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NW Fishletter #394 June 3, 2019

[3] Chinook Holding Back At Little Goose As Managers 'Adapt' Flexible Spill Deal

When switching to five, and then six consecutive hours of reduced spill each morning didn't work, fish managers agreed to try reducing spill at Little Goose Dam for eight hours in a row, hoping that will be enough time to convince adult Chinook to keep moving upstream.

At its May 29 meeting, the Columbia Basin Technical Management Team (TMT) approved the new operation, which reduces spill to the dam's performance standard levels from 4 a.m. to noon each day. Performance standard is the spill level intended for juvenile fish passage under the 2008 biological opinion, and at Little Goose is 30 percent of the flow.

A sudden drop in the number of adult Chinook salmon migrating upstream over Little Goose on May 18 initially prompted the change in operations to address the issue.

This year's higher spill levels--to 120 percent total dissolved gas (TDG) for 16 hours a day--was designed to give juvenile fish a faster and safer journey to the ocean. But higher flows and TDG can also cause adults to hold back in their journey upstream. That's apparently what happened on May 18 and 19, when 183 and 185 adults respectively migrated past Little Goose Dam, according to the Fish Passage Center. Previously, between 800 and 1,100 Chinook had been passing the dam daily.

The new plan is not technically part of this year's flexible spill agreement. However, Tony Norris, a TMT member and operations research analyst for the Bonneville Power Administration (BPA), noted that the agreement acknowledges that Little Goose has an adult passage problem. "This is really adaptively managing within the spill agreement," he told NW Fishletter.

Specifically, the agreement provides for adaptive management "to help address any unintended consequences that may arise in-season," such as the delayed migration of an estimated 3,500-4,000 adult Chinook due to the agreement, which increased spill to 120 percent total dissolved gas for 16 hours a day at the four Snake River dams starting April 3.

The flexible spill plan includes special provisions for adult passage at Little Goose. At all eight of the federal dams subject to the agreement, the U.S. Army Corps of Engineers can reduce spill and generate more power for a total of eight hours each day, and has more freedom to choose those hours at seven of the projects. "Only Little Goose would be set to at least 4 hours in the a.m. (beginning near dawn and not to exceed 5 hours in the a.m.) and no more than 4 hours in the p.m. (generally near dusk) to help with adult passage issues," the spill agreement states.

Russ Kiefer, TMT member who represents the Idaho Department of Fish and Game, said that's because more adults tend to migrate in the morning, starting at dawn, and Little Goose is known for its adult passage problem.

"We have a pretty good idea of what the problem is," he told NW Fishletter. "How to solve it is the challenge."

Kiefer explained that the increased spill levels cause an eddy at the entrance to the primary fish ladder. Flows in the eddy travel in the opposite direction from an eddy in a natural river, confusing the fish, he said. A surface weir at the dam only adds to the eddy problem, he said.

"The question is, is it better to reduce spill to 30 percent and use the surface weir, or shut off the weir and spill at a higher level?" he Kiefer said. "That gets to be a debate, and it's one where, without much data, we get into our belief systems."

Kiefer said Idaho doesn't support shutting off the surface weir just to maintain spill levels. "We need to come up with a plan that maintains spillway passage and doesn't delay adult," he said.

He also noted that the Corps can adjust the height of the weir at lower flows to reduce the eddy problem, but that won't work in the spring, when flows are higher.

Kiefer said fish mangers are continuing to discuss other options in case the eight consecutive morning hours of reduced spill doesn't work, or if the upcoming increase in runoff prompts a new round of adult delays. One option, he said, would be to reduce the flows to 30 percent and "pond" water in the reservoir above Little Goose in the morning, and spill that water later in the day. Fish managers have also discussed reducing spill to performance standards for 12 hours instead of eight hours, he said.

He said that as a fish manager in Idaho, he's more concerned about the delay than others. "How much effect that delay has is something else we've had some disagreements on," he said.

Kiefer said his own research has led him to believe that different populations of Chinook migrate at different times, and those adults spawning in the farthest places are the first to migrate. That timing provides a survival advantage. "Delaying them outside of their evolutionary timeframe is not likely a good thing for their ability to successfully put eggs in the right gravel at the right time," Kiefer said.

Bill Tweit, Columbia River fishery coordinator for the Washington Department of Fish and Wildlife, has a different view. He said spring Chinook--unlike some other salmon species--are essentially designed for a long, slow migration. "When you think about it, if you're entering the river in the peak of runoff, it's probably smart to give yourself plenty of time to work you way up," he said. They're not like sockeye, which hit the river all at once and move up through the system as quickly as possible, before the river gets too warm.

Tweit added, "I don't want to say delay is OK, or that we don't worry about it. But we view it differently for different species. And when you're balancing upriver and downriver survival, that's part of the perspective."

As of June 2, 18,679 adult Chinook had passed Lower Monumental Dam, and only 14,163 of them had continued on to pass Little Goose, according to Fish Passage Center numbers. But the difference of some 4,500 fish isn't all due to delayed migration. Some of these adults migrated up the Tucannon River instead of continuing up the Snake, and some are still making their way between Lower Monumental and Little Goose.

Others were caught by anglers. On Memorial Day, the Washington Department of Fish and Wildlife reopened fishing for hatchery Chinook in the pool below Little Goose. The state determined there was sufficient harvest allocation remaining. That day, only 21 adult Chinook made it past Little Goose Dam, compared with 119 on May 26, and 299 on May 28.

At least one fishing guide knows how to take advantage of the delay in adult passage. Toby Wyatt boasts on his website that his fishing guides target these adult Chinook by anchoring inside the back eddy and positioning their boats above the small hole, enabling clients to catch their limit by mid-morning. -K.C. Mehaffey

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NW Fishletter is produced by NewsData LLC.
Publisher/Editor-in-Chief: Mark Ohrenschall, Editor: K.C. Mehaffey
Phone: (206) 285-4848 Fax: (206) 281-8035

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