Variations in the fish community in lake Piediluco (Italy) caused by changes in the lake's trophic status and the introduction of alien species

The composition of fish populations in lake Piediluco has undergone significant changes in recent years, mainly as a result of environmental deterioration due to the eutrophication of its waters and the introduction of some alien species. Lake Piediluco is a natural, regulated lake, which has been used for the production of hydroelectric power since 1908. Over the years, the trophic status of the lake has been profoundly modified: until 1980 it was mesotrophic; by 1989 it had become eutrophic, and now it is deemed to be hyper-eutrophic. The aim of this research was to analyze variations in the composition of fish populations in relation to the trophic evolution of the lake and the introduction of alien species. The data on fish populations were gathered during four monitoring campaigns carried out in 1988, 1996, 1999 and 2004. To estimate the abundance of the various species, catches were standardized in terms of catch per unit effort (CPUE). The results of the research reveal that the increase of the trophic status of the lake has been accompanied by a qualitative and quantitative change in the composition and structure of the fish community, which is being increasingly dominated by omnivorous cyprinids, such as Scardinius erythrophthalmus and the alien Rutilus aula. This is taking place at the expense of species that are ecologically less resilient and commercially more interesting, supported by provincial management policies as annual repopulation programs and deployment of artificial spawning substrates. Moreover, in more recent years the presence of some new alien species has been recorded, such as Rutilus rutilus and Gymnocephalus cernuus. These species, which were not previously found, pose a further threat to commercial fishing in the lake.