Sei whale

Sei whales (Balaenoptera borealis) are dark grey or bluish-grey on their backs and sides, with a greyish white area on the ventral grooves of their lower jaws and underbellies. Parasites leave scars on their bodies, often giving them a "galvanized" appearance. They are 14 to 15m long and weigh about 20 tonnes.

Sei whales are regarded as the fastest swimmers among the great whales, reaching speeds of more than 37 kmh.

They are normally found alone or in groups of two to five individuals, although larger groups can be found at good feeding grounds.



Where are they found?
Sei whales are found worldwide. Like other great whales, they prefer to spend their summers feeding in the cooler northern waters before migrating south to warmer waters to breed and calve. 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 do they eat?
Like other baleen whales, sei whales feed by skimming and swallowing surface plankton, mainly copepods but also euphausiids. They appear to feed on whichever food species is most prevalent, including small schooling fishes and squid. Sei whales do not swim on their side, as other baleen whales often do, when feeding.

How long do they live?
Sei whales become sexually mature at six to eight-years-old. Calves are usually born in winter, after a gestation period of 10.5 to 13 months. A female gives birth to a single calf, which is nursed for six to nine months. The calving interval is two to three years. Sei whales can live until they are 65-years-old.

Sei whales and hunting
Humans have hunted sei whales commercially for oil, meat, and baleen, which has reduced their numbers in all areas where they were once abundant. Hunting was banned by the International Whaling Commission in 1978.

Conservation concerns
Sei whales can also be harmed by pollution, shipping strikes and entanglement in fishing gear.