Review of Comparative Survival Study draft 2017 Annual Report

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The Columbia River Basin Fish and Wildlife Program tasks the Fish Passage Center Oversight Board to work with the Fish Passage Center (FPC) and the ISAB to ensure independent and timely science review of FPC’s analytical products. These reviews include evaluations of the Comparative Survival Study’s (CSS) draft annual reports. The ISAB has reviewed these reports annually beginning seven years ago with the evaluation of the CSS’s draft 2010 Annual Report. This review of the draft 2017 CSS Annual Report is the ISAB’s eighth review of CSS annual reports.

The annual CSS report is a mature product, typically including only updates with the latest year of data and expansion of analyses as more data are acquired. Many of the methods have been reviewed in previous ISAB reports, and so these methods now receive only a cursory examination. 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 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.

Chapter 2 (Life-cycle modeling) has been 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. As in the last report, the model examined 12 spill/flow scenarios. Similar to last year’s results, more spill generally leads to higher in-river survival and improved SARs. A new component to this chapter is the modeled scenario exploring the impact of breaching four Snake River dams. The model predicts an increased in-river survival by about 10 percentage points and a doubling of SARs when dams are breached. The addition of the breach scenarios was a nice complement to the spill scenarios, producing interesting results. Further consideration of assumptions used in both sets of scenarios and recommendations for experiments (short of an actual breach) that could be done to test model results would be useful.

Chapter 3 (Effect of the in-river environment on juvenile travel time and survival) is updated with new data. In addition, a preliminary investigation of the impact of total dissolved gas (TDG) on the instantaneous mortality and survival probabilities parameters was made using a graphical approach. 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.

Chapters 4 (Patterns in SARs), Chapter 5 (SARs and productivity), and Chapter 6 (SARs for Snake River subyearling Chinook) are updated from previous years by including new population groups. As in past reports, pre-harvest SARs of 4%-6% are associated with pre-1970 levels of productivity for Snake River spring/summer Chinook. An unanswered question is that 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%-6%?

Chapter 7 (Patterns of variation in age-at maturity for PIT tagged fish) is the same model as past years with recent data incorporated. The chapter is exploratory, and now sufficient data may be available to try to elucidate factors associated with observed changes.

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.

Suggested Topics for Further Analysis

The latest CSS Report incorporates many of the ISAB’s past suggestions. For example, the current report has a substantial discussion of correlations among SARs from different regions or effects of transport on SARs, and the life-cycle modeling now allows for variation in stream productivity and hydrosystem survival and simulates the correlative impacts of these changes on predicted future population abundances. The ISAB appreciates this effort to respond to past queries.

Some of the past recommendations from the ISAB appear to be beyond the current scope of the CSS (see several from 2016) but will become increasing important in the future. Some of the ISAB’s earlier and current recommendations may seem repetitive and unachievable to be accomplished within a year to inform the next report, but they deserve some forward planning as these issues will become much more pressing in the future. In particular, if there are data gaps, these gaps should be identified for potential new data collection procedures. When life-cycle models are modified, the modification should be flexible enough to incorporate these issues. This is reflected in the ISAB’s recommendations for future work below.

The ISAB recommends 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. For example, rather than using a single year to represent future flow conditions, variable flow conditions should be used to study the impact of flow/spill modifications under future climate change, and examine correlations between Pacific Decadal Oscillations (PDOs) and flows. What assumptions are being made about in-river predation under dam breach scenarios? What assumptions are being made about harvest under dam breach scenarios? Why are there discrepancies between the results of the Life-Cycle Model (Chapter 2) and the COMPASS model (refer to #4 in 2016)? The same scenarios should be run through both models and discrepancies resolved.

  2. Include other important processes in the life-cycle models. In the current CSS analyses, each modeled population does not interact with other modeled populations as they migrate through the hydrosystem. 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. Similarly, there has been a great deal of interest in the impact of predator control programs on salmon returns, especially northern pikeminnow, birds and pinnipeds. Are these programs effective? Are there compensatory responses? Is there evidence in the existing data about either issue? What type of data would be needed to address these issues and include them in the life-cycle models? This recommendation builds upon previous ISAB recommendations.

  3. 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.

  4. 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.

  5. 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?

  6. 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.