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a close up of a fish

Sei whale
(Balaenoptera borealis)

Sei whales are considered rorquals due to their throat furrows. Instead of teeth, they have baleen plates along their upper jaw, which work as a filtering system (see further description for Bryde’s whales Portrait).

The name “Sei” is the Norwegian name for pollock, a fish that appear along the coast of Norway at the same time as these cetaceans. They are the third largest rorquals and, together with the Fin Whale, one of the fastest, reaching speeds of up to 50kmh over short distances.

They are easily confused with Bryde’s whales out at sea due to their similar appearance and are best distinguished through the single, central rostral ridge extending from their blowhole to their snout (as opposed to the Bryde’s three rostral ridges).

General information

Further names: Portuguese: Baleia-sardinheira

Size of adults: Females 16-19 metres (larger than males)

Prey: Primarily zooplankton (planktonic crustaceans) but also schooling fish. Like most other rorquals, Sei whales are lunge feeders accelerating to gulp large amounts of water before forcing it out through the sides of their mouths filtering out their prey in the process. 

Behaviour: Very little is known about their social behaviour. Usually react evasively towards boats but occasionally allow an approach. May be encountered in small groups of two to six individuals.

Range: Occurs worldwide from subtropical and tropical waters to colder regions. Inhabits shelf and oceanic waters. Sei Whales undertake seasonal migrations, moving to higher latitudes in summer and tropical waters in winter.

Madeira: Mainly encountered in the spring and summer months

Distinctive features: Tall, heart-shaped spout and prominent, falcate dorsal fin. Their build is similar to that of the  Bryde’s whale except slightly more robust. One central rostral ridge extending from the blowhole to the snout.

Taxonomy: Suborder: Mysticeti (Baleen whales); Family: Balaenopteridae (Rorquals)

Threats: Insufficient data on population size. Sei whales are still victims of whaling in the western Pacific and are additionally threatened by vessel collisions, fishing nets and noise pollution.