In recent years, scientists have uncovered a lot of new information about shark physiology, but the day-to-day life of sharks remains fairly mysterious. Most shark species are very difficult to study because they travel quickly over long distances, sometimes deep in the sea. They live in a world that is largely inaccessible to humans.
We do know that sharks are solitary animals, for the most part. They typically live and hunt by themselves, joining up with other sharks only in certain circumstances, such as mating. Some sharks will form schools on occasion, however. Researchers aren't really sure why this occurs because sharks don't really need protection from predators and they don't feed in schools. At this point, it's still unclear why sharks behave this way. In any case, the occurrence is very rare. Most of the time, sharks swim alone.
When they hunt, most sharks rely on the element of surprise in some way. In some camouflaged bottom-dwelling sharks, such as the various wobbegong species, this is a passive exercise. The shark blends in with the ocean floor, waiting for its prey. When a fish gets close enough, the shark opens its mouth wide and swallows the fish whole.
In active hunters, the element of surprise works a little bit differently. Great whites and other sharks that hunt bigger animals proceed very cautiously when approaching their prey. Once it has found a potential meal, the shark will circle at some distance, sizing up the situation. When it is ready, the shark moves in quickly, landing a good bite before the animal knows what's happening. Often, this first attack is sufficient to bring down the prey. Researchers have observed great whites behaving this way when hunting sea lions -- they will take one good bite, and then wait for the sea lion to die from blood loss. This sort of hunting takes a lot of energy out of a shark, so these species usually won't feed more than a couple times a week. Sharks that feed on smaller prey typically eat a few times every day.
On rare occasions, active sharks will cooperate in a hunt. Researchers have observed this phenomenon primarily in sevengill sharks. When these sharks hunt large fur seals, they rely on strength in numbers -- one large fur seal is too big for a single shark to take down itself. The sharks form a wide ring around a single seal, and slowly move in. When they get close enough, one shark will suddenly attack, and the rest will follow. This sort of behavior sometimes occurs in other shark species, but it is extremely rare.
Scientists also know that migration plays a big part in the lives of most shark species. The main reason most sharks migrate is that their food migrates. Different marine animals gather in certain areas throughout the year, for breeding, to lay eggs and other reasons. Sharks remember these annual patterns and return to these areas every year to take advantage of the population boom. Sharks will also remember human activity when it involves food supplies. Many species gather around fishing boats, for example, because they know fishermen might discard extra bait and small catches.
Despite what many of us think, sharks do face certain threats underwater. In the next section, we'll find out what a shark should be afraid of.