Our point estimates are larger than, but of similar magnitude to, a recent estimate for the period 2008-2016 ( 95% CI 1,522-5,944) derived from an integrated population model applied to a slightly smaller area. Estimates of 2016 abundance ( ) ranged from 3,435 (95% CI: 2,300-5,131) to 5,444 (95% CI: 3,636-8,152) depending on the proportion of bears assumed to be missed on the transect line during Russian surveys ( g(0)). Using spatio-temporal statistical models that related bear and track densities to physiographic and biological covariates (e.g., sea ice extent, resource selection functions derived from satellite tags), we predicted abundance and spatial distribution throughout our study area. Our surveys used a combination of thermal imagery, digital photography, and human observations. In a collaborative U.S.-Russian effort in spring of 2016, we used aerial surveys to detect and estimate the abundance of polar bears on sea ice in the Chukchi Sea. Polar bears are of international conservation concern due to climate change but are difficult to study because of low densities and an expansive, circumpolar distribution.
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