1. Discriminant factorial analysis (DFA) and artificial neural networks (ANN) were used to develop models of presence/absence for three species of small‐bodied fish (minnow, Phoxinus phoxinus, gudgeon, Gobio gobio, and stone loach, Barbatula barbatula).
2. Fish and ten environmental variables were sampled using point abundance sampling by electrofishing in the Ariège River (France) at 464 sampling points.
3. Using DFA, the percentage of correct assignments, expressed as the percentage of individuals correctly classified over the total number of examined individuals, was 62.5% for stone loach, 66.6% for gudgeon and 78% for minnow. With back‐propagation of ANN, the recognition performance obtained after 500 iterations was: 82.1% for stone loach, 87.7% for gudgeon and 90.1% for minnow.
4. The better predictive performance of the artificial neural networks holds promise for other situations with non‐linearly related variables.
Relationships between environmental variables and 0+fish in the upper River Garonne (France) were studied at different habitat scales during late August 1995. In total, 3911 0+ fish representing 21 species were sampled using point abundance sampling by electrofishing. Fish reproductive function of floodplain channels was evaluated using principal components analysis of 0+ fish distributions (in absence/presence), with distinction of the three main channel types (flowing, partially abandoned and abandoned channels). A descriptive model of microhabitat use and microhabitat profiles of 0+ fish was developed for the more frequently encountered species using canonical correspondence analysis and an electivity index combined with chi-square analysis. Water velocity, water depth and distance from the bank were the most important microhabitat variables, followed by bank gradient and bottom composition. Partially-abandoned channels provide conditions particularly suitable to 0+ fish, with submerged vegetation in these sidechannels serving many of the fishes as refuge and feeding areas. Similarities in microhabitat use were found with respect to 0+ juvenile fish in the Danube flood plain (Slovakia/Hungary), the upper River Rhône (France) and the River Great Ouse catchment (England).
Spatial patterns in the combinations of biological traits of fish communities were studied in the Garonne River system (57 000 km 2 , south-west France). Fish species assemblages were recorded at 554 sampling sites, and the biological traits of species were described using a fuzzy-coding method. A co-inertia analysis of species distributions and biological traits identified some spatial patterns of species trait combinations. Fish species richness progressively increased from up-to downstream sections, and the longitudinal patterns of fish assemblages partitioned the river into clear biogeographic areas, such as the brown trout Salmo trutta (headwater streams), the grayling Thymallus thymallus, the barbel Barbus barbus and the bream Abramis brama zones (most downstream sections), which fitted with Huet's well-known zonation for western European rivers. Only a few biological traits, chiefly related to life-history attributes, significantly influenced the observed fish distributions. Fecundity, potential size, maximum age and reproductive factor increased from headwater to plain reaches. As a theoretical framework for assessing and predicting the functional organization of stream fish communities, spatial variations in species traits can be related to habitat conditions, thus providing explicit spatial schemes that may be useful to the design of both scientific studies and river management. # 2005 The Fisheries Society of the British Isles
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