Bowhead whale and calf. Credit: NOAA Fisheries
Bowhead whale and calf. Credit: NOAA Fisheries
About the Species
Bowhead whale and calf. Credit: NOAA Fisheries
Bowhead whale and calf. Credit: NOAA Fisheries
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.
Population Status
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.
Appearance
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.
World map providing approximate representation of the bowhead whale's range.
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.
Threats
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
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.
Ocean Noise
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
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.
Predation
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.
Scientific Classification
| Animalia |
Chordata |
Mammalia |
Cetacea |
Balaenidae |
Balaena |
mysticetus |
Last updated by NOAA Fisheries on 11/22/2024
