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Survey of the catfish population in the Klíčava 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 the catfish population, individuals over 70 cm TL (total length). 2. To compare the abundance and size of catfish, expressed as the catch per unit of effort, with the other reservoirs surveyed under the management of the Vltava River Authority state enterprise (Žlutice and Římov). 3. To determine the average length and weight of catfish. 4. To evaluate the diet of catfish according to the stomach content analyses.
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Survey of the European catfish population in the Žlutice Reservoir in 2017
Vejřík, Lukáš ; Peterka, Jiří
The aim of the study was to estimate the population density of wels catfish in the Žlutice Reservoir and to compare it with other localities studied, to determine the average length and weight of the catfish, to determine the proportion of artificially stocked and naturally reproduced catfish, to estimate the annual growth and to evaluate the catfish diet based on stomach contents. A summary of the work carried out and the results achieved are the content of this report.
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Biology of predatory fishes in dam reservoirs and lakes
VEJŘÍK, Lukáš
This Ph.D. Thesis is focused mainly on the biology of two typical European predatory fishes, European catfish (Silurus glanis) and perch (Perca fluviatilis). Catfish is a typical apex predator, whereas perch is a smaller species that plays role of a mesopredator. Although, catfish is the third largest freshwater fish in the world, only few studies dealing with this species have been revealed thus far. The main reason is connected with capturing of the species that is inefficient by standard ichthyologic methods. Studies, that have been revealed recently, focused mainly on expansions of catfish to the West and South Europe. Catfish is unwanted in these localities due to a potential negative impact on native fish community, thus its reduction is desirable. In contrast, catfish occurrence is important in native localities where it plays a key role as a biomanipulative species (I). Catfish is a true generalist, which is a typical feature for large-bodied apex predators connected with high energy consumption of their bodies. The second typical feature is a wide diet plasticity and thus good adaptability to new food sources. It is associated with distribution of various food sources among individuals within the population (II). By contrast, perch is one of the most studied fish in the world and hundreds of studies with IF are revealed every year. However, the more information about biology of perch have been known, the more questions have been arisen. Several phenomena are revealed also in this thesis. For instance, crucial impact of juvenile perch on the entire ecosystem is described. High predation pressure on zooplankton may induce piscivory in primarily zooplanktivorous fish (III). Further, juvenile perch utilize hypoxic pelagic zones as a refuge against predation (IV). The last surprising phenomenon is described in the study dealing with both species, catfish and perch. Their coexistence may lead in strong discrimination of one species caused by special predation that was supposed to be implausible (V).
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Assessment of asp reproductive population in Švihov Reservoir in 2016
Šmejkal, Marek ; Blabolil, Petr ; Baran, Roman ; Kočvara, Luboš ; Bartoň, Daniel ; Kolařík, T. ; Prachař, Zdeněk ; Soukalová, Kateřina ; Děd, Vilém ; Vebrová, Lucie ; Vejřík, Lukáš ; Kubečka, Jan
The aim of the contract was to capture reproducing asp by electrofishing and tag fish individually using individual marking technique (PIT-tags). Estimate of asp reproductive population in the Švihov Reservoir was performed on the basis of mark-recapture methods. Furthermore, the length and weight increments were computed for recaptured asp individuals. Tagged individuals were monitored using passive telemetry systems on the tributary of Švihov Reservoir.
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Report on the status of the burbot populations in the Karhov, Lučina, Nýrsko and Zhejral reservoirs and Obecník Pond in 2016
Blabolil, Petr ; Jůza, Tomáš ; Matěna, Josef ; Muška, Milan ; Peterka, Jiří ; Říha, Milan ; Vejřík, Lukáš
The aim of the study was to monitor the burbot populations in four reservoirs and in a pond with previous stocking. The monitoring was carried out during the spring season 2016 and, in the case of the Nýrsko Reservoir, during winter and summer as well. The combination of harmless methods (traps of two types, visual survay, electrofishing, hydroacoustic), a method simulating fishing pressure (long-lines) and a fix-frame trawl were used to detect burbot. A novel monitoring scheme was developet and validated and burbot populatin characteristics described.
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Importance and species composition of non-fish prey in the diet of fish-eating predators
Mach, Jakub ; Čech, Martin (advisor) ; Vejřík, Lukáš (referee)
Piscivorous birds are usually considered to be exclusive fish eaters which are responsible for signifiant numerical and economical losses to fish populations. With a method of literary research the importace and species composition of non-fish prey is determine in the diet of selected fifteen species of piscivorous birds. The aim of this work is to determine the extent of non-fish part of the diet of particular piscivorous predators and categorize them on the grounds of differences between size of this part in their diet. Another goal is to determine any effects which can influence amount and species composition of non-fish part of nourishment, and also factors, which can influence obtained results based on the chosen method of analysis. According to the data found, diet of five bird species was composed almost exclusively with fish. Eight other bird species also showed preference for fish prey, but in most of these cases was present also important part of non-fish prey. Two bird species seems to be very oportunistic in case of composition their diet. As factors that can affect the extent of non-fish part in the diet was established especially the prey availability in environment, used method for diet composition analysis, insufficient attention for parts of prey other than fish, or also less...
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Ichthyological surveys of the Nýrsko and Karhov reservoirs and investigations of abundance, age composition and spawning dynamics of asp population in the Želivka Reservoir in 2015.
Vašek, Mojmír ; Soukalová, Kateřina ; Kočvara, Luboš ; Blabolil, Petr ; Baran, Roman ; Frouzová, Jaroslava ; Koliada, Ievgen ; Muška, Milan ; Šmejkal, Marek ; Draštík, Vladislav ; Kolařík, T. ; Prachař, Zdeněk ; Sajdlová, Zuzana ; Vebrová, L. ; Vejřík, Lukáš ; Kubečka, Jan
The species composition and the relative abundance and biomass of fish communities in the Nýrsko and Karhov reservoirs were evaluated by means of standardised multimesh gillnets. The spawning stock of asp in the Želivka Reservoir was individually marked using PIT tags and the density and behaviour of tagged fish at the main spawning grounds were examined through the whole spawning season. The total number of reproducing individuals in the asp population was estimated. The sex-specific length and weight growth rates of adult asp in the Želivka Reservoir were also calculated. \n\n
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The report on the asp and spined loach populations’ status in SCI – valley reservoirs.
Blabolil, Petr ; Šmejkal, Marek ; Bartoň, Daniel ; Baran, Roman ; Draštík, Vladislav ; Jůza, Tomáš ; Kočvara, Luboš ; Koliada, Ievgen ; Kolařík, T. ; Matějíčková, Ivana ; Prachař, Zdeněk ; Sajdlová, Zuzana ; Soukalová, Kateřina ; Vebrová, Lucie ; Vejřík, Lukáš ; Kubečka, Jan
The aim of the ichthyological survey was to assess the status of reproductively active population of asp (Leuciscus aspius) in the SCI (site of community importance) Želivka (Švihov Reservoir) and spined loach (Cobitis elongatoides) in the SCI Nová Říše (Nová Říše Reservoir).
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