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Relieving Thermal Stress in Pacific Salmon Rivers 

Targeted solutions for salmon runs on the brink

 

Problem Overview

In rivers all along the West Coast, salmon fry populations are in decline. Over the last 50 years, multiple factors have contributed to the current state of survival and return, including industrial dams, agriculture irrigation water diversion, overfishing, and the effects of climate change.

As climate change intensifies, river temperatures are rising while water volume levels simultaneously decline, and the combined effect creates considerable stress on salmon at the egg fertilization stage, fry stage and the returning adult spawning stage. Currently, the negative effects of lower water levels and higher water temperatures are most acute in California and Oregon. But they’re already being felt in the north.

Chinook, the largest species of salmon, have been in sharp decline as far north as the Kenai River in Alaska, and in even starker decline in warmer southern rivers. In the 1960s, Chinook returned to the Sacramento River in annual numbers of about 500,000. Now they return in numbers below 5,000.  

Due to decreased rainfall and snowpack, increased drought, and considerable agricultural water allocations, the foreseeable reality is that the Sacramento and San Joaquin rivers will continue to suffer escalating negative effects of low water levels combined with higher-than-normal water temperatures.

75% of the water in the Sacramento-San Joaquin delta comes from the Sierra Nevada Mountains. A recent study predicts a 79% decline in Sierra Nevada snowpack over the next 81 years.

Over the last three years, the State of California has attempted to shield salmon populations from thermal stress by reallocating water designated for agriculture back into rivers, in order to mitigate water loss and bring down water temperatures in the process. These efforts have not proved effective.