Estimating sustainable harvests of Patagonian toothfish in Chile
Creators: name: Quiroz Espinosa, Juan
Publisher: name: University of Tasmania
Year: 2024

description: This thesis outlines practical guidelines to analyse and discuss the Patagonian toothfish fishery management system in Chile, examining the usefulness of fishery modelling, which must be addressed to improve the effectiveness of harvest strategies off the austral zone of Chile. Stakeholder-based fisheries management aims to reconcile conservation and economic interests within the framework of sustainable fisheries management. Developing suitable population models and decision rules for managing exploited populations is important for achieving these goals. However, these tools need to expand beyond developing the optimal stock assessment model and the associated management actions, common operational attributes of fisheries management policy in Chile. <br>Understanding the linkages between the fisheries management elements (e.g., modelling approaches, fishing pressure control target, and management plans) relies on knowledge of drivers of the decision making. The Patagonian toothfish fisheries management system in Chile shows several deficiencies, such as limited flexibility for regulating the fishing fleets’ deployment to limit fishing pressure, limited understanding of population dynamics expressed in mis-specified stock assessment models, and the lack of key elements within harvest strategies such as a supportive fisheries management plan. These shortcomings arise from inconsistencies between management policies and their implementation, obstructing the integration of management, individual incentives, social interests, and cultural perspectives, all of which are components necessary to developing the ecosystem approach to fisheries (EAF). The EAF has been mandated by the laws and policies regulating fishing and exploited species in Chile, unfortunately however, the EAF has yet to be incorporated into the management of the Chilean Patagonian toothfish fishery. <br>The Patagonian toothfish monitoring program in Chile has detected imprecision in fishery data, such as catch series and fishing grounds, influencing the decision-making about deploying fishing efforts and catch limits. Detecting illegal fishing activities using a data mining machine learning method (Association Rule Mining, ARM) reveals important fishing attributes that could be used to identify biases that potentially distort Patagonian toothfish catches. It is expected that, while likely challenging to implement, the integration of these outcomes within the compliance management plan for the Patagonian toothfish will have substantial benefits for data collection and subsequent assessment and management of this stock. <br>In Chile, decision-making for the Patagonian toothfish fishery has relied upon outcomes from population assessment models and inflexible Harvest Control Rules (HCR) defining the target fishing mortality of Patagonian toothfish. A simulation-based HCR analysis extends the current strategic decision-making scope by integrating several options to define target fishing mortality. Trade-offs between several performance measures were used to define the relevance of candidate HCRs. The HCR’s importance varies according to both the biological Reference Points (RP) and the expected time to achieve the Patagonian toothfish management targets. Simulation suggests that all evaluated HCRs produce more robust outcomes than the HCR used by the current harvest strategy. <br>To improve the sustainable harvest of Patagonian toothfish, it is necessary to understand both the catch bias and HCRs selection impacts. A Management Strategy Evaluation (MSE) framework based on the current Chilean stock assessment model was used to evaluate the consequences of biased catches because of illegal, unreported and unregulated (IUU) fishing for Patagonian toothfish off the Chilean austral zone and the mis-specification of population biological productivity, which increase management uncertainty. The MSE also demonstrated that HCRs which are dependent upon the ratio of current spawning biomass to unfished spawning biomass are more efficient than the current fixed fishing mortality HCR. Future projections show that the impact of misreported catches specifically affects the average population levels, in contrast to HCRs, which impact the future trend populations and, as such, the achievement of Patagonian toothfish management objectives. This thesis aspires to help improve the current management system for Patagonian toothfish by enhancing some key elements of scientific advice and providing guidelines for improving fishery management for the Chilean toothfish stock