Stato delle popolazioni di Cottus gobio (Linnaeus, 1758) in due corsi d’acqua dell’Italia centrale dopo l’eradicazione delle trote atlantiche Salmo trutta Linnaeus, 1758

The European bullhead Cottus gobio is a bottom-dwelling freshwater species of great conservation interest, listed in the Annex II of Habitats Directive. Although the species is widely distributed in Europe, in many areas it is threatened by habitat alteration and water pollution. The populations of the Adriatic basins in central Italy are of particular conservation interest since they are located at the southern limit of the European distribution range of the species. In this area, the European bullhead colonizes the upper stream reaches of the rivers and it is often associated with the presence of the brown trout. The aim of the present research was to compare the population status of Cottus gobio before and after eradication activities of Atlantic brown trout, carried out in the Gorga and Cesano streams (Marche region), as specified by the concrete conservation actions of the LIFE+ Trout Project (LIFE12 NAT/IT/0000940). Fish data were collected during the years 2014-2016 in two sampling sites. A total of 1125 specimens of European bullhead were collected and five age classes (0+ to 4+) were identified. In both populations, the average density and standing crop values resulted higher after the eradication activities. The equation of the total length-weight relationship for the total sample was W=0.0326TL2.5727 and no differences were found among the slopes of the two different populations. The parameters of the theoretical growth curves performed separately for the two populations showed that, after the eradication actions, the populations were distinguished by greater performance, evaluated using the ’ parameter, and larger sizes in all age classes in comparison to the pre-eradication period. Furthermore, the results of the condition factor evaluation showed no differences in the comparison between the two periods; this result suggests that probably the effects of the trout eradication acted through decreased predation and not through interspecific competition mechanisms. The information obtained demonstrate the positive effects of management actions as eradication of alien species, that appear to be particularly effective for biodiversity conservation in freshwater ecosystems.