Low baby salmon numbers portend disaster for endangered California fish


An alarming number of baby salmon are surviving their journey down the Sacramento River to the sea, confirming fears among conservationists that the river’s low flows and high temperatures during the drought would wipe out most of the winter endangered salmon born last year.

Only 2.6% of eggs laid by overwintering chinook salmon in the Sacramento River yielded inch-long fry or baby salmon, according to a report from the state Department of Fish and Wildlife released Monday. . Used to monitor and project population health, this “egg-to-fry” survival rate is the first official estimate of baby salmon born last year and the lowest in two decades.

Conservationists say the implication for endangered winter run salmon is dire. Fish only have a three-year life cycle, so if they are wiped out a few years in a row, the population is at risk of extinction.

The report says the reason for the low survival rate was primarily due to high water temperatures in the Sacramento River, which caused countless eggs to die and hundreds of female fish to die before spawning.

“The basis is that these fish have multiple freshwater stages and they have to survive all of them,” said Jon Rosenfield, senior scientist at the nonprofit San Francisco Baykeeper, one of many critics of the policies. state and federal water management.

Last spring, biologists from the National Marine Fisheries Service predicted that these policies would lead to mass salmon egg mortality due to drought conditions.

Kaitlin Whittom pulls a dead salmon from the Sacramento River while working alongside US Fish & Wildlife biologists to investigate the amount of dead Chinook salmon in winter due to warming low-level water in the Sacramento River in Redding l ‘last summer.

Jessica Christian / The Chronicle

Named for the time of year when they head upstream to spawn after leaving the Pacific Ocean, where they spend two years as adults, winter fish are one of many historical upwellings of Sacramento River salmon that spawn during the warm months when the river is low. Chinook salmon from the fall run, the population caught by sport and commercial fishers, often face similar perils to the winter run because they spawn right after, although they are more numerous.

“The warm water that came out of Shasta Dam, flooded the Upper Sacramento Basin and killed off the majority of the winter hauls, persisted into the fall, and smothered the eggs of the fall hauled salmon,” said John McManus, president of Golden State Salmon. Association. “We probably won’t know for months what it means to fall running, but there is good evidence to show that they will suffer a very similar fate..”

Keswick Dam, located 9 miles downstream from Shasta Dam on the Sacramento River, discharges water into Chinook salmon spawning grounds.

Keswick Dam, located 9 miles downstream from Shasta Dam on the Sacramento River, discharges water into Chinook salmon spawning grounds.

Courtesy of Alexander Stephens

Critics attribute the deaths to the Federal Bureau of Reclamation’s temperature monitoring plan, which is used to determine the timing and flow of water leaving Shasta Dam and therefore the temperature of the river at stages reviews. They say the plan prioritized holders of higher water rights such as the large Sacramento Valley rice paddies, which got a relatively large percentage of their water allocation last year despite the drought.

Critics also say the state, which has the power to approve or reject the bureau’s plan, hasn’t done enough to protect the fish.

“So basically we have the state and the federal government agreeing that superior water rights are more important than avoiding species extinction,” McManus said.

In a statement, a spokesperson for the Bureau of Reclamation said the plan “was developed in close coordination with federal and state fisheries agencies and conditionally approved by the State Water Resources Control Board. It provided operations of spring, summer and fall to maximize survival in the poor conditions caused by the current drought.

The statement details other steps the bureau said it has taken to protect salmon, including an emergency installation of water coolers at the Shasta Dam hatchery, where it has also increased Chinook salmon production from winter to release it during the winter, when conditions were better. .

Monday’s report from the Department of Fish and Wildlife said another factor was at play in the low survival rate of baby salmon: thiamine deficiency.

The problem, which was observed recently in females at the Shasta Dam Hatchery, is caused by a diet high in anchovies which can kill eggs and juveniles. Federal scientists think recent unusual ocean conditions off the California coast has brought record numbers of anchovies into salmon feeding grounds, creating another threat to the species at risk.

An overwintering female chinook salmon was removed from the Sacramento River in Redding last June.  It died before spawning, like hundreds of salmon that were affected by high water temperatures during the drought.

An overwintering female chinook salmon was removed from the Sacramento River in Redding last June. It died before spawning, like hundreds of salmon that were affected by high water temperatures during the drought.

Courtesy of Rachel Johnson

Counts of salmon fry are made as the fish migrate up the river past Red Bluff, about 50 miles south of their spawning grounds below Shasta Dam. In 2021, wildlife officials counted 796,403 fry, or just 2.6% of an estimated 31 million eggs laid based on the number of female salmon they estimate can spawn before they die, according to the draft. report, which will be updated with the final figures. later this month.

The fry continue to swim in the river until they are large enough to enter the Sacramento-San Joaquin River Delta and then into the ocean. Many fry will die or be eaten on the way to the sea. The Department of Fish and Wildlife estimates that just over 100,000 will arrive in the delta.

The survival of these fish could be further threatened if the powerful state agency responsible for water allocation allows federal and state water managers to relax environmental rules regarding water quality in the delta in response to drought. This could reduce the water flow in the river, making it more difficult for fish to travel.

The State Water Resources Control Board accepted the petition from federal and state water managers at a meeting Wednesday.

Tara Duggan is a staff writer for the San Francisco Chronicle. Email: [email protected]: @taraduggan

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