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Fish as indicators for the assessment of the ecological integrity of large rivers
2000
Fish communities in large rivers are characterized by a high diversity, which reflects the structural diversity and habitat richness of inshore zones and connected floodplains. The connectivity of the different habitat elements in a broad spatio-temporal context, i.e., at various scales from catchment to microhabitat -and their nestednessdefine the fitness of fish species both on the individual level (e.g., growth performances) and population level (i.e., population structure, mortality, etc.). Relevant spatial scales can be the whole river course in the case of some anadromous migrators or the availability of complementary microhabitat elements, e.g., during the early ontogeny of a species. The significance of connectivity at various scales from whole river to local reach have to be evaluated based on the requirements, reaction norms, and ecological flexibility of individual species. Integrity has to be evaluated in several respects:
Fishes as Environmental Indicators of Riverine Ecosystem
International Journal for Research in Applied Science & Engineering Technology, 2020
The ecological condition of river is represented by the condition of their biotic communities-the living components of aquatic ecosystems that integrate many forms of human disturbances and modification of river stream and the measurements of this subject was the topic of particular interest. Stressors or the pressures that human being exert on aquatic systems through their use of the surrounding environment are commonly the chemical, physical and biological components of the ecosystem. These have the potential to degrade biotic integrity. Some common chemical stressors are toxic compounds, excess nutrients etc. Most of the physical stressors are created when we modify the physical habitat of a river network-excess sedimentation, bank erosion etc. All these can degrade biotic integrity. Water quality plays vital role in riverine ecosystem health regulation. Environmental indicators have been defined as "physical, chemical, biological or socioeconomic measures that best represent the key elements of a complex ecosystem or environmental issue. An indicator is embedded in a well developed interpretative framework and has meaning beyond the measure it represents. Using indicators, it is possible to evaluate the fundamental condition of the environment without having to capture the full complexity of the system. Indicators are based on the best scientific understanding currently available so that changes in these simple measures can be related to more complex environmental trends.
The gain of additional sampling methods for the fish-based assessment of large rivers
Fisheries Research
Fishes serve as indicators in ecological assessments of European large rivers. Electrofishing is the standard fishing method although it is restricted to the shallow littoral shoreline. Fish occurring in the open water zone of the main channel remain consequently underestimated. Additional sampling methods that cover the mid-channel of rivers could close the electrofishing-gap, but strengths', weaknesses and gains of both electrofishing and additional sampling methods for fish-based assessments of large rivers have not been contrasted yet. We analyzed a unique dataset consisting of 2,693 fish samplings in European large rivers and compared electrofishing with the additional sampling methods trawling, seining, and driftnetting. We compiled fish metrics commonly used in fish-based assessments yielded by the different gears and highlight the differences in fish species, biodiversity metrics (Shannon Index, Evenness, Simpson Index), the Fish Region Index (FRI) and densities of fish in selected guilds (eurytopic, rheophilic, lithophilic, phytophilic, psammophilic, potamal) that are considered indicative for the degradation of habitats in large rivers. Electrofishing yielded overall highest numbers of species, biodiversity metrics and densities of fish guilds, except for the number of migratory and Habitat Directive species, the FRI and densities of potamal fish. The additional gears, predominantly trawling, captured additional rheophilic and lithophilic species. Trawling also assessed most migratory and Habitat Directive species and yielded higher densities of potamal fish as well as larger fish than electrofishing. Trawl catches further estimated higher biodiversity compared to seining, while the latter yielded higher densities of eurytopic, rheophilic, lithophilic and phytophilic fish. Drift-netting yielded the lowest estimates overall but sample size was very low. We suggest that electrofishing is an appropriate method to assess and evaluate the effects of hydromorphological degradation and rehabilitation on fish, and to guide river management. It sufficiently well represents the typical fish assemblage of large rivers despite its restriction to the shoreline. In contrast, assessing specifically Habitat Directive, migratory and rare species, as well as obtaining complete species inventories, e.g., for biodiversity assessments, requires complementary sampling of the mid-channel of large rivers by additional gears such as trawling.
FISH COMMUNITIES AS INDICATORS OF BIOLOGICAL CONDITIONS OF RIVERS: METHODS FOR REFERENCE CONDITIONS
Fish communities are a key element in fluvial ecosystems Their position in the top of the food chain and their sensitivity to a whole range of impacts make them a clear objective for ecosystem conservation and a sound indicator of biological integrity. The UE Water Framework Directive includes fish community composition, abundance and structure as relevant elements for the evaluation os biological condition. Several approaches have been proposed for the evaluation of the condition of fish communities, from the bio-indicator concept to the IBI (Index of biotic integrity) proposals. However, the complexity of fish communities and their ecological responses make this evaluation difficult, and we must avoid both oversimplified and extreme analytical procedures. In this work we present a new proposal to define reference conditions in fish communities, discussing them from an ecological viewpoint. This method is a synthetic approach called SYNTHETIC OPEN METHODOLOGICAL FRAMEWORK (SOMF) th...
Brazilian Archives of Biology and Technology, 2005
Freshwater is a basic need for the mankind. Effective biological tools (ecologically based, efficient, rapid and consistently applicable to different ecological regions) are needed to measure the "health" of rivers. Adapting such tools over a broad geographic area requires a detailed understanding of both the patterns of organisms assemblage composition and distribution within and among water bodies under natural conditions, and the nature of the major environmental gradients that cause or explain these patterns. A comprehensive review of the available litterature dealing with the identification of environmental factors structuring riverine fish assemblages under natural conditions permits to identify the most consistent ones.
River Research and Applications, 2009
Ecological processes in lowland rivers are mostly dominated by hydrology and its interactions with other environmental factors. Fish-habitat relationships in rivers are also influenced by human impacts. In this study, we describe patterns of abundance and distribution of fish species in a group of natural lowland river lakes along spatial anthropogenic and abiotic gradients when four hydrologically different summers are compared. We also describe the proportion of the total variances in fish species abundances that can be accounted for by selected abiotic (water conductivity), hydrological (water residence time) and human activity-derived (total phosphorus (TP) concentration and NO 3 :NH 4) variables. Consequently, our main purpose is to explore how abiotic and anthropogenic factors interact to affect fish abundance and distribution together with consistent results across different hydrological conditions. We conclude with a briefly discussion of some management implications. The anthropogenic impacts on water quality, the extreme hydrological variability and the fluctuating abiotic environment affected fish abundance and distribution. Pampa inland silverside Odontesthes bonariensis was benefited from a less human disturbed environment with higher water residence time and total salinity, whereas species as Cyphocharax voga, Parapimelodus valenciennis and Cyprinus carpio found these conditions largely disadvantageous. On the other hand, while most species showed stronger-either negative or positive-response to anthropogenic, hydrological or abiotic factors Oligosarcus jenynsii was only slightly affected. This paper identified the ecological function of a lowland river under its natural flow regime. There are not many opportunities to study unmodified rivers worldwide. Therefore, our findings may help in assessment programmes of fish communities in flow altered and human disturbed aquatic ecosystems.
Challenges in developing fish-based ecological assessment methods for large floodplain rivers
Fisheries Management and Ecology, 2007
Large European floodplain rivers have a great diversity in habitats and fish fauna, but tend to be heavily modified. The complexity of these river systems and their multiple human impacts pose considerable challenges for assessment of their ecological status. This paper discusses: (1) the application of historical information on fish fauna and habitat availability to describe reference conditions; (2) responses of fish assemblages to human disturbance by comparing various rivers and river segments with different impacts and/or time series within rivers; (3) the role of floodplain water bodies in ecological assessment; and (4) monitoring of large rivers using different gears and sampling designs for main channels and floodplain habitats. The challenge for the future is to