The Iñuit peoples of the Arctic were probably the first to encounter and describe the bowhead whale as early as 10,000 years ago. The Iñupiat name “Aġviq” is similar, with only minor dialect differences, for the Iñuit people from Chukotka to Greenland. For 1000's of years, bowheads have remained an important nutritional, cultural and spiritual aspect of many Iñuit societies.
The earliest written records are probably the Norwegian sagas circa 1200, in which they describe bowheads as a whale that “feeds on rain and mist” that falls on the ocean surface.
Yankee commercial whalers recognized them as a “right whale” (the ‘right’ whale to catch), but were aware of the differences from other right whales species in their blubber quality and baleen length.
The bowhead whale was classified by Linnaeus in 1758 as Balaena mysticetus. English common names are numerous and include: Greenland right whale, arctic whale, great polar whale, bunchback, and others.
Size, shape and distinctive characteristics
Even among the remarkable cetaceans, bowheads exhibit several extreme traits that set them apart from other whales: they are among the largest, the longest lived (perhaps up to 200 years), have the longest baleen plates, the thickest skin and blubber, and perhaps the latest age of sexual maturity. Current records show they grow to 19 m (60 ft), but reliable records from Yankee whalers in the 1800's indicate animals to 24.5 m (80.5 ft) in length yielding a maximum of 375 barrels (11,812 US gallons) of oil! A bowhead of this size would have a body mass comparable to an adult blue whale.
Bowheads are black-skinned balaenids with robust bodies and a strongly arched rostrum (snout) from which the baleen plates are suspended. Thus the upper jaw looks like a “bow”, which gives them their name ‘bowhead’. They lack a dorsal fin (as is common in whales that live part of their lives below ice) and lack callosities on their heads typical of their right whale cousins. Flukes are stout and broad with a width 1/3 of the body length. Most have a white chin patch and a few have dramatic white areas on their ventrum or bellies much like right whales. The peduncle, flukes and eye region turn increasingly white with age. (The whale in the illustration is characteristic of an older animal.) Scars are white and are numerous on older whales. The head of an adult bowhead can exceed 1/3 of its body length and appears to grow throughout life. Baleen plates number about 320 per side, and the greatest reliable length record is 4.9 meters (16 feet, from Yankee whaling records). Females grow larger than males, like other mysticetes.
Bowheads inhabit the ice-covered Arctic seas and are circumpolar in distribution (see map). They are the only baleen whale that routinely winters within heavy sea ice and rarely, if ever, transit to low-latitude waters.
Ecology and Behaviour
Bowheads are the only baleen whales that live in Arctic waters year-round, spending summers at high latitudes and as the ice closes over the arctic ocean, and winters at only slightly lower latitudes such as the Bering sea. Most bowheads migrate as single animals within larger groups described by Eskimos as ‘schools’, which can number in the thousands. During migration these groups keep in near-constant vocal contact over tens of kilometers. Calves stay closely associated with their mothers for 9-12 months of life.
In the Chukchi and Beaufort Seas they tend to feed in groups ranging from a few to hundreds of animals, especially on their summer/fall feeding grounds. It is likely that bowheads feed in winter based on several lines of evidence including dive records from satellite-tagged animals. Their average dive time is about 10 minutes, but dives over 60 minutes are not uncommon (based on tag data and whaling records). They flex their peduncle when making a sounding dive, with “fluke-up” dives common while feeding, but less common (~10%) during migration. Bowheads swim slowly at about 4 km/h (2.5 mph) but are capable of speed bursts up to ~20 km/h. The blow is a tall column which goes straight up and can been seen over 5 km away under some conditions.
Bowheads have a remarkable vocal repertoire with a variety of complex calls and songs spanning a range of frequencies. Songs average about one minute in length but can range from minutes to hours. Some are “multi-voice” (from one individual) spanning several frequencies simultaneously sounding at times like heavy-metal rock music. Most calls made during migration are simple up-sweeps or moans. Aside from communication, these calls may be used to help assess ice conditions, since bowheads need to navigate between deep-keeled ice floes, heavy sea ice and locate ice-free cracks to breathe.
Bowheads are one of the few cetaceans capable of breaking through sea ice to breathe. Eskimo whalers have observed them break ice ~1 m thick but such events are uncommon. Ice less than 50 cm appears fairly easy for them to break, but they will avoid breaking ice if free water is available. They fracture the ice just enough to take air, making a small hummock.
Bowheads use a polyandrous mating system with one female associated with several males. Sperm competition is thought to be operative as the males show little overt aggression towards each other and testes of large adult males are huge, weighing 150 kg or more each.
Play behavior with a log by a sub-adult bowhead has been observed and aerial displays can be complex and last hours in duration. Aerial displays include spy-hoping, rolling, pectoral fin slaps, fluke slaps, breaching, under-water blowing, and other behaviors.
Conception likely takes place in March, with a gestation period of 13-14 months. Bowhead whales are born in April and May during spring migration in lead systems within the pack ice. Calves weigh about 1,000 kg at birth and are about 4 m in length. They likely nurse only 9 months and rapidly grow to about 8-9 m as yearlings. The Iñupiat term “iŋutuk” means “small fat whale”, which are often yearlings. The iŋutuk's girth is nearly equal to their body length of ~7-8 m.
Females bear a single calf at 3-4 year intervals and nurse less than one year. Age at sexual maturity for females is estimated at ~25 years; males may mature at a slightly younger age.
The estimated survival rate from photo-recaptures of adult whales is very high, which is consistent with age estimates. A technique which measures changes in the ratio of aspartic acid isomers in the eye lens suggests that bowheads can live 150-200 years. Ages estimated with this technique have large associated error but are consistent with other data. Recovery of stone whaling tools in recently harvested whales corroborates these estimates. Stone tools were largely phased out of use by Eskimo hunters in the 1880s but some could have been used later. Archaeologists however suggest that it is more likely that these tools were placed before that date. The recovery of a Yankee whaling projectile with an 1879 patent from a whale harvested in 2007 offers additional evidence of bowhead longevity, as that tool was probably used around its time of manufacture when commercial whaling was underway.
More than 50 species of invertebrates and fish have been identified in the bowhead’s diet. However, krill (euphausiids) and copepods form the bulk of their diet, with small relatives of shrimp and crabs (including amphipods and mysids) also variably important.
Bowheads are primarily water-column feeders but will “trawl feed”, swimming at the surface with their huge mouths open. Many whales show mud on their backs and rostrums suggesting they feed near the sea floor. It is unknown if they can actually filter invertebrate prey from muddy sediments.
Bowheads are distributed into 4 or 5 breeding stocks and probably number about 20,000 animals. The Western Arctic or Bering-Chukchi-Beaufort (BCB) Sea stock, about which most is known, numbered ~12,600 (95% CI=8,000-19,000) in a 2004 survey.
Bowhead whales are currently listed as a species of least concern (www.iucn.redlist.org) but some sub-populations such as the Sea of Okhotsk and Spitsbergen, are listed as endangered.
Bowhead whales have been subject to commercial hunting since the 1500's, and all stocks were severely depleted. The conservation status of the bowhead varies by geographic stock. The Spitsbergen or North Atlantic stock, at one time thought to be the largest numbering 50,000 or more animals, may now only number in the low hundreds. There is some weak evidence that the Spitsbergen bowheads are recovering.
The only stock known to be doing well is the Bering-Chukchi-Beaufort (BCB) Seas stock, which currently numbers about ~12,600 whales, and is increasing at about 3.5% annually. Some population models indicate this stock is nearing a full recovery from commercial whaling nearly 100 years ago.
Recent surveys indicate the “Eastern Arctic” stock numbers around 7,000 animals, whereas only a decade ago was believed to number in the hundreds. New satellite telemetry and genetic data suggest that the two former eastern stocks – Hudson’s Bay and Davis Strait – are actually one breeding group or stock; however this concept has not been formerly adopted. The Sea of Okhotsk stock numbers about 300 animals; its population trend is unknown.
Two stocks of bowhead whales are subject to a subsistence hunt by Iñuit peoples in Russia, USA, Canada and Greenland. Annual harvest numbers are low (2-4/year) for the Eastern Arctic stock but number about 40/year for the BCB bowheads. The subsistence harvest on the BCB stock by Yupik and Iñupiat communities is well-managed through an annual quota with periodic abundance surveys. The annual harvest is singularly important both nutritionally and culturally to Alaskan and Russian Native communities that hunt bowheads. Other anthropogenic mortality, from ship strikes and fishing-gear entanglements for example, are thought to be low.
Threats to the circumpolar population of bowhead whales vary by stock and region. Conservation concerns include: commercial fishing and crabbing, offshore oil and gas exploration and development in the US and Western Canadian arctic through seismic testing and the possibility of oil spills. Climate change and invasive disease are emerging concerns but have so far had little apparent negative effects to bowheads. Commercial shipping across the bowheads’ range is currently seasonal and relatively infrequent but with retreating sea ice this could become one of the biggest threats to bowheads if major shipping lanes are shifted through arctic seas.
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