E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Balaenoptera borealis Lesson, 1828
Sei Whale
Family: Balaenopteridae

Photo of species

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Distribution of Balaenoptera borealis in British Columbia
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Species Information

The Sei Whale is a large baleen whale in the family Balaenopteridae. It is smaller than the Blue Whale and the Fin Whale, reaching 18-20 m in length, although it is similar in appearance to the Fin Whale (Jefferson et al. 2008, Wikipedia 2011). It is sleek and streamlined in appearance, with dark gray or brown colouration, a whitish area on the underside, the dorsal fin rises at a steep angle from the back, 32-65 ventral pleats, 219-402 black, fringed baleen plates (Jefferson et al. 2008). Wikipedia (2011) provides the following description of size: "Mature adults typically measure between 12–15 meters (39–49 ft) and weigh 20–30 tonnes (20–30 long tons; 22–33 short tons). The southern sei whale is larger than the northern. Females are considerably larger than males. The largest known sei whale measured 20 meters (66 ft), and weighed between 40–45 tonnes (39–44 long tons; 44–50 short tons). The largest specimens taken off Iceland were slightly longer than 16 meters (52 ft).] At birth, a calf typically measures 4–5 meters (13–16 ft) in length."



This species is often observed in groups of two or three (Jefferson et al. 2008). It migrates from low-latitude wintering areas to high-latitude, summer feeding grounds, although wintering areas are mostly unknown (Gregr et al. 2006).


The Sei Whale is a migratory species and is a fast swimmer that can reach speeds of 25 km/hr (Jefferson et al. 2008). Its main natural predator is the Killer Whale.


Sei Whales feed by skimming the water surface, eating copepods and other small marine organisms (Jefferson et al. 2008). Gregr et al. (2006) say: "Stomach content analyses have revealed substantial regional differences in diet. In the Antarctic, euphausiids represented 54% of the sei whale diet, whereas calanoid copepods represented 83% of the diet in the North Pacific". Sei Whales both skim and engulf food (Gregr et al. 2006).


Information on reproduction in this species is given by Gregr et al. (2006): "Males and females reach sexual maturity between 5 and 15 years of age and live to approximately 60 years of age. In both hemispheres, the age of sexual maturity declined from 10-11 years to 8 years between the 1930s and the 1960s, likely in response to exploitation. Mating, followed by a gestation period of 10.5 to 12 months, and calving occur in winter. Calves nurse for about 6 months and are weaned on the feeding grounds. The calving interval is 2-3 years."


Global Range

The Sei Whale is a cosmopolitan, open ocean species that is often observed near the coast (Jefferson et al. 2008). Although it is known to occur in both hemispheres, from the tropics to the polar zones, it is mainly found in temperate waters (Gregr et al. 2006). Overall, however, its distribution is not well understood (Jefferson et al. 2008).
Distribution in British Columbia

This species was once described as abundant off the west coast of Vancouver Island (from June to August), however, recent whale surveys have not turned up a single confirmed sighting (there are 3 'confident' sightings (Gregr et al. 2006). With only a few observations reported for California, Oregon and Washington, it is likely that the Canadian population is very small (Gregr et al. 2006).


Conservation Issues

The Pacific population is considered endangered in Canada (Gregr et al. 2006). The reason for designation is given as: "This was one of the most abundant species sought by whalers off the British Columbia coast (with over 4000 individuals killed) and was also commonly taken in other areas of the eastern North Pacific. Sei whales have not been reported in British Columbia since whaling ended and may now be gone. There are a few, if any, mature individuals remaining in British Columbia waters, and there is clear evidence of a dramatic decline caused by whaling and no sign of recovery."

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
NativeSHNRedE (Apr 2013)
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Notes

Five Sei Whales were reported off the coast of BC by Coast Guard and research biologists in 2018.

View the Globe and Mail article by Mia Rabson here

Additional Photo Sources

Species References

Gregr, E.J., J. Calambokidis, L. Convey, J.K.B. Ford, R.I. Perry, L. Spaven, and M. Zacharias. 2006. Recovery Strategy for Blue, Fin, and Sei Whales (Balaenoptera musculus, B. physalus, and B. borealis) in Pacific Canadian Waters. IN Species at Risk Act Recovery Strategy Series. Vancouver: Fisheries and Oceans Canada. vii + 53 pp. Available online.

Jefferson, Thomas A., Marc A. Webber and Robert L. Pitman. 2008. Marine Mammals of the World: A Comprehensive Guide to their Identification. Elsevier, New York. Available online.

General References

Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2022-01-21 12:35:11 AM]
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