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Sexual dimorphism is common across the animal kingdom, but the contribution of environmental factors shaping differences between the sexes remains controversial. In ectotherms, life‐history traits are known to correlate with latitude, but... more
Sexual dimorphism is common across the animal kingdom, but the contribution of environmental factors shaping differences between the sexes remains controversial. In ectotherms, life‐history traits are known to correlate with latitude, but sex‐specific responses are not well understood. We analyzed life‐history trait variation between the sexes of European perch (Perca fluviatilis L.), a common freshwater fish displaying larger female size, by employing a wide latitudinal gradient. We expected to find sex‐dependent latitudinal variation in life‐history variables: length at age, length increment, and size at maturity, with females showing consistently higher values than males at all latitudes. We further anticipated that this gender difference would progressively decrease with the increasingly harsh environmental conditions toward higher latitude. We hypothesized that growth and length increment would decrease and size/age at maturity would increase at higher latitudes. Our results co...
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Stav populace bolena dravého (Leuciscus aspius) v EVL Želivka a sekavce podunajského (Cobitis elongatoides) v EVL Nová Říše: Current status of asp (Leuciscus aspius) in Želivka Reservoir Special Area of Conservation and Danubian spined loach (Cobitis elongatoides) in Nová Říše Reservoir Special A...more
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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
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.
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Fish body orientation significantly influences the size obtained with hydroacoustic signals, and thus the estimate of fish size and biomass. For this reason, each characteristic of a target’s echo can be advantageous for developing... more
Fish body orientation significantly influences the size obtained with hydroacoustic signals, and thus the estimate of fish size and biomass. For this reason, each characteristic of a target’s echo can be advantageous for developing algorithms to refine acoustic fish estimates. We measured pulse-compressed broadband acoustic signals from tethered fish (common bream Abramis brama) in different dorsal positions. Based on generalized additive mixed models (GAMM), we initially tested the influence of the fish dorsal aspect on the amplitude echo envelope and amplitude echo descriptors (amplitude maximum and amplitude echo length at seven different levels below the maximum) by altering the fish dorsal orientation. Our study confirmed that the dorsal aspect influenced the shapes of the amplitude echo envelopes in both fast- and slow-tapered pulses. Furthermore, we found that echo lengths approximately 15 dB below the amplitude maximum, especially for fast-tapered signals, could provide good...
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Until 2006, the Lipno Reservoir had the largest catches of pikeperch in the Czech Republic, but since 2007 it has partially collapsed. This collapse was preceded by oligotrophication, when phosphorus concentrations declined by 25%.... more
Until 2006, the Lipno Reservoir had the largest catches of pikeperch in the Czech Republic, but since 2007 it has partially collapsed. This collapse was preceded by oligotrophication, when phosphorus concentrations declined by 25%. Conservation measures from 2009 to 2015 partially improved the population from 2015, but pikeperch biomass did not reach previous levels. Unsuccessful spawning and low survival of pikeperch fry were suspected as possible reasons. Pelagic trawling for pikeperch younger juveniles in June and older juveniles in August indicated that extreme mortality in the first year of life, rather than limited spawning, was the reason for low pikeperch recruitment. Large interannual differences in pikeperch density were observed in both spring and summer, and the growth was generally low. Pikeperch fry density changed over a trophic gradient with the highest densities in the eutrophic upper reservoir parts, while differences between depths were much less pronounced due to...
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Abstract Obtaining a representative sample is fundamental to the assessment of fish communities. In this study we used data from 99 different surveys of 29 artificial lakes in the Czech Republic to evaluate the precision of fish community... more
Abstract Obtaining a representative sample is fundamental to the assessment of fish communities. In this study we used data from 99 different surveys of 29 artificial lakes in the Czech Republic to evaluate the precision of fish community indicator estimates based on reduced gillnet scenarios derived from triplet gillnets installed in each particular locality, depth strata and habitat. Forty-four indicators (based particularly on numbers and biomass per unit of effort – NPUE and BPUE, respectively) were compared between the full sampling design (three gillnets at every sampling location) and six reduced scenarios which were combinations removing one or two gillnets from the triplets. The whole community comparison found the accuracy (R2) between the full sampling design and reduced scenarios usually to be above 0.9. Strong accuracy was also found for species richness and mean fish weight. In individual species comparisons, accuracy above 0.75 was found for common species in a given habitat, whereas accuracy for less common species sometimes dropped below 0.5. Setting one gillnet in an appropriate depth strata and lake locality appears to be sufficient for unbiased overall NPUE, BPUE, and species composition estimates, and at the same time, reduces sampling effort and minimizes unwanted fish mortality. Capturing less common species in a given habitat is more or less accidental and additional sampling effort increased the probability of catching these species. On the other hand, methods targeting rare species of interest may be considered instead of increasing gillnet effort above the CEN standard.
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Gillnetting is a technique commonly used in relative abundance and biomass estimates of fish. However, due to its passive nature, the direct recalculation of the catch to reservoir volume or area is not trivial. This issue is often solved... more
Gillnetting is a technique commonly used in relative abundance and biomass estimates of fish. However, due to its passive nature, the direct recalculation of the catch to reservoir volume or area is not trivial. This issue is often solved by using hydroacoustics, which provides information about fish density, though without the ability to distinguish species. However, the precision of such density estimates are also questionable. In this study, we estimated the abundance and biomass of dominant fish species before and after a biomanipulation program (fish removal) in 2020 using gillnetting and hydroacoustic surveys in a temperate reservoir. Between the two sampling periods, nearly 27,000 individuals (9000 kg) older than 0 + of bleak (Alburnus alburnus) and bream (Abramis brama) were removed during the biomanipulation program. Decreases in abundance and biomass estimates were expected for both techniques and both species. The gillnet decrease was 68% in CPUE (catch per unit of effort) and 48% in BPUE (biomass per unit of effort) for both species and all gillnets grouped together. Hydroacoustic observations showed a decrease of approximately 79% in abundance and 74% in biomass after fish reduction. Considering the numbers and biomass of fish removed, the absolute hydroacoustic estimates were underestimated for fish abundance but credibly estimated for biomass. The average weight of the fish taken was between the values of the fish caught with gillnets and the weights determined by hydroacoustics. In terms of results, both methods appear to be a suitable tool for estimating fish abundance and biomass in large inland waters, although the spatial and temporal distribution of fish of different sizes should be considered when using different sampling methods for fish monitoring.
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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... more
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 (<25 mm in length) overlapped the...
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ABSTRACT
In reservoirs, perch fry create simultaneously three different communities – epipelagic, bathypelagic and littoral. Bathypelagic perch fry perform regular diel vertical migrations (DVM) staying in deep water during daylight hours and... more
In reservoirs, perch fry create simultaneously three different communities – epipelagic, bathypelagic and littoral. Bathypelagic perch fry perform regular diel vertical migrations (DVM) staying in deep water during daylight hours and spent the night close to water surface. Cech et al. (2005) stressed the question whether the DVM of perch fry is definitely under direct control of light intensity or whether the twilight is only a cue and all the behaviour is genetically coded. To test this hypothesis directly in the field, large black foil (50 x 50 m) was used to prevent light penetrate the water column. The behaviour of perch fry was continually monitored for 5 days using two SIMRAD EK60 echosounders working with frequency of 120 and 400 KHz. One stationary transducer (circular – ES120-7G) was deployed as up-looking and one semi-mobile transducer (circular – ES400-7C) was deployed as down-looking. With water surface exposed to light, perch fry performed DVM with amplitude of 12 m bei...
In central European meso- to eutrophic water bodies young-of-the-year European perch (Perca fluviatilis) belong to the most common fish species. On the other hand, water bodies with fish communities dominated by adult perch are... more
In central European meso- to eutrophic water bodies young-of-the-year European perch (Perca fluviatilis) belong to the most common fish species. On the other hand, water bodies with fish communities dominated by adult perch are disappearing rapidly and becoming extremely scarce. As a factor standing behind these declines in perch dominated fish communities, eutrophication and consequent better competitive abilities of juvenile roach for crustaceoplankton, the nearly exclusive food base in eutrophicated waters, have been suggested. Therefore, we have compared the growth rate of young-of-the-year perch in water bodies with abundant and non-abundant adult perch populations and related the observed differences to differences in the biotic and abiotic conditions of these water bodies, especially to differences in the food base and factors that affect these food base differences (macrophyte cover, oxygen vertical profiles etc.). Importance of the switch to piscivory in young-of-the-year p...
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1 Institute of Hydrobiology, Biology Centre of the Academy of Sciences of the Czech Republic, vvi, Na Sádkách 7, 370 05 České Budějovice, Czech Republic; e-mail: mojmir.vasek@seznam.cz 2 Faculty of Science, University of South Bohemia, ...
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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... more
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 bio...
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Freshwater protected areas are designated parts of the inland waters that restrict human activities. They were created as a mechanism to combat the decline of fauna and flora of the world. Some authors have questioned their actual... more
Freshwater protected areas are designated parts of the inland waters that restrict human activities. They were created as a mechanism to combat the decline of fauna and flora of the world. Some authors have questioned their actual effectiveness in terms of the purpose of protecting endangered fauna and flora. We conducted an experiment in Lipno reservoir in the Czech Republic to evaluate the impact of protection against angling pressure on the fish community. We selected data from two years of gill netting and analyzed the difference between areas of low anthropogenic impact (LAI) and those of high anthropogenic impact (HAI) in terms of abundance, biomass, standard length, and diversity indices. Three groups of fish were found to prefer protected areas with low anthropogenic pressure: 1. YOY (Young-of-the-year) perch (Perca fluviatilis), the dominant of the young-of-the-year fish community. 2. Pike (Esox lucius), wels catfish (Silurus glanis) and rudd (Scardinius erythrophthalmus), ...
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The sinusoidal swimming of fish, the swim-search feeding behaviour (Cech & Kubecka 2002, Journal of Fish Biology 61, 456-471), was studied with respect to season, fish length and solar radiation in mov Reservoir, Czech Republic, using a... more
The sinusoidal swimming of fish, the swim-search feeding behaviour (Cech & Kubecka 2002, Journal of Fish Biology 61, 456-471), was studied with respect to season, fish length and solar radiation in mov Reservoir, Czech Republic, using a bottom-mounted, split-beam transducer (7o, nominal angle; frequency 120 kHz). The proportion of sinusoidally swimming fish increased from April to August while this behaviour was absent in October. The occurrence of sinusoidal swimming showed an apparent pattern throughout the day; it increased sharply around sunrise, was highest within 5-6 hours around solar noon and sharply decreased around sunset. Significantly less frequent occurrence of sinusoidal swimming was recorded during cloudy days compared to sunny days. The vast majority of records came from fish of standard length ranging from 100 to 400 mm, which represents the typical size range of common bream Abramis brama and roach Rutilus rutilus of age >1+, the main zooplanktivores in the rese...
Research Interests: Biology, Ecology, Fish Biology, Age, Reservoir, and 15 moreFishing, Predation, Fauna, Abundance, Fisheries Sciences, Fishery, Stock, Maturity, FISH FAUNA, Cyprinidae, Perch, Rutilus, Percidae, Piscivore, and Fish Stock
Hydroacoustic counting and a three-year mark-recapture study with passive integrated transponders (PIT tags) were used to estimate the size of a spawning population of nase Chondrostoma nasus, a threatened potamodromous cyprinid that... more
Hydroacoustic counting and a three-year mark-recapture study with passive integrated transponders (PIT tags) were used to estimate the size of a spawning population of nase Chondrostoma nasus, a threatened potamodromous cyprinid that undertakes annual spawning migrations into a tributary of the Danube River. In 2005, the estimates of the size of the spawning population from the hydroacoustic counts (N = 2234, 95% CL 1929-2538) and from the Jolly-Seber model (N = 1198, 95% CL 461-5842) corresponded well. Estimates from the jackknife-estimator based on the hydroacoustic counts yielded slightly higher values (N = 2783, 95% CL 2529-3037), but were still in the same order of magnitude as those from the hydroacoustic and mark-recapture approach. At low run-size, hydroacoustic counting was more time consuming and technically demanding than mark-recapture studies. At the same time, it was non-invasive, provided real-time data on a fine temporal scale, and estimates showed less variability than the Jolly-Seber model. Mark-recapture of fish in spawning streams involved substantial disturbance at a sensitive stage of the life cycle. Hence, hydroacoustics is highly suited for population estimates of threatened potamodromous fishes, where interference needs to be minimized.
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... In Czech hydroelectric reservoirs, a daily level fluctuation of 1-2 m together with sparse soil ensures that the littoral area `B&amp;#x27; is virtually plant-free . ... In 78 ran-domly chosen Central and East European... more
... In Czech hydroelectric reservoirs, a daily level fluctuation of 1-2 m together with sparse soil ensures that the littoral area `B&amp;#x27; is virtually plant-free . ... In 78 ran-domly chosen Central and East European reser-voirs, 69.2% of fish species were phytophils and 86.9% were ...
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ABSTRACT
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Stav populace bolena dravého (Leuciscus aspius) v EVL Želivka a sekavce podunajského (Cobitis elongatoides) v EVL Nová Říše: Current status of asp (Leuciscus aspius) in Želivka Reservoir Special Area of Conservation and Danubian spined loach (Cobitis elongatoides) in Nová Říše Reservoir Special A...more