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 http://www.fpc.org/spawning/spawning_surveys/ODFW_reports/2017spawning.htm). 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
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
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.
--CBB, December 8, 2017, “ESA-Listed Chum
Salmon Spawning Below Bonneville, Weather Cooperating For River Ops Aiding
--CBB, November 3, 2017, “No Chum Yet, But
Annual Operations For Spawning Fish Slated To Begin Next Week,” http://www.cbbulletin.com/439811.aspx
-- CBB, October 27, 2017, “Operations For
Spawning ESA-Listed Chum Delayed; Early Basin Water Supply Forecast Normal,” http://www.cbbulletin.com/439785.aspx
--CBB, January 6, 2017, “ESA-Listed Chum
Salmon Below Bonneville Dam Show Good Spawning Rate; Flows Maintained To Cover