Wild Atlantic salmon face multiple anthropogenic threats as they migrate between rivers and the ocean. Their welfare is shaped by water temperature, barriers, pollution, and sea lice from fish farms.
Wild Atlantic salmon welfare involves multiple compounding stressors. Migrating salmon encounter barriers including weirs and culverts that prevent upstream passage, causing them to hold below obstacles burning energy reserves. Heat stress in warming rivers during summer migration is increasingly common. Sea lice from salmon farms colonise wild salmon during their ocean phase, weakening them before migration. Returning adults blocked from spawning grounds eventually exhaust their reserves and die without reproducing. The ecological collapse of wild salmon populations is both a conservation crisis and a welfare emergency for millions of individual fish.