Bowhead Whales



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. Its adaptations to this environment include an insulating layer of blubber up to 1.6 feet thick.

Commercial whaling for bowheads off Alaska began in the mid-1700s, 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 be still threatened by loss of food sources, climate change, vessel strikes, entanglement in fishing gear, ocean noise, offshore oil and gas development, and pollution.

This predominantly Arctic species is associated with ice floes. Its movement patterns are therefore influenced by the melting and freezing of the ice.

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 stock assessment report abundance data for the Western Arctic bowhead stock, collected during spring 2011, indicates there are over 16,000 Western Arctic bowheads.

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.

Protected Status

ESA Endangered

Throughout Its Range

CITES Appendix I

Throughout Its Range

MMPA Protected

Throughout Its Range

MMPA Depleted

Throughout Its Range

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 like 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 can allow for potential 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. They 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, which includes an estimated 10,400 to 23,000 whales. 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, entanglement in fishing gear, climate change, ocean acidification that can affect their prey, and noise pollution that may affect their feeding, navigation, communication, and ability to detect and avoid predators.

Entanglement

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 two percent of 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.

Scientific Classification

KingdomAnimaliaPhylumChordataClassMammaliaOrderCetaceaFamilyBalaenidaeGenusBalaenaSpeciesmysticetus

Source:

https://www.fisheries.noaa.gov/species/bowhead-whale

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CONTACT ME

Virginie Wyss

Biologist and Marine Mammal Observer

Based in Bern

 

Email:

wyss.virginie@gmail.com 

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