The performance of a management procedure for rock lobsters, Jasus edwardsii, off western Victoria, Australia in the face of non-stationary dynamics

The biomass of rock lobster, Jasus edwardsii, has declined across southern Australia, including western Victoria. Environmentally driven changes in recruitment and high fishing mortality are likely the major causes for this decline although trends in natural mortality, catchability and growth cannot be excluded. Management Strategy Evaluation is used to evaluate a management procedure which has been proposed for rock lobsters off Victoria. This management procedure aims to recover the resource to a target level of exploitable biomass and to maintain egg production above a limit reference point. The management procedure is evaluated in terms of (i) catches, (ii) the risk of not achieving conservation goals, and (iii) the bias of estimates from the stock assessment given scenarios in which natural mortality, catchability, growth and recruitment are exhibiting future trends. In general, the exploitable biomass is driven towards the target level as expected. Changes over time in natural mortality and growth are relatively inconsequential for the performance of the management procedure, and the impact of changes over time in growth can be mitigated through ongoing tagging programs. In contrast, trends in catchability and recruitment will lead to management goals not being satisfied, with trends in catchability the most problematic because such trends lead to bias in stock assessment outcomes even if data sources which provide unbiased information on abundance are available for assessment purposes.