Sei Whale (Balaenoptera borealis)

The sei (pronounced "say") whale is a streamlined baleen whale that is found throughout most of the world's oceans. The name sei comes from the Norwegian word seje, for pollock, a type of fish, since these whales would appear off the coast of Norway at the same time each year as the pollock.

Sei whales are one of the fastest cetacean species - they can travel as fast as 40 miles per hour.

An average sei whale is about 45-55 feet long - longer than a school bus, although they may grow up to 65 feet. Their weight can vary from about 20 tons to 50 tons.

A sei whale's coloration exhibits typical baleen whale countershading - they have a darker bluish-gray back and a white underside. They also may have round scars on their body from lampreys or cookie-cutter sharks, and they have a very curved dorsal fin. All sei whales have a ridge on their head, from their snout to their blowholes. This distinguishes them from the similar-looking Bryde's whale, which has three ridges on the top of its head.

Sei whales are often found alone, but they may also be found in small groups. They often travel just under the water surface, so when watching sei whales, you may see more "flukeprints" (the smooth, round patches on the water surface made by a whale's tail) than the whales themselves.

• Kingdom: Animalia
  
• Phylum: Chordata
  
• Class: Mammalia
  
• Order: Cetacea
  
• Suborder: Mysticeti
  
• Family: Balaenopteridae
  
• Genus: Balaenoptera
  
• Species: borealis
  

Sei whales are distributed around the world's oceans, generally in temperate and subtropical waters, and spend more time offshore than inshore. Their migration patterns are not well-known, although it is thought that they migrate toward lower latitudes during the winter and higher latitudes in the summer. They may also appear in high numbers suddenly to exploit prey, and then disappear to another area just as suddenly.

Sei whales, like other whale species, are not monogamous. After mating, gestation lasts 11-13 months, after which the female gives birth to a calf that is about 15 feet long and weighs about 1,500 pounds. The calf nurses its mother's rich milk for 6-9 months and is then weaned. Sei whales are sexually mature at 6-12 years of age, and are thought to live between 50-70 years.

The sounds that sei whales make are less-studied than some other whale species. A study in 2005 described sei whale sounds as low frequency, with some "growls" and "whooshes". The Discovery of Sound in the Sea web site states that since the whales are usually spread out, these are likely "contact" calls - long-range calls for coordinating feeding or breeding activities.

Sei whales are listed as endangered on the IUCN Red List, and in the U.S. under the Endangered Species Act.

Their great speed afforded sei whales protection in the early days of whaling, however, they were hunted in great numbers in the 19th and 20th century - according to NOAA, over 300,000 were killed. Sei whales are considered more abundant in the Northern Hemisphere than in the Southern Hemisphere, where populations are depleted. Widespread hunting of sei whales no longer occurs, but they have been hunted by Japan in recent years under a scientific research permit.

• American Cetacean Society. “Sei Whale & Bryde's Whale” (Online), American Cetacean Society. Accessed November 21, 2011.
• Discovery of Sound in the Sea (DOSITS). Sei Whale. University of Rhode Island. Accessed November 21, 2011.
• NOAA Fisheries Office of Protected Resources. Sei Whale (Balaenoptera borealis). Accessed November 21, 2011.
• Reilly, S.B., Bannister, J.L., Best, P.B., Brown, M., Brownell Jr., R.L., Butterworth, D.S., Clapham, P.J., Cooke, J., Donovan, G.P., Urbán, J. & Zerbini, A.N. 2008. Balaenoptera borealis IUCN Red List of Threatened Species. Version 2011.2. . Accessed November 21, 2011.
• Whale Center of New England. Species Info. Accessed November 21, 2011.