Climate Change and the Arctic
The global climate is changing, and the Artic is on the front line. Satellite imagery illustrates the dramatic loss of sea ice over the last several decades as air and water temperatures in the Arctic have warmed – one of many documented changes being tracked and reported on annually. The loss of sea ice in the Arctic has led to accelerated ocean warming, stronger winds and currents, and accelerated shoreline erosion in Arctic communities (Moon et al. 2019).
Marine mammals endemic to the Arctic are uniquely adapted to life in icy waters. These include bowhead whales, polar bears, several species of “ice seals,” beluga whales, and walruses. These and other marine species (e.g., Arctic seabirds) rely on the year round or seasonal presence of sea ice. Other species (e.g., humpback, fin, and gray whales) migrate to the Arctic from more temperate regions to feed during the summer months. These species follow the receding sea ice edge and take advantage of the region’s immense summer biological productivity.
The Marine Mammal Commission has long sought to further scientific understanding of the impacts of environmental changes on marine mammals, including Arctic-specific impacts, by working with and bringing together experts to discuss and publish the latest science. The Commission engages with other agencies on policy and management actions, such as assessing the conservation status of marine mammals in the Arctic and elsewhere that may be impacted by changing environmental conditions in U.S. waters (Gulland et al. 2022). The Commission supports baseline research and environmental monitoring in U.S. waters and around the Arctic to document changes to marine ecosystems, and engages in conservation and co-management of marine mammals with Alaska Native communities and federal and state resource agencies.
Environmental Changes and Impacts to Marine Mammals
Impacts of Sea Ice Declines
Sea ice is declining rapidly in both quantity and quality (Druckenmiller et al. 2021) with profound consequences for marine mammals that rely on sea ice platforms for foraging and resting. These “ice-obligate” marine mammals include polar bears, walruses, and bearded and ringed seals (Moore et al. 2014). Such consequences may be in the form of both reduced fitness of individual animals and changes in population abundance (Laidre et al. 2015).
A frequently cited example of how the decline in sea ice is affecting Arctic marine mammals is the polar bear, which relies upon sea ice to hunt seals, although these impacts vary by region and polar bear population. Generally, as the ice extent decreases, polar bears must spend more time and travel greater distances in search of prey, which can result in poor body condition and reduced reproductive success (Pagano et al. 2020, 2021). Polar bears have also responded to declines in sea ice by moving onto land to forage (Galicia et al. 2021, Obbard et al. 2016), bringing them closer to human communities and increasing the potential for inter-species conflict (Atwood and Wilder 2021). Efforts to mitigate conflict, like the use of “Bear-dar” in Churchill, Manitoba, which alerts the community to approaching polar bears, can help to keep both bears and humans safe.
Walruses in the Chukchi Sea have similarly been forced onto land to rest (or haul out) in large numbers (Garlich-Miller 2012) as sea ice extent retreats into deep waters beyond shallower walrus foraging areas (Jay et al. 2017, MacCracken 2012). The need to rest on land increases the species’ vulnerability to disturbance from predators or human activities. Disturbances can cause walruses to stampede, resulting in mass mortality from crushing, particularly of calves or smaller individuals (MacCracken 2012).
Ringed seals rely upon dense continuous pack ice and snow cover to dig lairs for shelter from weather and predation (especially when pupping). Loss of ice and decreased snow depth in a warming Arctic compromises the structure of lairs and may negatively affect adult body condition and pup survival (Hauser et al. 2021). Bearded seals prefer to haul out on broken ice pack (Ray et al. 2010). With the reduction of sea ice extent, bearded seals appear to be hauling out more frequently on land (Olnes et al. 2020, 2021). The extent to which ringed and bearded seals are switching from sea ice to land haulouts, or the impact of this or other behavioral adaptations to changing conditions on their reproductive success (Kovacs and Lydersen 2008), are not yet fully known.
Changes to the Food Web: Prey and Pathogens
Many Arctic marine mammals will also be indirectly affected as the food webs on which they depend undergo changes. Restructured food webs, changes in prey populations, the arrival of new marine mammal species (including new predators and competitors), and pathogens from more temperate seas will challenge Arctic species (Huntington et al. 2020, Meuter et al. 2021, Moore 2016, Moore and Gulland 2014, Moore and Reeves 2018).
Several studies have found that harmful algal blooms (HABs) are expanding north as sea ice extent declines and water temperatures rise (e.g., Lefebvre et al. 2016). HAB paralytic toxins like saxitoxin and domoic acid have been found in walruses, seals, and Arctic cetacean species (Lefebvre et al. 2016, 2022). More consistent and widespread monitoring of toxin levels in marine mammals and other marine species may help to alert scientists to potential HAB-related risks to both human and marine mammal health (Lefebvre et al. 2022).
Threats from Increasing Human Activity
Declines in the seasonal extent of sea ice are creating more opportunities for human activity in the Arctic, with resulting impacts on marine mammals (e.g., Hauser et al. 2018, Huntington et al. 2020, Moore and Reeves 2018, Reeves et al. 2014). The disappearance of sea ice from coastlines earlier in the year, coupled with the ice’s retreat farther from shore during the summer (and tendency to remain offshore longer) means there is now a large and increasing annual window of open water. These changes create opportunities for shipping, tourism, commercial fishing, oil and gas exploration and development, and military operations to expand into new areas. These activities create the potential to expose Arctic marine mammals to a variety of new threats, including vessel strikes, pollution, entanglement in fishing nets or lines, and exposure to human-caused sound and other forms of disturbance.
At the same time, these changing ice and weather conditions are affecting the movements of marine mammals and the conditions for subsistence hunting of marine mammals by Alaska Natives. Extended open water periods, lack of stable sea ice, high winds, stronger currents, and the need to venture farther from shore to hunt marine mammals along the ice edge may present new dangers in pursuing subsistence hunting activities (Huntington et al. 2017). There are also concerns over the potential danger to or conflict with subsistence hunters from new “industrial” or shipping activities in the Arctic.
The predicted increase in Arctic shipping has prompted the U.S. Coast Guard to seek input on vessel routing measures that would minimize impacts of shipping on marine mammals and Arctic communities. The Commission’s comments on the U.S. Coast Guard’s Alaskan Arctic Coast Port Access Study (Arctic PARS) were based on an analysis of best available scientific data on marine mammal distributions and seasonal movements in the U.S. Chukchi and Beaufort Seas. The Commission worked with biologists at NOAA and Duke University to generate recommended vessel routing through Alaskan Arctic waters and areas to avoid in order to protect marine mammals. The Commission also prepared a fact sheet summarizing its comments on the Arctic PARS.
Although many scientists have emphasized known and expected negative impacts on Arctic marine mammals (e.g., Burek et al. 2008, Evans et al. 2010, Huntington 2009, Kovacs and Lydersen 2008, Kovacs et al. 2011, Laidre et al. 2015, Moore and Reeves 2018, Wassmann et al. 2010), some species or populations are likely to experience little change or benefit from more favorable conditions.
If the impacts of climate change on Arctic species are to be avoided, the source of the problem on a global scale will have to be addressed. Regardless of the degree to which society and governments are able to alter the course of global warming, our challenge in the short-term is to understand the effects of climate change on the Arctic, and anticipate and mitigate the impact on Arctic species and the Alaska Native communities that depend on them to the fullest extent possible.
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