An on-ice aerial survey of the Kane Basin polar bear (Ursus maritimus) subpopulation

Øystein Wiig,Eric V Regehr,Todd Arnold,Kristin L Laidre,Nicholas J Lunn,Markus Dyck,Seth Stapleton,Stephen N Atkinson,Erik W Born

doi:10.1007/s00300-021-02974-6

Abstract

There is an imminent need to collect information on distribution and abundance of polar bears (Ursus maritimus) to understand how they are affected by the ongoing decrease in Arctic sea ice. The Kane Basin (KB) subpopulation is a group of high-latitude polar bears that ranges between High Arctic Canada and NW Greenland around and north of the North Water polynya (NOW). We conducted a line transect distance sampling aerial survey of KB polar bears during 28 April–12 May 2014. A total of 4160 linear kilometers were flown in a helicopter over fast ice in the fjords and over offshore pack ice between 76° 50′ and 80° N′. Using a mark-recapture distance sampling protocol, the estimated abundance was 190 bears (95% lognormal CI: 87–411; CV 39%). This estimate is likely negatively biased to an unknown degree because the offshore sectors of the NOW with much open water were not surveyed because of logistical and safety reasons. Our study demonstrated that aerial surveys may be a feasible method for obtaining abundance estimates for small subpopulations of polar bears.

Highlights

A growing body of evidence indicates that polar bears (Ursus maritimus) are being affected by long-term climate change, primarily through reductions in the availability and quality of their sea ice habitat (e.g. Regehr et al 2007; Rode et al 2010; Atwood et al 2015; Lunn et al 2016; Obbard et al 2016; Laidre et al 2018a, b; 2020a, b)
A longer period of open water may lead to increased marine productivity that affect higher levels of the food web (Laidre et al 2020a), including ringed (Pusa hispida) and bearded seals (Erignathus barbatus) that are the primary prey of polar bears; these habitat changes may enhance per capita food availability for some multi-year sea ice subpopulations of polar bears (Derocher et al 2004; Stirling and Derocher 2012; Laidre et al 2020a)
Neither mark-resighting nor distance-based estimates of detection probability were influenced by cluster size (AIC increased by 0.2 to 2.0 units whenever cluster size was included as a covariate), so we used mean cluster size for abundance estimation

Summary

Introduction

A growing body of evidence indicates that polar bears (Ursus maritimus) are being affected by long-term climate change, primarily through reductions in the availability and quality of their sea ice habitat (e.g. Regehr et al 2007; Rode et al 2010; Atwood et al 2015; Lunn et al 2016; Obbard et al 2016; Laidre et al 2018a, b; 2020a, b). A longer period of open water may lead to increased marine productivity that affect higher levels of the food web (Laidre et al 2020a), including ringed (Pusa hispida) and bearded seals (Erignathus barbatus) that are the primary prey of polar bears; these habitat changes may enhance per capita food availability for some multi-year sea ice subpopulations of polar bears (Derocher et al 2004; Stirling and Derocher 2012; Laidre et al 2020a). Given variability in timing and direction of responses exhibited by polar bears to climate change, research and monitoring are needed rangewide to implement state-dependent (i.e., dependent on current conditions) management (Regehr et al 2017a, b), assess population viability (Lunn et al 2016), and understand the species’ ability to adapt to changing conditions (Vongraven et al 2012). Accurate and timely information is essential for adaptive management measures such as harvest level adjustments or supplemental feeding, and for detecting sudden changes in subpopulation status (Derocher et al 2013)

Methods

Results

Conclusion