While farms and cities struggle with low water supplies, California wildlife managers are struggling to protect the fish facing the same problem. State officials are trying to avoid some of the worst impacts on endangered salmon, but helping some fish could actually harm others.
“I think everyone who works on salmon is concerned right now, looking at the drought unfolding,” said Mara Rea of the National Marine Fisheries Service.
Endangered winter-run Chinook salmon, a species that has struggled over the last decade, will likely be harmed by low water in the Sacramento River, even though water officials are trying to keep rivers flowing through these extremely dry conditions.
The adult salmon migrate from the ocean between November and May and swim up the Sacramento River, where they lay their eggs during the summer. The eggs need plenty of cold water to stay alive, so reservoirs are required to provide consistent water releases until the fall.
With reservoir levels critically low, the state ordered that some water that would normally flow downstream in February be reserved in reservoirs, so it can be released later this year.
“It’s probably a good idea to hold back some water so that we can try to maintain conditions for this year’s cohort of migrating adult salmon that will spawn later this summer and fall,” says Jon Rosenfield, a biologist with the Bay Institute.
But the decision could harm the very species it’s meant to protect. Young winter-run Chinook are migrating out of the Sacramento River this time of year, including some bred in fish hatcheries.
Young Endangered Salmon at Risk
As they leave the Sacramento River, the young fish head into a maze of islands and channels in the Sacramento-San Joaquin Delta, on their way to San Francisco Bay.
The juveniles face a gauntlet of predators, so water officials aim to minimize the amount of time they spend in the Delta by blocking off a water channel that leads over into the Central Delta, farther away from San Francisco Bay. That channel is usually closed off with large “cross-channel gates.”
But this month, officials ordered those gates to stay open. With river levels so low, water in the Delta is becoming saltier (see our post yesterday for more). Keeping the gates open allows more freshwater to flow into the Delta. That puts the young winter-run salmon at risk, potentially setting back the species’ recovery.
“It is about making really hard decisions on a real-time basis where we may have to accept some impact now to avoid much greater impact later,” said Chuck Bonham of the California Department of Fish and Wildlife.
Wildlife officials are monitoring the fish populations daily, hoping to limit the impact. On Monday, the gates were closed temporarily, as the weekend’s rains carried young salmon closer to the area.
Maria Rea says the conditions this year are particularly disappointing, because after years of decline, “we had a fairly healthy cohort of juveniles from last year.”
Chinook salmon live about three years in the ocean before returning to where they were born to spawn. That means each year, a different group of adults or “cohort” comes back (just as a different senior class graduates from high school each year).
“Any one cohort that suffers a loss can increase the chance of extinction,” Rea said.
Salmon Fishery Impact
Low river flows this month could also do damage to fall-run Chinook, the salmon species the California fishing industry depends on. Salmon runs are named for the season when the adults begin their migration back to freshwater.
Fall-run salmon recently laid their eggs in the riverbed, and as the water level drops, the egg clusters are exposed to the air.
“If dry conditions persist into the spring, all of our runs of Chinook salmon will be impacted,” says Rosenfield. “I would not want to be a commercial fisherman, sport fishing guide, or tackle shop owner two-and-a-half years from now when this year’s migrants return from the ocean.”
Fish released from hatcheries help boost the population of fall-run salmon. Fishing groups are asking that the young hatchery fish be trucked down below the Delta and released there, to increase the likelihood they’ll survive.
“Doing this could save dwindling numbers of protected fish while also providing plenty of hatchery-bred salmon for the tens of thousands of workers and their families that depend on salmon to make a living,” said John McManus of the Golden Gate Salmon Association.