JACK MACKEREL SCIENCE
Stock Assessment
Jack mackerel Trachurus murphyi was most recently assessed in 2022 as part of the 10th annual SPRFMO Scientific Committee meeting. The stock assessment followed from a benchmark workshop held in Seattle earlier in the year. During the benchmark, scientists from around the globe met to review the input data, evaluate and revise the assessment model, and develop and interpret model diagnostics to provide guidance on the best available science for the updated stock assessment.
The assessment was produced using the Joint Jack Mackerel (JJM) statistical catch-at-age model. This model was adopted as the assessment method in 2010 and continues to be used. A technical annex has been prepared, detailing the assessment process and management advice. Using updated data inputs and indicators the model results suggest that that the jack mackerel stock status remains relatively stable since the benchmark assessment (completed in 2022) and the population trend was estimated to be increasing. Based on the assessment results, the fourth tier of the jack mackerel rebuilding plan should be applied (i.e., FMSY should be used as the basis for catch advice).
Model retrospective of spawning biomass from 5 separate model runs, based on Model h1_1.02 (single-stock hypothesis), from SC10 Report Annex 8.
Stock projections are favourable, even under the most conservative stock recruitment scenarios. Biomass is projected to be above BMSY in 2024, with a high likelihood.
Several areas of research have been identified to improve the next assessment, including: harmonizing catch-at-age estimates (from different labs); standardising CPUE indices; investigating efficiency changes in the Peruvian and Chilean fishing fleets; and further investigating data weighting and retrospective patterns. In addition, the need for continued evaluation of the performance of the assessment model under the single-stock and two-stock hypotheses was noted and is expected to be explored using simulation as part of the Management Strategy Evaluation (MSE) planned for 2023.
Harvest Strategies
The current Proposed Jack Mackerel Harvest Control Rule (2022) will be discussed at the 11th SPRFMO Commission meeting in February 2023. During that meeting, a Management Strategy Evaluation (MSE) workshop will take place to bring managers and stakeholders together to refine the objectives for this important fishery and to develop perfomace indicators which will used to evaluate how well the objectives are being met. Intersessionally, a technical group will work to develop models to simulate the jack mackerel fishery and assess which harvest strategies may be best suited to meeting the pre-agreed objectives identified during the workshop(s).
For additional background on this fishery and management in SPRFMO, please have a read of the 2020 article Successful science-based fisheries management in the South Pacific, published in A Better World - Volume 6 (humandevelopmentforum.org).