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An Alternative Sardine Recruit Movement Model

An Alternative Sardine Recruit Movement Model. SPSWG Meeting 31 st October 2013 Carryn de Moor Doug Butterworth. Marine Resource Assessment and Management Group (MARAM) Department of Mathematics and Applied Mathematics University of Cape Town. Alternative Movement Relationship.

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An Alternative Sardine Recruit Movement Model

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  1. An Alternative Sardine Recruit Movement Model SPSWG Meeting 31st October 2013 Carryn de Moor Doug Butterworth Marine Resource Assessment and Management Group (MARAM) Department of Mathematics and Applied Mathematics University of Cape Town

  2. Alternative Movement Relationship • FISHERIES/2013/OCT/SWG-PEL/28 – movement may increase/decrease over time depending on whether a ‘favourable’/‘unfavourable’ environmental state exists on the south coast • Years of historic switches (1994, 2003, 2009) from STARS analysis

  3. Alternative Movement Relationship • Model assumes two possible regimes, each with its own “equilibrium” proportion moving • Predicted proportion moving approaches the equilibrium level asymptotically via a geometric series • Fit model to both estimated proportions at joint posterior mode and median values of posterior for annual movement

  4. Model Fits Joint Posterior Mode Posterior Medians

  5. Model Fits 90% Probability Interval - - - - Posterior Median Joint Posterior Mode Posterior Average

  6. Future Movement • Last “switch” was in 2009 to the higher equilibrium state (increasing proportions moving) • Future “switches” every 5-7 years • Based on model fit to posterior medians

  7. Future Projected Movement (No Catch Scenario) Ratio of “south” : “west” 1+ biomass (Bs:Bw) Environmental switching Posterior Median Joint Posterior Mode

  8. Future Projected Movement (No Catch Scenario) Favourable environment Unfavourable environment

  9. An Alternative Sardine Recruit Movement Model Thank you for your attention

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