Competitive interactions for food resources between the invasive Amur sleeper (Perccottus glenii) and threatened European mudminnow (Umbra krameri)

The European mudminnow (Umbra krameri) is a strictly protected, threatened fish species, endemic to the River Danube and Dniester basins. Population decreases have been observed for several decades, primarily due to habitat loss, but, recently, the adverse impact of invasive species, including the Amur sleeper (Perccottus glenii), has also been implicated in its decline. The correspondence in the disappearance of the European mudminnow and the appearance of the Amur sleeper has been observed in some waters, but the mechanism by which the invader has an impact has remained speculative until now. As both species have similar dietary preferences and habitat requirements, competitive interactions between them for the same limited food resource (gammarids) in the same space (aquarium with artificial plants) were investigated experimentally. The foraging of two-species and single-species pairs and single individuals was tested. Feeding rates and prey capture efficiency were similar in both species, but the Amur sleeper was a superior competitor compared with the European mudminnow; it negatively influenced the foraging efficiency of the latter, preventing its access to prey through aggressive interactions. In the presence of the alien competitor, the feeding rate of European mudminnow decreased to one third of that observed in single-species or single-individual treatments. These results demonstrate that interference competition for food may be the mechanism explaining the rapid decline of this threatened species. We conclude that the invasion of the Amur sleeper will accelerate the extinction of the European mudminnow, especially in isolated, small, shallow water bodies. The study illustrates that monitoring the Amur sleeper invasion is essential for the active conservation of the European mudminnow. For reintroduction attempts, special care must be taken to avoid invaded water bodies. Moreover, prevention of the introduction of the Amur sleeper, especially in waters occupied by the European mudminnow, must be pursued.