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Sei Whale (Balaenoptera borealis)

Sei Whale (Balaenoptera borealis)

All text on this page is copyright protected: © 2014 Kelvin Aitken.
All rights reserved. Students may use this information for personal research only. Not for commercial use.

Order: Cetacea
Family: Balaenopteridae
Genus: Balaenoptera
Species: borealis
Taxonomic name: Balaenoptera borealis
Other Common Names: Lesser Fin Whale.

Sei Whales (pronounced “say”) belong to the Balaenopteridae or Rorqual family of whales.

Sei Whales are born at 4.5-4.8 meters and grow to 21 meters.

This speedy species of Baleen whale can be found in all oceans in polar to warm temperate waters, usually in oceanic areas though sometimes found near shore in deep water.

The Sei Whale (Balaenoptera borealis) is dark grey on the back with this colour extending well down over the flanks towards the ventral surface which has pale grey/white markings from the chin to the genital area. All fins are dark on the ventral surface with no white markings. The long tapered body is covered in a spotted pattern of cookie cutter shark bites and other scars. The snout is narrower and sharper than a Blue Whale but less pointed than the Fin with a single ridge from the twin blowholes to the tip of the snout which also has a distinctive downward curve at the tip visible from above and from the side. The sharply pointed dorsal fin is strongly curved, sometimes with a boomerang shape to the leading edge, and situated well back on the body.

Being shallow feeders Sei Whales surface at a shallow angle so that the blowholes and dorsal fin are visible together. When they dive they almost never show their flukes but submerge in a similar manner as their ascent, with their shallow immersion shown by a pattern of “footprints” on the surface as they move along just below the surface. They feed in small groups of 2-5 adults on krill, copepods, squid and small schooling fish with a skimming technique; not lunge feeding like Humpback Whales.

They are regarded as the fastest of the Rorqual whales and may be easily confused with Bryde’s Whales. The most distinctive difference between these two species is the single rostral ridge on the Sei and the triple set of rostral ridges on the Bryde’s Whale.

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