Increased Arctic sea ice drift alters adult female polar bear movements and energetics

Abstract

Recent reductions in thickness and extent have increased drift rates of Arctic sea ice. Increased ice drift could significantly affect the movements and the energy balance of polar bears (Ursus maritimus) which forage, nearly exclusively, on this substrate. We used radio‐tracking and ice drift data to quantify the influence of increased drift on bear movements, and we modeled the consequences for energy demands of adult females in the Beaufort and Chukchi seas during two periods with different sea ice characteristics. Westward and northward drift of the sea ice used by polar bears in both regions increased between 1987–1998 and 1999–2013. To remain within their home ranges, polar bears responded to the higher westward ice drift with greater eastward movements, while their movements north in the spring and south in fall were frequently aided by ice motion. To compensate for more rapid westward ice drift in recent years, polar bears covered greater daily distances either by increasing their time spent active (7.6%–9.6%) or by increasing their travel speed (8.5%–8.9%). This increased their calculated annual energy expenditure by 1.8%–3.6% (depending on region and reproductive status), a cost that could be met by capturing an additional 1–3 seals/year. Polar bears selected similar habitats in both periods, indicating that faster drift did not alter habitat preferences. Compounding reduced foraging opportunities that result from habitat loss; changes in ice drift, and associated activity increases, likely exacerbate the physiological stress experienced by polar bears in a warming Arctic.

Estimating the energy expenditure of free‐ranging polar bears using tri‐axial accelerometers: A validation with doubly labeled water

“…To measure potential changes in energy expenditure, measures of body mass require repeated sampling of individuals, which is one of the limitations in the use of DLW itself. Movement rates can be calculated from satellite telemetry location data, but for polar bears, movement rates derived by satellite telemetry can be biased by sea ice drift (Auger‐Méthé, Lewis, & Derocher, ; Durner et al, ; Mauritzen, Derocher, Pavlova, & Wiig, ; Platonov et al, ). Such effects were considered minimal in the region and month of our study (Durner et al, ), where previous research indicates a bias would be more prevalent in other regions and months (Durner et al, ).…”

“…Movement rates can be calculated from satellite telemetry location data, but for polar bears, movement rates derived by satellite telemetry can be biased by sea ice drift (Auger‐Méthé, Lewis, & Derocher, ; Durner et al, ; Mauritzen, Derocher, Pavlova, & Wiig, ; Platonov et al, ). Such effects were considered minimal in the region and month of our study (Durner et al, ), where previous research indicates a bias would be more prevalent in other regions and months (Durner et al, ). In addition to this limitation, movement rates are typically calculated from comparatively infrequent location data, thus underestimating true movement paths and rates (Bidder et al, ; Kramer & McLaughlin, ; Prichard, Yokel, Rea, Person, & Parrett, ; Rowcliffe, Carbone, Kays, Kranstauber, & Jansen, ).…”

“…To measure potential changes in energy expenditure, measures of body mass require repeated sampling of individuals, which is one of the limitations in the use of DLW itself. Movement rates can be calculated from satellite telemetry location data, but for polar bears, movement rates derived by satellite telemetry can be biased by sea ice drift (Auger-Méthé, Lewis, & Derocher, 2016;Durner et al, 2017;Mauritzen, Derocher, Pavlova, & Wiig, 2003;Platonov et al, 2014).…”

Are polar bear habitat resource selection functions developed from 1985–1995 data still useful?

“…Nevertheless, the efficacy of RSFs applied at a future time should be verified, especially if environmental conditions have markedly changed (Garshelis, 2000). This is true for polar bears whose sea ice habitats have changed (Stern & Laidre, 2016) and, in the Beaufort Sea, may now use larger areas because movement rates have increased to compensate for faster sea ice drift in recent years (Auger-Méthé, Lewis, & Derocher, 2015;Durner et al, 2017). Verification is especially important when the target species is of conservation concern and efforts to monitor populations are either deficient, intermittent, or nonexistent; all of which are factors in the international attempts to monitor the 19 subpopulations of polar bears (Vongraven et al, 2012).…”

The seasonal energetic landscape of an apex marine carnivore, the polar bear

“…Nevertheless, our daily energy expenditure estimates were within range of estimates found in solitary female polar bears on the spring sea ice using doubly labeled water (Pagano et al ). Additionally, the use of accelerometers provides a method to quantify polar bear activity that is unbiased by sea ice drift unlike measures of movement rate derived from satellite telemetry location data (Mauritzen et al, , Platonov et al , Auger‐Méthé et al , Durner et al ).…”