Dietz, R., Rigét, F.F., Eulaers, I., Desforges, J.-P., Vorkamp, K., Bossi, R. Søndergaard, J., Ambus, P. McKinney, M., Letcher, R.L. & Sonne, C. 2021. Unexpected Increases of Persistent Organic Pollutant and Mercury levels in East Greenland Polar Bears (UNEXPECTED). Aarhus University, DCE – Danish Centre for Environment and Energy, 44 pp. Technical Report No. 214. http://dce2.au.dk/pub/TR214.pdf
Rapid climate changes are occurring in the Arctic, with substantial repercussions for arctic ecosystems which are all challenging to assess due to the remote polar environments. In the present study we were successful in monitoring the combined effects from climate change on the diet and the consecutive pollution-mediated biological health effects in EG polar bears. Quantitative fatty acid signature analysis (QFASA) and fatty acid-specific stable carbon isotope (δ13C-FA) signatures were used to assess diets of East Greenland polar bears (Ursus maritimus) over the past three decades. QFASA-generated diet estimates indicated that, on average across all years and groups, EG bears mainly consumed arctic ringed seals (44.9±18.27%), migratory subarctic harp seals (27.3±9.6%) and hooded seals (22.9±12.4%) and rarely, if ever, bearded seals (4.9±8.9%), narwhals (1.0±2.2%) and walruses (0.06±0.06%). We observed differences in this pattern among sex and age groups. Adult male polar bears deviated the most relatively to the juvenile and the adult female bears. The proportion of ringed seals was relatively stable around 50% prior to year 2000 after which it started to decline. The last year with FA data is 2016 where the ringed seal dietary percentage had declined to less than 25%. The opposite trend was observed for the hooded seals, which were in the magnitude of 15% up to 2000 after which it increased to more than 40% by 2016. Harp seals showed an increase from 15% to more than 25% from 1983 to 1994, after which their proportion in the diet remained relatively stable until 2016. No clear trends were observed for the proportions of bearded seals, walruses and narwhals. A clear relation in increased organohalogen compound (OHC) and mercury loads and a decline in per- and polyfluoroalkyl substance (PFAS) concentrations was linked to these diet shifts and for some years these relationships were quite pronounced such as in 1997 and 2013. As previously documented, declining δ13C-FA values supported shifts from more nearshore and ice-associated prey to more offshore pelagic associated prey, consistent with the diet estimates. Increased hooded and decreased ringed seal consumption occurred during years when the North Atlantic Oscillation index was lower. Thus, periods with warmer temperatures and less sea ice were associated with more subarctic (hooded seal and harp seal) and less arctic ringed seal species consumption. These changes in the relative abundance, accessibility, or distribution of arctic and subarctic marine mammals may have health consequences for East Greenland polar bears. For example, the diet change resulted in consistently slower temporal declines in adipose levels of legacy OHCs and PFASs, as the subarctic seals have higher contaminant burdens than arctic seals. Overall, considerable changes are occurring in the East Greenland marine ecosystem, with consequences for contaminant dynamics in arctic top predators and potentially also in subsistence societies.
