Sei Whale

## Description

The sei whale ( SAY, Norwegian: ; Balaenoptera borealis ) is a baleen whale, the third-largest rorqual after the blue whale and the fin whale. It inhabits most oceans and adjoining seas, and prefers deep offshore waters. It avoids polar and tropical waters and semi-enclosed bodies of water. The sei whale migrates annually from cool, subpolar waters in summer to temperate, subtropical waters in winter with a lifespan of 70 years.

Reaching 19.5 m (64 ft) in length and weighing as much as 28 t (28 long tons; 31 short tons), the sei whale consumes an average of 900 kg (2,000 lb) of food every day; its diet consists primarily of copepods, krill, and other zooplankton. It is among the fastest of all cetaceans, and can reach speeds of up to 50 km/h (31 mph) (27 knots) over short distances. The whale's name comes from the Norwegian word for pollock, a fish that appears off the coast of Norway at the same time of the year as the sei whale.

Following large-scale commercial whaling during the late 19th and 20th centuries, when over 255,000 whales were killed, the sei whale is now internationally protected. As of 2008, its worldwide population was about 80,000, less than a third of its prewhaling population.

## Appearance

A Sei whale is a slender cetacean, although it is more robust than a fin whale. These rorquals are long and slender, and so are much more streamlined than other large whales. They have a compressed tail stock which abruptly joins the flukes. Their snout is pointed, and their pectoral fins are short. Their dorsal fin is shaped like a sickle. They typically have a dark steel gray body with irregular white markings on the underside. These plates have whitish fine inner bristles.

## Distribution

Sei whales live in all oceans and seas, except tropical and polar regions. They occupy sub-polar and temperate regions during the summer, migrating to sub-tropical waters in the winter. These whales occur in the open ocean and generally avoid coastal waters.

## Behavior

Sei whales gather in groups that number two to five individuals, although larger groups can form where food is very plentiful. They prefer to eat at dawn and may demonstrate unpredictable behavior during foraging and eating. They are fast swimmers, and are believed to migrate to warmer waters in lower latitudes during winter. Sei whales are one of the fastest cetaceans. However, they are not remarkable divers, descending only to shallow depths, remaining submerged for just five to ten minutes. Sei whales typically do not rise high above the water when they dive, usually only sinking below the surface. Their dorsal fin and blowholes are often visible above the surface of the water almost simultaneously. A Sei whale almost never lifts its flukes up above the surface, it is generally less active at the surface of the water and it rarely breaches.

## Diet

Sei whales eat whatever is abundant locally, if it is a shoal (school) species: fish, squid or plankton.

## Reproduction

Sei whales are polygynous, one male having exclusive mating rights with many females. Mating takes place during the winter. Females mate every 2-3 years and gestation lasts 11-13 months. Females typically give birth to one calf. Mothers nurse their calves and look after them until they are weaned at the age of 6 - 9 months. Sei whales are sexually mature when they are about 10 years old.

## Population

### Population threats

Sei whales are under threat by climate change and also by pollution, entanglement in fishing gear and ship strike.

### Population number

According to the U.S. National Marine Fisheries Service, the total size of the Sei whale population is around 80,000 individuals. This species is classified as Endangered (EN) on the IUCN Red List.

## Fun Facts for Kids

The name "sei" comes from the Norwegian "seje", used to describe a type of fish which gathers Norway's coast around the same time as sei whales.

The scientific name of Balaenoptera borealis has the meaning “winged whale” and “northern.”

After the Blue whale and Fin whale, the Sei is the 3rd largest animal living on the planet. Being a baleen whale, the Sei has two blowholes and no teeth, which are replaced with as many as 400 baleen plates full of bristles that filter out prey from the water.

Seis can stay up to 20 minutes beneath the water while looking for food.

These whales communicate with growl-like low-frequency calls.

Sei whales eat a lot and can consume up to 2,000 pounds of food each day.

Roy Chapman Andrews, the American naturalist, compares Sei whales to the cheetah because, although they are able to swim very quickly for a short distance, they tire fairly quickly.

Sei whales prefer to travel on their own or in a small pod but they will sometimes gather in their thousands where there is abundant food.