Environmental Engineering Reference
In-Depth Information
not feasible. At the other end of the scale are simple diagrams of people's
understanding of how the system works, which are informed by data in only a
qualitative way, and can be generated at stakeholder meetings. As we outlined in
Chapter 5, our view is that management is best served by employing a quantitative
framework, including formal modelling based on data collected in a statistically
robust and rigorous way. But the process of decision analysis is worth proceeding
with regardless of whether formal modelling is possible.
7.5.2.4 Weighing up the options
Once the model of the system has been developed, the next step is to use it to evalu-
ate the likely outcomes of different management actions. This evaluation needs to
include some kind of robustness testing, in order to see how management stra-
tegies cope when things go wrong (Box 7.7 and Section 5.3.4). The first step is to
choose a quantitative method for evaluation of the performance of management
strategies. There are three components to performance, which should reflect the
objectives decided upon in Section 7.5.2.1:
A conservation constraint , representing ecological sustainability. For exam-
ple, the population size of the exploited stock must not drop below a certain
size. This is usually taken as the over-riding objective, which must be fulfilled
first.
Some measure of the overall profitability of the exploitation, based on the
requirements of the resource users, representing financial sustainability. This
may be the catch per unit effort in a subsistence system, or the monetary
profits in a commercial system.
Some measure of the stability of the system , representing social sustainabil-
ity. This might include the equitability of distribution of the profits, liveli-
hood security of the users, stakeholder attitudes towards management or
compliance with rules.
Next we need a set of scenarios for evaluation of strategy performance. For
example, how would each of our proposed management actions perform under the
following circumstances?
Our best guess at the system dynamics, using the data that we currently have.
A crisis—either biological (a crash in prey numbers due to a bad winter or dis-
ease) or social (a major immigration, a change in hunting efficiency).
A deteriorating situation (climate change-induced drought, or gradually
increasing hunter numbers).
A major failure in our understanding of the system (the population dynamics
are completely different, the size of the population is overestimated, the popu-
lation is aggregated in space, rather than being randomly distributed,
weapons are much more efficient than realised, people are selecting their prey
differently).
Implementation is not as we might hope (low compliance with management
rules, quotas actually set are higher than the decision-makers recommend).
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