Concept
The sei whale (seɪ , sæɪ; Balaenoptera borealis) is a baleen whale, the third-largest rorqual after the blue whale and the fin whale. It inhabits most oceans and adjoining seas, and prefers deep offshore waters. It avoids polar and tropical waters and semi-enclosed bodies of water. The sei whale migrates annually from cool, subpolar waters in summer to temperate, subtropical waters in winter with a lifespan of 70 years. Reaching in length and weighing as much as , the sei whale consumes an average of of food every day; its diet consists primarily of copepods, krill, and other zooplankton. It is among the fastest of all cetaceans, and can reach speeds of up to (27 knots) over short distances. The whale's name comes from the Norwegian word for pollock, a fish that appears off the coast of Norway at the same time of the year as the sei whale. Following large-scale commercial whaling during the late 19th and 20th centuries, when over 255,000 whales were killed, the sei whale is now internationally protected. , its worldwide population was about 80,000, less than a third of its prewhaling population. Sei is the Norwegian word for pollock, also referred to as coalfish, a close relative of codfish. Sei whales appeared off the coast of Norway at the same time as the pollock, both coming to feed on the abundant plankton. The specific name is the Latin word borealis, meaning northern. In the Pacific, the whale has been called the Japan finner; "finner" was a common term used to refer to rorquals. In Japanese, the whale was called iwashi kujira, or sardine whale, a name originally applied to Bryde's whales by early Japanese whalers. Later, as modern whaling shifted to Sanriku—where both species occur—it was confused for the sei whale. Now the term only applies to the latter species. It has also been referred to as the lesser fin whale because it somewhat resembles the fin whale. The American naturalist Roy Chapman Andrews compared the sei whale to the cheetah, because it can swim at great speeds "for a few hundred yards", but it "soon tires if the chase is long" and "does not have the strength and staying power of its larger relatives".
