Quote from Jaws... Quint: I'm not talkin' 'bout pleasure boatin' or day sailin'. I'm talkin' 'bout workin' for a livin'. I'm talkin' 'bout sharkin'!
Great whites like all other sharks have an extra sense given by the Ampullae of Lorenzini, which enables them to detect the electromagnetic field emitted by the movement of living animals.
Every time a living creature moves it generates an electrical field and great whites are so sensitive they can detect half a billionth of a volt.
This is equivalent to detecting a flashlight battery from 1000 miles away. Thus a great white's sense of sight is useful, but the shark does not depend on it.
A shark primarily uses its extra senses (i.e, Electrosense and Mechanosense) to locate prey from far off. Then, the shark uses smell and hearing to further verify that its target is food.
At close range, the shark utilizes sight for the attack. The shark will often in ambush deliver a massive disabling bite and then back off to allow the prey to expire.
This tactic allows the animal to avoid combat with dangerous prey, such as sea lions. It also has allowed occasional rescue of humans bitten by the animal, though it appears to attack humans mostly in error.
