Wrangel Island, Russia is well-known as a critical denning location in the Chukchi Sea polar bear (Ursus maritimus) population, but little is known about abundance and distribution of bears there. Our objective was to apply high-resolution satellite imagery (VHR; 0.3–0.5 m resolution) methods to estimate the density and abundance of bears on Wrangel Island. We used image-differencing to search 9% of the island and count polar bears on WorldView-3 imagery. We calculated potential densities of polar bears under three stratification scenarios: (1) one stratum, assuming constant density across the search area; (2) two strata, delineated into a higher-density area within 8 km around the coast and a lower density in the Wrangel Island interior; and (3) three strata such that the higher-density, coastal zone was bisected between the north and south coasts, since polar bears may be more likely to be present on the northern coast given the northward recession of sea-ice throughout summer. We counted 26 bears on this single image, resulting in density estimates ranging from 1 to 18 polar bears/100 km2. Assuming constant densities within each strata across the island, abundance estimates may range from 290 to 331 independent polar bears during August 2015. These estimates of density and abundance are comparable to previous research on Wrangel Island, although our estimates require ground validation and should be interpreted with caution. Using WV-03 imagery provides increased spatial resolution that is expanding applications and increasing our ability to detect polar bears.
Bibliographical noteFunding Information:
We thank the United States Geological Survey and the University of Minnesota for funding our work. We offer our thanks to M. Kshirsagar for consultation on methods, the Polar Geospatial Center for image processing, and to T. Arnold for advising and for reviewing previous drafts of this manuscript. We also thank three anonymous reviewers for their feedback on previous versions of this manuscript. The authors declare that they have no conflict of interest.
© 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
- High-resolution satellite imagery
- Marine mammal
- Population estimation
- Ursus maritimus
- Wrangel Island