Water is widely regarded as the most essential natural resource, yet freshwater systems are directly threatened by human activities and stand to be further affected by anthropogenic climate change. As a result of this, habitats associated with 65% of continental discharge are classified as endangered and are subjected to significant biodiversity loss, which costs the EU a 3% toll on GDP every year. At global level the WWF Living Planet Report disclosed an 84% decline in freshwater populations from 1970 to 2020. The main stressors that affect freshwater species are linked with anthropogenic alterations of inland aquatic habitats. Among these, the fragmentation of rivers by means of man-made structures (e.g. weirs, water intakes, dams) represents a critical issue as it prevents the movement and migration of aquatic organisms and, hence, their chance of survival through foraging and reproduction. This problem is exacerbated by the fact that, unlike in terrestrial and marine ecosystems, where multiple pathways for movement exist, the linear nature of rivers severely constrains dispersal and facilitates strong and far-reaching effects of barriers. In 2011 EU set the ambitious Biodiversity Strategy to 2020 for halting the loss of biodiversity and ecosystem services inherently correlated to the degradation of aquatic habitats, but remediation policies undertaken by Member States have not yet halted these severe negative trends. “EU Nature Restoration Law” recently adopted by the European Parliament foresees the restoration of at least 25000 km of free-flowing rivers by 2030. On the other hand, the December 2018 recast of the 2009 EU Directive on the promotion of the use of energy from renewable sources, and eventually, the recent Directive EU/2023/2413, have progressively raised form raised to from 32% to 42,5% the binding overall Union target share for 2030, bringing further input to the hydropower development which could place further pressures upon river ecosystems. This in addition to other significant stressors acting on freshwater habitats (e.g. invasive alien species, wastewater discharges, emerging contaminants, etc.), and to the significant hydrological regime and water temperature alterations already being induced by climate change.
Under this extremely complex and challenging scenario, the focus of this Action was to train 15 ESRs to research innovative solutions for the protection of freshwater fauna in anthropogenically altered rivers, as currently adopted strategies for freshwater exploitation incorporate key factors that negatively impact biodiversity. The research and training programme integrated well within the interdisciplinary field of Ecohydraulics, which merges expertise in physical sciences, (i.e. fluid mechanics, acoustics and bio-mechanics), with behavioural ecology and fish biology.
The main scientific challenge that needs to be met in this area is disentangling the intricate nexus that links fish locomotion, behavioural response to anthropogenic disturbances and associated stress, as this is essential to the understanding and the preservation of nearly all aspects of fish life-cycle. Accompanying technology development is also needed to magnify the potential of experimental observations into the actual range of conditions that fish can experience in rivers.
This ETN Network provided a contribution to increase the current knowledge of the key factors and stressors governing the interaction between fish and aquatic ecosystems to enable both research and applications to be taken beyond the current state of the art.
