Aerial survey estimates of polar bears and their tracks in the Chukchi Sea

PLoS One. 2021 May 6;16(5):e0251130. doi: 10.1371/journal.pone.0251130. eCollection 2021.

Abstract

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. 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. Our surveys used a combination of thermal imagery, digital photography, and human observations. 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. Estimates of 2016 abundance ([Formula: see text]) 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)). Our point estimates are larger than, but of similar magnitude to, a recent estimate for the period 2008-2016 ([Formula: see text]; 95% CI 1,522-5,944) derived from an integrated population model applied to a slightly smaller area. Although a number of factors (e.g., equipment issues, differing platforms, low sample sizes, size of the study area relative to sampling effort) required us to make a number of assumptions to generate estimates, it establishes a useful lower bound for abundance, and suggests high spring polar bear densities on sea ice in Russian waters south of Wrangell Island. With future improvements, we suggest that springtime aerial surveys may represent a plausible avenue for studying abundance and distribution of polar bears and their prey over large, remote areas.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Arctic Regions
  • Female
  • Male
  • Population Density
  • Spatio-Temporal Analysis
  • Ursidae*

Grants and funding

Funding for surveys was provided primarily by the U.S. National Oceanic and Atmospheric Administration (NOAA) and the U.S. Fish & Wildlife Service (USFWS). These funders provided support in the form of salaries for authors [PC, EM, ER, RW, and PB], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. Support for Russian surveys was provided by NOAA through the North Pacific Wildlife Consulting, LLC (http://www.northpacificwildlife.com/). Portions of the analysis were supported by joint subaward NA17NMF4720289, project 1813, from the North Pacific Research Board and The Prince William Sound Oil Spill Recovery Institute (https://www.nprb.org/core-program/about-the-program/; PL, ER, IT, EM, and PC were principal or co-investigators). Additional support for data processing and survey logistics on the Russian side was provided by USFWS, the RPO Marine Mammal Council (https://marmam.ru/en/) and WWF Russia (https://wwf.ru/en/about/) in funding agreements with VC. External funders (e.g., NPRB, WWF Russia) had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.