An empirical model for predicting microhabitat of 0+ juvenile fishes in a lowland river catchment.

Species-habitat relationships are an important aspect of fish life history, particularly in early ontogeny. To address the lack of information on the microhabitat use/requirements of European coarse fishes, particularly 0-group fishes in riverine systems, an empirical model was generated from data collected in the River Great Ouse catchment (UK). During 7 weeks in autumn 1990, data on young-of-the-year (0+) juvenile fishes and 15 environmental variables were collected at 2800 stratified, random point samples within 130 study sites (streams, rivers, side-channels, backwaters). Of 24 species of 0+ fish, only 10 were captured in ≥ 3% of non-null samples. Association analysis and canonical correspondence analysis of the samples-by-species (967×10) and samples-by-variables (967×15) data matrices revealed that the shallow, narrow, lotic, stony-pebbly channel microhabitat of riffles and runs was preferred by the progeny of substrate-spawning, substrate/plant-spawning and nest-guarding fishes. Moderately deeper and wider, sinuous channels, with slowto-moderate water velocities and medium-sized substrata were also favourable to progeny of substrate spawners. Assemblages of 0+ fish in deeper, wider, silted, trapezoidal-shaped channels with slow-to-lentic flowing water, i.e. channelised and regulated, were dominated by ubiquitous (plant/substrate) spawners.