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Chum Operations At Bonneville Dam Transition From Spawning To Incubation Flows
Posted on Friday, December 22, 2017 (PST)

It’s been a few weeks since spawning chum salmon have been observed downstream of Bonneville Dam, so fisheries and dam managers agreed this week to transition from flows that guarantee coverage of chum redds (nests) to minimum level of flows that will keep the redds covered until incubation of the eggs in April.


The last survey by biologists of spawning areas in the Columbia River below the dam was December 4, which found live adult chum salmon near Multnomah and Horestail falls, but no new fish in the Ives/Pearce island areas just downstream of the dam near the Washington shore (see the survey history for this season at Chum salmon are listed as threatened under the federal Endangered Species Act.


And few chum have traveled beyond Bonneville Dam. Just 21 have passed the dam and none have crossed since Nov. 29, said Paul Wagner of NOAA Fisheries.


Given the paucity of live adult chum and the likelihood that few or no more would arrive to spawn, the interagency Technical Management Team Wednesday, Dec. 20, agreed to transition to protective incubation flows Dec. 21 at 1 pm.


Annual chum operations ensure that enough water will flow over chum redds, or nests, near Ives Island downstream of Bonneville Dam to protect the redds and fertilized eggs until they emerge next spring. So the initial spawning operations seeks flows high enough to protect chum as they build their redds, but not so high that chum would be encouraged to spawn in areas that could be dewatered when flows drop.


Chum operations for spawning began Nov. 7, although at that time no chum were present or spawning at the Ives/Pierce island complex.


The initial operation follows a tiered approach that largely depends on the amount of water passing the dam and the Corps’ ability to maintain a tailwater elevation that is best for spawning chum and incubating eggs. Initially, the Corps operates project outflow to maintain the tailwater elevation between 11.5 and 13 feet during all hours. As river flows increase, chum operations adjust to protect the salmon.


With flows designed to protect the redds through incubation, an 11.8 foot tailwater elevation at the dam at all hours simply becomes the minimum flow allowed, and that will be held as long as up to April 10, 2018.


Doug Baus of the U.S. Army Corps of Engineers isn’t expecting an immediate change in tailwater elevation, however. As of Wednesday morning, average elevation was in the 12.7 foot with flows at the dam of 123,400 cubic feet per second, and that isn’t likely to change soon, he said.


With the high runoff in 2016, holding flows low for chum was difficult, but with this year’s steady flows the operation has been much easier and that will likely continue.


According to Baus, the current water supply at The Dalles Dam is 89 million acre feet or 102 percent of average and the weather outlook is for continued cool and dry conditions.


Also see:


--CBB, December 8, 2017, “ESA-Listed Chum Salmon Spawning Below Bonneville, Weather Cooperating For River Ops Aiding Fish,”


--CBB, November 3, 2017, “No Chum Yet, But Annual Operations For Spawning Fish Slated To Begin Next Week,”


-- CBB, October 27, 2017, “Operations For Spawning ESA-Listed Chum Delayed; Early Basin Water Supply Forecast Normal,”


--CBB, January 6, 2017, “ESA-Listed Chum Salmon Below Bonneville Dam Show Good Spawning Rate; Flows Maintained To Cover Redds,”


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