Sharks are a family of fish that has something very special in common – their skeletons are not made of bones but cartilage. Cartilage is a tissue much lighter and more flexible than bones. This is the same kind of flexible protein that makes our noses and ears. Since sharks live in the water, they breathe through 5-7 gills on each side of their body. They need to move at all times which forces water to go through the gill and supply them with oxygen. The iconic fin, called a dorsal fin, is situated on their back. Sharks have multiple rows of teeth, this means that if a shark loses a tooth, another one moves forward from a back row to replace it.
Although there is evidence that sharks existed as early as 450 million years ago, modern sharks have been swimming around for 100 million years. This makes them older than dinosaurs!!! Sharks have evolved very little during that time but despite that, they are very intelligent and have adapted very well to the conditions of their habitat. Nowadays, there are more than 500 different species of sharks!
Sharks generally live in oceans and seas although there are some species that are able to live in fresh water as well. Most sharks are night animals – they hunt predominantly in the evening and at night. A mother sharks gives birth to babies called pups. Even though they are small, they already have teeth and they are perfectly capable of taking care of themselves. Other sharks lay eggs like birds.
It is true that the occasional encounter of a shark with a human can have fatal consequences for the person but unfortunately we are much bigger threat to the sharks than they to us. The pollution of ocean water affects sharks’ food so chemicals slowly build up in their system; sharks try to eat the garbage thrown away in the water or they get accidentally caught up in fishing nets. However, the biggest threat is the ‘finning’ – sharks get their fins cut off and are thrown back in the water alive. But of course, they can not survive without fins. This practice is illegal and it causes the shark population to decline rapidly.
GREAT WHITE SHARK
gill – an organ of a fish for obtaining oxygen from water