Scientific name

Balaenoptera borealis

Where does it get its name?

Often found with pollock in Norway, the name “sei” (pronounced ‘say’) comes from the Norwegian word for pollock, “seje.” The words in the scientific name Balaenoptera borealis mean “winged whale” and “northern.”

Whale SENSE Region Found:


Protection status

Endangered Species act

Endangered throughout its range

Protected throughout its range

Where to watch:

Open ocean

During the summer, they are commonly found offshore in the Gulf of Maine, on Georges Bank and Stellwagen Bank off the U.S. coast in the western North Atlantic.

What to watch for:

Blow: Columnar or bushy blow that is about 10 to 13 feet in height. The dorsal fin usually appears at the same time as the blowhole when the animal surfaces to breathe.

Diving: They do not arch their backs or show their flukes before diving. They often leave “fluke prints”—smooth circles on the surface created by the movement of the fluke underwater.

Source: International Whaling Commission

Body: Sei whales’ bodies are primarily dark, with differing amounts of white on their pectoral fins, their bellies, and the undersides of their flukes (tails).

Size: Length: 40-60 feet, Weight: Up to 50 tons

Source: International Whaling Commission

Associations: Sei whales are usually observed alone or in small groups of two to five animals.

Surface activity: From a distance sei whales could be confused with other rorqual whales like blue, fin or Bryde’s whales.


Feed on plankton (including copepods and krill), small schooling fish, and cephalopods (including squid) by both gulping and skimming. They prefer to feed at dawn and may exhibit unpredictable behavior while foraging and feeding on prey.

Mating and Calving

Little is known about sei whale reproduction, but they generally mate and give birth during the winter in lower latitudes.

Photo: WDC

Did you know?

They are fast swimmers that can reach speeds of over 34 miles per hour.

Sei whales and North Atlantic right whales feed on similar prey! Where you see one species, you often see the other. Always look for a dorsal fin before approaching to make sure you are keeping the required 500 yards distance from North Atlantic right whales.

What do sei whales sound like?

Clip provided by NOAA Fisheries

Threats to sei whales

Learn more about sei whales