CreatureData

Sei whale

Balaenoptera borealis Lesson, 1828

ENEndangeredwhales and dolphins

The sei whale (Balaenoptera borealis) is a marine mammal in the family Balaenopteridae, within the order Cetacea and suborder Mysticeti. It falls in the giant size class, with a representative adult body mass of 20 tonnes.

Sei whale (Balaenoptera borealis)
Photo: NOAA, Right Wale Aerial Survey · Public domain · Wikimedia Commons

Quick facts about the sei whale

An invertivore active by day, it feeds on copepod, euphausiacea and zooplankton. It is listed as Endangered on the IUCN Red List, a threatened category, and has a lifespan of 74 years.

Weight
20 tsrc for Weight
Length
up to 19.5 msrc for Length
Lifespan
74 yearssrc for Lifespan
Diet
Invertivoresrc for Diet
Main food
copepod, euphausiacea, zooplanktonsrc for Main food
Habitat
Not recorded
Gestation
335 days – 346 dayssrc for Gestation
Young per litter or clutch
1.01src for Young per litter or clutch
Age at maturity
8.97 years – 10 yearssrc for Age at maturity
Litters or clutches a year
0.45src for Litters or clutches a year
Active
By day (diurnal)src for Active
Lifestyle
Marinesrc for Lifestyle
Migration
Migratorysrc for Migration
Conservation status
Endangered (IUCN)src for Conservation status
Countries on record
Not recorded

Photos of the sei whale

Only freely licensed photos are shown. Each carries its creator and licence.

Sei whale (Balaenoptera borealis)
Beddard, Frank E. · Public domain · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Solarence · CC BY 4.0 · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Carina Gsottbauer · CC BY-SA 4.0 · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Carina Gsottbauer · CC BY-SA 4.0 · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Carina Gsottbauer · CC BY-SA 4.0 · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Carina Gsottbauer · CC BY-SA 4.0 · Wikimedia Commons
Sei whale (Balaenoptera borealis)
Pablo · CC BY 4.0 · Wikimedia Commons

Where does the sei whale live?

Not recorded

What is the sei whale?

Quoted from WikipediaCC BY-SA 4.0

The sei whale ( SAY; Balaenoptera borealis) is a baleen whale. It is one of ten rorqual species, and the third-largest member after the blue and fin whales. It can grow to 19.5 m (64 ft) in length and weigh as much as 28 t (28 long tons; 31 short tons). Two subspecies are recognized: B. b. borealis and B. b. schlegelii. The whale's ventral surface has sporadic markings ranging from light grey to white, and its body is usually dark steel grey in colour. It is among the fastest of all cetaceans, and can reach speeds of up to 50–55 km/h (31–34 mph) over short distances.

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. It is a filter feeder, with its diet consisting primarily of copepods, krill, and other zooplankton. It is typically solitary or can be found in groups numbering half a dozen. During the breeding period, a mating pair will remain together. Sei whale vocalizations usually last approximately half a second, and occur at 240–625 hertz.

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. It is listed as endangered on the IUCN Red List, though populations are increasing. The Northern Hemisphere population is listed under CITES Appendix II, which indicates they are not threatened with extinction, while the Southern Hemisphere population is listed under CITES Appendix I, indicating that they are threatened and are given the highest levels of protection.

From the Wikipedia article “Sei whale” (en.wikipedia.org/w/index.php?title=Sei_whale&oldid=1384591267), by Wikipedia contributors, licensed under CC BY-SA 4.0 (creativecommons.org/licenses/by-sa/4.0). This block is kept separate from our own text.

Is the sei whale endangered?

The sei whale is listed as Endangered on the IUCN Red List: it faces a very high risk of extinction in the wild.

  1. LCLeast Concern
  2. NTNear Threatened
  3. VUVulnerable
  4. ENEndangered
  5. CRCritically Endangered
  6. EWExtinct in the Wild
  7. EXExtinct

Category via Wikidata (CC0). Find the full assessment on the IUCN Red List. See all Endangered species.

How is the sei whale classified?

  1. kingdomAnimalia
  2. phylumChordata
  3. classMammalia
  4. orderCetacea
  5. familyBalaenopteridae
  6. genusBalaenoptera
  7. SpeciesBalaenoptera borealis Lesson, 1828

Synonyms Balaenoptera alba, Balaenoptera arctica, Balaenoptera iwasi, Balaenoptera laticeps, Balaenoptera schlegelii, Balaenoptera schlegellii, Belaenoptera schlegeli, Pterobalaena alba, Pterobalaena schlegeli, Pterobalaena schlegeli alba, Sibbaldius schlegelii

Other names and names in other languages (96)
  • Coalfish whaleEnglish
  • Coalfish whaleEnglish
  • Dike whaleEnglish
  • Fish whaleEnglish
  • FlatbackEnglish
  • Northern rorqualEnglish
  • Pollack whaleEnglish
  • Pollack whaleEnglish
  • Rudolph's rorqualEnglish
  • Rudophi's rorqualEnglish
  • Rudophi’s rorqualEnglish
  • Rudophi’s rorqualEnglish
  • Sardine whaleEnglish
  • seiwalvisAfrikaans
  • حوت سايArabic
  • seyvаlBulgarian
  • Rorqual borealCatalan
  • balena del nordCatalan
  • rorqual del nordCatalan
  • pletvák severnýCzech
  • plejtvák sejvalCzech
  • morfil asgellog seiWelsh
  • Morfilod Asgellog SeiWelsh
  • sejhvalDanish
  • SeiwalGerman
  • ΒορειοφάλαιναGreek
  • ΑνταρκτοφάλαιναGreek
  • seihualSpanish
  • ballena bobaSpanish
  • ballena borealSpanish
  • Ballena de SeiSpanish
  • ballena seiSpanish
  • rorcual borealSpanish
  • rorcual de RudolphiSpanish
  • Rorcual NortenoSpanish
  • Rorcual NorteñoSpanish
  • rorqual del norteSpanish
  • rorqual nortenoSpanish
  • rorqual norteñoSpanish
  • ipar-zereaBasque
  • seitivalasFinnish
  • SeihvalurFaroese
  • Rorqual SeiFrench
  • baleine noireFrench
  • rorqual boréalFrench
  • rorqual de RudolphFrench
  • Rorqual de RudolphiFrench
  • muc-mhara SeiScottish Gaelic
  • mucan-mara SeiScottish Gaelic
  • Rudolfijev kit / Рудолфијев китSerbian (Latin)
  • לויתן צפוניHebrew
  • לווייתן צפוניHebrew
  • tőkebálnaHungarian
  • Paus SeiIndonesian
  • SandreyðurIcelandic
  • sandereydurIcelandic
  • balenottera borealeItalian
  • イワシクジラJapanese
  • イワシクジラ (Iwashi Kujira)Japanese
  • iwashi kujiraJapanese
  • iwasikuziraJapanese
  • kaguo kuziraJapanese
  • Tunnullit ilaatKalaallisut
  • TikaagulliusaarnaqKalaallisut
  • 멸치고래Korean
  • 보리고래Korean
  • bori-goraeKorean
  • seivalasLithuanian
  • SeivalisLatvian
  • seihvalNorwegian Bokmål
  • noordse vinvisDutch
  • nordsche vinvischDutch
  • seikvalNorwegian Nynorsk
  • seichvalNorwegian
  • sejwalPolish
  • Płetwal czerniakowyPolish
  • Baleia SeiPortuguese
  • Baleia-sardinheiraPortuguese
  • seivalRussian
  • Ивасевый китRussian
  • Ивасёвый китRussian
  • Сайдяной китRussian
  • ivasevyi kitRussian
  • ivasevyi polosatikRussian
  • saidianoi kitRussian
  • zajvalSlovenian
  • borealni kitSlovenian
  • sejvalSwedish
  • plawan klaebkhribdamThai
  • sey balinasıTurkish
  • Kuzey balinasıTurkish
  • СейвалUkrainian
  • Сайдяний китUkrainian
  • івасевий китUkrainian
  • 塞鲸Chinese
  • 鰮鯨Chinese

Catalogue of LifeWikipediaiNaturalistTAXREFWikidataWoRMSIUCN Red List

Relatives of the sei whale

Other species in the same genus Balaenoptera.

EN, Endangered
Blue whale (Balaenoptera musculus)

Blue whale

Balaenoptera musculus

Balaenopteridae

VU, Vulnerable
Fin whale (Balaenoptera physalus)

Fin whale

Balaenoptera physalus

Balaenopteridae

Bryde's whale

Balaenoptera omurai

BalaenopteridaeNo free photo yet

Rice's whale

Balaenoptera ricei

BalaenopteridaeNo free photo yet

CompareSei whale vs Blue whaleSei whale vs Fin whaleSei whale vs Common minke whaleSei whale vs Bryde's whale

Common questions

Each answer is written from the sourced facts on this page, and only where they hold the answer.

What kind of animal is the sei whale?

The sei whale is a mammal in the whales and dolphins group, belonging to the family Balaenopteridae and suborder Mysticeti.

How heavy is the sei whale?

The sei whale has a representative adult body mass of 20 tonnes, placing it in the giant size class.

What does the sei whale eat?

The sei whale eats copepod, euphausiacea and zooplankton. It is classed as an invertivore.

Is the sei whale endangered?

Yes. The sei whale is listed as Endangered (EN) on the IUCN Red List, which is a threatened category.

How long does the sei whale live?

The sei whale has a lifespan of 74 years.

How long is the sei whale's gestation period?

The sei whale's gestation period is 346 days, with 1.01 young per litter and 0.45 litters per year.

When does the sei whale reach sexual maturity?

The sei whale reaches sexual maturity at 9.5 years, with reported values from 9.0 to 10.0 years.

Who named the sei whale?

The sei whale, Balaenoptera borealis, was named by Lesson, 1828.

Sources and how to cite this page

Data as of 2026-11-11. How this page is put together.

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APA

CreatureData. (2026). Sei whale (Balaenoptera borealis). Retrieved from https://creaturedata.com/animals/sei-whale

MLA

“Sei whale (Balaenoptera borealis).” CreatureData, 2026, https://creaturedata.com/animals/sei-whale.

BibTeX
@misc{sei_whale_2026,
  title = {Sei whale (Balaenoptera borealis)},
  author = {{CreatureData}},
  year = {2026},
  url = {https://creaturedata.com/animals/sei-whale},
  note = {Data as of 2026-11-11}
}