CDFW Scientists Keeping an Eye on River Conditions to Protect Winter-and-Fall-Run Salmon
As California continues to feel the impacts of a heat dome that is bringing higher than normal temperatures to large portions of the state, it’s a good time to remember that fish and wildlife — especially salmon — need cold water, too. River temperature management is critical for salmon’s survival and spawning.
Earlier this year, the California Department of Fish and Wildlife (CDFW) announced that commercial ocean salmon fishing was back after being closed for three straight years. To avoid salmon impacts that could result in a return to salmon season closures, we need to ensure cold water pools are preserved, when possible, to help preserve and protect California’s salmon populations.
CDFW and federal and state partners are working to monitor river conditions to give endangered Sacramento River winter-run Chinook salmon eggs a chance for survival after their spawning was observed several weeks later than usual. The eggs of late-season spawning fish can be at risk due to decreases in river flows and warmer water temperatures.
CDFW and partners are also closely monitoring flow and temperature conditions for Sacramento River fall-run Chinook salmon spawning that will follow winter-run spawning.
In July, during peak winter-run Chinook salmon spawning, water releases from Shasta Dam were elevated to meet downstream water demand for municipal and agricultural uses, and Sacramento-San Joaquin River Delta water quality requirements, but those flows will drop significantly heading into fall. At the same time, Shasta Reservoir has below-average cold-water reserves despite high overall storage volume, making it harder to keep river temperatures cool through November and beyond when eggs are still developing.
Monitoring by CDFW, the U.S. Fish and Wildlife Service (USFWS) and the Pacific States Marine Fisheries Commission (PSMFC) will provide fisheries information and recommendations to the U.S. Bureau of Reclamation (Reclamation) to inform adjustments to Shasta Dam operations to protect these salmon that have deep cultural significance for Native American tribes and play a critical role in California’s biodiversity and commercial and recreational ocean salmon fisheries.
“CDFW and our partners are using a number of tools to help inform Reclamation operations to maximize survival of the next generation of Sacramento River winter-run Chinook salmon — one of the state’s most endangered fish — and for fall-run Chinook,” said CDFW Northern Region Manager Jason Roberts. “We are committed to providing data and technical input to Reclamation with the goal of maximizing the survival of these salmon eggs through an unfavorable situation.”
Fall-run Chinook salmon begin spawning in the Sacramento River when eggs from winter-run Chinook salmon that spawned in late July and early August may still be in their gravel egg nests, called redds. Great care must be taken to simultaneously ensure winter-run Chinook salmon redds are protected, establish suitable flow conditions prior to the onset of fall-run Chinook salmon spawning and refill Shasta Reservoir for the next season.
CDFW, USFWS and PSMFC teams are surveying 26 miles of river from Keswick Dam northwest of Redding to Balls Ferry east of Anderson. Using boat and aerial surveys, scientists map locations of salmon egg nests and measure water depths to understand which redds may face higher risks as river flows and temperatures change.
CDFW and PSMFC staff are closely monitoring 103 winter-run Chinook salmon redds that were constructed by salmon in shallow water this year when flow releases from Shasta were greatest. Crews will monitor these redds repeatedly as flow conditions change until the fry have emerged from the gravel.
Since May, field crews have also collected data from more than 6,300 winter-run Chinook salmon carcasses. Chinook salmon die after they spawn, and their bodies provide fisheries biologists with information to understand when they were born, where they’ve been and the health of the population.
Temperature loggers placed in the river help scientists estimate when eggs will finish hatching. This data informs Reclamation operations at Shasta Dam as they make flow decisions aimed at supplying enough water for redds to support successful hatching. Dam operators are also able to pull water from different reservoir depths, but cooling the river only works if enough cold water remains in the system.
CDFW scientists monitoring Sacramento River winter-run Chinook Salmon in the upper Sacramento River estimate that approximately 20 percent of the eggs spawned this year may not survive the rising temperatures, based on modeling from UC Santa Cruz and the NOAA Southwest Fisheries Science Center.
Winter-run salmon are so-named for the winter season in which they leave the ocean and enter the Sacramento River. They spawn in the summertime, building redds in the cool, clean gravel beds near Redding. Their eggs remain in the river for about three months, relying on steady, cold water flowing from Shasta Dam to survive the Central Valley heat. Fall-run Chinook salmon are traditionally the river’s largest run of Chinook salmon, and CDFW expects a robust return of fall-run Chinook salmon to the Sacramento River this fall. Critically important economically and environmentally, CDFW and partners are working to advocate for suitable river conditions this year for both winter-run and fall-run Chinook salmon.
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Media Contact
Alicia de la Garza, CDFW Communications