Baby salmon evolved to ride winter and spring runoff downstream to the ocean but dams now block that runoff in most years. When Central Valley rivers flow low, warm, and clear, predation on baby salmon becomes very significant. The NMFS Santa Cruz Science Center estimates survival of baby winter-run salmon between the upper river and the Delta at only 16 percent during drought years. With other losses taking place in the Delta and beyond, the overall damage is near 100 percent and the run becomes unsustainable.
One way to correct these problems is to release pulse flows of water from upstream reservoirs like lakes Shasta and Oroville to push the small salmon downstream to the Delta and to safer rearing areas. Pulse flows have been very successful in the past including one in 1985 associated with very high returns of adult fish several years later.
Recent NMFS studies show that spring run baby salmon are lost during out migration once they reach the mainstem Sacramento River from the tributaries they’re born in. NMFS and CDFW are calling for a spring pulse flow study in the mainstem Sacramento to see if these losses can be reduced or stopped. On the Feather River, spring pulse flows have also been requested in low water years by salmon advocates. In early 2018 the Dept. of Water Resources applied a small pulse flow to aid the out migration of hatchery reared spring run juveniles. GGSA supports spring pulse flows in low water years to reverse heavy losses.
A peer reviewed paper from the NMFS southwest Science center that shows loss of juvenile salmon along their out bound migration route in the Central Valley.