Limitations of PATH’s Models

PATH's escapement projections under the current operations scenario (option A1) were significantly higher that what was actually observed for recent years. This is primarily because the models were designed to make relative comparisons of actions over 100 years, and not short-term predictions. For example, year effects were sampled from the last 40 years of stock performance, not only from the poorer conditions that have generally prevailed since 1977. Although we have no reason to suspect differences in the relative performance of actions from this bias, the forecasted probabilities of survival and recovery are probably over-optimistic for all actions. Recent model projections have confirmed that most stocks would be likely to go extinct under current management if the poor post-1985 year effects were assumed to continue into the future.

As with any model, certain processes were deliberately excluded because of both a lack of understanding and a need to keep the scale of complexity reasonable. The PATH life cycle models did not consider interactions between populations (e.g., straying) that could affect productivity through changes in genetic diversity. The impacts of upstream storage projects were only considered in the models in terms of changes in smolt travel time to the estuary; other mechanisms of impact (e.g., changes in salinity) could also be important. The models also did not consider changes in the quantity and quality of mainstem river habitat other than those caused by the hydrosystem.

At a higher level, the PATH decision analysis only considered biological impacts. A logical next step would have been to combine biological, social, and economic performance measures into an integrated decision analysis that could examine all uncertainties and trade-offs. However, the social, economic, tribal, cultural, and recreation impacts of the actions under consideration were examined in a separate effort from PATH (the Lower Snake River Feasibility Study, under the direction of the U.S. Army Corps of Engineers), and it proved to be infeasible to complete an integrated decision analysis. The Water Use Planning Process developed to evaluate hydrosystem operations at 20 facilities in British Columbia offers a promising approach to integrating social, economic, and environmental objectives (McDaniels et al. 1999).