Sei Whale - Photo Cetacea

Sei Whale

Sei Whale Facts

Latin Name: Balaenoptera Borealis

The Sei Whale is found in virtually every ocean and sea in the world. However, it does not like extreme environments and is less likely to be found in polar waters than other rorquals. The subarctic and subantarctic are favoured for summer feeding, but the majority of Sei Whales are found in temperate and sub-tropical waters, and migrations between these areas are annual.


The Sei Whale was classified in 1828 by the French zoologist René Lesson, who named it Balaenoptera borealis (referring to the north).

Local Names

Coalfish Whale; Pollack Whale; Rudolphi’s Rorqual; Sardine Whale; Japan Finner. The name ‘Sei’ refers to the whales’ habit of arriving off the northern Norwegian coast with the seje (coalfish).


This is a slender cetacean, although more robust than the Fin Whale. The dorsal fin is well-defined and slightly hooked and is located about two-thirds back along the body. The head and jaws are rather narrow and slightly arched, unlike in other rorquals. It is a mottled dark grey in colour, with paler undersides and between 38-60 throat grooves. There are 636-680 dark baleen plates per animal, the longest of which is 78cm. The Sei Whale is between 13.6-16m long, with the longest recorded animal at 18.3m; females are generally larger than males. It weighs between 20-25 tonnes.

Recognition at Sea

The shape of the head and the poition of the dorsal (which is clearly visible on blowing ) distinguish the Sei Whale from other rorquals. The blow is a vertical, moderately tall ‘cloud’.


This species is essentially a dweller of the open ocean, not generally found inshore or in coastal waters. The Sei Whale tends to follow shelf contours and plankton gatherings.

Food & Feeding

The Sei Whale will take whatever is in abundance locally, whether it be fish (upto 30cm long), squid or plankton, as long as it is shoaling. It swims on one side through the shoaling fish and then filters out the water with its baleen plates and tongue.


Sei Whales tend to swim in pods of 3-5 animals, and rarely dive deeper than 300m. Although little is known about how this species communicates, it has been found that low-frequency pulses are common.


Approximately 70 years.

Estimated Current Population

65,000 animals. Vulnerable.

The Influence of Man

The Sei Whale was not traditionally a target for whalers because it lived in the same waters as Blue, Fin and Humpback Whales, which were the preferred quarry. However, when these stocks began to decline and then became protected, Sei Whales became the primary catch from the mid-1960s onwards. By the mid-1970s, the Sei Whale stocks were ‘fished out’ and the species earned protected status in 1979.


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