Migratory fish including salmon, eel and lamprey face welfare impacts from river barriers that prevent access to spawning habitat and cause physiological distress and mortality.
Migratory fish blocked by river barriers experience prolonged physiological stress as they attempt repeatedly to pass obstacles they cannot surmount. The energy expended in futile passage attempts depletes fat reserves needed for spawning. Fish concentrated below barriers are more susceptible to predation, disease and thermal stress in warming summer pools. The welfare impacts compound across the entire migration as multiple barriers may prevent passage at different points on journeys of hundreds of kilometres. Fish that fail to reach spawning grounds after full migratory investment die without reproducing, representing both individual welfare failure and population-level consequence.