Sei whale
 
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Balaenoptera borealis

Names

Azores : "Finbeque" - POR : Sardinheira - ITA : Balenottera boreale - SPAIN : Rorcual Negro - GB : Sei whale - GER : Seiwal - NEDER : Noordse vinvis - SWEEDS : Sejval - NOORS : Seihval. - DEENS : Sejhval - JAP : Iwashi kujira

Biology

Adults average size is 14 m but the males can reach 17 m in length. The females are larger and can reach a length of 16 to 20 m. Weight varies from 20 to 30 tons. Newborns measure 4.5 m and weigh up to 1 ton. Females bear a single calf every 3 to 4 years. Gestation lasts about 1 year, and lactation takes about 6 to 7 months. The Sei whale can live for up to 70 years. The body is dark gray on the back and sides and has a lighter coloration on the ventral surface with greyish or white scars caused by lamprey or small shark bites. There are 32 to 60 ventral grooves, all ending well before the navel. On their upper jaw they have 300 to 400 pairs of dark gray baleen plates. They feed primarily on small planktonic crustaceans (copepods), and small fishes such as the harenk and the sardines (this is the reason also for their Portuguese common name of sardinheira "). This species emits metallic sounds with frequencies of the order of 3 kHz.

Observation

Sei whales definitely pass through he Azores region throughout the year, but not particularly regularly, as results from our observations show. The animals that we found were usually alone or sometimes in pairs. From a distance it is impossible to differentiate this species from the other species of its family. It can be confused with the Fin whale and to a lesser degree with the Minke whale, given the shorter length of the latter. However, the Fin whale has an asymmetric coloration in its head, its ventral region is lighter than that of the Sei whale, and the latter can only blow to a hight of 3 m. It is, without a doubt, the fastest of its family, and it can reach speeds of 30 knots. Its swimming path is constant if not disturbed. On a calm day at sea it is possible to follow and trace it due to the waves that it generates with its tail movements. The team at Espaço Talassa was able to observe them passing through the southern region of Pico, breathing every 30 seconds, and they rarely dived more than a few meters for only 2 to 3 minutes. We were also able to observe them preying on horse mackerel.

Cetaceans in the Azores