American eel state of buoyancy and barotrauma susceptibility associated with hydroturbine passage

Abstract

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.

The Susceptibility of Juvenile American Shad to Rapid Decompression and Fluid Shear Exposure Associated with Simulated Hydroturbine Passage

“…Juvenile American shad tested in this study are also more susceptible to effects of shear and rapid decompression than other fish species, such as silver and yellow phase American eel (Anguilla rostrata), juvenile lamprey (Lampetra spp. ), juvenile rainbow trout (Oncorhynchus mykiss), and a few Australian species, which have been examined similarly [24,30,34,36]. This suggests that measures (i.e., turbine designs or operational modifications) taken to protect juvenile salmonids, or other fish species at hydropower facilities may not be sufficient to protect juvenile American shad.…”

“…Barotrauma injuries can result from gasses expanding within the body (explained by Boyle's Law) or bubble formation in the blood and tissues when gas comes out of solution (explained by Henry's Law) and can vary depending on the operating conditions of the hydropower facility and the species of fish [31,33,35]. Juvenile Chinook salmon (Oncorhynchus tshawytscha) have been observed to sufer mortality at pressure reductions as low as 50% [31], where American eel suffered very few injuries at much greater decompression (≈90% pressure reduction) [36] and lamprey (western brook lamprey, Lampetra planeri and Pacific lamprey, Entosphenus tridentatus) exhibited no physiological or behavioral response to extreme rapid decompression (>90% pressure reduction) [24].…”

Passage survival of European and American eels at Francis and propeller turbines

“…However, Pflugrath et al . () found that eels are not likely to be injured due to rapid pressure changes during downstream migration through hydroturbines.…”

“…Earlier publications suggest that the same injury symptoms could be manifested by two different sources and accurate delineation of a cause and effect relationship is difficult (Eicher Associates 1987). However, Pflugrath et al (2019) found that eels are not likely to be injured due to rapid pressure changes during downstream migration through hydroturbines.…”

Assessing turbine passage effects on internal fish injury and delayed mortality using X-ray imaging

“…During turbine passage, fish are exposed to rapid decompression (Colotelo et al, 2012), which causes an increase in swim bladder volume following Boyle's Law. Therefore, gas exchange in the swim bladder of physoclists is relatively slow and a rapid increase in volume is more likely to result in rupture than physostomous species such as salmonids or cyprinids (Blaxter & Batty, 1990, Boys et al, 2016Beirão et al, 2018;Pflugrath, Boys & Cathers, 2018;Pflugrath et al, 2019). American eel have been found to be exceptionally effective at expelling gas from the swim bladder which resulted in a very low susceptibility to barotrauma (Pflugrath et al, 2019) and this is also likely the case for European eel (Turnpenny et al, 1992).…”