Integrated Population Modeling Provides the First Empirical Estimates of Vital Rates and Abundance for Polar Bears in the Chukchi Sea

Abstract

Large carnivores are imperiled globally, and characteristics making them vulnerable to extinction (e.g., low densities and expansive ranges) also make it difficult to estimate demographic parameters needed for management. Here we develop an integrated population model to analyze capture-recapture, radiotelemetry, and count data for the Chukchi Sea subpopulation of polar bears (Ursus maritimus), 2008–2016. Our model addressed several challenges in capture-recapture studies for polar bears by including a multievent structure reflecting location and life history states, while accommodating state uncertainty. Female breeding probability was 0.83 (95% credible interval [CRI] = 0.71–0.90), with litter sizes of 2.18 (95% CRI = 1.71–2.82) for age-zero and 1.61 (95% CRI = 1.46–1.80) for age-one cubs. Total adult survival was 0.90 (95% CRI = 0.86–0.92) for females and 0.89 (95% CRI = 0.83–0.93) for males. Spring on-ice densities west of Alaska were 0.0030 bears/km2 (95% CRI = 0.0016–0.0060), similar to 1980s-era density estimates although methodological differences complicate comparison. Abundance of the Chukchi Sea subpopulation, derived by extrapolating density from the study area using a spatially-explicit habitat metric, was 2,937 bears (95% CRI = 1,552–5,944). Our findings are consistent with other lines of evidence suggesting the Chukchi Sea subpopulation has been productive in recent years, although it is uncertain how long this will continue given sea-ice loss due to climate change.

Interrelated ecological impacts of climate change on an apex predator

“…Such relationships also have not been identified for some polar bear subpopulations that are experiencing sea ice loss but inhabit biologically productive regions (e.g., the Chukchi Sea; Regehr et al. ). However, it is not clear whether this finding provides evidence that the current 90‐d ice‐free season in BB is sufficient to maintain survival, despite the apparent negative effects on BCS and reproductive indices.…”

“…Additional insight into reproductive performance and viability might be gained from an analysis of mark–recapture data using a multistate model based on the life history of polar bears (e.g., Regehr et al. ) coupled with a population viability analysis based on the estimated vital rates and their relationships with environmental conditions.…”

“…Although triplet litters may occur in some productive subpopulations (e.g., Regehr et al. ), only 2 of 299 litters for the BB subpopulation consisted of three cubs. Thus, we considered litter size for adult female i in year t to be a binary response variable (i.e., ls it = 1 or 2).…”

Incorporating citizen science data in spatially explicit integrated population models

“…Custom MCMC samplers may help alleviate implementation barriers, especially if model complexity is added to account for dependence between detection processes, temporal patterns, dispersal (Chandler and Clark ), or age‐related demographic rates (Regehr et al. ).…”

An integrated population model for estimating the relative effects of natural and anthropogenic factors on a threatened population of Pacific trout

“…Although IPMs have been widely developed and applied to mammals (e.g., Eacker et al . 2017; Regehr et al . 2018) and birds (e.g., Crawford et al .…”