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River Operations In Review: 2018 Smolt Travel Times Among Fastest, Survival Results Mixed
Posted on Friday, January 11, 2019 (PST)

The time it took juvenile salmon and steelhead to travel in-river through the four lower Snake River dams in the spring of 2018 was among the shortest recorded, with travel times similar to the those experienced in 2017, a year when both spill and flows were also high.


The median travel time for yearling chinook traveling in-river the 461 kilometers (286 miles) passing Lower Granite in mid-May and traveling to Bonneville was about 10 days, slightly quicker than in 2017, and faster than the mean of about 12 days. Travel time in mid-May 2001, a low flow year, was about 20 days.


At about 7 days, steelhead leaving Lower Granite Dam May 21 traveled even faster through the eight dams in May than they did in 2017.


Overall in 2018 spring flow and spill at the dams was higher than average (31 percent higher for flow and slightly higher spill) and fish transportation began earlier (some 45 percent of juveniles found their way downstream by barge), but not all species of salmonids that were left in river survived at the same rates, according to a presentation by Steve Smith, Fish Ecology Division, Northwest Fisheries Science Center, NOAA Fisheries, at the Technical Management Team’s Year End Review last month.


Yearling chinook, starting from a trap on the Snake River upstream of Lower Granite Dam (the upstream dam of the four lower Snake River dams), survived to Bonneville Dam at a 38.1 percent rate, far below the mean since 1997 of 49.7 percent. Steelhead did better, with a 52.3 percent survival (mean is 49.1 percent).


Snake River sockeye salmon, listed as endangered under the federal Endangered Species Act, had a relatively good year in 2018, with 64.3 percent survival from Lower Granite to Bonneville. The mean is 45.7 percent survival. However, sockeye out of the upper Columbia had a poor year, with survival from Rock Island Dam to Bonneville of just 34.4 percent (the mean is 47.1 percent).


TMT is made up of fisheries and hydro/reservoir managers from state, federal and tribal agencies. Every December the group looks back at actions taken during spring and summer in managing Columbia and Snake river federal hydro/fish operations.


Smith’s presentation was among nine reviewed in the day-long session (see


Survival for yearling chinook from the trap upstream of Lower Granite Dam was about average through the Snake River, but when the four lower Columbia River dams are added into the mix, overall survival from the trap to Bonneville Dam was at just 38 percent, Smith said.


Steelhead juveniles survived the trip much better, with an overall survival from the trap to Bonneville of 52 percent. Sockeye salmon juveniles also fared better with survival through both rivers of 64 percent.


Flow at Lower Granite Dam began to rise in late April and continued to increase through May. The 2017 flow was somewhat higher, but declined in mid-May to below 2018 levels before rebounding one week later. The extremely high flows of 1997 exceeded both years.


Even with court-ordered spill to state total dissolved gas limits, spill at Lower Granite was just slightly higher than the mean using data that began in 2001.


The additional spill to state TDG limits, known as gas caps, was mandated at lower Columbia and Snake river dams by an April 2017 order from Judge Michael H. Simon of the U.S. District Court of Oregon. Simon had ordered 24-hour spring spill for one year only in 2018 beginning April 3 at lower Snake River projects and April 10 at lower Columbia River projects, and ending June 20 on the Snake River and June 15 on the Columbia River.


TDG in 2018 in the Lower Granite tailrace was somewhat above the mean, but less than 2017 and not to the levels seen in 1997.


Survival for yearling chinook from seven Snake River hatcheries was 64.8 percent, normal survival for the years 1994 – 2018, whereas survival for upper Columbia River yearling chinook from hatcheries was an above normal 60.8 percent (the median is 56.8 percent).


Survival for upper Columbia River steelhead from hatcheries was a near normal 41.6 percent (median survival is 41.9 percent).


When evaluating survival through the eight dams, the devil is in the details. Reach survival between Snake River dams for yearling chinook was nearly normal: from the trap to Lower Granite, survival in 2018 was 88 percent, while the mean is 93.2 percent; survival from Lower Granite to Little Goose Dam was 94.2 percent (mean is 93.4 percent); from Little Goose to Lower Monumental, survival was 91.7 percent and the mean is 93.9 percent.


As yearling chinook traverse Columbia River dams, survival as compared to the mean drops. While the reach from Lower Monumental on the Snake to McNary Dam on the Columbia, a reach that includes Ice Harbor Dam on the Snake, was near normal at 87.7 percent (mean is 87.3 percent), the reach from McNary to John Day Dam at 77 percent survival was far below the mean of 86.6 percent.


The reach from John Day to Bonneville (which includes The Dalles Dam) was 74.3 percent (the mean is 82.2 percent). Survival in the reach from The Dalles pool to the Bonneville pool was 86.2 percent and the mean is 90.5 percent.


Reach survival for steelhead out of the Snake River was higher than the mean between reaches, and maintained the level of survival through the Columbia River dams. The reach survival of 94.8 percent from John Day to Bonneville was far above the mean of 81 percent.


Survival from Lower Granite to McNary for both steelhead and yearling chinook was 73.3 percent. For chinook, the mean is 75.4 percent and 67.7 percent for steelhead.


From McNary to Bonneville, survival for yearling chinook was 59 percent and the mean is 70.9 percent. For steelhead through the same reach, survival in 2018 was 72.7 percent and the mean is 70.9 percent.


Yearling chinook from the upper Columbia fared better, surviving at a 74.9 percent rate. Still, that’s below the mean of 82 percent.


Snake River sockeye survival from the Redfish Lake trap to Lower Granite Dam was 59.5 percent, higher than the mean of 46 percent and much higher than last year’s survival of Springfield Hatchery fish of about 20 percent. Lower Granite to McNary survival was 68.4 percent (mean 66.5 percent), McNary to Bonneville was 94 percent (mean 63.6 percent) and Lower Granite to Bonneville survival was 64.3 percent (mean 45.7 percent).


Columbia River sockeye from Rock Island to McNary had high survival at 92.7 percent (mean 72.9 percent), but survival moving downstream was much lower than normal. McNary to Bonneville survival was 56 percent (mean 64.7 percent) and survival through the system from Rock Island to Bonneville was 34.4 percent (mean 47.1 percent).


Some 44.8 percent (mean 31 percent) of yearling chinook were transported from one of the collection stations at the upper three of the lower Snake River dams. In 2017, just 20 percent of yearling chinook traveled downriver by barge and in the low flow year of 2015 about 12 percent were transported.


For steelhead, 47.6 percent were transported (mean 34.6 percent). In 2017 about 22 percent were transported and about 12 percent in 2015.


For Snake River sockeye, 56.1 percent (mean 43.4 percent) were transported. Last year some 22 percent were transported and about 41 percent were transported in 2015.

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