Hungry catfish – effect of prey availability on movement dynamics of a top predator

The availability and spatial distribution of prey determines the energetic costs of predators foraging and largely drives their space use, activity level and foraging timing. Consequently, predators in ecosystems with different prey availability and distribution should adjust their movement patterns to optimise their foraging success in order to maximise efficiency. The aim of this study was to investigate the ability of a top predator, European catfish ( Silurus glanis ), to adapt its space use, temporal activity and diet patterns in environments with varying prey density and distribution, and to examine the consequences for the catfish’s body growth. Catfish activity, tracked with high-resolution acoustic telemetry positioning systems deployed in two oligotrophic lakes with limited fish prey and one eutrophic reservoir with abundant fish prey, showed clear differences in their spatial and foraging behaviour. In oligotrophic, prey-poor lakes, catfish showed larger space use, altered diurnal activity patterns, reduced use of the open water, increased variability in inter- and intra-individual space use and had a more diverse diet compared to their conspecifics in the eutrophic, prey-rich reservoir. However, despite these behavioural alterations the reduced food availability in prey-poor lakes ultimately led to a reduced catfish growth, as these behavioural changes could not fully compensate for the lower prey fish abundance. The study showed that top predators can combine different behavioural mechanisms and individual strategies to adapt to different ecological contexts. The observed ability of catfish to optimize activity, space use and diet highlights the evolutionary need to maximise foraging efficiency and overall fitness in different habitats, giving catfish a significant competitive advantage. Such competitive abilities are prerequisites for the actual catfish success as an invasive species within a Europe.