Sei Whale

(Balaenoptera borealis)



  • to a maximum length of 16 metres


  • dark to bluish grey, often with many grey to white scars

Dorsal fin

  • 1/4 to 2/3 metre high, strongly curved towards the back
  • generally more erect compared to a fin whale
  • less than 2/3 from the front of the body


  • up to 3 metres in height
  • resembles the blow of a blue and fin whale, but is neither as high nor as dense

Tail fluke

  • seldom arch tail high or expose flukes

Surface behaviour

  • fastest swimmers of all the baleen whales, can exceed 40km/hr in short sprints
  • when surfacing, the dorsal fin is usually visible at the same time
  • arch their back less than fin whales during a deep dive

Group size / social behaviour

  • social behaviour of sei whales is poorly known
  • typically travel alone or in small groups of two to five, although larger aggregations may be seen in feeding areas

Can be confused with

  • fin whales – especially from a distance due to the tall blows and dark coloration of these species. However, the larger size and distinctive white coloration on the right lower jaw of fin whales distinguishes them from sei whales.

Natural History

A sei whale’s diet and feeding behaviour are more similar to those of a right whale than to other rorquals such as blue and fin whales. They feed mainly on copepods and are thought to skim the surface for their prey. They are also known to feed on fish and squid if they are encountered.

There have been few sightings of sei whales since the cessation of whaling.

In the eastern North Pacific, the reported take of sei whales by commercial whalers totaled 61,500 between 1947 and 1987.

Starting in 1962, the number of sei whales targeted by whalers in B.C. spiked to over 500 whales a year, after populations of blue and fin whales had been reduced by overharvesting. By 1967, whalers were only able to catch 100 sei whales, because their population was now overharvested, too. Between 1924 and 1967 more than 3200 sei whales were taken by whaling stations in B.C.


Status in Canada

The sei whale is designated as Endangered by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

COSEWIC’s assessment of the Pacific population of the sei whale is as follows:

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 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.


Gregr, E.J., J. Calambokidis, L. Convey, J.K.B. Ford, R.I. Perry, L. Spaven, 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 [PDF]

Laist, D.W., A.R. Knowlton, J.G. Mead, A.S. Collet, M. Padesta. 2001. Collisions between ships and whales. Marine Mammal Science 17(1): 35- 75.

Gregr, E.J.,L. Nichol, J.K.B. Ford, G.M. Ellis and A.W. Trites. 2000. Migration and population structure of northeastern Pacific whales off coastal British Columbia: An analysis of commercial whaling records from 1908-1967. Marine Mammal Science 16(4): 699-727.

Horwood, J. 2002. Sei whale, Balaenoptera borealis . In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (eds) Encyclopedia of Marine Mammals. pp 1069-1071.

Gregr, E.J. and A.W. Trites. 2001. Predictions of critical habitat for five whale species in the waters of coastal British Columbia. Canadian Journal of Fisheries and Aquatic Sciences 58(7):1265-1285.

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