Dall-Hafenschweinswal

 

Klassifikation:

Weltweite Population

Beschreibung und Lebensweise

Physical Description
The Dall’s porpoise, named after American zoologist William H. Dall, has a robust and stocky body, with a wide-based triangular dorsal fin and small, pointed flippers close to the head. The relatively small head has a small beak. The tail flukes are broad and the keel on the tail stock is pronounced on the top and bottom.

There are two types of striking body coloration: the dalli-type, which consists of a black body with bright white patches on the belly and flanks to about the mid-body; and the truei-type, which has a larger flank patch extending all the way to the front flipper. Both color types have a white or light gray portion (“frosting”) on the dorsal fin and on the trailing edge of the tail flukes. Adult males may reach 2.39 meters (7.84 feet) and females 2.10 meters (6.89 feet) in length, and weigh up to 200 kilograms (440 pounds). At birth, calves are about one meter (3.3 feet) long.

Natural History
Dall’s porpoises inhabit the Pacific Ocean and adjacent seas of the Northern Hemisphere between 30 degrees North and 62 degrees North. They prefer cold, deep, oceanic waters and are not found in the southern portion of their range during the summer months. The truei-type of Dall’s porpoise is found only along the Pacific coast of Japan, migrating annually to the Sea of Okhotsk. The dalli-type is found in all other areas of the range.

Dall’s porpoises usually travel in groups of two to 12 and may be found in association with white-sided dolphins (Lagenorhynchus obliquidens) or pilot whales (Globicephala spp).

For short bursts, the Dall's porpoise may be the fastest cetacean, swimming quickly and producing a characteristic "rooster tail" spray. They may also swim slowly and roll, creating little or no disturbance. They are frequently found riding on the bow or stern waves of boats. Dall’s porpoise do not tend to breach (jump out of the water) or display other types of acrobatic behavior.

Females reach sexual maturity at about 4.5 years, while males reach sexual maturity between 3.5 and four years of age. One calf is born about every three years in the spring or summer and is nursed for about two years. Adults feed on a wide variety of fish and cephalopods (molluscs).

The abundance estimate for Dall’s porpoises in the North Pacific and Bering Sea is 1,185,000 animals.

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Status der Art

Status
The Dall’s porpoise is listed as Lower Risk by the International Union for the Conservation of Nature and Natural Resources (IUCN). It is listed on Appendix II of the Convention on the Trade in Endangered Species of Fauna and Flora (CITES).

Threats to the Species
Dall's porpoises have been taken in large numbers in a variety of Asian pelagic (open ocean) drift net fisheries for salmon and squid. A small number are entangled in coastal nets of U.S. fisheries. A significant decrease in abundance in the western North Pacific was documented between 1984 and 1986 and may have been caused by high by-catches in commercial fisheries. Directed fisheries for Dall's porpoises also exist and tens of thousands of animals have been caught in an annual northern Japanese harpoon fishery.

International Trade
Trade is authorized under CITES Appendix II with the appropriate permits.

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Autor und Quellen

Sources
CITES. 2001. Phocoenoides dalli. http://www.cites.org

IMMA. 2001. Dall’s porpoise. www.phocoena.org  

IUCN. 2001. The 2000 IUCN Red List of Threatened Species—Phocoenoides dalli. http://www.redlist.org

Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine Mammals of the World. FAO Species Identification Guide. United Nations Environment Programme. Rome.

Leatherwood, S and R.R. Reeves. 1983. The Sierra Club Handbook of Whales and Dolphins. Sierra Club Books, San Francisco. 302pp.

Read, A. 1999. Porpoises. WorldLife Library. Voyageur Press. 72pp.

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