White-bellied dolphin
| White-bellied dolphin | ||||||||||||
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White-bellied dolphins on the surface of the water |
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| Cephalorhynchus eutropia | ||||||||||||
| Gray , 1846 |
The white-bellied dolphin ( Cephalorhynchus eutropia ), also known as the Chilean dolphin , is a species of dolphin that can only be found on the coast of South America from Chile to Cape Horn . With a maximum body length of about 1.70 meters, it is one of the smaller dolphin species.
features
The white-bellied dolphin is a relatively small dolphin with an average body length of 1.70 meters and a weight of about 63 kilograms. It has a blunted head without a clear snout, which is why it was partially classified as a porpoise . Its body shape is strong and appears "plump" with a width that corresponds to about 2/3 of the body length. The fin rises slightly behind the middle of the back and is comparatively large, flatly angled and clearly rounded. The flippers are rather small, slim and paddle-shaped, they are also rounded. The body is largely monochrome dark gray with a darker stripe that runs down from the blowhole to the eyes; there can also be darker spots around the eyes and on the sides of the head. The animal's throat and belly are white with the exception of a gray band that stretches across the chest between the flippers. In the area of the rear flipper attachment, they each have a white spot.
distribution
The white-bellied dolphin is endemic to the coast of Chile, which means it can only be found here. Its distribution extends from the height of Valparaíso on the 33rd southern parallel to Cape Horn on the 55th southern parallel.
Way of life
The animals live mainly in shallow and cool coastal areas with a maximum depth of 200 meters, sometimes in the areas of influence of rivers that flow into the ocean. Most observations of the animals come from the close coastal area with a distance of about 500 meters and shallow water depths of about 20 meters. They prefer areas with a strong tidal influence and sea bays. Several observations come from the outflow area of the Río Valdivia , the Gulf of Arauco near the city of Arauco and the areas around the island of Chiloé . Especially in the northern part of the range they sometimes approach boats, but in the south they usually stay away from them. The range partially overlaps with that of the Commerson's dolphin ( Cephalorhynchus commersonii ), especially in the Strait of Magellan and the Beagle Channel on the southern tip of South America. As a rule, the white-bellied dolphins form small groups of two to 15 individuals (schools), but groups of 20 to 50 animals also occur. In some cases, mixed groups of white-bellied dolphins with peale dolphins ( Lagenorhynchus australis ) have also been observed, but these two species usually occur separately. Larger and regular migrations do not occur with these animals and they are usually more or less true to location.
The white-bellied dolphin feeds mainly on crustaceans , cephalopods and small fish. Are documented as prey especially cancer Munida gregaria that the squid belonging Doryteuthis gahi and the Chilean herring ( Strangomera bentincki ), the South American anchovy ( Engraulis ringens ) and the Patagonian blenny ( Eleginops maclovinus ). They probably also feed on seaweed, especially ulva lactuca .
Little information is available about the reproduction of the animals. The births mainly take place between October and April and the young are born less than a meter in length. The animals reach sexual maturity at the age of five to nine years.
Systematics
The white-bellied dolphin is an independent species within the black-and-white dolphins ( Cephalorhynchus ), which are assigned to the dolphins (Delphinidae). The first scientific description comes from John Edward Gray from 1846, who described it as Delphinus eutropia . The description was given in the work The Zoology of the Voyage of the HMS Erebus & Terror , under the command of Captain Sir James Clark Ross , during the years 1839 to 1843 , in which numerous animal species were described that were on the expedition of James Clark Ross to the South Pole and were later described by John Edward Gray, among others.
The species is monotypical , so there are no subspecies besides the nominate form .
Status, threat and protection
The white-bellied dolphin is classified by the International Union for Conservation of Nature and Natural Resources (IUCN) as a type of warning list (Near Threatened, NT) and the stocks are considered stable. According to estimates, the total population of the animals is in the low thousands to tens of thousands, the number of sexually mature individuals is estimated at less than 10,000. This would classify the species as an endangered species, but it is not assumed that there has been a sharp decline in the number of animals in recent decades.
White-bellied dolphins are known to be caught and killed as by-catches in commercial fisheries, but the extent is unknown. The species also has a relatively narrow distribution area with at least two genetically different subpopulations. Sightings of the animals occur regularly, but are rare in parts of the distribution area.
In the past, dolphins were regularly hunted for food and crab bait in southern Chile, with fishermen harpooning them in the coastal areas north of Isla Grande de Chiloé or using the dolphins accidentally caught in their nets as bait for longlines, fishing rods or ring nets. Like sheep, seals, penguins and other sea birds as well as fish, they were used as bait for the lucrative fishing for king crabs ( Lithodes santolla and Paralomis granulosa ). In the early 1980s it was estimated that around two dolphins per boat were being caught per week in the Strait of Magellan, and in 1992 up to 600 dolphins, white-bellied dolphins and peale dolphins were harpooned per year in the area near the western Strait of Magellan. Dolphin hunting is illegal in Chile today, but enforcement of the law in remote areas is difficult and usually poor. However, the availability of alternative baits has led to a sharp decline in dolphin catches. Due to aquaculture farms for salmon and shellfish, the available habitats are partially limited and, especially in areas with high farm density, important habitat areas are not available for the dolphins. In addition to salmon farms, large-scale mussel farms were set up in bays and fjords. There is also evidence that Chilean dolphins are sometimes accidentally caught in nets that are set up around salmon farms to keep sea lions out of the southern bays and canals.
supporting documents
- ↑ a b c d e f g J.Y. Wang, KN Riehl, SZ Dungan: Genus Cephalorhynchos; Chilean Dolphin Cephalorhynchos eutropia In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; Pp. 524-525. ISBN 978-84-96553-93-4 .
- ↑ Cephalorhynchos eutropia . In: Don E. Wilson , DeeAnn M. Reeder (Eds.): Mammal Species of the World. A taxonomic and geographic Reference. 2 volumes. 3. Edition. Johns Hopkins University Press, Baltimore MD 2005, ISBN 0-8018-8221-4 .
- ↑ a b c d Cephalorhynchus Eutropia in the endangered Red List species the IUCN 2017 Posted by: S. Heinrich, R. Reeves, 2017. Accessed July 11, 2020th
literature
- JY Wang, KN Riehl, SZ Dungan: Genus Cephalorhynchos; Chilean Dolphin Cephalorhynchos eutropia In: Don E. Wilson, Russell A. Mittermeier: Handbook of the Mammals of the World. 4. Sea Mammals. Lynx Edicions, Barcelona 2014; Pp. 524-525. ISBN 978-84-96553-93-4 .
Web links
- Cephalorhynchus Eutropia in the endangered Red List species the IUCN 2017 Posted by: S. Heinrich, R. Reeves, 2017. Accessed July 11, 2020th