Milan Muska

Understanding spatial distribution of organisms in heterogeneous environment remains one of the chief issues in ecology. Spatial organization of freshwater fish was investigated predominantly on large-scale, neglecting important local conditions and ecological processes. However, small-scale processes are of an essential importance for individual habitat preferences and hence structuring trophic cascades and species coexistence. In this work, we analysed the real-time spatial distribution of pelagic freshwater fish in the Římov Reservoir (Czechia) observed by hydroacoustics in relation to important environmental predictors during 48 hours at 3-h interval. Effect of diurnal cycle was revealed of highest significance in all spatial models with inverse trends between fish distribution and predictors in day and night in general. Our findings highlighted daytime pelagic fish distribution as highly aggregated, with general fish preferences for central, deep and highly illuminated areas, w...

Data from nine reservoirs in the Czech Republic were used to investigate density and size distribution patterns for dominant fish species of the juvenile pelagic community at night. Clear trends of increasing density along the longitudinal gradient for bream, roach, bleak, and pikeperch were observed in long (>5 km) reservoirs but were absent in short reservoirs. Increasing body size towards the tributary was observed for bream, perch, pikeperch, and ruffe. Cyprinids showed a clear affinity to the surface layer (0–3 m) of long reservoirs, while pikeperch and ruffe juveniles occurred homogeneously at depths down to six meters. Perch juveniles had the highest densities especially in 3–6 m water layer. Size did not change with sampling depth for any species in the reservoirs studied. Our data showed gentle spatial segregation of different juvenile fish species. Although the tributary area is usually the most productive, it is not able to support all juveniles leading to inter- and intra-specific competition and the relegation of juveniles of some species to less productive habitat. This trend was more apparent in long reservoirs with strong trophic gradients. The gradient of nutrients seems to be an important factor driving fish distribution along longitudinal profile of reservoirs.

Interest in ratites has necessitated a review of available information on the unique endangered kiwi (Apteryx spp.). Five different species of kiwis, endemic to the three islands of New Zealand, are recognized by the Department of Conservation, New Zealand, according to genetic and biological differences: the North Island Brown Kiwi (Apteryx mantelli), Okarito Brown Kiwi/Rowi (A. rowi), Tokoeka (A. australis), Great Spotted Kiwi/Roroa (A. haastii), and Little Spotted Kiwi (A owenii). As predators were found to be the main reason for declining kiwi numbers, predator control is a main objective of management techniques to prevent kiwis becoming extinct in New Zealand. Further considerations include captive breeding and release, and establishment of kiwi sanctuaries. Body size and bill measurements are different between species and genders within species. Kiwis have the lowest basal rates of metabolism compared with all avian standards. A relative low body temperature (38 °C), burrowing, a highly developed sense of smell, paired ovaries in females, and a low growth rate, separate kiwis from other avian species. Kiwis have long-term partnerships. Females lay an egg that is approximately 400% above the allometrically expected value, with an incubation period of 75-85 days. Kiwis mainly feed on soil invertebrate, with the main constituent being earthworms, and are prone to parasites and diseases found in other avian species. It can be concluded that kiwis present a biological rarity, with several features more characteristic of small mammals than birds.

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.

Page 1. Knowledge and Management of Aquatic Ecosystems (2011) 403, 08 http://www.kmae-journal.org cO ONEMA, 2011 DOI: 10.1051/kmae/2011070 Location and timing of the deposition of egg strands by perch (Perca fluviatilis L.): the roles of lake hydrology, ...

ABSTRACT 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.

Internal seiches are common in stratified lakes, with significant effects on stratification patterns, hydrodynamics and vertical nutrient transport. In particular, seiche can change the vertical distribution of the thermocline and the cold hypolimnetic and warm epilimnetic water masses by several meters on a timescale of a few hours. The results are rapid and strong changes in temperature profiles and oxygen availability that can have profound effects on vagrant and sessile organisms. Internal seiche dynamics could therefore affect fish communities directly through physiological stress and elevated mortality, and indirectly through prey distribution.The aim of this study was to analyze the effects of internal seiche dynamics on lacustrine fish behaviour, and to characterize fish reaction patterns, with the main focus on vertical movement of fish in the vicinity of a shifting thermocline, and avoidance of cold hypolimnetic water.The analysis was based on acoustic telemetry data from ...

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.

For ethical reasons and animal welfare, it is becoming increasingly more important to carry out ecological surveys with a non-invasive approach. Information about fish distribution and abundance in the upper water column is often fundamental. However, this information is extremely hard to obtain using classical hydroacoustic methods. We developed a rigid frame system for pushing upward looking transducers of the scientific echo sounder (38 and 120 kHz) in front of the research vessel. The efficiency of the new approach for monitoring juvenile fish at night was investigated by comparing the results with a quantitative fry trawl in the Římov Reservoir in the Czech Republic. The experimental setup enabled comparisons for the 0-3 m and 3-6 m depth layers, which are utilized by almost all juvenile fish in summer. No statistically significant differences in the estimated abundance of juveniles were found between the two sampling methods. The comparison of abundance estimates gathered by t...