Why Do Juvenile Fish Strand? An Analysis of Ten Years of Monitoring Data from the Columbia River, Canada Below HLK Dam

Juvenile fish are stranded and may die when water levels drop due to hydroelectric dam operations or natural river fluctuations.  Data collected over ten years of monitoring flow reductions in the lower Columbia River, Canada allow questions to be posed regarding the environmental and operational factors that contribute to fish stranding and mortality.  The effects of the ramping rate (pace of change in water level), wetted history (period of shoreline inundation), the magnitude of the change in river level, time of day, day of year, river level at the potential stranding sites and the completion of physical habitat alteration to reduce stranding incidence were investigated using generalized linear mixed effects models (GLMM).  The most consistent and significant factors contributing to fish stranding were the minimum discharge of the river, the day of the year and whether a high risk site had been physically altered to reduce stranding.  Results from the analysis can be integrated into dam operational management as well as study design for improved understanding of the issues in future.