Predicting the likelihood of gas bubble trauma in fishes exposed to elevated total dissolved gas in the lower Clark Fork River, Idaho

Abstract

AbstractObjectiveGas bubble trauma (GBT) can occur in fish when water becomes supersaturated with gases, with effects ranging from minor tissue damage to death. Laboratory studies suggest that fish exposure to elevated total dissolved gas (TDG) at depths that compensate for gas supersaturation can result in reduced GBT incidence and that different fish species exhibit varying susceptibility to GBT. Elevated TDG levels associated with spill at Cabinet Gorge Dam in the lower Clark Fork River, Idaho, facilitated describing the incidence and severity of GBT, variables that affect GBT incidence, and the probability of observing GBT in different fish species.MethodsTotal dissolved gas and GBT data were collected during the typical spill period (i.e., April–July) in 2000, 2006, 2008, and 2017–2021.ResultA total of 6985 fish was examined for GBT at TDG of 101–137% saturation. Incidences of GBT varied with TDG levels, and the greatest incidence of GBT was typically observed near the date with peak daily mean TDG. Logistic regression models indicated that the probability of observing GBT was affected by TDG exposure and temperature but not length. The probability of observing GBT on fish was < 0.01 when 7‐day mean TDG was 110% saturation and < 0.04 when 7‐day mean TDG was 120% saturation. The models also indicated that the probability of observing GBT at a given TDG value differed between fish species.ConclusionWe suggest that species‐specific behavior and habitat composition in the sampled area (i.e., access to compensatory depths and locations with less TDG) were factors in our observations. We advocate that fisheries managers use a similar process to develop site‐ and species‐specific GBT probability curves where elevated TDG is an issue. These site‐specific curves can help managers evaluate the potential for population‐level effects to fisheries and need for TDG reduction or mitigation actions.