MIGRATORY ABILITY OF ORCONECTES LIMOSUS THROUGH A FISHPASS AND NOTES ON ITS OCCURRENCE IN THE CZECH REPUBLIC

The occurrence of the spiny-cheek crayfish in the Czech Republic was first reported in the 1980´s in the Elbe River and is a result of its upstream migration from Germany. This study confirms that this species occurs in many other localities across the Czech Republic. Its migration ability was experimentally studied at a thirty-chambers fishpass located at a hydroelectric power station in the Elbe River. Group-marked crayfish were placed into 3 selected chambers. Their up- and downstream movement was then registered for 30 min after crayfish stocking. We found that a large portion of the experimental crayfish was passively carried along the stream and was caught in the lowest chamber. The movement of crayfish against the water current towards the higher-positioned chambers was not recorded. However, crayfish showed to have a high ability to hold their position in a strong water flow. Overall, 56.7 ± 9.43%, 6.7 ± 9.43% and 3.3 ± 4.71% of crayfish remained in the chamber of insertion and 23.3 ± 4.71%, 30.0 ± 14.14% and 26.7 ± 17.00% of crayfish migrated to the lower-positioned chambers

MIGRATORY ABILITY OF ORCONECTES LIMOSUS THROUGH A FISHPASS AND NOTES ON ITS OCCURRENCE IN THE CZECH REPUBLIC

The occurrence of the spiny-cheek crayfish in the Czech Republic was first reported in the 1980´s in the Elbe River and is a result of its upstream migration from Germany. This study confirms that this species occurs in many other localities across the Czech Republic. Its migration ability was experimentally studied at a thirty-chambers fishpass located at a hydroelectric power station in the Elbe River. Group-marked crayfish were placed into 3 selected chambers. Their up- and downstream movement was then registered for 30 min after crayfish stocking. We found that a large portion of the experimental crayfish was passively carried along the stream and was caught in the lowest chamber. The movement of crayfish against the water current towards the higher-positioned chambers was not recorded. However, crayfish showed to have a high ability to hold their position in a strong water flow. Overall, 56.7 ± 9.43%, 6.7 ± 9.43% and 3.3 ± 4.71% of crayfish remained in the chamber of insertion and 23.3 ± 4.71%, 30.0 ± 14.14% and 26.7 ± 17.00% of crayfish migrated to the lower-positioned chambers

BIOMETRY AND DEMOGRAPHY OF THE INVASIVE CRAYFISH ORCONECTES LIMOSUS IN THE CZECH REPUBLIC

Biometry, population data and selected ecological parameters of populations of the spiny-cheek crayfish, Orconectes limosus, were measured to evaluate the differences between “marginal” (short-time, situated on margins of an area) and “residential” (longterm, well established inside an area) populations of this invasive crayfish. We selected three types of localities: 1. Large rivers – residential (Labe, Vltava); 2. Brooks (small and shallow running waters) – marginal; 3. Isolated standing waters – residential (old sandpits or flooded quarries). No significant differences in the total body length of crayfish were found between running and standing water localities as a whole, or between marginal and residential populations from running waters. There was, however, a low but distinct difference in the body weight between crayfish from brooks and other waters. Larger specimens (up to 116.5 mm in body length) were found only in isolated standing waters, whereas no crayfish longer than 100 mm were found in the rivers. The sex ratio of the crayfish was almost equal in rivers and isolated waters; males were more numerous in brooks. There was a significant difference between male and female body weight-length relations

DISTRIBUTION OF THE INVASIVE SPINY-CHEEK CRAYFISH (ORCONECTES LIMOSUS) IN THE CZECH REPUBLIC. PAST AND PRESENT

The American spiny-cheek crayfish, Orconectes limosus, was first introduced into European waters in 1890. The first literature record about the occurrence of O. limosus on the territory of the Czech Republic was published almost 100 years later – in 1989. The presence of this species in Czechia, however, was first recorded already in the 1960s, when crayfish were observed in the dead arms and pools adjacent to the river Elbe (Labe) in Central Bohemia. In the following few decades the spiny-cheek crayfish has spread into several larger rivers of the Elbe watershed and some of their smaller tributaries. The eastern part of the country (mostly belonging to the watershed of the river Morava) has not yet been colonised by this species. O. limosus can be found in lower reaches of a number of watercourses of a low stream order, but does not seem to penetrate far upstream in such localities. Its distribution in standing waters is largely the result of intentional humanmediated translocations. The long-term coexistence of Orconectes and native crayfish species has not yet been recorded, although both introduced and native crayfish at least occasionally come into contact. As O. limosus is a major carrier of the crayfish plague on the Czech territory, and crayfish plague outbreaks have been recently recorded, the dynamics of Orconectes invasion deserves careful monitoring in the future

Status and recovery of indigenous crayfish populations after recent crayfish plague outbreaks in the Czech Republic

<div><p>The crayfish plague pathogen (<i>Aphanomyces astaci</i>) is one of the most important threats to indigenous European crayfish. Although it belongs among the most studied pathogens of invertebrates, only a few recent studies are available on the epidemiology of crayfish plague and its long-term effects on crayfish populations. We provide detailed data on 11 populations of European crayfish (<i>Astacus astacus</i>, <i>A. leptodactylus</i>, <i>Austropotamobius torrentium</i>) hit by crayfish plague in the Czech Republic between 1998 and 2011. We repeatedly surveyed the affected localities in the years following the disease outbreaks to investigate potential recovery of crayfish populations and to search for the likely sources of infection. Although the mortalities severely decimated all studied populations, European crayfish could be found in the watercourse catchments after the disease outbreaks in all but two cases. In five cases, migration barriers apparently supported crayfish survival; in two cases, the disease stopped spreading even without the presence of any barrier. Indigenous crayfish were recorded directly in the affected parts of five studied streams after some time but in most cases populations have not yet reached the original densities. Their recovery seems influenced by the population size in unaffected refuges as well as time since the outbreak. Sources of infection and transmission pathways of <i>A. astaci</i> apparently vary in the Czech Republic. <i>Aphanomyces astaci</i> of three genotype groups originating in different crayfish plague pathogen carriers were involved in the outbreaks. Direct transmission of <i>A. astaci</i> from invasive American crayfish present in the same stream is likely in three cases; however, these host crayfish were not recorded at the remaining localities, and long-range dispersal or other pathogen sources may be assumed. We hypothesize that chronic <i>A. astaci</i> infections leading to disease outbreaks under specific conditions may occur in some populations of indigenous crayfish in the Czech Republic.</p></div