Migratory Fish Welfare: Salmon, Eels, and Passage Obstacles

Migratory Fish Welfare: Barriers, Passage, and Individual Suffering

Migratory fish — including Atlantic salmon, sea trout, European and American eels, shad, and lamprey — face welfare challenges throughout their complex life cycles. Human-built obstacles to migration, degraded water quality, and fishing mortality all create welfare impacts for individual fish that deserve consideration alongside conservation concerns.

Atlantic Salmon Migration Welfare

Atlantic salmon (Salmo salar) migrate from the North Atlantic to natal rivers to spawn — a journey of potentially thousands of kilometers requiring enormous physical exertion. During the freshwater migration phase, salmon do not feed, relying entirely on fat reserves. Obstacles encountered during this energy-depleting journey have serious welfare implications:

• Weirs and dams: Salmon attempting to ascend impassable weirs may attempt hundreds of jumps over hours or days, exhausting reserves. Fish that cannot ascend may become stranded, crowded below barriers, and vulnerable to predation and disease.
• Fish passes: Well-designed fish passes (pool-and-traverse, Denil, or nature-like bypasses) allow salmon migration with energy cost proportional to pass design quality. Poorly designed passes create exhaustion welfare events.
• Water temperature: Excessively warm summer river temperatures cause salmon to gather in cooler pools and cease migration — creating physiological stress, disease susceptibility, and starvation as energy reserves are depleted without successful migration.

European Eel Welfare

European eels (Anguilla anguilla) are critically endangered and face welfare challenges across their complex life cycle. Glass eels (juveniles) migrating upstream face pump mortality at water intake structures; turbine mortality at hydroelectric dams; accumulation of organochlorine pollutants throughout their 10-20 year freshwater phase; and mortality during downstream silver eel migration through turbines. Individual eels passing through turbines experience blade strikes, pressure changes, and cavitation injuries — welfare impacts on long-lived individual animals.

Passage Restoration as Welfare Action

Fish pass installation, weir removal, and flow management improvements simultaneously benefit conservation and individual fish welfare. Each barrier removed reduces the welfare burden on potentially millions of individual fish attempting migration annually. The welfare case for fish passage restoration is compelling: individual salmon and sea trout that successfully ascend experienced significantly less energy exhaustion, injury, and mortality than those attempting impassable structures.

Catch-and-Release Welfare

Sport fishing of migratory salmonids using catch-and-release techniques requires welfare consideration. Optimal catch-and-release technique — barbless hooks, minimal fight time, gentle unhooking with wet hands, no-photography quick release, avoiding warm water fishing — reduces but does not eliminate post-release mortality and injury stress. Research shows post-release mortality of 1-4% in well-managed catch-and-release, rising to 10-30%+ in suboptimal conditions.