How a California watershed sustains salmon when the streams stop flowing

By on September 4, 2014
Juvenille salmon or steelhead netted from a Russian River tributary (Credit: Cleo Woelfle-Erskine)

During the second half the of the 20th century, the Russian River’s annual run of coho salmon plummeted from more than 10,000 fish to fewer than 10. Recovery efforts in the northern California watershed have boosted recent runs to more than 100 spawners, but many offspring they produce spend the summer locked up in stagnant, disconnected pools that form when the creeks dry up seasonally.

That’s often a death sentence. Cleo Woelfle-Erskine, a doctoral candidate with the Energy and Resources Group at University of California, Berkley, is studying so-called “intermittent” creeks in a watershed adjacent to the Russian River. He and his research group are tracking water quality and counting young coho and chinook salmon and steelhead trout in these isolated pools, and they’ve seen groups of fish wiped out by degraded water quality.

“We have found some pools where there were fish in July and there were no fish in October,” Woelfle-Erskine said. “We’re pretty sure that dissolved oxygen was the cause.”

But that isn’t always the case. They’ve also found sanctuary pools dense with young coho and steelhead throughout the dry season that appear to get a continuous dose of oxygenated water from groundwater seeps and springs along the bed or bank.

Though they’re working in a small sub-watershed, their research on what allows one pool to sustain fish while another suffocates them could be useful throughout watersheds in Northern California, which is a major hub of salmon recovery with plenty of intermittent streams.

Netting fish in one of the study pools (Credit: Cleo Woelfle-Erskine)

Netting fish in one of the study pools (Credit: Cleo Woelfle-Erskine)

Interest in the results could expand beyond northern California if climate change dries up streams farther north.

“Streams in Oregon and Washington, where most of the salmon research has been done, typically flow year-round,” Woelfle-Erskine said. “As the dry season becomes more intense and rainfall more erratic, we’d expect to see this pattern propagating northward.”

Their work so far has shown that sometimes a pool doesn’t sustain over-summering salmon even though it appears hold cool water and enough cover to protect young fish from predators like raccoons or wading birds. Woelfle-Erskine said that seems to be a result of crashes in oxygen levels.

“We found that in these intermittent pools that they could go down to essentially no dissolved oxygen fairly early in the season,” he said.

A panoramic view of Fey Creek. Click to enlarge (Credit: Cleo Woelfle-Erskine)

A panoramic view of Fay Creek. Click to enlarge (Credit: Cleo Woelfle-Erskine)

Now they’re looking into how biological and physical processes in the pools combine to affect oxygen levels. That includes pool inputs from both groundwater seeps and the water that continues to flow beneath the gravel stream bed but doesn’t see the surface.

They’re working in two tributaries of Salmon Creek, which flows into the Pacific north of Bodega Bay. Fay Creek dries up into pools early in the summer. Tannery Creek, on the other hand, tends to flow year-round.

“It’s actually about to dry up now, but that’s a different story,” he said.

Top image: Juvenile salmon or steelhead netted from a Northern California stream (Credit: Cleo Woelfle-Erskine)

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