Milan Muška

Chaos and stability of age-0 fish assemblages in a temperate deep reservoir: unpredictable success and stable habitat use

Large year-to-year variability in different fish species recruitment has been confirmed by previous studies while diurnal patterns of occupation in two basic reservoir habitats (pelagic and littoral) by different age-0 fish species in late summer are still unclear. Data collected over an 11-year period regarding late-summer age-0 fish assemblages in pelagic and littoral habitats of a reservoir were used to test the recruitment instability and to investigate diurnal habitat use. Trawling was conducted in the pelagic habitat at night while beach seining was conducted in the littoral habitat during day and night. Fluctuations in age-0 fish abundance and species composition were observed with both sampling methods; however, the following spatio-temporal patterns were relatively stable in most investigated years: (1) pelagic species (pikeperch; Sander lucioperca, small perch; Perca fluviatilis, bream; Abramis brama at night), (2) littoral species (large perch, asp; Leuciscus aspius, dace; Leuciscus leuciscus), (3) migratory species likely performing diel horizontal migrations (bleak; Alburnus alburnus), (4) species abundant in the littoral habitat both during day and night and also in pelagic habitat at night (roach; Rutilus rutilus) and (5) species detected in both habitats exclusively at night (ruffe; Gymnocephalus cernuus).

Littoral age 0+ fish distribution in relation to multi-scale spatial heterogeneity of a deep-valley reservoir

Littoral age 0+ fish were studied with respect to spatio-temporal heterogeneity in the deep-valley Římov Reservoir (Czech Republic) from June to October 2007 using point abundance sampling by electrofishing. The abundance and diversity of age 0+ fish in different types of littoral habitats were examined along the longitudinal gradient of the reservoir during daytime. The impact of some physical attributes of the studied littoral habitats, e.g. slope steepness and substrate size, along with the season was the main factors affecting the distribution of age 0+ fish. The level of structural complexity was not a strong determinant, because the overall diversity and structural complexity of the available littoral habitats were relatively too low to have greater impact on the age 0+ fish distribution. The physical factors markedly influenced the spatial segregation between the two most important taxa in the reservoir—percids and cyprinids. Perch was the only representative of age 0+ percids in the littoral zone, which occupied steep-sloped habitats early in the season. In contrast, gently sloped habitats were mainly occupied by cyprinids later in the season. Species diversity was reflected in the occurrence of age 0+ cyprinids, achieving a maximum in gently sloped habitats in October. The effect of the longitudinal gradients on age 0+ fish distribution and diversity was generally far less significant, but was rather decisive during the period of a pronounced longitudinal trophic gradient during the summer season.

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 estimates.

Patterns in diel habitat use of fish covering the littoral and pelagic zones in a reservoir

We investigated diel habitat use of fish covering the littoral and pelagic zones of the Římov Reservoir (Czech Republic) and analyzed the influence of predator presence and of shifting feeding habitats in all dominant species and age groups. Our sampling revealed distinctive diel changes of fish distribution in the reservoir, which were age- and species-dependent. The overall abundance of subadult fish in littoral habitats was significantly higher at night than during the daytime. Subadults were almost absent in pelagic habitat during the day and their presence increased during the night, although densities were smaller than in the littoral. Adults preferred the pelagic zone during the day and partly migrated to the littoral at night. Potential fish predators were most likely responsible for small fish avoidance of the littoral and pelagic zones during day. Higher availability of food in the littoral was the most important driver of the high occurrence of subadults at night. Day preference of pelagic zone by adults is most likely caused by higher profitability of this habitat in comparison with littoral. The reasons for night inshore migration of adults are not obvious, but the homogenization of their distribution or resting in the littoral could explain such behavior.

Two step estimation for Neyman-Scott point process with inhomogeneous cluster centers

This paper is concerned with parameter estimation for the Neyman-Scott point process with inhomogeneous cluster centers. Inhomogeneity depends on spatial covariates. The regression parameters are estimated at the first step using a Poisson likelihood score function. Three estimation procedures (minimum contrast method based on a modified K function, composite likelihood and Bayesian methods) are introduced for estimation of clustering parameters at the second step. The performance of the estimation methods are studied and compared via a simulation study. This work has been motivated and illustrated by ecological studies of fish spatial distribution in an inland reservoir.

Development of non-lethal monitoring of stable isotopes in asp ( Leuciscus aspius ): a comparison of muscle, fin and scale tissues

We explored whether fin clips and scales can be used as potential non-lethal alternatives to muscle tissue for examining the isotopic composition of asp Leuciscus aspius, a locally threatened freshwater species. Dorsal fin clips, scales and muscle plugs were collected from two asp populations and subsequently analysed for nitrogen and carbon stable isotopes. Both fins and scales were consistently depleted in 15N and enriched in 13C relative to muscle. A linear regression found that the isotope values in asp fins and scales were significantly related to those in the muscle tissue. These results indicate that fins and scales have the potential to be a substitute for muscle in stable isotope studies of asp, thus providing a non-destructive sampling method for this species. Nevertheless, to determine reliable conversion factors between tissues, a subset of individuals covering a sufficiently wide range of body sizes may need to be sacrificed for any given population.

Towards a better understanding of small scale distribution of littoral age-0 fish in a deep-valley reservoir: day or night surveys?

The effect of diel period and littoral habitats on the distribution of age-0 fish was tested in a deep-valley reservoir using boat-modified point abundance sampling by electrofishing (PASE). Day and night samplings unveiled differences in abundance of age-0 fish while recognizing most of the commonly present age-0 fish species in the littoral zone. Night survey provided better information about the abundance of age-0 fish since most species appeared in higher numbers at night. Alternatively, night sampling underestimated bleak (Alburnus alburnus) and gudgeon (Gobio gobio), which were predominantly found in the littoral zone in the daytime. The structure of the age-0 fish assemblage was determined primarily by the characteristics of the littoral habitats, i.e. slope steepness and structure, and three different patterns of habitat use were detected among the fish species. To obtain the most comprehensive assessment of a littoral age-0 fish assemblage and to register all species-specific patterns of habitat use, it is necessary that all littoral habitats in the reservoir are sampled during both day and night periods. The boat-modified PASE could be also used as a standard monitoring tool for routine age-0 fish sampling under difficult conditions of steep-sloped shorelines in large inland waterbodies.

Invasive round goby Neogobius melanostomus has sex-dependent locomotor activity and is under-represented in catches from passive fishing gear compared with seine catches

The higher proportion of males of the invasive round goby Neogobius melanostomus in samples from two activity selective passive fishing gears compared with one activity non-selective fishing gear in three Dutch lakes is related to higher male locomotory activity and is a sex-dependent trait. This difference in activity reflects the different ecology of male and female N. melanostomus.

Seasonal and Spatial Dynamics of Gas Ebullition in a Temperate Water‐Storage Reservoir

Gas ebullition of river impoundments plays an increasingly significant role, particularly in transporting methane CH4 from their sediments to the atmosphere, and contributing to the global carbon budget and global warming. Quantifying stochastic and episodic nature of gas ebullition is complicated especially when conventionally conducted by using coverage-limited gas traps. Current knowledge of seasonality in a reservoirs gas ebullition is lacking in the literature. For this reason, advanced acoustic surveying was intensively applied to determine spatiotemporal distributions of gas ebullition in a European water-storage reservoir for two years. Additionally, the sampling was accompanied with gas collecting for analyzing gas composition. The gas released from the reservoir was primarily composed of CH4 (on average 52%, up to 94%). The longitudinal distribution of gas ebullition was mainly determined by a proximity to the river inflow as a source of organic matter. A magnitude of ebullitive fluxes within the reservoir varied up to 1,300 mL m−2 d−1 (30 mmol CH4 m−2 d−1). The most significant period of ebullition has turned out to be in fall, on average reaching a sevenfold ebullitive flux (70 mL m−2 d−1, 1.6 mmol CH4 m−2 d−1) higher than in the rest of the season. A substantial contribution to the fall peak was induced by an expansion of gas ebullition into greater depths, covering two thirds of the reservoir in late fall. The study demonstrates that the ebullitive fluxes of the temperate water storage reservoir were correlated to season, depth, and inflow proximity.

Comparison of diatom community structure from epilithon and fish guts: implications for inferring past changes in water quality

The sampling skills of three common European fish species (Barbus barbus, Chondrostoma nasus and Squalius cephalus) were tested to assess their potential as biomonitors of past changes in river water quality through the analysis of diatoms in fish guts. The study was performed on three rivers with different chemical and physical conditions. Comparison of similarity indices revealed low diatom assemblage resemblance between epilithic samples and samples collected from fish guts at the same locality. In contrast, a mixed-effect linear model identified significant differences between locations through comparison of diatom-based water quality indices. Among fish species, diatom indices calculated from gut samples of B. barbus and C. nasus were in most cases not significantly different from those from epilithic samples while those from S. cephalus were often significantly different. The results of the study demonstrate that diatom analysis of fish guts provides a clear distinction between eutrophic and hypereutrophic rivers. Finer nutrient variations within hypereutrophic conditions were also found to be significant for some diatom indices. In this context, choice of appropriate diatom water quality index proved to be crucial in maximizing the sensitivity of the method.