Species guide
Sei whale
Balaenoptera borealis
At a glance
Conservation, taxonomy and Madeira records reviewed . Review sources.
- Global IUCN conservation status
- Endangered — assessment published .
Global extinction risk is separate from sighting frequency in Madeira.
- Identification
- Large, slender, dark body with paler undersides.
- V-shaped head with a single, central, longitudinal ridge.
- Size
- Maximum length: 21 m
- Recorded occurrence in Madeira
- Reported on local trips, including July 2025.
- Madeira records and season
- The Madeira Whale Museum describes a spring/summer tendency, with occasional records in other months.
Identification and size summarize profile notes updated . Local records are past observations, not a prediction of sightings.
Read the identification notes ↓- Taxonomic authority
- Lesson, 1828
- Family
- Balaenopteridae
- Cetacean group
- Mysticeti
Sightings in Madeira
Our July 2025 trip report lists this species. This is an operator observation, not a population estimate.
The Madeira Whale Museum describes a spring/summer tendency, with occasional records in other months. Local seasonality source.
ID characteristics
Large, slender, dark body with paler undersides.
V-shaped head with a single, central, longitudinal ridge.
Tall dorsal fin with variable shape but commonly sickle-shaped
Flukes look small when compared to body size
Surface behaviour
Often swims close to surface with blow and dorsal fin visible simultaneously
When diving does not arch much its back and never shows flukes
Normally associated with large feeding frenzies of seabirds
Distribution
Worldwide, between parallels 65º North and 60º South.
Mainly in deep, temperate waters but can reach subarctic and subantarctic in summer.
Social
1 to 5 individuals together
Diet
Fish, squid, krill and crustaceans
Biometrics
Max length: 21 m
Adult weight: 20 to 30 ton
Blow
A narrow spray up to 3 meters high
Common names in other languages
- Portuguese: Baleia-sardinheira, Baleia-sei, Baleia boreal
- German: Seiwal
- French: Baleinoptère de Rudolphi, Rorqual Boréal, Rorqual de Rudolphi, Rorqual de Sei
- Spanish: Ballena Sei, Rorcual Boreal, Rorcual de Rudolphi, Rorcual Norteño
- Italian: Balenottera boreale
- Dutch: Noordse vinvis
- Polish: Sejwal
- Swedish: Sejval
- Danish: Sejhval
- Norwegian: Seikval, Seihval
Other English names
Coalfish Whale, Pollack Whale, Rudolphi's Rorqual, Sardine Whale
Names vary by language and region. This list is not exhaustive. Multilingual name records.
Review sources
Conservation, taxonomy, local occurrence and seasonality checked on . The assessment publication year is separate from this editorial review date. Identification, size, other biology notes and multilingual aliases are outside this review unless a specific source is cited alongside them.
- IUCN Red List: Balaenoptera borealis — global species assessment, published 2018.
- Society for Marine Mammalogy: species and subspecies list (April 2026) — Scientific names, authorities, families and English names. Mysticeti and Odontoceti are treated as unranked groups.
- IUCN SSC Cetacean Specialist Group: Red List status of cetaceans — Global species categories cross-checked against the specialist group's overview, updated October 2025. Regional and subpopulation assessments are separate.
- IUCN Cetacean Specialist Group: November 2018 assessments — Global assessment publication years and category changes. A category change need not indicate a recent population change.
- Freitas et al. (2012): New records of cetacean species for Madeira Archipelago with an updated checklist — Table 1 and species accounts distinguish sightings, catches and strandings. Record totals and last-record dates describe evidence available through December 2012.
- Madeira Whale Museum: sei whale — Local occurrence and a spring/summer tendency, with observations possible in other months.
The linked trip reports document operator observations. They do not independently confirm every identification or measure population size, abundance or the probability of a sighting.