The ICES MSY approach to reference point estimation is not precautionary

Abstract In the Northeast Atlantic, the International Council for the Exploration of the Sea (ICES) provides scientific advice under the precautionary approach (PA) and maximum sustainable yield (MSY) principles. FMSY, the exploitation level that achieves MSY in the long term, is derived in ICES through stochastic simulations with the software EQSIM for most of the stocks. The computed FMSY is then conditioned on the PA such that fishing at FMSY does not exceed a 5% probability of the spawning stock biomass falling below the limit reference point Blim. We compared reference points estimated using EQSIM and a short-cut management strategy evaluation (MSE) tool (RPETool), which approximates a full-feedback control loop, and, differently from EQSIM, mimics the stock assessment advice process, including all data lags, and retains the original structure of the assessment model. Here, we showed that the simplifications of the management system and the assessment model, which are necessary for conducting simulations with EQSIM, result in the breaching of the PA for 3 of 4 recently benchmarked stocks. For the only stock for which the PA was not violated, the EQSIM estimate of FMSY was still larger than the actual FMSY estimated within the assessment model, and long-term yields were not maximized. Considering that EQSIM has been used since 2017 to derive reference points in ICES for more than 75% of the data-rich stocks, it is urgent that it is phased out and substituted by a more appropriate approach, like RPETool. Furthermore, the analysis highlights the asymmetry between increased risk of breaching Blim when fishing at or above FMSY and low risk in terms of the minimal loss in long-term yield when fishing below FMSY, with <5% yield loss even if F were reduced to around 60% of FMSY. Considering the wide ranges of additional uncertainties about the assessment model and the associated FMSY estimate, we propose that it is time for a paradigm shift within ICES to advocate for FMSY being the upper limit for advice on fishing opportunities rather than the target.