Acute effects of gas supersaturation on Atlantic salmon smolt in two Norwegian rivers

Abstract

Total dissolved gas (TDG) supersaturation downstream of hydropower plants may cause gas bubble disease (GBD) and harmful effects in fish. Little is known about tolerance levels of TDG supersaturation on Atlantic salmon (Salmo salar Linnaeus, 1758) in natural rivers. The present study investigated the effects of TDG supersaturation on the survival of Atlantic salmon smolts at two field sites in Norway. Here, we kept smolts in cages at increasing distances from hydropower plants known to cause TDG supersaturation and at control sites. We recorded fish mortality and examined for GBD using a stereo microscope. Mortality and symptoms of GBD commenced in fish exposed to an average of 108.3% TDG (maximum 111.0%, water depth 0.55 m) for 2 days. Significant differences in time before mortality at the control sites and test sites commenced at 110.2% TDG (maximum 111.8%) for 3 days. The study indicates that Atlantic salmon may be more vulnerable to TDG supersaturation than Pacific salmonids, which are considered at risk when the TDG is above 110%. In addition, the study provides important data to link effects caused by TDG in the laboratory and in the field.

Perspectives on the environmental implications of sustainable hydro-power: comparing countries, problems and approaches

“…The harmful effects on fish from the supersaturation of total dissolved gas in the water downstream of hydropower plants have received relatively little attention in Norway compared with North America, even though Norwegian production systems with multiple intakes can cause significant air entrainment. The controlled field study by Stenberg et al (2021), however, indicates that Atlantic salmon may be more vulnerable to supersaturation than studied Pacific salmonids, with differences also being evident among life-history types. Landlocked Atlantic salmon were more susceptible to gas bubble disease and mortality than anadromous conspecifics, although it was not clear if the differences related to greater sensitivity to supersaturation in non-anadromous populations or other unmeasured differences between study sites and populations.…”

“…Technology and technological change emerging from environmental studies have important roles to play, in the context of providing researchers with new tools to understand the nuances of fish ecology, such as downstream larval dispersal (Brambilla et al, 2021), and fish interactions with hydropower facilities (Hahn et al, 2021). New hydropower engineering technologies will be similarly important for understanding how hydropower operational regimes may be adjusted to account for fish behaviour in ways that will reduce overall mortality (Smokorowski, 2021;Stenberg et al, 2021;Tuononen, et al, 2021). Thus digitalization and new methods for field data collections have improved applied environmental studies and pointed to the many subtleties of fish interactions with dams (Braga et al, 2021;Hahn et al, 2021;Sundt et al, 2021).…”

Behavioural response of brown trout (Salmo trutta) to total dissolved gas supersaturation in a regulated river

“…As supersaturated water flows downstream, it degasses at a rate that depends on a variety of environmental factors, especially mixing of the water column, and contact area at the air–water interface (Colt, 1986). Supersaturated water is toxic to many aquatic animals, causing the integration of gas bubbles in blood and tissues resulting in gas bubble disease (Pleizier, Algera, et al, 2020; Stenberg et al, 2020; Weitkamp & Katz, 1980).…”

“…Fish that are chronically exposed to supraphysiological (i.e., above physiological tolerance) levels of total dissolved gas supersaturation will eventually die, and high levels (i.e., >110% total gas pressure [TGP] in Atlantic salmon) in rivers can cause mortality of the wild animals that contract gas bubble disease (Pleizier, Algera, et al, 2020; Stenberg et al, 2020). Total dissolved gas supersaturation is most extreme at the water surface and attenuates at depth due to hydrostatic pressure (Pleizier, Nelson, et al, 2020).…”

“…High‐resolution monitoring of fish behaviour is possible with acoustic telemetry, which can be used to investigate relationships between individual animals and their environment (Hellström et al, 2016; Taylor et al, 2018), particularly how they respond to putative environmental stressors (e.g., Filous et al, 2017; Zięba et al, 2014). Brown trout in the Rysstad basin of the Otra River live in a 21‐km stretch of river that is highly impacted by total dissolved gas supersaturation caused by the Brokke powerstation (Pulg, Stranzl, et al, 2016; Stenberg et al, 2020). We predicted that individual trout depth distributions would respond to ambient total dissolved gas supersaturation and considered putative predictors of depth distribution (solar azimuth, lunar phase and day of year) with total dissolved gas supersaturation to test this prediction.…”