Polar bears stressed by Arctic warming
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Polar bears are stressed by Arctic warming, according to a new study published on the Global change biology. The polar bear lives in the Arctic and its habitat is included in 6 countries: Canada (Manitoba, Newfoundland, Northwest Territories, Nunavut, Ontario, Québec, Yukon), USA (Alaska), Russia (Krasnoyarsk, Magadan, Northwestern Federal District, Western Siberia, Yakutia), Greenland, Norway (Svalbard), Iceland.
The current population of polar bears, in sharp decline due to the climate crisis and the consequent melting of the Arctic ice, is estimated at around 20-25,000 units, of which 60% in Canada. In the article The stress of Arctic warming on polar bears, experts say: "Arctic ecosystems are changing rapidly in response to climate warming.
While Arctic mammals are highly evolved to these extreme environments, particularly with respect to their stress axis, some species may have limited capacity to adapt to this change. We examined changes in key components of the stress axis (cortisol and its carrier protein-corticosteroid binding globulin [CBG]) in polar bears (Ursus maritimus) from western Hudson Bay (N = 300) over a 33 year period (1983-2015) during which time the ice-free period was increasing.
Changing sea ice phenology limits spring hunting opportunities and extends the period of onshore fasting. We assessed the response of polar bears to a standardized stressor (helicopter pursuit , darting, and immobilization) during their onshore fasting period (late summer-autumn) and quantified the serum levels of the maximum corticosteroid binding capacity (MCBC) of CBG, the se rum protein that binds cortisol strongly, and free cortisol (FC).
We quantified bear condition (age, sex, female with cubs or not, fat condition), sea ice (breakup in spring-summer, 1 year lagged freeze-up in autumn), and duration of fasting until sample collection as well as cumulative impacts of the latter environmental traits from the previous year.
Data were separated into "good" years (1983-1990) when conditions were thought to be optimal and "poor" years (1991-2015) when sea ice conditions deteriorated and fasting on land was extended. MCBC explained 39.4% of the variation in the good years, but only 28.1% in the poor ones, using both biological and environmental variables.
MCBC levels decreased with age. Changes in FC were complex, but more poorly explained. Counterintuitively, MCBC levels increased with increased time onshore, 1 year lag effects, and in poor ice years. We conclude that MCBC is a biomarker of stress in polar bears and that the changes we document are a consequence of climate warming."