In the 1970s, Britain imported North American signal crayfish for farms; they escaped, bred in huge numbers and now infest rivers across England, Wales and Scotland, carrying a plague deadly to native crayfish

In the 1970s, British aquaculture businesses imported North American signal crayfish to stock farms, hoping to build a profitable new freshwater fishery. But the plan backfired: the hardy invaders escaped into rivers, multiplied rapidly and spread across England, Wales and Scotland. Today they dominate many waterways and carry crayfish plague, a disease that is usually fatal to the UK’s only native crayfish, the white-clawed species. The UK Government documents describe signal crayfish as a textbook case of how non-native species can damage biodiversity, out-compete natives and alter river ecosystems. This story is based on UK government policy reports and recent Environment Agency reporting on native crayfish conservation. Read on to know more:

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