Sei Whale - New Bedford Whaling Museum

Sei Whale

Sei Whale


  • "STW – Sei Whale." STW – Sei Whale. N.p., n.d. Web. 13 Mar. 2014.
  • "Sei Whale & Bryde’s Whale." American Cetacean Society. N.p., n.d. Web. 13 Mar. 2014.
  • "Sei Whales, Balaenoptera Borealis." N.p., n.d. Web. 13 Mar. 2014
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  • Carwardine, Mark. Whales, Dolphins, and Porpoises. London: Dorling Kindersley, 1995. Print.

Prepared by: Tatiana Grace, NBWM Apprentice, 2014

Last modified: June 26, 2014

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Fact Sheet

Common Name: Sei Whale

Scientific Name: Balaenoptera borealis

Length as an adult: An adult male sei whale measures about 45 to 55 feet (13.7 to 16.8 meters), sometimes reaching a length of 65 feet (19.8 meters).

Weight as an Adult: An adult male sei whale weights about 14 to 17 tons (34,000 pounds).

Length and weight at birth: At birth the sei whale is about 14 to 15 feet (4.3 to 4.6 meters) and approximately 2,000 pounds (909 kilograms).

Length of pregnancy: A full term is approximately 11 ½ months to 12 months.

Range: Sei whales are found near the Antarctic, and go as far north as Iceland in the North Atlantic.

Likelihood of being seen on a whale watch in Massachusetts coastal waters: Although this is possible, it is highly unlikely. Sei whales can travel into Massachusetts waters but the likelihood of being spotted during a whale watch is slim to none.

Preferred food: Sei whales will take whatever is in abundance locally, whether it be fish, squid or plankton, as long as it is schooling.

Unusual characteristics: The sei whale has been recorded holding its breath for up to 20 minutes, however their maximum underwater time is unknown.

Appearance: Sei whales have dorsal fins and long throat grooves on the lower side of their bodies. They are slim and streamlined. Their most noticeable feature is that the sei whale has a single ridge running from the tip of the snout to the blowholes; they also have 32 to 60 throat grooves. These whales have 300 – 400 baleen plates on each side of their mouths which measure about 19 inches long per plate.

General Information: Sei whales have two recognized subspecies. The Northern Hemisphere subspecies is borealis borealis. The Southern Hemisphere subspecies is borealis schlegelii. The sei whale is the 3rd longest of the whale species, after the blue whale and fin whale. The name of the sei whale is derived from a Norwegian name seje for pollock, a fish that is sighted off the coast of Norway every spring.

Unusual habits: More regular dive sequence than most other rorquals and stays near the surface more consistently.

Population status: Current population estimates for the sei whale are 56,000-64,000.

Threats: Predation by Orcas, also known as Killer Whales, and humans. Sei whales are also susceptible to ship strikes, entanglement as well as marine pollution.