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

Abstract

Knowledge on the extent and mechanisms of fish damage caused by hydropower facilities is important for the conservation of fish populations. Herein, we assessed the effects of hydropower turbine passage on internal fish injuries using X-ray technology. A total of 902 specimens from seven native European fish species were screened for 36 types of internal injuries and 86 external injuries evaluated with a previously published protocol. The applied systematic visual evaluation of X-ray images successfully detected skeletal injuries, swim bladder anomalies, emphysema, free intraperitoneal gas and hemorrhages. Injuries related to handling and to impacts of different parts of the hydropower structure could be clearly distinguished applying multivariate statistics and the data often explained delayed mortality within 96 h after turbine passage. The internal injuries could clearly be assigned to specific physical impacts resulting from turbine passage such as swim bladder rupture due to abrupt pressure change or fractures of skeletal parts due to blade-strike, fluid shear or severe turbulence. Generally, internal injuries were rarely depicted by external evaluation. For example, 29% of individuals with vertebral fractures did not present externally visible signs of severe injury. A combination of the external and internal injury evaluation allows quantifying and comparing fish injuries across sites, and can help to identify the technologies and operational procedures which minimize harm to fish in the context of assessing hydropower-related fish injuries as well as in assessing fish welfare.

Editorial: Green or red: Challenges for fish and freshwater biodiversity conservation related to hydropower

“…This comprises mortality or injuries from contact with structures, such as screens and bars, collision with turbine blades, shear stress, and barotrauma arising from abrupt pressure changes during turbine passage. Direct and delayed mortality (Ferguson et al, 2006) as well as types of external and internal injury (Mueller, Pander & Geist, 2017; Mueller et al, 2020b) are affected by the physical and hydraulic forces encountered by the fishes and can be predicted to some extent (Deng et al, 2007; Boys et al, 2018), although strong species‐specific differences related to anatomical properties prevail. Even less is known about how fish behaviour affects mortality and differences in injury, related to different species, personality types, and diurnal activity patterns, as well as route choice at hydropower facilities (Baumgartner et al, 2014b).…”

“…This target species for conservation receives great attention and has a unique life cycle in which adults metamorphose into silver eel that migrate down the rivers on their long spawning migration into the Sargasso Sea. Silver eel have a long, elongated body shape and thus are at high risk of getting injured when passing hydropower facilities in a downstream direction (Egg et al, 2017; Mueller, Pander & Geist, 2017; Mueller et al, 2020b). For this reason, there have been various proposals for adjusting turbine operations in relation to eel activity patterns, or for trapping eels, moving them around the barriers, and then releasing them near the ocean (‘trap and truck’).…”

“…The debate about how ‘green’ the green energies really are is controversial (Gibson, Wilman & Laurance, 2017). Opponents of hydropower production often refer to it as a ‘red’ energy because of the mortalities and injuries that fish face when passing turbines (Mueller, Pander & Geist, 2017; Mueller et al, 2020b), as well as other ecological harm to free‐flowing rivers associated with habitat fragmentation and alteration. Hydropower is often referred to as one of multiple impacts on river ecosystems that has potentially synergistic effects with other stressors (Ormerod et al, 2010; Mueller et al, 2020a; van der Lee & Verdonschot, 2020).…”

“…The debate about how 'green' the green energies really are is controversial (Gibson, Wilman & Laurance, 2017). Opponents of hydropower production often refer to it as a 'red' energy because of the mortalities and injuries that fish face when passing turbines Mueller et al, 2020b), as well as other ecological harm to free-flowing rivers associated with habitat fragmentation and alteration.…”

Sneaker, Dweller and Commuter: Evaluating Fish Behavior in Net-Based Monitoring at Hydropower Plants—A Case Study on Brown Trout (Salmo trutta)

“…In light of the controversy about the pros and cons of hydropower, a variety of monitoring programs have been initiated to examine the effects of conventional and innovative hydropower technologies on fish passage. Examinations of seasonal and diurnal patterns of fish passage [1], assessments of the acceptance of different corridors for downstream passage [2,3], as well as analyses of external and internal injury patterns after passage [4][5][6], all depend on stow-net catches of fish at hydropower facilities. Stow-net-based monitoring at hydropower turbine outlets in small-to medium-sized rivers is considered a gold standard to investigate turbine-related fish injury and bypass efficiency compared to cameraor sonar-based technologies [7][8][9][10].…”