Why do sharks swim all the time
What do sharks look like?
Sharks are one of the oldest animal groups and have been swimming through the world's seas for 400 million years.
They are vertebrates and belong to the class of cartilaginous fish. Your skeleton does not consist of real bones, but of a cartilaginous substance.
Typical of sharks are the triangular fins and their torpedo-like body shape, which make them perfect swimmers.
Only the rays, which like sharks also belong to the cartilaginous fish, have a different body shape: They are flat and have wing-like fins.
Unlike bony fish, sharks do not have scales on their skin, but rather tiny skin teeth made of the same material as their teeth.
Those skin teeth that keep growing back are all directed backwards. A shark's skin therefore feels smooth when stroked from head to tail, but rough and sharp like a grater when stroked the other way.
The skin teeth enable the sharks to swim very quickly because the teeth reduce the friction of the water.
In contrast to other fish, sharks do not have a swim bladder: they have to keep moving with the help of their fins in order not to sink to the bottom.
The open gill slits on the sides of the body are also typical of sharks. Depending on the group a shark belongs to, there are five, six or seven gill slits on each side of the body.
Where do sharks live?
Sharks are sea creatures and colonize all oceans.
Only a few species of sharks and rays migrate through estuaries into rivers or live entirely in rivers, such as the freshwater stingrays.
The bull shark is even found in a freshwater lake in Central America.
Depending on the species, sharks can be found from the shallow sea lagoons to the deep sea. Some stay in one region for their entire life. Other species, such as blue sharks, migrate more than 5000 kilometers across the Atlantic.
Researchers are trying to find out more about the shark species and their habitats by equipping animals with tiny transmitters. Thanks to the signals from the transmitter, the researchers know where the sharks are at any given time.
What types of sharks are there?
There are around 500 different species of shark around the world - from a minke shark that is just 25 centimeters long to a whale shark that is up to 14 meters tall.
Sharks are divided into two broad groups: sharks 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, sawshark-like, dogfish-like, hexaniformes, bullhead shark-like, nurse shark-like, mackerel shark-like and the ground sharks, which form the largest group with about 225 species.
How old do sharks get?
Sharks get different ages depending on the species. Small bamboo sharks live around 25 years, while large species such as the election shark are said to live to be 60 to 100 years old.
How do sharks live?
Except for a few species such as 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 at the front of the muzzle. The great importance of the sense of smell for sharks is shown by the fact that the olfactory center can make up up to two thirds of the brain.
Sharks find their prey almost blindly, even from a great distance, because they can still make out the tiniest traces of scent in the water.
With their hearing, sharks can also hear the sounds of sick or wounded fish wriggling.
And because the shark's taste sensory cells are distributed almost over the entire skin, sharks can also perceive an animal's taste by rubbing against it.
Sharks can see very well: Because their eyes are about ten times as sensitive to light as the human eye, they can still see something at great depths of the sea, where it is almost pitch black.
Most sharks can also see colors.
And sharks - like other fish - also have a special sensory organ: the lateral line organ.
It runs along the sides of the body from head to tail.
There sensory cells are embedded in a gelatinous mass, with which sharks sense the finest differences in pressure caused by movements in the water caused by prey animals.
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 sense organ, sharks can also recognize the magnetic field of the earth and use it for navigation.
The sharks' main weapon, their teeth, grow back for a lifetime.
And because your upper jaw is not firmly attached to the skull, the jaws are very mobile and can be pushed far forward when you bite.
Friends and enemies of the sharks
Some films and reports have led many people to mistake sharks for monsters. But that is not true: there are around 100 attacks by sharks on humans worldwide every year, 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 shark's prey scheme. Accidents therefore usually only occur when large sharks, such as the great white shark, attack a surfing person with a "test bite". From the sharks' point of view, when surfers lie on their boards and paddle through the water with arms and legs, they look like seals from below.
Shark attacks can also occur when people behave in a clumsy manner 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 by their posture before they attack: They lower their pectoral fins - a signal to humans or an animal 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, and many are now under protection.
But sharks also have natural enemies: killer whales hunt smaller, up to three meters long, and sperm whales hunt sharks too. And larger shark species also hunt smaller sharks.
How do sharks reproduce?
Sharks reproduce differently depending on the species. However, it differs fundamentally from that of the other fish: While in these the females usually release the eggs into the water and the males give their seeds in the water above, in sharks there is a correct pairing of males and females.
The eggs are fertilized in the body of the female shark. To do this, the males insert the so-called clamp organs, which have developed from the edge of the ventral fins, into the so-called cloaca of the female.
After fertilization, a shell is formed around each egg.
Depending on the type of shark, the female then lays egg capsules in which the cubs grow, or the fertilized eggs continue to develop in the body of the female shark and the female finally gives birth to live cubs.
Dogfish, for example, give birth to live young and the gestation period is 22 months.
What do sharks eat?
The largest sharks, of all things, feed on plankton:
The whale sharks, up to 14 meters long, and basking sharks, up to ten meters long, use their gills to filter plankton from the water.
Most other sharks, however, are predators and feed on fish and other marine animals - from octopus to seals and elephant seals to dolphins.
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