American eel are likely to encounter and pass through hydropower turbines, particularly during the downstream spawning migration, where exposure to stressors can potentially lead to injuries and mortality. Previous research has recovered dead eels downstream of hydropower facilities and, for some fish, injuries were easily attributed to blade strike; however, others showed no external signs of injury suggesting that other stressors, such as rapid decompression may be a potential source of mortality. For this research, yellow– and silver-phase American eel were held and allowed to acclimate to 172 kPa (absolute pressure) in hyper/hypobaric hydro-chambers for about 1 d. After acclimation, the state of buoyancy was determined prior to exposure to a rapid decompression simulating pressures encountered during hydroturbine passage. Fish were then examined for signs of barotrauma. Eel did not attain a state of neutral buoyancy but rather maintained negative buoyancy suggesting that eels, and possibly other benthic species, likely maintain a state of negative buoyancy to facilitate occupancy on or near the substrate. Additionally, eel were found to be resilient to rapid decompression, displaying no instantaneous mortality and minimal injuries, suggesting that barotrauma is not likely a major concern for American eel passing downstream through hydroturbines.

Global hydropower development is one solution proposed to address the increase in energy needs. However, hydropower-related impacts on riverine ecological systems are not well understood. The Mekong River Basin (MRB) is one of the world’s largest waterways and is presently experiencing significant hydropower expansion. It is also one of the most biodiverse rivers; serving as home to many species that are blocked or hindered by the development of dams. One source of injury and mortality for downstream moving fishes is passage through the turbine environment where fishes may be exposed to several physical stressors (e.g. shear forces, rapid decompression, blade strike and turbulence). The current study sought to understand the susceptibility of blue gourami (Trichopodus trichopterus) and iridescent shark (Pangasianodon hypophthalmus) to shear forces. Fishes were exposed to an underwater jet with velocities up to 21.3ms–1 (equating to strain rates of up to 1185s–1) and were assessed for behavioural effects, injuries and mortality. Overall, it was determined that both species were susceptible to the shear forces applied in this study and the effects were more pronounced at higher strain rates. Gouramis were more susceptible than sharks. To minimise impacts on these species, shear forces within turbines should not exceed critical limits.

Throughout many areas of their native range, American shad (Alosa sapidissima) and other Alosine populations are in decline. Though several conditions have influenced these declines, hydropower facilities have had significant negative effects on American shad populations. Hydropower facilities expose ocean-migrating American shad to physical stressors during passage through hydropower facilities, including strike, rapid decompression, and fluid shear. In this laboratory-based study, juvenile American shad were exposed separately to rapid decompression and fluid shear to determine their susceptibility to these stressors and develop dose–response models. These dose–response relationships can help guide the development and/or operation of hydropower turbines and facilities to reduce the negative effects to American shad. Relative to other species, juvenile American shad have a high susceptibility to both rapid decompression and fluid shear. Reducing or preventing exposure to these stressors at hydropower facilities may be a potential method to assist in the effort to restore American shad populations.