Winter-run Chinook, which are known only from the Sacramento Valley, have a unique life history strategy that differs from all other Chinook salmon. Their life histories were shaped in response to access to year-round, spring-fed, cold-water stream reaches, a rare hydrologic feature among salmon bearing streams in the headwaters of the Sacramento River watershed. Streams fed by rainfall, snowmelt, and cold water springs encircled the valley, fostering a diversity and abundance of Chinook salmon.
The endangered winter-run are particularly important among California’s salmon runs because they exhibit a life-history strategy found nowhere else on the West Coast. These Chinook salmon are unique in that they spawn during the summer months when air temperatures usually approach their warmest. Winter-run no longer have access to the cold headwaters, blocked by Keswick and Shasta dam. Ironically, the cold water releases from Keswick dam also kept the run from going extinct, allowing spawning to occur in a previously unsuitable river reach directly below. Today, only the one population of winter-run Chinook salmon spawning downstream of Keswick Dam exists. They were listed as a federally endangered species in 1997.
Had the epic 2012-2016 drought persisted one more season, we would have lost wild Sacramento River winter-run Chinook salmon. The CalTrout and UC Davis Center for Watershed Sciences report SOS II: Fish in Hot Water found the fish at a critical level of concern; they could go extinct within the next 50 years if we don’t change course. Sacramento River winter-run Chinook salmon’s continued persistence shows their remarkable resiliency, but they remain extremely vulnerable to loss or alteration of artificially maintained habitats, especially with respect to a warming climate.
The SOS II report revealed the principal threats for Sacramento River winter-run Chinook salmon:
Major dams: The biggest cause of decline of winter-run Chinook salmon was the construction of Shasta and Keswick Dams in the 1940s. These dams prevent access to all historical spawning and most juvenile nursery areas. The cold water releases from the dams also kept the run from going extinct. However, extended drought years and increased water usage renders the water unsuitable; low water levels in the reservoir become too warm for the fish. Climate change further exacerbates the issue, making it extremely difficult to maintain cold water conditions. Winter-run salmon are especially vulnerable due to their unique life history in which spawning and incubation takes place at the most thermally challenging time of the year.
Hatcheries: Hatchery-raised winter-run Chinook salmon account for nearly a third of the spawning population today. Hatchery production on wild stocks leads to competition, predation, and disease transfer from hatchery stocks to wild populations, plus loss of genetic diversity which facilitates adaptation to changing environmental conditions.
Agriculture: Agricultural diversions along the Sacramento River can trap or delay fish in canals and irrigation ditches. Federal and state pumps in the southern Delta alter flows and reduce survival of juveniles. Levees have cut off rivers from over 95% of critical floodplain habitats in the Central Valley.
Can the winter-run Chinook salmon be saved? While Chinook salmon face threats at virtually every life stage, CalTrout and partners are working toward solutions. Restoring function to once-productive but now highly altered habitats (such as floodplains, coastal lagoons, and estuaries) is imperative. Winter-run spend about 3 months on average rearing in the lower river, estuary, and Delta. These habitats have largely been lost since European settlement; over 95% of floodplain habitats have been drained and converted for other uses, such as agriculture.
We are unable to restore the Central Valley back to what it was centuries ago. But we can alter the landscape to mimic natural processes, exemplified by CalTrout’s floodplain restoration projects in the Central Valley led by Jacob Katz, CalTrout’s Senior Scientist. We’ve proven that off-season farmland can be used to replace traditional floodplains by reconnecting it to rivers and flooding it during the winter, allowing fish to grow big and strong there before their journey to sea. The juvenile fish feed off the bug buffet that’s created from the floodplain’s wetland habitat, earning the name “floodplain fatties”. This is just one example of how CalTrout is putting nature back into the mix to help our native salmon populations.
These efforts will help move the Sacramento River winter-run Chinook salmon away from the brink of extinction and back to a more abundant, resilient state.
Learn more about our plan to save our remaining native salmon from SOS II: Fish in Hot Water.
More Fish of the Month features: