About the Species
Bowhead whales are one of the few whale species that reside almost exclusively in Arctic and subarctic waters experiencing seasonal sea ice coverage, primarily between 60° and 75° north latitude. Of all large whales, the bowhead is the most adapted to life in icy water. Adaptations to this environment include an insulating layer of blubber that can be up to 1.6 feet thick.
Commercial whaling for bowheads off Alaska began in the early 1800s, and lasted until the early 1900s. The economic value of the bowheads’ oil and baleen, combined with their slow swimming speeds and tendency to float when killed, made them a prime target for whalers. By the time commercial whaling of bowheads effectively ended in 1921, the worldwide bowhead abundance had declined to less than 3,000 whales. Today, bowhead whales may still be threatened by loss of food sources, climate change, vessel strikes, entanglement in fishing gear, ocean noise, offshore oil and gas development, pollution, and predation.
Commercial whaling severely reduced bowhead whale numbers from historical levels. The worldwide number of bowheads prior to commercial exploitation is estimated at a minimum of 50,000, including an estimated 10,400 to 23,000 whales in the Western Arctic stock, the stock found in U.S. waters. Commercial whaling drove global abundance down to less than 3,000 by the 1920s.
The United States listed all bowhead whales as endangered under the Endangered Species Conservation Act in 1970 and the Endangered Species Act in 1973. Bowhead whales are also listed as depleted under the Marine Mammal Protection Act.
Western Arctic bowheads have shown considerable recovery since the end of commercial whaling in the early 1900s, and they now comprise the largest population of bowheads in the world. The most recent abundance estimate for the Western Arctic bowhead stock, collected during spring 2019, indicates there are approximately 12,505 Western Arctic bowheads, with a 95 percent confidence interval ranging from 7,994 to 19,560 whales.
However, the smaller Okhotsk Sea population, more heavily exploited in the past, remains at a dangerously low population of only a few hundred individuals. Genetic research has shown that these two North Pacific populations are distinct, indicating that movement of individuals between the two populations is rare.
Bowhead whales have a dark body with a distinctive white chin and unlike most cetaceans, do not have a dorsal fin. Bowheads have extremely large heads and stocky bodies. The bow-shaped skull can be over 16.5 feet long—about a third of a bowhead’s body length. The bowhead whale also has a 17- to 19-inch thick blubber layer—thicker than that of any other whale.
The bowhead’s large, thick skull allows them to break through 8-inch-thick sea ice. Some Alaska Native whalers have even reported whales surfacing through 2 feet of ice. Bowhead whales often accumulate scars on their bodies from breaking ice, killer whale encounters, entanglement in fishing gear, and propellers. Scientists use these scars to identify individual whales.
Behavior and Diet
Bowhead whales are baleen whales, so they filter their food by straining huge volumes of ocean water through their baleen plates (like the teeth of a comb). Bowhead whales have the longest baleen plates of all whales and feed almost exclusively on marine invertebrates, including small to moderately sized crustaceans, such as shrimp-like euphausiids (i.e., krill) and copepods. They also ingest other invertebrates and small fish. Scientists estimate that a bowhead whale needs to eat about 100 metric tons (over 220,000 pounds) of crustaceans per year.
Sound is critical to the survival of bowhead whales. They rely on keen hearing abilities to detect, recognize, and localize biologically important sounds for navigation, predator avoidance, foraging, and communication in the marine environment. Bowhead whales are highly vocal and have a large variety of calls. The echoes of some of their calls are used to help the whales find food and navigate through the ice as they migrate.
Although direct measurements of hearing ability in baleen whales are lacking, scientists predict, based on anatomy and vocalizations of other closely related whales, that bowheads hear best at low-frequencies. Low-frequency sounds are capable of propagating great distances through the ocean and may allow for communication over long ranges.
Where They Live
Bowhead whales inhabit the Bering, Chukchi, and Beaufort seas, Hudson Bay and Foxe Basin, Baffin Bay and Davis Strait, the Sea of Okhotsk, and in waters from eastern Greenland and Spitsbergen to eastern Siberia. The majority spend the winter near the southern limit of the pack ice and move north as the sea ice breaks up and recedes during spring.
Four stocks of bowhead whales have been recognized worldwide by the International Whaling Commission. Small stocks of only a few hundred individuals occur in the Sea of Okhotsk and the offshore waters of Spitsbergen. Genetic, aerial survey, and tagging data suggests that bowheads from western Greenland (Hudson Bay and Foxe Basin) and eastern Canada (Baffin Bay and Davis Strait) should be considered one stock that may number more than a thousand individuals. The only stock found within U.S. waters is the Western Arctic stock, also known as the Bering-Chukchi-Beaufort stock. Our conservation and management work focuses on this Western Arctic stock.
Lifespan & Reproduction
Historically, age determination in bowhead whales has been difficult, and life history parameters are better known in terms of body length than age. Based on the recovery of stone harpoon tips from harvested bowheads, it is evident that bowhead whales live well over 100 years. However, new techniques allow for more precise estimation of bowhead whale age, and studies suggest they may live to be over 200 years old. Genes that allow for repair of damaged DNA may be responsible for their longevity.
Bowhead whales reach sexual maturity at approximately 25 years of age, when their total body length is about 35 to 45 feet. Mating behavior has been observed year-round, though most conceptions are believed to occur during late winter or spring. Most calves are born between April and early June during spring migration. Females typically have one calf every 3 to 4 years after a gestation period of around 13 to 14 months. Calves are usually about 13 feet long, weigh about 2,000 pounds, and can swim at birth. Mothers and calves form a very close attachment.
Bowhead whale populations are exposed to a variety of human-caused stressors and threats, including:
- Pollution (e.g., spilled oil, heavy metals, chemicals, debris)
- Vessel strikes and disturbance
- Entanglement in fishing gear
- Climate change
- Ocean acidification that can affect their prey
- Noise pollution that may affect their feeding, navigation, communication, and ability to detect and avoid predators
Entanglement in Fishing Gear
About 12 percent of the Western Arctic stock show scars from entanglement in fishing gear, mostly from commercial pot-fishing gear. Entangled whales either swim off with the gear attached or may become anchored in place. Once entangled, whales may drag gear or lines for long distances, ultimately resulting in fatigue, compromised feeding ability, or severe injury, which may lead to reduced reproductive success and/or death. An unknown number of whales die from entanglement, as some entanglements likely go undetected. In cases where a carcass is still entangled or bears entanglement scars, it is not always possible to determine if entanglement was the cause of death.
Contaminants enter ocean waters from municipal wastewater discharges, runoff, accidental spills, atmospheric deposition of airborne contaminants, discharges from commercial operations, such as fishing, shipping, and oil and gas development, and other sources. Many contaminants move up the food chain and accumulate in top predators. Bioaccumulating contaminants are present in bowhead prey and in their environment. Bowheads accumulate these contaminants because of their long lifespan, position at the top of the food chain, and large blubber stores. These pollutants may harm bowheads’ immune and reproductive systems.
Underwater noise may threaten bowhead whales by interrupting their normal behavior and driving them away from areas important to their survival. Noise from seismic exploration for petroleum reserves was found to drive bowheads from waters within about 12 miles of the sound source, although avoidance behavior is likely related to the activity that the bowhead is engaged in at the time of exposure. For instance, feeding whales may be more reluctant to abandon food concentrations due to noise. In addition, evidence suggests that bowheads’ prey, primarily small marine invertebrates, may be negatively affected by noise from seismic exploration.
Vessel strikes can injure or kill bowhead whales. About 2 percent of subsistence-hunted bowheads show signs of scars from vessel strikes. However, as seasonal sea ice continues to retreat due to climate change, vessel traffic in Arctic waters is increasing and could increase the risk of future collisions.
Transient killer whales are known to prey on bowhead whales. Scars consistent with killer whale attacks were found on approximately 8 percent of subsistence hunted whales, and rates have increased each decade. This may be due to better reporting and/or sampling bias, an increase in killer whale population size, an increase in occurrence of killer whales at high latitudes, or a longer open water period offering more opportunities to attack bowhead whales. Bowhead whale carcasses that had injuries consistent with killer whale predation have been observed during aerial surveys since 2009. A recent study indicates that killer whale predation was the primary source of mortality for bowhead carcasses detected during aerial surveys in the region from 2009 to 2018.
In the Spotlight
Recovery Planning and Implementation
An ESA recovery plan has not been prepared for bowhead whales because:
- Only the Western Arctic stock occurs in U.S. waters and, therefore, a U.S. recovery plan for other stocks would not be appropriate
- All stocks are managed under the international authority of the International Whaling Commission (IWC), of which the United States is a member
- Co-management of bowhead whales is accomplished through cooperative agreements between NOAA and the Alaska Eskimo Whaling Commission (AEWC)
NOAA monitors the health of the Western Arctic stock of bowheads and co-manages the bowhead stock with the AEWC. We also seek to minimize the impact of activities that are authorized, funded, or carried out by Federal agencies. Through ESA section 7 consultations we help Federal agencies in fulfilling their duty to ensure that their actions do not jeopardize the continued existence of a species, or destroy or adversely modify designated critical habitat. We do this by collaborating with the action agency to develop project modifications intended to decrease or eliminate the effects of noise, pollution, and other project-related threats on bowheads. Proponents of any activity that will have unavoidable impacts on bowheads must also obtain MMPA incidental take authorization from NOAA Fisheries.
Co-managing Bowhead Subsistence Harvest
The IWC conserves and manages bowhead whale populations worldwide under the International Convention for the Regulation of Whaling (ICRW). In the United States, the Whaling Convention Act is the enabling act for the ICRW. This act allows whaling by aboriginal peoples to the extent it does not conflict with the ICRW.
Bowhead whales have been hunted by indigenous peoples for food and fuel for at least 2,000 years. For many Alaska Native communities, subsistence harvest of bowheads is the most important hunting activity of the year, both in terms of the amount of food obtained and the cultural significance of the hunt itself. The Marine Mammal Protection Act (MMPA) allows NOAA to enter into cooperative agreements with Alaska Native organizations to conserve marine mammals and to co-manage subsistence hunts.
Since 1981, the U.S. Government and the Alaska Eskimo Whaling Commission (AEWC) have co-managed the traditional subsistence harvest of bowhead whales under the terms of a cooperative agreement between NOAA and the AEWC. The purposes of this agreement are to “protect the bowhead whale and the Eskimo culture, to promote scientific investigation of the bowhead whale, and to effectuate the other purposes of the MMPA, the Whaling Convention Act, and the ESA as these acts relate to aboriginal subsistence whaling.” As part of this co-management agreement, the AEWC is responsible for enforcing the legal harvesting of bowhead whales, reporting on all strikes and landings of bowhead whales, and providing data on each whale landed. Only those whaling captains registered with the AEWC, along with their crew, may participate in subsistence harvest of bowhead whales.
The IWC establishes subsistence harvest quotas for the Western Arctic stock of bowhead whales based on an extensively tested strike limit algorithm. This bowhead quota is allocated by the AEWC among 11 Alaska Native communities that traditionally hunt bowhead whales and comprise the AEWC (Gambell, Savoonga, Wales, Little Diomede, Kivalina, Point Hope, Pt. Lay, Wainwright, Utqiaġvik (formerly Barrow), Nuiqsut and Kaktovik). A small portion of the IWC’s bowhead subsistence harvest quota is also allocated to whaling villages in Russia.
The authorization of the bowhead whale subsistence harvest quota includes the following bowhead catch limits, which were approved at the 2018 IWC meeting. From 2019 through 2025, the number of bowhead whales landed shall not exceed 392 total. The number of bowhead whales struck shall not exceed 67 per year, except that any unused portion of a strike quota from the three prior quota blocks shall be carried forward and added to the strike quotas of subsequent years, provided that no more than 50 percent of the annual strike limit shall be added to the strike quota for any one year. For 2020, the quota was 100 bowhead whales with the AEWC allocated 93 whales and the Russian Federation 7 whales. During 2020, 69 whales were struck, 54 of which were landed. Subsistence landings in Alaska have averaged about 45 bowhead whales per year since 2011.
We are working with the AEWC to improve the weapons that qualified subsistence whalers use to hunt bowheads. Penthrite projectiles developed specifically for bowhead whaling are used by many AEWC whaling captains. These projectiles may result in fewer struck and lost whales, and shorten the time between the initial strike and death. We are working with the AEWC to refine these weapons and educate hunters in their use.
Every five years the NOAA Fisheries Alaska Regional Office generates an Environmental Impact Statement for issuing annual catch limits to the Alaska Eskimo Whaling Commission for subsistence hunting bowhead whales.
Addressing Ocean Noise
NOAA Fisheries is investigating all aspects of acoustic communication and hearing in marine animals, as well as the effects of sound on whale behavior and hearing. In 2018, we issued revised technical guidance for assessing the effects of anthropogenic (human-caused) sound on marine mammal hearing.
Overseeing Marine Mammal Health and Stranding Response
We work with volunteer networks in all coastal states to respond to marine mammal strandings including all whales. When stranded animals are found alive, NOAA Fisheries and our partners assess the animal’s health and determine the best course of action. 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 attribute strandings 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 may also have implications for human health and welfare.
Marine Mammal Unusual Mortality Events
Bowhead whales have never been part of a declared unusual mortality event. Under the Marine Mammal Protection Act, an unusual mortality event 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.
Prior to the ESA of 1973, bowhead whales were protected at different times under the 1931 League of Nations Convention, the Endangered Species Preservation Act of 1966, and the Endangered Species Conservation Act (ESCA) of 1969. The ESCA ended commercial whaling in the United States. Bowhead whales are also listed in Appendix 1 of the Convention on International Trade in Endangered Species of 1973 (CITES), which prohibits international trade of the species. Bowhead whales also receive protection under the MMPA of 1972.
The IWC, established in 1946, continued a prohibition on commercial whaling that began with the 1931 League of Nations Convention. In 1964, the IWC began to regulate commercial whaling among nations that signed the International Convention for the Regulation of Whaling. In 1972, the IWC asked the United States to gather data on aboriginal subsistence whaling. The IWC subsequently called for a ban on subsistence bowhead whaling in 1977, based on increasing concerns about the status of bowhead whale populations, documented increases in subsistence whaling in Alaska, and increases in the number of struck whales that were lost at sea and, therefore, unable to be harvested. The United States requested a modification of the ban and the IWC responded with a limited quota.
Key Actions and Documents
NOAA Fisheries conducts various research activities to monitor bowheads and study their biology, behavior, and ecology of the bowhead whale. The results of this research are used to inform management decisions and enhance recovery efforts for this endangered species.
Determining the number of bowhead whales in each population—and whether a stock is increasing or decreasing over time—helps resource managers assess the success of conservation measures and the need for additional measures. Our scientists, along with scientists from other entities, collect stock information that we present in annual stock assessment reports.
Scientists use small aircrafts to observe bowhead whales to record their numbers, behavior, and distribution, and to collect photo-identification data. Surveys typically occur during the spring, summer, and fall months when weather is conducive to visual surveys and the whales are found on the continental shelf (0–200 m depth). By comparing data across years, scientists can look for trends, such as whether the population is increasing, decreasing, or remaining stable during a given time period.
Visual and acoustic surveys conducted by the North Slope Borough from sea ice during the spring bowhead whale migration have historically provided the best estimates of population size. However, climate change-driven reductions in sea ice are making safe conditions for this survey less frequent. Research conducted in 2019 began the process of calibrating aerial surveys to these ice-based surveys to improve the accuracy of aerial survey population estimates.
Acoustic ecology is the study of how animals use, and are influenced by, sounds in their environment. This research involves increasing our understanding of the basic acoustic behavior of marine animals (including bowhead whales, as well as other marine mammals, fishes, and sea turtles), describing their repertoire of signals, studying their hearing sensitivity, and monitoring how exposure to noise affects their communication, distribution, behavior, and hearing. Researchers are also developing better techniques to map the underwater acoustic environment and detect, classify, localize, and track individuals using satellite tags, autonomous gliders and passive acoustic arrays.
Acoustic research suggests that noise from airguns cause bowhead whales in summer in the Beaufort Sea to increase their call rates. These call rates continue to increase as noise increases, up to a noise threshold, after which the whales stop calling altogether. This has implications for communication, which in turn may affect migratory or feeding behavior. Scientific research has documented that human-caused ocean noise can also cause marine mammals to change the frequency or amplitude (loudness) of calls, decrease foraging behavior, leave their preferred habitat, and increase the level of stress hormones in their bodies. If loud enough, noise can cause permanent or temporary hearing loss.
Satellite Tagging and Tracking
The Alaska Department of Fish and Game works with subsistence whalers to attach satellite transmitters to bowheads to study their movements, habitat use, and behavior throughout their range. These transmitters gather valuable data including migration routes and timing, feeding areas, diving behavior, and time spent within the spring and summer ranges. They also study how bowhead whales interact with oil and gas exploration, extraction, and transportation activities. The Alaska Department of Fish and Game is also investigating the use of tags that record oceanographic information to identify ocean features, such as fronts where whales prefer to feed, and are developing an acoustic tag that will record ambient sound and the vocal behavior of the whales to better understand the effects of high noise level activities.
Bowhead Whales in Alaska
Our research on the population dynamics, distribution, abundance, behavior, and movement patterns of bowhead whales provides information crucial for understanding and protecting bowhead whale populations in Alaska.
Recent Science Blogs
Alaska Eskimo Whaling Association Cooperative Agreement Amendments from 2011, 2014. 2015 and 2016.
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ESA Section 7 Biological Opinion on the Issuance of a LOA to Hilcorp Alaska, LLC and Eni U.S…