The sei whale's streamlined shape makes it a very fast swimmer, reaching speeds of 50 km/h (26 mph).

Subspecies
Possibly two (Northern and Southern).

Life span
Up to 74 years.

Statistics
Northern subspecies of sei whales can reach lengths of up to 18m and Southern subspecies can reach up to 21m in length. They weigh 20-30 tonnes.

Physical description
Sei whales have a relatively slender body with a sickle-shaped dorsal fin. The body is dark grey with irregular white markings on the underside and they have a longitudinal ridge on the head.

Distribution
They are found in all oceans and adjoining seas, except polar and subtropical regions. They occupy temperate and sub-polar regions in the summer.

Diet
Sei whales feed on krill, small fish and squid.

Reproduction
Mating occurs during the winter months and females typically give birth every year.

Conservation status
Sei whales are classified as Endangered by the 2000 Red List. They were heavily exploited, especially in the 1960s and 70s.