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Study of the limnological components of the ecosytem of Lake Medard in 2022
Peterka, Jiří ; Hejzlar, Josef ; Nedoma, Jiří ; Znachor, Petr ; Seďa, Jaromír ; Vejřík, Lukáš
The report summarizes the results of research into the limnological and biological components of the ecosystem of the newly created Medard post-mining lake. The aim of the presented report is to summarize the results achieved for the year 2022 and recommendations for further monitoring. The year 2022 was the fifth year after the lake was completely filled, when water from the Ohře River was no longer added. Only small tributaries flowed into the lake from its own catchment area, and at the same time, water from the lake drained through seeps, which are apparently drained into the nearby rivers, the Ohře and the Svatava. The lake ecosystem reached the final state of its initial phase in terms of hydrological regime and nutrient load. This condition is characterized by very little water exchange and a low nutrient level with low productivity of plankton communities. There is the development of submerged macrovegetation in littoral zone and a specific seasonal change in chemistry and biological parameters. However, the aquatic ecosystem is still far from stabilized and the biological communities of the littoral zone (littoral) and open water (pelagial), including the fish community, still show significant interannual dynamics.
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Ellimination of unwanted fish species from dam reservoirs - Possibilities, efficiency and economic evaluation.
Jůza, Tomáš ; Blabolil, Petr ; Čech, Martin ; Draštík, Vladislav ; Holubová, Michaela ; Hůda, J. ; Kočvara, Luboš ; Kolařík, Tomáš ; Muška, Milan ; Peterka, Jiří ; Prchalová, Marie ; Říha, Milan ; Sajdlová, Zuzana ; Tušer, Michal ; Vašek, Mojmír ; Vejřík, Lukáš ; Kubečka, Jan
spontaneous development of populations and the influence of human interventions. For situations where a certain part of the fish population needs to be caught, within the project 'Biomanipulation as a tool for improving the water quality of reservoirs', we tested the available approaches in terms of their effectiveness and difficulty. The target species of catches were mainly cyprinid fish (bream, bleak, roach, rudd, white bream), which feed mainly\non zooplankton and tend to form very large populations. Among the most effective methods of catch during spawning are catches using electrofishing boats and fyke nets. In the non-spawning period, it is possible to carry out mass catches using trawl nets. Catches are effective both before spawning (in April) and during the summer. However, with repeated catches in the same places, their effectiveness decreases as a result of the fish being spooked. The efficiency of the catches partially improves again if the catches are repeated with a break of approximately 1–2 weeks. Catches also vary according to the stocking density of a given water body. With effective catches, the cost of catching 1 kg of fish is in the range of CZK 15–50.
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Analysis of photo-records of non-fish prey in the diet of selected species of fish-eating birds
Mach, Jakub ; Čech, Martin (advisor) ; Vejřík, Lukáš (referee)
Piscivorous birds are often blamed for causing significant damage to fish stocks. Various methods are used to determine the composition of their food, each of them has limits in its ability to determine the complete food spectrum. This work maps the complete food composition of 14 species of fish-eating birds with a method that is not commonly used. Method used in this work uses analysis of publicly available photos on Google.com. In addition to the complete composition of the food, the species composition of the non-fish part of the prey was also determined, and in the case of the Great Cormorant (Phalacrocorax carbo), also the length of the fishes it catches. The aim of this work is to reveal the usability of this method for these purposes. A total of 2350 retrieved photographs were analyzed. The results obtained by photo analysis are in all cases compared with data in the available literature. For representatives of heron birds (Ardeidae), the analysis of photographs provided good information on the food spectrum of individual birds and on the qualitative composition of the non-fish component. It also provided relatively good information on the diet of the White-tailed Eagle (Haliaeetus albicilla), but the bird part of the prey was slightly underestimated. In the diet of the Great Crested Grebe...
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Study of the state of wels catfish population and its diet in the Římov reservoir in 2018
Vejřík, Lukáš
Based on the capture of wels catfish using longlines, the aim of the study was: 1. To estimate the abundance of catfish population, over 70 cm TL (total length), in 2017 and 2018. 2. O compare the abundance of catfish, expressed as catch per unit effort, with the other localities surveyed. 3. To determine the average length and weight of catfish. 4. To determine the proportion of artificially introduced and naturally stocked catfish into the reservoir. 5. To determine the annual growth of catfish on the basis of the catches of stocked pit tagged catfish and the size of the catfish identified in catches in 2017. 6. To evaluate the diet of catfish according to the stomach content analyses for 2017 and 2018.
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