4.1. Definition of the decision problem
The decision problem of interest is summarized in Table 1. The only possible action available to the decision maker concerns the amount of hectares of new concessions to be granted to clam farmers. The solution is constrained in the interval [1300, 1450] ha, where 1300 ha corresponds to the current allocated area, while 1450 ha is the maximum extension the administrators estimate as feasible. Three indicators are considered for assessing the performance of the evaluated control options:
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The Net Present Value (NPV) of aquaculture cash flows takes into account the pure economic aspect of the problem. End-users aim at maximizing the revenue from aquaculture to boost the economic development of the area.
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The Lagoon Water Quality Index (LWQI) (Viaroli et al., 2005) expresses a pure environmental criterion related to water quality. Local administrators aim at preserving water quality, and hence at maximizing this indicator, in order to ensure a sustainable development.
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The ratio of the Wasted Exergy (WE) to the NPV (Verdesca et al., 2006) for the aquaculture economic sector (denoted by WE/NPV) expresses a mixed environmental and economic criterion. Minimizing this indicator corresponds to a more efficient use of the lagoon ecosystem.