Modelling the effect of hydropeaking‐induced stranding mortality on Atlantic salmon population abundance

Abstract

Studies of hydropeaking‐induced stranding mortality on fish populations have been confined to analysis of empirical data and/or short‐term hydraulic‐habitat modelling of individual events and are thus limited as to how they may be used to infer long‐term effects in fish populations. In this study, the effects of stranding mortality on an Atlantic salmon population were simulated using an individual‐based Atlantic salmon population model with the objective of determining the sensitivity of population dynamics to stranding. It was found that density‐dependent mortality (an alternative source of mortality in juvenile Atlantic salmon) partially compensated for stranding mortality, acting as a negative feedback mechanism that dampened change in population abundance. Stranding caused a perturbation in population dynamics, and effects of individual stranding events persisted in time across the life stages of the population. Effects on population abundance depended on the time of year when stranding was applied, both because of intra‐annual changes in stranding mortality probability and because of intra‐annual changes in the ability of density‐dependent mortality to compensate for stranding mortality. We concluded that empirical measurements of stranding mortality have limited potential for inference of overall effects on the population, and a more dynamic modelling approach, incorporating system feedback, allows for a better modelling of the impact of stranding. Sensitivity analysis showed that population abundance was highly sensitive to density‐dependent mortality, and we suggest that this area should be prioritized for further research when investigating the effects of hydropeaking on rivers.

Performance of A Two-Dimensional Hydraulic Model for the Evaluation of Stranding Areas and Characterization of Rapid Fluctuations in Hydropeaking Rivers

“…Hydropeaking operations lead to rapid fluctuations in river flow that cause several impacts. These effects can lead to mortality of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) due to stranding [12,17,34], desiccation or drift of the benthos [6]. However, hydropeaking impact is strongly dependent on river morphology [21,35].…”

“…The seasonal analysis showed the highest percentage of rapid decreases were during darkness in winter (21%), classified as big impact effect by Envipeak guidelines, and autumn (24%), classified as moderate impact [5]. According to Hedger et al [17], Sauterleute et al [36], Scruton et al [37] and Saltveit et al [12], a far higher risk of fish stranding occurs during daylight in winter conditions due to the activity pattern of the fish. Therefore, based on our results, dewatering during night might reduce the risk of stranding.…”

“…Although fish stranding experiments have been performed in laboratories [7,16] or in limited areas in rivers [12], few studies exist on a larger scale in rivers about stranding. Hedger et al [17] developed an individually based population model that showed how hydropeaking-induced stranding mortality affects Atlantic salmon population along multiple generations.…”

The Impact of Hydropeaking on Juvenile Brown Trout (Salmo trutta) in a Norwegian Regulated River

“…The main effect of hydropeaking on juvenile salmonids in rivers is mortality due to stranding and desiccation [11,14,29]. However, hydropeaking can also lead to increased mortality due to increased energy consumption and stress [30].…”

“…However, stranding is not always equivalent to mortality, as fish can survive for several hours after dewatering [11]. Hydropeaking-induced stranding mortality may affect the Atlantic salmon population across multiple generations [14]; this is also likely for brown trout.…”