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Management plan evaluation of western horse mackerel

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Scott Large, ICES, at BlueBRIDGE workshop on "Data Management services to support stock assessement", held during the Annual ICES Science conference 2016

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Management plan evaluation of western horse mackerel

  1. 1. Management Plan Evaluation of western horse mackerel José A. A. De Oliveira, Beatriz A. Roel
  2. 2. HCR and MSE • Objective: – to find an HCR that would meet ICES criteria for sustainability and precaution. • Method: – modelled 100 populations w/ different stock- recruit relationships to tease apart what is causing the long recovery times and high risk of collapse.
  3. 3. MSE and BB • “simple” implementation of an MSE using R • BB: – speed up run time – Simplify adjusting parameters – Etc.
  4. 4. • Operating Model  Conditioned on WGWIDE 2014 assessment  Uncertainty based on variance-covariance matrix  Stock-recruit modelling: o Three forms (Bev-Holt, Ricker, Hockeystick) o Resampled residuals o Serial correlation included o Recruitment spikes included • Reference points (WKMSYREF3)  Long-term simulations (>100 years) • HCR  Model-free (Eggs) and model-based (SSB)  Medium-term simulations (50 years)  Include protection rule Management Plan Evaluation
  5. 5. Conclusions • Given assessment uncertainty and the status of the population at the start of projections, a suitable HCR could not be identified
  6. 6. Trade-offs: risk vs. ave catch 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 20 40 60 80 100 120 140 160 180 aveP(SSB<Blim) med (ave Catch) Years 2055-2064 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 20 40 60 80 100 120 140 160 aveP(SSB<Blim) med (ave Catch) Years 2015-2034 No Catch Current HCR Egg: g=1 Egg: g=2 Egg: g=3 SSB: g=1 SSB: g=2 SSB: g=3 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 20 40 60 80 100 120 140 160 aveP(SSB<Blim) med (ave Catch) Years 2035-2054
  7. 7. • Based on the existing information on western horse mackerel, catches above 100 000 t cannot be sustained without occasional high recruitment events (spikes). • Even under no fishing, risk 1 ≤ 5% is achieved only during the final years of a 50-year projection, and therefore, under current conditions and assuming the already-set 2014-2016 TAC/advice levels are fully adhered to, there is no HCR that will meet this risk criterion in the short- to medium-term. • Given the precautionary criterion of risk 1 ≤ 5%, the current HCR cannot be considered precautionary in the short- medium- or long-term. • The current HCR associated with a protection rule activated at low stock size is precautionary only in the long term. • Egg HCRs perform best in terms of minimising risk 1 and maximising average catch by setting the egg threshold to around 1 000×1015 eggs and applying a rapid reduction below this threshold (𝑔 ≥ 2). • For the options tested, Egg HCRs outperform SSB HCRs in terms of risk 1 and average catch in the long term (final years of a 50-year projection). • Without a mechanism for stabilising catch, SSB HCRs currently lead to more variable catches than Egg HCRs, with values of 𝛼 beyond 0.1 leading to markedly poorer performance in terms of risk 1 and average catch. Conclusions

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