Sounds: Certain types of irregular sounds, such as those made by a swimmer in trouble or an injured fish, definitely attract sharks. Sound, rather than sight or smell, seems to be a shark's primary cue for moving toward a target, even from a long distance. Anything unusual, such as the impact of an aircraft plunging into the sea or the mass of sounds transmitted through the sea when a ship sinks, appears to attract sharks, and may trigger attacks.
Colors: Sharks seem to be able to distinguish light colors from dark. Sharks of at least some species may be able to tell one color from another. Yellow, white, and silver seem to attract sharks. Many divers maintain that clothing, fins, and tanks should be painted in dull colors to avoid shark attacks. One group of experimenters, noticing the sharks' preference for a certain shade, dubbed the standard life jacket color"yum-yum yellow."
Movement: Certain irregular movements, such as those made by a swimmer in trouble or a wounded fish or seal, seem to attract sharks. Diving from a boat at sea or even in a harbor may invite shark attack. There are several records of divers who were attacked the moment they entered the water. Similarly dangerous is the sport of being towed in the water by a moving ship. When a person is being towed he or she may look like a fish to a shark.
Blood: Even greatly diluted and in small quantities, fresh blood, from any animal, definitely attracts sharks. So does vomit, offal, garbage, and carrion. In one case, a scuba diver was swimming near the bottom when his nose began bleeding. Some of the blood was draining into his mouth exiting in a stream of blood-tainted bubbles. A small shark, apparently aiming for the source of the alluring blood, twice struck at the diver's head and face, then darted away. The diver was only slightly injured. Even the trace of blood from a woman who is menstruating is believed enough to lure a shark.
Details mentioned in this article were accurate at the time of publication