Monday August 24, 2026
EurekAlert! —
Sacramento River winter-run Chinook salmon are California’s most endangered salmon, with a single surviving population and an average of a few thousand returning fish in recent decades. Shasta Dam blocks their original habitat in cold mountain rivers draining Mount Shasta, leaving them to spawn in the low-lying Sacramento River heated by the summer sun.
The research, published this week in Science Advances, found that cool river temperatures in the first 15 days after their eggs were fertilized was crucial for their survival. In warm years with less water, cold water barely covered this critical thermal window, sharply limiting survival in what may become an increasing reality for salmon as the climate warms.
“Salmon may spawn throughout the summer season, but our results suggest that only a small fraction of those spawning events ultimately produced the juveniles that survived,” said Kohma Arai, who authored the research as a postdoctoral scholar at UC Davis with other scientists from the university, NOAA Fisheries, UC Santa Cruz, UCLA, and the Norwegian Institute for Nature Research.