How farmed salmon affect wild salmon welfare through disease, genetic introgression, and competition.
The welfare relationship between farmed and wild salmon is one of the clearest examples of how commercial animal production can harm wild animal populations. Sea lice proliferating in dense salmon farm populations spread to wild juvenile salmon who pass farms during their downstream migration — a life stage when lice infestation is often fatal. The welfare harm to wild salmon involves the physiological stress and tissue damage of lice infestation before the fish have the immune capacity to respond. Regulatory solutions including minimum distances between farms and migration routes, mandatory lice monitoring with treatment thresholds, and transition toward closed containment systems can address this welfare pathway. Consumer demand for responsibly farmed salmon creates market pressure for better practices.