Mackerel are caught in massive quantities by industrial fishing vessels, and their welfare during capture and killing rarely receives consideration.
Mackerel caught in purse seine nets experience the welfare horrors of wild capture at scale. Crushing pressure from millions of crowded fish causes injury. Suffocation as fish are pumped from nets to processing takes minutes to hours. No stunning is used in bulk processing. Their pain reception and stress hormones demonstrate that these are not simple reflexive deaths but potentially involving significant suffering.