Sharks can hide themselves because of their colouring. They are dark on top and silver on the underside and look like the colour of the water in which they live. In order to stay alive, animals need to have keen senses. Fish and some shellfish have sharp eyes. Almost all animals are sensitive to touch. Fish detect movements in the water by means of their lateral lines. Fish and other sea animals can hear well and many of them can make different types of warning sounds. In the future you will be hearing more and more about the sea. It is one of the last training places on Earth, which has not been fully explored by men. Today, more and more scientists are exploring the sea. This is because the population of the Earth is increasing so fast that very soon the land alone will not be able to provide enough food for everbody. That is why man is turning to the sea. It is like a huge storehouse. It contains not only food but also many other valuable things such as oil and minerals. The sea can also provide us with a lot of fresh water.