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Global advances in fish passage research and practice

The water-food-energy nexus is central to sustainable development (Poff and Olden 2017). Demand for all three is increasing, driven by a rising global population, rapid urbanization, changing diets and economic growth. In response, many countries are implementing unprecedented irrigation and hydropower expansion programs infrastructure to secure food, water and energy resources. Globally, irrigation has doubled in the last 50 years (Foley et al. 2011) and hydropower is expected to double again by 2050 (Ziv et al. 2012). Therefore, it is important that such development is planned, implemented and managed appropriately (Lynch et al. 2019) because any structure which diverts or stores water will impede the free movement of fish; in both an upstream and downstream direction. The environmental impacts of migration barriers have been recognised globally as one of the major threats for aquatic biota, particularly riverine species (Poff and Hart 2002). But there is always a significant challenge developing technical solutions that minimise impacts on fish, and create mutually beneficial outcomes for the environment and society. Fish passage has long been an intervention applied by irrigation and fisheries managers to mitigate the impacts of riverine development on fish (Clay 1995). But getting fish passage implemented correctly represents a significant engineering and biological challenge (Silva et al. 2018). Often, there are multiple solutions that may fit any given site but the best for implementation depends on a range of factors including target species and size classes, the expected ecological outcomes, local site hydrology, constructability and available budget (Larinier and Marmulla 2004). At many sites, data availability is often limited and so engineers and biologists must work collaboratively to implement functional solutions. This often requires design compromises which can only be agreed upon in collaboration (MallenCooper and Brand 2007). As has been famously noted, “An engineer may learn a lot of biology, and a biologist may learn a lot of engineering but, ultimately, both skills are needed to implement a functional solution” (Clay 1995). This special issue of Journal of Ecohydraulics explores recent biological and engineering advances in fish passage technology to help mitigate the impacts of barriers on fish migrations. The articles highlight the impacts of river infrastructure on fish and key knowledge advances for biologists and engineers to apply at future sites. Whilst these contrasting perspectives are explored from different angles, they essentially seek to arrive at the same outcome; winwin benefits for both fish and river development. Key topics include: