Europe’s rivers are so clogged with dams, weirs, and sluices that fish can no longer swim between feeding and spawning grounds, and the fish ladders meant to help them often work only for salmon. This matters because river fragmentation has driven steep declines in freshwater fish diversity and abundance across Europe, yet most fish passes are designed for a single type of fish—diadromous species like salmon—while ignoring the dozens of other species that also need to move. The project will track fish movements, measure their physical traits, and analyse their genetic diversity in the reconnected lower River Severn in western Britain. Using that data, the team will build computer models that predict which fish survive, breed, and pass on their genes when a barrier or fish pass is in place. If successful, the models will give river managers a practical tool to decide where to remove barriers or redesign fish passes so that reconnection works for all species, not just salmon. This is applied ecology with a clear end-user: the people who manage Europe’s rivers and are tasked with making 25,000 kilometres free-flowing by 2030.
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Europe's rivers are highly fragmented by human constructed barriers that block the movement of fish, with this fragmentation driving substantial declines in freshwater fish diversity and abundance. The EU Biodiversity strategy aims to remove riverine barriers wherever possible so that 25000 km more river will be free-flowing in Europe by 2030. However, barrier removal is only occasionally feasible and so engineered fish passes provide alternative re-connection tools. The passes provide an easier route for fish to use to bypass the barrier. Although these fish passes are frequently on rivers with a diverse fish assemblage, they tend to be constructed to primarily facilitate the passage of diadromous fishes, especially anadromous salmonid fishes, despite most fish species being impacted by the fragmentation. This inter-specific selectivity of fish passes is potentially compounded by their intra-specific selectivity, where only specific phenotypes and genotypes are able to use the pass successfully. Thus, while fish passes are used frequently to provide river reconnection in Europe, the extent to which they impose new selection pressures on fish communities - and the associated consequences - remain highly uncertain. Our project overcomes this high uncertainty in river reconnection by bringing together an outstanding European researcher with potential to develop into a global science leader with a research group with strong competencies in fish tracking technologies and molecular ecology. Together, we generate new knowledge on the ecological and genetic responses of fish populations and communities in the reconnected lower River Severn in western Britain. Through data generated on fish movements, traits and genotypic diversity, we apply these data to the development of novel individual based models (IBM) that predict the ecological and evolutionary consequences of barriers and fish passes. The results of the project, including predictions of the outcomes for fish populations and communities across time and space of simulations of different riverine connectivity scenarios, will then provide river managers with the knowledge to on how river fragmentation caused by barriers can be managed in a manner that works for all species.
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