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NW Fishletter #384, August 1, 2018

[5] Dam Operations Adjusted To Help Struggling Snake River Sockeye

With an eye on returning Snake River sockeye, fish managers and dam operators agreed July 18 to adjust operations at two dams, hoping to aid the fish in their long journey back to Redfish Lake.

The Technical Management Team (TMT) reached consensus to keep more of the cold North Fork Clearwater River water flowing through Dworshak Dam, to continue cooling the lower Snake River, where adult sockeye are working their way upstream.

And--although it's a long shot--team members also agreed to shut off the surface weir at Lower Monumental Dam on July 19 and 20, in case some sockeye are hanging back in the pool below. If they are, the changed hydraulics may convince them to continue to battle their way upstream.

Sockeye--which dropped to dangerously low numbers in the 1980s and 1990s--have been making a comeback in Idaho, thanks to the Idaho Department of Fish and Game's captive broodstock program, which developed into a hatchery program. Adult returns crossing Lower Granite Dam that once measured in the dozens in good years have since increased to several hundred returning adults since 2008, with numbers as high as 2,786 in 2014.

But recovery efforts have suffered setbacks in recent years. After the agency started using a converted trout hatchery near Springfield in 2013 to raise sockeye, biologists discovered smolt survival had plummeted compared to previous releases. And in 2015, 99 percent of the returning adults that crossed Bonneville Dam died before reaching their spawning grounds due to high water temperatures in both the Snake and Columbia rivers.

Russ Kiefer, an IDFG fish biologist and a member of the TMT, NW Fishletter that 2015 was a setback in the agency's long-term goal of getting more of the sockeye population to complete their life cycle in the wild. But because of the captive broodstock program, it didn't significantly affect their ability to continue the hatchery program, which has been vital to retaining a genetically diverse population, and pulling the Redfish Lake sockeye back from the brink of extinction.

He said the larger concern has been death rates of Springfield Hatchery smolts--more than 70 percent were dying by the time they reached Lower Granite Dam, and more than 90 percent by Bonneville Dam. But last month, IDFG confirmed its theory that sockeye smolts could not handle the shock of the change from hard water conditions in the hatchery to the soft water chemistry in Redfish Lake Creek, where they were released. "Sockeye are notoriously sensitive to stress, and apparently messing up their water chemistry during smolting was not a good thing for them," Kiefer said.

This year, IDFG tested the theory by releasing smolts in four different groups: a small group of smolts that were raised at the Springfield Hatchery and released into the stream as in previous years, and three more that were allowed to acclimate in different ways before being released. According to the agency's report to the Northwest Power and Conservation Council, the most promising option--which produced a 75 percent survival rate at Lower Granite Dam--may be to release the smolts into Redfish Lake Creek after acclimating them at the Sawtooth Hatchery, where the water is harder than in the creek, but softer than at the hatchery. Regardless of which option they use next year, "It was clear water chemistry was the issue," Kiefer said.

The problem with smolts has taken its toll on the recovery program. Last year, according to the Fish Passage Center, only 228 adults made it back to Lower Granite Dam; so far this year, 178 sockeye have done the same. The run generally peaks in late June and early July, and is over by August. With depressed returns expected again this year, IDFG and other fish managers are looking to help those that are still returning to the Snake River make their way back to Redfish Lake. At more than 900 miles and an elevation gain of 6,500 feet, it's the longest journey of any of Idaho's salmon runs.

Beginning July 9, the U.S. Army Corps of Engineers increased the flow at Dworshak Dam to 12.9 kcfs, to add more of the North Fork Clearwater's 44-degree water into the rapidly warming Snake River.

On July 18, Steve Hall, the Corps' Walla Walla District reservoir manager, told TMT members that except for a few hours on July 17, the temperature in Lower Granite Dam's tailwater has remained below 68 degrees, which is when sockeye begin to experience stress.

He said that with cooling outside temperatures and a conservative estimate for how much warm water would be coming out of Hells Canyon Dam, modeling showed they could reduce those cold water flows through Dworshak Dam to 9 kcfs and still keep tailwater temperatures at about 67 degrees. Releasing less water means they can conserve the cooler water for later in the summer, he noted.

But after discussion, the team opted for keeping flows at Dworshak higher, at 10.5 kcfs. Kiefer said that while temperatures at Lower Granite Dam are the focus, adding more cool water will help cool temperatures throughout the lower Snake River. "I just want to be cautious and protective, since it's a critical time for the sockeye run," he told the team, and others agreed.

There was far less certainty in the team's second action to protect this year's adult sockeye--adjusting the flows at Lower Monumental Dam for 10 hours each day on July 19 and 20. While total flows will be maintained at 17 kcfs, dam operators will take the removable surface weir out of service and use a uniform spill pattern, just in case the current spill pattern was impacting returning sockeye's willingness to use fish ladders.

The suggestion arose because counts recorded by the Fish Passage Center through July 17 showed that 600 sockeye had crossed Ice Harbor Dam, but only 250 were counted at Lower Monumental, the next dam upstream. The team discussed the issue at length before agreeing to make the changes, although many members voted simply not to object.

In an interview, Kiefer said he thinks it's unlikely that a difference in spillway flows at Lower Monumental is causing a problem with conversion rates--how many of the sockeye that made it past Ice Harbor have continued past Lower Monumental.

However, because of the water chemistry issues and the loss of so many smolts, they don't have the PIT tag data to help explain why fish counters saw so many sockeye at Ice Harbor and not at Lower Monumental. In addition, counters at Ice Harbor don't check to see if fins on sockeye have been clipped, so it's impossible to know if they're mostly Snake River sockeye--which are mostly clipped, or Columbia River sockeye--which are mostly not clipped.

Kiefer said he and an IDFG sockeye researcher both calculated rough estimates of Snake River sockeye at Bonneville Dam at between 265 and 282 fish. "It just gives us an idea--a really ballpark estimate," he said. But it's another indication that the 350 sockeye lost somewhere between Ice Harbor and Lower Monumental dams may not be Snake River fish.

With a total run of almost 200,000 sockeye at Bonneville Dam so far this year, the vast majority are headed up the Columbia River. "We're thinking that likely what is going on is that a very small percentage of the much larger returns to the Mid-C are poking into the Snake a little and going over Ice Harbor, realizing they made a wrong turn and heading back down," Kiefer said.

So far, Kiefer said, all other indications--including the few Snake River sockeye that were PIT tagged--point toward a likelihood that the 350 extra fish are not Snake River sockeye. He said the lower numbers counted at other dams are also on track with preseason estimates, he said.

"The only warning light blinking is the count differential between Ice and LoMo," he said. But, he added, he supported changing the hydraulics in case he's wrong. "We would sure not like to miss them if we're wrong in our calculations, and they are Snake River fish," he said.

The Technical Management Team planned to revisit the decision after looking at sockeye counts at the two dams on July 20. -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
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