Des Belugas

[Gualtar Pennington]

The beluga is adapted to life in the Arctic, with anatomical and physiological characteristics that differentiate it from other cetaceans. Amongst these are its all-white colour and the absence of a dorsal fin, which allows it to swim under ice with ease.[5] It possesses a distinctive protuberance at the front of its head which houses an echolocation organ called the melon, which in this species is large and deformable. The beluga's body size is between that of a dolphin and a true whale, with males growing up to 5.5 m (18 ft) long and weighing up to 1,600 kg (3,530 lb). This whale has a stocky body. Like many cetaceans, a large percentage of its weight is blubber (subcutaneous fat). Its sense of hearing is highly developed and its echolocation allows it to move about and find breathing holes under sheet ice.

Belugas are gregarious and form groups of 10 animals on average, although during the summer, they can gather in the hundreds or even thousands in estuaries and shallow coastal areas. They are slow swimmers, but can dive to 700 m (2,300 ft) below the surface. They are opportunistic feeders and their diets vary according to their locations and the season. The majority of belugas live in the Arctic Ocean and the seas and coasts around North America, Russia, and Greenland; their worldwide population is thought to number around 200,000.[6][7] They are migratory and the majority of groups spend the winter around the Arctic ice cap; when the sea ice melts in summer, they move to warmer river estuaries and coastal areas. Some populations are sedentary and do not migrate over great distances during the year.

The native peoples of North America and Russia have hunted belugas for many centuries. They were also hunted by non-natives during the 19th century and part of the 20th century. Hunting of belugas is not controlled by the International Whaling Commission, and each country has developed its own regulations in different years. Currently, some Inuit in Canada and Greenland, Alaska Native groups and Russians are allowed to hunt belugas for consumption as well as for sale, as aboriginal whaling is excluded from the International Whaling Commission 1986 moratorium on hunting. The numbers have dropped substantially in Russia and Greenland, but not in Alaska and Canada. Other threats include natural predators (polar bears and killer whales), contamination of rivers (as with Polychlorinated biphenyl (PCBs) which bioaccumulate up the food chain), climate change and infectious diseases. The beluga was placed on the International Union for Conservation of Nature's Red List in 2008 as being "near threatened"; the subpopulation from the Cook Inlet in Alaska, however, is considered critically endangered and is under the protection of the United States' Endangered Species Act. Of all seven extant Canadian beluga populations, those inhabiting eastern Hudson Bay, Ungava Bay, and the St. Lawrence River are listed as endangered.

Belugas are one of the most commonly kept cetaceans in captivity and are housed in aquariums, dolphinariums and wildlife parks in North America, Europe and Asia. They are considered charismatic because of their docile demeanour and characteristic smile, communicative nature,[8] and supple, graceful movement.[9]

The beluga was first described in 1776 by Peter Simon Pallas.[1] It is a member of the family Monodontidae, which is in turn part of the parvorder Odontoceti (toothed whales).[1] The Irrawaddy dolphin was once placed in the same family, though recent genetic evidence suggests these dolphins belong to the family Delphinidae.[10][11] The narwhal is the only other species within the Monodontidae.[12] A skull has been discovered with intermediate characteristics supporting the hypothesis that hybridisation is possible between these two species.[13]

The whale is also colloquially known as the "sea canary" on account of its high-pitched squeaks, squeals, clucks, and whistles. A Japanese researcher claimed that he taught a beluga to "talk" by using these sounds to identify three different objects, offering hope that humans may one day be able to communicate effectively with sea mammals.[15] A similar observation has been made by Canadian researchers, where a beluga which died in 2007 "talked" when he was still a subadult. Another example is NOC, a beluga whale that could mimic the rhythm and tone of human language. Beluga whales in the wild have been reported to imitate human voices.[16]

Mitochondrial DNA studies have shown modern cetaceans last shared a common ancestor between 25 and 34 million years ago[17][18] The superfamily Delphinoidea (which contains monodontids, dolphins and porpoises) split from other toothed whales, odontoceti, between 11 and 15 million years ago. Monodontids then split from dolphins (Delphinidae) and later from porpoises (Phocoenidae), their closest relatives in evolutionary terms.[17] In 2017 the genome of a beluga whale was sequenced, comprising 2.327 Gbp of assembled genomic sequence that encoded 29,581 predicted genes.[19] The authors estimated that the genome-wide sequence similarity between beluga whales and killer whales is 97.87%.[citation needed]

The fossil record also indicates that, in comparatively recent times, the beluga's range varied with that of the polar ice packs expanding during ice ages and contracting when the ice retreated.[25] Counter-evidence to this theory comes from the finding in 1849 of fossilised beluga bones in Vermont in the United States, 240 km (150 mi) from the Atlantic Ocean. The bones were discovered during construction of the first railroad between Rutland and Burlington in Vermont, when workers unearthed the bones of a mysterious animal in Charlotte. Buried nearly 10 ft (3.0 m) below the surface in a thick blue clay, these bones were unlike those of any animal previously discovered in Vermont. Experts identified the bones as those of a beluga. Because Charlotte is over 150 mi (240 km) from the nearest ocean, early naturalists were at a loss to explain the presence of the bones of a marine mammal buried beneath the fields of rural Vermont.[citation needed]

The remains were found to be preserved in the sediments of the Champlain Sea, an extension of the Atlantic Ocean within the continent resulting from the rise in sea level at the end of the ice ages some 12,000 years ago.[26] Today, the Charlotte whale is the official Vermont State Fossil (making Vermont the only state whose official fossil is that of a still extant animal).[27]

Preliminary investigations suggested a beluga's life expectancy was rarely more than 30 years.[28] The method used to calculate the age of a beluga is based on counting the layers of dentin and dental cement in a specimen's teeth, which were originally thought to be deposited once or twice a year. The layers can be readily identified as one layer consists of opaque dense material and the other is transparent and less dense. It is therefore possible to estimate the age of the individual by extrapolating the number of layers identified and the estimated frequency with which the deposits are laid down.[29] A 2006 study using radiocarbon dating of the dentin layers showed the deposit of this material occurs with a lesser frequency (once per year) than was previously thought. The study therefore estimated belugas can live for 70 or 80 years.[30] However, recent studies suggest that it is unclear as to whether belugas receive a different number of layers per year depending on the age of the animal (for example young belugas may only receive an additional one layer per year), or simply just one layer per year or every other year.[31][citation needed]

Individuals of both sexes reach their maximum size by the time they are 10 years old.[37] The beluga's body shape is stocky and fusiform (cone-shaped with the point facing backwards), and they frequently have folds of fat, particularly along the ventral surface.[38] Between 40% and 50% of their body weight is fat, which is a higher proportion than for cetaceans that do not inhabit the Arctic, where fat only represents 30% of body weight.[39][40] The fat forms a layer that covers all of the body except the head, and it can be up to 15 cm (5.9 in) thick. It acts as insulation in waters with temperatures between 0 and 18 C, as well as being an important reserve during periods without food.[41]

The adult beluga is rarely mistaken for any other species, because it is completely white or whitish-grey in colour.[42] Calves are usually born grey,[33] and by the time they are a month old, have turned dark grey or blue grey. They then start to progressively lose their pigmentation until they attain their distinctive white colouration, at the age of seven years in females and nine in males.[42] The white colouration of the skin is an adaptation to life in the Arctic that allows belugas to camouflage themselves in the polar ice caps as protection against their main predators, polar bears and killer whales.[43] Unlike other cetaceans, the belugas seasonally shed their skin.[44] During the winter, the epidermis thickens and the skin can become yellowish, mainly on the back and fins. When they migrate to the estuaries during the summer, they rub themselves on the gravel of the riverbeds to remove the cutaneous covering.[44]

Like most toothed whales, the beluga has a compartment found at the centre of the forehead that contains an organ used for echolocation called a melon, which contains fatty tissue.[45] The shape of the beluga's head is unlike that of any other cetacean, as the melon is extremely bulbous, lobed and visible as a large frontal prominence.[45] Another distinctive characteristic it possesses is the melon is malleable; its shape is changed during the emission of sounds.[12] The beluga is able to change the shape of its head by blowing air around its sinuses to focus the emitted sounds.[46][47] This organ contains fatty acids, mainly isovaleric acid (60.1%) and long-chain branched acids (16.9%), a very different composition from its body fat, and which could play a role in its echolocation system.[48]

c80f0f1006