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|A Commerson's dolphin in an aquarium.|
|Size compared to an average human|
|Commerson's dolphin distribution near South America|
|Commerson's dolphin distribution near Kerguelen Island|
Commerson's dolphin (Cephalorhynchus commersonii) is one of four dolphins in the genus Cephalorhynchus. The species has also the common names skunk dolphin, piebald dolphin and panda dolphin. The dolphin is named for Philibert Commerson, who first described them in 1767 after he sighted them in the Strait of Magellan.
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 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 9 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 two disjunct subspecies are separated by 130° of longitude and about 8,500 km (5,300 mi). The larger population (C.c.commersonii) is found inshore in various inlets in Argentina, in the Strait of Magellan and near the Falkland Islands. The second subspecies (C.c.kerguelenensis, discovered in the 1950s) resides near the Kerguelen Islands. 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 Puerto Deseado, Tierra del Fuego and the Falkland Islands, and
- waters near the Kerguelen Islands in the southern part of the Indian Ocean.
A vagrant individual was sighted on the Agulhas Bank off South Africa in 2004. This specimen was isolated from the Kerguelen population by 4,200 km (2,600 mi) and from the South American by 6,300 km (3,900 mi). However, the Antarctic Circumpolar Current would force an individual from the Kerguelen population to swim against the West Wind Drift.
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. It is also known to swim upside-down, which is thought to improve the visibility of its prey.
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.
The Commerson's dolphin population of South America is listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). It is listed on Appendix II as it has an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
A few are accidentally killed in gill nets set for crabs along the Argentine coast, and local fishermen may kill them for food. Several have been shipped abroad to aquariums. Commerson's dolphins also inhabit waters heavy with human activity, creating a large danger for them.11
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- Mead, J.G.; Brownell, R.L., Jr. (2005). "Order Cetacea". In Wilson, D.E.; Reeder, D.M. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Reeves, R.R., Crespo, E.A., Dans, Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Pedraza, S., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, JY. & Zhou, K. (2008). "Cephalorhynchus commersonii". IUCN Red List of Threatened Species. Version 2012.2. International Union for Conservation of Nature. Retrieved 18 January 2013.
- Sharks and Whales (Carwardine et al. 2002), p. 370.
- Wood, The Guinness Book of Animal Facts and Feats. Sterling Pub Co Inc (1983), ISBN 978-0-85112-235-9
- Bruyn, P. J. N., de; Hofmeyr, G. J. G.; Villiers, M. S., de (2006). "First record of a vagrant Commerson’s dolphin, Cephalorhynchus commersonii, at the southern African continental shelf" (PDF). African Zoology 41 (1). Retrieved February 2015.
- "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
- Convention on Migratory Species page on the Commerson's dolphin
- National Audubon Society: Guide to Marine Mammals of the World ISBN 0-375-41141-0
- Encyclopedia of Marine Mammals ISBN 0-12-551340-2
- The Sierra Club Handbook of Whales and Dolphins