Endangered coho salmon beaten by 3rd year of drought. Here’s why it matters

Nossaman Pierce was involved in collecting young fish for the initial broodstock and remains cautiously optimistic. But she said she wants area residents to care about the problem and the solution.

“We almost lost our native fish,” she said recently at the edge of Green Valley Creek as a crew tended to a smolt trap. “Literally, this population would have disappeared a few years after the launch of this program.”

Late last summer, members of the monitoring program mapped 36 streams in the lower Russian River watershed. They found that tanks that had hosted about half of all juvenile coho and rainbow trout in previous surveys remained wet. Another 40% were completely dry; about 10% were intermittent.

It is not known how many fish perished, said Nossaman Pierce.

Come winter, heavy rains early in the season gave adult salmon and rainbow trout access to small tributaries they hadn’t been able to reach in years, prompting cheers in the wildlife community.

But the months that followed were so dry that the streams quickly receded, leaving many gravel nests they had created at the edge of shallow, high, dry rapids with the eggs.

Observations this spring were disheartening: 28% of spawning grounds were dry or partially dry, said Nossaman Pierce.

Meanwhile, several hundred smolts and other young fish washed up in a tributary of Green Valley Creek, said David Hines, coho salmon recovery coordinator, senior environmental scientist with the California Department of Fish and Wildlife.

Usually the problem is the summer disconnect where a stream should join the river but dries up, Hines said. Any rescue, in which an electric shock is applied to the water and the fish quickly caught, is required in late May or early June, he said.

With each fish having only three years of life to rise in fresh water, swim to the ocean, and be mature enough to return upstream to spawn, a few years of drought could spell disaster for the coho population. , most of which are hatchery born.

“That’s what we live with,” said Nossaman Pierce. “A bad year has an impact on three age classes of fish. And if they keep taking those hits every year, you won’t be able to live without them, even with the spawner program. The conditions just can’t stand it.

Lose ground

Since the first release of hatchery offspring into the watershed, the number of adults returning to spawn has risen from a handful in 2004 to around 763 in the 2017-18 season, according to the river monitoring program. Russian.

In 2020-21, that number dropped to 214, with adults seen in just eight of the 33 coho streams surveyed, the program reported. A similar, although less extreme, reduction in adult rainbow trout was also observed.

Federal fisheries managers have set a target of 10,100 adult coho salmon returning each winter to the Russian River basin as a benchmark for recovery, which leaves a long way to go.

And they appear to be facing another harsh summer ahead, although mid-April rains provided an unexpected buffer when conditions appeared to offer little hope.

“It was a close call,” said Gregg Horton, principal environmental scientist at Sonoma Water. “I mean, if that rain hadn’t happened, it could have been pretty much a complete loss, or almost a complete loss, of a class of coho smolts.”

Instead, strong flows filled creeks and reconnected tributaries with the main arm of the Russian River just in time for peak coho smolt migration in early May, Horton said.

That may be enough to see yearlings through their emigration, although latecomers in late June may struggle, he said.

It’s a different story for the young hatchlings who must spend the summer feeding and rising in streams with little moisture accumulated in the surrounding landscape to replenish themselves after three extremely dry months at the start of the year.

This means summer ‘young of the year’ – fish that emerged from gravel nests around March – will likely face the same dire conditions as last year and in past droughts.

Field teams will be on hand to rescue those they can. But, Horton said, “it’s not an ideal management strategy.”

“These watersheds have been altered by years of development and various land uses, and they have lost some of their hydrological resilience,” he said. “So the habitat is more fragile, basically, and we still have a lot of work to do with the ecosystem to build resilience to climate change. The fish rescue is just a short-term effort to try to save the genetic material that we currently have in the landscape.

You can reach editor Mary Callahan at 707-521-5249 or [email protected] On Twitter @MaryCallahanB.

Comments are closed.