Preserving Trout Spawning Habitat for Sustainable Hydropower Development

Estimating habitat availability for fish is important to quantitatively assess the impacts of environmental stressors on natural systems and it’s essential for an effective legislation, protection and restoration of ecosystems. This study aimed to establish a biunivocal relationship between trout spawning habitat and flow rate in three rivers of the Aosta Valley, using trout as a bioindicator. Building on the literature analysis conducted by PhD Giovanni Negro, it was possible to define approximate baseline conditions for a model capable of predicting suitable areas for trout spawning, based on the characteristics of the riverbed. In October 2023, field surveys were conducted to characterize hydromorphological monitoring units (HMUs) using the MesoHABSIM method. Additionally, the presence and maturity of trout individuals were also recorded. In December 2023, the presence of trout nests was verified and both the nests and the HMUs in which they were identified were characterized. The study resulted in the development of an innovative model that integrates the literature analysis conducted by PhD Giovanni Negro with the collected field data. This model serves a dual purpose: to identify potentially suitable areas for trout reproduction and, consequently, to define the relationship between available habitat and flow rate. The developed model has a sensitivity value of 1, a crucial aspect to minimize the oversight of potentially suitable reproduction zones, whilst the habitat flow rating curves highlight a positive correlation between habitat availability and flow rate within the studied rivers. The three curves exhibit a similar trend, all characterized by an initial peak followed by a steady decrease. The model has proven successful in identifying suitable areas for trout reproduction and quantifying the available habitat based on flow rate. These results are of significant value for trout conservation and the sustainable management of rivers. The model provides a foundation for future research aimed at demonstrating that strategically regulating discharges from hydroelectric plants can enhance the habitat for trout and other river organisms, or simply maintain and improve the reproductive habitat of these organisms during low-flow periods, without having a significant impact on hydroelectric power generation. Ultimately, this study represents a significant step forward in understanding the interaction between trout and the river environment, offering valuable tools for the conservation and sustainable management not only of the trout species, but of the entire river ecosystem.