Wild Atlantic salmon populations have collapsed across much of their range due to ocean mortality, habitat loss, and river barriers, with welfare implications for both surviving wild fish and farmed populations.
Wild salmon that encounter river temperatures above 23 degrees Celsius experience heat stress, immune suppression, and death during spawning migration. Fish blocked by dam structures may exhaust themselves attempting to ascend barriers, suffering physiological depletion. Sea lice burdens from fish farms cause skin lesions and osmoregulatory disruption in wild smolts whose small size makes them particularly vulnerable. Anglers who practice catch-and-release fishing cause acute stress responses that may be fatal in thermally stressed fish. The collapse of wild salmon populations represents aggregate welfare harm across millions of individual animals over decades, as each generation faces an increasingly hostile gauntlet of stressors that did not exist historically.