American signal crayfish have devastated native white-clawed crayfish populations in Britain, causing both conservation harm and welfare implications for both species.
Freshwater crayfish welfare involves both the invasive and native species. Signal crayfish caught in traps experience drowning stress. White-clawed crayfish exposed to plague die from fungal infection that destroys their cuticle — a potentially painful process in an animal whose sentience is uncertain but possible. The conservation emergency of white-clawed crayfish extinction affects ecosystem function and the welfare of river species dependent on crayfish ecological services. Control is necessary but requires humane trapping protocols.