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Water Temperature A Concern For Salmon

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Sonora, CA — While the number of Chinook salmon migrating along the Stanislaus River this year has been near record high, there is a cause for concern.

Since 2003, the environmental consulting firm FISHBIO has been using a fishing weir to count the salmon population. FISHBIO Senior Biologist Andrea Fuller reports that nearly 7,000 salmon have passed through the weir so far in 2015. It is near the previous record of 7,250 that passed through in 2012.

However, Fuller says the numbers are not a reason for celebration. She cautions, “The concern is that the water temperatures in the river this year have been exceptionally high, so what happens is that the fish come up, they spawn and lay their eggs in the gravel, and if the temperatures are very warm, those eggs don’t survive to produce baby salmon in the spring. So, we’re very concerned about the high water temperatures in the river, and what it is going to mean when it comes to production.”

Water temperatures in the Stanislaus River are currently about five degrees warmer than average, and are above what is considered suitable for egg survival. Fuller points out that “pulse flows” prescribed by the federal government, intended to help salmon, have actually contributed to this quandary. Earlier water releases have drawn down New Melones Reservoir past the point where water downstream can stay cool enough for the salmon to strive.

Factoring in the drought, there is less water in the reservoir than past years, and that increases the temperature.

The saving grace could be that this fall has seen cooler temperatures than last year. Fuller says “As long as this cooler weather continues, there is some hope that we are going to avoid disaster. The temperature of the water coming out of the reservoir is warmer than usual, but thankfully we have cooler weather temps on our side that are bringing the temperatures down, and hopefully that holds.”

It is something that FISHBIO will continue to monitor over the coming months to see how things unfold.

FISHBIO has helped consult several water agencies in the region on environmental issues, and its closest office is in Oakdale.

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