Atlantic and Pacific herring are among the most commercially caught fish on Earth. Their welfare in massive purse seine operations and as bycatch involves enormous numbers of animals.
The welfare of herring in purse seine fisheries involves staggering numbers of individual animals. When a purse seine encircles a school, fish are compressed into an ever-smaller space, causing extreme crowding stress, oxygen depletion, and physical injury from pressure. Fish are then pumped aboard or onto ice in a process that causes significant trauma. Most herring are not killed before processing — they suffocate or are crushed. Given the billions of fish caught annually, even small improvements in killing methods would have enormous welfare impact. The scale of herring fishing dwarfs most terrestrial animal farming in terms of individual animal numbers.