Health and Energetics of Polar Bears

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Research in this focal area is centered on (i) collecting data on a variety of systems that help determine and mediate polar bear health and energetics, and (ii) developing monitoring and surveillance programs for detecting changes in population health over time. Additionally, this work will allow us to develop an understanding of how polar bear populations will respond to a variety of stressors modulated by climate change, including contaminant and pathogen exposures, changes in food web structure and prey accessibility, and changes in spatial distribution.

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A view across the ice in the Arctic

A view across the ice in the Arctic.
​​​​​​​(Credit: Mike Lockhart, USGS. Public domain.)

Effects of declining sea ice on polar bear energetics

Recent declines in sea ice have been linked to reductions in body condition, survival, and population size of polar bears (Ursus maritimus). Reduced access to prey is hypothesized as the primary mechanism of sea-ice linked declines, but polar bears may also experience increased energy expenditure as they respond to changing sea ice composition and extent and prey distributions.  As a result, information on the degree to which polar bears can balance food intake with energetic costs has become increasingly important.

A recently published study from this work found that metabolic rates of polar bears were 1.6 times higher than previously assumed.  Importantly, this study also documented that low predation success by adult female polar bears in the Beaufort Sea during the spring coupled with high energetic costs resulted in a loss of ≥10% body mass of an 8-11 day period.  Spring is typically a period of increasing body mass for polar bears, particularly for females that spent the previous 4 months or more denning and have additional energetic costs to lactate for their cubs.

Linking changes in nutritional ecology to individual- and population-level consequences

Although polar bears could be affected by declining sea ice habitat in a variety of ways, the primary way in which sea ice loss is expected to affect polar bears is by reducing foraging opportunities. Polar bears may experience fewer hunting opportunities if sea ice is reduced to the point of limiting access to their primary prey, ringed seals (Phoca hispida), or if ringed and bearded seals (Erignathus barbatus) respond to sea ice loss by spending more time in open water and less time hauled out on ice, or if changes to sea ice affect reproduction and survival in seal populations. Prey populations may change in abundance and distribution altering the composition of polar bear diets or changing total food intake.  Bears may spend less time on the sea ice and more time in terrestrial habitats where the availability of marine mammal carcasses may be a determinant of body condition and reproduction, or they may respond to declining food availability by conserving energy through resting and reducing their metabolic rate. In total, the long-term consequences of changes in foraging ecology associated with a changing Arctic will depend on limits in physiology and behavioral plasticity. In the short-term, behavioral plasticity and ecosystem productivity may be important factors that determine the variation in bear responses.

 

 

Drawing blood samples from an anesthetized polar bear

Drawing blood samples from an anesthetized polar bear. (Public domain.)

Risk factors of exposure to contaminants and pathogens

Health is a difficult concept to articulate and measure, but it’s critically important to understand: an animal’s health reflects the interaction between its behavioral choices and the environment. A warming climate has the potential to drive profound changes in the health of Arctic fauna including polar bears. We are collecting data on a variety of systems that help determine polar bear health and using those data to develop monitoring and surveillance programs for detecting changes in population health over time. Additionally, this work is allowing us to develop a deeper understanding of how polar bear populations will respond to a variety of stressors modulated by climate change, including pathogens, pollutants and contaminants, and food web structure. Identifying and monitoring health-based threats to polar bears was identified as a priority information need by wildlife managers.

Polar bears have been shown to be increasingly spending time on land during the summer in response to sea ice loss.  A recent study published from this project found that exposure to some pathogens, including Toxoplasma gondii, was higher for bears that summered on land compared to those that summered on the sea ice.  Two pathogens, Toxoplasma gondii and Brucella spp., appeared to increase over time and several new pathogens were observed in polar bears that had not been documented previously.  These results suggest that changes in the Arctic marine ecosystems not only have direct effects on polar bear access to food resources and energetic costs, but may also increase exposure risk to pathogens that polar bears had previously not been exposed to.