Survival of migrating juvenile salmon depends on stream flow thresholds

by Tim Stephens, UC Santa Cruz
May 20, 2021

Juvenile salmon migrating to the sea in the Sacramento River face a gauntlet of hazards in an environment drastically modified by humans, especially with respect to historical patterns of stream flow. Many studies have shown that survival rates of juvenile salmon improve as the amount of water flowing downstream increases, but “more is better” is not a useful guideline for agencies managing competing demands for the available water.

Now fisheries scientists have identified key thresholds in the relationship between stream flow and salmon survival that can serve as actionable targets for managing water resources in the Sacramento River. The new analysis, published May 19 in Ecosphere, revealed nonlinear effects in the flow-survival relationship, meaning it changes in stepwise fashion, with significant jumps in survival rates at two key steps.

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