AN EVALUATION OF A HARVEST CONTROL RULE USING LIMITS AND TARGET REFERENCE POINTS: AN ATLANTIC YELLOWFIN EXAMPLE

SUMMARY Managing the risks associated with uncertainty is a key concept of the precautionary approach to fisheries management. An important tool is there Management Strategy Evaluation which is able to incorporate the main sources of uncertainty into the scientific advice. A simple harvest control rule incorporating both a target F and Biomass trigger was tested for the Atlantic yellowfin tuna population using an MSE framework. The operating model was based on the 2008 ADAPTVPA base case assessment model. The MSE framework included two scenarios related to stock dynamics (OMs), two levels of data quality (OEMs) and two harvest control rules (MPs). The model simulations indicated that the major impact on the model outputs was due to value uncertainty, i.e., choice of natural mortality (M). Relatively minor changes in assumed M resulted in stock collapse. This is a matter of concern given that M is poorly known in most assessments. The MSE evaluations also demonstrated that the use of a Btrigger resulted in better performances in all cases. This would indicate that good management can compensate for deficiencies in the stock assessment. In addition, the MSE showed that under a harvest control rule, variations in advice on fishing effort and TACs are likely to occur. Future HCR development should take this into account, possibly restricting inter-annual variability in TACs and fishing effort. Although this work is considered preliminary and much additional effort is needed, the benefit of the MSE process is clear. It must be noted however, that the process is usually an iterative one where certain sources of information/uncertainty can be shown to be less important than others, and thus excluded from further analysis, effectively streamlining the evaluations.