Salmon restocking programmes release hatchery-reared fish into rivers to supplement declining wild populations, raising welfare questions about hatchery conditions and post-release survival.
Salmon restocking welfare involves hatchery conditions and post-release experiences. Hatchery fish raised at high densities experience chronic mild stress that shapes their physiology and behaviour — they are less predator-aware, less aggressive in territory establishment and less skilled at finding food than wild-reared conspecifics. Release into rivers exposes them to predation, river hydraulics and food competition for which their hatchery experience has not prepared them. High post-release mortality involves individual suffering from predation and starvation. Welfare-conscious restocking uses enriched hatchery environments that better prepare fish for wild conditions, and releases fish at sizes and times that maximise survival. However, habitat restoration is ultimately more impactful for wild salmon populations than stocking.