Ascanner has it right; you have a better chance of being struck by lightning- seriously! The shark is way more afraid of you than you are of them. I paddle board the ocean daily, we see sharks a lot. The minute they see our boards they scram. A shark only attacks when it mistakes a person for a sea turtle or some other type of sea creature. If you were swimming and one came near you, stay calm. If by some miracle they were to attack, fight back. Aim for the nose and eyes.. at least that's what my fellow paddle boarders say! ;)
falling coconuts kill more people annually than sharks on a yearly average, this and the fact that humans are not in a sharks diet tells us that sharks are really not interested in humans as food. that's why when people get attact they lose a limb or get bit and not fully eaten becaust the shark knows its not its typical meal, just mistaked.. fyi. now for sure do not panic and swim, like other wild animals its the thrill of the chase, stay calm and get out your first clear chance but stay aware of the sharks where abouts. good luck :-)
If you're still treading water and waiting for a response at this time...SWIM TO SHORE NOW! Or be ready to punch it in the nose or eye. Do not get cut in the water. They can smell blood for up to a mile away.
Kivettome is speaking from experience and her answer is sound. Nevertheless we've had a number of shark attacks in Oz over the past few months -- and that's unusual. Almost all the victims survived (I think one was fatal). Several of them punched the shark's nose and drove it off.
If you keep out of the water near dawn and dusk you minimise the risk of being attacked.