While the Independent Scientific Advisory Board’s (ISAB) review of the Anadromous Fish Appendix (AFA) was underway, the National Marine Fisheries Service (NMFS) requested that the ISAB also review an addendum to that document, titled "A Cumulative Risk Analysis," and generally referred to as "the CRI." The ISAB found that:
- The CRI represents a very recent undertaking for NMFS. We understand, therefore, that our review is as much an evaluation of the future potential for this approach as it is an evaluation of the results obtained thus far. The ISAB is favorably impressed with this new approach, and recommends that it be developed further. However, the substantive results that are reported in the CRI document seem preliminary and limited.
- The CRI does not bring new "data" to the extinction analysis, and actually uses less data than were considered by the AFA for the calculation of extinction probabilities under present conditions. The "data" that the CRI uses are derived quantities and estimates obtained from other projects; the uncertainties in these quantities, which in the opinion of the ISAB could be considerable, are not analyzed in the CRI. The CRI does not resolve the major outstanding uncertainties raised in the AFA, regarding "differential delayed mortality" or "extra mortality."
- The CRI does not present an explicit synthesis of its own analysis and conclusions with those of the AFA or PATH. Such a synthesis definitely is needed, since the AFA and the CRI documents come to quite different conclusions on several important points, and arrive at those conclusions via different kinds of analysis. Because the analyses use different techniques, and operate on different subsets of the data, some careful diagnosis is warranted to explain the different conclusions, and to choose between them in making actual recommendations for the eventual decisions that these documents are intended to support. The ISAB recommends that this be done.
- The CRI brings a new element to modeling for salmon management decision support by announcing a policy of "transparency" in modeling and data analysis.
- The present CRI document only partially lives up to the intention of achieving transparency, but it represents an important step in the right direction. The modeling package has a nice logical coherence, but it still involves some difficult technical steps that need more thorough documentation. The web presentation so far is incomplete. And since the "data" are largely derived quantities obtained from other data analysis projects, simply listing those estimates does not provide enough of a paper trail to do justice to an evaluation of their uncertainties. The ISAB considers the espousal of clarity and openness in the CRI an important contribution to the use of science for supporting a decision process. We hope that NMFS will follow through on these good intentions. The model presented in the CRI needs to evolve a bit in the direction of greater complexity, to address a wider spectrum of possible interventions in greater detail, and this will add to the burden of documentation. Furthermore, some effort needs to be devoted to diagnosing reasons for the differences that may emerge between the results of the CRI modeling and other more complex and more detailed models, so as not to have a decision impasse when "the models disagree." We recognize that a commitment to thorough documentation of this sort will prove demanding of time and institutional resources, but we believe that the benefits to the quality of the science and the credibility of results are worth the institutional cost.
- The CRI presents a new modeling package for estimating extinction probability and relating this to the life table and to the effects of possible interventions.
- The new modeling package provides a clear logical framework that holds much promise. However, the actual implementation in the CRI document under review, seems very preliminary, and has some deficiencies that weaken its usefulness for the pending decision. The ISAB recommends continued development and application of this approach, recognizing, realistically, that this will require more time and resources. The present version of the model has some structural limitations that merit future attention. The particular extinction model employed represents the population growth rate as a random variable with a constant distribution. This assumes no density dependence, no deterioration of viability at very small population sizes, and no sustained trends in population growth rate over time. In the long run, these assumptions are not tenable theoretically. And in the case at hand, the assumption of no trend appears to be contradicted directly by the data. The exclusive focus on the linkage between mean growth rate and probability of extinction, in the program of analysis presented in the CRI, neglects the equally important linkage between variability in growth rates and the probability of extinction. More attention needs to be paid to factors, such as life history pattern, life history diversity, and metapopulation structure, that mediate between environmental variability and its expression in variation in salmon population dynamics.
- The CRI presents an application of the modeling package to estimate extinction probabilities for the Snake River index stocks
- The CRI largely corrects the most glaring shortcoming of the April 14, 1999 draft AFA, which reported implausibly low estimates of extinction risk. The CRI, significantly, shows quite high probabilities of extinction, if present conditions continue. The ISAB believes that these estimates are still underestimates of the actual extinction risk, because the particular extinction model employed in the CRI program of analysis ignores the apparent declining trend in growth rates over time in the listed stocks, and does not incorporate a representation of the demographic, genetic, and ecological mechanisms which generally cause population viability to decline at very small population sizes.
- With computed extinction probabilities as high as are shown with this preliminary analysis, there is no point to splitting hairs over the question whether the extinction probabilities are high enough to cause concern. The extinction probabilities definitely are high enough to cause concern. But the calculation of extinction probability will also play a role in other questions, such as analysis of the delay option, or eventual evaluation of recovery plans, and in those applications the difference between the first cut analysis of extinction probability and a more detailed and biologically realistic analysis may well matter.
- The CRI presents an application of the modeling package to identify, for the Snake River index stocks, which portions of the life history offer, theoretically, the greatest scope for reducing the probability of extinction The CRI analysis shows that the risk reduction that would hypothetically be achieved by eliminating the remaining juvenile mortality within the migration corridor (not considering delayed effects) is considerably smaller than the risk reduction that would hypothetically be achieved by eliminating the remaining mortality in some other life history stages. But this theoretical comparison does not take account of feasibility of reducing the remaining mortality in the various life history stages.
- The identification of life history stages with potential for mortality reduction to bring about reduced risk of extinction remains theoretical in the CRI, because the discussion of interventions to achieve improvements in survival (and reproduction) is pursued only superficially, and relates explicitly to defined management actions only in connection with in-river harvest, barging and passage mortality, to the neglect of effects of habitat on fecundity and rearing success, neglect of effects of hatchery production on wild populations, and without discussion of feasible measures to increase estuary and ocean survival. The CRI program of analysis shows great promise as a framework for considering a broader spectrum of management options for salmon recovery; but this promise remains to be fulfilled.
- The CRI presents an application of the modeling package to consider specifically whether dam breaching alone, or habitat improvement and harvest reduction without dam breaching, are likely to reduce the extinction risk significantly The conclusions presented in the CRI explicitly consider two questions: (a) Is it likely that dam breaching alone could raise the average growth rate enough to reduce the extinction risk significantly? (b) Is it likely that habitat improvement and harvest reduction by themselves could raise the average growth rate enough to reduce the extinction risk significantly? The tentative answer of the CRI to both questions is "possibly yes" for fall chinook and steelhead; but it seems to be a qualified "probably no" for spring/summer chinook.
- The ISAB does not find the scope of the CRI analysis of effectiveness of dam breaching versus effectiveness of habitat improvement and harvest reduction to be entirely satisfactory. The prospects for risk reduction through modification of artificial production operations needs to be evaluated as well. And, logically, the analysis should also evaluate the prospects for significantly reducing risk by the action of dam breaching AND addressing habitat and harvest and hatcheries.
- The high probabilities of extinction that the CRI shows for many of the stocks should raise the sense of urgency about the management decisions bearing on hydrosystem operations, possible dam breaching, and other interventions as well.
- The ISAB is not comfortable with the apparent drift toward delay of the actual decisions about the management decisions bearing on hydrosystem operations, possible dam breaching, and other interventions as well. The possibility that there is no time to lose in beginning to implement management experiments, while there are still enough local populations of listed stocks to work with, should put a premium on a deeper and more detailed analysis of the options. The ISAB believes that the stakes are high enough to warrant a detailed formal probabilistic decision analysis.
