Teacher Background

Sharks are a type of fish that have lived on the earth for millions of years. They have not changed much in all of that time. While most fish have bony skeletons, a shark's skeleton is made of cartilage. Cartilage is a tough, hard material that bends easily. A shark is held together mostly by its muscles and skin. 

Sharks come in many different sizes and shapes, but they are the same in several ways:

1. Sharks have 5 - 7 pairs of gills that they use to get oxygen out of the water.

2. They have a rough skin covered with little tooth-like scales called denticles.

3. A shark's mouth is under its snout. The snout bends up and out of the way when the shark eats.

4. Sharks have several rows of teeth. As they lose teeth in front, the other teeth move forward to take their place.

5. Sharks have five different types of fins (dorsal fins- both on the top, tail fin, anal fin- bottom back, pelvic fin- bottom past midway, pectoral fin- on the sides). These fins work together to help the shark move through the water. The strong back tail fin pushes the shark forward at a fast rate. The pectoral fins help lift the shark up as it swims. The pelvic, anal, and dorsal fins help stabilize the shark.

6. A shark's eyes are on the sides of its head.

Sharks are found all over the world, from the icy waters of the Arctic, to the warm waters of the tropics, and even in some freshwater rivers and lakes.

Many things affect where species of sharks are found. The temperature of water, the amount of light available, the amount of salt in the water, the water currents, the amount and kinds of food that are available, and the types of predators all have an effect. One of the most important of these is temperature. Sharks cannot stand large changes in temperature. So sharks that like cold water stay near the Arctic, while sharks that like warm water stay in the tropics. Some sharks that like cold water can live in warmer places by swimming down deep where the water is colder.  Many kinds of sharks live near the water's surface, and a few live deep in the sea. There are even some sharks that live at the bottom of the sea. Open-ocean sharks are the fastest of the sharks but they are not as fast as many fish. Bottom dwelling sharks usually crawl along the ocean floor on their pectoral fins. When they swim, they wiggle their entire bodies in the same way eels move.

Sharks will sink if they stop swimming. Other types of fish have a special part called a swim bladder that is filled with air or gas. When the fish wants to float, it adds air to the swim bladder; when it wants to sink, it releases air. The shark doesn't have a swim bladder, so it must keep swimming or gravity will pull its body downward. The shark does get some help in staying afloat from its cartilaginous skeleton which is lighter than bone. It also gets help from its large liver. The oil in the liver is less dense than water, so it helps the shark be more buoyant.

Sharks are carnivorous animals and eat fish, crustaceans, mollusks, marine mammals, other sharks and sometimes garbage floating in the sea. Some sharks will eat almost any of these things, but others prefer only one or two types of food. Sharks swallow their food whole or in hunks. 

Features:

The teeth of a shark are suited to the type of food it eats. Most teeth are triangular in shape. Some are smooth while others have zigzag edges. Different shapes are used for seizing prey, cutting, or crushing. These teeth often fall out when the shark is eating, but it has rows of extra teeth waiting to move forward in the mouth.

The jaw of a shark is connected loosely to its skull. When the shark is ready to catch and eat its prey, the snout raises up and the top jaw protrudes. The lower teeth catch and hold the prey while the upper teeth slice it. Sharks have very powerful jaws, so they can bite through tough, thick prey. Sometimes groups of sharks become so excited while eating, they begin to act in a crazy way. They bite everything they can reach including themselves. This is called a feeding frenzy.

Sharks are usually shades of grey, blue, or brown with many variations in pattern.

Some sharks have unusual features:

Size:

The largest shark is the whale shark. It can be as long as 15 meters (50 feet). Sharks can be as small as the pygmy ribbontail catshark which can be as small as 24 cm (9") long.

Life Cycle:

Sharks grow slowly, some taking up to 20 years to grow up and reproduce. Shark babies are called pups and they look exactly like their parents and are ready to take care of themselves as soon as they are born.

Most sharks give birth to live babies, anywhere from 1 or 2 up to 100 at a time. However, some sharks hatch from eggs. The horn shark and swell shark lay leather egg cases in the sea and they rest on the bottom of the ocean until the eggs hatch out. Because of the size and shape of these cases they are nicknamed "mermaid purses". The mako shark and sandtiger shark have thin-shelled eggs which they keep inside their body until the pups hatch out.

A Shark's Senses:

Scientists have discovered many interesting facts about how the shark senses its environment. Sharks use their keen senses to find their way around and to locate and track down prey.

Shark Attacks:

Of all the species of sharks, only a small number are considered dangerous to people. Most of the attacks are by three sharks: great white shark, tiger shark and the bull shark. Most sharks are small and harmless and more apt to run away than to attack a human. Surveys have been made throughout the world to see how many shark attacks happen. These studies show that an average of 36 people are attacked by sharks in a year. Only a small number of these have died. Most attacks occur during warm weather, because this is the time when people and sharks are in the water at the same time.

Predators:

Species:

Below is a list of some of the species of sharks that could become topics of study for children's research. Add others as you find them, or contact the webmaster to be included in this table.

Shark Internet Links

Clip Art:

Copy and paste these into a word document and enlarge to fit the space required.