Drivers of Chinook Salmon Population Dynamics in the Columbia River Basin

Abstract:

Pacific salmon populations in the Columbia River Basin declined precipitously in recent years, resulting in renewed scrutiny of driving factors and the efficacy of mitigation efforts. An array of environmental and man-made variables impact population and geographical distribution, and understanding this complex system of interactions is essential to develop an effective recovery plan. In this study, we utilize information theory measures to analyze interdependencies between Chinook population dynamics and driving variables, such as flows, water temperatures, and climate variables, at dam sites across the Columbia River Basin. On a daily timescale over a 10-year study period, we find that water temperature is a more significant driver of Chinook populations than stream flow. Moreover, populations on the Upper Columbia are generally less sensitive to temperature drivers than populations on the Lower Columbia or Snake River Basin, especially with increasing lag time. On an annual timescale over a 35-year period, we find that stream temperature and the Pacific Decadal Oscillation, a reoccurring pattern of climate variability, are among the most significant drivers of Chinook population and that the most prominent interactions between the Pacific Decadal Oscillation and Chinook populations are observed for lag times between three to five years. Further, we determine that the Snake River Basin is generally more sensitive to these drivers than the Upper Columbia. These results stress the importance of mitigation efforts that focus on preventing extreme temperature events, especially as such events become more likely with climate change expected to bring regional warming to the Pacific Northwest.