COMMON DOLPHIN

                                           COMMON DOLPHIN

The common dolphin is the name given to two species (and possibly a third) of dolphin making up the genus Delphinus. Prior to the mid-1990s, most taxonomists only recognised one species in this genus, the common dolphin Delphinus delphis. Modern cetologists usually recognise two species — the short-beaked common dolphin, which retains the systematic name Delphinus delphis, and the long-beaked common dolphin Delphinus capensis. Some studies suggest a third species, the Arabian common dolphin (D. tropicalis), found in the Red Sea and Indian Ocean, can be characterized by an extremely long and thin beak.The common dolphin is not the dolphin of popular imagination despite its name; that distinction belongs to the bottlenose dolphin due to its widespread use in marine parks. However, this dolphin was the most frequently represented in the art and literature of ancient Greece and Rome. Described as long ago as the the time of the height of Ancient Greece, it has been the source of more misinformation and misidentification than any other species of small cetacean. Specimens may be found in all temperate and tropical waters of the world. The common dolphin is a remarkably gregarious animal, and can dive to a depth of more than 243 meters. In addition, it is one of the fastest and highest jumping cetaceans.

Distribution :

The common dolphin can be found in all of the world's temperate and tropical waters, probably making it the second most widely distributed cetacean, right behind the killer whale, which can also be found at the poles. This dolphin is found on the coasts of North America as far north as British Columbia, on European coasts and in the Mediterranean, Black, and Azov Seas. It can be found on the coasts of Africa, southeast Asia, Australia, New Zealand, Japan, and in the Indian Ocean. Although it prefers mostly warm, and temperate waters, it is very occasionally reported in Nova Scotia, Iceland, and Greenland. Strandings have been reported at Tierra del Fuego.

The common dolphin is found both along the coasts and offshore, although it is mostly found in depths of greater than 180 meters. More pelagic than the bottlenose dolphin, it is rarely seen close to the shore. There does exist an inshore form in the eastern tropical Pacific. There are several different forms of the common dolphin, which are sometimes regarded as subspecies, racial groups, or even different species. The common dolphin prefers water of a temperature between 10 and 28° C.

The most detailed distribution and taxonomy studies have been performed in the eastern tropical Pacific. Four stocks have been recognized in the area: a northern form, a central form, a southern form, and a Baja neritic form. The stocks are divided by areas of relatively low population density. Although there is much observer effort in these areas, there are relatively few sightings. The central stock extends the farthest west of the four, to 140° W. The Baja stock differs from the northern stock by modal length, color pattern and relative beak length. It extends from the Gulf of California to 185 kilometers off the Pacific coast of Baja California. There also appears to be a stock off of southern Mexico in the central stock area; it is called "Guerrero." The research performed by W. E. Evans similarly identified four population stocks off of southern California and Baja California, differentiated by the lengths of their sounts. The Pacific, Baja California, and eastern tropical Pacific forms each have short snouts, while the inshore neritic form has a long snout. In fact, Baja California is the only area where the long-snouted variety may be found. The short-snouted and long-snouted varieties are not considered separate species. The large differentiation in the eastern tropical Pacific also occurs in other areas. There are distinct forms in the Mediterranean and Black Seas, along Europe, Africa, and Japan, and in the Indian Ocean.

In Californian waters, there is a discontinuous distribution, possibly indicating competition with resident species of the genus Stenella, or that different stocks prefer different water temperatures. A similar phenomenon is seen in the eastern Mediterranean. In nearly all areas, seasonal movements follow changes in the water temperature or changes in prey migrations. Compared to the white-sided dolphin, the common dolphin is found in warmer and more saline waters. Both species are found in areas of high sea floor relief. These phenomena are related to the abundance of their prefered prey.

Scientific classification :

Kingdom   :           Animalia

Phylum      :          Chordata

Class          :          Mammalia

Order         :          Cetacea

Family       :          Delphinidae

Genus        :          Delphinus                                     

Species                 

                            Delphinus capensis

                            Delphinus delphis

                                     (Delphinus tropicalis)