A group of independent scientists that reviewed the scientific modeling used to predict salmon and steelhead return rates in the Columbia River System Operations draft environmental impact statement said impacts from climate change and other variables should be considered in the analysis.
That's the top-line result of the review released April 29 by the Independent Scientific Advisory Board of Chapter 2 of the Fish Passage Center's 2019 Cumulative Survival Study.
Federal action agencies had asked the CSS Oversight Committee to analyze the six alternatives in the draft EIS using CSS modeling with an 80-year water record. While the 2019 CSS came out last year, Chapter 2 was not made public until Feb. 28, when the draft EIS was released.
ISAB is an 11-member group of scientists that provides independent scientific advice and recommendations on issues relating to fish and wildlife programs of NOAA Fisheries, Columbia River tribes, and the Northwest Power and Conservation Council.
In its review, the board critiqued only the CSS modeling of the draft EIS as part of its longstanding review of the annual study, and not the draft EIS itself.
The independent scientists wrote that they had difficulty reviewing the chapter because methods and reporting styles are different from those used in the annual CSS reports, and said it's not clear whether those changes were mandated by the action agencies.
"The results from the mandated task of using the modified flow dataset to compare operational alternatives are useful, but the results may not be indicative of future benefits," the scientists found, adding, "Climate, ocean, and in-river conditions are unlikely to remain static in their current state or range of conditions."
They noted that authors of the CSS chapter recognized the issue, and noted it in a sentence at the end of the chapter's introduction. "This caution needs to be described more prominently in the report," the independent scientists said.
The ISAB also said that the CSS models do not incorporate the relationship of fish characteristics to survival, such as body size, body mass, condition, and date of entry to the ocean.
The scientists also said that the chapter's discussion of issues with the draft EIS' preferred alternative is a "potentially" important section which should be more prominent. The section points out that the flexible spill operation involves hourly changes in spill operations with high spill for 16 hours and lower spill levels for eight hours. The CSS analysis says that benefits to fish are overestimated in the preferred alternative because powerhouses are more efficient at catching fish at night than during the day. The CSS chapter says that lower spill at night will increase powerhouse passage—one of the metrics in CSS modeling.
"This warrants more discussion, including a better evaluation of the magnitude of the effect," the ISAB review says.
The scientists said the coordinated use of multiple models is a powerful approach to answering difficult questions. They note that using a common hydrological input with different management alternatives to get a common predictor of smolt-to-adult returns, or SARs, can provide more confidence in the modeling results. But the chapter does not explain why the models resulted in different SARs or abundances.
The ISAB noted that SARs and marine survival may be impacted by smolt body size, the timing of juvenile migration downstream, and the date when they enter the ocean. "Are these expected to remain the same under all operational alternatives? Do other variables used in the model, partially or completely, capture these effects?" the review asked.
The review says that using the 80-year modified flow record assumes that past conditions represent future conditions. It also says that ending the 80-year water record in 2008 may be an issue, since the world's warmest years from 1880 to 2019 have all occurred since 2015, and nine of the 10 warmest since 2005. "Future projections based on the modified flow dataset are therefore likely to be overly optimistic about survival," it said.
"For such an important study, caveats of interpreting current findings as representing future benefits should be more fully presented in the chapter's Discussion section," the review said. "For example, not only may the flow record change with climate change, but maturation schedules, conversion probabilities (what fraction of adults survive from Bonneville to the spawning ground), harvest rates, habitat improvements, fish passage improvements, ocean conditions, and such may change from those used in the models," the scientists noted.
The review also said the limitations of the predictions that increasing spill will at least double SARs and breaching the four lower Snake River dams will increase SARs by up to four times should be discussed and explained. "Despite all the earlier caveats in the chapter that results are only relative and not absolute, the above statement seems very strong," the scientists wrote. "These are only modeled results, and there are many examples where model predictions, especially of abundances, are not fully realized due to the inherent limitation that models are a simplification of reality."