California Department of Fish and Wildlife staff are on the ground monitoring drought impacts — and among the alarming findings is “the possibility of a near-complete loss” of young, winter-run Chinook salmon on the Sacramento River this fall due to a dwindling water supply and persistent dry, hot weather.
The waters of Northern California’s main river may become so hot that nearly all the eggs and juveniles of this endangered species, which migrates from the Golden Gate in winter and spawns just below Shasta Dam in the Sacramento River in spring and summer, could die, according to California wildlife officials.
To cool the waters of the Sacramento River and protect the incubating eggs and young in summer and fall, the state releases water from Shasta Lake into the river. But after two consecutive dry winters, water in California’s largest reservoir is quickly disappearing. The lake was at 46% of its historical average as of Monday, state data showed. There may not be enough water to release sufficient amounts of cold water to support fish survival.
“Modeling of monthly operations predicts high levels of mortality for Chinook salmon during egg incubation in the Sacramento River due to limited cold-water pool in Lake Shasta and downstream water deliveries,” Fish and Wildlife said in a statement. “Unanticipated depletions downstream have resulted in increased releases from numerous reservoirs in the Central Valley. The State Water Project and Central Valley Water Project are attempting to balance many beneficial uses, including municipal drinking water.
“Chinook salmon mortality during egg incubation could be higher than originally predicted. It’s an extreme set of cascading climate events pushing us into this crisis situation.”
The Sacramento River supports one of the southernmost large runs of Chinook salmon in North America. There are four different salmon runs on the river that flows for 400 miles from the Klamath Mountains through the Central Valley before reaching the Sacramento–San Joaquin River Delta and San Francisco Bay.
The winter-run salmon enter the Sacramento River system in late January to February but runs can persist into June. The adult fish spawn, or lay their eggs, in the Sacramento River upstream of Red Bluff and spawn from late April through August.
The fish are conditioned to spawn in cold waters, as the winter run historically laid their eggs in the ice-cold rivers of the High Sierra fed by snowmelt, such as the Little Sacramento, McCloud and Pit rivers.
“But they can’t get up there anymore,” said fish ecologist Andrew Rypel, an associate professor at UC Davis and co-director of the Center for Watershed Sciences. “One of the big dams that gets in their way is Shasta. There’s no fish passage around it. Dams have blocked them off from their historical spawning habitat.”
The winter run now spawn in the Sacramento River, and their environment is controlled by cold-water released from Shasta Lake.
“This is a fish that’s very vulnerable to climate change,” said Rypel. “Most of the management around the winter-run salmon is temperature management. Shasta Reservoir is a big deep lake … It all revolves around the cold water pool in Shasta. There’s a certain finite volume of cold water. If the drought goes on for too long, you run out of cold water. When you run out of cold water, a large fraction of the juveniles will die.”
A view down the spillway of the Shasta Dam into the Sacramento River in Shasta Lake, Calif., on Wed. April. 4, 2018. The Trump administration and Republicans want to raise the height of the Shasta Dam. San Francisco Chronicle/Hearst N/San Francisco Chronicle via Gett
Sacramento River winter-run Chinook salmon have suffered serious declines in population size for decades and are federally listed as endangered. The fish population saw a long, slow decline after Shasta Dam was built between 1938 and 1945, and then a rapid decline during certain periods like the late 1970s, Rypel said.
Data going back to 1967 shows that the population of spawning adults hit a high of 117,800 in 1969 and went all the way down to only 200 fish in 1994, according to a 1998 paper published in the North American Journal of Fisheries Management.
Pacific States Marine Fisheries Commission fisheries technician Kaitlin Whittom pulls a dead salmon from the Sacramento River while working alongside U.S. Fish & Wildlife biologists to spear and survey the amount of dead winter-run Chinook salmon due to low-level, warming water in the Sacramento River in Redding, Calif. Wednesday, July 7, 2021. San Francisco Chronicle/Hearst N/San Francisco Chronicle via Gett
The winter-run salmon saw significant die offs in both 2014 and 2015 during the last major drought.
“It has happened before, but the problem is if we start losing multiple year classes in a row,” said Rypel. “This is an animal that spends one year in fresh water and two years in the ocean. So, every year class matters, and if you lose one you inch ever closer to the possibility of an extinction event. We’re not far off from extinction for the winter run.”
While there’s talk of long-term solutions to help save the winter run, such as trapping the fish and hauling them to colder reaches and tributaries, this year it all comes down to the cold water pool in Shasta Lake.
“If they can conserve that cool water pool in Shasta Reservoir long enough to meet the demand, we can save them, but most experts think that will probably not happen,” Rypel said. “We’re very worried about a large mortality event this year.”