Pacific and Atlantic salmon undergo one of nature's most extraordinary journeys — from freshwater birth, ocean maturation, back to natal rivers to spawn. This migration involves extreme physiological transformations and exposes fish to multiple welfare challenges.
Salmon migration is physiologically extreme. Fish undergo smoltification (ocean-to-freshwater transition involves osmotic stress), navigate using magnetic fields and olfactory memory, and in spawning migrants, completely redirect energy from feeding to reproduction. Plasma cortisol (the primary stress hormone) is elevated throughout migration, but this is physiologically normal — distinguishing "natural" stress from welfare-relevant "distress" is a key scientific challenge.
Key welfare metrics in migratory salmon include:
Fish ladder efficiency varies enormously. Poorly designed ladders on the Columbia River see passage rates as low as 20-40% for some salmon runs. Fish that fail to pass and hold in tailwater pools face predation from birds and sea lions, temperature stress in warming water below dams, and energy depletion.
Dam removal — as on the Elwha, Klamath, and Penobscot Rivers — eliminates these welfare challenges while restoring access to hundreds of kilometers of spawning habitat. Post-removal salmon recolonization has been dramatic, with welfare benefits for surviving populations in restored habitat.
Salmon are cold-water specialists. Critical thermal maximums: 23-25°C for most Pacific salmon, 21°C for sockeye. Climate change is pushing river temperatures toward and beyond these limits during summer migration windows. Salmon encountering lethal temperatures face behavioral thermoregulation (seeking cold-water refugia at tributary mouths), physiological heat stress leading to immune failure, and pre-spawn mortality.
The 2015 Columbia River heatwave killed an estimated 250,000 adult sockeye salmon — visible mortality as fish beached and died along river margins. Climate models project significant expansion of thermally hostile migration windows through 2050.
Ocean conditions during the salmon's marine growth phase affect welfare through: prey availability (warm-water regimes reduce copepod and forage fish availability), marine predation pressure, and physiological condition at return. Poor marine survival produces smaller, less energetically capable adults that face greater challenges completing freshwater migration.
Most Pacific salmon runs are supplemented by hatcheries. Hatchery practices with welfare implications include: crowded rearing densities, disease outbreaks (IHNV, BKD), chronic handling stress from regular sampling, and abrupt release transitions. Research shows that hatchery salmon have elevated baseline cortisol compared to wild fish, suggesting chronic welfare compromise.
Best welfare practices for salmon migration management: maintaining cold-water refugia; removing obsolete dams; designing passage facilities for high passage efficiency; limiting sport and commercial fishing interceptions on thermally stressed runs; and integrating welfare metrics into salmon recovery plans.
Fishing methods vary in welfare impact. Hook-and-line fishing with rapid dispatch is preferable to gill net drowning. Traditional Indigenous fishing using dip nets at falls allows rapid dispatch. Commercial seine and gillnet fisheries vary in time-to-death. Animal welfare organizations advocate for mandatory dispatch guidelines and stunning in commercial salmon fisheries.