Details

Area of research and problem identification

Stone crayfish (Austropotamobius torrentium) and noble crayfish (Astacus astacus) are classified as critically endangered species according to § 56 paragraphs 1 and 2 of Act No. 114/1992 Coll., on nature and landscape protection. Stone crayfish is also a priority species according to Annex II. Habitats Directive 92/43/EEC.

The distribution of noble crayfish and stone crayfish in the Czech Republic is currently limited to small watercourses. In the case of stone crayfish, only 38 locations are registered in the Stone Crayfish Species Action Plan (NCA, 2024), or streams with documented current occurrence of the species. A total of 44 locations are recorded in the Stone Crayfish Species Action Plan where the stone crayfish is found, or was found there in previous years due to the crayfish plague or for other reasons its occurrence was not reconfirmed here by the latest surveys. In the Czech Republic, 13 locations of European importance have been declared for the protection of stone crayfish. In addition to habitats preference, the main reason for population fragmentation is inappropriate water quality in larger streams and especially the occurrence of crayfish plague, which decimates our populations native crayfish since the beginning of the 20th century.

While water quality has improved over the past thirty years, the risk of crayfish infection is still present or even increasing. The reason is gradual the spread of non-native North American crayfish, which are carriers of crayfish plague, as well as the intensive use of aquatic ecosystems by humans. A typical example of the direct human contribution to the spread of crayfish plague is recreational fishing and stocking activities operated by local fishermen's union organizations.

However, the current fragmentation of native crayfish populations is paradoxically an advantage that limits the spread of crayfish plague. For this reason, it is, for example, a Stone Crayfish Species Action Plan, where is recommended not to cross obstacles on waterways with the occurrence of this critically endangered species. Action Plan even recommends it in conditions of danger crayfish plague or the spread of non-indigenous crayfish species (which is practically the same thing) the modification of existing migration barriers or the temporary establishment of new barriers. These measures are described in the methodology of Svobodová et al. (2020). Their construction and effectiveness were verified in a recent Norwegian Funds project (Koženy et al. 2024). Foreign experiences are also available, e.g. in Norway or Spain (Dana et al. 2011,...).

In order to effectively use the temporary migratory separation of the crayfish population from its surroundings, it is also necessary to map in detail the current occurrence of crayfish plague and invasive crayfish. For monitoring based on classic manual trapping, this is too demanding a task. Using modern methods based on environmental DNA (eDNA) analysis sub-basins affected by crayfish plague and areas of native or non-native crayfish species can be detected with a high degree of confidence.

Monitoring of crayfish populations using eDNA is a well-known method in the world, but in the Czech Republic it is used rather only as part of research. It was used as a supplement to routine monitoring used so far only sporadically.

The project aims to improve conditions for the protection of stone crayfish and noble crayfish populations. The sub-goals of the project are as follows:

• for selected localities with the occurrence of native species of crayfish, check the occurrence of invasive species and Aphanomyces astaci in the surroundings using eDNA in combination with classic manual monitoring,,
• in the event of crayfish plague, verify the ability to locate the infection as accurately as possible using eDNA analysis, determine the boundaries of the affected stream section and propose appropriate measures to prevent further spread
• for selected localities with the occurrence of native crayfish species, describe existing migration barriers (steps on streams) and select objects suitable for temporary modifications in the event of the progress of the crayfish plague or invasive crayfish population,
• for individual localities prepare a study describing the risks of the spread of crayfish plague and invasive species of crayfish and objects on streams recommended to be retained or modified for the sake of population protection,
• increase awareness of the issue of protecting native crayfish species and practices that reduce the risk of crayfish plague transmission among basin managers, regional authorities, ORPs, local organizations of sports fishermen and the public.

The project is implemented at locations in three areas:

• Locations of current and recent occurrence of stone crayfish in the Pilsen region:
  A total of 17 streams will be monitored using eDNA here (4 EVL sites, streams with recent occurrence of stone crayfish, 5 streams with a current stable population according to Action Plan, 5 tributaries of the Mže with occurrence of river crayfish). Total at min. eDNA samples will be taken at 45 locations for the detection of stone crayfish, river crayfish, invasive crayfish and crayfish plague.
• Locations of noble crayfish occurrence in the Svratka basin:
  We assume monitoring using eDNA on the middle course of the Svratka between Tišnov and VN Vír, as well as on 8 left-hand tributaries and 9 right-hand tributaries. Closer attention will be focused on the surroundings of the experimentally modified migration barriers on the Besének stream. In total, we anticipate taking eDNA samples at at least 35 locations.
• EVL Horní Malše basin including tributaries:
  Monitoring of invasive crayfish (signal crayfish) using eDNA will be carried out here for approx. 40 river kilometers of the main flow of the Malše in the territory of EVL and selected 12 tributaries. monitoring will be carried out at a minimum of 22 locations.

Initial status and current solutions

The essential document for the project activities is the Action Plan. The project will fulfill the requirements of Action Plan for planned measures, monitoring, necessary research and education and awareness.

The action plan of the Action Plan explicitly states:

• regulation of fishing management in streams with the occurrence of stone crayfish and systematic education and work with the fishing public,
• implementation of biotope measures linked to the issue of crayfish plague, namely to modify existing migration barriers in priority streams so that so that they are effective and invasive species of crayfish cannot spread through them and, in the case of priority locations, to select places for the construction of temporary migration barriers in case of the spread of crayfish plague (spread of invasive species) upstream,
• regulation and eradication of populations of invasive species of crayfish, namely preventing the expansion of populations of non-native species of crayfish in accordance with the Regulation and Eradication Methodology invasive species of crayfish: selection of suitable methods depending on the nature of the water body (Svobodová, 2020).

In the chapter "Monitoring stone crayfish", Action Plan states, among other things:

• mapping sites potentially inhabited by stone crayfish,
• monitoring of invasive crayfish species,
• use of environmental DNA (eDNA).

In the "Research" chapter, Action Plan also includes important topics in the area of predicting the risk of stone cancer:

• research on the transmission of crayfish plague (migratory abilities of crayfish...),
• continuation of crayfish plague testing using eDNA from water,
• continue testing for crayfish infestation of invasive crayfish.

In the chapter "Education and education", among other things, Action Plan emphasizes education in the following issues:

• cray plague (what it is, what causes it, how it spreads, what are its consequences, how to defend against its spread),
• non-native species of crayfish.

The project supplements the information needed for updates to the Concept of Migration Accession of the River Network of the Czech Republic (MŽP, 2020), with which it does not conflict, since the crayfish habitats are located in the upper parts of the basin and are therefore outside migration corridors established by this concept.

Objectives and benefits of the solution

The main goal of the proposed project is to improve the conditions for the protection of stone crayfish and noble crayfish populations. The sub-goals of the project are as follows:

• for selected localities with the occurrence of native species of crayfish, check the occurrence of invasive species and Aphanomyces astaci in the vicinity using eDNA in combination with classic manual monitoring,
• in the event of crayfish plague, verify the ability to locate the infection as accurately as possible using eDNA analysis, determine the boundaries of the affected stream section and propose appropriate measures to prevent further spread
• for selected localities with the occurrence of native crayfish species, describe existing migration barriers (steps on streams) and select objects suitable for temporary modifications in the event of the progress of the crayfish plague or invasive crayfish population,
• for individual localities prepare a study describing the risks of the spread of crayfish plague and invasive species of crayfish and objects on streams recommended to be retained or modified for the sake of population protection,
• increase awareness of the issue of protecting native crayfish species and practices that reduce the risk of crayfish plague transmission among basin managers, regional authorities, ORPs, local organizations of sports fishermen and the public.

The results of the project will bring a fundamental expansion of knowledge about the occurrence of the critically endangered stone crayfish using eDNA analysis. Monitoring will be carried out at 4 sites of European significance declared for the protection of stone crayfish and at 5 other sites included in its Action Plan. The occurrence of a potential weak population of stone crayfish, which was not detected by classic manual monitoring in recent years, will be verified at the other 3 localities listed as extinct in the Action Plan.

The results of the project will bring new information about the distribution of the causative agent of crayfish plague, Aphanomyces astaci, and its vectors - North American crayfish species (signal crayfish and spiny-cheek crayfish in the areas covered).

The survey of migration barriers at localities with stone crayfish will be used to compile a list of obstacles suitable for migratory isolation of protected populations in the event of the spread of crayfish plague in the watershed.

The results of the monitoring of the invasive signal crayfish in EVL Horní Malša and its tributaries, in the context of the recent removal of several stages on the Malša, will bring up-to-date data on the spread and the potential effect on the pearl oyster population

The research carried out on the middle reaches of the Svratka, focusing on the experimental site of the Besének stream, will bring new information about the spread of crayfish plague and invasive crayfish in the basin and the effect adjusted migration barriers. At the same time, the study will provide information on the occurrence of isolated crayfish populations in this area.

The results of the project will fulfill the Action Plan in the areas of monitoring using eDNA, prevention of the threat of crayfish plague, creation of plans for the protection of individual sites of occurrence, increasing the level of knowledge and techniques usable for the protection of EVL and other sites of occurrence

In addition to state nature protection authorities, information will be disseminated to the lay and professional public, with a focus on local organizations of fishermen's unions.

The results of the project will further serve as a starting point for further research on the topic of protecting native crayfish species, preventing the spread of invasive North American crayfish and crayfish plague.