Sei Whale

Balaenoptera borealis

Description

The sei whale (pronounced SAY), Balaenoptera borealis, is a large, streamlined baleen whale that ranges in length from 45-69 ft (14-21 m). Mature weight is about 30 tons. The back, flanks, and rear belly are dark gray with a bluish tinge. Throat grooves on the undersurface are white or pale gray. The head is slender with a slightly arched forehead. Flippers are narrow and pointed. The dorsal fin is erect, strongly sickle-shaped, and placed slightly less than two-thirds of the way along the back. The back and flanks are often dotted with white scars caused by lampreys and other parasites.

The sei whale is also known as the pollack whale, Rudolphi's rorqual, or Japanese finner.

Behavior

One of the fastest swimmers among the whales, the sei whale is capable of bursting speeds up to 30 mph (48 kph). It feeds on euphausiids, copepods, and small fish, which it strains through the baleen. After a gestation period of 11 or 12 months, a single calf measuring about 15 ft (4.6 m) long is born. Cows nurse for about seven months. Sei whales usually travel in groups of two to five animals, although larger numbers sometimes gather at feeding grounds.

Habitat

The sei whale is found in all oceans. Like many other whales it migrates to northern temperate waters in summer and returns to warm tropical breeding grounds in winter. It prefers waters with a surface temperature of 46-77°F (8-25°C).

Distribution

Found worldwide, the sei whale once numbered in the hundreds of thousands. With the decline in other whale species, whalers turned to pursue this strong swimmer, heavily depleting the population in the early 20th century.

The sei whale continues to be found worldwide, but in considerably diminished numbers. In the North Pacific in summer, sei whales are found from the Bering Sea to California in the east and to Japan and Korea in the west. In the North Atlantic, sei whales occur off Nova Scotia, Labrador, and Greenland in the west, and from Norway to Spain and northwest Africa in the east. In the Southern Hemisphere sei whales migrate from summer feeding grounds in the Antarctic Ocean to concentrate off the coasts of Brazil, Chile, South Africa, and Australia.

Current estimates place the total population at less than 51,000. About 14,000 are believed to occur in the northern hemisphere, 37,000 or less in the southern hemisphere. In 1989 the International Whaling Commission (IWC) presented the results of a survey of whales summering in the Antarctic. The survey found only 1,500 sei whales in an area where they expected to find perhaps 10,000, raising concern among biologists.

Threats

For a long time the sei whale's speed made it less threatened by commercial whaling than other whales. It has, nevertheless, suffered from commercial whaling, particularly after stocks of slower whales had been depleted. As many as 20,000 sei whales were taken in a single year by Antarctic whaling fleets.

Conservation and Recovery

Sei whale numbers have rebounded only slightly (if at all) since most whaling was stopped by international treaty. Taking the sei whale in the North Pacific has been prohibited since 1971.

The taking of whales worldwide is administered by the IWC, which sets quotas for member countries. In 1986, members voted a complete moratorium on whaling in preparation for phasing it out entirely. The agency unfortunately has no statutory authority nor any means of enforcing the whaling ban, other than the pressure of public opinion. Several countries, including Japan, Iceland, and the Republic of Korea, continue to take whales for "scientific purposes," exploiting a loophole in the international treaty. Japan remains the largest market for products derived from whales.

In U.S. territorial waters, oversight of the sei whale falls under the jurisdiction of the National Marine Fisheries Service, a subagency of the Department of Commerce.

In June, 1993, Still Wagon Bay, off the coast of New England, was designated as a protected Marine sanctuary. Whale species that occur there include finback, humpback, northern right, Minke, and sei whales.

Contacts

Office of Protected Resources
National Fisheries Service
1315 East-West Highway
Silver Spring, Maryland 20910

U.S. Fish and Wildlife Services
Division of Endangered Species
Mail Stop 420ARLSQ
1849 C St., NW
Washington, D.C. 20240

References

Baker, M. L. 1987. Whales, Dolphins, and Porpoises of the World. Doubleday, Garden City.

Evans, P. G. 1987. The Natural History of Whales and Dolphins. Facts on File Publications, New York.

Ridgway, S. H., and R. H. Harrison, eds. 1985. Handbook of Marine Mammals; Vol. 3, The Sirenians and Baleen Whales. Academic Press, London and New York.

Balaenoptera borealis (sei whale) See BALAENOPTERIDAE.

sei whale (Balaenoptera borealis) See BALAENOPTERIDAE.