Accounting for risk-catch-cost trade-offs in a harvest strategy for a small, highly variable fishery

Abstract

Formal harvest strategies (HS) confer increased certainty for stakeholders in decision-making processes because they include pre-agreed, transparent rules that can be simulation tested prior to implementation. An important trade-off for small, low-value fisheries relates to balancing the value of the fishery with the costs of data collection, analysis and completing a stock assessment. Harvest strategies also need to effectively balance risks to the fish stock with the objective of maximising yield or economic returns from a fishery. As part of this balancing act, short-lived highly-variable stocks present some unique challenges that need to be accounted for in a HS. We describe the process used to revise the HS for Australia’s redleg banana prawn fishery (Penaeus indicus) to address these challenges. The fishery is managed using input controls and recently implemented a seasonal closure (based on management strategy evaluation testing) to improve the robustness of the HS to extreme environmental variability while providing ecological and economic benefits. An additional positive trade-off was that this conservative measure simplified the HS and added a risk buffer to counter uncertainties due to relying solely on catch-per-unit-effort (CPUE) data as an index of relative abundance. The stock assessment model and associated hockey-stick control rule were modified to account for the high natural variability of the stock by stipulating that closure of the fishery in any given year is only deemed necessary if the limit reference point is breached in two consecutive years prior. In years with low fishing effort (whether due to ecological or economic factors), it may not be necessary to conduct a stock assessment or there may not be sufficient data to inform a reliable assessment. We analysed fishery data to inform selection of a data-sufficient cut-off threshold that triggers whether or not a stock assessment is required in any particular year. We also considered potential risks to the fishery of not doing an assessment as well as the impact of this decision rule on the performance of future stock assessments. Finally, we summarise some general lessons around pragmatic design of a HS for a small, highly variable fishery needing to balance risk to the stock with optimising catches and reducing management costs.