Optimization of a large-scale scallop hanging culture operation

Scallop aquaculture may be conducted by deploying the bivalves in a sequence of suspended containers in the ocean. The growth and mortality rates at each stage depend partly on the period in which they are deployed and the duration until they are harvested. For a large-scale hanging culture operation, a linear program was created to determine the optimal duration for each stage of the growout process which maximizes the net present value of the profits. Evaluations were made on the effects of limits on the handling of containers during each period, bounds on the sales of mature scallops to smooth the system output, and restricted overall capacity. At the general level, the model illustrates the nature of the start-up period, and the expected cycles of expenditures and revenues. From a detailed perspective, the fluctuations in activity levels between periods and seasons provides insights for streamlining production and the relative value of the resources for planning purposes. Some interesting phenomena appear in an analysis of a representative aquaculture farm. In maximizing profits, the scallop sales pattern is very spiky. Placing a smoothing restriction on final harvests does not affect profit much, and has an unexpected benefit of levelling manpower better than a constraint on labour. The effect of increasing the workforce or productivity is demonstrated by the use of shadow prices. The maximum scallop throughput for a given lease area and spacing can also be estimated. (C) 1999 Elsevier Science B.V. All rights reserved.