BC Conservation Data Centre: Conservation Status Report
Balaenoptera borealis
Sei Whale
| Scientific Name: | Balaenoptera borealis |
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| English Name: | Sei Whale |
| Provincial Status Summary | |
| Status: | S1N |
| Date Status Assigned: | March 21, 2021 |
| Date Last Reviewed: | March 21, 2021 |
| Reasons: | |
| Range | |
| Range Extent: | U = Unknown |
| Range Extent Comments: | The current range extent in BC waters is unknown. During the whaling period, almost 4,000 Sei Whales were taken in BC waters, 99% of which were in deep offshore areas (more than 1000m deep; Ford 2014). Since whaling for Sei Whales ended in 1974, there had been fewer than 10 sightings in BC waters until July 2021, when an aggregation of more than 50 individuals was sighted during a DFO cetacean survey approximately 190 nm west of Estevan Point, Vancouver Island (Ford 2014; J. Ford, pers. comm.; Doniol-Valcroze et al. in press). |
| Area of Occupancy (km2): | U = Unknown |
| Area of Occupancy Comments: | Given the current rarity of Sei Whales in BC waters, it is not possible to estimate an area of occupancy. |
| Occurrences & Population | |
| Number of Occurrences: | U = Unknown |
| Comments: | It is not possible to determine number of occurrences from the very few recent sightings. |
| Number of Occurrences with Good Viability / Ecological Integrity: | U = Unknown |
| Percent Area with Good Viability / Ecological Integrity: | U = Unknown |
| Comments: | Sei Whale habitat is primarily in deep waters offshore of the continental shelf slope, where they feed on copepod zooplankton and small schooling fishes. This habitat presumably has good integrity, but the current rarity of Sei Whales in BC waters may be at least partly due to a lack of ecosystem integrity for this species. |
| Number of Occurrences Appropriately Protected & Managed: | U = Unknown |
| Comments: | Number of occurrences unknown. |
| Population Size: | B = 50 - 250 individuals |
| Comments: | A coast-wide systematic ship survey of BC waters in 2018 resulted in only 5 sightings of a total of 6 individuals (Doniol-Valcroze et al. in press). A similar large survey off the US mainland west coast in 2018 made 4 sightings of a total of 4 individuals (Henry et al. 2020). No sightings of Sei Whales were made during over 28,000 km of transect ship survey effort along the BC coast during 2002-2008, although only 13% of this effort was in deep offshore waters typical of Sei Whale habitat (COSEWIC 2013t). A recent large-scale survey of central and eastern North Pacific, including the outer portion of Canada?s EEZ, resulted in an abundance estimate of 29,632 (CV = 0.24; 95% confidence interval, 18,576?47,267; Hakamada et al. 2017). Only 2 sightings of a total of 4 individuals were made in Canadian waters during this survey (Ford 2014). In July 2021, a DFO cetacean survey in the area of Explorer Seamount (~190 nm W of Vancouver Island) observed an aggregation of over 50 Sei Whales. Given the abundance of Sei Whales during the whaling period that ended in 1975, it is unclear why little recovery of the population is apparent. Hakamada et al. (2017) noted that densities north of 50°N were lower than in the past, which may suggest a shift in distribution in the post-whaling era. The current scarcity of the species off the US and Canadian west coast suggests an offshore shift as well. |
| Threats (to population, occurrences, or area affected) | |
| Degree of Threat: | U = Unknown |
| Comments: | Anthropogenic threats to Sei Whales are likely those common to most baleen whales: ship strikes, fisheries interactions, acoustic disturbance, habitat degradation, and pollution (COSEWIC 2003, 2013; Gregr et al. 2006). |
| Trend (in population, range, area occupied, and/or condition of occurrences) | |
| Short-Term Trend: | A = Decline of >90% |
| Comments: | Given an estimated generation time of 23.3 years (Taylor et al. 2007), current abundance has likely decreased substantially since 1951 (i.e., 3 generations ago). Approximately 2,819 Sei Whales were processed at the Coal Harbour Whaling Station on northwestern Vancouver Island between 1951 and 1967, when the station closed (Ford 2014). During the final years of whaling in the 1960s, the proportion of Sei Whales increased due to a shift to this species driven by depletion of Fin and Blue Whales. Over 600 Sei Whales in each of 1964 and 1965 were killed in BC waters. The population today must be a very small fraction of its former abundance as late as the 1960s. |
| Long-Term Trend: | U = Unknown |
| Comments: | No estimates for abundance of Sei Whales in BC waters prior to the whaling era are available. The pre-whaling abundance of Sei Whales in the entire North Pacific has been estimated at 42,000 (Tillman 1977). Recent surveys suggest that the recent abundance is about 35,000 (Hakamada et al. 2017). This suggests that substantial recovery of the overall abundance of Sei Whales in the North Pacific may have taken place since whaling ended, but clearly this has not been the case for BC waters. |
| Other Factors | |
| Intrinsic Vulnerability: | U=Unknown |
| Comments: | Although Sei Whales would not appear to be any more intrinsically vulnerable than most other rorqual whales, their lack of recovery in BC waters may reflect unknown vulnerabilities. |
| Environmental Specificity: | BC=Narrow to moderate. |
| Comments: | Fin Whales have a narrow to moderate ecological niche. They feed by either ?gulping? or ?skimming? on copepod and euphausiid zooplankton as well as small schooling fishes (COSEWIC 2003; Ford 2014). Their diet is somewhat broader than congeneric Blue and Fin Whales (Ford 2014). |
| Other Rank Considerations: | |
| Information Gaps | |
| Research Needs: | See Action Plan (Fisheries and Oceans Canada 2017) |
| Inventory Needs: | See Action Plan (Fisheries and Oceans Canada 2017) |
| Stewardship | |
| Protection: | See Action Plan (Fisheries and Oceans Canada 2017) |
| Management: | See Action Plan (Fisheries and Oceans Canada 2017) |
| Version | |
| Author: | Ford, J. |
| Date: | March 31, 2021 |
| References | |
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COSEWIC. 2003l. COSEWIC assessment and status report on the sei whale Balaenoptera borealis in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. vii + 27 pp.
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COSEWIC. 2013t. COSEWIC status appraisal summary on the Sei Whale Balaenoptera borealis, Pacific population, in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 12 pp.
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Doniol-Valcroze, T., L. Nichol, B. Wright, et al. In press. Abundance estimates of cetaceans from the 2018 Pacific Region International Survey of Marine Megafauna. DFO Can. Sci. Advis. Sec. Res. Doc.
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Fisheries and Oceans Canada. 2017. Action Plan for Blue, Fin, Sei and North Pacific Right Whales (Balaenoptera musculus, B. physalus, B. borealis, and Eubalaena japonica) in Canadian Pacific Waters. Species at Risk Act Action Plan Series. Fisheries and Oceans Canada, Ottawa. iv + 28 pp.
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Ford, J.K.B. 2014. Marine Mammals of British Columbia. Royal BC Museum Handbook, Mammals of BC, volume 6. Royal B.C. Mus., Victoria, BC. 460 pp.
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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 pp.
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Hakamada, T., K. Matsuoka, H. Murase, et al. 2017. Estimation of the abundance of the sei whale Balaenoptera borealis in the central and eastern North Pacific in summer using sighting data from 2010 to 2012. Fisheries science, 83:887-895.
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Henry A.E., J.E. Moore, J. Barlow, et al. 2020. Report on the California Current Ecosystem Survey (CCES): Cetacean and Seabird Data Collection Efforts, June 26 - December 4, 2018, U.S. Department of Commerce, NOAA Technical Memorandum NMFS-SWFSC-636.
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Taylor, B.L., S.J. Chivers, J. Larese, and W.F. Perrin. 2007. Generation length and percent mature estimates for IUCN assessments of cetaceans. Administrative Report LJ-07-01. National Marine Fisheries Service, Southwest Fisheries Science Center. LaJolla, CA. 24 pp.
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Tillman, M.F. 1977. Estimates of population size for the North Pacific sei whale. Rept. Int. Whal. Commn., Special Issue 1:98-106.
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Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website http://www.natureserve.org/.
Suggested Citation:
B.C. Conservation Data Centre. 2021. Conservation Status Report: Balaenoptera borealis. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jun 6, 2026).