This passage is mainly about_________.

Every year sharks kill or injure a number of unfortunate bathers in the warmer parts of the world. They are particularly common around the beaches of southeast Australia, where special precautions are taken against them. Near some popular beaches shark-proof wire fences have been built in the sea. In other places helicopters or small aircraft regularly patrol the sea, ready to send a radio message to the shore and to give an alarm as soon as a shark is seen.
    One of the richest men in Australia owed some of his success to his courage in facing a shark. When he was an unemployed youth in 1922, Frank Beaurepaire saw a young man being attacked by a shark off a Sydney beach. He saw a lifesaver swim out to help the young man but realized that the lifesaver could not fight off the shark and rescue the injured man at the same time. Although he was not an expert swimmer, he dived into the water and helped the lifesaver to bring the injured man to the beach.
    Unfortunately the shark had attacked so viciously that its victim soon died.  However, the public heard about the rescue and collected a large sum of money for the rescuers. Frank Beaurepaire received $ 500 and started a small motor-tyre business. He worked hard and soon became prosperous. By the time the Second World War started he was a millionaire.