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Agencies Identify Spawning Areas For Chum, Confirm Safe Water Levels Over Redds
Posted on Friday, January 19, 2018 (PST)

This year the larger portion of chum redds downstream of Bonneville Dam are nearer the dam in an area dubbed the Strawberry chum spawning area, according to information provided by Tony Norris of the Bonneville Power Administration.

 

Historically, he told the interagency Technical Management Team this week, chum spawning was mostly at two Ives Island pocket spawning areas west of the Strawberry area. There was no chum spawning in Hamilton Slough.

 

(See maps of chum spawning areas at http://pweb.crohms.org/tmt/agendas/2018/0117_Ives_Island_Spawning_Areas_2017.pdf)

 

TMT transitioned to protective incubation flows for chum Dec. 21 that call for a minimum flow of 11.8 feet at the dam’s tailwater.

 

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 in spring. Initial spawning operations sought flows high enough to protect chum as they built their redds, but not so high that chum would have been encouraged to spawn in areas that could be dewatered when flows drop. Chum operations for spawning began Nov. 7.

 

Current flows are designed to protect the redds through incubation. The 11.8 foot minimum tailwater elevation at the dam at all hours will be held for as long as up to April 10, 2018, or through incubation.

 

Current tailwater elevation is at a hefty 17.8 feet with total outflow at the dam of 216,600 cubic feet per second as of Wednesday, Jan. 17, the day TMT met. Flows will likely remain at that level or higher with the expected rain events this week. That’s plenty of water to keep the chum redds and eggs watered, Norris said.

 

However, a tailwater elevation of 11.8 feet does not guarantee that the redds will have that much water (11.8 feet) between them and the river’s surface.

 

Norris had graphs of both the Ives Island and Strawberry chum spawning areas that showed just how deep the redds were on Nov. 29 when the tailwater was 12 feet 6 inches and on Dec. 21 when the tailwater was 12 foot 2 inches.

 

The Ives Island upper pocket, where the depth is less than the lower Ives pocket, was about 1.5 feet from water surface to redds on Nov. 29 and just slightly lower in December. The lower Ives pocket depth was 3.5 feet in November and just under 3 feet in December.

 

Redd depths at the Strawberry site were generally between 2 and 3 feet in November and 1.5 to 2.5 feet in December.

 

McCord Creek, on the south side of the Columbia River, had redds as deep as 3.25 feet and down to 2 feet in November, with nearly equal depths in December.

 

The Break spawning area downstream of Ives Island had redd depths ranging from 1.6 to 3.5 feet in November and 1.25 to 3.2 feet in December.

 

Emergence is generally in April after the eggs have warmed over time. Emergence occurs when the cumulative temperature units add up to about 930 TUs. River TUs Dec. 21 were about 420, while areas where groundwater and river water mix (hyporheic) were higher at about 580 TUs.

 

The weather forecast for the next couple of weeks is for lower than normal temperature and higher than normal precipitation, said Doug Baus of the U.S. Army Corps of Engineers.

 

“Even if we go as low as (tailwater elevation) 11.5 these redds would still be protected,” Norris said. “We’ll revisit this when we run out of manageable water down the road.”

 

Also see:

 

--CBB, January 5, 2018, “Coast Guard Removal Of Sunken Boat Near Bonneville Dam Could Change Chum Operations,” http://www.cbbulletin.com/440008.aspx

 

--CBB, December 22, 2017, “Chum Operations At Bonneville Dam Transition From Spawning To Incubation Flows,” http://www.cbbulletin.com/439969.aspx

 

--CBB, December 8, 2017, “ESA-Listed Chum Salmon Spawning Below Bonneville, Weather Cooperating For River Ops Aiding Fish,” http://www.cbbulletin.com/439925.aspx

 

--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 Redds,” http://www.cbbulletin.com/438156.aspx

 

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