Pelagic vs Coastal—Key Drivers of Pollutant Levels in Barents Sea Polar Bears with Contrasted Space-Use Strategies

Abstract

In the Barents Sea, pelagic and coastal polar bears are facing various ecological challenges that may explain the difference in their pollutant levels. We measured polychlorinated biphenyls, organochlorine pesticides, polybrominated diphenyl ethers in fat, and perfluoroalkyl substances in plasma in pelagic and coastal adult female polar bears with similar body condition. We studied polar bear feeding habits with bulk stable isotope ratios of carbon and nitrogen. Nitrogen isotopes of amino acids were used to investigate their trophic position. We studied energy expenditure by estimating field metabolic rate using telemetry data. Annual home range size was determined and spatial gradients in pollutants were explored using latitude and longitude centroid positions of polar bears. Pollutant levels were measured in harp seals from the Greenland Sea and White Sea-Barents Sea as a proxy for a West-East gradient of pollutants in polar bear prey. We showed that pelagic bears had higher pollutant loads than coastal bears because: (1) they feed on higher proportion of marine and higher-trophic level prey, (2) they have higher energy requirements and higher prey consumption, (3) they forage in the marginal ice zones, and (4) they feed on prey located closer to pollutant emission sources/ transport pathways.

The influence of global climate change on accumulation and toxicity of persistent organic pollutants and chemicals of emerging concern in Arctic food webs

“…177,179,180 A comparison of selected polar bears with similar body conditions in the Barents Sea, showed that offshore polar bears were exposed to higher concentrations of pollutants than coastal bears and that this was related to differences in feeding habits, energy expenditure, and geographical distribution. 41 Nonetheless, since offshore bears were, on average, fatter than coastal ones, 181,182 plasma concentrations of lipophilic POPs were overall similar in bears with different strategies, and only proteinophilic PFASs were higher in pelagic bears. 181 Compound-specic and bulk stable isotopes (d 15 N and d 13 C), home range, eld metabolic rates (based on telemetry), as well as contaminant levels in harp seal prey from different locations, cumulatively indicated that higher POP concentrations in offshore Barents Sea polar bears were related to a combination of factors, including the consumption of greater proportions of high-trophic level and marine-based prey, higher levels of POPs in prey species, larger energy requirements, and distribution in marginal ice zones (Fig.…”

“…Studies from the Barents Sea have reported higher levels of lipophilic POPs and per-and polyuoroalkyl substances (PFASs) in polar bears (Ursus maritimus) that use high-quality sea ice habitats (i.e., the marginal ice zone) in eastern Svalbard/Barents Sea, compared to bears using habitats with less or no sea ice in western Svalbard. [38][39][40][41] These differences may be inuenced by the presence/absence of sea ice, 14 in addition to other biotic factors, which are discussed in Section C. The presence of sea ice is likely to increase uptake of atmospherically-deposited POPs into the marine food web. For example, PFASs deposited on surface snow are released and concentrated into the meltwater at the base of the snowpack by the end of the melting period, 42 which is followed by phytoplankton bloom and subsequently large increases of zooplankton biomass.…”

“…(A) Concentrations of lipid-soluble POPs are similar in fatter, offshore polar bears and in thinner, coastal bears from the Barents Sea, whereas PFAS concentrations are more elevated in the offshore bears 181. (B) When comparing offshore and coastal bears of similar condition, however, offshore polar bears are exposed to higher levels of POPs than coastal polar bears due to differences in feeding habits, energy expenditure, and geographical distribution 183. Tracks of offshore polar bears shown in blue, and tracks of coastal polar bears shown in orange.…”

Comparison Between Trophic Positions in the Barents Sea Estimated From Stable Isotope Data and a Mass Balance Model

“…The whale FGs with SI data in this study included baleen and toothed whales and long distance seasonal migrants (blue whales, fin whales, minke whales) and all-year resident whales in the Barents Sea (e.g., harbor porpoise and killer whales). Individual feeding specialization was found for killer whales and polar bears (Blévin et al, 2019;Jourdain et al, 2020). Some killer whales specialize in feeding on coastal seals and show high δ 15 N values while the majority of the individuals feed on herring (Jourdain et al, 2020), and have relatively low δ 15 N values and low standard deviation of δ 15 N value (SD = 0.05) (Supplementary Table 4).…”

Harbour Seals: Population Structure, Status, and Threats in a Rapidly Changing Environment

“…Southern populations in close proximity to human settlements, typically carry heavier pollutant loads compared to their northern counterparts. Heavy contaminant loads in marine mammals are associated with compromised immune systems, hormonal disruptions and increased parasite burden [204][205][206]. Although few major sources of pollution typically originate in the Arctic, this region is nevertheless exposed to pollutants through atmospheric and marine transport and freshwater runoff.…”