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Pronounced “say,” the sei is a close relative of the fin whale, about the size of a sperm whale and slightly larger than the humpback. Its narrow body grows to about fifty feet, weighing up to forty tons. The sei’s body is dark gray with a white underside, and any scarring from encounters with other species appear as white spots. It has a dorsal ridge, thirty to sixty short throat grooves and 300 to 400 pairs of baleen plates. Besides its smaller size, the sei may be distinguished from the fin whale by the fact that both sides of sei’s jaws are the same color. The sei is more difficult to distinguish from a Bryde’s whale because they are similar in size, shape and markings. The sei has a more dominant dorsal fin and one ridge instead of three on its head. The sei is the third largest of the rorqual baleen species that visitors on whale watching tours to South America will see if they are lucky.
Seis are usually found in deep water and can stay submerged for five to ten minutes. They prefer copepods but their diet also includes krill, other crustaceans and small fish. Blowing as it moves along the surface, the sei feeds with mouth open in a similar fashion to the southern right whale.
During mating periods and when feeding, they may be found in small pods and sometimes in very large groups. Females give birth about every other year, after a gestation of between ten and twelve months. The calf is weaned in six months. Seis reach maturity by age ten and live about seventy years.
The sei was named for its timing. It was a favorite species of northern whalers because its migratory pattern brought it conveniently near the Norwegian coast about the same time that fish species called “sej,” including cod and Pollock, arrived to feast on the same diet.
Seis are found throughout the world but do not travel to Antarctica. During the summer months, they feed in sub-Antarctic waters further north than most baleens of the Southern Hemisphere. Though some venture south of the Antarctic Convergence, most do not. Seis winter in subtropical waters, mating between May to July, though scientists are unsure where exactly.
Until modern times, seis were mostly ignored by their human predators, in part because they swam too fast for the whalers to kill, traveling at speeds of thirty miles an hour for short stretches. Whalers preferred to go after more lucrative species with more blubber such as the blues and fins, but as these larger species became commercially depleted and ship design and technology improved, hunting of the sei began. It wasn’t until 1979 that the species received protection from the International Whaling Commission. Today, the sei is considered endangered, and an estimated population of around 50,000 is thought to exist.
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