December is soon, so prepare some warm clothes as we are heading to the Arctic to meet a whale with unusual head - Beluga whale.
Beluga whale
The beluga whale is an Arctic and sub-Arctic cetacean. It is one of two members of the family Monodontidae, along with the narwhal, and the only member of the genus Delphinapterus. It is also known as the white whale, as it is the only cetacean to regularly occur with this colour; the sea canary, due to its high-pitched calls; and the melonhead, though that more commonly refers to the melon-headed whale, which is an oceanic dolphin.
Its body is round, particularly when well fed, and tapers less smoothly to the head than the tail. The sudden tapering to the base of its neck gives it the appearance of shoulders, unique among cetaceans. The tail-fin grows and becomes increasingly and ornately curved as the animal ages. The flippers are broad and short—making them almost square-shaped.
The adult beluga is rarely mistaken for any other species, because it is completely white or whitish-grey in colour. Calves are usually born grey, 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. 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. Unlike other cetaceans, the belugas seasonally shed their skin. 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.
Like most toothed whales, it has a compartment found at the centre of the forehead that contains an organ used for echolocation called a melon, which contains fatty tissue. 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. Another distinctive characteristic it possesses is the melon is malleable; its shape is changed during the emission of sounds. The beluga is able to change the shape of its head by blowing air around its sinuses to focus the emitted sounds. 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.
These cetaceans are highly sociable and they regularly form small groups, or pods, that may contain between two and 25 individuals, with an average of 10 members. Pods tend to be unstable, meaning individuals tend to move from pod to pod. Radio tracking has even shown belugas can start out in one pod and within a few days be hundreds of miles away from that pod. Beluga whale pods can be grouped into three categories, nurseries (which consist of mother and calves), bachelors (which consist of all males) and mixed groups. Mixed groups contain animals of both sexes. Many hundreds and even thousands of individuals can be present when the pods join together in river estuaries during the summer. This can represent a significant proportion of the total population and is when they are most vulnerable to being hunted.
Belugas play an important role in the structure and function of marine resources in the Arctic Ocean, as they are the most abundant toothed whales in the region. They are opportunistic feeders; their feeding habits depend on their locations and the season. For example, when they are in the Beaufort Sea, they mainly eat Arctic cod and the stomachs of belugas caught near Greenland were found to contain rose fish, Greenland halibut and northern shrimp, while in Alaska their staple diet is Coho salmon. In general, the diets of these cetaceans consist mainly of fish; apart from those previously mentioned, other fish they feed on include capelin, smelt, sole, flounder, herring, sculpin and other types of salmon. They also consume a great quantity of invertebrates, such as shrimp, squid, crabs, clams, octopus, sea snails, bristle worms and other deep-sea species. Belugas feed mainly in winter as their blubber is thickest in later winter and early spring, and thinnest in the fall. Inuit observation has led scientists to believe that belugas do not hunt during migration, at least in Hudson Bay.
Distribution
The beluga inhabits a discontinuous circumpolar distribution in Arctic and sub-Arctic waters. During the summer, they can mainly be found in deep waters ranging from 76°N to 80°N, particularly along the coasts of Alaska, northern Canada, western Greenland and northern Russia. The southernmost extent of their range includes isolated populations in the St. Lawrence River in the Atlantic, and the Amur River delta, the Shantar Islands and the waters surrounding Sakhalin Island in the Sea of Okhotsk.
Belugas exploit a varied range of habitats; they are most commonly seen in shallow waters close to the coast, but they have also been reported to live for extended periods in deeper water, where they feed and give birth to their young.
In coastal areas, they can be found in coves, fjords, canals, bays and shallow waters in the Arctic Ocean that are continuously lit by sunlight. They are also often seen during the summer in river estuaries, where they feed, socialize and give birth to young. These waters usually have a temperature between 8 and 10 °C. The mudflats of Cook Inlet in Alaska are a popular location for these animals to spend the first few months of summer. In the eastern Beaufort Sea, female belugas with their young and immature males prefer the open waters close to land, while the adult males live in waters covered by ice near the Canadian Arctic Archipelago. The younger males and females with slightly older young can be found nearer to the ice shelf. Generally, the use of different habitats in summer reflects differences in feeding habits, risk from predators and reproductive factors for each of the subpopulations.
Conservation
Prior to 2008, the beluga was listed as "vulnerable" by the International Union for Conservation of Nature (IUCN), a higher level of concern. The IUCN cited the stability of the largest sub-populations and improved census methods that indicate a larger population than previously estimated. In 2008, the beluga was reclassified as "near threatened" by the IUCN due to uncertainty about threats to their numbers and the number of belugas over parts of its range (especially the Russian Arctic), and the expectation that if current conservation efforts cease, especially hunting management, the beluga population is likely to qualify for "threatened" status within five years. In June 2017, its status was reassessed to "least concern".
There are about 21 sub-populations of beluga whales and it is estimated that 200,000 individuals still exist. However, the nonmigratory Cook Inlet sub-population off the Gulf of Alaska is a separate sub-population that is listed as "critically endangered" by the IUCN as of 2006 and as "endangered" under the Endangered Species Act as of October 2008. This was primarily due to unregulated overharvesting of beluga whales prior to 1998. The population has remained relatively consistent, though the reported harvest has been small. As of 2016, the estimated abundance of the endangered Cook Inlet population was 293 individuals. The most recent estimate in 2018 by NOAA Fisheries suggested that the population declined to 279 individuals.
Despite beluga whales not being threatened overall, sub-populations are being listed as critically endangered and are facing increased mortality from human actions. For example, even though commercial hunting is now banned due to the Marine Mammal Protection Act, beluga whales are still being hunted to preserve the livelihood of native Alaskan communities. The IUCN and NOAA Fisheries cite habitat degradation, oil and gas drilling, underwater noise, harvesting for consumption and climate change as threats to the prolonged survival of beluga whale sub-populations.
That's it for today. See you all next time.
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