Pacific salmon undertake extraordinary migrations from ocean to freshwater spawning grounds. Their welfare is threatened by dam barriers, rising water temperatures, and fishing pressure that intercepts migrating fish in deteriorating condition.
Pacific salmon welfare during migration is shaped by the extraordinary physiological demands of their reproductive journey. Fish intercepted by fishing pressure early in migration are in better condition than those caught late — late-run fish are nutritionally depleted and physiologically stressed. Catch-and-release of late-run salmon in warm water is particularly welfare-problematic — thermal stress combined with anaerobic exertion during the fight can cause post-release mortality even in fish that swim away. Dam barriers force fish to expend energy on ladder passage, reducing what remains for spawning. River temperature above 21°C causes thermal stress, immunosuppression, and pathogen vulnerability — disease outbreaks during warm-year migrations cause significant pre-spawn mortality. Dam removal is among the most welfare-positive river management interventions available — restored free passage allows natural migration timing and reduces energy cost. Water temperature management through shading, tributary preservation, and flow augmentation also reduces thermal stress.