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2017 Juvenile Salmon/Steelhead Survival In Snake/Columbia: Fish Take Hit In McNary To John Day Reach
Posted on Friday, October 06, 2017 (PST)

NOAA’s Northwest Fisheries Science Center released its annual survival estimate of juvenile salmon and steelhead that migrated through Snake and Columbia river dams, finding that one particular river reach was less friendly for the fish than others.

 

That is the reach from McNary Dam to John Day dam, which for yearling chinook, survival was the lowest on record.

 

The information was delivered in a September 18, 2017 memo from Rich Zabel, director of the Fish Ecology Division at NOAA, 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, 2017,” is at http://pweb.crohms.org/tmt/agendas/2017/1004_2017_Preliminary_Survival_Estimation_Memo.pdf.

 

For the study, which was funded by the Bonneville Power Administration, NOAA PIT-tagged 22,049 hatchery steelhead, 18,422 wild steelhead and 14,241 wild yearling chinook salmon. All were released into the tailrace of Lower Granite Dam, the upstream of the four lower Snake River dams. NOAA has produced the survival estimate study since 1993.

 

The study estimates survival of both hatchery and wild yearling chinook, survival of both hatchery and wild steelhead and survival of hatchery and wild sockeye salmon in lower Snake River reaches through Bonneville Dam as well as from Rock Island Dam through Bonneville. It also estimates the percentage of migrating fish in the lower Snake River that were transported by barge and summarizes environmental conditions, such as flow, spill and water temperature.

 

NOAA also estimated survival of yearling chinook hatchery fish from seven Snake River hatcheries upstream of Lower Granite. The mean survival in 2017 from the hatcheries to Lower Granite was 65 percent. While lower than the past three years, the mean for the period 1998-2017 is 65.1 percent (the range has been 49.4 percent in 1997 to 71.7 percent last year).

 

Survival in 2017 downstream of Lower Granite for yearling chinook (both hatchery and wild) was nearly average at 91.6 percent (average is 92.5 percent) in the Lower Granite to Little Goose reach and survival in the Little Goose to Lower Monumental reach was 90.8 in 2017 (average is 92.2 percent). Survival was above average at 91.2 percent (average is 86.3 percent) in the Lower Monumental to McNary reach and John Day to Bonneville reach (2017 was 87.1 percent, average is 80.9 percent), the study says.

 

However, because the estimated survival in the McNary to John Day reach (2017 was 72 percent, average is 86.5 percent) was the lowest on record, the estimates resulted in above average survival from Lower Granite to McNary, but below average survival in the remaining combined reaches through Bonneville.

 

The mean estimated survival for yearling chinook salmon from Lower Granite Dam tailrace to McNary Dam tailrace was 74.3 percent (average is 73.6 percent) and from McNary to Bonneville it was 64.3 percent (average is 70 percent).

 

The estimated survival for yearling chinook from Lower Granite to Bonneville was 47.8 percent, while the average over the years 1999 – 2017 was 52.4 percent.

 

The 2016 estimate (Lower Granite to Bonneville) was 50.5 percent. Survival through the power system has remained relatively stable since 1999, NOAA says, with the exceptions of lower estimates in the low flow years of 2001 (27.9 percent), 2004 (39.5 percent) and 2015 (42.8 percent).

 

To focus in on the wild yearling chinook from the Snake River, the mean estimated survival from Lower Granite to McNary was 70.9 percent, but dropped significantly to just 43.6 percent from McNary to Bonneville.

 

Estimated survival for wild yearling chinook from Lower Granite to Bonneville tailraces was 30.9 percent.

 

Survival for combined hatchery and wild Snake River steelhead was above average in all of the individual reaches except for John Day to Bonneville.

 

Survival (75.9 percent) was above average (65.3 percent) from Lower Granite to McNary, but below average (2017 was 60.5 percent, average is 67.4 percent) from McNary to Bonneville.

 

Lower Granite to Bonneville (45.9 percent) was close to the average (46.3 percent). The 2016 estimate was 44.4 percent.

 

This is the third consecutive year with below average survival for Snake River steelhead after seven consecutive years of survival estimates above the mean, NOAA says.

 

Zeroing in on just the wild steelhead, survival from Lower Granite to McNary was 72.3 percent, McNary to Bonneville was 41.3 percent, and Lower Granite to Bonneville was 29.9 percent.

 

The sockeye salmon juvenile survival estimate from Lower Granite to Bonneville for the combined hatchery and wild fish was 17.6 percent, the fourth lowest survival estimate from 1998 to 2017.

 

This is the third consecutive year that juvenile Snake River sockeye survival has been below the average of 39.2 percent. 2016 survival was estimated at 11.9 percent and 2015 was 37.3 percent. The highest survival was 82 percent in 2008.

 

However, for upper Columbia River sockeye, the juvenile survival estimate from Rock Island Dam to Bonneville was significantly higher at 50 percent, which was still slightly below the average of 50.3 percent and is a highly uncertain estimate, but mortality was not nearly so high as that for Snake River sockeye, NOAA says.

 

Survival for hatchery yearling chinook from the upper Columbia River cannot be estimated for reaches upstream of McNary Dam. However, their survival from McNary to Bonneville was 94.4 percent, which is above the average of 81.8 percent.

 

Hatchery steelhead survival from the upper Columbia River was 96.4 percent from McNary to Bonneville, which is above the average of 74.7 percent. However, NOAA says the estimate has “high uncertainty.”

 

Smolts arrived earlier in the season than normal. When transportation began May 2 at Lower Granite, Little Goose, and Lower Monumental dams, about 70 percent of wild yearling chinook and 53 percent of hatchery yearling chinook had already passed. The average in years 2006-2014 was 42 percent for wild and 31 percent for hatchery yearling chinook  

 

In addition, about 60 percent of wild steelhead had already passed Lower Granite when transportation began, far more than the average of 29 percent. Some 63 percent of hatchery steelhead was estimated to have passed the dam before May 2, also higher than the average of 33 percent.

 

Some 17.8 percent wild spring-summer smolts were transported, while 21.6 percent of hatchery spring-summer smolts were transported. Some 23.3 percent of wild steelhead and 20.9 percent of hatchery steelhead were transported.

 

Water temperatures were about average, but river flows and spill were far above average during the migration season (April 1 to June 15).

 

During the period, Little Goose flows averaged 138,700 cubic feet per second, far higher than the 1993 – 2017 daily mean of 91.8 kcfs. Only 1997 had a higher daily mean flow. Mean water temperature at the dam during this period was 11.2 degrees Celsius (52.34 degrees Fahrenheit). The long-term mean is 11.3 C.

 

Spill at Snake River dams at 63.7 kcfs mean and far above the long-term mean of 27.2 kcfs was the most spill during the time period 1993 – 2017.

 

Spill as a percentage of flow averaged 44.5 percent, again far above the long-term mean of 26.8 percent. It was the highest mean spill percentage during the time period.

 

High flows and spill resulted in shorter travel times, April through June, for all fish than in any other year (1998 – 2017).

 

Also see:

 

--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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