Balaenoptera borealis

The sei whale is the least known of the rorqual family and can easily be confused with other species. Their relatively large dorsal fin can be used to distinguish them from other baleen whales.

They have a single ridge on the top of the head, unlike the Bryde’s whale which has three parallel ridges. Sei whales lack the asymmetrical white lower jaw found in fin whales, assisting in identification at close range.

Upon surfacing, the back of the sei whale is usually visible on the surface for a relatively long time. They usually travel alone or in small groups, but more may be seen in areas where food is plentiful. They are known to breed with fin whales, producing at least first generation young. Sei whales are found in nearly all waters of the world, including polar regions where they feed in the summer.

The sei whale does not gulp-feed like other whales in its family and while swimming, the dorsal fin and backstays visible longer. In the Azores, they are encountered during the spring months on a fairly regular basis, as they complete their northerly migration.

Video Footage

Species Details


Male: 17 m
Female: 20 m
Calf:  5 m


Female: 45,000 kg

Species Specs:

Global population: c.40,000 (population trend unknown)
Status: Endangered
Diet: Small schooling fish like sardines, squid, krill
Baleen: 300 – 400 pairs (dark grey)
Longevity: 70 years
Breeding age: Unknown
Gestation: 1 year
Nursing: 6 – 7 months

In other languages:

Portuguese: Baleia-sardinheira
Spanish: Ballena sei
French: Rorqual Sei
Italian: Balenottera boreale
German: Seiwal
Dutch: Noordse vinvis
Swedish: Sejval
Norwegian: Seihval
Danish: Sejhval
Finnish: Seitivalas
Polish: Sejwal
Russian: Ivasevyi kit, saidianoi kit, ivasevyi polosatik, seival


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