Protected... once it was already depleted
Previous Population and DistributionThe 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.