Effects of high and low flows on abundances of fish species in Central European headwater streams: The role of ecological species traits

Hydrological variability is considered a major structuring factor for biotic and abiotic processes in freshwater ecosys-tems and is of particular importance to fish communities. We used hydrological indices to investigate the short intermediate-and long-term effects of high-and low-flow patterns on the population abundances of 17 fish species in headwater streams in Germany. Generalized linear models, on average, explained 54 % of the variability in fish abundance, whereas long-term hydrological indices performed better than indices based on shorter periods. Three clusters of species were differentiated in their response patterns to low-flow conditions. Cold stenotherm and demersal species were susceptible to high frequency and long duration but tolerant to the magnitude of low-flow events. In con-trast, species with a more benthopelagic habitat preference and tolerance to warmer water were susceptible to magni-tude but tolerated larger frequencies of low-flow events. The euryoecious chub (Squalius cephalus), tolerating both long durations and large magnitudes of low-flow events, formed its own cluster. Species responses to high flows were more complex and five clusters of species were differentiated. Species with an equilibrium life history strategy were posi-tively affected by longer durations of high-flow conditions, which may allow them to take advantage of the extended floodplain, whereas opportunistic and periodic species significantly differed by thriving in events characterized by high magnitude and frequency. These response patterns of fish species to high and low flows help understand species-specific risks when hydrological conditions are altered by climate change or direct human intervention.

Automated summary

Hydrological variability is important for fish communities in freshwater ecosystems. This study examined the effects of high and low flow patterns on the abundance of 17 fish species in headwater streams in Germany. The results showed that long-term hydrological indices were better predictors of fish abundance than shorter-term indices. Different clusters of species had different responses to low-flow conditions, with some species being tolerant to frequency but susceptible to duration, while others were tolerant to magnitude but susceptible to frequency. Species responses to high flows were more complex, with different clusters of species showing different preferences for duration, magnitude, and frequency. Understanding these response patterns is crucial for assessing the risks to fish species from climate change and human intervention.