Biomass and abundance biases in European standard gillnet sampling

The European Standard EN 14757 recommends gillnet mesh sizes that range from 5 to 55mm (knot-to-knot) for the standard monitoring of fish assemblages and suggests adding gillnets with larger mesh sizes if necessary. Our research showed that the recommended range of mesh sizes did not provide a representative picture of fish sizes for larger species that commonly occur in continental Europe.We developed a novel, large mesh gillnet which consists of mesh sizes 70, 90, 110 and 135mm (knot to knot, 10m panels) and assessed its added value for monitoring purposes. From selectivity curves obtained by sampling with single mesh size gillnets (11 mesh sizes 6 – 55mm) and large mesh gillnets, we identified the threshold length of bream (Abramis brama) above which this widespread large species was underestimated by European standard gillnet catches. We tested the European Standard gillnet by comparing its size composition with that obtained during concurrent pelagic trawling and purse seining in a cyprinid-dominated reservoir and found that the European Standard underestimated fish larger than 292mm by 26 times. The inclusion of large mesh gillnets in the sampling design removed this underestimation. We analysed the length-age relationship of bream in the Římov Reservoir, and concluded that catches of bream larger than 292mm and older than five years were seriously underrepresented in European Standard gillnet catches. The Římov Reservoir is a typical cyprinid-dominated water body where the biomass of bream > 292mm formed 70% of the pelagic trawl and purse seine catch. The species-specific relationships between the large mesh gillnet catch and European Standard catch suggested that the presence of carp (Cyprinus carpio), European catfish (Silurus glanis), tench (Tinca tinca) or bream warrants the use of both gillnet types.We suggest extending the gillnet series in the European Standard to avoid misinterpretation of fish community biomass estimate

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

Securing expert leadership on the fishing out Laz reservoir and other connected activities according to Brdy conservation agency needs.

The report describes fish community reduction in Laz Reservoir

Assessment of the status of rheophilic fish in the Vltava basin and key factors affecting their populations.

The report describes ecological status of fish in Vltava River basin with special attention to rheophilic fish species

How football clubs costs determines sports results

Tato práce zkoumá, jaké vztahy existují mezi nákladovostí českých fotbalových klubů a sportovním úspěchem na dvou úrovních. První úrovní je nejvyšší profesionální liga (Gambrinus liga) a úrovní druhou je až 6. nejvyšší, neprofesionální fotbalová soutěž (1. A třída). Na začátku práce bylo vycházeno z hypotézy, že fotbal na nejvyšší tuzemské úrovni množství finančních prostředků, utracených během dané sezóny, nijak zvlášť neovlivňuje, neboť sportovní výsledky mezi "bohatými" a "chudými" kluby nezaznamenávají zásadní rozdíly. Zatímco množství utracené v nižších fotbalových soutěžích může značně výsledky ovlivnit (např. zaplacením kvalitnějších hráčů, vybavení apod.). Během výzkumu došlo k jednoznačnému prokázání nezávislosti finančních prostředků na neprofesionální úrovni, čímž došlo v této části k nepotvrzení hypotézy a dospění k závěru, že na sportovní výsledek má vliv mnoho další determinantů. Na úrovni nejvyšší k jednoznačnému závěru nedošlo. Výzkum vycházel z dat za poslední tři sezóny.This bachelor thesis examines relationship between costs of Czech football clubs and their sports performance in different seasons on two levels. First level examines top Czech league -- Gambrinus liga, second level examines unprofessional sixth league -- 1.A třída. The hypothesis marked out that there is no substantial relationship between money and sports results in top league. It is based on observed results in last couple of seasons. On the other hand relationship between cost and sports results in unprofessional leagues might be proven based on greater influence of money on this sports level. Result of analysis proved that on unprofessional level is unequivocally no relationship between sport result and cost of clubs therefore there is more complex system that influences sport result. Results from top league have proven examined relationship in one statistical model, in the other relationship has not been proven definitely. Analysis applies on last three seasons

Ichthyological survey of the asp spawning stock in the Švihov Reservoir in 2018

The aim of the study was to evaluate the results of the asp population development in relation to the current fishery management and to develop proposals for the management of this predatory species in the future

Evaluation of reophilic fishes state in Vltava river basin and key factors influencing their populations.

The report describes advancement in evaluation of rheophilic fish data

Preparation of the project within the framework of the joint project 'Mapping the occurrence of the critically endangered common bream in the South Bohemian Region and preparation of a regional action plan for its conservation'.

The report decribes mionitoring and conservation work on crucian carp in 2022 in South Bohemia region

Associations of fish with various types of littoral habitats in reservoirs

The study investigated fish habitat association within littoral habitat of four Czech reservoirs. Three most common habitats within reservoir: beaches (former meadows), stump fields (former forest) and rubble slopes were chosen for the study. The patterns of fish biomass, abundance and species structure were analysed based on robust data obtained from gillnet sampling. Adult bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields with gentle slope of the bank, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Leuciscus aspius and pike Esox lucius were associated with rubble slopes. We demonstrated fish species are not distributed homogeneously in the littoral and that that most common species are associated with distinct habitats