Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutc... 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.
Intra-species variability in isotopic niches, specifically isotopic total niche width (ITNW), iso... more Intra-species variability in isotopic niches, specifically isotopic total niche width (ITNW), isotopic individual niche width (IINW), and isotopic individual specialization (IIS), was studied using an innovative approach without sacrificing the vertebrates. Stable isotopes (δ13C, δ15N) in four body tissues differing in isotopic half-life were analyzed from four freshwater fish species representing different trophic positions. ITNW was widest for the apex predator (European catfish) and narrowest for the obligate predator (Northern pike). IINW exhibited a polynomial trend for the European catfish, Northern pike, and Eurasian perch (mesopredator), decreasing with body mass and increasing again after exceeding a certain species-dependent body mass threshold. Thus, for ectotherms, apex predator status is linked rather to its size than to the species. In herbivores (rudd), IINW increased with body mass. The IIS of predators negatively correlated with site trophic state. Therefore, eutrop...
Until 2006, the Lipno Reservoir had the largest catches of pikeperch in the Czech Republic, but s... 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...
Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ j... more Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ juveniles were monitored in the epipelagic and bathypelagic layers near the dam, and in the middle and upper sections at the canyon‐shaped Římov Reservoir (Czech Republic) during the day on 26 and 29 May, and during the night on 5 and 11 June in 2008. The greatest abundance of 0+ fish was observed in the middle section of the reservoir and their LS increased upstream from the dam towards the reservoir's tributary. Moreover, larger and older pikeperch 0+ juveniles migrated to the bathypelagic layer during the day. The epilimnetic temperature and productivity (expressed as chlorophyll‐a concentration) gradients were suggested as the main drivers affecting the distribution and growth of the fish.
To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied lo... more 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 lucioperca) and catfish (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found significant differences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfish 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 catfish 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 catfish 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.
It is difficult to understand the composition and diversity of biological communities in complex ... more It is difficult to understand the composition and diversity of biological communities in complex and heterogeneous environments using traditional sampling methods. Recently, developments in environmental DNA metabarcoding have emerged as a powerful, non-invasive method for comprehensive community characterization and biodiversity monitoring in different types of aquatic ecosystems. In this study, water eDNA targeting fish (wf-eDNA) and four traditional fish sampling methods (electrofishing, gill netting, seining, trawling) were compared to evaluate the reliability and efficiency of wf-eDNA (vertebrate mitochondrial 12S ribosomal RNA (rRNA) as an alternative approach to assess the diversity and composition of freshwater fish communities. The results of wf-eDNA showed a consistency between the traditional sampling methods regarding species detection. However, some fish species detected using wf-eDNA assay were not detected using traditional sampling methods and vice versa. Comparison ...
Fish communities differ significantly between the littoral and the pelagic habitats. This paper a... more Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic ...
Structural complexity is known to influence prey behaviour, mortality and population structure, b... more Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake—LSC; high structural complexity—HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent...
The applications of environmental DNA (eDNA) metabarcoding are constantly increasing. Many valida... more The applications of environmental DNA (eDNA) metabarcoding are constantly increasing. Many validation studies have been performed in laboratories, however, field experiments are necessary to verify the robustness of eDNA based monitoring. In summer and autumn 2019 water samples in 39 sites and an inflow across three ponds of sizes of approximately 3 (A), 10 (B) and 29 (C) hectares in the Czech Republic were collected. 500 ml from each sample was filtered through 0.45 µl membrane filters and extracted using the Mu-DNA water protocol. Uniquely indexed vertebrate primers aligning mitochondrial 12S ribosomal RNA gene were utilised for eDNA amplification. PCR negative and positive controls were included to each sublibrary. Sequence reads were analysed using metaBEAT pipeline. The sequences were assigned to species level with exception Perca fluviatilis and Sander lucioperca which could not be differentiated, further referred as Perca+Sander and used as a single species. At the end of aut...
A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba diver... more A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba divers, two types of fyke nets and longlines, was tested in four reservoirs (including their inlets and outlets) to monitor a population of burbot Lota lota. This was supplemented by fry trawling and vertical hydro‐acoustics, to detect L. lota larvae in two deep reservoirs that have had a long‐term stocking programme. The majority of the L. lota detected were juveniles, captured by electrofishing in the littoral zones of the reservoirs and in running waters. Older individuals were rarely captured with longlines or fyke nets in deeper zones or structured habitats within the reservoirs. A combination of multiple sampling methods provided an assessment of the whole population. Population establishment could not be demonstrated as the age structure of the sampled fish corresponded with that of the stocked fish. Low post‐stocking survival, migratory behaviour, interactions with other species and w...
Knowledge & Management of Aquatic Ecosystems, 2019
Year to year fluctuations in 0+ fish cohort strength are a common phenomenon. Many factors can af... more Year to year fluctuations in 0+ fish cohort strength are a common phenomenon. Many factors can affect cohort strength during the fish's early life period. In this study, development of a 0+ pikeperch Sander lucioperca cohort in the pelagic zone was studied by trawling for 50 days from first larvae hatching, in two consecutive years. In 2007, an abundant S. lucioperca cohort collapsed suddenly soon after hatching. After the incident, slow-growing S. lucioperca prevailed in the catch. In 2008, the catch gradually increased during the whole study period because of prolonged hatching. Environmental factors differed mainly in a slower temperature increase, higher water level and higher zooplankton abundance in 2008 compared to 2007. Our study revealed that a strong 0+ S. lucioperca cohort at the time of hatching might not result in a strong S. lucioperca cohort in general.
Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environ... more Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. Undertaking a large‐scale field experiment in a thermally stratified, canyon‐shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (d...
Late summer sampling of pelagic age-0 year fish communities in five Czech reservoirs and one Dutc... 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.
Intra-species variability in isotopic niches, specifically isotopic total niche width (ITNW), iso... more Intra-species variability in isotopic niches, specifically isotopic total niche width (ITNW), isotopic individual niche width (IINW), and isotopic individual specialization (IIS), was studied using an innovative approach without sacrificing the vertebrates. Stable isotopes (δ13C, δ15N) in four body tissues differing in isotopic half-life were analyzed from four freshwater fish species representing different trophic positions. ITNW was widest for the apex predator (European catfish) and narrowest for the obligate predator (Northern pike). IINW exhibited a polynomial trend for the European catfish, Northern pike, and Eurasian perch (mesopredator), decreasing with body mass and increasing again after exceeding a certain species-dependent body mass threshold. Thus, for ectotherms, apex predator status is linked rather to its size than to the species. In herbivores (rudd), IINW increased with body mass. The IIS of predators negatively correlated with site trophic state. Therefore, eutrop...
Until 2006, the Lipno Reservoir had the largest catches of pikeperch in the Czech Republic, but s... 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...
Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ j... more Abundance, size (standard length, LS) and growth rate of early pikeperch (Sander lucioperca) 0+ juveniles were monitored in the epipelagic and bathypelagic layers near the dam, and in the middle and upper sections at the canyon‐shaped Římov Reservoir (Czech Republic) during the day on 26 and 29 May, and during the night on 5 and 11 June in 2008. The greatest abundance of 0+ fish was observed in the middle section of the reservoir and their LS increased upstream from the dam towards the reservoir's tributary. Moreover, larger and older pikeperch 0+ juveniles migrated to the bathypelagic layer during the day. The epilimnetic temperature and productivity (expressed as chlorophyll‐a concentration) gradients were suggested as the main drivers affecting the distribution and growth of the fish.
To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied lo... more 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 lucioperca) and catfish (Silurus glanis) in the Římov Reservoir, using an autonomous telemetry system for 11 months. We found significant differences among these species in studied parameters that varied considerably over tracked period. Pike consistently used the same sections of the reservoir, while pikeperch and catfish 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 catfish 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 catfish 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.
It is difficult to understand the composition and diversity of biological communities in complex ... more It is difficult to understand the composition and diversity of biological communities in complex and heterogeneous environments using traditional sampling methods. Recently, developments in environmental DNA metabarcoding have emerged as a powerful, non-invasive method for comprehensive community characterization and biodiversity monitoring in different types of aquatic ecosystems. In this study, water eDNA targeting fish (wf-eDNA) and four traditional fish sampling methods (electrofishing, gill netting, seining, trawling) were compared to evaluate the reliability and efficiency of wf-eDNA (vertebrate mitochondrial 12S ribosomal RNA (rRNA) as an alternative approach to assess the diversity and composition of freshwater fish communities. The results of wf-eDNA showed a consistency between the traditional sampling methods regarding species detection. However, some fish species detected using wf-eDNA assay were not detected using traditional sampling methods and vice versa. Comparison ...
Fish communities differ significantly between the littoral and the pelagic habitats. This paper a... more Fish communities differ significantly between the littoral and the pelagic habitats. This paper attempts to define the shift in communities between the two habitats based on the European standard gillnet catch. We sampled the benthic and pelagic habitats from shore to shore in Lake Most and Římov Reservoir (Czech Republic). The 3 m deep pelagic nets were spanned across the water body at equal distances from two boundary points, where the depth was 3.5 m. The benthic community contained more fish, more species, and smaller individuals. The mild sloped littoral with a soft bottom attracted more fish than the sloping bank with a hard bottom and less benthos and large Daphnia. The catch of the pelagic nets was dominated by eurytopic fish—rudd (Scardinius erythrophthalmus) and roach (Rutilus rutilus) in Most and bleak (Alburnus alburnus) in Římov. With the exception of one case where overgrown macrophytes extended the structured habitat, the largest shift from the benthic to the pelagic ...
Structural complexity is known to influence prey behaviour, mortality and population structure, b... more Structural complexity is known to influence prey behaviour, mortality and population structure, but the effects on predators have received less attention. We tested whether contrasting structural complexity in two newly colonised lakes (low structural complexity lake—LSC; high structural complexity—HSC) was associated with contrasting behaviour in an aquatic apex predator, Northern pike (Esox lucius; hereafter pike) present in the lakes. Behaviour of pike was studied with whole-lake acoustic telemetry tracking, supplemented by stable isotope analysis of pike prey utilization and survey fishing data on the prey fish community. Pike displayed increased activity, space use, individual growth as well as behavioural differentiation and spent more time in open waters in the LSC lake. Despite observed differences between lakes, stable isotopes analyses indicated a high dependency on littoral food sources in both lakes. We concluded that pike in the HSC lake displayed a behaviour consistent...
The applications of environmental DNA (eDNA) metabarcoding are constantly increasing. Many valida... more The applications of environmental DNA (eDNA) metabarcoding are constantly increasing. Many validation studies have been performed in laboratories, however, field experiments are necessary to verify the robustness of eDNA based monitoring. In summer and autumn 2019 water samples in 39 sites and an inflow across three ponds of sizes of approximately 3 (A), 10 (B) and 29 (C) hectares in the Czech Republic were collected. 500 ml from each sample was filtered through 0.45 µl membrane filters and extracted using the Mu-DNA water protocol. Uniquely indexed vertebrate primers aligning mitochondrial 12S ribosomal RNA gene were utilised for eDNA amplification. PCR negative and positive controls were included to each sublibrary. Sequence reads were analysed using metaBEAT pipeline. The sequences were assigned to species level with exception Perca fluviatilis and Sander lucioperca which could not be differentiated, further referred as Perca+Sander and used as a single species. At the end of aut...
A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba diver... more A novel sampling scheme, using a combination of electrofishing, visual exploration by scuba divers, two types of fyke nets and longlines, was tested in four reservoirs (including their inlets and outlets) to monitor a population of burbot Lota lota. This was supplemented by fry trawling and vertical hydro‐acoustics, to detect L. lota larvae in two deep reservoirs that have had a long‐term stocking programme. The majority of the L. lota detected were juveniles, captured by electrofishing in the littoral zones of the reservoirs and in running waters. Older individuals were rarely captured with longlines or fyke nets in deeper zones or structured habitats within the reservoirs. A combination of multiple sampling methods provided an assessment of the whole population. Population establishment could not be demonstrated as the age structure of the sampled fish corresponded with that of the stocked fish. Low post‐stocking survival, migratory behaviour, interactions with other species and w...
Knowledge & Management of Aquatic Ecosystems, 2019
Year to year fluctuations in 0+ fish cohort strength are a common phenomenon. Many factors can af... more Year to year fluctuations in 0+ fish cohort strength are a common phenomenon. Many factors can affect cohort strength during the fish's early life period. In this study, development of a 0+ pikeperch Sander lucioperca cohort in the pelagic zone was studied by trawling for 50 days from first larvae hatching, in two consecutive years. In 2007, an abundant S. lucioperca cohort collapsed suddenly soon after hatching. After the incident, slow-growing S. lucioperca prevailed in the catch. In 2008, the catch gradually increased during the whole study period because of prolonged hatching. Environmental factors differed mainly in a slower temperature increase, higher water level and higher zooplankton abundance in 2008 compared to 2007. Our study revealed that a strong 0+ S. lucioperca cohort at the time of hatching might not result in a strong S. lucioperca cohort in general.
Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environ... more Diel vertical migrations (DVMs) belong among the most pronounced movements in the aquatic environment. A general pattern of DVMs has been well described, particularly in European perch (Perca fluviatilis), but whether the migrations are directly controlled by light and what is the ultimate cause of the diel vertical shifts, remains poorly understood. Undertaking a large‐scale field experiment in a thermally stratified, canyon‐shaped reservoir, we demonstrated for the first time that DVMs of a bathypelagic early juveniles community, dominated by European perch larvae and juveniles prior the metamorphosis, were under direct control of the light intensity; that is, they did not operate as a genetically fixed behaviour. Prior to the experiment, the depth distribution of the bathypelagic perch early juveniles was strongly correlated with the light intensity on the water surface (p < .001). The community underwent regular DVMs between the epilimnion (depth <2.0 m) and hypolimnion (d...
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