The freshwater pearl mussel is one of the UK's most critically endangered animals, requiring salmon and trout host fish and pristine water quality to complete its life cycle.
Freshwater pearl mussel conservation involves the welfare of both mussels and their salmon host fish. Whether mussels experience welfare-relevant states is uncertain, but the restoration of their habitat serves the wider ecosystem that supports many species. Salmon parasitised by mussel larvae show no detectable adverse effects - the relationship is commensal rather than harmful to the host. The primary welfare significance is ecological: restoring mussel populations improves water quality for all river inhabitants. Illegal pearl fishing kills individual mussels that may have survived for a century - a significant individual welfare harm for any animal with long-term invested survival.