Abstract
Climate warming has resulted in extensive sea ice loss across the Arctic. Polar bears (Ursus maritimus) rely on sea ice for hunting, resting, travelling and in some parts of the Arctic also maternity denning. In the European Arctic, polar bears rely on snow drifts on land to den and give birth. Consequently, timely arrival of sea ice around land masses during autumn is important for pregnant females to reach their denning habitat from their sea ice hunting grounds. We defined denning habitat as landforms necessary to accumulate snow to a depth sufficient for dens. We quantified availability of terrestrial denning habitat across the three European Arctic archipelagos throughout the last four (1979–2020) and the next eight decades (until 2100) using arrival of autumn sea ice around these islands. Across the study area, a clear trend was visible towards later sea ice arrival, varying up to 102 days. Female polar bears in the European Arctic now have 33% denning habitat available compared to the 1980's as many areas became inaccessible in time to start maternity denning. By the 2090's, all areas were projected to be inaccessible to pregnant bears. This decline was unequally distributed, with most reduction in Svalbard and Novaya Zemlya until 2020, whilst denning habitat availability in Franz Josef Land remained unchanged until 2020 but is predicted to become inaccessible by the end of the century. This work emphasizes the importance of the temporal dimension of sea ice dynamics for the persistence of polar bear populations.
Highlights
Climate change impacts are already evident in every ecosystem globally (Scheffers et al 2016)
As polar bears in general spend much of the year on sea ice, their life cycle is tightly linked to its seasonality, as it retreats in the spring and advances in the fall
Timing of arrival of pregnant females in maternity denning areas varies amongst populations ranging from months to days before den entry, depending on local sea ice dynamics around these denning areas (Ramsay and Stirling 1990; Fischbach et al 2007)
Summary
Climate change impacts are already evident in every ecosystem globally (Scheffers et al 2016). Ice-associated species such as polar bears Ursus maritimus are vulnerable to the effects of climate change due to the recent dramatic losses of Arctic sea ice and warming of their environment in general (Laidre et al 2015b). This apex predator has a circumpolar distribution (Amstrup 2003) and uses sea ice as its primary habitat, as a platform to travel and hunt, the main prey being ice-associated seal species, in particular the ringed seal Pusa. Derocher et al (2011) highlighted that for polar bears to persist the amount of available sea ice habitat for hunting is essential, but crucially its seasonal availability and accessibility around denning areas must be sufficient for successful polar bear reproduction
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