Threats

All native crayfish species in Central Europe are of major conservational concern, and are included in national or international red lists of threatened species. Globally, Noble crayfish are listed as `vulnerable´ and White-clawed crayfish are considered `endangered´. The Stone crayfish is currently listed as `data deficient´ in the global IUCN list, but regional and national red lists indicate at least an `endangered´ status throughout its Central European range.

The negative population trends of native crayfish are driven by multiple threats, most of which fall into one of three general categories:

• loss, degradation, and fragmentation of habitats,

• water pollution, and

• invasive alien species, i.e. alien crayfish and the crayfish plague agent.

While the drivers in the first two categories can theoretically be turned off (in particular in Special Areas of Conservation), and have potentially reversible effects, invasive alien species may represent a long-term threat that cannot be removed. Invasive alien crayfish and crayfish plague pose therefore a significant threat to the long-term survival of native crayfish and have been among the leading causes of native crayfish population declines during the last 140 years (see also here).

Nevertheless, the threat from alien crayfish and crayfish plague is growing because of active spread and human-mediated translocation of already established alien crayfish and ongoing introductions of new alien crayfish species (e.g., Marmorkrebs and O. juvenilis). This holds especially true in Central European countries, as high human population densities and economic growth were suggested to be positively related to alien crayfish introductions (see Perdikaris et al. 2012 and here).

Thus, prevention, control, and – wherever possible – eradication of invasive alien crayfish represent a priority of environmental management, in line with the new strategic plan of the Convention on Biological Diversity for 2011–2020 (the “Aichi Biodiversity Targets”).

Other threats are predators (e.g., eel and otters) and poaching, which, however, are not considered major threats and may only impact native crayfish populations on a local level. Legal harvest of native crayfish is largely restricted to Noble crayfish and there are strict regulations in place to prevent overharvesting.

Further reading:

• Holdich, D.M., Reynolds J.D., Souty-Grosset C., Sibley P.J. (2009) A review of the ever increasing threat to European crayfish from non-indigenous crayfish species. Knowledge and Management of Aquatic Ecosystems 11: 394–395.

• Perdikaris, C., Kozák, P., Kouba, A., Konstantinidis, E., Paschos, I. (2012) Socio-economic drivers and non-indigenous freshwater crayfish species in Europe. Knowledge and Management of Aquatic Ecosystems 402, doi: 10.1051/kmae/2011077

• Reynolds, J., Souty-Grosset, C. (Eds.) (2012) Management of freshwater biodiversity. Crayfish as Bioindicators. Cambridge University Press, Cambridge, 374 p.

• IUCN red list assessments:
• Noble crayfish
• Stone crayfish
• White-clawed crayfish