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Restoring the Lower Snake River

Friday, October 27, 2017

Sockeye in RiverAn independent panel of scientists has completed its eighth annual review of the Fish Passage Center’s draft 2017 report on Columbia River basin salmon survival, again finding that the methodology used by the FPC when calculating such items as smolt-to-adult survival and juvenile migration time and survival is already developed and useful.
The Independent Scientific Advisory Board’s first review of the Bonneville Power Administration-funded Comparative Survival Study was in 2010 and many of the methods the FPC uses in the report have already been reviewed by the ISAB.
The survival report now typically includes only updates to the previous year’s data and expands the analyses as more recent data are acquired.
“As more data are acquired, new patterns and questions arise on the interpretation of the results—this interpretation is now the primary focus of the ISAB’s reviews,” the ISAB said in its review. “The ISAB appreciates the CSS’s detailed responses to suggestions provided in previous reviews and does not expect the CSS to necessarily respond immediately to new requests for further analyses by the next report.”
The CSS is an annual study that looks at salmonid survival through Snake and Columbia river dams. For the first time it evaluated juvenile fish survival in the Snake River with and without the presence of the four lower dams on the river and it assessed the impact on survival if spill is increased, something that may occur by court order beginning next spring.
(See CBB, June 23, 2017, “Litigants In Salmon BiOp Case Working Together To Develop Court-Ordered Spill-For-Fish Plan In 2018,”
The Fish Passage Center released its draft report in late August and took comments from fisheries managers and the public through October 15. The final CSS is scheduled for completion by the end of December. The full draft report, titled “Comparative Survival Study of PIT-tagged Spring/Summer/Fall Chinook, Summer Steelhead and Sockeye, Draft 2017 Annual Report,” is at
The Northwest Power and Conservation Council’s 2014 Columbia River Basin Fish and Wildlife Program tasks the ISAB to ensure an independent and timely science review of FPC’s analytical products, including its annual survival study. The ISAB’s full October 18 review of the report is at
The ISAB noted some changes from previous survival reports. The chapter on life-cycle modeling (Chapter 2) was updated “with a revised fit of the life-cycle model using more data, and now separate smolt-to-adult ratios (SARs ) are modeled for in-river and transported fish.”
Examining 12 spill and flow scenarios, the report found similar results as last year, that more spill generally leads to higher in-river survival and improved SARs, the ISAB said. A new component was dam breaching and additional spring spill, with the report concluding that breaching would result in 10 percent better in-river survival and a doubling of SARs.
Chapter 3 that looked at juvenile travel time and survival was also updated and added an investigation of the impact of total dissolved gas on the instantaneous mortality and survival probabilities of juvenile salmon and steelhead.
“While this approach did not show any evidence of an impact of TDG on either instantaneous mortality or survival probabilities, a more comprehensive approach of including TDG directly in the modeling process would address concerns about the interrelationship between TDG, spill, and flow that may confound results,” the ISAB review said.
Chapters 4, 5 and 6 evaluated SARs, finding that pre-harvest SARs of 4 percent to 6 percent are associated with pre-1970 levels of productivity for Snake River spring/summer chinook.
What the CSS didn’t answer, according to the ISAB, was “given the large amount of effort in the past to improve SARs through dam passage improvements, habitat improvements and other changes, to what extent might further improvements in hydrosystem management, predator control, and estuarine habitat lead to achieving SARs of 4 percent-6 percent?”
Chapter 8 (CSS adult success) is a new chapter that looks at the relationship between survival of adults upstream of Bonneville and travel time, temperature, and arrival date. “A complex modeling framework was used, but the ISAB is concerned that not enough assessment of the fit of the model to the data has been done to ensure that conclusions are appropriate,” the ISAB review said.
The ISAB further recommended the following topics for future reports:
1. Modeling flow, spill, and dam breach scenarios is very useful for policy makers. Consequently it is important that all assumptions be clearly stated and that the results are robust to these assumptions.

  1. Include other important processes in the life-cycle models. Interactions among the various populations, including compensatory responses, are important and whenever possible should be folded into future modeling efforts, particularly if restoration actions increase the abundance of out-migrants. Are predator control programs effective and what is needed to address the impacts of predators, such as pikeminnow, birds and pinnipeds?
  2. There appear to be sufficient data to try to elucidate reasons for shifts in the age distribution of returning spring/summer chinook. The ISAB suggests doing so.
  3. The graphical analysis of the impact of TDG could be improved using direct modeling to deal with potential confounding effects of spill, flow, TDG, and temperature.
  4. The (new) modeling of adult survival upstream of Bonneville should be continued and improved to identify the limiting factors to adult returns. Once these factors are identified, are there modifications to the hydrosystem operations that could be done to mitigate some of the factors?
  5. The CSS report is a mature product and the authors are very familiar with the key assumptions made and the impact of violating the assumptions. These should be collected together in a table for each chapter to make it clearer to the readers of the report.
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