Motivation: We compiled a global database of long-term riverine fish surveys from 46 regional and national monitoring programmes and from individual academic research efforts, with which numerous basic and applied questions in ecology and global change research can be explored. Such spatially and temporally extensive datasets have been lacking for freshwater systems in comparison to terrestrial ones. Main types of variables contained: The database includes 11,386 time-series of riverine fish community catch data, including 646,270 species-specific abundance records, together with metadata related to the geographical location and sampling methodology of each time-series. Spatial location and grain: The database contains 11,072 unique sampling locations (stream reach), spanning 19 countries, five biogeographical realms and 402 hydrographical basins worldwide. Time period and grain: The database encompasses the period 1951-2019. Each timeseries is composed of a minimum of two yearly surveys (mean = 8 years) and represents a minimum time span of 10 years (mean = 19 years). Major taxa and level of measurement: The database includes 944 species of rayfinned fishes (Class Actinopterygii). Software format: csv. Main conclusion: Our collective effort provides the most comprehensive long-term community database of riverine fishes to date. This unique database should interest ecologists who seek to understand the impacts of human activities on riverine fish biodiversity and to model and predict how fish communities will respond to future environmental change. Together, we hope it will promote advances in macroecological research in the freshwater realm.
To quantify relative digestion rates of zooplankton prey, we removed alimentary tracts of vendace Coregonus albula and whitefish Coregonus lavaretus larvae, cut them into four equal quarters, and analyzed them separately. Hard-bodied zooplankton taxa (e.g., Bosmina sp. and Daphnia sp.) were distributed fairly evenly across these four quarters, whereas soft-bodied taxa (e.g., Synchaeta sp. and Polyarthra sp.) were concentrated in the first quarter. Thus, zooplanktonic prey digest at different rates. We then ranked prey according to their resistance to digestion, deriving prey-specific coefficients to eliminate the bias associated with entire gut analysis. For Synchaeta sp. to be comparable to Bosmina sp., their numbers had to be multiplied by 7.3. Similar patterns of food degradation likely exist among other fishes that are feeding on a mixed diet of soft-and hard-bodied zooplankton. To eliminate bias, we suggest that investigators analyze only foregut contents.
A fish-based assessment method was developed to estimate the ecological status of boreal rivers. Electric fishing data were collected from 902 rapids, together with information on the land use, channel modification and water chemistry. Discriminant function analysis was used to select fish variables that most correctly classified the undisturbed reference sites and human impacted sites into exact classes. The relationship between the level of human alteration and fish metrics was examined. Five metrics were selected for the index: the number of fish species, proportion of sensitive species, proportion of tolerant species, density of cyprinid individuals and the density of age-0+ salmonids. The value for each metric (between 0 and 1) was calculated according to a point estimate for classical probability. The index is used to estimate the ecological classification of rivers according to the EU Water Framework Directive.
Studies focusing on the effects of spatial processes versus environmental filtering on aquatic metacommunities have so far been focused almost entirely on relatively isolated systems, such as sets of different lakes or streams. In contrast, metacommunity patterns and underlying processes within a single aquatic system have received less attention. In this study, we aimed to examine how strongly variations in different diversity indices are affected by spatial processes (dispersal) versus local environmental conditions (species sorting) within a large lake system. Modern biodiversity research focuses on multiple diversity facets because different indices may be uncorrelated within and between facets, and they may thus describe different phenomena. We investigated the relationship of littoral macroinvertebrate diversity with environmental and spatial factors using 10 indices of species, functional and taxonomic diversity. Using spatial factors as proxies of dispersal, we decomposed variation in diversity indices into fractions attributable to environmental and spatial factors. Our results highlighted generally equal or higher importance of spatial processes in controlling the variation in diversity indices when compared to local environmental variables. Local environmental conditions accounted for higher proportion of variation only in a single index (i.e. taxonomic diversity). These findings suggest that the effects of high dispersal rates (mass effects) may override the influences of local environmental conditions (species sorting) on the diversity in highly-connected aquatic system, such as large lakes and marine coastal systems. Our results further suggest that biodiversity assessment and environmental monitoring in highly-connected systems cannot rely solely on the idea of environmental control. We hence recommend that the roles of both environmental and spatial processes should be integrated in basic and applied ecological research of aquatic systems.
Parallel sampling of fish, using electrofishing and NORDIC multimesh gillnets, was performed in the littoral areas of eight boreal lakes. Some fish species were caught only by electrofishing (e.g. bullhead, Cottus gobio (L.); burbot, Lota lota (L.)), while some were caught only with gillnets (e.g. pikeperch, Stizostedion lucioperca (L.); smelt, Osmerus eperlanus (L.)). The fish species that were caught with both methods (e.g. perch, Perca fluviatilis (L.) exhibited gear-specific length distributions. A combination of NORDIC gillnetting (passive gear) and electrofishing (active gear) is suggested to reasonably well cover the entire species composition in the littoral zones (≈ 0-3 m depth) of boreal lakes. This gear combination is recommended for evaluating the ecological status of lakes within the European Water Framework Directive.
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