THE chance of being killed by a shark in United States waters, scientists say, is far less than that of dying from a bee sting, a snake bite or even lightning .
But that does not mean there is no risk. Worldwide, there are probably 50 to 75 shark attacks every year, resulting in 5 to 10 deaths, according to the records in the International Shark Attack File at the Florida Museum of Natural History in Gainesville. About half occur off the United States, where affluence and leisure and hundreds of miles of prime beaches draw people into the ocean.
Once there they often unwittingly find themselves in or near the primary feeding zone of large coastal sharks, often near a dropoff or inshore of a sandbar where a shark may be trapped at low tide. Natural prey tends to congregate in there.
Almost any shark six feet or longer is a potential assailant, but three species have been mainly implicated: the great white, bull shark and tiger. All are found around the world, all are large and all eat large prey like seals or sea turtles.
Some scientists speculate that most attacks on humans -- except when a plane crash or the sinking of a ship throws many into the water and causes a shark feeding frenzy -- are cases of mistaken identity. Humans are roughly the same size as seals, for instance, and seals are prime prey of the adult great white shark.
Sharks frequently adopt a "bite and spit" tactic. Some scientists believe that a great white, for instance, attacks its prey with a single bite of its formidable teeth, then backs off so as to avoid possible injury in a struggle and waits for the prey to go into shock or bleed to death. Then it moves in and consumes the prey.
Rarely, if ever, has a shark been known to consume a human. The reason may be that the person is rescued before the shark can complete its feeding or because it recognizes that its victim is not normal prey. But if the shark takes a big enough bite, the person may die anyway.
Some scientists believe that the advent of smaller, rounder surfboards with "V" tails since the early 1970's may provoke some California shark attacks. Viewed from below, the silhouette of a surfer paddling on such a board looks very much like that of a swimming seal.
Experts advise swimmers not to wander too far from assistance; to stay in groups, and to stay out of the water if bleeding or menstruating and at twilight and after dark, when sharks are most active and have an overwhelming sensory advantage.
Swimmers are also urged to avoid excessive splashing and shiny jewelry that might look like scales of a prey fish; to avoid uneven tanning and bright-colored clothing, since sharks see contrast very well; to keep pets, with their erratic movements, out of the water; and to avoid areas where fishermen are active and bait fish or other signs of feeding activity are in evidence.