Impacts of run‐of‐river hydropower on coho salmon ( <i>Oncorhynchus kisutch</i> ): the role of density‐dependent survival

Abstract Predicting whether anthropogenic sources of mortality have negative consequences at the level population dynamics is challenged by mechanisms like density‐dependent survival that can amplify or offset loss individuals from disturbances. Run‐of‐river (RoR) hydropower a growing industry cause frequent salmonid fry through rapid reductions in streamflow, leading to stranding on dewatered shores. However, individual‐level impacts reduce growth rates increase local extinction risk difficult predict. We used stochastic stage‐structured matrix model evaluate how timing and magnitude flow fluctuations impacted abundance coho salmon ( Oncorhynchus kisutch ), which spend up 1.5 yr many streams regulated RoR hydropower. additionally assessed (spring, winter) strength (weak, moderate, high) natural bottlenecks experienced freshwaters tempers amplifies potential for RoR‐induced scale emergent dynamics. compared sizes 45‐yr probability quasi‐extinction under 12 scenarios varied frequency (0–20 events per year) (1–10% event) fluctuations, as well occurring during first year freshwater. found even mild impact dynamics, especially if density dependence weak occurs early freshwater residency (spring). When was strong winter, population‐level lessened, but populations still declined 13–42% when severe (5–10%) (10–20 events/yr). conclude could partially mitigate occur late residency, not all intensities fluctuations. Even with our models predict declining 70% very should serve caution those tasked regulating flows affected