page_title: Signal crayfish
section_title: Introduction into Europe
hierarchical_section_title: Signal crayfish / Introduction into Europe
caption_attribution_description: English: Signal Crayfish (Pacifastacus leniusculus). River Arlanza, near Santo Domingo de Silos, Burgos (Spain). Español: Cangrejo señal (Pacifastacus leniusculus) en el río Mataviejas —afluente del Arlanza—, cerca de Santo Domingo de Silos, Burgos (España).
context_page_description: The signal crayfish is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the North European Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease. The signal crayfish is now considered an invasive species across Europe, Japan, and California ousting native species there.
context_section_description: From 1907, crayfish plague, an infectious disease caused by the water mould Aphanomyces astaci, damaged stocks of the native European crayfish Astacus astacus. Since the signal crayfish occupied a similar ecological niche in its native range, it was imported in the 1960s to Sweden and Finland to allow recreational and commercial crayfish capture. At the time, the signal crayfish was not recognized as a carrier of the crayfish plague. All American species carry the infection, but it is only lethal to individuals that are already stressed; to European species, the infection is rapidly fatal.
  The signal crayfish is now the most widespread alien crayfish in Europe, occurring in 25 countries, from Finland to Great Britain and from Spain to Greece. It was first introduced to Great Britain in 1976, and is now widespread across the British mainland as far north as the Moray Firth. It has also been observed on the Isle of Man, but not in Ireland. Ireland is  the last European country having no alien crayfish.
  In both Sweden and Finland (where crayfish are eaten), the catch of signal crayfish exceeds that of the noble crayfish. The former is sold at roughly half the price compared to the latter.
caption: A signal crayfish in Spain
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