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 - - - - Posterior Median 90% Probability Interval
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