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 Whales (Balaena mysticetus). Source: David Rugh, National Marine Mammal Lab, NMFS, NOAA
|Size comparison of an average human and a Bowhead whale (Balaena mysticetus). Source: Chris Huh|
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:
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 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.
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.
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).
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
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).
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)
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 IUCN Red 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.
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