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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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Hejnové chování jako odezva na změny prostředí, přehledová studie
JAKŠ, Jiří
The aim of my bachelor thesis was to create a review about effect of some parameters on shoal of fish. In my thesis may be found information about effects of different parameters on shoal of freshwater, marine and aquarium fish species. Review describes several parameters that effect fish in several ways and it is also contains a lot of information about shoal behaviour in general. Review gradually passes from general definition of shoal, creation of shoal, types of shoal, advantages and disadvantiges of shoal, communication and recognizing of fish inside the shoal, to enumeration of parameters that effect fish both positively and negatively. In conclusion may be found possibilities of modeling fish and their behaviour on two model examples. Information come from Czech literature, but also from foreign literature, which makes my thesis more creative and objective. Shoal behaviour is still relatively unexplored topic and many questions still remain unanswered. Exploring and assesing of shoal behaviour is relatively complicated, therefore the answers are only author´s opinions and several experiments results. Although there are speculations about this topic, many authors and experiments have similar opinion. My bachelor thesis may appreciate those, who want to know more about the shoal behaviour. In future it is necessary to realize more research about shoal behaviour and fish modeling because of its use and and less public awareness.
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