Each spring to early summer, the continental shelves of the Chukchi and Beaufort seas north of Alaska emerge from a cloak of winter sea ice. Such seasonal phases of sea ice break-up in the spring and sea ice freeze-up in the fall govern the accessibility and productivity of Alaska’s Arctic Ocean for several migratory marine species. Open water in spring serves as a welcome mat for beluga whales (Delphinapterus leucas) and bowhead whales (Balaena mysticetus) that transit the Pacific’s only gateway into the Arctic through the narrow Bering Strait. Each year, these Arctic whales pass the coastal boundaries of Bering Land Bridge National Preserve and Cape Krusenstern National Monument, dispatched from their winter haunts in the Bering Sea. After passing through the Bering Strait each spring, they enter the southern Chukchi Sea, one of the most seasonally productive regions of the global oceans (Grebmeier 2012). Some belugas and most bowhead whales continue on their >1,500 mile (>2,500 km) migration north of Alaska to the Canadian Beaufort Sea for the summer.
For beluga whales, recent cooperative research has provided deeper insights into the relative distribution, movements, and behavior of two distinct populations. The Eastern Chukchi Sea and Eastern Beaufort Sea beluga populations (“Chukchi” and “Beaufort” populations) return each summer to the nearshore regions of Kasegaluk Lagoon in northwest Alaska and the Mackenzie River Estuary, Canada, respectively (Figure 1). A mixture of large, white adults and dark grey calves arrive around June-early July, presumably for an annual molt of their skin in the warmer, less saline coastal water (St. Aubin et al. 1990). These coastal regions also provide a more protected area to nurture their young. Scientists working collaboratively with local communities have tagged beluga whales from the Chukchi and Beaufort populations with satellite-linked transmitters since 1993.
Listen to beluga whale sounds.
- Date created:
- 2020-10-14 00:00:00.0
Location data from the transmitters reveal extensive movements around the Chukchi and Beaufort seas and deep (1.9 miles, or more than 3,000 m) Canada Basin, with some animals ranging to nearly ~80°N latitude (Richard et al. 2001, Suydam et al. 2001). Two decades of tracking data, combined, in some cases, with data on underwater diving behavior, help clarify why these populations use the Pacific Arctic as well as when and where they may overlap. Chukchi and Beaufort belugas are spatially segregated during July and August. However, both populations use the Alaskan Beaufort Sea and overlap during September when Beaufort belugas rapidly shift their distribution from the Canadian Beaufort Sea to the western Chukchi Sea, a month ahead of the Chukchi population’s westward migration (Figure 2; Hauser et al. 2014). There is also limited spatial overlap in fall months in the Chukchi Sea. Adult males generally separate from females during summer and use deeper water, farther from shore, and denser sea ice concentrations (Hauser et al. 2017a).
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Figure 2. An animation of daily locations from Chukchi Sea (‘Chukchi’: purple dots) and Beaufort Sea (‘Beaufort’: green dots) beluga whales tagged from 1993-2007. Data were collected in collaboration with the Alaska Beluga Whale Committee, North Slope Borough, Village of Point Lay, Alaska Department of Fish and Game, National Marine Fisheries Service (for Chukchi Sea belugas) as well as Fisheries and Ocean Canada, Fisheries Joint Management Committee, and Hunter and Trapper Committees of villages in the Inuvialuit Settlement Region (for Beaufort Sea belugas). See Hauser et al. (2014) for more details and additional acknowledgements of the individuals, organizations, and funding sources that supported tagging and analysis efforts.
These complicated seasonal distributions beg the question of why migrate and what factors influence their movements? Belugas have encountered this highly seasonal and ephemeral sea ice environment since at least the Late Miocene (Harington 2008), so their population-specific fidelity to distinct summer areas, sexual segregation, and offset migration timing are presumably shaped by seasonal fluctuations in summer to fall conditions and sea ice in particular. Beluga philopatry (site fidelity) and migration patterns are also culturally transmitted, passed down from their mothers (O’Corry-Crowe et al. 2016). Belugas mediate their behavior to respond to patchily distributed prey, as illustrated by variations in diving behavior among Pacific Arctic regions. For example, both beluga populations dive to depths and portions of the water column that would presumably optimize foraging opportunities, based on the available information of prey distributions as well as oceanographic properties that concentrate prey (Hauser et al. 2015). Therefore, beluga distribution, movements, and behavior are ultimately driven by combined effects of genetic, social, and environmental influences.
Beluga Migrations in the Face of a Changing Pacific Arctic
The Arctic is undergoing rapid and unprecedent-ed change, with warming twice as fast as the rest of the planet (AMAP 2017). The Pacific Arctic ecosystem is transforming with an expanded open-water summer season, increased wind-forcing and upper-ocean heat content, more freshwater, and upwelling (Wood et al. 2015). How are belugas and other Arctic marine mammals mediating these changing conditions, and to what extent, given tradeoffs in social versus environmental forcing?
Tagging data are again useful in helping assess beluga responses to shifts in their environment. The annual spring ice break-up in both the Chukchi and Beaufort seas now occurs earlier while fall freeze-up has shifted later, meaning that the overall duration of the open-water season has increased (13-15 days/decade during 1979-2013; Laidre et al. 2015). Comparing tagging data from 1998-2002 to 2007-2012 (when sea ice cover significantly declined), Chukchi belugas delayed fall migration to allow for a prolonged presence in the Beaufort Sea as sea ice freeze-up also occurred later (Table 1; Hauser et al. 2017b). These results support the hypothesis that Chukchi belugas are coping with a changing Pacific Arctic environment by shifting migration timing. In contrast, there were few examples where migration timing of Beaufort belugas changed between the 1990s and 2000s, nor was there evidence that freeze-up timing cues migration for the Beaufort population. Rather, Beaufort beluga migration timing appears to be somewhat “pre-programmed” for a particular time each fall. More research is needed to determine how the migration strategies of Chukchi and Beaufort belugas affect their population dynamics, vital parameters, or potential for persistence. In the case of Pacific Arctic bowhead whales, current sea ice and oceanographic conditions seem to support enhanced foraging opportunities that have improved recent body condition and population growth (George et al. 2015), which may also be the case for belugas. However, later migration from the Beaufort Sea in the fall may expose Chukchi belugas to more variable freeze-up patterns and the potential for fatal ice entrapments. Ultimately, it seems that beluga responses to changing sea ice conditions vary among populations, which not only complicates predictions for future conditions, but also suggests some beluga populations may be more likely than others to persist in a changing climate.
|Migration Passage Location||Median Migration Day of the Year in
Early, Late Periods
|Days Between Median Dates
(Late - Early)
|Eastern Chukchi Sea belugas (tagged 1998-2002 and 2007-2012|
|Exit Beaufort Sea (first day west of 157°W)||6 Oct, 8 Nov||+33|
|Commence southward migration (last day north of 70°N)||22 Oct, 12 Nov||+21|
|Enter Bering Sea (first day south of Bering Strait, 65.9°N)
||11 Nov, 25 Nov||+14|
|Eastern Beaufort Sea belugas (tagged 1993-1997 and 2004-2005)|
|Exit Canada (first day west of 141°W)||8 Sept, 2 Sept||-6|
|Exit Beaufort Sea (first day west of 157°W)||17 Sept, 9 Sept||-8|
|Commence southward migration (last day north of 70°N)||16 Oct, 18 Oct||+2|
|Enter Bering Sea (first day south of Bering Strait, 65.9°N)||None tagged,
In the face of sea ice loss, belugas and other Arctic marine mammals are also likely to experience increased anthropogenic activities and changes in the marine mammal community. For example, Arctic marine mammals and the subsistence communities that rely on them are vulnerable as sea ice loss expands the navigability of Arctic sea routes (Huntington et al. 2015) and possibilities for oil and gas development (Reeves et al. 2014). An increasingly ice-free Pacific Arctic may also affect the more temperate marine mammal species that ply Alaska’s northern waters on a seasonal basis. Some baleen whales, such as fin and humpback whales (Balaenoptera physalus and Megaptera novaeangliae), are more commonly sighted now in the Chukchi Sea north of Bering Strait. This is either the result of a lack of sea ice or simply reflects the recovery of North Pacific populations following the cessation of commercial whaling (Clarke et al. 2013). Killer whales (Orcinus orca), a relatively novel Arctic predator, are also increasingly observed in the Pacific Arctic, similar to the Eastern Arctic. Overall, additional research is needed to understand the impacts of sea ice loss on Arctic marine mammals (Laidre et al. 2015).
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