Distribution and Movements of Polar Bears

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Polar bears are tied to the sea ice for nearly all of their life cycle functions. Most important of these is foraging, or access to food. Polar bears almost exclusively eat seals, and they are equally as dependent upon the sea for their nutrition as are seals, whales, and other aquatic mammals. Polar bears are not aquatic, however, and their only access to the seals is from the surface of the sea ice. 

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Sea ice blocks pushed up in a pressure ridge of ice

Sea ice blocks pushed up in a pressure ridge of ice. (Public domain.)

In winter, there have been dramatic reductions in the amount of old ice, predominantly in the western Arctic. This loss of stable old ice has catalyzed additional losses of sea ice cover each summer because the thinner younger ice is more easily melted during the recent warmer summers. Research in this focal area seeks to develop a better understanding of how changes in the distribution and characteristics of sea ice habitat are likely to affect polar bear fitness, distribution, and interactions with people. If we know how polar bears respond to changes in ice quantity and quality, we will be able to predict how forecasted changes in the ice may affect future polar bear populations. This will give managers the best chance of adapting strategies to assure the long-term persistence of polar bears in a changing ice environment.

 

 

Effects of declining ice on polar bear behavior and habitat selection

Among all polar bear subpopulations, those occurring in the Beaufort and the Chukchi seas have experienced some of the greatest losses of sea ice in the entire Arctic Ocean. The mechanisms that link habitat to population trend, however, have not been quantitatively described. The role of habitat preference on behavior (i.e., movement and activity) or whether some habitats are important for life history requirements is uncertain. Movements of polar bears are linked to foraging success and energetic costs. Hence, movements, as a proxy for behavior and energetics, may be indicative of habitat value and provide a quantifiable means to elucidate mechanisms of polar bear population response to a changing Arctic. We are using polar bear location data collected by the USGS since 1985 to develop models of polar bear distribution that account for long-term changes in behavior and habitat function. This research will provide products that can be used by managers to mitigate adverse impacts to polar bears and polar bear habitats from anthropogenic activities.

 

Characterizing the on-shore ecology of Alaska’s polar bears

Polar bear populations have varying strategies for coping with seasonal sea ice formation and recession. In some regions of the Arctic, where sea ice melts completely during summer, bears migrate to on-land refugia where they remain until sea ice returns in the fall. In regions where sea ice persisted year-round, polar bears were able to remain on the pack ice even as it receded from land each summer. However, in Alaska, the progressive decline in sea ice coverage in summer and fall— particularly over the biologically productive continental shelf waters— has led to a novel and increasing trend of land use. The effectiveness of this new behavioral strategy is unknown. Further, there is a lack of information available regarding habitat selection of polar bears while on shore. These data gaps pose a challenge to managers tasked with balancing needs to maintain accessibility to critical habitat with recreational and economic development activities. Our investigations of on-shore ecology will address those data gaps and provide information that can be used to aid in decisions regarding the management of terrestrial habitats.

 

Female and cub polar bear on land near Kaktovik, Alaska

Female and cub polar bear on land near Kaktovik, Alaska. (Public domain.)

Factors influencing human-polar bear interactions on Alaska’s North Slope

Loss of sea ice is expected to foster an increase in anthropogenic activities in the Arctic by allowing greater access to the Arctic Ocean, and facilitating the extraction of oil and gas reserves and the opening of new shipping routes. On Alaska’s North Slope, polar bears are regularly observed in close proximity to industrial operations during summer and fall. Because of protections conferred by the Marine Mammal Protection Act (MMPA) and Endangered Species Act (ESA), human activities that result in the harassment, injury, or death of polar bears (considered a “take”) are prohibited. However, activities with the potential to result in “incidental takes” are allowed under a permit that requires permit holders (private, non-federal entities) to take steps to mitigate and minimize risk of harm to polar bears. Objectives of this research include identifying drivers and patterns of human-polar bear interactions, and quantifying and characterizing the types of “incidental take” occurring within industrial areas to begin to understand impacts to both bears and people (including industrial operations). Better knowledge about when and where interactions are likely to occur, and how they are likely to impact polar bears, humans, and industrial activities are needed to inform proactive and reasonable management strategies for minimizing human-polar bear interactions.