When farmed salmon escape from aquaculture pens, they interact with wild salmon populations in ways that create welfare and conservation harms for wild fish over multiple generations.
The welfare implications of salmon escape events extend beyond the farmed fish themselves to affect wild salmon populations across entire river catchments. Wild salmon experiencing increased competition from escaped farmed fish during spawning are physiologically stressed and may fail to obtain spawning sites after the energetically demanding return migration. Sea lice transferred from farm fish to wild juvenile salmon during their migration cause physical damage, impaired osmoregulation, and death in heavily infested fish. The long-term genetic changes caused by introgression of farmed genes into wild populations reduce adaptation to natural conditions, compromising the welfare of wild fish over multiple generations.