Migratory freshwater fish provide essential food security and livelihoods globally. Yet regulation of large rivers continues to be a major threat. Providing passage for migratory fish holds promise of sustaining populations, but it also has an inconsistent history. In recent decades increasing knowledge of fish ecology has led to more appropriate fish passage objectives; whilst understanding the influence of fishway hydraulics (e.g. turbulence and water velocity) on fish passage, has greatly improved designs.
Worldwide, there is a fundamental enthusiasm for fishways but, despite successes, variable quality and effectiveness persist. This can be partly due to budget constraints, but more often it is an insular approach to design. We know that engineers and biologists are needed, but asset owners and operators are also essential, because they know what is practical in their region, and they will live with the result. Peer review at all stages of a project should also be encouraged. A constructive approach for governments or agencies responsible for water management is to establish an expert group, which provides review of designs by experts and stakeholders to ensure consistency and practicality; and education and training to encourage mentoring and continuity of skills.
A project focus on site-specific issues and internal fishway design can overlook broader aspects of fish life cycles and ecology, with detrimental impacts on populations. For example, lentic impoundments, upstream of dams/weirs, create hydraulic barriers that drifting larvae of riverine fishes cannot negotiate. Mitigating these impacts may involve selection of the dam to avoid major migration routes – providing lotic reserves - or, a radical departure in present dam design / operation. Regardless of the measure, research on the behavioural ecology of drifting larvae and spatial scale of migrations is urgently required.
Funding for fishways needs to be strategic, both at a project and catchment scale. Cost estimates of fishways require detailed concepts for the Business Case, early in the project timeline. Unfortunately, underestimates are often used, leading to compromises in detailed design when budgets are fixed. This often happens in large hydropower projects which, for example, may not provide 10% of flow for fish passage – a fundamental design criterion – because the Business Case has assumed most of the flow will be used for power generation.
Funding is also mostly dedicated to capital expenditure, leaving monitoring under-resourced and focused on passage efficiency. The more complex, but equally important assessment of attraction efficiency is relegated to a few species or not undertaken. Nonetheless, monitoring techniques have become increasingly sophisticated over the last decades, so funding issues would seem potentially solvable by articulating these benefits to stakeholders early in the project development phase.
Ultimately, project-based funding does not sustain long-term research, which is left to government agencies and universities. Engineering and ecological research is essential to foster innovation and to develop performance indicators that recognise life history strategies (e.g. short-lived semelparous species and long-lived iteroparous species) and integrate with population models. Funding for strategic research is presently a minor fraction of capital expenditure on fishways. Conceivably, new funding models are needed where water infrastructure projects contribute a percentage to long-term research projects.
Providing fish passage captures imaginations and is a powerful tool in mitigating the impact of dams and weirs. There have been great successes at low-level barriers and issues of variable quality are solvable. Nevertheless, sustaining migratory fish populations in regulated rivers, including facilitating the passage of all life stages past large dams, remains a major challenge.