In Italian freshwaters the introgressive hybridization with the alien Atlantic trout represents the principal threat to the native endangered Mediterranean trout. The aim of the research was to test the effectiveness of alien trout removal activities carried out by electrofishing in four streams in Central Italy. The four sites were chosen on the basis of the severe genetic introgression level of the trout populations. The removal activities were carried out from December 2014 to July 2017, for a total of 10 eradication campaigns in each site. During each field activity, five environmental parameters (flow rate, conductivity, average depth, average width, accessibility) were collected, since they could influence both the effectiveness of the electrofishing and the biological characteristics of the fish populations. A total of over 22,000 alien trout accounting for a biomass of over 700 kg were removed from the removal sites. For each site, a progressive drastic decrease over time in density and standing crop values was observed. Removal rates ranged from 94.22% to 100.00% for density, and from 96.57% to 100.00% for standing crop. The correlation analysis showed an inverse significant relationship between catchability and populations abundance, confirming that low density populations are more suitable to removal efforts. The progressive removal of specimens improved the catchability over time, indicating that even the largest populations could be eradicated, providing the necessary number of steps in a fishing season. The improved body condition and the greater growth rates observed during the eradication period, in low abundance conditions, seemed to confirm the key role that intraspecific competition and density-dependent phenomena play in the Apennine trout population dynamics. The results obtained in the present research provided evidence that electrofishing removal could be an effective management tool for the Mediterranean trout conservation, especially in watercourses of modest dimensions in terms of flow rates, width and depth.
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