Sharks are among the most feared and, at the same time, the most beautiful and most complex creatures of the seas and oceans. They have a very bad reputation for being mean and aggressive creatures, but this is only a myth – as a matter of fact, there are only four species out of more than 400 that have ever attacked humans, the others being tame, often very cute animals.
Sharks live in all marine environments – whether it is a turbulent region of the sea or it is calm waters that you are looking at, sooner or later you will meet a shark. Many species prefer shallow waters, but they feel at home in the deeper layers as well. Greenland sharks, for example, can swim 2,200 meters (over 7,200 feet) below the surface, but very few sharks have ever been recorded in layers of the sea that are deeper than 3,000 meters.
Sharks are fish distinguished from other groups of fish species by a number of physical features that make them very special. One of these features is the cartilaginous body, that is, a skeleton made of a material more flexible and softer than bone. Other distinctive features include the 5-7 gill slits on the sides of their head and the pectoral fins that are not fused with the head. Sharks are incredibly varied in terms of size. They can be sized anything from a few inches long to several dozens of feet long. Pygmy sharks are among the tiniest in the world, with adults measuring only a few inches in length, while the whale shark can reach over 4 feet in length.
Sharks have very acute senses, making them very aware of their environment and very quick to react to the information coming from their surroundings:
their senses are extremely well-developed, being able to detect a single drop of blood in the water from miles away;
their eyesight is also excellent – their eyes are very similar to the eyes of vertebrates, “equipped” with pupils and eyelids (they never blink, though, they don’t need to because the water cleans and lubricates their eyeballs). For a long time, it was believed that sharks can’t see colors, but it turned out that they aren’t color blind – they are actually attracted to certain hues such as “yummy yellow”
sharks are believed to have very sharp hearing as well, being able to hear their victim from miles away.
Nobody knows all about sharks, but what it’s sure is that they are very quick. They generally cruise around at a speed of around 8 km an hour, but when they sense the proximity of prey, some of them, such as the shortfin mako shark, are able to speed up to 50 km an hour, even though only on short distances. Another feature that sharks are famous for is that most of them need to be in continuous motion to be able to breathe. This is because most shark species breathe by swimming with their mouth open, passing water through their body and filtering out the oxygen on the go. However, some shark species can take a rest, too: angel sharks, for example, are able to hold water in their cheeks and pump it over their gills, an activity called buccal (cheek) breathing that allows them to get oxygen even when they are resting.