Sei Whale
Sei Whale
Balaenoptera borealis
Quick Facts
Weight
Up to 100,000 pounds
Length
40 to 60 feet
Lifespan
50 to 70 years
Threats
Climate change,
Entanglement in fishing gear,
Ocean noise,
Vessel strikes
Region
Alaska,
New England/Mid-Atlantic,
Pacific Islands,
Southeast,
West Coast
Sei whale mother and calf. Credit: NOAA Fisheries
Sei whale mother and calf. Credit: NOAA Fisheries
About the Species
Sei whales occur in subtropical, temperate, and subpolar waters around the world. Often found with pollock in Norway, the name "sei" comes from the Norwegian word for pollock, "seje."
The global sei whale population was greatly decreased by historical commercial whaling during the 19th and 20th centuries. An estimated 300,000 sei whales were killed for their meat and oil.
Member countries of the International Whaling Commission (IWC) agreed to cease sei whale catches in the North Pacific in 1975 and in the Antarctic in 1979. In 1982, the IWC decided to cease commercial whaling on all whale species and populations from the 1985/1986 season onward. Although whaling is no longer a major threat, some whaling of this species continues today in Japan. Vessel strikes and entanglement pose the biggest threat to sei whales today. The sei whale is listed as endangered under the Endangered Species Act and depleted under the Marine Mammal Protection Act.
NOAA Fisheries and our partners are dedicated to conserving and rebuilding the sei whale population. We use a variety of innovative techniques to study, protect, and rescue these endangered whales. We engage our partners as we develop regulations and management plans that foster healthy fisheries and reduce the risk of entanglements, create whale-safe shipping practices, and reduce ocean noise.
Population Status
The sei whale is listed as endangered under the Endangered Species Act. The species is also designated as depleted under the Marine Mammal Protection Act. The total population of sei whales in all U.S. waters is unknown.
The most recent population assessments can be found on the sei whale stock assessment reports.
Protected Status
ESA Endangered
- Throughout Its Range
MMPA Protected
- Throughout Its Range
MMPA Depleted
- Throughout Its Range
CITES Appendix I
- Throughout Its Range
SPAW Annex II
- Throughout the Wider Caribbean Region
Appearance
Sei whales have a long, sleek body that is dark bluish-gray to black in color and white or cream-colored on the underside. The body is often covered in oval-shaped scars (probably caused from cookie-cutter shark and lamprey bites) and sometimes has subtle "mottling," or discolored spots or blotches.
Sei whales have a tall, hooked dorsal fin located about two-thirds down their back. Sei whales have 219 to 410 baleen plates (long plates made out of keratin, the same material as our fingernails, instead of teeth) that are dark in color with gray/white fine inner fringes in their enormous mouths. They also have 30 to 65 relatively short accordion-like creases, or throat grooves, that extend from below the mouth to the naval area. The number of throat grooves and baleen plates may differ depending on geographic population.
At the water's surface, sei whales can be recognized by a columnar or bushy blow that is about 10 to 13 feet high. The dorsal fin usually appears at the same time as the blowhole when the animal surfaces to breathe.
Biology
Sei whales are usually observed alone or in small groups of two to five animals. They are fast swimmers that can reach speeds of over 34 miles per hour.
Sei whales dive differently than most whales. They do not arch their backs or show their flukes before diving; they simply sink below the surface. They often leave “fluke prints”—smooth circles on the surface created by the movement of the fluke underwater.
An average sei whale eats about 2,000 pounds of food per day. They can dive 5 to 20 minutes to 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.
Where They Live
Range
Sei whales have a wide distribution and live in subtropical, temperate, and subpolar waters around the world. They prefer temperate waters in the mid-latitudes, and can be found in the Atlantic, Indian, and Pacific Oceans. During the summer, they are commonly found in the Gulf of Maine, and on Georges Bank and Stellwagen Bank off the U.S. coast in the western North Atlantic. The movement patterns of sei whales are not well known, but they are typically observed in deeper waters far from the coastline. Sei whales have an unpredictable distribution. Many whales may be found in one area for a period and then not return for years or decades. This behavior is unusual for large whales, who generally have a predictable distribution. It is currently unknown where sei whales breed.
Sei Whale Range Map
Scientific Classification
Sei whales have a wide distribution and live in subtropical, temperate, and subpolar waters around the world. They prefer temperate waters in the mid-latitudes, and can be found in the Atlantic, Indian, and Pacific Oceans. During the summer, they are commonly found in the Gulf of Maine, and on Georges Bank and Stellwagen Bank off the U.S. coast in the western North Atlantic. The movement patterns of sei whales are not well known, but they are typically observed in deeper waters far from the coastline. Sei whales have an unpredictable distribution. Many whales may be found in one area for a period and then not return for years or decades. This behavior is unusual for large whales, who generally have a predictable distribution. It is currently unknown where sei whales breed.
| Kingdom | Animalia | Phylum | Chordata | Class | Mammalia | Order | Cetacea | Family | Balaenopteridae | Genus | Balaenoptera | Species | borealis |
|---|
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Science Overview
NOAA Fisheries conducts research activities on the biology, behavior, and ecology of the sei whale. This research informs management decisions and enhances recovery efforts for this endangered species.
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Stock Assessments
Determining the number of sei whales in each population—and whether a stock is increasing or decreasing over time—helps resource managers assess the success of conservation measures. Our scientists collect information and present these data in annual stock assessment reports.
Acoustic Science
NOAA conducts research on the acoustic environment of cetaceans, including sei whales. Acoustics is the science of how sound is transmitted. This research increases our understanding of the basic acoustic behavior of whales, dolphins, and fish; maps the acoustic environment; and develops better methods to locate cetaceans using autonomous gliders and passive acoustic arrays.
Acoustics are used to monitor hearing levels and feeding behavior in sei whales. We also study how underwater noise affects the way sei whales behave, eat, interact with each other, and move within their habitat.