The Tana River in northernmost Norway is the most diverse Atlantic salmon river in the world. Its native salmon population has declined dramatically and resulted in a fishing ban that has affected indigenous life and distressed the local economy. Concern is mounting over the secondary infestation of Pacific pink salmon, transplanted decades ago, which creates a potential threat to the river’s genetic diversity and challenges the regime structures of international fisheries. This Article reviews the problem of anadromy in the context of the Tana River, and suggests that international regime theory must adopt a broadened ecosystem approach to the Arctic that accounts for this and other consequences of transplanted species into waters where they never were before.