The sei (pronounced “sigh”) whale is named for the Norwegian word for the pollack, a fish whose arrival often coincided with that of the sei whale. One of the longest whales, it rivals the bowhead, right and sperm whale for the title of third largest in terms of length. It’s also one of the fastest whales, able to travel at speeds of over 30 miles per hour.
Scientific & Common Names
Kingdom - Animalia
Phylum - Chordata
Class - Mammalia
Order - Artiodactyla
Infraorder – Cetacea
Family - Balaenopteridae
Genus - Balaenoptera
Species – B. borealis
Common Name – Sei Whale, Pollack Whale, Sardine Whale, Japan Finner, Rudolphi’s Rorqual, Lesser Fin Whale
Sei whales are large, sleek whales that are usually dark gray above, and cream-colored or white below, with variable patterns on their upper bodies that resemble paintbrush strokes. Their bodies are often pockmarked with scars that are believed to be bites from the cookie-cutter shark. They are similar in appearance to other baleen whales in the rorqual family, especially the Bryde’s whale. The sei whale can be distinguished from the Bryde’s by its dorsal fin, which is more upright and pointed, and the single ridge on its head, as opposed to three ridges on the Bryde’s.
Sei whales breed in the winter, and gestation can last up to a year, though exact timelines for this are not precisely known as a full pregnancy has not been observed. The mating process is also not well understood. Females will birth a single calf every two to three years. Calves will separate from their mother at around 6-8 months of age.
There are reports, though unconfirmed, of sei whales hybridizing with fin whales, a similar but larger rorqual species.
Sei whales are filter feeders and lack teeth. They feed using highly modified skin-based structures called baleen to strain plankton, krill and small fish from the water.
Little is known about the social behavior of sei whales, and they are typically observed alone or in small groups.
Sei whales began to be targeted by whalers with the advent of steam-powered boats in the late 1800s, as they were too fast for previous whaling ships. They were not hunted in large numbers until other, more profitable whale stocks (including blue whales, right whales and humpbacks) had been overhunted and thus less abundant.
The whale was not initially differentiated from the Bryde’s whale, so accurate counts of its pre-whaling population cannot be calculated. In fact, for a time all whales in the rorqual family (Balaenopteridae) were simply known as “finners”.
Sei whales earned serious protected status in 1970 when international catch quotas were set for individual whale species. The International Whaling Commission instituted a complete ban on commercial whaling in 1986, protecting the sei and other species. They are considered endangered, though the Northern Hemisphere subspecies is more abundant than the southern population.
Princeton Field Guide: Whales, Dolphins and Other Marine Mammals of the World, Jarrett & Shirihai, 2006
Guide to Marine Mammals of the World; Reeves, Stewart, Clapham, Powell; 2008
Whales, Dolphins and Porpoises: The Visual Guide to All the World’s Cetaceans, Mark Carwardine, 1995
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