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Commerson's dolphin


'''Commerson's Dolphin'(Cephalorhynchus commersonii) is one of four dolphins in the Cephalorhynchus'' genus. The species has also the common names Skunk Dolphin and Piebald Dolphin. The dolphin is named for Philibert Commerson, who first described them in 1767 after he sighted them in the Strait of Magellan.

Physical description

Commerson's Dolphin has a very distinctive patterning. It has a black head, dorsal fin, and fluke, with a white throat and body. The demarcation between the two colours is very clear-cut. This stocky creature is one of the smallest of all cetaceans growing to around 1.5 m (5 ft). A mature female caught off of south Patagonia, at 23 kg (51 lb) and 1.36 m (4.5 ft), may be the smallest adult cetacean on record. Its appearance resembles that of a porpoise, but its conspicuous behaviour (see behaviour below) is typical of a dolphin. The dorsal fin has a long, straight leading edge which ends in a curved tip. The trailing is typically concave but not falcate. The fluke has a notch in the middle. This dolphin has no rostrum. It is not known why their distribution is limited to the southern coast of South America and the Kerguelen Islands.

Sexes are easily distinguished by the different shape of the black blotch on the belly - it is shaped like a teardrop in males but is more rounded in females. Females reach breeding age at six to nine years. Males reach sexual maturity at about the same age. Mating occurs in the spring and summer and calving occurs after a gestation period of 11 months. The oldest known Commerson's Dolphin died at age 18.

Population and distribution

The species is distributed in two locations. The larger population is found inshore in various inlets in Argentina, in the Strait of Magellan and near the Falkland Islands. The second population (discovered in the 1950s) resides near the Kerguelen Islands, 8,000 km to the east of their nearest special cousins. They prefer shallow waters. Global populations are unknown, but the species is accepted to be locally common. A survey in 1984 estimated there to be 3,400 individuals in the Strait of Magellan.

The dolphin is found in two geographically disparate areas:

the southern coast of South America around Tierra del Fuego and the Falkland Islands, and

waters near the Kerguelen Islands in the southern part of the Indian Ocean.

Behavior

The Commerson's Dolphin is very active. It is often seen swimming rapidly on the surface and leaping from the water. It also spins and twists as it swims and may surf on breaking waves when very close to the shore. It will bow-ride and swim behind fast-moving boats. They are also known to enjoy swimming upside-down, which is thought to improve visuality of its prey.

This dolphin feeds on a mix of coastal and pelagic fish and squid. Those in the South American sub-population supplement their diet with crustaceans.

Conservation

The IUCN lists Commerson's Dolphin as data deficient in its Red List of Threatened Species. The proximity of the dolphin to the shore makes accidental killing in gillnets a common occurrence. The dolphin was killed for use as crab bait by some Argentinian and Chilean fishermen in the 1970s and 1980s, but this practice has since been curtailed.

Captivity

About two dozen Commerson's Dolphins live in aquariums in the world, including SeaWorld San Diego, Aquatica in Florida, Zoo Duisburg in Germany (till 2004), and several aquariums in Japan.

References

National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0

Encyclopedia of Marine Mammals ISBN 0-12-551340-2

External links

Whale and Dolphin Conservation Society

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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Commerson's dolphin


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