(12-11-09) Commerson's dolphin, also known as Tonina overa, is famous for its black and white colour, and the way it swims, smart and fast. It is one of native cetaceans that star in the Patagonian marine life.

    This dolphin is famous for its colour black and white, and its high speed when swimming. It is one of the stars of the coasts of Rawson, there it even has its own monument. However, it roams in all the seas in Patagonia.

    Its scientific name is Cephalorhynchus commersonii. They can weight up to 60 kilograms, although their average weight is 45 kilos. They are small compared to other cetaceans; they can be up to 5 feet long. They are excellent swimmers and are able to jump very high: one of the main attractions is that they move in groups of up to twenty specimens, so it is presumed that they have a community life.

    Commerson´s dolphin is one of four species of genus Cephalorhynchus and lives exclusively in the Southern Hemisphere. Its common name in Castilian (“tonina overa”) refers to its color pattern, characteristically black and white, while in English, it refers to Philibert Commerson, who was the first one to describe the species in 1767.

    It happened while he was crossing the Strait of Magellan during his trip around the world on the expedition of the Bougainville. Later, his descriptions came into the hands of Lacépède, classified it scientifically in 1804 and, more recently, the Commerson's dolphins were documented by the expert Francis P. Moreno.

    It has a characteristically robust body with a conical head, with no distinctive peak. It has 28 to 34 pairs of teeth in upper jaw, and 26 to 35 in the lower jaw. Males do not exceed 42 kg, while females are slightly bigger, reaching 50 kg. Head, pectoral fins, genital area, back of the dorsal fin insertion until the entire caudal fin are black, while the rest of the animal, including the throat is white.

BABIES DO NOT SEPARATE FROM THEIR MOTHERS IN ONE YEAR

    The newborn are about 70 cm long, they are gray -brownish completely gray. During the first year of life they are supervised by the mother. The dorsal fin is located just behind the middle of the back; meanwhile the tail fin is wide in comparison to the body size, presenting a central depression of about 2 cm deep.

    They generally inhabit shallow coastal waters, moving according to tidal patterns, and are usually found in groups of 1-3 animals, although groups of up to 100 individuals have been seen. They are characterised by their rapid and erratic swimming, their inquisitiveness, and their habit of interacting with boats.

    Like all cetaceans, present natural markings so individuals can be recognized and thus kept track of by means of photos. Many of the Commerson’s dolphin populations have already been identified in this way, and various possible options have been presented in order to solve some of the problems which this species has to face. Photo-identificationenables many of the mysteries surrounding the Commerson’s dolphin population to be uncovered, including their reproductive biology and social behaviour.

    They mainly feed on Fuegian spratt (Sprattus fuegensis), Argentine anchovy (Engraulis anchoita), silverside (Austroatherina nigricans and A. smitii), crayfish (Arthromysis magellanica), squid (Loligo sanpaulensis), longtail hake (Macruranus magellanicus) and krill (Euphasis sp.).

EFFECTIVE COMMUNICATION AND INFORMATION SYSTEM

     As the rest of dolphins, Commerson’s dolphins have a complex communication system that works as radar called Echolocation System.

     The echolocation enables the dolphin emit different sounds as small bursts of sound pulses (both high and low frequency) called "clicks", from which it produces a return of these signals in the form of "echoes" that, when analyzed, become precise information about the environment.

    Additionally, a highly sensitive directional hearing facilitates an extremely precise echolocation and provides all dolphins with a unique sensory system in the sea.

    Commerson’s dolphins are brave and curious animals that often approach ships alongside they swim, sometimes in the bow with their belly up. It is also possible to observe them from the shore because one of their hunting techniques is bringing their prey (small fish and squid) closer against the coast, in shallow water, or take advantage of tides in the area to intercept them at low tide.

    Some of the threats confronting this species are related, as with the majority of cetaceans, to being killed in fishing nets, over-fishing, and pollution. For many years they were caught for exhibition in aquariums and as bait for king crab and false southern king crab, although its capture is now prohibited.

    The IUCN (The World Conservation Union) considers that there is not sufficient information about the species to carry out a direct or indirect evaluation on the risk of its becoming extinct based on the status of its population or distribution, therefore it is classified in the Red Book in the Data Deficient (DD) category and it is listed in Appendix II of CITES.

    In its natural habitat, from July 2001, it has been declared a protected species thanks to Provincial Law No. 2582, awarding it the status of “Natural Provincial Monument.”