Shark

Although sharks can be dangerous predators, they are not bloodthirsty monsters, but fascinating sea creatures and very skilled hunters.

Characteristics

What do sharks look like?

Sharks are one of the oldest animal groups and have been swimming in the world’s oceans for 400 million years. They are vertebrates and belong to the class of cartilaginous fish. Their skeleton is not made of real bones but of a cartilage-like substance.

Typical of sharks are the triangular fins and their torpedo-like body shape, which make them perfect swimmers. Only rays, which, like sharks, belong to the cartilaginous fish family, have a different body shape: they are flat and have wing-like fins. Unlike bony fish, sharks don’t have scales on their skin, but rather tiny skin teeth made of the same material as their teeth.

These skin teeth, which keep growing back, are all pointing backward. A shark’s skin is therefore smooth to the touch when stroking from head to tail, but rough and sharp like a grater when stroking in the other direction. The skin teeth enable the sharks to swim very quickly because the teeth reduce the friction of the water.

Unlike other fish, sharks don’t have a swim bladder, so they have to use their fins to keep moving to keep from sinking to the bottom. The open gill slits on the sides of the body are also typical of sharks. Depending on the group to which a shark belongs, there are five, six, or seven-gill slits on each side of the body.

Where do sharks live?

Sharks are sea dwellers and inhabit all the world’s oceans. Only a few shark and ray species also migrate through estuaries into rivers or, such as freshwater stingrays, live entirely in rivers. The bull shark is even found in a freshwater lake in Central America.

Depending on the species, sharks can be found from the shallow ocean lagoons to the deep sea. Some stay in one region their entire lives. Other species, such as blue sharks, migrate more than 5000 kilometers across the Atlantic. Researchers are trying to find out more about shark species and their habitats by equipping animals with tiny transmitters. Thanks to the transmitter signals, the researchers know where the sharks are at all times.

What types of sharks are there?

There are around 500 different shark species worldwide – from the dwarf shark, which is only 25 centimeters long, to the whale shark, which can be up to 14 meters long. Sharks are divided into two major groups: those with an anal fin (the fin on the ventral side in front of the caudal fin) and those without a caudal fin.

These groups are divided into several subgroups: angel sharks, saw sharks, dogfish, hexaniformes, bullhead sharks, nurse sharks, mackerel sharks, and ground sharks, which form the largest group with around 225 species.

How old do sharks get?

Sharks live differently depending on the species. Small bamboo sharks live about 25 years, and large species like the whale shark are said to live 60 to 100 years.

Behavior

How do sharks live?

Except for a few species like whale sharks and basking sharks, which are peaceful giants and feed on plankton, sharks are perfect hunters. Their fantastically trained senses make them the most successful predatory fish we know. The nose is in front of the snout. The great importance of the sense of smell for sharks is shown by the fact that the olfactory center can make up two-thirds of the brain.

Sharks find their prey almost blind even from great distances because they can still make out the tiniest traces of scent in the water. Sharks can also use their hearing to pick out the sounds of wriggling sick or wounded fish. And because sharks’ taste-sensing cells are spread almost all over the skin, sharks can also sense an animal’s taste by rubbing against it.

Sharks can see very well: Because their eyes are about ten times more sensitive to light than the human eye, they can still see something at great depths of the sea, where it is almost pitch black. In addition, most sharks can also perceive colors. And sharks – like other fish – also have a special sensory organ: the lateral line organ. It runs down the sides of the body from the head to the tail.

Embedded in a gelatinous mass there are sensory cells that sharks use to sense the finest pressure differences caused by movements in the water caused by their prey. The so-called Lorenzini ampoules are also located in the snout. With them, sharks can perceive electrical fields that are triggered by the heartbeat or muscle movement of other animals.

With this sensory organ, sharks can also recognize the magnetic field of the earth and use it for navigation. Sharks’ most important weapon, their teeth, grow back throughout their lives. And because their upper jaw is not firmly attached to their skull, their jaws are very mobile and can be pushed far forward when biting.

Friends and foes of sharks

Some movies and reports have caused many people to mistake sharks for monsters. But that’s not true: there are around 100 shark attacks on humans every year worldwide, and five to ten people are killed by sharks every year. But the risk of being struck by lightning is much greater. Basically, humans do not fit into the prey pattern of sharks. Accidents therefore usually only occur when large sharks, such as the great white shark, attack a surfer with a “test bite”. So they want to find out what they actually have in front of them.

However, shark attacks can also occur when people behave clumsily and, for example, get too close to sharks so that they feel threatened. However, some sharks, such as the gray reef shark, give a clear warning with their posture before attacking: they lower their pectoral fins – a signal to humans or animals to keep more distance from the shark. Conversely, millions of sharks are hunted and fished by humans every year.

More than 70 shark species are therefore threatened with extinction, many are now under protection. But sharks also have natural enemies: killer whales prey on smaller sharks, up to three meters long, and sperm whales also prey on sharks. And larger shark species certainly hunt smaller sharks.