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          1. The Species

Sei whale

Key Facts

  • Common Name

    Sei whale, coalfish whale, pollack whale, Rudolphi's rorqual; Baleinoptère de Rudolphi, rorqual boréal, rorqual de Rudolphi, rorqual sei (Fr); Ballena boba, ballena sei, rorcual boreal, rorcual de Rudolphi, rorcual norteno (Sp)

  • Scientific Name

    Balaenoptera borealis

  • Status

    IUCN: Endangered

  • Length

    14 to 20 m

  • Weight

    About 20 tons

  • Skin colour

    Dark grey or bluish-grey

Related Links

Background

This information has been reviewed.

This fast cetacean inhabits all oceans and adjoining seas except in tropical and polar regions. The sei whale became a major target for commercial whaling after the preferred stocks of blue and fin whales had been depleted.

Today, although commercial whaling has been officially halted, the species is subject to "scientific whaling" by Japan. It also remains vulnerable to pollution, shipping strikes and entanglement in fishing gear.

Recently a number of South Pacific countries, including five island nations, have declared their EEZs (Exclusive Economic Zone) to be whale sanctuaries in which commercial whaling is prohibited and where additional research on large whales is encouraged.

Physical Description

This species is identified by a dorsal fin, 38 to 56 ventral grooves, and two rows of 300-380 baleen plates. The sei whale is one of the fastest cetaceans, reaching speeds of up to 50 km per hour. A sei whale marked in the Antarctic and killed by whalers 10 days later had traveled more than 4,000 km (2,200 miles) during that period.

It is not usually a deep diver and periods of submergence generally last 5-10 minutes. To feed, the sei whale swims through swarms of prey, twisting on its side and also uses the skimming method of filtering food with its baleens. Although the species does not use echolocation to search for prey, it has been heard to emit a sonic burst of 7-10 pulses.

Like other great whales, the sei whale prefers to spend the summer feeding in the cooler northern waters before migrating south to warmer waters to breed and calve.

Size
This whale is 14 to 20 m long and weighs about 20 tons. Females are about 1-2 m longer than males.

Colour
The species is dark grey or bluish-grey on the back and sides, with a greyish white area on the ventral grooves of the lower jaw and underbelly. Its similarity to the Bryde's whale caused much confusion among whalers in the 19th Century, who often reported sei kills as Bryde's, or either as fin whales.

Habitat

Range States
Argentina, Australia, Canada, Chile, Cuba, Falkland Islands (Malvinas), Iceland, India, Indonesia, Japan, Kenya, Democratic People's Republic of Korea, Republic of Korea, Malaysia, Mexico, Mozambique, Norway, Poland, Russian Federation, Réunion, South Africa, Spain, Suriname, Taiwan, United Republic of Tanzania, Thailand, United Kingdom, United States, Uruguay

Ecological Region
Antarctic Peninsula and Weddell Sea , Bering-Beaufort-Chukchi Seas, Barents-Kara Seas, Mediterranean Sea, Northeast Atlantic Shelf Marine, Grand Banks, Chesapeake Bay, Yellow Sea, Okhotsk Sea, Patagonian Southwest Atlantic, Southern Australian Marine, New Zealand Marine, California Current, Benguela Current, Humboldt Current, Agulhas Current, Western Australia Marine, Panama Bight, Gulf of California, Galapagos Marine, Canary Current, Nansei Shoto, Sulu-Sulawesi Seas, Bismarck-Solomon Seas, Banda-Flores Sea, New Caledonia Barrier Reef, Great Barrier Reef, Lord Howe-Norfolk Islands Marine, Palau Marine, Andaman Sea, Tahitian Marine, Hawaiian Marine, Rapa Nui, Fiji Barrier Reef, Maldives, Chagos, Lakshadweep Atolls, Red Sea, Arabian Sea, East African Marine, West Madagascar Marine, Mesoamerican Caribbean Reef, Greater Antillean Marine, Southern Caribbean Sea, Northeast Brazil Shelf Marine.

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