Seasonal habitat use of three predatory fishes in a freshwater ecosystem

To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius), pikeperch (Sander lucioerca) and catfsh (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found signifcant diferences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfsh frequently visited a tributary during the warm season (late spring and early autumn), and moved closer to the dam during the cold season (late autumn to early spring). Pike longitudinal activity was highest in the cold season, pikeperch in the warm season, and catfsh activity peaked in both seasons. Overlap in the depth use among species was higher in the warm season, when all species used the upper layer of the water column, and lower in the cold season, when pikeperch and catfsh used deeper areas. These results demonstrated overlay and temporal variation of habitat use among these predators, as well as potential spatiotemporal space for their direct ecological interactions. Acoustic telemetry · Predators · Habitat use · Movement ecology · Winter ecologypublishedVersio

A simple fish-based approach to assess the ecological quality of freshwater reservoirs in Central Europe

The assessment of ecological quality in freshwater ecosystems is a key issue in many countries, but conditions for the development of assessment methodologies are often country-specific. This study proposes a simple methodology for the assessment of the ecological potential of reservoirs based on fish communities using a dataset covering major environmental and pressure gradients in reservoirs in the Czech Republic. Fish data obtained by gillnet sampling were correlated with a proxy of eutrophication as a key indicator of anthropogenic pressure for selecting appropriate fish-based indicators, establishing scoring criteria and developing the index of ecological quality. Expert judgement was also used to select potential fish indicators. Nine indicators were selected for the final fish-based index, fulfilling the criteria required by the Water Framework Directive. Two steps were used to validate the fish-based index quantification of its inter annual stability and sensitivity analysis of individual indicators. Finally, the index was compared to a previously developed general index for Central and Western Europe. Our study demonstrates that a combination of expert judgement and strict validation methods can result in an informative assessment of the ecological conditions, which can help identify conservation and restoration priorities. © P. Blabolil

Long-term monitoring of fish in a freshwater reservoir: Different ways of weighting complex spatial samples

Anthropogenic activities continue to pose the greatest challenges to freshwater ecosystems. Therefore, long-term monitoring is essential for the management and conservation of these resources. Monitoring programs for freshwater bodies often use a range of indicators, including biological elements such as fish. Existing European standard provides a depth-stratified gillnet sampling approach mainly in benthic habitats and at the deepest part of lakes to account for the uneven distribution of fish. However, the commonly used CEN (European Committee for Standardization) protocol does not weight sufficiently habitat volumes and underrepresent pelagic habitats to calculate whole-lake catch and biomass per unit effort (CPUE and BPUE, respectively). Extended European standard gillnet (4 larger mesh-sizes added in the geometric series) catch data collected over 18 years (2004–2021) in Římov Reservoir (Czech Republic) were used for a method comparison on indices for relative abundance and biomass of fish: CEN protocol without volume-weighting and two volume-weighted approaches. We also evaluated changes in species composition and trends in these fish population over time. Results indicated interannual changes in species composition, relative abundance, and biomass of fish community. The CEN protocol tended to put greater emphasis on benthic habitats which generally have larger CPUE and BPUE. Consequently, the two volume-weighting approaches produced lower estimates of the two parameters, with the exception of the most dominant pelagic bleak Alburnus alburnus (L.). All approaches consistently showed an increasing trend in whole-reservoir fish abundance and a decreasing trend in biomass over the study period. Following our assessment, we put forward the volume-weighting approach that considers the Volume of the depth Stratum (VOST) for weighting as the most realistic approximation of fish populations and therefore recommend its use

Redundant fingerling of perch (Perca fluviatilis L.) in Vír Reservoir and its impact on other trophic levels

The composition and preferences of depth levels and habitats of pelagic fingerling was studied in the canyon-shaped Vír Reservoir during years 2009-2011. The perch (Perca fluviatilis) fingerling was dominant in all three years. The density of fingerling was above the mean in years 2009 and 2010. It was as many as 278 individuals in 100m3(mean is 52 individuals in 100m3). A marked fall on 1,9 individual in 100m3 was registered in 2011. Perch fingerling was mainly observed in metalimnion during the day and also at night, where concentration of oxygen was very low. The highest density of perch fingerling was observed in the middle part within longitudinal profile. A significant difference was found in food composition among the years with high density and low density of fingerling. A predation of carp (Cyprinus carpio) and bream (Abramis brama) was proved during the years with high density of fingerling

Food, growth, sex ratio and depth distribution of perch \kur{(Perca fluviatilis L.)} in newly created lakes in Podkrušnohoří

Food, growth, sex ratio and depth distribution of perch (Perca fluviatilis L.) were studied in Milada Lake, Most Lake and Barbora Lake. These lakes were artificialy created after a coal mining. Sex ratio and depth distribution were also compared with data gathered from Vír Reservoir and Římov Reservoir. Fish designed for the research were captured by gillnets. Age analysis was carried out by otolite scanning. Food, growth and depth distribution were analysed with consideration of size and sex of the fish

Survey of the European catfish population in the Žlutice Reservoir in 2017

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

Survey of the catfish population in the Klíčava reservoir in 2018

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

Využití umělých třecích substrátů za účelem porozumění vlivům, které ovlivňují výběr třecí lokality, hloubku uložení jikrných pásů a třecí periodu okouna říčního (Perca fluviatilis L.)

The distribution of egg strands of perch was studied in Chabařovice Lake, Czech Republic, using areas with an artificial spawning substrate. It was found that egg strands were deposited in deeper and colder water in dependence on the duration of the daylight period. At the end of the spawning season, egg strands were deposited in deep and cold water where larvae development is very slow. For this reason the latest larvae are present a month and half later than the first perch larvae. Perch have evolved a powerful mechanism to protect their population against the vagaries of the weather and temporary bad biological conditions in the lake

Study of the state of wels catfish population and its diet in the Římov reservoir in 2018

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

Determining the amount of poached fish in a water reservoir based on direct simulation of the main poaching fishing methods: model case of Žlutice Reservoir

The report summarizes the results of the survey of poaching pressure on the Žlutice water reservoir carried out on the basis of contract No. PVL-1480/2022/SML