Quantification of Chaoborus and small fish by mobile upward-looking echosounding

Chaoborus larvae inhabit frequently the water column of lakes, when they can be mistaken for small fish. Because larvae ascend up to the blind zone of downward-looking echo sounding at night, quantitative acoustic estimation of them is possible only with upward-looking approach. For this reason, the mobile hydroacoustic upward-looking system (120 and 38 kHz split-beam echosounder) in combination with a direct catch method (trawling) was tested to investigate the night community of invertebrates and juvenile fish in the surface layer of the Římov reservoir (Czech Republic). In the target strength range of invertebrates (smaller than -59 dB), the 38 kHz echosounder recorded only a small proportion of targets while the 120 kHz echosounder recorded distinct peaks corresponding to high densities of Chaoborus (target strength, TS range -70 to -60 dB, average TS -66 to -64 dB). At 120 kHz frequency, the TS distribution of smaller cohort of juvenile fish ( 1.5 ind.m-3.

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

Report of the ichthyological survey of the Bagr reservoir in 2023

The report summarizes the results of a survey of fish in the Bagr reservoir using benthic gillnets and seine. The aim of the survey was to describe the spatial distribution of fish populations in the nearshore and bottom habitats of the reservoir during the day and night

Report on the course and results of fish catches in the districts of the South Bohemian Czech Anglers Union in 2021.

The report describes the results of an ichthyological survey of selected localities of the Lužnice, Stropnice and Malše rivers, that are under Czech Anglers Union management

Results of ichthyological survey of Hněvkovice reservoir in 2013

The report summarizes results of complex ichthyological survey of Hněvkovice water body done in 2013. The aims of the survey were to estimate fish species composition, and abundance and biomass of fish on the longitudinal profile of the water body and within all of its habitats according to valid certified national methodology of fish sampling in standing waters (Kubečka a Prchalová 2006 and Kubečka a kol. 2010)

Methodology of predatory fish quantification in reservoirs and lakes.

The publication contains an evaluation of surveying 36 reservoirs and artificial lakes in the years 1985–2020 in different parts of the Czech Republic by four sampling methods, which are further divided according to the sampling environment, daily periods and targeted age groups of predatory fish. The methods are gillnets, seines, trawls and continuous boat electrofishing. The catchability, standardized and relative abundance of asp, pikeperch, pike and catfish are evaluated. Based on these data, the reader can decide which method to use to detect a particular predatory species and compare the results with the situation in other localities

Report from the monitoring of Danubian spined loach (Cobitis elongatoides) populations in special areas of conservation of Nová Říše and Podtrosecká údolí

The aim of the study was to carry out a monitoring of the Danubian spined loach populations in several localities of selected and nearby areas. In all localities, fish sampling was carried out by the generator powered electrofisher and traps, the basic parameters of fish populations and environmental characteristics were described