Reframing Fish Passage Prioritization for Human Nutrition Outcomes

Rivers and floodplains have historically benefited and continue to benefit human societies by providing nutritious aquatic foods, water for agriculture, and hydropower generation among many other services (Arthur et al. 2015; Grill et al. 2019). Dams, weirs, and floodplain infrastructure (Fig. 1) substantially affect river systems and the ecosystem services they provide by changing the timing and magnitude of water flows, and fragmenting aquatic habitats (McCartney et al. 2019). Fragmentation prevents or restricts free movement of aquatic organisms including migratory fish to diverse habitats within the river catchment (Fuller et al. 2015). The combined effect of large irrigation infrastructure is substantial, accounting for 70% of freshwater abstraction (McDermid et al. 2023). Simultaneously, underestimation of the effect of hundreds of thousands of small water infrastructure barriers (<10 m in height) indicates abstraction rates may be much higher than previously realized (Baumgartner et al. 2021). Almost 70% of area under irrigation is in Asia, particularly China and India, but also southeast Asia in the Lower Mekong Basin (LMB) where it mainly supports rice agriculture (McDermid et al. 2023).

Bild vergrößern

Water infrastructure development in the LMB is typical of the global dynamics of river regulation. Traditionally, the LMB’s tropical climate and extensive annual flooding drove immense biological productivity and strongly connected local human livelihoods to fisheries and flooded agriculture (Morton and Olson 2018). In recent years, inland fisheries have increasingly faced multiple pressures, with water infrastructure being a major threat (Reid et al. 2019; Stokes et al. 2025). Presently thousands of water infrastructure barriers fragment aquatic habitats (McCartney et al. 2019). Up to 86% of the LMB’s floodplain has been converted to rice agriculture (Fig. 2), with expansion driving reclamation of natural wetlands, loss of floodplain vegetation (Carling 2009), and contributing to fisheries decline (Dudgeon 2005; Halls and Hortle 2021). This decline affects mainly family fishers, especially women and children using the relatively safe and accessible floodplain habitats for subsistence (Garaway et al. 2013; Freed et al. 2020; Nurhasan et al. 2022). While some communities benefit from intensified rice production, others are made more vulnerable through loss of free, accessible, and nutritious wild capture fisheries (Duncan et al. 2021; Friend et al. 2012). The social and ecological trade-offs of irrigation and development are acknowledged in the United Nations (UN) Sustainable Development Goals (SDGs), which emphasize socially inclusive modes of production and development that occur within planetary boundaries to improve present and future people’s wellbeing (United Nations [UN] 2015). Specifically, SDG 2: Zero Hunger, but also SDG 1: No Poverty, SDG 3: Good Health, SDG 5: Gender equality, and SDG 15: Life on land (including freshwater resources) are undermined by the loss of inland capture fisheries as a critical food resource including for vulnerable or marginalized peoples who may not receive full benefit from profit driven development (Bush 2008; Elliott et al. 2022).

Bild vergrößern

SDG 2: Zero Hunger sets the ambitious aim of providing a reliable and adequate supply of nutritious food for all. Nutrition security is a central concern in the LMB’s least developed countries, Cambodia and Lao People’s Democratic Republic (PDR), where iron, vitamin A, calcium, omega 3 fatty acid, and zinc deficiencies are problematic (Barrett 2020; Nurhasan et al. 2010; UNICEF 2021). Nutrition security refers to the provision of essential dietary nutrients, as opposed to food security which relates to providing adequate daily caloric (energy) intake, but not the nutritional quality of food (Simelane and Worth 2020). Nutrition security is multidimensional, including nutrient supply, but also access, utilization, and production sustainability (Simelane and Worth 2020). Globally, reliable access to adequate nutritious food is a major challenge (FAO et al. 2022), and capture fisheries have traditionally filled an important role as abundant, accessible, sustainable, and socially acceptable food (Arthur et al. 2015; Youn et al. 2014). Many fish contain nutrients often lacking in disadvantaged people’s diets (Funge-Smith and Bennett 2019), including all those essential for women’s and children’s health in the first 1000 days of human life (Nurhasan et al. 2022). Wild fish are more nutritious than aquaculture fish, owing to species diversity and nutrient density in small fish which are rarely cultured and are viewed as having low commercial value, but which constitute the majority portion of capture fisheries yield in the LMB (Belton and Thilsted 2014; Nam et al. 2009). The superior nutrition of wild fish underlines the importance of inland fisheries to the nutrition security of marginalized groups until more accessible, sustainable, and equitable alternative food systems can be developed (Tezzo et al. 2018). It is paradoxical that the supply of nutritious fish is potentially being sacrificed for nutrient-poor irrigated rice, with the required water infrastructure often justified based on its production of rice, but failing to account for the loss of fisheries. This is especially problematic where people may have restricted access to alternative nutritious food, either economically or because of their location (Duncan et al. 2021; Friend et al. 2012). Rather, both fish and rice can be maintained in the landscape with appropriate management (McCartney et al. 2019; Freed et al. 2020). Consequently, investments in fishery restoration are taking place to maintain migratory fisheries and protect the nutrition security they provide (ACIAR 2024; ADB 2020b). Fishery restoration interventions target ecological, social, and technical aspects of fisheries, such as habitat restoration, community management, and fish-friendly infrastructure (Mekonen et al. 2025; Rogosch et al. 2024). Their influence on food security varies and is often shaped by local socio-political contexts (Nguyen-Khoa et al. 2020; Arthur et al. 2023). For instance, while aquaculture can boost fish supply, it often has reduced nutritional output and requires land and capital investments that limit broader benefits (Belton and Thilsted 2014; Tezzo et al. 2018). In contrast, fish passage technologies restore connectivity in regulated rivers and can support the >70% of LMB fish species that migrate (Conallin et al. 2019). These technologies benefit shared fisheries resources, including for marginalized groups with limited land or capital (Basurto et al. 2025; Hall et al. 2013; Thilsted et al. 2016). Fish passage can also amplify the effectiveness of other interventions, such as floodplain restoration, by enabling fish to reach breeding and nursery habitats. Without connectivity or habitat quality, ecological gains can be lost (Piczak et al. 2023). Similarly, if fishing is unregulated, fish populations may decline despite improved access to quality habitat. Thus, fish passage is a foundational intervention that supports other restoration efforts. This paper focuses on how fishways are implemented to support both fish populations and human communities.

Given the extent of fragmenting barriers, which are estimated to number ~13,000 in the Mekong basin alone (Sun et al. 2024), and limited financial, technical, and human resources with which to remediate them, fish passage barrier prioritization frameworks have been developed to guide strategic fishway implementation. Prioritization frameworks enable systematic consideration of barriers within river basins in relation to their physical characteristics and environmental context (Kemp and O’Hanley 2010). They do so via a hierarchical process using one or a combination of methods (e.g., rank and score, geographic information systems [GIS], optimization modeling; refer to Table 1) and aim to aid decision-makers in choosing the most important and best value barriers to remediate according to local management objectives. Rank and score methods evaluate barriers according to programmed criteria, for example, budget constraints, maximizing connected habitat area, or prioritizing barriers of certain heights (Kemp and O’Hanley 2010). The simple format and reporting of this approach are advantageous however, rank and score approaches neglect relationships between barriers within catchments (Flitcroft et al. 2019; Virbickas and Kesminas 2024). Ignoring the catchment context, specifically the spatial relationship between barriers is problematic given fish passage is about restoring strongly relational habitat connectivity and processes (e.g., Stanford and Ward 1992). In contrast, Geographic Information Systems (GIS) methods analyze the spatial relationships between barriers and landscape features in catchments (Cote et al. 2009); however these are constrained by available spatial data which can be limited in developing country contexts (Ali et al. 2025), for example in Cambodia. Optimization approaches use statistical modeling to determine priority barriers in the river network but typically require expert programming and operation which can limit their accessibility to diverse users (Kemp and O’Hanley 2010). Some hybrid frameworks combine spatial information in rank and score (e.g., upstream habitat length and barrier characteristics – Atkinson et al. 2020) or in optimization modelling with other habitat, hydrologic, and/or socio-economic data (e.g., cost of fishway construction) which can enhance their applicability in data poor scenarios by drawing from a broader database (e.g., Oregon Department of Fish and Wildlife 2019; Marsden et al. 2023).

Prioritization frameworks can be designed by resource management agencies, (e.g., U.S. Fish and Wildlife Service 2016), environmental consultants (e.g., Catchment Solutions), fishway implementers (e.g., Marsden et al. 2023), or academic researchers (e.g., Ioannidou and O’Hanley 2019) to support natural resource managers or funding organizations making fish passage decisions. Some are published in peer-reviewed journals while others are produced by natural resource management agencies as internal documents to standardize barrier prioritization in river basins under their remit. Many frameworks exist, some dating back several decades (Paulsen and Wernstedt 1995; Wernstedt and Paulsen 1995); however, evaluations of their effectiveness are challenging to find (the authors did not locate any although restoration action effectiveness is examined in Rogosch et al. (2024) and fish community recovery like changes in other ecological processes can take years to be realized (Rosenfeld and Hatfield 2006). Over time, methods to identify barriers have improved, and have been supplemented with basic fish surveys to characterize local fisheries to support prioritization. Most prioritization frameworks focus on North American salmonid fisheries (e.g., O’Hanley et al. 2013; US Fish and Wildlife Service 2016; Atkinson et al. 2020) where billions of dollars have been spent to conserve fish stocks threatened by water infrastructure development (Denkmann and Leibovitz 2024). Likewise, abundant research into salmonids, a temperate climate species, sharply contrasts with lack of investment demonstrated in megadiverse tropical regions like the LMB where much less data exist but people are highly dependent on fish for food (Cowx et al. 2025).

Data and metrics used to inform barrier prioritization can privilege some communities over others (King and Fonner 2024). Commonly, barrier prioritization frameworks use upstream habitat length as a decision-making metric, sometimes supported by other technical (e.g., presence of a downstream barrier) or ecological metrics (e.g., surrounding land use, flow metrics). Alone, these metrics lend themselves to maximizing biological processes in rivers, and benefiting river fishers, however social (e.g., nutritional, economic, and traditional) outcomes at best only indirectly result. The lack of socially, or nutrition sensitive metrics implies families and subsistence fishers, many of whom use off-channel fishing grounds like floodplain rice fields (Freed et al. 2020) commonly overlooked in river focused prioritizations, are unaccounted for. Theoretically, metrics relating to habitats or species fished by SDG focal demographics could be an entry point for integrating nutrition security into prioritization frameworks (Conallin et al. 2019), however it is unclear if this is occurring. Alternatively, social demographic, health or livelihoods data could be leveraged to understand spatial patterns of fish dependency and prioritize barriers that might represent greater community benefits if remediated for fish passage (Table 2). Expansion of fisheries management intervention evaluation to include social metrics is observable in policies of influential partners like the National Oceanic and Atmospheric Administration (NOAA 2021) in their Human Integrated Ecosystem Based Research Strategy and the United Nations Food and Agriculture Organization’s Ecosystem Approach to Fisheries (FAO 2025). Where interventions aim to maintain fish productivity for nutrition security as in the case of fish passage restoration in the Mekong, integration of social data could help inform evaluation as the logical next step of barrier prioritization and impact evaluation.

Our goal was to conduct a scoping review to better understand fish passage prioritization framework metrics and to identify criteria relevant to supporting and delivering on nutrition security outcomes generally, and specifically in the LMB. Our findings point to the emergence of nutrition security as a motivating factor for fish passage investment in the LMB, but that relevant metrics are underrepresented in frameworks both developed for the LMB, and globally. The present work has implications relevant to fish migration, fish passage, and international development disciplines beyond current fish passage investments in the LMB region. These metrics will be relevant to future investments in tropical and developing regions, and in a global environmental policy context where natural resource management of fish and rivers increasingly needs to contend with multiple, competing demands of resource beneficiaries (refer to Lynch et al. 2025).