The Bottlenose Dolphin

The Bottlenose is the most common and well-known dolphin, recent molecular studies showing it is in fact two species, Common Bottlenose (Tursiops truncatus), and Indo-Pacific Bottlenose (T. aduncus).

It inhabits warm and temperate seas worldwide and may be found in all but the Arctic and the Antarctic Oceans.

The Bottlenose is grey, varying from dark grey at the top near the dorsal fin to very light grey and almost white or maybe even a pinkish colour at the underside. This makes it harder to see both from above and below when swimming. The elongated upper and lower jaws form what is called the rostrum, which gives the animal the name bottlenose. The real nose, however, is the blowhole on top of its head, and the nasal septum is visible when the blowhole is open. Its face shows a characteristic "smile". The "smile" does not mean that it is happy; it is unable to move its jaw to any other position.

Adults range in length from 2 to 4 metres (6 to 13 ft) and in weight from 150 to 650 kilograms (330 to 1430 lb); however, in most parts of the world, the adult's length is about 2.5 m (8 ft) and adult weight ranges from 200 to 300 kg (440 to 660 lb), with males being slightly longer and considerably heavier than females, on average. The size of the appears to vary considerably with habitat. Most research in this area has been restricted to the North Atlantic Ocean, where researchers have identified two ecotypes. Those dolphins in warmer, shallower waters tend to have a smaller body than their cousins in cooler pelagic waters. For example, a survey of animals in the Moray Firth in Scotland, the world's northernmost resident population, recorded an average adult length of just under 4 m (13 ft). This compares with a 2.5 m (8 ft) average in a population of Florida. Those in colder waters also have a fattier composition and blood more suited to deep-diving.

The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and don't contain bones or muscle. The animal propels itself forward by moving the flukes up and down. The pectoral flippers (at the sides of the body) are for steering; they contain bones clearly homologous to the forelimbs of land mammals (from which dolphins and all other cetaceans evolved some 50 million years ago). In fact, recently, a Bottlenose was discovered in Japan that has two additional pectoral fins, or "hind legs," at the tail, appearing to be about the size of a human's pair of hands. Scientists believe that a mutation must have caused the ancient trait to reassert itself.

Every 5-8 minutes, the Bottlenose Dolphin, like all other dolphins, needs to rise to the surface to breathe through its blowhole, though it generally breathes more frequently - up to several times per minute. Its sleep is thus very light; some scientists have suggested that the two halves of its brains take turns in sleeping and waking. It has also been suggested that it has tiny periods of 'microsleep'.

The Bottlenose normally lives in groups called pods, usually containing up to 12 animals. These are long-term social units. Typically, a group of adult females and their young live together in a pod, and juveniles in a mixed pod. Several of these pods can join together to form larger groups of one hundred dolphins or more. Males live mostly alone or in groups of 2-3 and join the pods for short periods of time.

The species is commonly known for its friendly character and curiosity towards humans immersed in or near water. It is not uncommon for a diver to be investigated by a group of them. Occasionally, dolphins have rescued injured divers by raising them to the surface, a behaviour they also show towards injured members of their own species. Such accounts have earned them the nickname of "Man's best friend of the sea". In November 2004, a more dramatic report of intervention came from New Zealand. Three lifeguards, swimming 100 m (328 ft) off the coast near Whangarei, were reportedly approached by a 3 m (10 ft) Great White Shark. A group of Bottlenose Dolphins, apparently sensing danger to the swimmers, herded them together and tightly surrounded them for forty minutes, preventing an attack from the shark, as they returned to shore.

Dolphins are predators however, and they also show aggressive behaviours. This includes fights among males for rank and access to females, as well as aggression towards sharks, certain (but not all) Orcas, and other smaller species of dolphins. Male dolphins, during the mating season, compete very vigorously with each other through showing toughness and size with a series of acts such as head butting. At least one population, off Scotland, has been observed to practice infanticide, and has also been filmed attacking and killing Harbour Porpoises. Researchers at the University of Aberdeen in Scotland have discovered that the local Bottlenose Dolphins attack and kill Harbour Porpoises without eating them due to competition for a decreasing food supply.

Female Bottlenose Dolphins live for about 40 years, whereas males rarely live more than 30 years