Commerson's Dolphin
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 A Commerson's Dolphin in an aquarium.
 Size comparison against an average human
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| Cephalorhynchus commersonii Lacépède, 1804 |
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 Commerson's Dolphin range
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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.
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[edit] 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.[1] 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.
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 maturation 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.
[edit] 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 Malvinas 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 distinct areas:
- around the southern tip of South America around Tierra del Fuego and the Falkland Islands, and
- near the Kerguelen Islands in the southern part of the Indian Ocean.
[edit] Behaviour
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.
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.
[edit] 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.[citation needed]
[edit] References
- ^ Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc (1983), ISBN 978-0851122359
- Cetacean Specialist Group (1996). Cephalorhynchus commersonii. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006. Database entry includes justification for why this species is listed as data deficient
- National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0
- Encyclopedia of Marine Mammals ISBN 0-12-551340-2
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