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 Celti c Sea cod. This cost function is a flexible weighed compromise between : (i) minimizing the variability in fishing effort; (ii) minimizing th e variability in yields; (iii) achieving an agreed fishing effort targ et; and (iv) achieving an agreed yield target. Increasing the weight o n the criteria (ii) and (iii), and decreasing the weight on the criter ia (i) and (iv), results in a more rapid movement of fishing effort to wards the agreed long-term target, a decrease in short-term yields, an d an increase in long-term yields. When the weight attached to (iii) i s non-zero, the optimization of the cost function provides a non-oscil latory, convergent, and near-linear control. When the weight attached to (iii) is zero, the optimization of the cost function usually result s in a non-linear divergent control, which is an artefact related to t he choice of the length of the management period. (C) 1998 Internation al Council for the Exploration of the Sea.