Still More Sharks!

Tiger sharks will try almost any food. A tiger shark’s diet includes fish of all kinds, other sharks, crabs, sea snakes, turtles, and sea lions. The tiger shark will eat dead, floating animals and snatch sea gulls off the water’s surface. It will even eat cardboard boxes and other garbage floating in the water near coastal cities.

Although it is as ferocious as the animal it is named for, the tiger shark has no stripes. It has spotted markings.

They are looking for food, of course. Unlike most sharks that can live only in salt water, bull sharks can adapt to the fresh water of rivers and lakes.

Bull sharks have been found hundreds of miles from the sea in major rivers such as the Amazon in Brazil, the Ganges (GAN jeez) in India, and even the Mississippi River in the United States. Bull sharks have also been discovered in lakes with access to the sea, such as Lake Jamoer in Indonesia (in deh NEE zhuh) and Lake Nicaragua (nihk uh RAH gwuh) in Central America.

While hunting fish and other sharks, bull sharks have been known to attack swimmers.

Nurse sharks find their favorite foods—crab, lobster, and shrimp—on the ocean floor. While whale and basking sharks feed near the surface of the ocean, nurse sharks feed on the ocean bottom. They lie there without moving, waiting for prey to come near.

Unlike many other sharks, a nurse shark does not need constant motion to breathe. It breathes in a different way. Opening and closing its mouth makes a muscle expand and contract. The muscle acts like a valve in the nurse shark’s throat. This “pump action” keeps water and oxygen flowing, even when the nurse shark isn’t moving.

The habit of staying motionless in shallow water makes nurse sharks a danger to people. Thinking they were a different kind of fish, swimmers have tried to capture nurse sharks by their tails. These swimmers have been attacked.

Lantern sharks include some of the smallest sharks. In fact, the dwarf lantern shark is the smallest known shark. It grows only 8 inches (20 centimeters) long and weighs only 1/2 ounce (15 grams).

Lantern sharks are deep-water feeders that eat shellfish and small squid. These sharks are members of the dogfish family of sharks. Most of them are small and slender.

The belly of a lantern shark lights up like a lantern. That is how this shark got its name. Many small light organs are embedded in the skin of the lantern shark’s belly. The light lantern sharks give off may help attract prey.

The saw shark uses its long, pointed snout more like a rake than a weapon.

A saw shark uses its barbels (bahr buhlz) to detect the small bony fish it likes to eat. Barbels are long, fleshy barbs that grow from the sides of the shark’s mouth. When its barbels sense prey, the saw shark uses its snout to stir up the sand. This brings the prey out of hiding, and the saw shark quickly captures its dinner.

Most saw sharks live off the coast of southern Australia. They are usually shy and harmless. They will, however, strike out at anyone who tries to handle their snouts. Since saw sharks grow to about 5 feet (1.5 meters) in length, it’s best to leave them alone—even if they seem harmless.

Think about this description and you decide. A goblin shark has a long snout, similar to that of the saw shark. The shovel-shaped snout hangs over its jaws. Long, needlelike teeth stick out from an expandable mouth that is one of the largest of any shark.

Goblin sharks were thought to be extinct. Then in the 1890’s, one was caught off the coast of Japan. Since then this strange shark has also been found in deep waters off South America, Europe, southern Australia, and Asia.

Many sharks, such as hammerheads and saw sharks, use their heads to capture prey. Thresher sharks, however, use their tails.

Thresher sharks grow to 20 feet (6.1 meters) in length. Nearly half of this length is tail. When a thresher finds a school of small fish, it whips its tail around the fish. It swims in smaller and smaller circles—enclosing the fish. The fish panic and draw themselves into an even tighter circle. When the fish are packed very tightly together, the thresher shark moves in for the kill. It quickly snatches a meal with its sharp teeth.

Its name may sound cute, but it comes from the grisly method this shark uses to attack its prey. These sharks are only about 20 inches (50 centimeters) long. But unlike most sharks, cookie cutter sharks prey on fish that are larger than themselves. They also attack dolphins, seals, and even whales.

A cookie cutter shark latches onto its prey with its sucking mouth. Then it sinks its sharp lower teeth into the fish and twists around. It carves out a plug of flesh, using its teeth like a cookie cutter.

Sometimes sharks attack prey so forcefully that they break and swallow their own teeth. A cookie cutter shark does this. It is common to find one with a whole row of teeth in its stomach.

Zebra sharks are another type of shark named after a land animal. A young zebra shark has stripes like a zebra. But the stripes gradually break up into spots as the shark grows older.

Like many other sharks, a zebra shark lays its eggs in tough, leathery egg cases. It uses long, barblike threads to attach the egg cases to coral, rocks, and other objects on the ocean floor. This helps to protect the eggs and keep them safe from predators.

In time, the baby zebra sharks hatch. They split open the cases, which often wash up on shore where people find them. The egg cases are called mermaids’ purses.

While most sharks hunt their own food, blue sharks often let fishing crews do the hunting for them.

The powerful blue shark follows schools of herring, tuna, and sardines. Fishing crews use large nets to catch these schools of fish. All too often, a blue shark will rip open the nets. The shark will then help itself to the catch.

Blue sharks sometimes become trapped in the fishing nets. The fishing crews will then capture the sharks and send them to be processed for food.

Maybe newest is not the right word. Much of the world’s vast ocean is still unexplored. Sharks that have been living there for millions of years are regularly being discovered.

One of the latest discoveries is the megamouth shark. A megamouth was first seen in 1976. Since then, several others have been found. In 1990, one survived being caught in a fishing net near Los Angeles, California. The 16-foot (4.9-meter) shark would have died if kept in captivity. So a team of scientists implanted transmitters in its head and released it. The scientists then tracked the shark’s movement at sea for several days.

The megamouth, as its name suggests, has a huge mouth and gigantic jaws. But it uses them to eat only tiny plankton. As other megamouths are found and studied, scientists will learn more about this “newest” shark.

It’s a shark—disguised as seaweed. Many animals have colors and patterns that help them blend into their surroundings. Most animals use this camouflage to hide from predators. But sharks are different. They camouflage themselves from prey.

The tasseled wobbegong (WOH buh gong), for example, has many branched lobes, or tassels, around its mouth. When the wobbegong lies in seaweed, its tassels wave just like the seaweed. Unsuspecting shrimp and fish swim by—only to be gobbled up by the wobbegong.

Another shark that hides from prey is the angel shark. It covers its flat body with sand and hides on the sandy ocean floor.

Not all sharks use camouflage to hide from prey. Some small sharks hide from predators. The swell shark’s brown blotches help it hide among rocks. If danger is nearby, it will even wedge itself into a crevice by puffing out its stomach.

Surprisingly, we might learn how to live longer. Many scientists believe sharks are among the healthiest creatures in the sea. Sharks rarely get cancer or other diseases. For many years, scientists have been studying sharks to learn about the excellent immune system in their bodies. The scientists hope that they will be able to use this knowledge to make humans just as resistant to disease.

We can also learn about how the ocean’s environment works from studying sharks. Sharks are the highest link in the ocean’s food chain. They help to keep the population of different fishes at normal levels. They also help keep the ocean clean by eating dead and diseased fish.

People may fear sharks, but sharks have much more reason to fear people. Over 30 million sharks are killed by people each year.

Some sharks are killed for their meat, liver oil, or skins. Others are killed simply for sport. Among the most threatened sharks today are makos, basking sharks, and great white sharks.

Most sharks have very low birth rates. This means that each year sharks have very few young. When too many adults of one kind are killed, survivors may not be able to raise enough young to keep the species from becoming extinct.

Some countries have passed laws to protect endangered sharks. Perhaps the best way to save sharks is to educate people about them. We should realize that sharks are not “bad” animals. Although they eat other fish to survive, sharks are an important part of their environment, and they pose little danger to humans.

Sharks make up several families of the class Chondrichthyes. The whale shark is Rhincodon typus; the basking shark, Cetorhinus maximus; the great white shark, Carcharodon carcharias, the great hammerhead, Sphyrna mokarran; the mako, Isurus oxyrinchus; the leopard shark, Triakis semifasciata.