Intraguild predation as a potential explanation for the population decline of the threatened native fish, the European mudminnow (Umbra krameri Walbaum, 1792) by the invasive Amur sleeper (Perccottus glenii Dybowski, 1877)

Biotic interactions exerted by invasive species have a strong effect on ecosystems. Intraguild predation may contribute to the decline in the distribution, abundance and population size of native species and may facilitate the spread of non-native taxa. In this study, we investigated the feeding ecology of the invasive fish Amur sleeper (Perccottus glenii Dybowski, 1877) in a lowland watercourse, where it co-exists with the threatened native fish European mudminnow (Umbra krameri Walbaum, 1792). We used two sampling protocols that differed in the frequency of sampling time (e.g. monthly samplings and samplings in 10-day intervals) to provide evidence of predation, an interaction that may lead to the decline of mudminnow populations with the spread of the Amur sleeper. Aquatic macroinvertebrates comprised a major part of the diet for both sampling intervals. However, finer temporal resolution revealed the importance of fish, especially mudminnow juveniles, as a periodically available food source in the Amur sleeper's diet. A high degree of dietary overlap was found between the different size groups of the Amur sleeper, but larger specimens tended to feed on a relatively higher proportion of fish. Our results suggested that temporal resolution of stomach content analyses may largely determine inferences on the importance of predation on juvenile mudminnow. Overall, we found that intraguild predation could contribute to the decline of European mudminnow populations, which underscores the importance of effective control measures to prevent the further spread of the invasive Amur sleeper.