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Scientists say Steadier Flows may be Key
to Improving Fish Survival

by Bill Rudolph
NW Fishletter, February 21, 2003

Two representatives from a panel of independent scientists told the Power Planning Council this week that hourly fluctuations in hydro operations may impact survival of juvenile salmon in the Snake River more than changes in flow itself. The scientists' hypothesis was contained in a report released earlier this month that was commissioned by the council last November to help evaluate elements of their mainstem amendment process.

The Independent Scientific Advisory Board was charged with answering a spate of questions about the value of flow augmentation, but they seemed more interested in advancing their own theory about fluctuating flows and fish survival. They did say that the council's mainstem amendments were unlikely to have major effects on yearling chinook when flow were above 100 kcfs, but fall chinook could suffer when flows were below 50 kcfs in July and August.

Montana member John Hines said the ISAB report backs up what his state has been saying for years, "that yo-yoing reservoir fluctuations is not good." Pointing out that most fish were barged from the Snake, he asked the scientists about the benefits of adding more flow in low flow years.

ISAB member Charles Coutant said there didn't seem to be enough water available to add in low flow years to make a difference, "so stable flows or barging is a good solution in an 'ambulance' sense." Citing work by University of Washington professor Jim Anderson, he said that that by simply adding more water to lower Snake flows from the already warm Brownlee reservoir could compound temperature problems for summer migrants.

Most spring and summer migrants are barged out of the Snake to below the last dam on the Columbia River. According to data posted on the University of Washington's DART [Data Access in Real Time] website, about 80 percent, or 1.1 million juvenile fall chinook were barged last year out of the 1.39 million estimated to have migrated from the lower Snake.

In 2001, the second-worst water year on record, over 99 percent of the more than 600,000-plus fall chinook in the lower Snake were barged or trucked downstream, leaving less than 4,000 in-river migrating juveniles to cope with the extremely low flows.

"But flow might be important for a lot of other reasons than just survival in the Snake," Coutant cautioned, though he did not enumerate. NMFS scientists have suggested that flow augmentation may play a role in estuary and near-ocean survival of juvenile fish, as well as timing their entry into the ocean.

Sloshing Bathtub Theory Explained
The council's preferred alternative calls for changing operations mandated in the hydro BiOp to reduce flow augmentation in the spring, but add more water in late summer for fall chinook migrants in the Snake, with the overall effect of draining federal reservoirs more slowly and evenly in Idaho and Montana to benefit of resident fish species in those states.

The new ISAB report does say the "prevailing rationale for flow augmentation is not supported by the present evidence," and they suggested that a management alternative that stabilized within-day flows when overall flows were low "may be more important than simply adding water," although they offered no direct survival data to back up their hypothesis.

"Maybe we stepped outside our bounds a bit," said Dr. Charles Coutant, who cited some recent radio-tag studies that showed fish wandering back up reservoirs during periods of low flows at dams.

His enthusiasm was shared by fellow scientist, retired University of Washington professor Richard Whitney, who told council members "this is the first time you'll ever see anything like this, maybe the last."

Yearling Chinook Salmon Survival vs. Reservoir Flow Rate (Source: National Oceanic and Atmospheric Administration) The two exhibited NMFS graphs that showed higher fish survivals during years of higher flows, and much lower survivals in 2001 when flows were extremely low, which gave the plot the look of a broken stick. They said the complex pattern suggests "a different rationale than just flow for the smolt survival and behavior data."

Radio telemetry studies from 1995-2001 show that fish behavior changed at low flows, they said. Migration rates of spring chinook declined to near zero in Lower Granite Pool around 100 kcfs, and smolts wandered in the dam forebay and swam upstream many kilometers. Fall chinook experienced the same sort of behavior in Little Goose Pool. The ISAB said reduced migration rates at a certain "threshold" agree with the NMFS data and "broken stick" graph.

Coutant and Whitney spent the next half-hour explaining their idea that daily flow fluctuations could have adverse effects on juvenile migrating salmon. They said when overall flows were below 100 kcfs, the frequency of flow fluctuations increased, mostly at night, averaging five to six hours. Such fluctuations induce complex reservoir hydraulics, which could create large waves in lower Snake reservoirs much like water sloshing in a bathtub. When a wave reversed, it could change the current in the river and cause smolts to become disoriented and slow their migration.

"Actually, you're seeing science at work here," said Coutant. "Because we began to realize that looking at the survival data something was happening about 100,000 cfs that implied one different mechanism at one side of the break point and another different mechanism at the high side."

"If you were a smolt trying to migrate through a reservoir," Coutant said, "where the flow was actually reversing on you every two hours, it could be pretty confusing." He said the idea of pulsing flows to move fish "is pretty much discredited" and contributed to fish declines rather than improvements in survival. He said it would be difficult to find enough water to flush the fish successfully. "The time you've got the problem is when you don't have the water."

When asked if these reservoir waves could actually help the fish when they were traveling in the same downriver direction, Coutant said "it might," but there wasn't enough data to make that fine a distinction.

Idaho member Jim Kempton said there was no reason not to look at the ISAB hypothesis and investigate the possibility that power peaking operations in the Snake may be hampering fish migration and survival.

Washington council member Tom Karier said the report focused debate on low water years, but showed there is still "great confusion how flows make a difference."

Bill Rudolph
Scientists say Steadier Flows may be Key to Improving Fish Survival
NW Fishletter, February 21, 2003

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