Increasing fisheries management options with a flexible cost function

This study proposes a dynamic control of fisheries by fishing effort, calculated so as to optimize a novel cost function, over a long period of management, based upon an example of the exploitation of the Celtic Sea cod. This cost function is a flexible weighed compromise between: (i) minimizing the variability in fishing effort; (ii) minimizing the variability in yields; (iii) achieving an agreed fishing effort target; and (iv) achieving an agreed yield target. Increasing the weight on the criteria (ii) and (iii), and decreasing the weight on the criteria (i) and (iv), results in a more rapid movement of fishing effort towards the agreed long-term target, a decrease in short-term yields, and an increase in long-term yields. When the weight attached to (iii) is non-zero, the optimization of the cost function provides a non-oscillatory, convergent, and near-linear control. When the weight attached to (iii) is zero, the optimization of the cost function usually results in a non-linear divergent control, which is an artefact related to the choice of the length of the management period.