Space and habitat use of polar bears (Ursus maritimus) in Davis Strait in relation to sea ice conditions and harp seals (Pagophilus groenlandicus)

• Author / Creator

  Thelin, Larissa

• Patterns of space use and habitat selection by polar bears (Ursus maritimus) vary among subpopulations where they have been studied. The Davis Strait subpopulation is one of the least researched polar bear subpopulations and their spatial ecology is largely unknown. As an obligate carnivore, polar bears rely largely on seals as their primary prey, yet predator-prey spatial relationships are poorly studied. In order to assess the spatial relationship between polar bears in Davis Strait and harp seals, one of their primary prey, we first analyzed trends in sea ice dynamics to understand sea ice conditions that may affect each species’ distribution. We found that the availability of sea ice for polar bears decreased over time, resulting in a significant lengthening of the ice-free season (10.9 d/decade). We used remotely sensed imagery of sea ice (1979 – 2021) in relation to the movements of both polar bears (n=27) and harp seals (n=29) as determined by satellite telemetry. We calculated annual home range sizes, seasonal movement rates, and seasonal directionality for the Davis Strait subpopulation of polar bears (1991 – 2001). The mean annual home range size of polar bears was 101,775 km2 (range=699-280,539 km2) but varied with the statistical method used. Bears travelled a mean speed of 0.53 km/h (range=0-2.19 km/h) with the fastest rates in winter and slowest in freeze-up. Bears showed significant southward orientation during break-up and northward orientation during freeze-up but had no significant orientation in winter. We used resource selection functions to analyze seasonal habitat selection for both polar bears (1991 – 2001) and harp seals (1993 – 2005). The only covariate important to bear resource selection was distance to land during break-up, with null models placing top for the other seasons. For harp seals, ocean depth, sea ice concentration, distance to land, distance to open water, and distance to open water 2 were selected but their importance varied by season. To investigate the seasonal overlap in habitat between these two species, we compared resource selection and mapped seasonal kernel density overlap. We found that sea ice season affected space use and habitat selection for both species. Polar bears and harp seals were more likely to overlap during break-up and freeze-up but did so to a greater extent during freeze-up, but this may be due to sampling methods. This study illustrates the need to collect more polar bear telemetry data, particularly for those in less-studied regions. With climate change altering available habitats for all polar bear subpopulations, there is an urgency to understand how they are being spatially affected by a changing environment and our study provides a starting point for future studies.

• Subjects / Keywords

  • space use
  • habitat selection
  • polar bear
  • harp seal
  • Arctic
  • climate change

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-ktsj-ed93

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.