Review of the Comparative Survival Study (CSS) Draft 2014 Annual Report

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Note: The original ISAB report dated October 14, 2014 was updated October 29, 2014. See the correction statement.


The Northwest Power and Conservation Council’s 2009 amendments to the Columbia River Basin Fish and Wildlife Program call 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 draft annual reports. The Independent Scientific Advisory Board’s (ISAB) reviews began four years ago with the evaluation of the CSS’s draft 2010 Annual Report (ISAB 2010-5), followed by a review of the draft 2011 Annual Report (ISAB 2011-5), the draft 2012 Annual Report (ISAB 2012-7), and most recently a review of the draft 2013 Annual Report (ISAB 2013-4). This ISAB review of the draft 2014 CSS Annual Report is the ISAB’s fifth review of CSS annual reports in response to the Council’s 2009 Program.


This ISAB evaluation begins by suggesting topics for further CSS review, then provides comments on each chapter of the CSS Draft 2014 Annual Report, and ends with editorial suggestions. Most of the CSS's draft 2014 report is an annual update of information in previous years’ reports.

Overall, this year’s report was well done. Many of the previous reviews’ suggestions have been implemented, making current reports much easier to read and digest. Our review, therefore, focuses on new information presented. For all chapters, except Chapter 2 (Life Cycle Model), the ISAB therefore had, at most, minor concerns. However, for the new material in Chapter 2, the ISAB had significant questions and concerns about the methodology used to combine information from multiple sources, particularly the approach to combine likelihood and Bayesian paradigms. The ISAB suggests that, in the final 2014 annual report and future project documents, the authors provide additional rationale and justification for the approaches used to combine information from multiple sources. Further, results presented in Figures 2.7 onwards produced some unexplained patterns. For example, why did the models tend to consistently underestimate observed survival in freshwater and overestimate survival in the ocean? These patterns may indicate a systematic error in the models. If so, what is the cause of this, and can it be addressed?

The results of Chapter 6 (tag-effects experiment) are very preliminary. However, by the end of 2014, half of the adult production expected from this study will have returned to the Carson Hatchery. Next year’s report should also include information on the number of adults produced and the tag loss rates experienced by each tag group. As the SARs become available in future years, this should result in an important peer-reviewed publication.

Overall, the ISAB believes the CSS reports provide valuable information and analyses that are fundamental for evaluating the survival of Columbia Basin salmonids.

Suggested Topics for Further Review

(a)    Hypotheses on mechanisms regulating smolt-to-adult return rates (SARs). The previous ISAB review had several suggestions on mechanisms regulating SARs,to which the CSS response was that it was “out of scope” of their mandate. That being the case, and since the CSS reports provide much of the data necessary for investigation of these questions, the ISAB strongly recommends that the information be available in digital formats. This will allow researchers interested in mechanisms regulating SARs to have easy access to the data. With the time series now approaching 20 years for some stocks, methods such as those in Pyper et al. (2001) may be suitable to investigate correlational patterns in migration timing, in-river survival, ocean survival, and SARs among stocks over large spatial scales to infer common effects on disparate stocks.

(b)   Life-cycle modeling questions and Fish and Wildlife Program SAR objectives. The previous ISAB review provided two questions that the life-cycle model should be able to answer.

(1)    "What changes in stream productivity [salmonid productivity in rearing streams] would be required to achieve population recovery if hydrosystem survival were to remain at the status quo?"

(2)     "What changes in hydrosystem survival would be required to achieve a 20% increase in population abundance by a particular time in the future?"

The CSS response agreed that these were important questions and felt that the next iteration of the model would be able to answer at least one of the questions. However, potential problems in the current model’s implementation may preclude answering either question at this time. The ISAB believes that it is still important to answer these questions in subsequent years.

(c)    New PIT/CWT study. The current study design, described in Chapter 6, may only detect the minimal potential adverse PIT tag effects experienced by fish in the Basin. In this experiment, larger fish are tagged before smoltification and fish are allowed to recover for several months from tagging stress. However, many field studies in the Basin apply PIT-tags to migrating smolts (some as small as 60 mm) captured in the field during warm water periods and release them soon afterward. To fully appreciate the potential impacts of PIT tags on survival and to adequately link these effects to fish tagged, a study paralleling those conditions should be performed.

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