Sei whale

 

Learn More About Our Campaigns

Classification:

Global Population

Description and Natural History

Physical Description
Sei whales (pronounced, "say") are the least known of the Family, Balaenopteridae, which includes the blue, Bryde’s, fin and minke whales.

Smaller than the fin whale and larger than the Bryde’s whale, the sei whale shares the same streamlined body shape and broad, flat, u-shaped rostrum as the other species. There is a noticeable longitudinal ridge from the blowhole to the tip of the rostrum.

Adult sei whales measure 12 - 16 meters (39.4 - 52.5 feet) in length. Females are typically larger than males. Calves are about 4.5 meters (15 feet) long at birth. The body is slate-gray above and lighter below, although there is individual variation. Some have light-colored oblong spots on their sides that are probably scars resulting from parasites.

The head is uniformly dark on both sides, unlike the asymmetrical coloring of the fin whale, and there is an area of grayish-white that is almost always confined to the ventral grooves on the throat. There may be a white or light-colored area on the flipper and a white streak may extend down the leading edge of the flipper from behind the eye.

The tall, sickle-shaped dorsal fin, located midway along the back, appears simultaneously with the blow when the animal surfaces.

Natural History
Southern right whales have a circumpolar distribution in the Southern Hemisphere. They move north and south from inshore waters along the coasts of South America, South Africa and Australasia in the winter, to summer feeding grounds in the waters around Antarctica. Southern right whales are not gregarious, although large groups can be found on the feeding grounds.

Back to Top

Status of the Species

Status
Today, the sei whale is listed as Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN) and is included on Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).

Threats to the Species
As with other fast swimming baleen whales, the sei whale was spared from early hunting because of its size, speed and deep-water habits. However, by the early 20th century, whaling technology had changed to include steam-powered vessels and the exploding harpoon.

In 1925, the floating factory ship was introduced and could operate independently around the clock and stay at sea for months. After the blue whale populations were depleted in the 1930s, whalers directed their energies to catching the next largest species, the fin whale. When the fin whale populations declined, whalers moved on to the sei whale.

It is difficult to isolate the history of whaling for this species because sei and Bryde’s whales were combined in the catch statistics up until about 1975. It is known, however, that the sei whale was heavily exploited in all areas where it was previously abundant. Because sei whale numbers were so depleted, it was provided worldwide protection by the International Whaling Commission (IWC) in 1978.

It gained further protection under the IWC moratorium on commercial whaling in 1986, although Iceland continued "scientific" whaling for sei whales until 1988. In March 2002, Japan announced its intention to expand its "scientific" whaling in the North Pacific to include 50 sei whales, despite the fact that there is no available population estimate for the North Pacific population. Norway has also been whaling commercially since 1993 under objection to the IWC moratorium but has not taken any sei whales. Other threats to the sei whale include disturbance from seismic operations, collision with large vessels, entanglement in fishing gear, and pollution (including noise pollution and increasing amounts of plastic debris at sea, oil spills and dumping of industrial wastes).

International Trade
Listed on CITES Appendix I which prohibits international trade.

Back to Top

Authors and Sources

CITES. 2001. Balaenoptera borealis. http://www.cites.org.

IUCN. 2001. The 2000 IUCN Red List of Threatened Species. www.redlist.org.

Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine Mammals of the World. FAO Species Identification Guide. UNEP, Rome. 320pp.

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

Back to Top