Changes in winter and spring resource selection by polar bears Ursus maritimus in Baffin Bay over two decades of sea-ice loss

Abstract

Loss of Arctic sea ice has implications for the distribution and population structure of ice-dependent species such as polar bears Ursus maritimus. We used remotely sensed sea-ice concentration data for Baffin Bay, Canada, and satellite telemetry for adult female polar bears in the 1990s (n = 43) and 2000s (n = 38) to assess whether sea-ice habitat changes have influenced movements and habitat selection. Both the timing and availability of sea-ice habitat changed significantly between the 1990s and 2000s. Mean sea-ice concentration in June−October declined from 22 to 12%. Spring sea-ice retreat occurred 2 wk earlier and fall sea-ice advance 2 wk later in the 2000s. These changes translated directly to changes in habitat use by polar bears. In the 2000s, bears used significantly lower sea-ice concentrations in winter and spring. Also, bears were significantly closer to land in all months, except at the end of spring breakup when they remained on offshore sea ice as long as possible, likely to maximize foraging time prior to coming on land where they are largely food deprived. The presence of summer offshore sea ice facilitated broad movement of bears in the 1990s; however, this ice disappeared in the 2000s and resulted in significant declines in monthly movement rates. In the 2000s, adult females selected for lower sea-ice concentrations if they facilitated access to the continental shelf (< 300 m). Our findings indicate that significant changes in available sea-ice habitat and habitat use in Baffin Bay have occurred since the mid-1990s and this subpopulation will likely experience negative population-level impacts related to a changing climate in the coming decades. In some other parts of the Arctic, such changes have preceded negative nutritional and demographic impacts.

Interrelated ecological impacts of climate change on an apex predator

“…, Stirling and Parkinson , Laidre et al. , b). In other regions, bears may remain on offshore pack ice (e.g., Wiig et al.…”

Correlates of seasonal change in the body condition of an Arctic top predator

“…The largest decrease occurred during late winter–early spring (February/March–April/May) in all subpopulations and was likely a result of low prey availability (Stirling & Øritsland, ). Consistent with reduced foraging success, polar bears significantly reduce movement rates and activity levels from late summer through to winter (Ferguson et al, ; Laidre et al, ; Messier, Taylor, & Ramsay, ; Ware et al, ), which may help conserve stored energy during periods of low prey accessibility.…”

“…These bears travel along the advancing ice edge, presumably searching for prey (McCall, Pilfold, Derocher, & Lunn, ). Laidre et al () suggested bears in Baffin Bay follow the ice edge eastward towards Greenland with access to feeding areas off west Greenland during the winter months. Winter feeding may explain the increase in body condition from November to January in Baffin Bay bears.…”

“…Polar bears prefer ice over the continental shelf (≤300 m depth; e.g. Derocher et al, 2004;Durner et al, 2009;Laidre et al, 2018;Rode et al, 2014), which accounts for less than 30% of the Baffin Bay and…”

“…Laidre et al (2018) suggested bears in Baffin Bay follow the ice edge eastward towards Greenland with access to feeding areas off west Greenland during the winter months.Winter feeding may explain the increase in body condition from November to January in Baffin Bay bears.The ecological and environmental factors influencing seasonal changes in polar bear body condition appeared to differ regionally.…”