Non-native fishes occupy broader isotopic niche than native fishes in an impaired river system

This study aimed to compare the trophic ecology of native and non-native fish species in the Doce River basin, which has been subjected to various anthropogenic impacts, including Brazil's largest environmental disaster: the rupture of the Fundão iron ore tailings dam. Using carbon and nitrogen stable isotopes, we evaluated the isotopic niche and trophic position occupied by fish species sampled at eight sampling points along the Doce River. Currently, non-native species exhibit a broader isotopic niche than the native assemblage, occupying all trophic levels. The historically most impacted points in the basin, which also received the tailings from the dam breach, presented a higher percentage of non-native species, with a greater isotopic overlap with native species. Non-native species seems to consume released resources in most disturbed regions, represented by more enriched δ13C signatures. However, locally, their range of δ13C compared to native species was not different among less and more disturbed sites. Our results indicate how human disturbances create favorable scenarios for non-native fish, and underscore the urgent need for strategies to control non-native species populations, in the context of current programs for watershed restoration and conservation of its native fish species.