WHY DO SHARKS ATTACK PEOPLE?
Sharks do not attack humans for the sole purpose of hunger. In fact, sharks do not know what the feeling of hunger is, and can go for many months without eating. This is not to say that sharks do not attack with the intention of seeking prey. Many attacks on divers and surfers especially can be attained to searching for food.
To a shark, a surfer on a surfboard slightly resembles that of a seal or sea lion, or a diver in a black wetsuit can look like other prey. That won't improve your mood if you're the person getting bitten but it might explain* why most shark attacks are non-fatal. They take a bite, don't like it and swim off.
Sharks also attack humans because they have been provoked or agitated by the person: some attacks happen when humans stray into an area of the sea that the shark considers its own. The shark hits back to defend its territory.
Many spear-fishers have been attacked by reef sharks because when they spear fish, the blood from the fish and it's vibrations can sometimes result in a feeding frenzy by many sharks. Bright colours can also be counted for attacks. As many people have believed in the past, sharks do in fact can see colours, and do indeed have very good eyesight. wearing orange/yellow can aggravate the shark, and possibly lead to attacks.
Sharks are in fact attracted by splashing and vibrations in the water, and it can sometimes be attributed to attacks. Most scientists have not been able to predict why and where sharks attacks.
Cases when a shark specifically targets a human are very rare, George Burgess, of the University of Florida has estimated this only happens about once a year.
* Some experts say non-fatal attacks can also happen when the shark takes a bite, then swims away to allow you to bleed to death. At this point most humans are rescued by people nearby.