Predation of European catfish on anadromous fish species in an anthropised area

Increases in both food availability and intraspecific competition downstream of dams have the potential to trigger the emergence of trophic specialisation among fish predators, with considerable implications for prey species populations. The aim of this study was to assess whether the presence of a dam located on the River Garonne (France) affected the dietary preference of the European catfish Silurus glanis towards anadromous prey. Stable isotope analysis showed that the contribution of marine-derived carbon in the diet of the European catfish was substantial (on average 53% of the diet) and was similar between individuals caught downstream of the dam and those caught from the free running part of the river. In contrast with previous studies, a significant relationship between the size of European catfish individuals and their consumption of marine-derived nutrients was found in this study. Anadromous fish populations are in decline; therefore, this significant predation is concerning.