Meet the Sei Whales: Fast and Important, but Somehow Forgotten

In the world of whales, a few species get all the glory; the blue whale is the largest in the world, and then there are the humpback whales, which leap out of the ocean to the delight of film crews and tourists. Beluga whales may be famous for their unusual appearance and killer whales for their sinking yachts (and aren’t whales at all), but what about some of the lesser-known species? Have you ever heard of the sei whale?

Appearance, population and ecology

Sei whales (Boreal Balaenoptera) weigh approximately 20 tonnes (18,144 kilograms) and measure 13.7 to 20 meters (45 to 66 feet) in total length, making them the third largest whale species after blue and fin whales. The name “sei” comes from the Norwegian word for pollock, “seje”, because the two species are often found together.

The ecology of these whales is poorly understood and, as a result, the species has been nicknamed the “forgotten whale” due to this lack of information. However, it is thought to be found in most of the world’s oceans, with the exception of polar and tropical regions. There are believed to be three “stocks” of sei whales, with distinct populations in the North Atlantic, North Pacific and Southern oceans.

They also have a wide dietary range, eating plankton, krill, small fish and squid. Whales feed on these creatures by skimming them from the water and filtering them through their baleen plates.

Social behavior and migration

Typically, sei whales are found alone or in small groups of around five individuals, although larger aggregations of whales can be found in areas of high prey density.

Sei whales also make extensive seasonal migrations, spending the summer at higher latitudes and, although somewhat understudied, the whales are thought to return to lower latitudes when calves are born in winter. Gestation lasts between 10 and 13 months, according to the Mammal Society.

Recently, 93 sightings of sei whales were made off the coast of New England, the largest number of sightings ever made during a single survey flight.

History

Sei whales are believed to have no natural predators, but they have historically been hunted for their meat and oil. It is estimated that up to 300,000 people were killed for this reason, of which more than 110,000 are believed to have occurred between 1960 and 1970. Hunting turned to sei whales after the decline in populations of blue and fin whales.

Currently, the IUCN classifies sei whales as endangered and estimates their global population at 50,000 individuals. Although hunting sei whales and other whale species is banned, Japan continues to hunt them in the North Pacific. Other modern threats include entanglement in fishing nets and disruption from boat traffic.