Because of their annual migration patterns, and with difficulties in sampling and studying these animals in the field, stock identification for beluga is currently not well defined. Determination of stocks for beluga is particularly important since in several areas beluga numbers have declined considerably over the past century. Because people wish to continue to hunt beluga, it is essential to have knowledge of stock structures, their distribution and population sizes in order to determine sustainable harvest levels.
Genetic studies have been used to try to differentiate beluga stocks, though results have not been as clear cut as with some other animals. Difficulties arise in using genetics for beluga because adequate sampling designs are hard to achieve (de March et al. 2002). Sample numbers are sometimes lower than desired, due to the difficulty and expense of obtaining samples, and sampling is usually concentrated in areas and times where belugas are hunted rather than throughout their seasonal range. Additionally, because beluga are social animals and occur in pods of closely related animals, sampled animals may be close relatives rather than random individuals from a stock (Palsbøll et al. 2002). These difficulties mean that genetic studies alone will probably not be enough to define beluga stocks, and that a combination of methods and information is needed. For beluga, the annual migration path and the hunters who have access to the whales along this path may best describe the term “stock” (Innes et al. 2002b).
A further complication arises because different genetic analyses yield conflicting results for beluga. Analysis of mitochondrial DNA from beluga harvested in and around Hudson Bay suggests that several separate stocks inhabit the area (Turgeon et al. 2012). In contrast, there is little evidence of separate stocks from analyses of nuclear DNA. As mitochondrial DNA is inherited maternally only, this suggests that maternally-led “cultural” stocks go to separate summering areas, but mix together during the mating season. This also means that hunters in the same community might take a single stock during the summer, but a mixture of two or more at other times of the year.
A recent genetic study has however revealed that beluga stocks can be divided into two major groups: (1) Arctic (Svalbard–White Sea–Greenland–Beaufort Sea), and (2) Subarctic (Gulf of Alaska) regions (O’Corry-Crowe et al. 2010). This study suggests a deep divergence between the two major groupings, but periodic gene flow within them, probably during warm periods with lighter ice cover. A further deep division has been found between the St Lawrence River and Eastern Hudson Bay populations and all other Canadian and Greenlandic populations (COSEWIC 2004, de March et al. 2002). The former grouping might have originated from an Atlantic glacial refugium, while the other areas may have been colonized from the west.
Belugas are found in the Barents Sea and around Svalbard. In summer, belugas are observed close to shore on the west, south and southeastern parts of the archipelago (NAMMCO 2000). Their distribution overlaps the winter distribution of the Karskaya (see below) belugas, and it is possible that there could be mixing of these two groups.
Belugas are rare along the east coast of Greenland, likely due to lack of suitable habitat. Whales which do appear there from time to time probably belong to the Svalbard population (Dietz et al. 1994).
There are two main groups of belugas in the Russian Arctic. Also called the “Karskaya” group, these beluga inhabit the western and central parts of the Russian Arctic, including the Barents, White, Kara and Laptev Seas (NAMMCO 2000). Another group inhabits the Bering Sea.
Beluga distribution in the eastern Atlantic.
On the west coast of Greenland, belugas are found from Qaanaaq in the north to Paamiut in the south in the fall, winter and spring. Belugas are rare along this coast in summer (NAMMCO 2000). Beluga migrate past the Upernavik region in October and are found later in the fall and winter between Disko Bay and Sisimiut (NAMMCO 2000). It is unclear how many stocks winter off the west coast of Greenland (Palsbøll et al. 2002), but it is known that these animals spend the summer in the straits and channels of the Canadian High Arctic islands (Richard et al. 2001).
Beluga whales occur throughout the Canadian Arctic. With the exception of one group in the Beaufort Sea, all other groups are found in the eastern Arctic.
Fifteen groups are currently recognised in the eastern and High Arctic, and it appears in general that there are more separate groups or populations than was previously thought (NAMMCO 2000). In the Canadian High Arctic, for example, both satellite tracking and genetic studies have been unable to determine the stock structure of the beluga which spend the summer there (NAMMCO 2002a). Some beluga from this area migrate to western Greenland in the winter, while others winter in the "North Water" in Baffin Bay and Smith Sound (Richard et al. 2001). Heide-Jørgensen et al. (2003) estimated that the proportion of animals moving to West Greenland in the winter was approximately 15% (95% confidence limit 6-35%) based on satellite tagging data. It is likely that this “High Arctic” stock consists of two or more smaller stocks (de March et al. 2002), one or more of which winters off West Greenland and one or more of which winters in the North Water. The Joint Scientific Working Group of the NAMMCO and the JCNB agreed upon a stock structure model for Baffin Bay beluga that describes a summering aggregation in the Somerset Island area and two wintering aggregations in the North Water and in east Baffin Bay (NAMMCO 2013).
Beluga distribution in the western Atlantic.
This population of belugas was originally defined by their summering area. It is thought that this population may have been extirpated, or if it still exists, has very low numbers (DFO 2004). Past genetics studies showed high levels of genetic diversity (Mancuso 1995, Smith and Hammill 1986), however belugas from Ungava Bay may now be part of other populations (DFO 2004).
Easter Hudson Bay belugas are genetically different from Western Hudson Bay belugas (Mancuso 1995, Brennin et al. 1997, Brown-Gladden et al. 1997, de March and Postma 2003). They spend the summer mainly in coastal waters extends from Kujjuarapik to Inukjuak, but they can also be found in offshore waters (Smith and Hammill 1986, Kingsley 2000, Gosselin et al. 2002).
Recent studies indicate that belugas in James Bay may be a separate population from the rest of the Eastern Hudson Bay population (Bailleul et al. 2012). In this study, belugas captured and tagged in James Bay remained very close to where they were captured, while the majority of Eastern Hudson Bay belugas migrated between distinct summer and wintering areas. Bailleul et al. (2012) suggested that decreases in sea ice in recent years may have made James Bay a suitable area for belugas to remain year-round, while ice conditions in the rest of Eastern Hudson Bay still make it necessary for the belugas there to migrate.
The beluga of Western Hudson Bay are a large, possibly diverse stock that may contain several sub-stocks, including Northern Hudson Bay, Foxe Basin, and Southern Hudson Bay. The Western Hudson Bay belugas contain many genetic similarities to all other Canadian beluga populations, yet are genetically distinguishable. More information is needed to understand the population structure.
The Cumberland Sound stock summers in the inner part of Cumberland Sound and winters beyond the ice edge near the mouth of the Sound (DFO 2002a). They are considered a separate population based on results from satellite tagging, genetics, organochlorine contaminant signatures, and traditional knowledge (Kilabuk 1998).
St Lawrence River
The St Lawrence River is a small population that is thought to have once been part of the Arctic populations (DFO 2004). There does not appear to be any geographic overlap with the other current populations of belugas, and they are also genetically distinct from all the other populations (DFO 2004).