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Balaena mysticetusbowhead

By James Justice

Geographic Range

Bowhead whales (Balaena mysticetus) once inhabited oceans throughout the northern hemisphere. Over the last hundred years the population of bowhead whales has been greatly reduced into five geographically secluded stocks. These stocks are: the Spitsbergen stock, which inhabit the north Atlantic; the Davis Strait and Hudson Bay stocks, which both inhabit the west-northern Atlantic; the Okhotsk stock, which are found in the Okhotsk Sea; and Bering Sea stock, found in the area of the Bering Sea (Shelden and Rugh 1995). Bowhead whales inhabit the Arctic Ocean and associated seas. They are rarely found below 45 degrees north latitude (Nowak 1999). (Nowak, 1999; Shelden and Rugh, 1995)

Habitat

Balaena mysticetus lives in the colder waters of the northern hemisphere. Of the current total population, approximately 700 are found in the north Atlantic while 7,000 are located in the north Pacific. Balaena mysticetus usually follow the receding ice drifts (Shelden and Rugh 1995). During summer they can be found in bays, straits, and estuaries (Nowak 1999). (Nowak, 1999; Shelden and Rugh, 1995)

  • Average depth
    100 m
    328.08 ft

Physical Description

Balaena mysticetus is the second largest whale in the world, second only to the blue whale (Balaenoptera musculus) . The name "bowhead" comes from their bow-shaped mouth. The lower jaw makes a U-shape around the upper jaw. This lower jaw is usually marked with white spots, contrasting with the rest of the whale's black body (Nowak 1999). Baleen in the bowhead whale's mouth is the largest of any cetacean with 300 baleen plates measuring 300-450 centimeters in vertical length. The skull makes up almost one-third of the total body length, is curved and asymetric (Lanier 1998). Bowhead whales, on average, are sixty feet in length and weigh around 100 tons. Contributing to the whale's mass is a two foot thick layer of insulating blubber (Nicklen 2000). Balaena mysticetus also has a small pectoral fin for its size, less than 200 centimeters in length (Nowak 1999). Bowhead whale females measure between 16 and 18 meters in length, males measure between 14 and 17 meters in length. Bowhead whales weigh from 75,000 to 100,000 kg. (Lanier, 1998; Nicklen, 2000; Nowak, 1999)

  • Sexual Dimorphism
  • female larger
  • Range mass
    75000 to 100000 kg
    165198.24 to 220264.32 lb
  • Range length
    14 to 18 m
    45.93 to 59.06 ft

Reproduction

Males attract female B. mysticetus through songs. It is unknown how long these pair bonds last or how many matings male bowhead whales take part in during mating season.

Mating in Balaena mysticetus usually occurs during late winter and early spring. Spring migration takes place soon after this and the female gives birth between April and June, with most births occurring in May. It takes twenty years for a Bowhead whale calf to reach sexual maturity. At this time, they can be between 12.3 and 14.2 m in length (Shelden and Rugh 1995). Females usually reach sexual maturity before males and are also 1 to 2 meters larger than males at this time (George et al. 1999). In some cases pseudohermaphroditism can occur, leaving a whale to appear female, but also having male sex organs (Shelden and Rugh 1995). (George, et al., 1999; Shelden and Rugh, 1995)

  • Breeding interval
    Typical calving intervals are every 3 to 4 years in bowhead whales.
  • Breeding season
    Breeding occurs in late winter to early spring.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    12 to 16 months
  • Average gestation period
    13-14 months
  • Range weaning age
    9 to 15 months
  • Average age at sexual or reproductive maturity (female)
    20 years
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    9125 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    20 years
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    9125 days
    AnAge

When a calf is born, its average length is 4.25 to 5.25 m. Calves grow approximately 1.5 cm a day. The calf is fed with its mother's milk until it is weaned, which occurs between nine and fifteen months after birth. After weaning, growth rate decreases. After births occur, whales segregate into groups in order to migrate. Calves and mothers are in the front group. Perhaps this is to allow them to be the first to feed on food aggregations that are encountered. For the most part it seems that females take care of the young, although there have been some cases of Balaena mysticetus travelling in groups of three: a mature male, a mature female, and a calf (Shelden and Rugh 1995). (Shelden and Rugh, 1995)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • protecting
      • female

Lifespan/Longevity

Balaena mysticetus has a remarkable lifespan. The average age of animals captured during whaling is estimated at 60 to 70 years old, based on examination of changes in the nucleus of the eye over time. However, several individuals have been discovered with ancient ivory and stone harpoon heads in their flesh and examination of their eye nucleus has resulted in estimated lifespans up to 200 years (George et al. 1999), making bowhead whales the longest lived mammalian species. There is little knowlege of diseases in B. mysticetus that would effect the average lifespan (Stover 2001). (George, et al., 1999; Stover, 2001)

  • Range lifespan
    Status: wild
    200 (high) years
  • Typical lifespan
    Status: wild
    0.01 to 0.02 years

Behavior

When migrating, bowhead whales divide into three smaller groups in which to migrate during the spring and fall. The groups they segregate into are: subadults, intermediate mature whales, and large adults. Each of the five stocks show distinct migration patterns dependent on the supply of food and the extension or recession of the polar ice cap (Shelden and Rugh 1995). (Shelden and Rugh, 1995)

Communication and Perception

Food Habits

Balaena mysticetus is a baleen whale, which means that they filter water through baleen plates, feeding on the organisms caught in the plates and pushing the rest of the water out. Balaena mysticetus can sometimes feed opportunistically during the spring migration, but mostly feed during the winter months on their feeding grounds. They eat crustacean zooplankton, epibenthic organisms, and some benthic organisms. Crustacean zooplankton, such as copepods, are not important food sources for young B. mysticetus, but increase in importance with age (Shelden and Rugh 1995). Copepods are small crustaceans, which a bowhead whale can filter at approximately 50,000 per minute (Stover 2001). Balaena mysticetus sometimes form groups of up to fourteen individuals, in which they make a V-shape formation. In this formation they travel at the same speed and filter feed together (Nowak 1999).

Foods commonly eaten include: euphausiids, copepods, mysids, gammarid amphipods, other benthic organisms (Nowak, 1999; Shelden and Rugh, 1995; Stover, 2001)

Predation

Bowhead whales are protected from predators by their large size. They are also known to take shelter under ice drifts. As the oceanic waters of the polar regions become frozen, bowhead whales will swim beneath the extending polar ice cap. In order to survive under the ice cap, B. mysticetus can break through the ice in order to breathe without making themselves accessible to other marine predators (Stover 2001). In a study in 1995, it was found that one-third of the animals of the Davis Strait stock showed scars from killer whale attacks (Shelden and Rugh 1995). (Shelden and Rugh, 1995; Stover, 2001)

Ecosystem Roles

Barnacles use B. mysticetus as both a mode of transportation and a way to encounter fresh food supplies (Lanier 1998). Bowhead whales play an important role as predators of plankton in the arctic ocean. (Lanier, 1998)

Commensal/Parasitic Species
  • barnacle species

Economic Importance for Humans: Positive

Balaena mysticetus is a benefit to the whaling industry. Because of their large size, one whale can bring a large bounty of whale meat, massive baleen, and the blubber for which it is primarily hunted. In fact, B. mysticetus is the most economically valuable of all cetaceans (Nowak 1999). Many native people such as Eskimos also depend on these resources for the survival of their communities economically by using baleen for tools, blubber for fuel, and whale meat for food and trade (Nicklen 1995). (Nicklen, 2000; Nowak, 1999)

  • Positive Impacts
  • food
  • body parts are source of valuable material
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

The only way in which Balaena mysticetus may interfere with humans is in marine fishing. The large bowhead whale has been known to collide with sailing vessels on rare occassions as well as get caught in nets fishing for other oceanic life (Shelden and Rugh 1995). (Shelden and Rugh, 1995)

Conservation Status

Primary conservation efforts for Balaena mysticetus involve reducing or ending the hunting of this species. Agencies who are playing parts in the conservation of the species are the Alaskan Eskimo Whaling Commission (AEWC) and the National Oceanic and Atmospheric Administration (NOAA) (Shelden and Rugh 1995). Native people have been allowed to take only one whale every two years (Nicklen 2000). Whale populations plummeted as a result of a huge expansion in the whaling industry from the 1600s to the early 1900s (Shelden and Rugh 1995). (Nicklen, 2000; Shelden and Rugh, 1995)

Contributors

James Justice (author), University of Northern Iowa, Jim Demastes (editor), University of Northern Iowa.

Glossary

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

filter-feeding

a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

planktivore

an animal that mainly eats plankton

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Clark, C., W. Ellison. 2000. BIOACOUSTICS (80)- Calibration and Comparison of the Acoustic Location Methods Used During the Spring Migration of the Bowhead Whale, Balaena mysticetus, off Pt. Barrow, Alaska, 1984-1993. The Journal of the Acoustical Society of America, 107(6): 3509.

George, J., J. Bada, J. Zeh, L. Scott, S. Brown. 1999. Age and Growth Estimates of Bowhead Whales (*Balaena mysticetus*) Via Aspartic Acid Racemization. Canadian Journal of Zoology 77: 571-580.

Krutzikowsky, G., B. Mate. 2000. Dive and Surfacing Characteristics of Bowhead Whales (*Balaena mysticetus*) in the Beaufort and Chukchi Seas. Canadian Journal of Zoology 78: 1182-1198.

Lanier, K. 1998. Legends of the Sea. Christian Science Monitor, 90(199): 16.

Nicklen, P. 2000. Into the Sea With Giants.. International Wildlife, 30(3): 48..

Nowak, R. 1999. Walker's Mammals of the World, 6th ed. Volume II. Baltimore, MD: The John Hopkins University Press..

Raloof, J. 2000. Cetacean Seniors: Whales That Give New Meaning to Longevity. Science News, 158(26/27): 422.

Shelden, K., D. Rugh. 1995. The Bowhead Whale, Balaena mysticetus: Its Historic and Current Status. Marine Fisheries Review, 57 (3/4): 1-20.

Stover, D. 2001. Science and Technology: The Wisest Whale of the Sea. Popular Science, 258(4): 23.

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