Research Document 2020/021
Evaluation of Rebuilding Strategies for northwestern Atlantic Mackerel (NAFO Subareas 3 and 4)
By Van Beveren, E., Marentette, J.R., Smith, A., Castonguay, M., and Duplisea, D.E.
Abstract
In 2017, the biomass of the northern spawning contingent of Western Atlantic mackerel was estimated to have been below its Limit Reference Point (LRP) since 2011, and this resulted in the establishment of a Rebuilding Plan Working Group (RPWG). Within this context and with the participation of all RPWG members, a Management Strategy Evaluation focusing on rebuilding strategies was developed. This included the specification of nine potential Harvest Control Rules (HCRs), of which the performance was measured in terms of three management objectives under eight uncertainty scenarios. The analyses corroborated the 2019 assessment results regarding the stock being below its LRP. Few HCRs met the developed objectives and no single HCR met all objectives under all uncertainty scenarios, mainly as a result of the current stock state and the large uncertainty in total removals. The HCR that most closely reflected the current 2019 Canadian TAC (8,000 t) failed to meet all candidate performance thresholds for all objectives and shorter-term milestones. Simulation also showed that high future floor catches (6,000 t to 10,000 t) were over the next 3 to 10 years progressively more likely to result in stock declines than increases. Given that stock rebuilding above the LRP might not be possible over the short term, the use of rebuilding milestones (3-5 years) is recommended, as well as improving management through a reduction of total catch uncertainty.
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