Scientific name Pacifastacus leniusculus Common name Signal Crayfish Broad group Invertebrate Number of and countries wherein the 18: AT, BE, CZ, DK, UK, FI, FR, DE, IT, LV, LT, NL, PL, PT, SI, ES, SE, GR species is currently established Risk Assessment GB NNRA Method https://secure.fera.defra.gov.uk/nonnativespecies/downloadDocument.cfm? Links id=54 Other EU countries where the species occurs (5): Croatia, Estonia, Greece, Luxenburg, Slovakia (Holdich et al., 2009, Kouba et al., 2014). Socio-economic benefits: In many countries, especially Sweden and 1. Description Finland, the signal crayfish populations support a large, commercially and (Taxonomy, invasion recreationally important, fishery (Ackefors, 1998). In Europe as a whole, a history, distribution total of 355 tonnes of signal crayfish was estimated from capture fisheries range (native and in 1994 (Ackefors, 1998). This level has increased considerably, and in introduced), 2001 the Swedish catch was estimated to 1200 tonnes. geographic scope, Fishing statistics for crayfish in Sweden states total yield in 2013 was socio-economic about 3.1 million € (28 972 000 SEK), which includes both signal crayfish benefits) and noble crayfish, but it is estimated that noble crayfish is up to 10% catch. This only considers fishing in public water bodies, not commercial rearing in ponds (Statistics Sweden, http://www.scb.se/Statistik/JO/JO1102/2013A01/JO1102_2013A01_JO56 SM1401.pdf). Very rarely used in the pet trade in Europe (Chucholl, 2013). 4. Has the capacity to assess multiple The crayfish introductions in some cases have been accidental (e.g., pathways of entry and through canals, escapes from holding facilities), but most have been spread in the deliberate (for aquaculture, legal and illegal stocking, and live food trade, assessment, both as aquarium pets and live bait, for snail and weed control, and as supplies intentional and for science classes) (Gherardi, 2013). unintentional 5. Can broadly assess Crayfish cause major environmental impacts in Europe by outcompeting environmental impact native species and altering habitat structure. Alien crayfish, such as with respect to Procambarus clarkii and Pacifastacus leniusculus, are responsible for the biodiversity and largest range of impacts (i.e., crayfish plague dissemination, ecosystem patterns bioaccumulation of pollutants, community dominance, competition and and processes predation on native species, habitat modifications, food web impairment, herbivory and macrophyte removal) (Gherardi, 2013). Provisioning services. The signal crayfish is the most abundant crayfish in natural waters and aquaculture facilities in much of Europe because of the existence of commercial markets supplying this crayfish for human consumption (Holdich et al., 2009). Because signal crayfish largely replaced native crayfish in Palearctic natural environments and in markets, the net impact of the species replacement on the marketplace is difficult to assess. What is clear is that, under the current circumstances, native crayfishes are much more highly valued; the 2010 market price of native Astacus astacus was double that of signal crayfish in Sweden (L. Edsman, personal communication). Supporting services. Like red swamp crayfish in warmer waters, signal crayfish also reduces the abundance of a wide range of native organisms 6. Can broadly assess in the cooler waters it inhabits in both the Palearctic and Oriental realms. environmental impact In Scandinavia, signal crayfish reduces species richness and abundance of with respect to macrophytes and macroinvertebrates, and it reduces organic matter ecosystem services content of sediments (Holdich et al., 2009). Competition with signal crayfish, and its interactions with predation, contribute to the displacement of native crayfishes in Japan (Cambaroides japonicas) and the western Palearctic realm (Holdich et al., 2009). Regulating services. As a major vector of crayfish plague, signal crayfish introductions have caused the continued loss of populations of native crayfish. Although not typically a burrowing species in its native range, signal crayfish causes considerable damage to English river banks (A. Stancliffe-Vaughan, unpublished data). Cultural services. The loss of native crayfishes caused by signal crayfish in northern Europe, especially the loss of the noble crayfish (Astacus astacus) in Scandinavia, is perceived as a serious cultural blow (Lodge et al., 2012). 8. Includes status The following Red List assesses species (6: EX = 1; EN = 1; VU = 1; DD = 2; (threatened or LC = 1) are under threat because of the Signal Crayfish (GISD 2014): protected) of species • Astacus astacus VU or habitat under • Astacus leptodactylus LC threat • Austropotamobius pallipes EN • Austropotamobius torrentium DD • Cambaroides japonicus DD • Pacifastacus nigrescens EX The White-clawed crayfish Austropotamobius pallipes is affected by a range of threats, however the most widespread threat is that of the invasive alien crayfish species such as the Signal Crayfish (Pacifastacus lenisculus) and Red Swamp Crayfish (Procambarus clarkii), as well as the Crayfish Plague (Aphanomyces astaci). Invasive crayfish are aggressive predators for food and habitat, and often prey upon the White-clawed Crayfish (Füreder et al., 2010, Kozák et al., 2011). Significant declines are occurring across much of this species range: approximately ~52% decline over 10 years in England, ~52% decline between 1995 and 2003 within France, and a 99.5% decline estimated for a ten year period in the South Tyrol region of Italy. These countries once held the greatest abundance of this species (Füreder et al., 2010). For example, the situation concerning A. pallipes is considered critical in South-West England, where P. leniusculus has become widespread and this has been at the expense of A. pallipes, mainly through outbreaks of crayfish plague since the 1980s. It has also colonised waters not suitable for A. pallipes (Holdich et al., 2009). In France, a national survey conducted in 2006 shows the same trend and the situation of three indigenous species is considered alarming: Austropotamobius torrentium and Astacus astacus are close to extinction, and A. pallipes, with mortalities observed in 47 departments, can now only be found in the uppermost parts of the watersheds (Füreder et al., 2010). These mortalities are due not only to disease, but also to the pressure of non-indigenous species, which are still expanding their range. Both P. leniusculus and P. clarkii showed their strongest geographical expansion during the 2001–2006 period. They appear to be ubiquitously very strong competitors; being more aggressive; resistant to disease, although there are outbreaks of disease at times associated with either a chronic or epizootic mortality; and are able to colonise varied environments. They are in the process of colonising new departments, new watersheds, and eliminating indigenous species (Holdich et al., 2009). Italy is considered a “hot-spot” for the genetic diversity of the European crayfish genus Austropotamobius. The fragmentation of the A. pallipes complex populations is due to among other threats the diseases, notably crayfish plague carried by P. leniusculus and P. clarkii, and interspecific competition with the non-native crayfish species. In Italy, the decline is about 74% over the last 10 years (Holdich et al., 2009). With the introduction of the two North American species into the Iberian peninsula, first, P. clarkii in 1973, and then P. leniusculus in 1974, the fate of A. pallipes was effectively sealed. Today this crayfish is believed extinct in Portugal and only remnant populations remain in Spain, chiefly in Atlantic regions of Asturias, Girona and Pais Vasco, Navarra, Castilla and Leon, Cuenca and Granada. As elsewhere when NICS have ousted ICS from the majority of their habitat, A. pallipes is now restricted in Spain to small headwater streams and springs (Holdich et al., 2009). In Croatia P. leniusculus has adverse effects on the populations of A. astacus in the Mura River, where the species has disappeared from many sites. Pacifastacus leniusculus entered Croatia in 2008 via the Mura River, which borders Hungary and Slovenia and is expected to spread downstream toward the Drava River (Holdich et al., 2009). The effect of climate, invasive species, and disease on the distribution of native European crayfishes has been studied (Capinha et al., 2013). They developed a model for the native crayfish in Europe and three North American plague-carrying crayfish species (O. limosus, P. leniusculus, and P. clarkii). The authors anticipate that P. clarkii, but not the other invasive alien crayfish, will enlarge its distribution range in both accessible (areas 9. Includes possible within basins where a given species is currently established) and effects of climate inaccessible areas. This result has been confirmed by a behavioral study change in the that analyzed antagonism, at different temperatures, of dyads composed foreseeable future of the same three species (Gherardi, 2013). All other conditions being equal, P. clarkii was dominant over the other species at the highest temperature analyzed (27°C), which corresponds to the maximum temperature expected at the latitudes of the study area (central France) in the next 80 years under the more pessimistic greenhouse gas-emission scenario. On the contrary, at that temperature, O. limosus will become less active, which may be a strategy to avoid thermal shocks, and P. leniusculus, being