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River Managers Ponder Passage Gaps For Snake River Sockeye At Lower Snake Dams
Posted on Friday, July 27, 2018 (PST)

For the second straight week, fish managers want to temporarily change spill operations at a Snake River dam hoping to increase the percentage of listed sockeye salmon that move upstream.


At its meeting last week, the interagency Technical Management Team changed the spill configuration for two consecutive days at Lower Monumental Dam on the lower Snake River as a test that fish managers hoped would stimulate passage of the sockeye at the dam.


Some 600 sockeye had passed Ice Harbor Dam, the downstream of the four lower Snake River dams, but just 250 had made it past Lower Monumental Dam, which had the lowest conversion rate of the four dams. With no improved change observed in the daily passage of sockeye over the 12-hour, two-day test (Thursday and Friday, July 19 and 20, TMT returned the removable spillway weir to 24-hour operations Friday afternoon.


(See CBB, July 20, 2018, “River Managers Test Lower Monumental Spill Change To Stimulate Sockeye Passage,”


At this week’s TMT meeting, Wednesday, July 25, fish managers were again worried, but this time about the 100 fish that were missing downstream of Little Goose Dam, the next dam upstream from Lower Monumental. An eddy that may be caused by the combination of low river flow and the RSW could be slowing passage at the dam. Flow has been as low as about 30,000 cubic feet per second and with a 30 percent of the river summer spill target, about 11 kcfs is being spilled and 6.6 kcfs of that is through the RSW.


The fish managers asked the U.S. Army Corps of Engineers to remove the Little Goose RSW for 12 hours two days in a row (4 am to 2 pm Thursday and Friday, July 26 and 27) and transfer spill to deep spillgates to provide more uniform spill, according to Russ Kiefer of the Idaho Department of Fish and Game.


They also asked the Corps to videotape the eddy before and after the change for future reference about how low flows combined with RSW usage impact both the eddy and upstream passage.


As of July 24, passage of sockeye at Little Goose Dam stood at 238 of the fish, but passage at the downstream Lower Monumental Dam was 337 fish, nearly a 100 fish difference and a conversion rate of about 71 percent.


Fish managers are still uncertain why there is a gap in passage between Ice Harbor and Lower Monumental dams, as well as Lower Monumental and Little Goose dams. As they conjectured this week and last week, it could be stray mid-Columbia River fish coming in but not traveling far upstream, it could be attributed to counting errors, or in the case of Little Goose, it could be the eddy caused by low flows and the RSW.


According to Kiefer, fish counters at Lower Monumental made a special effort to count clipped and unclipped sockeye this week. The clipped sockeye belong in the Snake River and the unclipped are Mid-C fish, he said. Of 17 fish, 13 were clipped and four were unclipped.


“There’s a lot of uncertainty about the benefits of the RSW for juveniles at this time of year and there’s a lot of uncertainty about why we have this count differential,” Kiefer said, as he asked the Corps to set aside the surface weir (RSW) and work for a more consistent spill pattern. “But the sockeye are endangered and all of these sockeye are important.”


Passage of sockeye at Bonneville Dam was 192,617 fish July 24. That’s about 60 percent of the 10-year average of 320,185. Last year on this date 86,984 fish had passed the dam. Some 186,520 had already passed Priest Rapids Dam in the mid-Columbia River, about 71 percent of the 10-year average of 263,262. Last year on this date, the count at Priest Rapids was 65,543.


The U.S. v Oregon Technical Advisory Committee, which forecasts fish runs, doubled its forecast of sockeye into the Columbia River at its June 25 meeting. The preseason forecast was 99,000 sockeye. TAC increased its estimate to 209,000 fish.


Also on July 24, some 624 sockeye had passed Ice Harbor Dam, 337 had passed Lower Monumental (a 54 percent conversion rate), 238 had passed Little Goose and 223 had passed Lower Granite (a 94 percent conversion rate).


Conversion rates are the percentage of fish that pass one dam and then pass the next dam upstream. Snake River sockeye salmon are listed as endangered under the federal Endangered Species Act.


Passage at Ice Harbor (624) is 68 percent of the 10-year average of 922 and much higher than last year’s passage by July 24 of 382. Passage at Lower Monumental (337) is 31 percent of the 10-year average of 1,099, but about the same as last year’s passage 343. Passage at Little Goose (238) is about 25 percent of the 10-year average of 971 and less than last year’s 282. Passage at Lower Granite (223) is about 23 percent of the 10-year average of 954 and about the same as last year’s 224.


Also see:


--CBB, July 13, 2018, “With Temps Rising, Corps Cools Snake River With Dworshak Water To Aid Endangered Snake River Sockeye,”


--CBB, April 1, 2016, “Corps Report On 2015 Columbia/Snake Warm Water, Fish Die-Off Will Discuss Actions To Avoid Repeat,”


-- CBB, September 11, 2015, “Snake River Sockeye: Lowest Return Since 2007, Captive Broodstock Program Increases Spawners,”


-- CBB, June 12, 2015, “NOAA Fisheries Releases Snake River Sockeye Salmon Recovery Plan: 25 Years Of Actions At $101 Million”


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