The bowhead whale (Balaena mysticetus), sometimes known as the Greenland right whale, Arctic whale, and polar whale, is a species of baleen whale belonging to the family Balaenidae and is the only living representative of the genus Balaena. It is the only baleen whale endemic to the Arctic and subarctic waters, and is named after its characteristic massive triangular skull, which it uses to break through Arctic ice.
Bowheads have the largest mouth of any animal, representing almost one-third of the length of the body. They also have the longest baleen plates among whales, with a maximum length of . They may be the longest-lived of all mammals, with the ability to reach an age of more than 200 years.
The bowhead was an early whaling target. Their population was severely reduced before a 1966 moratorium was passed to protect the species. Of the five stocks of bowhead populations, three are listed as endangered, one as vulnerable, and one as lower risk, conservation dependent according to the IUCN Red List. The global population is assessed as of least concern.
Taxonomy
Carl Linnaeus named this species in the tenth edition of his Systema Naturae (1758). It was seemingly identical to its relatives in the North Atlantic, North Pacific, and Southern Oceans, and as such they were all thought to be a single species, collectively known as the "right whale", and given the binomial name Balaena mysticetus.
Today, the bowhead whale occupies a monotypic genus, separate from the right whales, as proposed by the work of John Edward Gray in 1821. For the next 180 years, the family Balaenidae was the subject of great taxonometric debate. Authorities have repeatedly recategorized the three populations of right whale plus the bowhead whale, as one, two, three or four species, either in a single genus or in two separate genera. Eventually, it was recognized that bowheads and right whales were different, but there was still no strong consensus as to whether they shared a single genus or two. As recently as 1998, Dale Rice listed just two species – B. glacialis (the right whales) and B. mysticetus (the bowheads) – in his comprehensive and otherwise authoritative classification.
Studies in the 2000s finally provided clear evidence that the three living right whale species comprise a phylogenetic lineage, distinct from the bowhead, and that the bowhead and the right whales are rightly classified into two separate genera. The right whales were thus confirmed to be in a separate genus, Eubalaena. The relationship is shown in the cladogram below:
The earlier fossil record shows no related cetacean after Morenocetus, found in a South American deposit dating back 23 million years.
An unknown species of right whale, the so-called "Swedenborg whale", which was proposed by Emanuel Swedenborg in the 18th century, was once thought to be a North Atlantic right whale. Based on later DNA analysis, those fossil bones claimed to be from Swedenborg whales were confirmed to be from bowhead whales.
Description
The bowhead whale is among the largest baleen whale species and is distinguished by its round body with an exceptionally curved rostrum, a large head, and long, dark baleen plates. Relative to its size, the bowhead whale has the largest head of any cetacean, measuring nearly 40% of the total body length. Two blowholes are situated atop its head, and help propel a stream of water up to in the air. The lower lips encompasses the baleen racks and resembles a curved circular shape when viewed from the side. It also has wide, trigonal flukes and fairly large, oar-shaped flippers. The skin is mostly black with white patches around the flukes, tail, eyes, and chin. These patches develop throughout life, with the exception of the patch surrounding the chin, which is usually visible in newborn calves, and increases in size at the same rate with the whale's overall growth.
An adult whale usually measures in length and in weight. The fluke of this species measures long and the 230 to 360 baleen plates are thought to grow to long, which is longer than that of any other whale by more than a meter. This species is sexually dimorphic as females usually reach lengths of , while males average . There are, however, some specimens that exceed these sizes. In one instance, a female killed off the waters of Pond Inlet in the 1800s allegedly measured . Some estimates put the total maximum length higher at about .
A 2013 discovery has clarified the function of the bowhead's large palatal retial organ. The bulbous ridge of highly vascularized tissue, the corpus cavernosum maxillaris, extends along the centre of the hard plate, forming two large lobes at the rostral palate. The tissue is histologically similar to that of the corpus cavernosum of the mammalian penis. This organ is thought to provide a mechanism of cooling for the whale (which is normally protected from the cold Arctic waters by or more of fat). During physical exertion, the whale must cool itself to prevent hyperthermia (and ultimately brain damage). This organ becomes engorged with blood, and as the whale opens its mouth cold seawater flows over the organ, thus cooling the blood.
In one study, the brain size of two males that measured in total length, were recorded at , respectively. With a gyrencephalic index of 2.32, the brains of the two males were found to exhibit extreme gyrification. Compared to other cetaceans, their brain had a lower level of gyrification in the cerebral cortex, more vertically-aligned gyri, and a relatively dull temporal pole region.
The bowhead whale's penis can reach up to in length, and its testicles usually weigh less than in adults, but an individual estimated to weigh about had testicles weighing and measuring in length.
Behaviour
Swimming
The bowhead whale typically travels alone or in small pods of up to six. It is able to dive and remain submerged under water for up to an hour. The time spent under water in a single dive is usually limited to 9–18 minutes.Würsig, B. and C. Clark (1993). "Behavior". In Burns et al. The bowhead is not thought to be a deep diver, but can reach a depth down to . It is a slow swimmer, normally travelling around . When fleeing from danger, it can travel at a speed of . During periods of feeding, the average swim speed is increased to .
Feeding
The head of the bowhead whale comprises a large portion of its body length, creating an enormous feeding apparatus. The bowhead whale is a filter feeder, and feeds by swimming forward with its mouth wide open. It has hundreds of overlapping baleen plates consisting of keratin hanging from each side of the upper jaw. The mouth has a large, upturning lip on the lower jaw that helps to reinforce and hold the baleen plates within the mouth. This also prevents buckling or breakage of the plates from the pressure of the water passing through them as the whale advances. To feed, water is filtered through the fine hairs of keratin of the baleen plates, trapping the prey inside near the tongue where it is then swallowed.Bowhead Whale . American Cetacean Society. Retrieved on 16 November 2015. The diet consists of mostly zooplankton, which includes krill, copepods, mysids, amphipods, and many other crustaceans. About of food are consumed each day. While foraging, bowheads are solitary or occur in groups of two to 10 or more.Lowry, L. F. (1993). "Foods and Feeding Ecology". In Burns et al.
Vocalization
Bowhead whales are highly vocal and use low frequency (<1000 Hz) sounds to communicate while travelling, feeding, and socialising. Intense calls for communication and navigation are produced especially during migration season. During breeding season, bowheads make long, complex, variable songs for mating calls. Many tens of distinct songs are sung by a population in a single season. From 2010 through to 2014, near Greenland, 184 distinct songs were recorded from a population of around 300 animals.
Reproduction
Sexual activity occurs between pairs and in boisterous groups of several males and one or two females. Breeding season is observed from March through August; conception is believed to occur primarily in March when song activity is at its highest. Sexual maturity is estimated to be reached at 15–25 years, and physical maturity at 50–60 years. The gestation period is 13–14 months with females producing a calf once every three to four years. There is no evidence of reproductive aging in males, and a case of penile sperm discharge from a male bowhead whale estimated to be 159 years old has been reported. However, there is evidence of possible reproductive aging in female bowhead whales, with females aged 133, 139, and 149 years, respectively, suggesting reproductive cessation or senescence. The oldest female captured with a fetus was estimated to be 121 years old.Koski, William R., Rolph A. Davis, Gary W. Miller, and David E. Withrow (1993). "Reproduction", p. 245 in Burns et al. Lactation typically lasts about a year. Female bowheads may be capable of producing calves for 100 years. To survive in the cold water immediately after birth, calves are born with a thick layer of blubber. Within 30 minutes of birth, bowhead calves are able to swim on their own. A newborn calf is typically long, weighs roughly , and grows to within the first year.
Health
Lifespan
Bowhead whales are considered to be the longest-living mammals, living for over 200 years. In May 2007, a specimen caught off the Alaskan coast was discovered with the head of an explosive bomb lance of a model manufactured between 1879 and 1885 lodged in its body, so the whale was probably bomb lanced sometime between those years, and its age at the time of death was estimated at between 115 and 130 years. Spurred by this discovery, scientists measured the ages of other bowhead whales captured between 1978 and 1996; one male specimen was estimated to be 211 years old. Other bowhead whales were estimated to be between 135 and 172 years old. This discovery showed the longevity of the bowhead whale is much greater than originally thought. Researchers at CSIRO, Australia's national science agency, estimated that bowhead whales' maximum natural lifespan is 268 years based on genetic analysis.
Genetic benefits
A greater number of cells present in an organism was once believed to result in greater chances of mutations that cause age-related diseases and cancer. Although the bowhead whale has thousands of times more cells than other mammals, it has a much higher resistance to cancer and aging. In 2015, scientists from the US and UK were able to successfully map the whale's genome. Through comparative analysis, two alleles that could be responsible for the whale's longevity were identified. These two specific gene mutations linked to the bowhead whale's ability to live longer are the ERCC1 gene and the proliferating cell nuclear antigen (PCNA) gene. ERCC1 is linked to DNA repair and increased cancer resistance. PCNA is also important in DNA repair. These mutations enable bowhead whales to better repair DNA damage, allowing for greater resistance to cancer. The whale's genome may also reveal physiological adaptations such as having low metabolic rates compared to other mammals. Changes in the gene UCP1, a gene involved in thermoregulation, can explain differences in the metabolic rates in cells.
Ecology
Range and habitat The bowhead whale is the only baleen whale to spend its entire life in the Arctic and subarctic waters.Moore, S. E., and R. R. Reeves (1993). "Distribution and Movement". In Burns et al. The Alaskan population spends the winter months in the southwestern Bering Sea. The group migrates northward in the spring, following openings in the ice, into the Chukchi and Beaufort seas. The whale's range varies depending on climate changes and on the forming/melting of ice.