Dolphins are among one of the most intelligent animal species. Dolphins are marine mammals closely related to toothed whales (orcas) and porpoises. There are approximately 32 dolphin species, being the most familiar the bottle nose dolphin. Most dolphin species are found in the shallow waters of the tropical and temperate oceans of the world; however, some species live in rivers. Dolphins feed principally on fish, squid, and shrimp. The hunting techniques of dolphins are based on speed and collaboration. Dolphins are considered as some of the most intelligent creatures after humans.
Dolphins produce a broad range of sounds by releasing air through their blowholes. Dolphins communicate by emitting whistle-like sounds. Dolphins often have been recorded producing the signature whistles of the other dolphins. It is believed that dolphins make burst-pulsed sounds when they're frightened, angry, or frustrated. These sounds can be addressed towards other dolphins, humans, or inanimate objects. Clicks are believed to be exclusively for echolocation, usually occurring in a short series known as click train. Echolocation allows dolphins to locate and identify objects underwater. Echolocation is also used for hunting.
There is a number of hunting techniques practiced among different dolphin species; however, some techniques appear to be exclusive to a particular dolphin population. Dolphins feed most commonly on fish, including herring, mackerel and cod, while others eat exclusively squid. Large dolphins, such as the killer whale (orca), usually eat other marine mammals, such as seals, sea lions, turtles, and even other whales. The amount of food depends on the type of fish or squid they eat. Herring and mackerel are high in fat, while squid is not. Dolphins that feed on herring and mackerel will get a lot of energy, while those that feed on squid will have to eat great amounts to obtain the desired energy.
Some dolphin species will work together in highly coordinated groups to squeeze their prey into higher densities in a technique known as herding. After the school of fish has been squeezed to about 200 times its original density, pairs of dolphins take turns plowing within the aggregation of fish created, feeding on the stunned fish. It is thought that each dolphin participating in the maneuver has more access to prey than if they were feeding individually. The high degree of coordination, timing, strict geometry and orderly turn taking demonstrates the advantage of this technique.
Corralling, another technique to capture fish, consists in chasing a school of fish into shallow waters where they're more easily captured. Bottle neck dolphins use a particular hunting technique called strand feeding which involves driving fish and shrimp towards mud banks, where they hurl themselves out of the water to feed more easily. This event, which is believed to be learned behavior, has only been seen occurring in South Carolina. Some dolphin species use their flukes to stun their prey, occasionally flipping them out of the water. Orcas (killer whales) often approach the beach to capture sea lions.
Records dating back to 1847 state that cooperative fishing between local fishermen, from Laguna, Santa Catarina, Brazil, and a resident population of bottle dolphins take place every day except during bad weather. During this human-dolphin fishing cooperation, dolphins drive fish towards fishermen who are waiting along the shore with a circular nylon net. One or two dolphins stand several meters outside the line of fishermen. A dolphin submerges moving seaward, and when it reappears, it's usually the signal for men to cast their nets. Fishermen recompense dolphins with the fish that escaped the nets.