How fish benefit from floodplain restoration along the lower River Rhine

The objectives of this study were to test the beneficial value of newly created secondary channels and reconnected oxbow lakes along the lower River Rhine for fish and to give advice on position, shape and character of future water bodies. These water bodies should contribute to the rebuilding of the population of rheophilic cyprinids that are endangered due to embankment and normalization of the Rhine. The functions these water bodies fulfil during the life cycle of distinct fish species, were inferred from the description of patterns of presence of fish in time and space in 25 floodplain water bodies (secondary channels, oxbows, lakes). In all water bodies, depth, flow velocity and the presence of vegetation determine the fish community present. Secondary channels and reconnected oxbow lakes do have a beneficial value for the riverine fish community. They function as nursery areas for all rheophilic cyprinids (e.g. Barbus barbus , Leuciscus idus and Gobio gobio ). Secondary channels probably also function as spawning areas for L. idus and G. gobio but not for lithophilic species ( B. barbus , Leuciscus leuciscus ) since suitable substrate lacks. Eurytopic species ( Abramis brama , Rutilus rutilus and Stizostedion lucioperca ) use all types of floodplain water body to reproduce. For A. brama , isolated turbid clay-pits form important source areas from which juveniles recruit to the main channel during floods. The dominance of eurytopic species in the lower Rhine is caused by the large area of suitable spawning and nursery areas for these species relative to those of rheophilic species. For limnophilic species ( Tinca tinca , Rutilus erythrophthalmus ) suitable habitat (vegetated lakes) is also scarce and should be preserved. Within plans on flood protection, floodplain management should focus on increasing the number of secondary channels and on restoring the natural interaction between the river and its floodplains.