Sharks are notoriously carnivorous hunters. There are a small number of species that do not feed on fish and similar prey but, for the most part, this reputation holds true. Fish, squid and crustaceans are generally the most freely available, but sharks will include seals, other sharks and even the odd human being in their diet, depending on availability.
In general, however, a certain shark species will stick to a specific diet with little deviation from that particular prey. There are exceptions to the rule as is the case with Tiger Sharks, which are known to feed on almost anything.
There are three known methods that sharks use to eat. These are 1) filter feeding, 2) tearing and 3) swallowing the prey whole. Filter feeding is the method used by Whale Sharks, Basking Sharks and Megamouths. They feed mainly on plankton and, although they all make use of filters, their methods differ. Whale Sharks suck plankton and small fish in, Basking Sharks swim through large groups of plankton with their mouths gaping (allowing plankton to enter in naturally) and Megamouths have luminescent tissue inside their mouths, which works well to attract prey. The filters inside their mouths are made up of filaments that act as a sieve, allowing only plankton and tiny fish through. These sharks do have teeth, but they are small and ill-developed as they are unnecessary to their feeding.
Sharks that tear chunks of meat from their prey are known as cookiecutters. These species have incredibly well-developed, large, sharp teeth. They grab their prey with their teeth, secure them with their lips and twist their heads, ripping large pieces of meat off. Many surfers and swimmers have fallen victim to such an attack, leaving them very badly mauled if not dead. Once a piece of flesh has been torn from the prey, it is swallowed whole;sharks do not chew their food.
The third type of feeding involves swallowing the entire animal being eaten whole. These sharks hunt their prey, seize it using their teeth and gulp it down at once. Examples of these species include the Viper Dogfish, Thresher Shark and Sawshark.
Some sharks hunt in packs, which can exceed 100 animals in the case of Scalloped Hammerheads, and other prefer to hunt alone. Pack hunters cooperate with one another, herding and catching prey together. In these cases, they will often travel vast expanses of ocean in order to pursue food sources.
When hunting, sharks are known for appearing rather discreetly below their prey. Their dorsal side is dark,
making is difficult to spot them from above against the darkness of the ocean bed. They circle their prey, getting increasingly closer and more menacing. This behaviour then changes to a rapid crisscrossing until a rapid and violent attack is made. When sharks hunt in packs, their excitement frequently builds to such an extent that a feeding frenzy occurs. This chaotic attack results in the death of many fellow sharks.
Sharks kept in captivity may refuse to eat, displaying their ability to go for extended periods of time with no food. Similarly, males that are in a courtship period and females that are on nursery grounds may not feed for some time.
Sharks have a particularly short intestine. Food is first stored in the J-shaped stomach. If any unwanted prey or items entered the shark's mouth during an attack, it is discovered in the stomach and vomited out before entering the intestines.