Signal crayfish (Pacifastacus leniusculus) is important invasive species in European freshwaters. Its influence on other freshwater organisms is well known from the literature, as well as direct and indirect impact on fish assemblages. This work was focused on the experimental evaluation of non-indigenous signal crayfish as a predator of salmonids compared to indigenous noble crayfish (Astacus astacus). Moreover, the possible importance of young-of-the-year signal crayfish as a prey for salmonids was assessed. There were carried out experiments using eggs and hatchings of grayling (Thymallus thymallus) as a prey for adult and subadult specimens of both, signal and noble crayfish. Next experiment used young-of-the-year signal crayfish as a prey for young-of-the-year of brown trout (Salmo trutta). Results showed that the danger of signal crayfish for grayling eggs is slightly higher. However, detected differences were surprisingly lower and in the majority of parameters even insignificant. In the case of grayling hatchings, was not detected any significant difference at all. The abilities of both tested species to prey on eggs and hatchings are therefore very similar, comparable. Even so, the effect of signal crayfish can be importantly higher in natural conditions because of its more dense populations, higher growth rate and fast maturation. In accordance to our findings, it is evident that brown trout has no so high effect of crayfish juveniles compared with crayfish effect on salmonids early developmental stages. Crayfish are therefore more likely able to limit salmonids than conversely.

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This thesis is composed of two parts - research part, focused on field research of occurence and abundance of the Stone Crayfish and the Noble Crayfish in the basin of Zákolanský stream, and a pedagogical part, project Crayfish in the Czech Republic and their protection, aimed for grammar school students. The literature outline summarizes contemporary knowledge about all five species of crayfish in the Czech Republic. Our native species are the Stone Crayfish (Austropotamobius torrentium) and Noble Crayfish (Astacus astacus). The non-native are Narrow-clawed Crayfish (Astacus leptodactylus), Spiny-cheek Crayfish (Orconectes limosus) and Signal Crayfish (Pacifastacus leniusculus). Aside from the chapters concerning the particular species and their determination, the literature outline also contains general information about the life and endangerment of crayfish. I have conducted the field research from April to September 2009. I also noted and evaluated the environmental conditions of the crayfish habitats. Based on the adjusted AOPK ČR methodology, I selected eight 100-meter long brook-sections of the Europe-important locality of Zákolanský stream, with the previously confirmed occurrence of crayfish. From the eight sections, I found crayfish only in three. All the captured specimens were of the...

This thesis deals with monitoring the occurrence of crayfish in selected river basins in the western Bohemia, considering the human impact on freshwater ecosystems and his influence on crayfish and other aquatic organisms. The selected river basin territory was Úhlava, Úslava and Otava. In the localities, numerical and species-wise representation of crayfish was monitored by finding data from the Agency for Nature Conservation and Landscape of Czech Republic database. The flow and environment characteristics were also monitored. This thesis focuses on water quality in streams of selected major river basins, Úhlava, Úslava and Otava rivers in the period from 2006 to 2011. Results of the findings show a sympatric occurrence of original species, stone crayfish (Austropotamobius torrentium), noble crayfish (Astacus astacus) and part of the original danube crayfish (Astacus leptodactylus) with invasively spreading species of spiny-cheek crayfish (Orconectes limosus) and signal crayfish (Pacifastacus leniusculus). With respect to this fact, the sensitivity of spiny-cheek crayfish (Orconectes limosus) and signal crayfish (Pacifastacus leniusculus) are evaluated in a form of own test results on acute toxicity. The thesis compared current results of occurrence and the protection of crayfish in the Czech Republic and abroad. The conclusion of this thesis is a proposal of a freshwater biomonitoring system, using the crayfish.

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Understanding where and why organisms are distributed in the environment are central themes in ecology. Animals live in environments in which they are subject to competing demands, such as the need to forage, to find mates, to reproduce, and to avoid predation. Optimal habitats for these various activities are usually distributed heterogeneously in the landscape and may vary both spatially and temporally, causing animals to adjust their locations in space and time to balance these conflicting demands. In this dissertation, I outline three studies of Procambarus fallax in the ridge-slough landscape of Water conservation Area 3A (WCS-3A). The first section outlines an observational sampling study of crayfish population distribution in a four hectare plot, where I statistically model the density distribution at two spatial scales. ... Secondly, I use radio telemetry to study individual adult crayfish movements at two study sites and evaluate habitat selection using Resource Selection Functions. In the third section, I test the habitat selection theory, ideal free distribution, by assessing performance measures (growth and mortality) of crayfish in the two major vegetation types in a late wet season (November 2007) and early wet season (August 2009). / by Craig van der Heiden. / Thesis (Ph.D.)--Florida Atlantic University, 2012. / Includes bibliographical references at the end of each chapter. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

This diploma thesis deals with non-native species of crustaceans, which are already present not only in Europe but also successfully inhabit the territory of the Czech Republic. The species that this work deals with is the signal crayfish (Pacifastacus leniusculus), marbled crayfish (Procambarus fallax f. virginalis) and the killer shrimp (Dikerogammarus villosus). The main goal of this study was to demonstrate the ability of killer shrimp to attack and prey on the crayfish eggs and hatchlings of above mentioned species, which were used not only for theuir presencein Czech Republic but also as model representatives of families Astacidae and Cambaridae. It was therefore the confirmation of high aggressiveness of killer shrimp and point out, that this species is capable of negatively influencing even the bigger invertebrates by direct predation on their early developmental stages. Another aim was to assess whether the killer shrimp can be a suitable prey for a crayfish. As the experiments have shown, killer shrimp is able to predate on crayfish eggs and hatchlings even directly on females abdomens wehre they are incubated and protected. The results confirmed the theory of killer shrimp hazards to aquatic ecosystems and its potential to directly influence the populations of larger organisms. At the same time, it has been found that killer shrimp may be a suitable prey for adult and subadult individuals of signal crayfish and adults of marbled crayfish.

- ABSTRACT (IN ENGLISH) - Biological invasions by crustaceans represent a serious threat for native species in Europe. In my thesis I focus on non-indigenous freshwater crayfish introduced to Europe and their parasite Aphanomyces astaci, the pathogen of the crayfish plague. The thesis consists of four already published first-author papers (chapters I, II, IV and V), two first-author manuscripts (chapters III and VI), and one paper which I co-authored (chapter VII). The first part (chapters I-V) focuses on genetic variation in North American crayfish introduced to Europe. We showed that in two crayfish species, both successful invaders in Europe, genetic variation differs significantly, reflecting their different colonization histories on the continent. The spiny-cheek crayfish Orconectes limosus was likely introduced to Europe just once, in small numbers (90 individuals). Variation at the mitochondrial DNA (mtDNA) level in the spiny-cheek crayfish in Europe is much lower compared to North America (chapter I), although some variation was revealed by nuclear markers in its Central European populations (chapter II). In contrast, the signal crayfish Pacifastacus leniusculus was introduced to Europe several times, in large numbers. Its European populations are highly diverse genetically and belong to a single...

The most widespread of invasive crayfish in the Czech Republic is the spiny-cheek crayfish (Orconectes limosus). It is a major disease carrier of crayfish plague, caused by the pathogen Aphanomyces astaci. The infection is lethal to European native species of crayfish. Transmission of this disease is usually associated with the spread of crayfish, which is dependent on their movement. The main aim of this work was to evaluate the differences in crayfish migratory activity in the Pšovka brook among seasons, and assess the factors that may affect it, by the use of radiotelemetry and trapping. We tested the hypothesis that crayfish use brook in the period from spring to autumn and then return back into a pond to overwinter. Furthermore, we evaluated how far from the pond crayfish migrate, and whether there is any relationship between migration and the season or water temperature. The results demonstrate that the activity varies among seasons (being strongly affected by breeding season) but in most studied periods did not significantly depend on water temperature. According to our monitoring, the spiny-cheek crayfish does not spread substantially to upstream parts of the Pšovka. Seasonal migration between the pond and the brook was monitored using two-way flow-through traps installed at the mouth of...