Sei Whale - Balaenoptera borealis

Status: Endangered … The ninth-largest living animal on the planet and yet can swim 35 miles per hour

Type: Mammal

Location: Found in virtually every ocean and sea in the world, especially the temperate waters in the mid latitudes of the Atlantic and Indian Oceans.

Size: Usually measures about 16 metres in length, with a maximum recorded of 20 metres, and females are usually bigger than males.

Habitat: Prefers subtropical to sub-polar waters on the edge of the Continental shelf.


Main Threats:
Sei whales were hunted almost to extinction by commercial whalers in the 19th and 20th centuries when all known populations were exhausted and an estimated 300,000 sei whales were killed. The IUCN reports that sei whale stocks have probably recovered somewhat since the International Whaling Commission ban on commercial whaling in 1985, with some current estimates suggesting there are up to 80,000 worldwide. This would be less than 25% of the population prior to the impact of whaling, but estimates of current numbers are uncertain and there is no direct evidence of any increase in population worldwide.

Sei whales have been protected by the international ban on whaling since the mid 1970s, with a limited catch of about 100 animals per year reported by Japan for ‘scientific whaling’. Other threats may include reduction in prey fish stocks, pollution, and occasional entanglement in fishing gear.

Sei whales are baleen whales, which have no teeth but instead have unique filter-like structures growing from their jaws known as baleen plates. When feeding, baleen whales engulf huge volumes of water in their vast mouths, and then raise their tongue to expel the water out of the sides of the mouth and through the baleen filter plates. The whale then uses its massive tongue to effectively lick off food such as small fish, plankton and other invertebrates stuck on the baleen or caught in the mouth, before swallowing the lot. They eat about 900kgs of food a day, usually plankton or krill, but also small fish and squid, so it is no wonder that they weigh up to 45 tons – roughly the weight of six adult African elephants! And growing up to 20m in length, they are the ninth largest living animal on this planet - the eight heavier animals are different species of whale.

Sei whales are known as skimmer feeders, in that they often swim at the surface, twisting from side to side, passing through and engulfing shoals of prey. They can often be recognised when feeding through this behaviour, when they will swim on their sides at the surface for several minutes with their flipper sticking up in the air! Usually seen singly or in small groups of 2 -5 individuals, they generally mate and give birth in southern waters. Females breed every 2-3 years, producing a single calf after a gestation period of 11 – 13 months. Mothers continue to feed the calf milk for up to 9 months.

Sei whales were hunted almost to extinction in the 19th and 20th centuries


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