Simulating changes in polar bear subpopulation growth rate due to legacy persistent organic pollutants – Temporal and spatial trends

Renske P.J Hoondert,Ad M.J Ragas,A Jan Hendriks

doi:10.1016/j.scitotenv.2020.142380

Renske P.J Hoondert, Ad M.J Ragas + Show 1 more

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https://doi.org/10.1016/j.scitotenv.2020.142380

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Abstract

Although atmospheric concentrations of many conventional persistent organic pollutants (POPs) have decreased in the Arctic over the past few decades, levels of most POPs and mercury remain high since the 1990s or start to increase again in Arctic areas, especially polar bears. So far, studies generally focused on individual effects of POPs, and do not directly link POP concentrations in prey species to population-specific parameters. In this study we therefore aimed to estimate the effect of legacy POPs and mercury on population growth rate of nineteen polar bear subpopulations. We modelled population development in three scenarios, based on species sensitivity distributions (SSDs) derived for POPs based on ecotoxicity data for endothermic species. In the first scenario, ecotoxicity data for polar bears were based on the HC50 (the concentration at which 50% of the species is affected). The other two scenarios were based on the HC5 and HC95. Considerable variation in effects of POPs could be observed among the scenarios. In our intermediate scenario, we predicted subpopulation decline for ten out of 15 polar bear subpopulations. The estimated population growth rate was least reduced in Gulf of Boothia and Foxe Basin. On average, PCB concentrations in prey (in μg/g toxic equivalency (TEQ)) posed the largest threat to polar bear subpopulations, with negative modelled population growth rates for the majority of subpopulations. We did not find a correlation between modelled population changes and monitored population trends for the majority of chemical-subpopulation combinations. Modelled population growth rates increased over time, implying a decreasing effect of PCBs, DDTs, and mercury. Polar bear subpopulations are reportedly still declining in four out of the seven subpopulations for which sufficient long-term monitoring data is available, as reported by the IUCN-PBSG. This implies that other emerging pollutants or other anthropogenic stressors may affect polar bear subpopulations.

Highlights

Arctic ecosystems are subjected to many threats induced by human activity
Previous research has focused on especially Arctic marine mammals, because persistent organic pollutants (POPs) levels are elevated in top predators; the fact that the marine environment accounts for a large percentage of area of the Arctic; and, the fact that many marine mammals are important components of the human diet (De Wit et al, 2004)
For the vast majority of polar bear subpopulations, variation in the model outcomes did not result in changing conclusions regarding changes in population growth rate imposed by POP exposure: Negative values remained negative in the low risk scenario, and positive values remained positive in the high-risk scenario for the majority of subpopulations

Summary

Introduction

Arctic ecosystems are subjected to many threats induced by human activity. Especially polar bears (Ursus maritimus) have received much attention, as these species are suspected to be significantly impacted by climate change, with sea ice decline hindering these species in finding prey (i.e. seals) on the ice (Jenssen et al, 2015). Polar bears depend on a lipid-rich diet, mainly consisting of ringed seal (Phoca hispida) and bearded seal (Erignathus barbatus), sometimes including other prey, such as hooded seals (Crystophora cristata), beluga whales (Delphinapterus leucas), narwhals (Monodon monoceros) and walrus (Odobenus rosmarus) (Derocher et al, 2004; Stirling and Archibald, 1977). Due to their diet and the bioaccumulative nature of POPs and mercury, high levels of these compounds have been detected in polar bears in several subpopulations in the Arctic (Letcher et al, 2010). Previous research has focused on especially Arctic marine mammals (including polar bears, beluga whales and ringed seals), because POP levels are elevated in top predators; the fact that the marine environment accounts for a large percentage of area of the Arctic; and, the fact that many marine mammals are important components of the human diet (De Wit et al, 2004)

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