Bowhead whale
The bowhead whale, 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
named this species in the tenth edition of his Systema Naturae. 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 and B. mysticetus – 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 maximum weight. The fluke of this species measures long and the 230 to 360 baleen plates The smallest baleen plates specimen was, the largest baleen plates specimen size was, but it is estimated to grow up to, which is longer than that of any other whale by more than a meter. The tongue is long and wide. 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. The length of the baleen plates of this individual was measured to be. The maximum reliable length of the female is currently believed to be about, while the maximum length of the male is thought to be. The longest whale measured in photographs was.
Analysis of hundreds of DNA samples from living whales and from baleen used in vessels, toys, and housing material has shown that Arctic bowhead whales have lost a significant portion of their genetic diversity in the past 500 years. Bowheads originally crossed ice-covered inlets and straits to exchange genes between Atlantic and Pacific populations. This conclusion was derived from analyzing maternal lineage using mitochondrial DNA. Whaling and climatic cooling during the Little Ice Age, from the 16th century to the 19th, is supposed to have reduced the whales' summer habitats, which explains the loss of genetic diversity.
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. During physical exertion, the whale must cool itself to prevent hyperthermia. 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.
Beluga whales often accompany bowhead whales, for curiosity and to secure polynya feasibility to breathe as bowheads are capable of breaking through ice from underwater by headbutting. Bowhead whales have been shown to be able to break through ice less than thick, and can break through ice up to thick. Bowhead whales use rocks to scrub away dead skin cells from their bodies. Bowhead may interact with other cetacean species, such as right whales and fin whales. A specimen believed to be a hybrid between a bowhead whale and a right whale has also been found.