8. Vital Sign vs. Assessment Indicators

Ranking schemes provide a mechanism for narrowing the long list of indicators presented above to a more manageable set that facilitates inference about the status of the Puget Sound ecosystem. Here we suggest that focusing on the specificity and sensitivity of an indicator, in combination with its performance against the “understood by the public and policymakers” criterion introduced above, provides a framework for reporting on the status of Puget Sound.

Previous indicator development efforts in the Puget Sound region (e.g. O’Neill et al. 2008) and beyond (e.g. Recchia and Whiteman 2009) have advocated a two-pronged approach to indicator reporting. Recchia and Whiteman (2009) refer to a coarse-grained evaluation of ecosystem status and trends. This level of indicator reporting is aimed at the general public and policy makers with the goal of providing a limited number of “vital signs” of the ecosystem. Vital Signs may not be very specific, and they do not need to be sensitive on any particular time scale. For instance, abnormalities in blood pressure or temperature indicate some malady, but do not suggest a specific pathology. Likewise, changes in Chinook salmon abundance may be brought about by alterations to water quality, habitat, climatic factors, fishing or numerous other factors, in the marine, freshwater, or terrestrial domains of Puget Sound. Nonetheless, it is likely that changes in Chinook salmon represent a shift in the “health” of the system (Figure 8). As regional managers and scientists consider assembling portfolios of Vital Sign indicators, some indicator criteria may be more important than others. For example, it is clearly crucial that the indicator be understandable to the general public. On the other hand, understanding the variance structure of such indicators may be less critical. By carefully crafting a weighting scheme as described in Section 5.6, it is possible to systematically sift through a large inventory of indicators to generate a short-list of scientifically credible vital sign indicators. Ultimately, the goal of Vital Sign indicators is to provide a limited number of scientifically meaningful, but simple metrics that can generally inform the public and policy makers about the state of the ecosystem.

Figure 8. Indicator species in Puget Sound plotted according to whether they reliably track few (diagnostic) or many (non-specific) Species and Food Web attributes (x-axis) and whether they respond quickly (early warning) or slowly (retrospective) to perturbations. The ranking of indicators as diagnostic vs. non-specific is relative and based on the analysis in Samhouri 2009. The ranking of indicators as early warning vs. retrospective is also relative, and based on the production to biomass ratios of these seven species. Adapted from Rapport 1985.

Figure 8

In contrast to Vital Sign indicators, Ecosystem Assessment indicators provide a technically more robust and rigorous understanding of ecosystem structure and function. Assessment indicators provide the detailed information necessary to diagnose specific problems, develop strategies to mitigate these problems, and monitor responses of the ecosystem to management actions on multiple time scales. Thus, Ecosystem Assessment indicators should be diagnostic rather than non-specific, but can span a range of sensitivities, so that a full set includes both early warning and retrospective indicators. The audience for these indicators is scientists and managers who require a detailed understanding of the ecosystem; consequently, criteria related to the technical performance of the indicator should be given increased weight relative to criteria related to salience.

Key Point: Ranking indicators requires careful consideration of the relative importance of evaluation criteria. The importance of the criteria will certainly vary depending on the context within which the indicators are used and the people using them. Thus, ranking requires that managers and scientists work together to weight criteria. Weighting schemes that emphasize communication will inform the selection of Vital Sign indicators, while weightings that stress technical aspects of the data will inform the selection of Ecosystem Assessment Indicators.