Comparative biodiversity of rivers, streams, ditches and ponds in an agricultural landscape in Southern England

Much effort has been devoted to developing, constructing and refining fish passage facilities to enable target species to pass barriers on fluvial systems, and yet, fishway science, engineering and practice remain imperfect. In this review, 17 experts from different fish passage research fields (i.e., biology, ecology, physiology, ecohydraulics, engineering) and from different continents (i.e., North and South America, Europe, Africa, Australia) identified knowledge gaps and provided a roadmap for research priorities and technical developments. Once dominated by an engineering-focused approach, fishway science today involves a wide range of disciplines from fish behaviour to socioeconomics to complex modelling of passage prioritization options in river networks. River barrier impacts on fish migration and dispersal are currently better understood than historically, but basic ecological knowledge underpinning the need for effective fish passage in many regions of the world, including in biodiversity hotspots (e.g., equatorial Africa, South-East Asia), remains largely unknown. Designing efficient fishways, with minimal passage delay and post-passage impacts, requires adaptive management and continued innovation. While the use of fishways in river restoration demands a transition towards fish passage at the community scale, advances in selective fishways are also needed to manage invasive fish colonization. Because of the erroneous view in some literature and communities of practice that fish passage is largely a proven technology, improved international collaboration, information sharing, method standardization and multidisciplinary training are needed. Further development of regional expertise is needed in South America, Asia and Africa where hydropower dams are currently being planned and constructed.

/pdf/the-future-of-fish-passage-science-engineering-and-practice-4v49f72c79.pdf

The future of fish passage science, engineering, and practice

The general perception of small run-of-river hydropower plants as renewable energy sources with little or no environmental impacts has led to a global proliferation of this hydropower technology. However, such hydropower schemes may alter the natural flow regime and impair the fluvial ecosystem at different trophic levels. This paper presents a global-scale analysis of the major ecological impacts of three main small run-of-river hydropower types: dam-toe, diversion weir, and pondage schemes. This review's main objective is to provide an extensive overview of how changing the natural flow regime due to hydropower operation may affect various aspects of the fluvial ecosystem. Ultimately, it will inform decision-makers in water resources and ecosystem conservation for better planning and management. This review analyses data on ecological impacts from 33 countries in five regions, considering the last forty years' most relevant publications, a total of 146 peer-reviewed publications. The analysis was focused on impacts in biota, water quality, hydrologic alteration, and geomorphology. The results show, notably, the diversion weir and the pondage hydropower schemes are less eco-friendly; the opposite was concluded for the dam-toe hydropower scheme. Although there was conflicting information from different countries and sources, the most common impacts are: water depletion downstream of the diversion, water quality deterioration, loss of longitudinal connectivity, habitat degradation, and simplification of the biota community composition. A set of potential non-structural and structural mitigation measures was recommended to mitigate several ecological impacts such as connectivity loss, fish injuries, and aquatic habitat degradation. Among mitigation measures, environmental flows are fundamental for fluvial ecosystem conservation. The main research gaps and some of the pressing future research needs were highlighted, as well. Finally, interdisciplinary research progress involving different stakeholders is crucial to harmonize conflicting interests and enable the sustainable development of small run-of-river hydropower plants.

Ecological impacts of run-of-river hydropower plants—Current status and future prospects on the brink of energy transition

This study was undertaken as part of a long-term investigation of the ability of high-level fishways to rehabilitate fish communities upstream of high dams. Effects of Tallowa Dam on fish of the Shoalhaven River system were studied by comparing species abundances, population size-structures and the structure of fish communities above and below the dam. Fish were sampled twice yearly for two years at 12 sites throughout the catchment. Species richness was greater downstream of the dam, with 21 species, compared to 16 species upstream of the dam. Ten diadromous species are believed to be extinct above the dam because of obstructed fish passage. Another four migratory species capable of climbing the wall have reduced abundances upstream. Accumulations of fish, particularly juveniles, directly below the dam were evident for nine species. Fish communities upstream and downstream of the dam differed significantly, identifying the dam as a significant discontinuity in the available fish habitats within the system. Historical evidence suggests that before the dam was built, fish communities from the tidal limit to at least 130 m elevation were largely continuous. This study has demonstrated that Tallowa Dam is a major barrier to fish migration and has had adverse effects on the biodiversity of the system. The creation of Lake Yarrunga by Tallowa Dam has resulted in distinctive fish communities in riverine and lacustrine habitats. Populations of five species that occur both upstream and downstream of the dam have developed differences in their size structures. The fish community downstream of the dam also differs from its historical condition because of the virtual disappearance of Australian grayling (Prototroctes maraena) and the establishment of non-native species.



A high-level fishway is now being designed for the dam to restore fish passage. Data from this study will serve as a baseline against which to assess the effectiveness of the fishway in rehabilitating fish communities of the river system. Copyright © 2002 John Wiley & Sons, Ltd.

Changes in fish communities of the Shoalhaven River 20 years after construction of Tallowa Dam, Australia

Salmonid fishways have been used in many countries for non-salmonid fishes, including Australia, but generally with poor results. Trapping the entrance and exit of a 1:9 gradient salmonid fishway on the Murray River confirmed very poor passage of native fish, with <1% of the most abundant species ascending. Fifty years of fish passage monitoring showed the numbers of three native species declining by 95–100% and non-native fish becoming dominant. Fishways are now being designed for native fish and being quantitatively assessed, but daily flow management also needs to be addressed. The ecological model for passage of potamodromous fishes has changed from passing adults of a few species to one that incorporates the whole fish community, specifically: immature fish of large-bodied species that dominate numbers migrating upstream; a diverse range of movement strategies; and small-bodied species, crustaceans and low numbers of less-mobile species.

Non‐salmonids in a salmonid fishway: what do 50 years of data tell us about past and future fish passage?

Declining fish communities characterise global freshwater environments, including those in Australia. Lost river connectivity through water resource development is a key cause of decline, disrupting fish migrations and threatening species productivity, viability and fisheries. Millions of dams, weirs and lesser barriers arising from water resources projects, road and rail transport and hydro-electricity schemes obstruct fish passage in rivers worldwide. Fishways are in place at few sites in Australia and globally relative to the numbers of barriers, and few mitigate the effects of barriers adequately. Most constrain the passage of fish communities and few have performed effectively when assessed against appropriate biological standards. Herein we focus on Australian experience within the global context of obstructed fish migrations, declining fish biodiversity and inadequate fishway performance. We review the migratory characteristics of Australian freshwater fish, identify the effects of different in-stream barriers and other habitat changes on the four classes of migratory behaviour and note how Australia’s highly variable hydrology presents particular challenges in mitigating fish passage barriers. Mitigation options include: basin-scale approaches; improved management of barriers, environmental flows and water quality; barrier removal; and development of improved fishway designs. Mitigation of fish-passage problems can aid in adapting to climate change effects, reversing fisheries declines and rehabilitating fish communities.

Mitigating the effects of barriers to freshwater fish migrations: the Australian experience

Effective fishways are required for restoring fish migrations and reversing worldwide declines in freshwater fish while making sustainable use of water resources. Mitigation of barrier effects at h...

Laboratory testing of an innovative tube fishway concept

Australia’s first trap-and-haul fishway was built to overcome site-related and biological challenges of providing upstream fish transfer at a 62 m dam. Challenges included multiple barriers, major ...

A trap-and-haul fishway for upstream transfers of migrating fish at a challenging dam site

Piping fish over dams

Freshwater fisheries of Australasia

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