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Aktivita raka signálního v podmínkách malého toku
DAVID, Jaroslav
The signal crayfish is one of the oldest invasive crayfish species in Europe, causing ecological and often economic damage in newly invaded locations. The invasion and associated problems can be monitored in real-time on the Křesanovský brook, where regular eradication measures have been carried out for six years. However, the detailed and comprehensive impact of these activities on the crayfish population as a whole and any changes in individual behaviour have not yet been studied in detail. To obtain relevant data for this purpose, this thesis video-recorded the situation in the stream in monthly cycles from May to September 2021, with recordings taken the night before and the night after thorough manual crayfish catching in the brook, evaluating the number and activity of observed crayfish. The results did not show that the trapping had changed the overall crayfish activity. Even with a high number of captured crayfish, the weakened crayfish population after trapping showed the same overall activity as the complete population before trapping (presumably due to an increase in individual activity in response to catching and accompanied habitat disturbance). Furthermore, the results underline the previously assumed low success rate of eradication efforts at the site and confirm that barriers in the stream are not sufficient to stop the signal crayfish spread. These findings will help to better understand the impact of eradication measures on signal crayfish populations. As this was the first research of its kind, this thesis opens up opportunities for methodological improvements and further development, as well as posing many new questions that need to be addressed. The ultimate goal of these efforts is to improve management interventions against invasive signal crayfish.
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Dynamika společenstva makrozoobentosu podhorského toku s početnou populací raka signálního.
ŠŤASTNÁ, Hana
Assessment of macroinvertebrates population at the Křesanov brook above the town of Vimperk. It contains a large population of the signal crayfish. It is non-native in Europe. Sampling was carried out in 2020. Macroinvertebrates sampling was done. Then, in the laboratory, its determination and detection of abundance and biomass was done. Statistical analyses were subsequently made using hydrobiological indices from the collected data. The analyses compared two stream segments that were different in some parameters.
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Proti americkému brouku! Lze odstranit raka signálního z malého toku?
JAKŠ, Jiří
Biological invasion by invasive alien crayfish species is a serious problem for the whole ecosystem. Non-native crayfish species have significantly better biological equipment and ability to adapt to the environment in which they live. This makes them very dangerous animals not only for our native crayfish species. One of these dangerous alien species is the signal crayfish (Pacifastacus leniusculus - Dana, 1852). This species was imported from North America because of economic reasons. At the time of introduction of this non-native species, such massive spreading was not expected as well as negative impacts on native species. Now it is necessary to reduce the number of crayfish and thus significantly help the whole ecosystem. There are several ways how to reduce the population of signal crayfish and other non-native crayfish species. It was the subject of this work and it was only necessary to choose the appropriate method. Finally, one of the least invasive methods was chosen for this work, which is catching crayfish by hand and the net. The Křesánovský brook near Vimperk was chosen as a locality, where is located the dense population of the signal crayfish. This species already significantly reduced all the typical fish species that normally lived in this trout brook, and also significantly reduced the number of native crayfish (Astacus astacus - Linnaeus, 1758). This species can be seen there only rarely and often of a poor fitness. At the beginning of presented work, the main question was how successful this catch method would be. According to current theoretical knowledge, the method of catching crayfish by hand with net has a low success rate and it is not possible to remove the crayfish completely from the stream using this method. However, no one has conducted such a study at small accessible stream and it was therefore appropriate to carry out such a study. After intensive catches in the period from April to November, it was found that we are not able to remove or significantly reduce the number of crayfish living in this stream. However, there are several alternatives that can be used. These alternatives can be found in this work.
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