The Columbia River Basin Fish and Wildlife Program calls for a regular system of independent and timely science reviews of the Fish Passage Center’s (FPC) analytical products. These reviews include evaluations of the Comparative Survival Study’s (CSS) draft annual reports. This ISAB review of the draft 2021 CSS Annual Report is the ISAB’s twelfth review of CSS annual reports. CSS reports have thoroughly documented trends in survival and productivity, and these long-term data become more valuable with each additional year.
The annual CSS report is a mature product, produced by the Fish Passage Center since 1998 and reviewed by the ISAB since 2010. The reports typically include mostly updates with the latest year of data, continuation of the analysis of long-term trends, and addition of new analytical approaches. As more data are acquired, new patterns and questions arise on the interpretation of the results—this is now the primary focus of the ISAB's reviews.
A few key observations and suggestions for future analyses from this year’s ISAB review include:
- The CSS Report does not emphasize the benefits of its program and the use of its data and analyses in other reports and peer-reviewed publications. These data inform fisheries managers in the Columbia River Basin and provide critical data for research in the Pacific Northwest. The annual report could describe major applications of the CSS data that have been published or reported over the last year, briefly highlight important findings based on CSS data, and make the regional importance of its analyses abundantly clear to the Council, BPA, co-managers, and the public.
- Many things have changed in the system over the 25 years of data collection, and the impacts of these changes on the long-term analyses are largely unknown. Many of the changes in the system are summarized in Chapter 1, but the reader must infer possible impacts. The ISAB again suggests a table of the history of changes in the system, along with a brief indication of the possible impacts of these changes on the estimates of the effects of the hydrosystem on salmon and steelhead survival.
- The introductory section (Chapter 1) should also highlight 1) overall survival and SARs, 2) new analyses, 3) major changes that signal emerging management concerns, and 4) recommendations for management of the hydrosystem. This recommendation from the 2020 ISAB report was not implemented in the latest report, and the Conclusions sections of most chapters were identical to those in previous reports.
- The CSS should consider recent analyses outside of the CSS to identify possible new analyses (or extensions to existing analyses) that would inform important management decisions in response to these external analyses.
- Chapter 2 updates the analysis of the patterns of survival of wild steelhead in the Basin to include wild spring Chinook. The chapter should more clearly describe the environmental variables used and discuss the potential consequences of failure of the standard assumptions in the regression methods.
- Chapter 3 continues and expands previous analyses of the effects of the in-river environment on juvenile travel time, instantaneous mortality, and survival. The CSS now analyzes PIT tag data from Rocky Reach to McNary dams rather than Rock Island to McNary dams. The CSS could explore analytical methods to use data from both reaches and capitalize on a longer period of record.
- Chapter 4 also continues and extends past years’ work on patterns in annual overall SARs. By now, the low level of SARs relative to the Council’s 2%-6% objectives has been established. These essential but lengthy data sets and extensive summaries of results may overwhelm decision makers and the public, inadvertently giving the impression that persistently low values of SARs are inevitable. The CSS could consider developing an Impact Report to communicate the most critical conclusions and recommendations for the Council, BPA, and co-managers.
- Chapter 5 presents work in progress on the analysis of upstream migration success, with the addition of fall Chinook and steelhead to the original analysis of spring Chinook only. All survival probability estimates are very high, with two segments having values of essentially 1.0. The ISAB is concerned that the lack of contrast in survival in many reaches over time will make it difficult to determine effects of other factors. What is the end-goal of this analysis and what are the management implications?
- Chapter 6 updates previous analyses to estimate the number of outgoing smolt (both tagged and untagged) that pass Bonneville. This proposed methodology appears promising, and the ISAB looks forward to its application to other species and stocks.
- The ISAB strongly emphasizes the importance of the CSS reports. There may be a tendency to think it is “more of the same” each year; however, with more than 25 years of data, the conclusions reached are now at the stage where the uncertainty in the results are small and substantial investments in physical and human capital infrastructure have been made. When funding is constrained, it is tempting to apply reductions uniformly over the entire program (e.g., reduced tagging), which will lead to an overall erosion in the quality of results (i.e., larger standard errors). A sequence of such cuts can lead to a situation where the past data are high quality, but current data are poorer quality, which makes it difficult to assess the effects of habitat restoration, climate change, or other management actions (e.g., changes in spill management). If funding is to be constrained, the entire CSS product should be reviewed in detail to see which parts are essential and which parts can be reduced without critically damaging the overall CSS program.
The ISAB appreciates the CSS’s detailed responses to suggestions provided in previous reviews. The ISAB’s full report contains an overview of the draft 2021 CSS report’s findings, suggested topics for further CSS review, and general comments and specific editorial suggestions on each chapter of the draft 2021 CSS report.