September 26, 2019

Survival estimates for juvenile salmon and steelhead during the 2019 spring migration through Snake and Columbia river dams – Lower Granite Dam to Bonneville Dam – varied: Snake River sockeye survival was above average, while Snake River yearling chinook survival was near average, and Snake River steelhead survival fell below average, according to a recently released NOAA Fisheries memorandum.

The Sept. 19 memo from Richard Zabel, director of the Fish Ecology Division at of NOAA’s Northwest Fisheries Science Center, to Ritchie Graves, chief of the NOAA Fisheries’ West Coast Region Columbia River Hydropower Branch summarizes conditions in the rivers and provides preliminary estimates of survival for salmon and steelhead passing through the reservoirs and dams.

The memo also includes estimates of travel times and the proportion of juveniles that were transported this year from Snake River dams.

The memo, “Preliminary survival estimates for the passage of spring-migrating juvenile salmonids through Snake and Columbia River dams and reservoirs, 2019,” is at http://pweb.crohms.org/tmt/agendas/2019/0925_2019_Preliminary_Survival_Estimates_Memo_.pdf.

It was introduced this week at the interagency Technical Management Team meeting Wednesday, Sept. 25, by Paul Wagner and Claire McGrath, both of NOAA Fisheries. Wagner said a final report with updates will be published in February or March 2020. Survival estimates could change at that time by as much as 4 percent, he said.

The study, funded by the Bonneville Power Administration, relies on information from PIT-tagged salmon and steelhead, including 21,332 river-run hatchery steelhead, 15,261 wild steelhead and 6,363 wild yearling chinook salmon released into the tailrace of Lower Granite Dam, the memo says.

Overall, water temperatures were average during the spring migration, with just a few spikes with higher temperatures; flows were generally high, especially in the Snake River; and with a new spill agreement, spill was higher than in most past years, the memo says. Spill as a percentage of flow at Snake River dams averaged 38.5 percent, higher than the long-term mean (2006-2019) of 34.6 percent. In addition, total dissolved gas was higher and averaged between 115 to 120 percent.

In general, here is how juvenile salmon and steelhead survived their outmigration from upstream of Lower Granite Dam on the Snake River to the tailrace at Bonneville Dam on the Columbia River:

After several years of juvenile survival that was far below average due to water chemistry issues at the Springfield Hatchery in Idaho, Snake River sockeye salmon, listed as endangered under the federal Endangered Species Act in 1993, continued to rebound. At 43.4 percent from Lower Granite to Bonneville, Snake River sockeye survival (hatchery and wild) was above the long-term average of 40.7 percent.

Survival of Snake River sockeye outmigrating juveniles took a hit in 2017, with a survival estimate from Lower Granite to Bonneville for combined hatchery and wild fish of just 17.6 percent, which was the fourth lowest survival estimate from 1998 to 2017, according to that year’s survival estimate by NOAA. That was the third consecutive year the juvenile Snake River sockeye survival had been below the 39.2 percent average. 2016 survival was 11.9 percent and 2015 was 37.3 percent. The highest survival – 82 percent – was in 2008.

Upper Columbia sockeye survival from Rock Island Dam to Bonneville was higher than Snake River survival, with an estimated survival of 73.7 percent, far higher than the 10-year average for that reach of 50.6 percent.

At 54.5 percent, survival estimates for PIT-tagged yearling chinook salmon from seven hatcheries upstream of Lower Granite Dam down to the dam were some of the lowest on record since 1998. Mean survival was 63 percent. 

Yearling chinook salmon traveling from the Lower Granite tailrace to McNary Dam survived at an average of 62.8 percent (long-term average is 73.3 percent), and survival from McNary to the Bonneville tailrace was 83.8 percent (average is 70.2). The mean estimated survival for yearling chinook from Lower Granite to Bonneville was 52.6 percent and the long-term average is 52.1 percent.

For yearling chinook, adding the Lower Granite pool, survival from the Snake River trap to Bonneville Dam was 41.3 percent, far below the long term average of 48.9 percent.

“Yearling Chinook survival through the hydropower system was below the mean in the previous four years 2015-2018; these low system survival estimates were driven mostly by poor survival in the McNary to Bonneville reach, while survival in Snake River reaches was generally high. These trends were reversed in 2019, with above average survival in the McNary to Bonneville reach but poor survival in several Snake River reaches,” the memo says.

Wild Snake River yearling chinook survived at a higher rate. Survival from Lower Granite to McNary was 66.9 percent and from McNary to Bonneville 81.3 percent. Survival from the Snake River trap to Bonneville was 47.2 percent, which is slightly above the long-term average of 44.9 percent.

Survival for Snake River steelhead (hatchery and wild combined) was above average in all individual reaches except for the John Day Dam to Bonneville reach where survival was below average. It was above average from Lower Granite to McNary (71.8 percent), but below average for McNary to Bonneville (59.5 percent). The combined Snake River steelhead survival estimate from the Snake River trap to Bonneville Dam tailrace was 41.2 percent, below the long-term average of 45.7 percent. From Lower Granite to Bonneville, survival was 42.7 percent, below the long-term mean of 47 percent.

“In contrast to Chinook in 2019, this below-average estimate is driven by poor survival in the McNary to Bonneville reach; steelhead generally had above average survival in the Snake River,” the memo says.

Again wild fish fared better. Wild Snake River steelhead survival from Lower Granite to McNary tailraces was 77.2 percent, and from the McNary tailrace to Bonneville tailrace it was 64.0 percent. Estimated survival from the Snake River trap to the Lower Granite tailrace was 97.3 percent, which resulted in estimated survival from the Snake River trap to the Bonneville tailrace of 48.1 percent, which is higher than the long-term average of 41.8 percent.

Fish from the upper Columbia River also had mixed results:

The estimated survival of hatchery yearling chinook migrating from the upper Columbia from the McNary tailrace to the Bonneville tailrace was 78.5 percent, near the long-term average of 81.2 percent.

Hatchery steelhead survival from the upper Columbia was 60.6 percent from McNary to Bonneville, which is below the long-term average of 76.4 percent.

Some 41.6 percent of wild spring-summer chinook smolts were transported this spring and 33.6 percent of hatchery spring-summer chinook smolts were transported. Some 36.7 percent of wild steelhead and 36.4 percent of hatchery steelhead were transported. The study estimates that 32 percent of hatchery chinook and 47 percent of hatchery and wild steelhead had migrated prior to transporting. Juveniles were transported either from Lower Granite, Little Goose or Lower Monumental dams beginning April 24. The date transport started in 2018 was April 23.

In April chinook travel times were several days longer than they were in 2017 and 2018. However, in May chinook travel times decreased to levels similar to 2017 and 2018.

Steelhead travel times were about one day longer in 2019 than they were in 2017 or 2018, the memo says.

“Since the institution of court-ordered spill in 2006, and the concurrent installation of surface collectors at four additional federal dams during that period, travel times have decreased on average between Lower Granite and Bonneville dams for steelhead, but the effect is smaller for Chinook,” the memo says.