Demographic response of a high-Arctic polar bear (Ursus maritimus) subpopulation to changes in sea ice and subsistence harvest

Abstract

Climate change is a long-term threat to polar bears. However, sea-ice loss is hypothe-sized to provide transient benefits in high latitudes, where thick multiyear ice historically limited biological productivity and seal abundance. We used joint live-recapture and dead-recovery mark-recapture models to analyze data for one of the most northerly polar bear subpopulations, Kane Basin. The data consisted of 277 initial live captures and genetic identifications (1992-1997 = 150, 2012-2014 = 127), 89 recaptures or re-identifications (1992-1997 = 53, 2012-2014 = 36), and 24 harvest returns of research-marked bears during 1992-2014. We estimated mean annual abun-dance of 357 bears (95% CI: 221-493) for 2013-2014. This suggests a likely increase relative to our estimate of 224 (95% CI: 145-303) bears in the mid-1990s and relative to a previously published estimate of 164 (95% CI: 94-234) bears in the mid-1990s that used some of the same data. This is also supported by an apparent increase in the density of bears in eastern Kane Basin during 2012-2014. Estimates of total survival for females >3 yr old (mean ± SE: 0.95 ± 0.04) and their dependent offspring were similar to previous estimates from the 1990s, and estimates of unharvested survival for females >3 yr (0.96 ± 0.04) appear sufficient for positive population growth. Estimates of total survival were lower for males >3 yr (0.87 ± 0.06). We documented a reduction in mortality associ-ated with subsistence harvest, likely attributable to implementation of a harvest quota by Green-land in 2006. Our findings, together with evidence for increased range sizes, improved body condi-tion for all sex and age classes, and stable reproductive metrics, show that this small high-Arctic polar bear subpopulation remains productive and healthy. These benefits are likely temporary given predictions for continued climate change.