Stone Crayfish

Stone Crayfish (Austropotamobius torrentium) is a specially protected species according to the Czech Act No. 114/1992 Coll., on nature and landscape protection, more specifically it is classified as critically endangered by implementation Decree No. 395/1992 Coll. It is listed as critically endangered animal in the Red List of endangered invertebrate species in the Czech Republic (Hejda et al. 2017). At the EU level, it is a priority species protected by the Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora, listed in its Annexes II and V.

Original distribution of the Stone Crayfish in the Czech Republic cannot be described, because gradual uncovering of its occurrence keeps going to the present. Current occurrence of the Stone Crayfish is known from 38 localities in Central, Northern and Western Bohemia, including one isolated population at the foothills of the Giant Mountains.

To the most significant threats that the Stone Crayfish is facing belong crayfish plague and habitat loss. Crayfish plague, a disease caused by a water mould Aphanomyces astaci, is lethal to the Stone Crayfish (as well as to the European Crayfish). There is currently no known means of treatment for this disease. Under present conditions, it is practically impossible to effectively prevent the spread of the disease, however, it is necessary to try to at least limit the spread or slow it down. Non-native and invasive crayfish species coming originally from North America are the primary hosts of Aphanomyces astaci, but they themselves do not die due to the infection, and become chronic carriers of the disease instead. Three species of invasive crayfish currently occur on our territory – Signal Crayfish (Pacifastacus leniusculus), Spiny-cheek Crayfish (Faxonius limosus) and Marbled Crayfish (Procambarus virginalis). Moreover, these crayfish species represent strong competitors for the autochthonous crayfish species. The crucial fact is that no presence of infected crayfish is necessary in order to introduce crayfish plague to a site, the spores can survive in aquatic environment even without a host for almost one month. Therefore, just water infected by the spores of crayfish plague, fishing equipment, machines (e.g. excavators), or animals with the spores attached to their bodies are enough to cause a new infection. Given the total population number estimate for Stone Crayfish in the Czech Republic, it seems that up to 20 % of the total population has died out in the last 5 years as a result of crayfish plague infection. Although crayfish plague is a huge threat to Stone Crayfish populations, habitat loss represents in many cases even a more fundamental problem, luckily with a better potential for elimination. Inappropriate interventions to watercourse beds, watercourse pollution or silting with fine-grained material are examples of impacts that cause loss of suitable habitat for the Stone Crayfish. At least four localities are known to have disappeared due to these causes in recent years.

The long-term goals of the Action Plan are: to achieve a favourable status of Stone Crayfish population (considering its protection on the territory of the Czech Republic), to preserve Stone Crayfish occurrence at a minimum length of 200 km of watercourses and to maintain the species at a maximum possible number of localities.

The Action Plan determines the scope of measures, whose implementation should have a positive effect on Stone Crayfish populations in the Czech Republic. In terms of habitat management, the plan focuses on taking care of the hydromorphological properties of watercourse beds, ensuring adequate water quality (construction and parameters of new and existing wastewater treatment plants, elimination of poisoning cases, prevention of clogging watercourse beds with fine-grained material) and preventing the spread of crayfish plague. Other measures include providing guidelines to fishing management (especially support of the natural ichthyofauna in watercourses) and measures aimed at ensuring compliance with the minimum residual flow. Active species management in the form of ex situ rescue breeding programmes is not expected in the Czech Republic (only deposition of individuals in case of a crisis situation). Species management will be carried out as a reaction to a crisis situation (rescue transfers when a stream is poisoned or drying out, rescue transfers to save individuals from crayfish plague infection or during stream bed modifications). That will be valid for the entire country, according to known issues at the moment. Another measure proposed by the Action Plan as part of the species management is the elimination and eradication of invasive crayfish and mammal species. Further measures concern maintenance of transverse barriers at key points of streams, where there is a risk of contact with invasive species, placement of temporary barriers where appropriate, or rescue transfers of populations in the event of acute threat to the Stone Crayfish. The Action Plan also puts a lot of emphasis on ensuring public education and cooperation with fishermen, stream managers and other interest groups, as well as on increasing the quality of professional documents for nature protection authorities.