River lampreys are a primitive but ecologically important species whose populations have declined due to river barriers and water quality degradation. Their conservation requires clean rivers and free passage for migration.
River lamprey welfare is primarily a conservation and habitat concern. Their complex lifecycle - with larval, migratory, and spawning phases each requiring different conditions - makes them vulnerable to disturbance at any stage. Barriers that prevent upstream migration prevent spawning entirely, eliminating entire year classes from affected rivers. Water quality problems during the 7-year larval phase in sediment can cause high mortality. The ecological importance of lampreys as nutrient transporters (carcasses after spawning provide marine-derived nutrients to freshwater systems) means that their welfare and conservation supports broader ecosystem function. Individual lampreys that attempt to pass barriers face exhaustion and increased predation risk while congregating below impassable obstacles.