How salmon aquaculture operations affect wild salmon welfare and populations through sea lice transmission, genetic dilution, disease spread, and habitat degradation.
Conventional salmon aquaculture in open net-pen systems causes substantial welfare harm to wild salmon and broader marine ecosystems at geographic scales. Sea lice produced in the dense conditions of salmon farms attach to and feed on wild juvenile salmon during their coastal migrations, causing lesions, osmoregulatory failure, and death before they can reach open ocean. The aggregated effects on wild pink and coho salmon populations in regions with intensive salmon farming have been documented in multiple peer-reviewed studies, with some populations showing dramatically reduced returns. The welfare of individual wild salmon infested with sea lice involves prolonged tissue damage and physiological stress — not merely statistical population impact. Closed containment aquaculture systems (recirculating aquaculture systems or submerged cages) dramatically reduce sea lice transmission, escape risk, and waste discharge, but have not been adopted at scale due to higher capital and operating costs. Consumer and regulatory pressure for closed containment requirements represents the most direct lever for reducing wild salmon welfare impact.