Impact of climate change on the structure of fish assemblages in European rivers

Fish assemblage structures show non-random patterns along the longitudinal gradient of rivers. We analysed the impact of climate change on riverine fish assemblages using the Fish Zone Index-a structural index reflecting these conditions. The dataset contained 92 fish species at 559 sampling sites spread over 14 European countries. We regressed the Fish Zone Index in a hierarchical modelling framework with independent variables describing river characteristics and climate conditions. Future changes were predicted according to three future emission scenarios (A1b, A2, and B1) and two time periods (2050s, and 2080s). The final model contained seven independent variables (river slope, size of upstream catchment, wetted width, elevation, maximum temperature of warmest month, mean temperature of warmest quarter of the year in the upstream catchment, and temperature range) and showed highly satisfactory performance (adjR2 > 0.6). The mean increase of the Fish Zone Index was between 0.25 and 0.36 for the 2050s and between 0.36 and 0.41 in the 2080s. Maximum values reached levels of 0.92 and 1.18, respectively, for the two time periods. Major changes of fish assemblages were found in mediterranean as well as in small rivers highlighting the need of timely conservation management.