Report on the Assessment of a Long-term Management Strategy for Southern Horse Mackerel (hom.27.9a), 15-16 February 2018

The development of the long-term management strategy (LTMS) for southern horse mackerel (Trachurus trachurus) started in October 2014 through a dialogue process between scientists and stakeholders. The process involved the definition of management objectives, a Harvest Control Rule and several TAC setting options, the FMSY target year, and catch stability levels proposed by the stakeholders of Pelagic Advisory Council (PelAC) and the South Western Waters Advisory Council (SWWAC). The PelAC in October 2017 sent a proposal for a LTMS for southern horse mackerel to the European Commission with a request that this be scientifically assessed. The Commission re quested ICES to evaluate whether the proposed plan is seen as precautionary and to assess if the plan ensures that the stock is fished and maintained, also in future, at levels which can produce Maximum Sustainable Yield (MSY). This report presents the Management Strategy Evaluation (MSE) on the performance of the LTMS. The conditioning of the operating model is based on the latest stock assessment, following the stock benchmark in early 2017, and with recruitment stochasticity. To implement a full-feedback MSE the management procedure component includes a stock assessment and ad vice cycle. The stock assessment cycle, with observation error, is performed using a statistical catch-at-age model that mimics the current assessment method. Two hundred populations are simulated from 2017 to 2080. Performance statistics for catch, spawning–stock biomass and fishing mortality are computed for the short (2017–2027) and long term (2070–2080). The proposed LTMS, with a Harvest Control Rule defined by FMSY at 0.11, F_bycatch at 0.01, MSY B_trigger at 181 kt and Blim at 103 kt and with a ±15% catch constraint is precautionary as the probability of SSB being below B_lim is less than 5% over the entire simulated period. The long-term equilibrium catches of the LTMS are very close to MSY. Sensitivity analyses indicate that the LTMS is also precautionary in a low productivity scenario.