Impacts of current and future large dams on the geographic range connectivity of freshwater fish worldwide

Abstract

Dams contribute to water security, energy supply, and flood protection but also fragment habitats of freshwater species. Yet, a global species-level assessment of dam-induced fragmentation is lacking. Here, we assessed the degree of fragmentation of the occurrence ranges of ∼10,000 lotic fish species worldwide due to ∼40,000 existing large dams and ∼3,700 additional future large hydropower dams. Per river basin, we quantified a connectivity index (CI) for each fish species by combining its occurrence range with a high-resolution hydrography and the locations of the dams. Ranges of nondiadromous fish species were more fragmented (less connected) (CI = 73 ± 28%; mean ± SD) than ranges of diadromous species (CI = 86 ± 19%). Current levels of fragmentation were highest in the United States, Europe, South Africa, India, and China. Increases in fragmentation due to future dams were especially high in the tropics, with declines in CI of ∼20 to 40 percentage points on average across the species in the Amazon, Niger, Congo, Salween, and Mekong basins. Our assessment can guide river management at multiple scales and in various domains, including strategic hydropower planning, identification of species and basins at risk, and prioritization of restoration measures, such as dam removal and construction of fish bypasses. habitat fragmentation | hydropower | river management | migratory fish | biodiversity Barbarossa et al. PNAS | February 18, 2020 | vol. 117 | no. 7 | 3649 ECOLOGY ENVIRONMENTAL SCIENCES Downloaded by guest on July 3, 2020

A Participatory Science Approach to Expanding Instream Infrastructure Inventories

“…At the global scale, our existing understanding of instream infrastructure impacts on sociohydrology and ecology are skewed toward those caused by larger infrastructure such as dams (see Grill et al, 2017; Liermann et al, 2012), but we increasingly understand that smaller infrastructure are more numerous and likely to have greater cumulative changes on our river ecosystems that remain poorly understood (Couto & Olden, 2018; Csiki & Rhoads, 2010; Januchowski‐Hartley et al, 2013; Lange et al, 2019). By mapping infrastructure that does not create large reservoirs behind it, spatially explicit data sets like GROD will enable both finer‐resolution analyses and better understanding of impacts caused by instream infrastructure on hydrological flow alterations (Poff & Hart, 2002), geographic range connectivity for species, particularly fishes (sensu Barbarossa et al, 2020), and important fisheries resources (sensu Carvajal‐Quintero et al, 2017). Equally, GROD will enable spatially explicit scenarios and potential solutions for restoring hydrological and ecological connectivity through the remediation (fish passages and structure modifications) or removal of existing infrastructure along global river networks (sensu Hermoso et al, 2018, Neeson et al, 2015).…”

Controlling biodiversity impacts of future global hydropower reservoirs by strategic site selection

“…60% of the world's land surface, and 9 out of 14 of the world's terrestrial biomes, have already fallen below a safe planetary boundary threshold. To fully understand how much of the hydropower potential could be used without substantially damaging the surrounding biodiversity, other biodiversity impact pathways such as impacts of discharge regulation 19 , habitat fragmentation 40 or water regulation in the reservoir 61 should be considered as well.…”

“…refs. 2 , 11 , 18 , 40 – 43 ) have assessed how hydropower electricity production can affect the state of the environment, only a few studies have quantified the resulting biodiversity impacts on a global scale (e.g. refs.…”

How to choose? A bioeconomic model for optimizing river barrier mitigation actions

“…However, more than 50% of rivers globally are impacted by physical infrastructure (e.g., dams, weirs, and culverts) that disrupt the longitudinal connectivity and obstruct sh from accessing essential habitats and resources. Numerous studies have demonstrated the negative eect that articial barriers have on migratory (Catalano et al, 2007;Lucas et al, 2009;Gough et al, 2018;O'Hanley et al, 2020) and resident sh populations (Nislow et al, 2011), including restricted range, altered population structure, reduced spawning and recruitment success, genetic isolation, and local extinction (Woord et al, 2005;Nunn and Cowx, 2012;Barbarossa et al, 2020;Pereira et al, 2020). This, in turn, can compromise the ability of river ecosystems to deliver the full range of ecosystem services (Rounsevell et al, 2018).…”