Mortality rates in farmed salmon are both a production metric and a welfare indicator. High mortality reflects welfare problems earlier in the production cycle that require investigation and intervention.
Salmon mortality is not just a financial loss — each death represents an individual animal that experienced the failing conditions that ultimately killed it: lice infestation, disease-related suffering, handling stress, hypoxia, or injury. Mass mortality events during treatment operations are particularly acute welfare incidents where thousands of fish may die in distress over hours. The welfare case for monitoring and reducing mortality goes beyond production economics: it is a proxy measure for the cumulative welfare burden experienced by the fish that died and an indicator of conditions for survivors. Farms achieving low mortality rates through better husbandry provide measurably better welfare for all stocked fish.