Results of gradient forest for Secchi depth (Secchi, left, log scale) and median nitrate concentration (NO3, right, log scale). The specific cumulative importance indicates locations of potential thresholds in the responses of the different fish species to the gradients. Examples of fish responses are provided with Sander lucioperca and Salmo trutta for Secchi and NO3, respectively, and with Abramis brama for both variables. Plain lines are local regressions on strictly positive BPUE values and dashed lines are probabilities of presence along the gradients.