Long-term changes in fish community structure revealed by gillnet monitoring in a shallow, lowland reservoir

Background. Fish communities can support or hinder water quality management. Sulejów Reservoir, which is situated on the Pilica River in Central Poland, serves as a strategic reserve of drinking water for the Łódź Agglomeration. Precise knowledge of the long-term dynamics of the structure of the fish community, what was the aim of this study, is important for proper management to slow the eutrophication of the reservoir and prevent toxic algal blooms. Materials and methods. To determine fish species composition, multimesh gill nets with mesh sizes ranging from 11 to 80 mm were used. From 1993 to 2015, gillnetting was conducted 1–2 times per month from June through November in two representative parts of the reservoir, and principal component analysis (PCA) was applied to explore the temporal variation in fish community structure expressed as the relative contribution of each species to the total fish biomass. Results. Dominance fluctuated among four species in the fish community: common bream, Abramis brama (Linnaeus, 1758); roach, Rutilus rutilus (Linnaeus, 1758); white bream, Blicca bjoerkna (Linnaeus, 1758); and pike-perch, Sander lucioperca (Linnaeus, 1758). PCA revealed three principal components with eigenvalues larger than one that explained 73.3% of the observed variance in the temporal changes in fish community composition. A negative correlation was found between pike-perch biomass and roach biomass (r = 0.82), while a positive correlation was observed between the biomass of pike-perch and that of common bream (r = 0.73). Consequently, there was a highly negative correlation between the biomasses of common bream and roach (r = 0.80). Furthermore, an interesting temporal pattern was observed; from 1993 to 2000, the fish community was dominated by common bream and pike-perch but then shifted towards domination by roach and white bream, despite declining phosphorous and carbon concentrations. Recently, this trend has been reversed, and a more balanced fish community structure has been established. Conclusion. Fish community succession, which is usually reported to be a one-directional process in reservoirs, i.e., from a riverine fish or percid-dominated to a cyprinid (bream)-dominated state, was more ambiguous in Sulejów Reservoir. This was likely a consequence of both restoration issues related to decreasing nutrient loads and the influence of zebra mussel, Dreissena polymorpha invasion on the trophic relations in the reservoir

Getting off on the right foot: Integration of spatial distribution of genetic variability for aquaculture development and regulations, the European perch case

International audienceKnowledge of spatial genetic variability patterns allows improving conservation actions, translocation regulations, and farming productivity. However, these genetic variability patterns are often considered after issues are observed, long after the beginning of production. By taking into account lessons from other species, we investigate the genetic variability of Perca fluviatilis, a species at a nascent stage of production. The genetic variability has been previously studied but, due to discrepancies between conclusions and methodological limits, the spatial distribution of genetic variability in P. fluviatilis has not been demonstrated conclusively. Here, we characterise the genetic variability across 84 West-Palaearctic sampling sites using mitochondrial and microsatellite markers. We aim to provide (i) a genetically-based population structure that could act as an impetus for further production improvement and (ii) guidelines for translocation regulations. Our analyses show an uneven distribution of genetic variability. Based on inter-populational genetic differentiation, we identify five large geographic scale clusters which are further divided into several subgroups. Local genetic diversity mapping highlights a spatial pattern with several hotspots, which has serious implications in the development of appropriate regulations of translocations. Moreover, we here report an association between genetic differentiations and previously reported zootechnical performances. We ultimately propose guidelines for further investigations of population-specific performances in aquaculture and potentially efficient regulations for policy-makers

Over 200,000 kilometers of free-flowing river habitat in Europe is altered due to impoundments

European rivers are disconnected by more than one million man-made barriers that physically limit aquatic species migration and contribute to modification of freshwater habitats. Here, a Conceptual Habitat Alteration Model for Ponding is developed to aid in evaluating the effects of impoundments on fish habitats. Fish communities present in rivers with low human impact and their broad environmental settings enable classification of European rivers into 15 macrohabitat types. These classifications, together with the estimated fish sensitivity to alteration of their habitat are used for assessing the impacts of six main barrier types (dams, weirs, sluices, culverts, fords, and ramps). Our results indicate that over 200,000 km or 10% of previously free-flowing river habitat has been altered due to impoundments. Although they appear less frequently, dams, weirs and sluices cause much more habitat alteration than the other types. Their impact is regionally diverse, which is a function of barrier height, type and density, as well as biogeographical location. This work allows us to foresee what potential environmental gain or loss can be expected with planned barrier management actions in rivers, and to prioritize management actions

Magnetomechanical coupling, magnetostriction and structure the as-quenched and annealed in vacuum Fe-Cu-W-Si-B alloy

Magnetomechanical coupling coefficient as a function of magnetic bias field in Fe23.5Cu1W3Si15.5B7 alloy in as-quenched state and after annealing in vacuum for 1 h from 400 to 500°C were investigated. The maximum values of the k coefficient were equal to 0.10-0.14 for as-quenched state and increased to 0.61 after annealing at 450°C. The results were somewhat worse than those with Nb instead of the W. Nanocrystallization begins after annealing above 450°C and the magnetostriction rapidly drops and the magnetomechanical coupling practically vanishes after annealing at 520°C