Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines

Abstract

Loss of Arctic sea ice owing to climate change is the primary threat to polar bears throughout their range. We evaluated the potential response of polar bears to sea-ice declines by (i) calculating generation length (GL) for the species, which determines the timeframe for conservation assessments; (ii) developing a standardized sea-ice metric representing important habitat; and (iii) using statistical models and computer simulation to project changes in the global population under three approaches relating polar bear abundance to sea ice. Mean GL was 11.5 years. Ice-covered days declined in all subpopulation areas during 1979–2014 (median −1.26 days year−1). The estimated probabilities that reductions in the mean global population size of polar bears will be greater than 30%, 50% and 80% over three generations (35–41 years) were 0.71 (range 0.20–0.95), 0.07 (range 0–0.35) and less than 0.01 (range 0–0.02), respectively. According to IUCN Red List reduction thresholds, which provide a common measure of extinction risk across taxa, these results are consistent with listing the species as vulnerable. Our findings support the potential for large declines in polar bear numbers owing to sea-ice loss, and highlight near-term uncertainty in statistical projections as well as the sensitivity of projections to different plausible assumptions.

Range contraction and increasing isolation of a polar bear subpopulation in an era of sea‐ice loss

“…Genetic variation in polar bears is relatively low, and genetics is a relatively insensitive means of identifying, defining, or detecting change in subpopulation structure, especially when compared to individual‐based telemetry and tag recoveries. Time‐lag effects in genetic composition are influenced by the relatively long generation length for polar bears (~11.5 years; Regehr et al., 2016), and several generations may be needed to demonstrate increased genetic isolation as a consequence of climate‐induced range contraction.…”

Projecting Marine Mammal Distribution in a Changing Climate

“…Ice-obligate species that use ice as a platform for raising young (e.g., ringed seal pupping lairs) (NOAA, 2012) or for hunting (e.g., for polar bears, Ursus maritimus), or whose prey species are closely or directly linked to ice [e.g., Antarctic fur seals (Arctocephalus gazella) (Forcada et al, 2008)] may be particularly vulnerable to declines in the extent of seasonal and multi-year ice. While some forecasting work has already been done for polar bears, ice seals, and walruses (Odobenus rosmarus) in the context of endangered species determinations under the ESA (Jay et al, 2011;Regehr et al, 2016), additional work is required to develop and refine models for species residing or occurring seasonally in high latitudes.…”

Polar bears: proceedings of the 18th working meeting of the IUCN/SSC Polar Bear Specialist Group, Anchorage, Alaska, 7-11 June 2016

“…The ice-free season within the SH subpopulation boundaries increased by about 30 days from 1980 to 2012 (Obbard et al 2016). Concurrently, body condition declined in all age and sex classes, though the decline was less for cubs than for other social classes.…”

“…There is uncertainty about the discreteness of the less studied subpopulations, particularly in the Russian Arctic and neighbouring areas, due to a lack of capture and genetic data. The total number of polar bears worldwide is estimated to be 26,000 (95% CI=22,000-31,000; Regehr et al 2016). The following subpopulation summaries are the result of discussions of the 18 th Working Meeting of the IUCN/SSC Polar Bear Specialist Group held in Anchorage, Alaska, 7-11 June, 2016.…”