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Marine Ecology Progress Series

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MEPS 677:233-244 (2021)  -  DOI:

Feeding habits of Baffin Bay polar bears Ursus maritimus: insight from stable isotopes and total mercury in hair

Jennifer H. Stern1,*, Kristin L. Laidre2,3, Erik W. Born3, Øystein Wiig4, Christian Sonne5, Rune Dietz5, Aaron Fisk6, Melissa A. McKinney7,8

1School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105, USA
2Polar Science Center, Applied Physics Laboratory, University of Washington, Seattle, WA 98105, USA
3Greenland Institute of Natural Resources, PO Box 570, 3900 Nuuk, Greenland
4Natural History Museum, University of Oslo, PO Box 1172 Blindern, 0318 Oslo, Norway
5Department of Ecoscience, Arctic Research Centre, Aarhus University, 4000 Roskilde, Denmark
6School of the Environment, University of Windsor, Windsor, ON N9B 3P4, Canada
7Department of Natural Resource Sciences, McGill University, Ste.-Anne-de-Bellevue, QC H9X 3V9, Canada
8Department of Natural Resources and the Environment and Center for Environmental Sciences and Engineering, University of Connecticut, Storrs, CT 06269, USA
*Corresponding author:

ABSTRACT: Loss of sea ice brought on by climate change affects polar bear Ursus maritimus access to prey. Here we investigated variation in feeding habits of the Baffin Bay (BB) polar bear subpopulation in relation to sea ice, habitat use, season, and demography using hair carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) stable isotope values and total mercury (THg) concentrations as ecological tracers. We analyzed hair samples from BB polar bears (n = 131) of all age and sex classes live-captured in West Greenland during the spring in 2009-2013. BB polar bears occupied a narrow isotopic space, suggesting limited variation in carbon sources and trophic position within the subpopulation. THg concentrations (median ± SE: 5.1 ± 0.2, range: 0.3-12.5 µg g-1 dry weight, DW) were related to age class, and nearly half exceeded the suggested threshold for neurological effects in polar bears at 5.4 µg g-1 DW. Although distinct coastal and offshore space-use strategies have been reported for BB polar bears, our results suggest that both strategies lead to similar carbon sources and trophic positions. We found seasonal variation in δ13C and δ34S across both space-use strategies, with δ34S suggesting that all BB polar bears may prey on a higher proportion of benthic-feeding bearded seals Erignathus barbatus in late summer relative to spring. Despite wide fluctuations in inter-annual sea ice conditions and differences in space-use strategies among individuals, stable isotope values and THg concentrations suggested limited variation in feeding habits among BB polar bears. The variation of habitat tracers (δ13C and δ34S) was related to season, whereas trophic tracer (δ15N and THg) variation was driven by demographic group. The specialized BB polar bear diet suggests limited feeding plasticity under continued climate warming.

KEY WORDS: Arctic · Polar bear · Ursus maritimus · Feeding ecology · Dietary tracers · Greenland · Mercury

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Cite this article as: Stern JH, Laidre KL, Born EW, Wiig Ø and others (2021) Feeding habits of Baffin Bay polar bears Ursus maritimus: insight from stable isotopes and total mercury in hair. Mar Ecol Prog Ser 677:233-244.

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