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.
Commercial whaling ended for this species in 1980. Although whaling is no longer a major threat to this species, some scientific whaling continues today in Iceland and 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.
Today, there are around 8,600 sei whales in the North Pacific. This is only little more than 20 percent of the original population estimate of 42,000 for this area.
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.
- Throughout Its Range
CITES Appendix I
- Throughout Its Range
SPAW Annex II
- Throughout the Wider Caribbean Region
- Throughout Its Range
- Throughout Its Range
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 30-65 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 sighted by a 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.
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 burse their calves for 6 to 9 months before weaning them when 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 gear including 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.
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.
In the Spotlight
The sei whale is listed as endangered under the Endangered Species Act [link to: ESA subpage]. 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 Marine Mammal Protection Act.
Recovery Planning and Implementation
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.
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.
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.
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.
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.
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
Incidental Take Authorization: Atlantic Shores Offshore Wind, LLC Marine Site Characterization Surveys off of New Jersey and New York
Incidental Take Authorization: Vineyard Wind LLC Marine Site Characterization Surveys off of Massachusetts, Rhode Island, Connecticut, and New York
- Issued IHA (pdf, 13 pages)
- IHA Application (pdf, 92 pages)
- Public Comments (pdf, 41 pages)
- References (pdf, 13 pages)
Incidental Take Authorization: THwaites Offshore Research (THOR) Project in the Amundsen Sea, Antartica
- Issued IHA (pdf, 11 pages)
- Draft IHA (pdf, 11 pages)
- Application (pdf, 101 pages)
- Biological Opinion (pdf, 205 pages)
- References (pdf, 16 pages)
Incidental Take Authorization: Scripps Institute of Oceanography Low-Energy Geophysical Survey in the South Atlantic Ocean
- Issued IHA (pdf, 16 pages)
- IHA Application (pdf, 114 pages)
- References (pdf, 42 pages)
- Biological Opinion (pdf, 188 pages)
- Draft IHA (pdf, 15 pages)
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.
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.
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.
This report provides a summary of large whale entanglements that occurred in U.S. waters in 2017…
Biological Opinion on the Replacement of the Unalaska Marine Center Dock Positions III and IV and associated Proposed Issuance of an Incidental Harassment Authorization in Dutch Harbor, Unalaska, Alaska
Biological opinion considers the effects to ESA-listed species from the proposed replacement of the…
Biological Opinion on the Issuance of Scientific Research Permit No. 18059 for Research on Fin and Sei Whales
Biological opinion on the effects of this permit and the continued, long-term research of whales in…
Data & Maps
Tracks the implementation of recovery actions from Endangered Species Act (ESA) recovery plans.