Czech Reservoirs Research Articles

Fish scale stable isotopes as potential indicators of nutrient pollution: Exploring the response of roach (Rutilus rutilus) scale δ15N and δ13C to a gradient of land use disturbance

To examine the suitability of fish scales as potential tracers of nutrient pollution, we analysed the nitrogen and carbon stable isotope values (δ15N and δ13C) in scales of a generalist fish species, roach Rutilus rutilus, collected from 22 Czech reservoirs covering wide gradients of catchment land use and nutrient enrichment. Using generalised additive mixed models in the first step and generalised linear mixed models in the second step, we evaluated the response of roach scale stable isotope values to catchment land use variables (percentage of agricultural land and human population density) and in-reservoir water quality variables. Roach scale δ15N values varied by 15 ‰ among the reservoirs and were strongly, linearly, and positively associated with the percentage of agricultural land in the reservoir catchments, pointing to agriculture as the dominant source of nitrogen pollution in the investigated systems. Roach scale δ13C values differed by 8 ‰ among the studied reservoirs and were not related to catchment land use variables or in-reservoir primary production (chlorophyll-a levels). Possible variation in roach foraging strategies (littoral versus pelagic) between reservoirs or the contrasting effects of eutrophication-related autotrophic and heterotrophic processes on baseline δ13C values may explain the lack of relationships between roach scale δ13C values and the explanatory variables. In summary, our findings show that fish scale δ15N values are sensitive bioindicators of catchment-derived anthropogenic nitrogen inputs to freshwater ecosystems. Because scales can be sampled in a nonlethal way and δ15N analysis is relatively inexpensive, we suggest that measuring the δ15N values of fish scales could be an effective method for monitoring nitrogen pollution in aquatic environments.

An assessment of the ecological potential of Central and Western European reservoirs based on fish communities

In this study we developed a novel methodology based on fish communities to assess the ecological potential of central European reservoirs. Using the hindcasting approach, our index predicts values that could be observed in the absence of pressures for each reservoir depending on their environmental characteristics. Fish data were collected from 144 French and Czech reservoirs between 2005 and 2013 by standardized benthic gillnet sampling and transformed to functional and taxonomical metrics. After all validation by multiple testing of models redundancy and pressure-response, the final index was composed of three metrics: total biomass of fish, abundance of invertivores/piscivores, and abundance of planktivorous fish. The index accurately identifies reservoirs that are lightly, moderately and heavily affected by eutrophication. In addition to French and Czech reservoirs, this index could be a useful tool for countries with few reservoirs and the basis for further collaborative studies.

Accumulation of heavy metals in crayfish and fish from selected Czech reservoirs.

To evaluate the accumulation of aluminium, cadmium, chromium, copper, lead, mercury, nickel, and zinc in crayfish and fish organ tissues, specimens from three drinking water reservoirs (Boskovice, Landštejn, and Nová Říše) and one contaminated site (Darkovské moře) in the Czech Republic were examined. Crayfish hepatopancreas was confirmed to be the primary accumulating site for the majority of metals (Cu > Zn > Ni > Cd > Cr), while Hg and Cr were concentrated in abdominal muscle, and Al and Pb were concentrated in gill. Metals found in Nová Říše specimens included Cu > Zn > Ni and those found in Boskovice included Zn > Hg > Cr. Cd concentrations were observed only in Landštejn specimens, while contaminated Darkovské moře specimens showed the highest levels of accumulation (Cu > Al > Zn > Pb). The majority of evaluated metals were found in higher concentrations in crayfish: Cu > Al > Zn > Ni > Cr > Cd > Pb, with Hg being the only metal accumulating higher in fish. Due to accumulation similarities of Al in crayfish and fish gill, differences of Hg in muscle, and features noted for the remaining metals in examined tissues, biomonitoring should incorporate both crayfish and fish to produce more relevant water quality surveys.

Occurrence of age‐0 year dwarf pikeperch Sander lucioperca in late summer – an overlooked phenomenon in reservoirs

Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutch reservoir revealed extremely small age-0 year pikeperch Sander lucioperca (mean 24 mm standard length, LS , minimum 13 mm LS ) alongside more normal-sized S. lucioperca that are found at the end of the first growing season (mean 50 mm LS ), resulting in two clearly size-separated cohorts. Reference to such small age-0 year S. lucioperca in lakes or reservoirs at this time of year and in such large numbers are almost absent the scientific literature, and the presence of these small S. lucioperca is contradictory to the common understanding of the reproductive biology of this species. This overlooked phenomenon may have a major effect on the population dynamics of this valuable species because of size-dependent winter mortality.

Effect of habitat conditions on parasite infection in 0+ juvenile perch (Perca fluviatilis L.) in two Czech reservoirs

The objective of this study was to identify potential effects of habitat conditions on parasite infection risk in reservoirs. For this, we compared parasite infection in 0+ perch (Perca fluviatilis L.) between reservoir sections: (1) along the longitudinal profile of Brno reservoir (inflow—main body—outflow), and (2) the transversal profile of Hamry reservoir (littoral and pelagic zones). Perch were predominantly infected with trophically transmitted endoparasites. Longitudinal parasite infection differed between sampling sections, showing different trends in particular parasite species between sections. The abundance of dominant Bunodera luciopercae was highest in the main body and lowest in the outflow, abundance of Proteocephalus sp. and Camallanus spp. decreased between the inflow and outflow, and abundance of Acanthocephalus lucii and ectoparasites (Gyrodactylus sp. and Argulus foliaceus) increased from the inflow to the outflow. Parasite diversity was higher in the outflow compared to other sections. No difference was observed in parasite abundance between littoral and pelagic perch subpopulations, though higher endoparasite diversity was found in the littoral zone. The results indicate that habitat type can influence parasite infection in perch through local food (intermediate host) availability. Fish–host behaviour is also discussed as a factor possibly influencing infection in perch.

The utility of predatory fish in biomanipulation of deep reservoirs

Piscivorous fish may drive trophic cascades and maintain good water quality in lakes and reservoirs. Biomanipulation by stocking piscivores has been therefore suggested as a useful tool to regulate phytoplankton biomass in anthropogenically eutrophicated systems. We evaluated the top-down effects of piscivores on lower trophic levels in 13 deep, stratified Czech reservoirs that were built by damming rivers. In addition, the importance of piscivores was assessed in three deep, bank-side Dutch reservoirs that are artificially destratified. All the Czech reservoirs are regularly stocked with piscivores while the Dutch reservoirs have never been stocked. The piscivores had no significant top-down effect on the biomass of planktivorous and benthivorous fish and on phytoplankton biomass (measured as chlorophyll-a concentration) in the Czech reservoirs, although the proportion of piscivores in the fish community was high in half of them. The planktivore and benthivore biomass and the phytoplankton biomass correlated strongly with phosphorus concentration, which is in line with bottom-up control by nutrient supply. On the other hand, piscivores in the Dutch reservoirs dominated the fish community and apparently contributed to good water quality. Nevertheless, the primary cause of relatively low phytoplankton biomass in the Dutch reservoirs was the artificial destratification inducing light limitation on phytoplankton. We conclude that biomanipulation cannot substantially reduce phytoplankton biomass in the eutrophicated systems with high external nutrient input. The input should be reduced to control phytoplankton and if it is not possible, artificial destratification can be applied.

Eel attacks—A new tool for assessing European eel (Anguilla anguilla) abundance and distribution patterns with gillnet sampling

Because of its complex life cycle, cryptic behavior, body shape, ability to excrete mucus and excellent maneuvering, the European eel ( Anguilla anguilla ) is difficult to monitor. During many years of gillnetting in Dutch and Czech freshwaters, we registered characteristic involutions of gillnet netting with a partially eaten fish inside. We concluded that these involutions were the result of eels attacking fish caught in gillnets and called the occurrences eel attacks. When we compared the abundance of eel attacks in gillnets with the abundances of eels recorded using active gears (beach seining and trawling), we found a positive and significant correlation (partial Spearman R = 0.640) that can be used for rough eel-abundance assessment. The most frequently attacked fishes were young individuals of abundant species ( Perca fluviatilis , Sander lucioperca , Rutilus rutilus and Osmerus eperlanus ) and small species ( Gymnocephalus cernua ) up to 100 mm standard length. The eels preferred pikeperch and avoided roach and smelt. The reason for prey species preferences was most likely prey species distribution rather than size selectivity. The eels attacked fishes in gillnets during the night, most likely after midnight. The eel attacks were not distributed homogenously among the studied reservoirs, geographical areas and years. The frequency of eel attacks was higher in benthic than in pelagic habitats. Eel attacks were more frequent in Dutch than in Czech reservoirs, corresponding to a general decline of eel densities with increasing distance from the sea. The number of eel attacks also declined significantly from 1998 to 2008. The present study showed that eel attacks can be successfully used as a new, simple and nonintrusive tool for monitoring eel abundance using gillnets. Gillnets are widely used in fish monitoring, and hence, gillnet sampling performed throughout Europe has a great potential for eel-abundance assessment.

Stock–catch analysis of carp recreational fisheries in Czech reservoirs: Insights into fish survival, water body productivity and impact of extreme events

In culture-based fisheries, managers strive for high stocking efficiency, the ratio between the total weight of caught and stocked fish. Here we present a new time series approach to examine the dependence of reported anglers’ catches on stocking and external events, using data on carp (Cyprinus carpio L.) from 14 reservoirs in the Czech Republic. Average stocking efficiency varied between 0.25 and 2.2, with values close to unity in most reservoirs. The lowest efficiencies occurred in three reservoirs receiving cold hypoxic water from a large upstream reservoir, while the highest efficiencies were found in two shallow, highly productive reservoirs. Analyses further indicate that stocked carp are typically caught during the year of release or the year after; but also that the mean time lag between stocking and capture increases with reservoir area. External events can be important: major floods in the years 2002 and 2006 were in many cases followed by large, up to 10-fold, increases in catches in subsequent years; we attribute the surplus catch to carp washed down from upstream aquaculture and river stretches. In contrast, the “Velvet Revolution” (demise of the communist regime in 1989) had no discernible effect on catches in subsequent years. In conclusion, the proposed method can simultaneously estimate the likely mean survival time of stocked carp and identify the impact of major environmental and societal events on recreational fisheries. The approach thus sheds light on the performance of current stocking practices at individual reservoirs, and could be used to monitor and improve stocking strategies and management of culture-based recreational fisheries.

Size selectivity of standardized multimesh gillnets in sampling coarse European species

We studied gillnet selectivity by using a direct method to compare fish-size distributions from gillnet catches (Nordic type, mesh size range 5–135 mm, knot-to-knot, factor between adjacent mesh sizes 1.25) with a reference distribution obtained using beach seines for fry and adult fish (net length 10, 40 and 50 m, mesh size 1, 6 and 10 mm, respectively) in five Czech reservoirs. Target species were roach Rutilus rutilus (L.), perch Perca fluviatilis L. and rudd Scardinius erythrophthalmus (L.). The most common pattern of difference in fish-size distributions between the two gears was that more 0+ and 1+ year old fish were caught by beach seines and slightly higher proportions of larger fish were observed in gillnet catches. For the three species, gillnets were unable to enmesh fish smaller than approximately 40 mm in standard length. We developed average species-specific corrections that increased proportions of 0+ and 1+ year old fish and decreased proportions of larger fish. However, the average correction gave corrected size distributions that were biased in about 20% of cases. We also applied Kurkilahti’s correction given in European Standard EN 14 757, but it had a negligible effect on reducing the bias in size distributions. Future research is needed to develop more accurate corrections for size distributions, otherwise interpreting results from gillnet sampling can be very misleading especially for those including data on 0+ and 1+ year old fish.

CORRESPONDENCE BETWEEN PHYLOGENY AND MORPHOLOGY OF SNOWELLA SPP. AND WORONICHINIA NAEGELIANA, CYANOBACTERIA COMMONLY OCCURRING IN LAKES1

In this study, the first reported isolates of the genera Snowella and Woronichinia were characterized by 16S rRNA gene sequencing and morphological analysis. Phylogenetic studies and sequences for these genera were not available previously. By botanical criteria, the five isolated strains were identified as Snowella litoralis (Häyrén) Komárek et Hindák Snowella rosea (Snow) Elenkin and Woronichinia naegeliana (Unger) Elenkin. This study underlines the identification of freshly isolated cultures, since the Snowella strains lost the colony structure and were not identifiable after extended laboratory cultivation. In the 16S rRNA gene analysis, the Snowella strains formed a monophyletic cluster, which was most closely related to the Woronichinia strain. Thus, our results show that the morphology of the genera Snowella and Woronichinia was in congruence with their phylogeny, and their phylogeny seems to support the traditional botanical classification of these genera. Furthermore, the genera Snowella and Woronichinia occurred commonly and might occasionally be the most abundant cyanobacterial taxa in mainly oligotrophic and mesotrophic Finnish lakes. Woronichinia occurred frequently and also formed blooms in eutrophic Czech reservoirs.

Summer changes in cyanobacterial bloom composition and microcystin concentration in eutrophic Czech reservoirs

In mid-July and August 2003 and 2004, 18 reservoirs in the Czech Republic were sampled for phytoplankton species composition and concentration of intracellular microcystins (MCs). As a consequence of high nutrient loading, most of the reservoirs experienced cyanobacterial blooms of various intensities, with the prevalence of cyanobacteria increasing markedly in August, along with a conspicuous shift in species composition toward dominance of Microcystis spp. Microcystins were detected in 90% of the samples, and their amount also increased considerably in August, reflecting the cyanobacterial biomass. In Microcystis-dominated samples, a significantly higher amount of MCs (p < 0.001) occurred than in samples in which other taxa prevailed. Microcystins were positively correlated with chlorophyll a and cyanobacterial biovolume (p < 0.05, R2 = 0.61 and 0.66, respectively), with the strongest correlation found for Microcystis spp. biovolume (p < 0.001, R2 = 0.87). This taxon was the most important producer of MCs in Czech reservoirs. The main structural variants of MCs were MC-LR, MC-RR, and MC-YR. This study's data also indicate that the relative share of MC variants (MC-LR and MC-RR) varies considerably with time, most likely as a consequence of different species and strain compositions during the summer. This study clearly demonstrates a high prevalence of MC-producing cyanobacteria in Czech reservoirs. Therefore, regular monitoring of these reservoirs is highly desirable in an effort to minimize potential health risks to the human population.

A polyphasic approach to assess the cyanobacterial diversity of summer samples from Czech reservoirs

A polyphasic approach to assess the cyanobacterial diversity of summer samples from Czech reservoirs

Trophic structure of nine Czech reservoirs regularly stocked with piscivorous fish

For nearly 20 years, most Czech reservoirs supplying drinking water have been under statutory protection which permitted reservoir managers to manipulate fish stocks in order to maintain a sustainable water quality. The most common biomanipulative measure adopted was stocking with piscivorous fish (mostly 5 cm fry) using an annual stocking level of approx. 25 000 fish per reservoir. Nine reservoirs were studied for signs of top-down food web effects, as predicted by the trophic cascade hypothesis based on levels of total phosphorus (TP), chlorophyll a (Chl a), zooplankton biomass (ZB) and zooplankton community structure. In all nine reservoirs, only small Daphnia species were recorded, such as D. galeata and D. cucullata. The proportion of large-bodied daphnids retained on a 0.71 mm sieve was less than 10% of the total crustacean biomass in all reservoirs. The relationship of Chl a level – TP, and of ZB – Chl a, was positive under enhanced piscivory and did not differ statistically from the relationships in other reservoirs with natural fish stocks. This implies that bottom-up forces remained stronger than top-down ones in the studied reservoirs, despite the stocking of piscivorous fish. The failure of this attempt at biomanipulation may be due to an insufficient stocking rate of predatory fish and/or inadequate data on the resident planktivorous fish levels.

Horizontal beaming as a crucial component of acoustic fish stock assessment in freshwater reservoirs

During the summer of 1992 and spring and summer of 1995 and 1996, the fish stocks of four Czech reservoirs, Lipno, Orlik, Slapy and Řimov, were surveyed acoustically. Two acoustic systems (BioSonics model 102 dual-beam 420 kHz echosounder and SIMRAD EY500 split-beam 120 kHz echosounder) were employed to survey the whole bodies by vertical and near-surface horizontal beaming with the transducer at a depth of 40–60 cm. Day and night acoustic surveys were carried out during the spring and summer when fish were unlikely to be undetectable `hiding' in the `acoustically-blind' zone near the bottom. Fish more than one pulse length from the bottom could be detected in the sonar beam. The main finding of this study was that vertical beaming must be supplemented by horizontal beaming in all the water bodies as the fish were usually confined to depths of 0–4 m due to attraction to warm surface waters in spring and, later, due to avoidance of de-oxygenated hypolimnions. This applied to all the coarse fish species (mainly Perca fluviatilis, Rutilus rutilus and Abramis brama) apart from their larval stages. Fish densities estimated by vertical beaming were two to fifty times lower than those estimated by horizontal beaming due to avoidance of the boat. Split-beam tracking showed that fish remained very close to the surface even within the strata surveyed by the horizontal beam.

Influence of Diffuse Pollution on the Eutrophication and Water Quality of Reservoirs in the Morava River Basin

Diffuse (nonpoint) pollution from the river basin is responsible for a substantial part of Czech reservoirs' deterioration caused by eutrophication and water pollution. The research results of two model drinking water supply reservoirs (different area and depth) in the Morava river basin showed that the main nutrient sources in the period 1960-1991 were: agricultural land use (overland and subsurface transport of nutrients, effects of drainage and erosion), point sources (urban activities, agricultural farms) and atmospheric depositions of N and P compounds. The accelerated eutrophication was manifested by the increasing development of phytoplankton. The main problems entail occurrence of toxic species of Cyanophyta/Cyanobacteria (blue-green algae) Aphanizomenon flos-aquae, Microcystis aeruginosa and some other species (e.g. Pseudanabaena limnetica). In the small and shallow drinking water reservoir of Ludkovice the living algae penetrated drinking water. In the deep reservoir of Vír the situation was more favourable. The increase of nutrient input (N,P) during the period 1969-1992 was highly significant Various measures have been proposed to slow the reservoir eutrophication (sustainable use of land, best management practices - soil retention, buffer strips, constructed wetlands etc.).

The biology (size, growth, food) of pike (Esox lucius L.) in three Czech reservoirs

The biology (size, growth, food) of pike <i>(Esox lucius</i> L.) in three Czech reservoirs

Two interesting algae from Czech reservoirs

Paulschulzia pseudovolvox (Schulz)Skuja, a member of theTetrasporales, is recorded for the first time for Czechoslovakia.Amphidinium radiatum Javorn., a member of theGymnodiniales is recognized. Further information about its variability is supplemented. The algae were studied in two reservoirs.