Considered to be the finest edible crayfish, the noble crayfish was once abundant in Europe, but was expensive to buy. The American ‘signal crayfish’ (Pacifastacus leniusculus) was introduced to European waterways as a cheaper alternative, but the presence of this species was to have disastrous effects on the noble crayfish. An outbreak of crayfish plague, carried by the signal crayfish, spread through populations of all of Europe’s Astacus species. Caused by the freshwater fungus Aphanomyces astaci, crayfish plague infects and kills the noble crayfish, leaving the resistant signal crayfish unharmed (3).
Dredging of waterways has further threatened Astacus crayfish species as it leaves the water cloudy and disturbs the habitat. Acid rain, also causing a decrease in water quality, is thought to be responsible for a decline in breeding success, as the egg cases of young crayfish are unable to form properly (2).