. Some stay in the same general area, while others travel hundreds or even thousands of miles. Some sharks migrate during certain seasons to find food, reach suitable waters, or return to places where they mate or give birth.

Sharks are also active at different times. Nurse Sharks often rest during the day and become more active at night. Other sharks are active during the day, and some move between shallow and deeper water at different times.

Some sharks usually live alone, while others gather in groups. Scalloped Hammerheads can form large schools. Sharks may also gather where food is plentiful or at resting, mating, or nursery areas.

Sharks use their senses to understand what is happening around them. They can see, hear, smell, detect movement in the water, and sense tiny electrical signals made by other animals. These senses help them find food, avoid danger, and move through their environment.

What Do Sharks Eat?

Sharks eat many different kinds of food. What a shark eats depends on its species, size, habitat, and the food available where it lives.

Many sharks eat fish, squid, crabs, shrimp, and other ocean animals. Larger sharks may also eat rays, sea turtles, seabirds, seals, and other marine mammals. Some sharks have very specialized diets. Whale Sharks and Basking Sharks feed mainly on tiny animals called plankton, which they filter from the water.

A shark’s teeth often give clues about what it eats. Sharks that catch fish may have narrow, pointed teeth for gripping slippery prey. Sharks that eat hard-shelled animals may have flatter teeth for crushing shells. Great White Sharks have broad, sharp-edged teeth that help them bite into larger prey.

Shark Reproduction and Life Cycle

Sharks reproduce in several different ways. Unlike most fishes, shark eggs are fertilized inside the mother’s body.

Some sharks lay eggs. The young shark develops inside a tough egg case until it is ready to hatch. In many other species, the young develop inside the mother and are born alive.

Sharks usually produce far fewer young than many other fishes. Depending on the species, a shark may have only a few pups at a time, while others can have much larger litters. Some young sharks spend their early lives in nursery areas, where shallow or sheltered water provides food and some protection.

Young sharks must survive on their own after they are born or hatch. As they grow, they learn to find food and move through their habitat. Many sharks grow slowly and take several years to become adults. Some species live for many decades, and a few can live for more than a century.

Amazing Shark Abilities

Sharks have some abilities that may seem almost like superpowers. These abilities are adaptations that developed over many generations and help different sharks survive in their environments.

They Can Sense Electricity

Every living animal produces tiny electrical signals when its muscles and nerves work. Sharks can detect these signals using special sense organs. This can help a shark find prey even when it is hidden beneath the sand.

Some Sharks Glow

Several deep-sea sharks can produce their own light. This ability is called bioluminescence. Depending on the species, glowing can provide camouflage, help sharks recognize one another, or serve other purposes.

Some Sharks Can Warm Parts of Their Bodies

Most sharks have body temperatures close to the temperature of the surrounding water. But some sharks, including mako sharks and white sharks, can keep parts of their bodies warmer. This helps important muscles and organs work well in cooler water.

Some Sharks Use Camouflage

Sharks use camouflage in different ways. Wobbegongs have patterns and skin flaps that help them blend into reefs and the seafloor. Angel Sharks can partly bury themselves in sand. Many open-ocean sharks have dark backs and pale bellies that make them harder to see from above or below.

Sharks Can Replace Lost Teeth

Sharks continually grow new teeth throughout their lives. New teeth develop behind older teeth and move forward to replace teeth that are lost.

Sharks Have Very Different Body Designs

A Hammerhead Shark, Whale Shark, Sawshark, Angel Shark, and Lanternshark may look very different, yet all of them are sharks. Their unusual features are adaptations to the different ways they live.

Sharks are an important part of ocean ecosystems, and different kinds of sharks have different roles within them.

Many sharks are predators. By eating other animals, they can help shape which animals live in an area and how many there are. Some sharks also eat weak, injured, or dead animals.

Other sharks have very different roles. Whale Sharks and Basking Sharks eat tiny organisms called plankton. Sharks that live near the seafloor may eat crabs, shellfish, fish, octopuses, and other animals. Each kind of shark is connected to the other living things in its habitat.

Sharks can also help move nutrients through the ocean. When sharks eat in one place and travel to another, they carry nutrients with them. Those nutrients eventually return to the environment, where they can be used by other living things.

Scientists study sharks to learn more about ocean ecosystems. Changes in where sharks live, what they eat, or how many are found in an area can give scientists clues about changes happening in the ocean.

Sharks are not important because they all do the same thing. With hundreds of different species, sharks are connected to ocean life in many different ways.

Many shark populations around the world are decreasing. Sharks have survived enormous changes on Earth, but today many species face dangers caused by human activities.

Fishing is one of the greatest threats. Some sharks are caught on purpose for their meat, fins, and other products. Others are caught accidentally on hooks or in nets meant for other kinds of fish. This accidental capture is called bycatch.

Many sharks grow slowly, take years to become adults, and produce only a small number of young. This means that when too many sharks are caught, it can take a long time for their populations to recover.

Sharks can also be harmed when important habitats are damaged. Coral reef decline, the loss of mangroves and seagrass beds, pollution, and coastal development can change the places sharks use to find food, rest, and raise their young.

People can help protect sharks in many ways. Fishing rules can limit how many sharks are caught, and changes in fishing equipment and methods can reduce bycatch. Protecting important habitats gives sharks safer places to live and raise their young. Scientists also study and track sharks to learn which species and habitats need the most protection.