Recommendations
That WG-SAM note these preliminary explorations of alternative decision rules for managing toothfish fisheries, which indicate that an approach based on a harvest rate H:
- Would be consistent with the CCAMLR decision rule and its objective, and;
- Could provide a higher level of predictability and certainty about the likely changes in future catch limits, and reduce fluctuations in stock size around the target level in the long term.
Abstract
In this paper, we conducted simple simulations to outline alternative decision rules with the potential to manage toothfish fisheries according to the current CCAMLR decision rule. In contrast to the current decision rule, the rules in this paper were based on a harvest rate H which was stochastically estimated from the stock productivity and fishery selectivity to result in the long-term 50% SSB depletion with a probability of 50%. Catch limits were then calculated from the harvest rate, the fishery selectivity and the current vulnerable stock biomass, bound by minimum and maximum levels of change to reduce short-term variability in the catch limit. We evaluated two different types of decision rules (constant H and hockey-stick response function for H). All evaluated scenarios demonstrated that:
- The SSB target level was reached in around 35 years in all simulations, indicating that an approach based on a harvest rate would be consistent with the CCAMLR decision rule and its objective;
- The expected catch limit variability between assessments would be around 5–10% on average and rarely hitting the 20% maximum level used here.
An alternative rule based on a harvest rate could provide a higher level of predictability and certainty about the likely changes in future catch limits, and reduce fluctuations in stock size around the target level in the long term.