The native white-clawed crayfish is critically endangered due to crayfish plague brought by invasive North American signal crayfish, creating conservation and welfare challenges across British waterways.
Native crayfish welfare is threatened by a disease that spreads invisibly through waterways via infected signal crayfish. Individual white-clawed crayfish exposed to crayfish plague die of systemic fungal infection - a welfare harm that arrives with no warning in previously healthy populations. Conservation management through ark site protection and strict biosecurity reduces exposure risk but cannot reverse plague spread in invaded catchments. The welfare cost to signal crayfish from lethal control programmes is real; these animals are not responsible for their invasive role but do cause significant ecological harm. Biosecurity that prevents further plague spread is the most important action available.