Species Directory
Sei Whale
Overview Conservation & Management Science Resources
Balaenoptera borealis
Protected Status
ESA Endangered
Throughout Its Range
CITES Appendix I
SPAW Annex II
Throughout the Wider Caribbean Region
MMPA Protected
MMPA Depleted
Up to 100,000 pounds
Vessel strikes, Entanglement in fishing gear, Ocean Noise
Alaska, New England/Mid-Atlantic, Pacific Islands, Southeast, West Coast
See Regulatory Actions
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 sei whale population has been greatly decreased by commercial whaling. During the 19th and 20th centuries, sei whales were targeted and greatly depleted by commercial hunting and whaling, with an estimated 300,000 animals killed for their meat and oil.
Member countries of the International Whaling Commission agreed to cease sei whale catches in the North Pacific in 1975 and the Antarctic in 1979. In 1982, the IWC decided to cease commercial whaling on all whale species and populations from the 1985/1986 season onwards. 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.
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.
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, finger-nail like plates 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.
Behavior and Diet
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
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. No one knows where sei whales breed.
Lifespan & Reproduction
Sei whales become sexually mature at 6 to 12 years of age when they reach about 45 feet in length. They generally mate and give birth during the winter in lower latitudes.
Females breed every 2 to 3 years, with a gestation period of 11 to 13 months. Calves are about 15 feet long and weigh about 1,500 pounds at birth. Mothers nurse their calves for 6 to 9 months before weaning them at their preferred feeding grounds.
Inadvertent vessel strikes can injure or kill sei whales. The projected increase in ship traffic arising from the opening of trans-polar shipping routes (as arctic sea ice melts) will increase the risk of vessel strikes as well as ambient noise and pollution.
One of the main threats to sei whales is getting caught in fishing gear. They can become entangled in gear such as traps, pots, and gillnets. Once entangled, whales may swim for long distances with gear attached, resulting in fatigue, compromised feeding ability, or severe injury. These conditions can lead to reduced reproductive success and death.
Learn more about entanglement
Ocean Noise
Underwater noise threatens whale populations, interrupting their normal behavior and driving them away from areas important to their survival. Increasing evidence suggests that exposure to intense underwater sound in some settings may cause some whales to strand and ultimately die.
Balaenopteridae
Balaenoptera
Conservation & Management
NOAA Fisheries is committed to the protection and recovery of sei whales, and takes targeted management actions to protect these whales:
Minimizing the effects of noise disturbance.
Responding to stranded sei whales.
Developing oil spill response plans.
Reviewing projects that could harm sei whales.
Educating the public about sei whales and the threats they face.
Monitoring population abundance and distribution.
Learn more about our conservation efforts
Our research projects have discovered new aspects of sei whale biology, behavior, and ecology, and helped us better understand the challenges that all sei whales face. This research is especially important in rebuilding endangered populations. Our work includes the following:
Stock assessments.
Measuring sei whales response to sound.
Learn more about our research
Be responsible when viewing marine life in the wild. Observe all large whales from a safe distance of at least 100 yards and limit your time spent observing to 30 minutes or less.
Learn more about our marine life viewing guidelines >
Report Marine Life in Distress
Report a sick, injured, entangled, stranded, or dead animal to make sure professional responders and scientists know about it and can take appropriate action. Numerous organizations around the country are trained and ready to respond. Never approach or try to save an injured or entangled animal yourself—it can be dangerous to both the animal and you.
Learn who you should contact when you encounter a stranded or injured marine animal >
Call the NOAA Fisheries Enforcement Hotline at (800) 853-1964 to report a federal marine resource violation. This hotline is available 24 hours a day, 7 days a week for anyone in the United States.
You may also contact your closest NOAA Office of Law Enforcement field during regular business hours.
Celebrate Whale Week with Wallpapers for Your Digital Devices
North Atlantic Right Whale
North Pacific Right Whale
The sei whale is listed as endangered under the Endangered Species Act. It was originally listed as endangered under the Endangered Species Conservation Act, the precursor to the ESA, in June of 1970. The species is also designated as depleted under the Marine Mammal Protection Act.
Recovery Planning and Implementation
Recovery Action
Recovery Action Under the ESA, NOAA Fisheries develops and implements recovery plans for the conservation and survival of listed species. The Recovery Plan for the Sei Whale was published in December 2011. The plan aims to recover the species, with an interim goal of down-listing the sei whale status from "endangered" to "threatened."
The major actions recommended in the plan are:
Reduce or eliminate injury or mortality caused by ship collision.
Reduce or eliminate injury and mortality caused by fisheries and fishing gear.
Protect habitats essential to the survival and recovery of sei whales.
Minimize effects of vessel disturbance.
Continue international ban on hunting and other directed take.
Monitor the population size and trends in abundance.
Maximize efforts to free entangled or stranded sei whales.
Acquire scientific information from dead specimens.
Learn more about the recovery plan for sei whales
A sei whale seen feeding during a NOAA survey in 2014. Photo: NOAA Northeast Fisheries Science Center/Christin Khan.
NOAA Fisheries is working to minimize effects from human activities that are detrimental to the recovery of sei whale populations in the United States and internationally. Together with our partners, we support the goals of the sei whale recovery plan, with the ultimate goal of delisting the species.
Reducing Vessel Strikes
Collisions between whales and large vessels can injure or kill the whales and damage the vessels, but strikes often go unnoticed and unreported. The most effective way to reduce collision risk is to keep whales and vessels away from one another. If this is not possible, second best is for vessels to slow down and keep a lookout.
Learn more about reducing vessel strikes
Addressing Ocean Noise
Underwater noise may threaten sei whales by interrupting their normal behavior and driving them away from areas important to their survival. Mounting evidence suggests that exposure to intense underwater sound may cause some whales to strand and ultimately die. NOAA Fisheries is investigating acoustic communication and hearing in marine animals, as well as the effects of sound on whale behavior and hearing. In 2016, we issued technical guidance for assessing the effects of anthropogenic sound on marine mammals' hearing.
Learn more about ocean noise
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings. When stranded animals are found alive, NOAA Fisheries and its partners assess the animal's health and try to return it to the water. When stranded animals are found dead, our scientists work to understand and investigate the cause of death. Although the cause often remains unknown, scientists can sometimes identify strandings due to disease, harmful algal blooms, vessel strikes, fishing gear entanglements, pollution exposure, and underwater noise. Some strandings can serve as indicators of ocean health, giving insight into larger environmental issues that can have implications for human health and welfare.
Learn more about the Marine Mammal Health and Stranding Response Program
Marine Mammal Unusual Mortality Events
Under the Marine Mammal Protection Act, an unusual mortality event (UME) is defined as "a stranding that is unexpected; involves a significant die-off of any marine mammal population; and demands immediate response." To understand the health of marine mammal populations, scientists study unusual mortality events.
Get information on active and past UMEs
Get an overview of marine mammal UMEs
Regulatory History
The sei whale has been listed as endangered under the ESA since 1970. It was originally listed as endangered under the Endangered Species Conservation Act, the precursor to the ESA, in June 1970. The species is also designated as depleted under the MMPA.
In 1980, the International Whaling Commission, a group composed of countries from all over the world, made commercial whaling of sei whales illegal in all the world's oceans except for the North Atlantic Ocean.
In December 2011, NOAA Fisheries published a final recovery plan for the sei whale.
Key Actions and Documents
Actions & Documents Incidental Take
Initiation of 5-Year Reviews for the Endangered Fin Whale, Endangered Gray Whale Western North Pacific Distinct Population Segment, and Endangered Sei
NOAA Fisheries announces its intent to conduct 5-year reviews for the endangered fin whale (Balaenoptera physalus), the endangered gray whale (Eschrichtius robustus) Western North Pacific distinct population segment (DPS), and the endangered sei whale …
Notice of Initiation of 5-Year Review/Request for Information
Fin Whale 5-year Review (2019)
Sei whale 5-year Review (2012)
Five Year Review for the Sei Whale
NOAA Fisheries announces a 5-year review of sei whales (Balaenoptera borealis) under the Endangered Species Act of 1973, as amended (ESA). A 5-year review is based on the best scientific and commercial data available at the time of the review; therefore…
Notice of Initiation of 5-Year Review
Sei Whale Five Year Review (06/2012)
Sei Whale Recovery Plan
NOAA Fisheries announces the availability of the final Recovery Plan for the sei whale (Balaenoptera borealis).
Notice of Availability of Draft Recovery Plan
Sei Whale Final Recovery Plan (12/2011)
Incidental Take Authorization: Ørsted Wind Power North America, LLC Site Characterization Survey off New York to Massachusetts
NOAA Fisheries has issued an incidental harassment authorization (IHA) to Ørsted Wind Power North America, LLC, (Ørsted) to incidentally harass, by Level B harassment only, marine mammals during marine site characterization surveys in coastal waters…
Correction to Notice of Issued IHA
Issued IHA, (pdf, 13 pages)
Application (pdf, 89 pages)
Biological Opinion (pdf, 256 pages)
Amendment to Biological Opinion (pdf, 19 pages)
Public Comment (23 pages)
References (pdf, 13 pages)
Incidental Take Authorization: Lamont-Doherty Earth Observatory Marine Geophysical Survey in the Aleutian Islands
NOAA Fisheries has issued an incidental harassment authorization (IHA) to the Lamont-Doherty Earth Observatory of Columbia University (L-DEO) to incidentally harass marine mammals during a marine geophysical survey in the Aleutian Islands, Alaska. …
Issued IHA (pdf, 18 pages)
Application (pdf, 126 pages)
Final Environmental Assessment
Finding of No Significant Impact (pdf, 14 pages)
Public Comments (external link)
References (pdf, 6 pages)
Incidental Take Authorization: Equinor Wind, LLC Marine Site Characterization Surveys off of Massachusetts, Rhode Island, Connecticut, New York and
NOAA Fisheries has issued an incidental harassment authorization (IHA) to Equinor Wind, LLC to incidentally harass, by Level B harassment only, marine mammals during site characterization surveys off the coast in the Atlantic Ocean in the area of the…
Public Comments (pdf, 31 pages)
Incidental Take Authorization: Mayflower Wind Energy, LLC Marine Site Characterization Surveys off of Massachusetts
NOAA Fisheries has issued an incidental harassment authorization to Mayflower Wind Energy LLC to incidentally harass, by Level B harassment only, marine mammals during site characterization surveys off the coast of Massachusetts in the area of the…
Alaska Marine Mammal Stranding Network
Marine Mammal Permits and Authorizations
International Marine Mammal Conservation
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.
A feeding sei whale. Photo: NOAA Northeast Fisheries Science Center/Allison Henry.
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.
Learn more about acoustic science
Recovery Action Database
Tracks the implementation of recovery actions from Endangered Species Act…
February 10, 2020 - Database ,
NOAA's Alaska Fisheries Science Center Marine Mammal Laboratory
Scientific Research Permitting
Draft Biological Opinion on 10 Fishery Management Plans
This draft Biological Opinion on 10 Fishery Management Plans in the Greater Atlantic Region and the…
Biological Opinion Alaska Liquefied Natural Gas (LNG) Project
Endangered Species Act (ESA) Section 7(a)(2) Biological Opinion Alaska Liquefied Natural Gas (LNG)…
National Report on Large Whale Entanglements (2017)
This report provides a summary of large whale entanglements that occurred in U.S. waters in 2017…
Letter of Concurrence on the Issuance of Permit No. 20294 to Robert DiGiovanni Jr. for Vessel and Aerial Surveys of Blue, Fin, North Atlantic Right, Sei, and Sperm Whales
Data & Maps
Tracks the implementation of recovery actions from Endangered Species Act (ESA) recovery plans.
Other Southeast Gillnet Waters
Alaska Endangered Species and Critical Habitat Mapper Web Application
Spacial data and maps of critical habitat and Endangered Species Act (ESA) threatened and…
More Data and Maps
Passive Acoustics Research Group News & Media
Our Passive Acoustics Research Group frequently makes the news. This page links to articles and other media featuring our staff and their research.
Acoustic Studies Sound Board of Marine Mammals in Alaska
This resource features passive acoustic sound clips of many amazing marine mammals that can be…
More Outreach and Education Materials