Bowhead whale

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Bowhead Whale. Dave Rugh, Alaska Fisheries Science Center, NOAA Fisheries Service

The Bowhead whale (scientific name: Balaena mysticetus) is one of four species of marine mammal in the family Balaenidae, part of the order of cetaceans. The Bowhead whale is the second largest whale in the world, second only to the blue whale. Bowheads live in icy Arctic seas. To insulate against the cold Arctic waters, bowhead blubber may be 70 centimetres thick and the whales can break through ice of a foot deep to make breathing holes. They were hunted to the brink of extinction during the 1800s, and have been slow to recover. There are likely 20,000 to 40,000 bowheads alive today, living in four or five populations. Amazingly, this whale is known to live to over 100 years of age, a fact established by the discovery of stone harpoon heads (out of use since the late 1800s) in the flesh of specimens. If this high longevity is correct, the Bowhead whale may be the longest living mammal.

Bowhead-whale.jpg Bowhead Whales (Balaena mysticetus). Source: David Rugh, National Marine Mammal Lab, NMFS, NOAA

752px-bowhead whale size.jpg.png Size comparison of an average human and a Bowhead whale (Balaena mysticetus). Source: Chris Huh

Conservation Status

-IUCN Conservation Status - Least Concern.png.jpeg

Scientific Classification

Kingdom: Animalia
Phylum:--- Chordata
Class:------ Mammalia
Order:-------- Cetacea
Family:-------- Balaenidae
Genus:--------- Balaena
Species:--------Balaena mysticetus (Linnaeus, 1758)

Common Names:
Arctic right whale
Arctic whale
Common whale
Great polar whale
Greenland white whale
Polar whale
Whalebone whale
Bowhead
Bowhead whale

A smooth back with no dorsal fin, a blowhole placed in a high crown at the top of the head, and a thick layer of blubber for insulation equip them for this icy environment.

Bowheads skim-feed tiny crustaceans. A whale draws a huge amount of water into its mouth, then raises its tongue, which forces the water back out through baleen filters. The tongue then sweeps the trapped food back toward the throat. The diet consists of planktonic crustaceans, which are filtered through the baleen plates. Bowhead whales often skim-feed on the surface of the sea but also gather food from the sea floor.

Bowheads are social animals, and communicate through long-distance vocalizations, some carrying five to ten kilometres. Males become involved in showy bouts of breaching and fluke-slapping, probably because they are competing with one another for access to females.

Bowheads are slow breeders, and sexual maturity may not be reached for 20 years. A single calf is born every three or four years after a gestation period of about 13 months.

Other members of the family Balaenidae are:

Physical Description

Balaena mysticetus is the second largest whale in the world, second only to theBlue 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 to 450 centimetres 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 overall body size, less than 200 centimetres in length (Nowak 1999).

Bowhead whale females measure between 16 and 18 metres (m) in length when fully mature, males measure between 14 and 17 m in length. Bowhead whales achieve a body mass from 75,000 to 100,000 kilograms.

Behaviour

Key identifying behaviours include:

  • Slow Swimming velocity
  • Capability of breaking through 60 centimetres of ice
  • Usually single or in small groups, sometimes in aggregations during feeding

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).

Voice and Sound Production

Males attract female Balaena 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.

Reproduction

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 takesup to twenty years for a Bowhead whale calf to reach sexual maturity. At that time, they can achieve a length between 12.3 and 14.2 metres. (Shelden and Rugh 1995) Females usually reach sexual maturity before males and are also one to two metres longer than males at this point of sexual maturity. (George et al. 1999) In some cases pseudo-hermaphroditism can occur, leaving a whale to appear female, but also having male sex organs (Shelden and Rugh 1995).

Typical calving intervals are every three to four years for the female Bowhead whale. 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 separation 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 forward group. Perhaps this behaviour allows them to be the first to feed on prey 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).

Lifespan/Longevity

Length at birth ranges from 3.0 to 4.5 metres; Sexual maturity arrives between 12 and 20 years of age; the female typically gives birth every three to seven years; Longevity can extend over 200 years

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 Balaena mysticetus that would effect the average lifespan (Stover 2001). (George et al., 1999; Stover, 2001)

Distribution and Movements

Distribution of Bowhead Whale.png.jpeg

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 Davis Strait stock;
  • The Hudson Bay stock;
  • The Okhotsk stock which inhabits the Okhotsk Sea;
  • The Bering Sea stock;
  • The Spitsbergen stock which inhabits the North Atlantic.

Bowhead whales inhabit the Arctic Ocean and associated seas. They are rarely found below 45 degrees north latitude (Nowak 1999).

Habitat

Balaena mysticetus lives in the colder waters of the northern hemisphere. 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).

Food and Feeding 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 Balaena 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 fundamentally 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, Balaena 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).

Barnacles use Balaena 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)

Economic Importance for Humans

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).

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, Balaena 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).

Threats and Conservation Status

The IUCNRed List reports:

Heavy commercial hunting, beginning in the 1500s, depleted all populations of bowheads. The Bering-Chukchi-Beaufort Seas stock has recovered substantially since the end of commercial whaling in the early 20th century, while recent provisional estimates of the Hudson Bay-Foxe Basin and Baffin Bay-Davis Strait stocks also suggest significant recovery. There is no reliable evidence of recovery of the Svalbard-Barents Sea (Spitsbergen) and Okhotsk Sea stocks.

Limited aboriginal subsistence whaling on the BCB stock (by native peoples of Alaska, and the Russian Federation (Chukotka) is permitted by the IWC on the basis of advice from its Scientific Committee (most recently under its new aboriginal subsistence whaling management procedure). These takes have not impeded the recovery of the stock. Very small takes by aboriginal hunters are allowed in Canadian waters. So far these have been too few to impede recovery of the stocks, but there will be pressure to increase take levels given the recent, higher population estimates in the eastern Canadian Arctic.

There has been concern since the 1970s that disturbance from oil and gas exploration and extraction activities in the Arctic region might affect bowhead whales. There is also evidence of incidental mortality and serious injury caused by entanglement in fishing gear and ship strikes (Philo et al. 1992, 1993; Finley 2000). Environmental threats, such as pollution (Bratton et al. 1993) and disturbance from tourist traffic (Finley 2000), may affect bowhead whales but the impacts have not yet been well characterized or quantified.

During this century, a profound reduction in the extent of sea ice in the Arctic is expected, and possibly a complete disappearance in summer, as mean Arctic temperatures rise faster than the global average (Anonymous 2005). The implications of this for bowhead whales are unclear but warrant monitoring.

Further, while the range-wide abundance is not known with precision, numbers over 10,000 individuals exist, with estimates of:

  • 10,500 (8200–13,500) (in 2001) in the Bering- Chukchi-Beaufort Seas (Zeh and Punt 2005),
  • 3633 (1382-9550) (Koski et al. 2006) in Hudson Bay-Foxe Basin
  • 7300 (3100–16,900) in Baffin Bay-Davis Strait (Cosens et al. 2006).
  • No reliable abundance estimates for small Okhotsk Sea stock
  • No reliable abundance estimates for small Svalbard-Barents Sea (Spitsbergen) stocks.

The main conservation strategy for the Bowhead whale is to reduce or end hunting which allowed hunting limited to native Inuit under the guidance of the International Whaling Commission (IWC).

IUCN Red List: Lower Risk - Conservation Dependent The US Migratory Bird Act provides the Bowhead whale with no special status.

Further Reading

  1. Balaena mysticetus, Linnaeus, 1758, Encyclopedia of Life, Accessed 2-10-2011
  2. Reilly, S.B., Bannister, J.L., Best, P.B., Brown, M., Brownell Jr., R.L., Butterworth, D.S., Clapham, P.J., Cooke, J., Donovan, G.P., Urbán, J. & Zerbini, A.N. 2008. Balaena mysticetus. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. Downloadedon 30May2011
  3. Justice, J. 2002. "Balaena mysticetus" (On-line), Animal Diversity Web. Accessed May 30, 2011 .
  4. WDCS. (2002) Pers. Comm.
  5. CITES (March, 2008)
  6. Convention on Migratory Species (March, 2008)
  7. UNEP-WCMC (March, 2008)[1]
  8. Carwardine, M., Hoyt, E., Fordyce, R.E. and and Gill, P. (1998) Whales and Dolphins. Harper Collins, London.[2]
  9. Banks, R. C., R. W. McDiarmid, A. L. Gardner, and W. C. Starnes. 2003. Checklist of Vertebrates of the United States, the U.S. Territories, and Canada
  10. Banks, R. C., R. W. McDiarmid, and A. L. Gardner. 1987. Checklist of Vertebrates of the United States, the U.S. Territories, and Canada. Resource Publication, no. 166. 79
  11. Bratton, G. R., Spainhour, C. B., Flory, W., Reed, M. and Jayko, K. 1993. Presence and potential effects of contaminants. In: J. J. Burns, J. J. Montague and C. J. Cowles (eds), The Bowhead Whale, pp. 701-744. Society for Marine Mammalogy, Lawrence, KA, USA.
  12. 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.
  13. Cosens, S. E. 2004. Baffin Bay-Davis Strait and Hudson Bay-Foxe Basin Bowheads: Update on Research 2003/04. International Whaling Commission Scientific Committee.
  14. Cosens, S. E., Cleator, H. and Richard, P. 2006. Numbers of bowhead whales (Balaena mysticetus) in the eastern Canadian Acrtic, based on aerial surveys in August 2002, 2003 and 2004. International Whaling Commission Scientific Committee.
  15. Dueck, L. P., Heide-Jorgensen, M. P., Jensen, M. V. and Postma, L. D. 2006. Update on investigations of Bowhead whales (Balaena mysticetus) movements in the eastern Arctic 2003-2005, abse don satellite-linked telemetry. International Whaling Commission Scientific Committee.
  16. Finley, K. J. 1990. Isabella Bay, Baffin Island: an important historical and present-day concentration area for the endangered bowhead whale (Balaena mysticetus) of the eastern Canadian arctic. Arctic 43(2): 137-152. Finley, K. J. 2000. Natural history and conservation of the Greenland whale, or Bowhead whale, in the Northwest Atlantic. Arctic 54: 55-76.
  17. Finley, K. J., Marko, J., Fissel, D. B. and Goodyear, J. D. 1998. The Calanus connection: feeding ecology and habitat of bowhead whales (Balaena mysticetus) within the Baffin marine ecosystem, in relation to climatic oscillations. Symposium on Arctic Seas: Currents of Change.
  18. George, J. C., Bada, J., Zeh, J. E., Scott, L., Brown, S. E., O'hara, T. and Suydam, R. S. 1999. Age and growth estimates of Bowhead whales (Balaena mysticetus) via aspartic acid recemization. Canadian Journal of Zoology 77: 571-580.
  19. George et al. (1999) Age and growth estimates of bowhead whales (Balaena mysticetus) via aspartic acid racemization. Can J Zool, 77:571?580.
  20. 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.
  21. Heide-Jorgensen, M. P., Laidre, K. L., Jensen, M. V., Dueck, L. and Postma, L. D. 2006. Dissolving stock discreteness with satellite tracking: Bowhead whales in Baffin Bay. Marine Mammal Science 22(1): 34-45. Holst, M. and Stirling, I. 1999. Sightings of bowhead whales in the North Water polynya, northern Baffin Island, in May-June 1998. Journal of Cetacean Research and Management 1: 153-156. International Whaling Commission. 2005. Report of the subcommittee on Bowhead, Right and Gray whales. Journal of Cetcaean Research and Management 7: 189-209.
  22. Hershkovitz, Philip. 1966. Catalog of Living Whales. United States National Museum Bulletin 246. viii + 259
  23. IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species.
  24. International Whaling Commission. 2007. Report of the subcommittee on Bowhead, Right and Gray whales. Journal of Cetcaean Research and Management 9.
  25. Koski, W. R., Heide-Jorgensen, M. P. and Laidre, K. L. 2006. Winter abundance of bowhead whales, Balaena mysticetus, in the Hudson Strait, March 1981. Journal of Cetacean Research and Management 8(2): 139-144.
  26. Koski, W. R., Rugh, D. J., Punt, A. E. and Zeh, J. 2004. A new approach to estimating the length-frequency distribution of the Bering-Chukchi-Beaufort bowhead whale population using aerial photogrammetry and a summary of other life-history parameters estimated from photoidentification/photogrammetry data. International Whaling Commission Scientific Committee.
  27. 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.
  28. Lanier, K. 1998. Legends of the Sea. Christian Science Monitor, 90(199): 16.
  29. Linnaeus, C., 1758. Systema Naturae per regna tria naturae, secundum classis, ordines, genera, species cum characteribus, differentiis, synonymis, locis. Tenth Edition. Laurentii Salvii, Stockholm, 1:75, 824 pp.
  30. Lowry, L. F., Sheffield, G. and George, J. C. 2004. Bowhead whale feeding in the Alaskan Beaufort Sea, based on stomach contents analyses. Journal of Cetacean Research and Management 6(3): 215-224.
  31. Macdonald, D. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  32. Mead, James G., and Robert L. Brownell, Jr. / Wilson, Don E., and DeeAnn M. Reeder, eds. 2005. Order Cetacea. Mammal Species of the World: A Taxonomic and Geographic Reference, 3rd ed., vol. 1. 723-743
  33. Moore, S. E. and Reeves, R. R. 1993. Distribution and movement. In: J. J. Burns, J. J. Montague and C. J. Cowles (eds), The Bowhead whale, pp. 313-386. Society for Marine Mammalogy.
  34. Nicklen, P. 2000. Into the Sea With Giants.. International Wildlife, 30(3): 48..
  35. Northwest Atlantic Ocean species (NWARMS)
  36. Nowak, R. 1999. Walker's Mammals of the World, 6th ed. Volume II. Baltimore, MD: The John Hopkins University Press..
  37. One Species at a Time is brought to you by the Encyclopedia of Life, hosted by Ari Daniel Shapiro and produced by Atlantic Public Media.
  38. Perrin, W. (2010). Balaena mysticetus, Linnaeus, 1758. In: Perrin, W.F. World Cetacea Database. Accessed through: Perrin, W.F. World Cetacea Database on 2011-02-05
  39. Philo, L. M., George, J. C. and Albert, T. F. 1992. Rope entanglement of Bowhead whales (Balaena mysticetus). Marine Mammal Science 8: 306-311.
  40. Philo, L. M., Shotts Jr., E. B. and George, J. C. 1993. Morbidity and mortality. In: J. J. Burns, J. J. Montague and C. J. Cowles (eds), The Bowhead Whale, pp. 275-312. Society for Marine Mammalogy.
  41. Raloof, J. 2000. Cetacean Seniors: Whales That Give New Meaning to Longevity. Science News, 158(26/27): 422.
  42. Reeves R. R. and Heide-Jørgensen M. P. 1996. Recent status of Bowhead whales, Balaena mysticetus, in the wintering grounds off West Greenland. Polar Research 15: 115-25.
  43. Rice, Dale W. 1998. Marine Mammals of the World: Systematics and Distribution. Special Publications of the Society for Marine Mammals, no. 4. ix + 231
  44. Ross, W. G. 1993. Commercial whaling in the North Atlantic Sector. In: J. J. Burns, J. J. Montague and C. J. Cowles (eds), The Bowhead Whale, pp. 511-561. Society for Marine Mammalogy.
  45. Rugh, D. J., Miller, G. W., Withrow, D. E. and Koski, W. R. 1992. Calving intervals of bowhead whales established through photographic identifications. Journal of Mammalogy 73: 487-490.
  46. Shelden, K., D. Rugh. 1995. The Bowhead Whale, Balaena mysticetus: Its Historic and Current Status. Marine Fisheries Review, 57 (3/4): 1-20.
  47. Slijper, E.J. (1938). Die Sammlung rezenter Cetacea des Musée Royal d'Histoire Naturelle de Belgique Collection of recent Cetacea of the Musée Royal d'Histoire Naturelle de Belgique. Bull. Mus. royal d'Hist. Nat. Belg./Med. Kon. Natuurhist. Mus. Belg. 14(10): 1-33
  48. Stover, D. 2001. Science and Technology: The Wisest Whale of the Sea. Popular Science, 258(4): 23.
  49. Taylor, B. L., Chivers, S. J., Larese, J. and Perrin, W. F. 2007. Generation length and percent mature estimates for IUCN assessments of Cetaceans. Southwest Fisheries Science Center.
  50. UNESCO-IOC Register of Marine Organisms
  51. van der Land, J. (2001). Tetrapoda, in: Costello, M.J. et al. (Ed.) (2001). European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: pp. 375-376
  52. Wilson, Don E., and DeeAnn M. Reeder, eds. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed., 3rd printing. xviii + 1207
  53. Wilson, Don E., and F. Russell Cole. 2000. Common Names of Mammals of the World. xiv + 204
  54. Wilson, Don E., and Sue Ruff, eds. 1999. The Smithsonian Book of North American Mammals. xxv + 750
  55. Woodby, D. A. and Botkin, D. B. 1993. Stock sizes prior to commercial whaling. In: J. J. Burns, J. J. Montague and C. J. Cowles (eds), The Bowhead Whale, pp. 387-407. Society for Marine Mammalogy.
  56. Zeh, J. E. and Punt, A. E. 2005. Updated 1978-2001 abundance estimates and their correlations for the Bering-Chukchi-Beaufort seas stock of Bowhead whales. Journal of Cetacean Research and Management 7(2): 169-175.

Citation

Encyclopedia of Life (2011). Bowhead whale. ed. C. Michael Hogan. Encyclopedia of Earth. National Council for Science and Environment. Washington DC Retrieved from http://editors.eol.org/eoearth/wiki/Bowhead_whale
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