River lampreys are parasitic but ecologically important fish species whose upstream spawning migrations are increasingly blocked by weirs and barriers, with population-level welfare consequences.
River lampreys unable to complete their spawning migration cannot fulfil their reproductive purpose - a welfare harm at the individual level and a population-level conservation concern. The recent focus on river connectivity through barrier removal benefits lampreys alongside salmon and other migratory species. Each successfully completed migration represents individual welfare through reproductive success.