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)
14 to 20 m
About 20 tons
Dark grey or bluish-grey
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.
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.
This whale is 14 to 20 m long and weighs about 20 tons. Females are about 1-2 m longer than males.
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.
A global open water diverSei whales are pelagic, occurring far from shore in temperate oceanic waters worldwide.
Although sei whale groups mostly consist of two to five individuals, thousands may aggregate where plenty of food is available.
Sei whales become sexually mature between 6 to 8 years old. Sei whales can live for 65 year.
Mating season ranges from November to February in the Northern Hemisphere and from May to July in the Southern Hemisphere. Females generally give birth to a single calf every other year in winter, after a gestation period of 10.5-12 months.
Although we know very little about their breeding habits, some data indicate that sei whale migration is loosely organized around sex, age, or reproductive function. This presumably relates to mating strategies, but at this time nothing is known of their mating habits or calving grounds.
Like other baleen whales, sei whales feed by skimming and swallowing surface plankton, mainly copepods (tiny marine crustaceans) but also euphausiids (krill - shrimp-like crustaceans).
Population and Distribution
Protected... once it was already depletedPrevious population and distribution
The species was intensively exploited worldwide after blue and fin whale stocks had been reduced. Evidence shows that the stocks of sei whales were depleted before they were protected from commercial whaling in the 1970s and 1980s.
In 1980, it was estimated that the Southern Hemisphere population had been reduced to around 24,000 from an initial level of 100,000 or so. In the North Pacific, the most recent study, in 1977, indicated a decline from 42,000 in 1963 to 8,600 in 1974. Figures in the North Atlantic are the most uncertain, although some surveys have suggested a figure of around 10,000.
Current population and distribution
Sei whales inhabit all oceans and adjoining seas except in polar regions, feeding in cold water during the summer and migrating to warm tropical and subtropical waters during the winter.
In the western North Pacific, sei whales are common in the south-west Bering Sea to the Gulf of Alaska, and offshore in a broad arc between about 40 degrees North and 55 degrees North across the Pacific.
In the North Atlantic, sei whales can be found from the coast of Labrador, and along the coasts of Greenland and Iceland. In the East Atlantic, sei whales migrate north to northern waters off Norway, Shetland, Orkney and the Faeroe Islands and occasionally, Svalbard. Sei whales are also present in the Denmark Strait.
What little we know about sei whale population structure comes largely from whaling data. There are two separate populations in the Northern and Southern Hemispheres, but it is unclear whether they are separate populations within each ocean basin.
Estimates from the U.S. National Marine Fisheries Service puts the southern population at 24,000; 4,600 in the North Atlantic; and 22,000-37,000 in the Pacific. However, the extent to which stocks have recovered generally is uncertain, as little research has been carried out on this species over the last few decades.
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
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.
Unwanted attention from whaling fleets
While the sei whale has been hunted by humans since the 1860s, it wasn't until the 1950s and 1960s and the declining availability of blue and fin whales that the killings seriously expanded.Since 1985, the International Whaling Commission has officially halted all commercial whaling of this species. Today, 50 sei whales are killed annually by Japanese whalers in the North Pacific in Japan's "scientific whaling" programme.
They are threatened by global warming, but they can also be harmed by pollution, shipping strikes and entanglement in fishing gear.
The majority of WWF's global conservation work to protect whales and dolphins takes place within the context of the International Whaling Commission (IWC).
How you can help
- Support efforts to improve fishing gear by only buying seafood that is MSC certified. This can help to reduce the incidence of marine bycatch, which kills whales and other marine life like turtles, dolphins, and seabirds.
- Vote Earth by taking part in Earth Hour! As climate change is a growing threats for whales, we need to send a message to our leaders that warming must be limited to under 2 degrees Celsius.
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