Thousands of endangered coho salmon moved from Lake Sonoma hatchery amid rising water temperatures

As Lake Sonoma plummeted to record low levels this summer, the water has warmed enough to threaten the coho salmon raised in the state hatchery at the base of its 319-foot dam northwest of Healdsburg.

With signs of disease appearing in the juvenile coho, an endangered species in the Russian River, federal biologists took an unprecedented step in the local watershed: trucking about 2,000 fish nearly 50 miles south to a student-operated hatchery at Casa Grande High School in Petaluma.

“They’re welcome here,” Dan Hubacker, a science teacher and director of the school’s 38-year-old United Anglers program, said after the final load of 92 fish arrived Tuesday afternoon. “We’re here to help.”

The remarkable strategy comes during a severe statewide drought and escalating climate change that has crimped water supplies to North Bay farms and cities and caused rural wells to run dry.

Further north, Chinook and coho salmon have suffered a massive kill on the Klamath River due to record low precipitation, and state officials have trucked millions of hatchery-raised juvenile Chinook salmon from the Sacramento River to San Pablo Bay and San Francisco Bay in hopes of averting a complete die-off.

Ben White, the supervisory fisheries biologist at Lake Sonoma’s Warm Springs Hatchery, said water temperatures edged into the low-60s last week about 10 degrees above the ideal level for coho salmon, which need cold, clear water to thrive.

Fish afflicted by pathogens had to be treated with chemicals and none perished, but the expansive hatchery — with 20-foot wide round green tanks clustered under a roof the size of an aircraft hangar — lacks a chiller to offset the heat, he said.

The water has since cooled a bit, but White determined to transfer half the juvenile coho intended for breeding to Casa Grande.

“We wanted to be proactive,” he said. “You don’t want to wait too long.”

California coho are “on the brink of extinction,” he noted, while coho in Oregon and farther north remain plentiful enough to continue closely regulated sport fishing.

Hatchery-bred fish are released into about 20 tributaries in the lower Russian River watershed so their offspring will return to those streams instead of the hatchery on Dry Creek.

The final batch of fish dropped off at Casa Grande were six- to eight-inch juveniles, one and a half years old, that will return from the ocean to spawn in the winter of 2022-23, he said.

Each female coho releases more than 2,000 eggs that will result in up to 1,000 offspring.

Shannon Bockmon, a fisheries biologist, donned waders to net the juveniles in a tank with knee-deep water.

“Those are the smartest ones,” White called out as the last five coho repeatedly evaded capture.

At Casa Grande’s more modest hatchery, Hubacker said, “I thought I’d never see the day coho are in this building.”

The United Anglers’ mission has focused on restoring steelhead in the Petaluma watershed, starting with nearby Adobe Creek.

But when the call for help came from the Warm Springs facility to it was “all hands on deck,” said Hubacker, a Casa graduate in 2000 who was a United Anglers member.

The campus hatchery draws water from a 500-foot well and has chillers to assure the proper temperature.

Hudson Naber, a senior in his second year with United Anglers, said it was “a privilege” to help the coho.

Dillon Arellanes, a classmate, said each truckload of fish was a thrill for him, “like a kid in a candy store.”

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.