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

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

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

Model Fits Joint Posterior Mode Posterior Medians

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

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

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

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

An Alternative Sardine Recruit Movement Model Thank you for your attention