Simulating performance of trend analysis for setting catch limits in exploratory toothfish research plans

Catch limits for toothfish in research blocks were set for the 2017/18 season using a qualitative analysis of trends in biomass estimated in each research block and a series of simple decision rules developed by WG-FSA-17. The Scientific Committee recommended that the approach be further developed and tested as a matter of priority for WG-SAM-18. We formalised and codified the rules and developed a simulation approach to examine the performance of the trend analysis rules for scenarios with high or low abundance, high or low uncertainty in biomass estimates, and for populations with increasing, stable, or decreasing trends in abundance. The trend analysis rules performed well given the expected inter-annual variability in biomass estimates, and they increased or decreased catch limits as the simulated population increased or decreased in abundance, though with a longer lag when population abundance was increasing. Further evaluations are needed to implement scenarios where populations change in response to catches and to test the overall management approach.