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Sei Whale

Balaenoptera borealis

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The Sei Whale is the third largest rorqual species behind the Blue Whale and the Fin Whale. Like other rorquals, the Sei Whale uses hundreds of heavy plates of baleen attached to its upper jaw to filter krill and other tiny crustaceans out of sea water. Large, deeply-grooved folds of skin run from beneath the whale’s jaw to mid-body. These folds allow the Sei Whale to greatly expand its jaw and engulf huge amounts of water for filtration. It is estimated they will extract two tons (907 kg) of food from the water every day.

The whale has a pointed rostrum and a small dorsal fin which is located two-thirds of the way down its back. Its skin is generally dark gray and heavily scarred. Adult whales in the North Pacific will measure up to 45 feet (13.7 m) for males and 49 feet (15 m) for females. Sei Whales in other parts of the world may grow up to 64 feet (19.5 m). Despite their enormous proportions, they are the fastest of all cetaceans and have been clocked swimming as fast as 31 mph (50 kph). Due to their size and speed, the Sei Whale has few natural predators outside of Orcas which may hunt them in groups.

Range and Habitat

Sei Whales have an extremely large range and are found in nearly every part of every ocean on Earth. They prefer subtropical and subpolar waters and may be found swimming along the edge of the continental shelf where food is plentiful. During the winter, it may migrate to warmer areas to mate and rear its young.

Conservation Status

Endangered. The Sei Whale’s population was devastated by commercial whaling starting in the late nineteenth century. In the North Pacific Ocean alone, it is estimated over 72,000 whales were hunted in just sixty-five years. The whale is now protected from hunting by international law, although Japan still hunts this species. A 2008 census of the whale put its global population at approximately a quarter million individuals, or one-fourth its pre-whaling numbers. There are approximately 8,600 Sei Whales in the North Pacific Ocean.