Evaluation of polar bear movement patterns in relation to sea ice drift

Abstract

The polar bear inhabits mainly the Arctic sea ice, where it moves and hunts. The study of polar bear movements aimed mostly at determining the bear sea sonal habitats [1] and evaluating the size of its home ranges [2]. However, the ice where the polar bear lives is drifting, and the ice drift have a substantial influence on the trajectory of animal relocations. The sea ice motion has been earlier assessed only qualitatively, but the rate and direction of sea ice drift should be mea sured quantitatively to evaluate correctly the animal movements on ice. A technique of quantitative mea surement has been elaborated in this study.To study the polar bear movements, a collar with a built in radio transmitter of the Argos satellite system is usually mounted onto an adult female. The sea ice drift in Arctic is estimated using autonomous buoys, satellite images, and modeling. Data assimilation improves the accuracy of estimation.The object of our study was one out of three female polar bears that we have tagged on the island Alexan dra Land of the Franz Josef Land archipelago [3]. This animal moved throughout the Barents Sea, which is an area of high sea ice dynamics. The data transmitted from the satellite collar on the bear provided informa tion about the accuracy of coordinates, which were used to plot the trajectory with a standard 24 h time step of vertices, which corresponded to the animal position at 12:00 UTC. Erroneous locations were excluded manually from the trajectory. Position coor dinates were calculated using the weighted mean of locations (±12 h), accuracy class, and time interval from the noon. The resultant trajectory has been con structed using 165 locations from Several datasets of ice drift have been used from OSISAF [4], CERSAT [5], and NSIDC [6] providers. To verify visually these datasets, an independent eval uation of ice drift used the data on the concentration and brightness temperature measured with an AMSR E microwave radiometer [7].The ice drift is evaluated from the satellite data by the method of maximum cross correlation [3]. Each out of four 36 and 89 GHz channels of both polariza tions is treated independently with different sizes of the search areas and with overview of the ice edge posi tion, surface wind, and sea level pressure.To localize the female polar bear, the vectors of sea ice drift have been constructed using spatial interpola tion by the method of ordinary kriging [8] with a max imum distance of 200 km. Variogram is approximated by Bessel function yielding the least error values as compared to other functions.The OSISAF dataset estimates ice drift for a 2 day interval, CERSAT reflects ice movement for 2, 3, and 6 days according to AMSR E and for 3 and 6 days according to ASCAT, the combined ASCAT and SSM/I data for 3 and 6 days, and the combined Quik SCAT and SSM/I data for 3 and 6 days. The average daily ice drift is withdrawn from the original NSIDC set in the uniform grid.To match the data on sea ice drift and the data on the polar bear movements, the animal locations wer...

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

“…() and Platonov et al. () as well as the disparity between our estimates and those provided by Kwok et al. () could be attributed to methodology.…”

“…In contrast, Platonov et al. () found that a female polar bear in the Barents Sea covered approximately 25% less distance when her path was corrected for sea ice drift. It is likely that regional and temporal variations in ice motion, and the distribution of prey, affect the relationship between collar displacement and drift‐corrected bear movements.…”

“…() estimated ice drift at bear locations in the Barents Sea during 1988–2001 at 4.28 km/day whereas in 2011, Platonov et al. () observed ice drift rates of 8.2–10.2 km/day for locations from one polar bear in this area. However, some of the differences in estimates of sea ice drift between Mauritzen et al.…”

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, ).…”

“…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).…”