Implications of a fuel spill in the Bering and Chukchi Seas for two sentinel marine species: A simulation study.

Sea-ice decline has opened Arctic shipping routes lengthening the maritime transit season. Along the Northern Sea Route (NSR), vessel traffic is projected to increase primarily from natural resource development-related traffic. The NSR traverses the range of the Chukchi Sea (CS) polar bear (Ursus maritimus) subpopulation, and Pacific walrus (Odobenus rosmarus divergens) haulouts dot Russian islands and mainland, the Alaska coast, and the Bering Strait along the NSR. Oil spills are a primary threat to marine Arctic wildlife from maritime traffic with the potential to affect many individuals. We estimated the number of polar bears and walruses potentially exposed to oil from a CS or Bering Strait ship-based spill. We simulated five large-scale boat-based spills in two NSR locations in August and October for crude and marine gas oil (MGO). We overlaid polar bear radio collar locations onto trajectories to estimate the number exposed. If oil was ≤0.5 nm from a haulout, we deemed the haulout exposed. We report the most impactful scenario to help managers and emergency responders understand the upper levels of impact to these species and inform response planning. Crude oil remained on the surface for the entire 60-day simulations and >20% stranded onshore. Little surface MGO remained after 5 days or reached the shoreline. The Chukchi October crude spill exposed 24% of radio-collared polar bears to lethal and sublethal oil, or 711 (95% CI = 438-1052) individuals as a proportion of the total population (n = 2937). During the Chukchi August crude spill, oil exposure occurred at ≥0.50 probability at four walrus haulouts. No polar bears or walrus haulouts were exposed to lethal levels of MGO from a spill. Our simulations suggest an oil spill would contaminate large areas of the marine environment and could have significant consequences for polar bears and walruses. The inability to conduct timely, effective cleanup underscores the importance of understanding and attempting to mitigate an Arctic oil spill. Spill preparation is expensive, time-consuming, and increasingly challenging geopolitically, yet a lack of preparation could have catastrophic consequences to marine life, regional subsistence users, and the fishing and tourism industries.