Environmental drivers of benthic fish assemblages and fish‐habitat associations in offshore areas of a very large river

Fish-habitat associations are poorly known in offshore areas of very large rivers. We examined physical habitat structure and its effect on use assemblage formation benthic fishes the main channel Danube River, Hungary. Principal component analysis variables showed that sample unit (i.e., 500 m long reaches) cross-channel transect-level data corresponding reaches were highly correlated. found clear gradients from with high velocity higher proportion hard substratum (pebble cobble) to low velocity, mean depth finer (mainly sand) composition. Variation was coupled variation both composition Shannon diversity sediment composition) silt material. Differences (flow, substrate) also manifested among river segments. Classification regression tree analyses (CART) fish abundance – occupancy patterns PCA template revealed many species responses environmental heterogeneity (barbel, Barbus barbus; schraetser, Gymnocephalus schraetser; streber, Zingel streber; whitefinned gudgeon, Romanogobio vladikovy; round goby, Neogobius melanostomus) while others (white bream, Blicca bjoerkna) elusive patterns. Multivariate confirmed results CART indicated most important determinant assemblages. These can contribute more effective conservation management assemblages, which is due increasing inland navigation River.