Stream temperature variability: why it matters to salmon

Abstract

Salmon evolved in natural river systems, where temperatures fluctuate daily, weekly, seasonally, and all along a stream’s path—from the mountains to the sea. Climate change and human activities alter this natural variability. Dams, for example, tend to reduce thermal fluctuations.

Currently, scientists gauge habitat suitability for aquatic species by establishing minimum/maximum temperature thresholds and relying on mean temperature readings to establish management priorities. But temperature effects on salmon are more complex. A new study demonstrates that temperature variability can affect emergence timing in Chinook salmon, potentially altering predictions about how these fish may respond to a changing climate. It also reveals that genetics can make a difference in how an individual responds to stream temperature variance.

The study indicates that the commonly used degree-day accumulation model is not sufficient to predict how organisms respond to stream temperature. Changes in how the degree days are delivered have the potential to alter the timing of life history transitions in Chinook salmon and other organisms. Emerging from the gravel a few days earlier or later could directly affect their survival due to changes in available food resources, competition for feeding grounds, or strong currents.

Citation

Steel, E. Ashley; Beckman, Brian; Oliver, Marie. 2014. Stream temperature variability: why it matters to salmon. Science Findings 163. Portland, OR: US Department of Agriculture, Forest Service, Pacific Northwest Research Station. 6 p.