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NOAA Releases Preliminary 2018 Juvenile Salmonid Survival Estimates Through Columbia/Snake Dams
Posted on Friday, October 12, 2018 (PST)

Yearling chinook salmon from upstream of Lower Granite Dam on the Snake River down through Bonneville Dam on the Columbia River survived at a below average rate this spring if they were from a hatchery and at an above average rate if they were wild, according to a recent preliminary report from NOAA Fisheries on juvenile survival through the hydro system.

 

The information was delivered in a September 19, 2018 memo from Richard Zabel, director of the Fish Ecology Division at NOAA Fisheries’ Northwest Fisheries Science Center, to Ritchie Graves, chief of the NOAA Fisheries' West Coast Region Columbia River Hydropower Branch.

 

The memo, “Preliminary survival estimates for the passage of spring-migrating juvenile salmonids through Snake and Columbia River dams and reservoirs, 2018,” is at http://pweb.crohms.org/tmt/agendas/2018/1003_2018_Preliminary_Survival_Estimates_Memo.pdf.

 

The final report is generally released the following February, said NOAA’s Paul Wagner at the interagency Technical Management Team meeting Wednesday, Oct. 3. Survival estimates in the final report could change by as much as 4 percent, the report says.

 

The report says that Snake River yearling chinook estimated survival from Lower Granite Dam tailrace to the Bonneville Dam tailrace was 43.2 percent, which is “substantially below the long-term (1999-2018) average of 52.1 percent.

 

“Yearling Chinook survival through the hydropower system has been consistently below the mean for the past four years, despite a range of different environmental conditions within these years,” the report says. “These low system survival estimates seem to be driven mostly by poor survival in the McNary to Bonneville reach.”

 

For Snake River steelhead the overall estimated survival from Lower Granite tailrace to Bonneville tailrace was 53.3 percent, higher than the long-term mean of 47.0 percent. This above-average estimate follows three consecutive years of survival estimates below the mean.

 

Estimated survival of Snake River sockeye between Lower Granite and Bonneville tailrace was 64.3 percent, the third highest from 1998 through 2018, the report says. The component survival estimates for the Lower Granite Dam to McNary Dam reach and the McNary Dam to Bonneville Dam reach were both above average. This above-average estimate follows three consecutive years with very low survival.

 

“The Idaho Department of Fish and Game has adjusted their acclimation methods this year in order to address the causes of the low Snake River Sockeye survival from the past three years; their efforts almost certainly contributed to the higher survival estimate this year,” the report says.

 

Survival of juvenile Upper Columbia River sockeye in the McNary to Bonneville Dam reach was also above average.

 

Factors that impacted survival in 2018 were higher water, more spill as a result of a U.S. District Court order and near average water temperatures during the spring migration period.

 

In more detail:

 

Survival for yearling chinook from hatcheries upstream to Lower Granite have been relatively stable since 1998, the report says. The 2018 mean survival was 64.8 percent. Last year’s survival was 65 percent and survival 1998 through 2018 is 65.1 percent.

 

Estimated survival through the four lower Snake River projects (combined hatchery and wild) for yearling chinook was above average, but survival dropped to “substantially” below average on the trip from McNary Dam to the John Day Dam and the John Day Dam to Bonneville Dam.

 

For Snake River hatchery yearling chinook:

-- Mean estimated survival from Lower Granite tailrace to McNary tailrace in 2018 was 73.3 percent.

-- Mean estimated survival from McNary tailrace to Bonneville tailrace was 59.0 percent.

-- Mean estimated survival from Lower Granite tailrace to Bonneville tailrace was 43.2 percent

-- Estimated survival for the Lower Granite project (head of reservoir to tailrace) was 88.0 percent based on fish PIT tagged at and released from the Snake River trap.

--The combined yearling chinook salmon survival estimate from the Snake River trap to Bonneville tailrace was 38.1 percent, substantially below the long-term average of 48.9 percent.

 

For Snake River wild yearling chinook:

-- Mean estimated survival from Lower Granite tailrace to McNary tailrace was 76.0 percent.

-- Mean estimated survival from McNary tailrace to Bonneville tailrace was 76.2 percent.

-- Estimated survival from the Snake River trap to Lower Granite tailrace was 87.1 percent, which resulted in estimated survival from the Snake River trap to Bonneville Dam tailrace of 50.4 percent. The long-term average is 44.8 percent.

 

Survival for Snake River steelhead (both wild and hatchery) was above average in all reaches between dams, although, according to the report, the reach from John Day to Bonneville was uncertain.

 

For hatchery steelhead:

--Mean estimated survival from Lower Granite tailrace to McNary tailrace was 73.3 percent.

-- Mean estimated survival from McNary tailrace to Bonneville tailrace was 72.7 percent.

--The combined Snake River steelhead survival estimate from the Snake River trap to Bonneville tailrace was 52.4 percent, which was above the long-term average of 45.6 percent.

 

For wild Snake River steelhead:

-- Mean estimated survival from Lower Granite tailrace to McNary tailrace was 73.6 percent.

-- Mean survival from McNary tailrace to Bonneville tailrace was 82.2 percent.

-- Estimated survival from the Snake River trap to Lower Granite tailrace was 84.8 percent, which resulted in estimated survival from the Snake River trap to Bonneville Dam tailrace of 51.3 percent.

 

For Snake River sockeye, both wild and hatchery, the estimated survival from the tailrace of Lower Granite to the tailrace of Bonneville was 64.3 percent. The long-term average is 40.6 percent.

 

The report also looked at survival for chinook and steelhead coming from the upper Columbia River. For hatchery yearling chinook:

-- Estimated survival from McNary tailrace to Bonneville tailrace was 74.9 percent, which was below the long-term average of 81.4 percent.

 

For hatchery steelhead from the upper Columbia River:

-- Estimated survival from McNary tailrace to Bonneville tailrace was 116.1 percent, but the estimate has high uncertainty.

-- The long-term average is 77.4 percent.

 

“For fish released from upper Columbia River hatcheries, we cannot estimate survival in reaches upstream from McNary Dam (other than the overall reach from release to McNary Dam tailrace) because of limited PIT-tag detection capabilities at Mid-Columbia River PUD dams,” the report says.

 

It also said that in this preliminary report some estimates for “technical reasons” exceed 100 percent.

 

“When this occurs, we report the actual estimate, but for practical purposes these estimates should be interpreted as representing survival probabilities which are less than or equal to 100 percent,” the report says.

 

The estimated survival of Columbia River sockeye salmon (hatchery and wild combined) from the tailrace of Rock Island Dam to the tailrace of Bonneville was 66.7 percent. The long-term average is 51.1 percent.

 

Some 44.1 percent of wild spring-summer chinook smolts in the Snake River and 45.4 percent of hatchery smolts were transported in 2018. This is substantially higher than in most recent years, and one of the highest rates since 2006, reversing the trend of very low transportation rates during the 2015 – 2017 period, the study says.

 

A reason for the higher rates is that transportation began eight days earlier on April 23, as opposed to May 1 in past years.

 

“We estimate that 45 percent of the annual total passage of wild yearling chinook and 24 percent of hatchery yearling chinook occurred at Lower Granite Dam before transportation began, compared to averages between 2006-2014 of 42 percent and 31 percent respectively.”

 

“These estimates represent the percentage of smolts that arrived at Lower Granite Dam that were subsequently transported, either from Lower Granite Dam or downstream at Little Goose or Lower Monumental Dam,” the report says.

 

Mean flow at Little Goose Dam (April 1 – June 15) was 110,800 cubic feet per second, well above the long-term average of 92.6 kcfs.

 

Mean water temperature at Little Goose Dam was 11.5 degrees Celsius (52.16 degrees Fahrenheit), which was near the long-term mean of 11.2 degrees C.

 

Mean spill discharge at the Snake River dams was 41.3 kcfs, substantially above the long-term (1993-2018) mean of 27.7 kcfs. Spill as a percentage of flow at Snake River dams averaged 37.2 percent, higher than the long-term mean of 27.2 percent.

 

As a result of higher flows and more spill, travel time for both chinook and steelhead from Lower Granite to Bonneville was substantially shorter than the long-term average.

 

“Travel time was a record,” Wagner said. “Flow and spill resulted in the time from Granite to Bonneville in less than ten days, so they were cookin’ through the river.”

 

Also see:

 

--CBB, October 6, 2017, “2017 Juvenile Salmon/Steelhead Survival In Snake/Columbia: Fish Take Hit In McNary To John Day Reach,” http://www.cbbulletin.com/439683.aspx

 

--CBB, October 7, 2016, “Report Details 2016 Juvenile Salmon/Steelhead Survival In Snake/Columbia; Snake Sockeye Take A Hit,” http://www.cbbulletin.com/437701.aspx

 

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