3. Target, benchmark, limit, and precautionary reference levels

A construct that has been particularly successful in the realm of fisheries management is the distinction between target and limit reference levels (Figure 9). A target is a reference level that signals a desired state, whereas a limit is a reference level pegged to an extreme value beyond which undesired change occurs (Jennings and Dulvy 2005, Caddy 2002).

In fisheries and marine EBM limit reference levels thus identify what is to be avoided (Sainsbury 2000), and can be used to redirect and prioritize management action before irreversible harm occurs. Because of uncertainty inherent to the measurement of any indicator, precautionary or warning reference levels that are more conservative than the limit reference levels may be used (Figure 9; Jennings and Dulvy 2005, Link 2005). Target reference levels identify what is to be achieved (Sainsbury et al. 2000), and in so doing allow managers and policymakers to determine when their efforts and resource allocations have been sufficient (Bottrill et al. 2008). Because indicators respond at varying rates to management actions, target reference levels may be most useful when accompanied by benchmarks, or indicator values suggestive of progress toward targets (Figure 9).

In Puget Sound, the PSP has taken it upon itself to establish targets and benchmarks. Because of legislated restoration and protection deadlines, the PSP has associated a timeline with target and benchmark reference levels. The PSP defines a target as a “desired future numeric value for an ecosystem status indicator in 2020.” Similarly, the PSP describes a benchmark as a “measurable interim (i.e., pre-2020) milestone set to demonstrate progress toward a target for an ecosystem status indicator” (Puget Sound Partnership 2009c).

Importantly, the indicator associated with a target reference level need not be identical to the indicator associated with the corresponding benchmark. The current financial crisis provides a useful parallel to illustrate this point. The onset of the economic recession in the U.S. was characterized in part by a Gross Domestic Product (GDP) that fell for several months (National Bureau of Economic Research 2008). Thus a target reference level for economic recovery could be measured in terms of a consistent month-to-month rise in GDP. Benchmarks for measuring progress toward this target included a variety of indicators other than GDP, however, such as the number of new unemployment claims filed and new construction permits issued each week (The Business Conference Board 2001).

In the context of Puget Sound, a fundamental goal is to achieve a healthy and sustaining population of southern resident killer whales (SRKWs) (Puget Sound Partnership 2008a), and one indicator of SRKW population status is the number of individuals in the population. The target reference level associated with the goal of SRKW population recovery may be measured using this indicator, but because the likely response time for achieving the target is several decades, a benchmark might be set using a different indicator, such as a reduced infant mortality rate or an increased annual population growth rate (National Marine Fisheries Service 2008).

Because they are a primary interest of the PSP, we focus on approaches for determining target reference levels rather than limits. Though our discussion is framed largely in terms of reference points, we see no reason why targets cannot be defined in terms of reference directions, at least in the short term. However, it is not obvious how to distinguish a benchmark from a target using reference directions alone.