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 2020 CSS Annual Report is the ISAB’s eleventh 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 from this year’s ISAB review include:
This CSS Annual Report includes 25 years of smolt-to-adult return (SAR) data for wild Snake River spring/summer Chinook salmon (1994–2018). Averaged values calculated over time series change very little because the additional year of data represents a small fraction of the total record. For most chapters, the final conclusions are similar to conclusions in previous reports. However, 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 complex. Many of the changes in the system are summarized in Chapter 1, but the reader must infer possible impacts. The ISAB recommends the CSS to develop a table of the changes in the system over the years and a brief description of possible impacts of these changes on salmon and steelhead survival.
Chapter 2 includes a new, exploratory analysis of the patterns of survival of wild steelhead in the Basin. The life history of steelhead is more complex than the life histories of Pacific salmon, and a more thorough explanation is warranted of the consequences of steelhead life histories on the analysis and associated assumptions. Comparison of survival among the stocks that share similar migration routes may increase our understanding of factors related to steelhead survival.
Chapter 3 expands analyses of the effects of the in-river environment on juvenile travel time, instantaneous mortality, and survival. The CSS could consider a more detailed evaluation of differences detected in these variables across individual reaches to reveal factors that may affect survival.
Chapter 4 also extends the ongoing analysis of long-term patterns in annual overall SARs. By now, the low level of SARs relative to the Council’s 2%-6% objectives has been well documented. 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. In the long term, this can desensitize them to the potential consequences and relative effectiveness of alternative management actions that can better achieve the Council’s SAR objectives. The life cycle models of CSS and NOAA Fisheries rely on these estimates and provide important syntheses. In addition, the CSS could develop an Impact Report collectively with other groups to communicate the most critical take-home messages for the Council, BPA, and co-managers.
Chapter 5 continues the analyses of SARs and productivity. The ISAB suggests a number of approaches to strengthen this analysis.
Finally, Chapter 6 presents a work in progress on the analysis of spring Chinook upstream migration success. All survival probability estimates are very high, and the lack of contrast in survival in many reaches over time will make it difficult to determine effects of different factors. The CSS could clearly identify the ultimate application of this analysis and highlight alternative management actions and their potential impacts on Chinook survival.
Since 2011, the ISAB has suggested topics that warrant further CSS or regional review. The following are some of the topics recommended in 2020 for future reports:
Given the large amount of information in the CSS reports and similarity of the reports, it would be helpful to have an introductory section that highlights 1) an overall summary for the survival of salmon and steelhead survival and how the SARs for the year compare to the long-term means, 2) new analyses in the report, 3) major changes that signal emerging management concerns, and 4) recommendations for management of the hydrosystem that potentially alter or reinforce previous decisions.
The CSS could identify ways to address the spatial and temporal aspects of the effects of total dissolved gas (TDG) on acute and long-term survival.
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 2020 CSS report’s findings, suggested topics for further CSS review, and general comments and specific editorial suggestions on each chapter of the draft 2020 CSS report.
