Polar cod early life stage exposure to potential oil spills in the Arctic.

Arctic amplification of climate change is causing sea ice to retreat at unprecedented rates, potentially opening up large vulnerable Arctic areas for oil and gas exploration and new shipping routes. This rapid warming marginalizes sympagic species habitats making them more sensitive to other anthropogenic pressures. Here, we assess potential impacts of hypothetic oil spills from the northernmost licensed oil field Wisting and additional neighbouring spill sites in areas currently not open to oil exploitation on the key ice-associated Arctic fish species polar cod (Boreogadus saida). We do this by developing and running combined data-driven models for the ocean, oil spill dispersal and fate, and the early life stages of polar cod. Sea ice and the Polar Front act as natural barriers limiting the exchange of polar cod eggs and larvae and oil spill between Atlantic and Polar Water. However, both barriers vary seasonally so that the sea ice retreats and the Polar Front weakens towards summer causing significant increases in oil exposure to early life stages of polar cod under varying oil spill scenarios investigated here. Previous literature emphasizes that fall feeding conditions must be sufficient for juvenile polar cod to allocate lipids and survive their first winter. Here, we show that less than half the exposed individuals experience these suitable feeding conditions in the fall. The seasonal exposure intensity suggests a need for petroleum regulations with temporal and spatial limitations varying through the year. However, even with these seasonal dynamic regulations in place, climate change induced by the use of fossil fuel will likely reduce these natural barriers through continued sea ice retreat and a weakening of the Polar Front thereby reducing their barrier effects. Risk assessments of anthropogenic impacts on key Arctic ecosystem components in the vicinity of the ice edge zone and the Polar Front will therefore have to be updated to account for these major changes.