Sharks are amazing creatures. I often fish for them off the sand, and have developed a respect for them. I intended to keep small ones for the pan, but five years later I have put them all back. I haven't caught any at high risk times for swimmers, it is all dawn and dusk stuff. They are amazing creatures, and are able to pick up magnetic interference from the heartbeat of a creature through the ampule of lorenzini on their snout, they can pick up vibrations such as splashing through their lateral lines, and can detect blood/oil through a highly adapted nose. I read somewhere that people are pretty safe as sharks can detect we don't have a high enough fat content (such as seals etc) and they leave us alone. Unless you eat a fair bit at Macca's, then you should stay in knee deep water.