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Peale's dolphin


'''Peale's Dolphin'(Lagenorhynchus australis) is a small dolphin found in the waters around Tierra del Fuego at the foot of South America. It is also commonly known as the Black-chinned Dolphin or even 'Peale's Black-chinned Dolphin'''. However since Rice's work Peale's Dolphin has been adopted as the standard common name.

Taxonomy

Though it is traditionally placed in the genus Lagenorhynchus, recent molecular analyses indicate that Peale's Dolphin is actually more closely related to the dolphins of the genus Cephalorhynchus. If true, this would mean that this species must either be transferred to Cephalorhynchus or be given a new genus of their own. An alternate genus that has been proposed for this species (as well as the Pacific White-sided Dolphin and Dusky Dolphin is Sagmatias. There is some behavioral and morphological to support moving Peal's Dolphin to Cephalorhynchus. According to Schevill & Watkins (1971), Peale's Dolphin and the Cephalorhynchus species are the only dolphins that do not whistle. Peale's Dolphin also shares with several Cephalorhynchus species the possession of a distinct white "armpit" marking behind the pectoral fin.

Physical description

Peale's Dolphin is of typical size in its family - about 1m in length at birth and 2.1m when fully mature. Its adult weight is about 115kg. It has a dark grey face and chin. The back is largely black with a single off-white stripe running curving and thickened as it runs down the back on each side. The belly is white. Conspicuously there is also a white patch under just behind each flippers. These are known as the "armpits". The flanks also have a large white-grey patch above the flipper. The dorsal fin is large for this size cetacean and distinctively falcate. The flippers themselves are small and pointed. The tail fin too has pointed tips, as well as a notch at its middle.

The species looks similar to the Dusky Dolphin when viewed at a distance, and may be confused with it.

Population and distribution

Peale's Dolphin is endemic to the coastal waters around southern South America. On the Pacific side they have been seen as far north as Valdivia, Chile at 38 S. On the Atlantic side sightings typically peter out at about 44 S - near Golfo San Jorge, Argentina. In the south they have been seen at almost 60 S - well into the Drake Passage.

They are often found in areas of fast-moving waters such as entrances to channels and narrows, as well as close to shore in safe areas such as bays.

The total population is unknown but is thought to be locally common.

Behaviour

Peale's Dolphins congregate in small groups - usually about 5 in size and sometimes up to 20. On rare occasions in summer and autumn much larger groups have been recorded (100 individuals). A typical pattern is for the group is move in a line parallel to the shore. They usually swim slowly but are prone to bursts of activity.

Conservation

Peale's Dolphins' propensity for moving over only small areas, and staying close to shore, has rendered them vulnerable to interference by man. During the 1970s and 80s Chilean fisherman killed and used thousands of Peale's Dolphins for crab bait each year. This practice has tailed off but not been made illegal.

In Argentina there have been reports of Peale's Dolphins becoming trapped in gillnets but the extent of this is not known. Conservation groups such as the Whale and Dolphin Conservation Society demand further research be made into this species.

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

LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999). Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Marine Mammal Science 15, 619648.

May-Collado, L., Agnarsson, I. (2006). Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344-354.

Schevill, W.E., Watkins, W.A. (1971). Pulsed sounds of the porpoise Lagenorhynchus australis. Breviora 366, 110.

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


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