The Mediterranean brown trout Salmo macrostigma (Duméril, 1855) is at high risk of extinction in Italy, mainly due to the introduction of the alien Atlantic trout Salmo trutta Linnaeus, 1758: the genetic integrity of the native species is being threatened by the introgressive hybridization with the Atlantic trout, caused by stocking programs carried out since the last century. The LIFE+ TROTA – Trout population RecOvery in central iTAly (LIFE12 NAT/IT/000940) project, started in November 2013 and concluded in January 2018, was aimed to: i) analyze 32 trout populations in seven river basins of central Italy (Metauro, Cesano, Esino, Potenza, Chienti, Tevere e Tenna), ii) detect the presence of residual Mediterranean trout populations, and iii) undertake a series of concrete conservation actions in order to preserve these native populations. The genetic, demographic and ecological analysis of the trout populations, combined with the environmental characterization of the river stretches, allowed us to: i) detect the presence of low introgressed populations from which to collect breeders for the production, in hatchery, of pure juveniles Mediterranean specimens, ii) select the suitable sites for the alien trout eradication programs and for the re-introduction of Mediterranean trout, iii) quantify the available habitat for the Mediterranean trout in relation to the flow rate oscillations, using the MesoHABSIM method. The eradication activities were carried out on 4 watercourses in which was detected the presence of highly introgressed populations; the eradicated sites were selected to be isolated from the rest of the basin, as delimited by the presence of natural and human-made weirs that are insurmountable from fish fauna. The eradication activities were carried out by electrofishing and a total of 13 sampling periods for each site were carried out between December 2014 and July 2017. These results showed the effectiveness of electrofishing in the eradication programs, especially in watercourses of modest dimensions in terms of flow rates, width and depth, and for populations characterized by modest abundance values. The positive effects of the eradication activities have also been highlighted in relation to the results obtained for another species of high conservation interest, such as the European bullhead Cottus gobio Linnaeus, 1758. The introduction of Atlantic trout causes negative impacts on bullhead populations due to predation of juveniles and interspecific competition. From the comparison of the population status of C. gobio before and after Atlantic trout removal, a notable increase in the abundances of bullhead populations was observed, and also the juveniles percentage increased after the trout eradication. Moreover, after the trout removal, C. gobio populations were distinguished by higher growth performance and larger sizes in all age classes in comparison to the pre-removal period.

Life+ TROTA Project for the recovery and conservation of the Mediterranean trout (Salmo macrostigma) populations

Lorenzoni M.
;
Carosi A.;La Porta G.;
2018

Abstract

The Mediterranean brown trout Salmo macrostigma (Duméril, 1855) is at high risk of extinction in Italy, mainly due to the introduction of the alien Atlantic trout Salmo trutta Linnaeus, 1758: the genetic integrity of the native species is being threatened by the introgressive hybridization with the Atlantic trout, caused by stocking programs carried out since the last century. The LIFE+ TROTA – Trout population RecOvery in central iTAly (LIFE12 NAT/IT/000940) project, started in November 2013 and concluded in January 2018, was aimed to: i) analyze 32 trout populations in seven river basins of central Italy (Metauro, Cesano, Esino, Potenza, Chienti, Tevere e Tenna), ii) detect the presence of residual Mediterranean trout populations, and iii) undertake a series of concrete conservation actions in order to preserve these native populations. The genetic, demographic and ecological analysis of the trout populations, combined with the environmental characterization of the river stretches, allowed us to: i) detect the presence of low introgressed populations from which to collect breeders for the production, in hatchery, of pure juveniles Mediterranean specimens, ii) select the suitable sites for the alien trout eradication programs and for the re-introduction of Mediterranean trout, iii) quantify the available habitat for the Mediterranean trout in relation to the flow rate oscillations, using the MesoHABSIM method. The eradication activities were carried out on 4 watercourses in which was detected the presence of highly introgressed populations; the eradicated sites were selected to be isolated from the rest of the basin, as delimited by the presence of natural and human-made weirs that are insurmountable from fish fauna. The eradication activities were carried out by electrofishing and a total of 13 sampling periods for each site were carried out between December 2014 and July 2017. These results showed the effectiveness of electrofishing in the eradication programs, especially in watercourses of modest dimensions in terms of flow rates, width and depth, and for populations characterized by modest abundance values. The positive effects of the eradication activities have also been highlighted in relation to the results obtained for another species of high conservation interest, such as the European bullhead Cottus gobio Linnaeus, 1758. The introduction of Atlantic trout causes negative impacts on bullhead populations due to predation of juveniles and interspecific competition. From the comparison of the population status of C. gobio before and after Atlantic trout removal, a notable increase in the abundances of bullhead populations was observed, and also the juveniles percentage increased after the trout eradication. Moreover, after the trout removal, C. gobio populations were distinguished by higher growth performance and larger sizes in all age classes in comparison to the pre-removal period.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/1431187
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