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Gulf of Maine cod SCAA/ASPM vs ADAPT-VPA Doug Butterworth and Rebecca Rademeyer

Analysis of Gulf of Maine cod stock using ADAPT-VPA and ASPM methods. Detailed examination of age data errors and stock-recruit relationships. Comparison of VPA methods and assessment results post-1991. Key conclusions and recommendations provided.

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Gulf of Maine cod SCAA/ASPM vs ADAPT-VPA Doug Butterworth and Rebecca Rademeyer

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  1. Gulf of Maine codSCAA/ASPM vs ADAPT-VPADoug Butterworth and Rebecca Rademeyer __________________________________________________________________ Marine Resource Assessment and Management Group, University of Cape Town

  2. METHODS ADAPT-VPA- Backward calculation- Oldest-age F assumption- Catches-at-age exact SCAA/ASPM- Based on separability: Fy,a = SaFy- Forward estimation, typically likelihood based- Errors in proportions-at-age SCAA - Statistical treatment of age data errors May include S/R relationshipASPM - Age-structured dynamics Must include S/R relationship Age data not necessary

  3. Ricker-like not Beverton-Holt S/R relationship ASPM methodology updates • M fixed (0.2) (not estimated) - All Sa’s estimated (no functional form imposed) - Model to 11+, though fit to 7+ data • MSY calculated internally - Fully Bayesian PI computations

  4. - Alt-VPA (a=est): estimates a where VPA methodology • RC-VPA: as Mayo and Col (2006) – asymp. flat selectivity - Alt-VPA (a=1): removes inconsistency in plus-group eqns Fit either to ages 1-6 or 1-7+MSY calculated externally

  5. BUTScaled to get Data used Mayo and Col (2006)

  6. 2003 ResultsGulf of Maine cod

  7. ResultsRC-ASPM(M=0.2, Ricker) Shading shows 95% PIs

  8. Abundance index fitsRC-ASPM(M=0.2, Ricker)

  9. Average age-proportion fitsRC-ASPM(M=0.2, Ricker)

  10. Selectivity estimatesRC-ASPM(M=0.2, Ricker) Commercial, pre-1992 Commercial, post-1991

  11. Selectivity estimatesRC-ASPM(M=0.2, Ricker) Commercial, pre-1992 Commercial, post-1991 NEFSC-Spring NEFSC-Autumn

  12. ASPMStock-recruit relationships Ricker -lnL = -46.3

  13. ASPMStock-recruit relationships Ricker Beverton-Holt -lnL = -46.3 -lnL = -39.9 If estimate g parameter (g =1 for Ricker): 1.05 [0.54; 1.15]

  14. -lnL = -11.4 Asymp. flat selectivity ASPMSelectivity dome -lnL = -46.3 S7/S6 =0.52 [0.41; 0.64]

  15. Per-recruit contribution to cohort biomass ASPMPast catch selectivity 1992-2004: Estimated 1981-1991: Estimated Pre-1982: Set equal to 1982-1991 Second order effect (Important assumption is unchanging survey selectivity)

  16. ASPM Results

  17. ASPM Results

  18. ASPM Results

  19. ADAPT-VPA comparisons VPA as Mayo and Col (2006)

  20. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA

  21. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA Alt-VPA, a=1

  22. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA Alt-VPA, a=1 Alt-VPA, a=est

  23. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA Alt-VPA, a=1 Alt-VPA, a=est ASPM – Data from 1982

  24. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA Alt-VPA, a=1 Alt-VPA, a=est ASPM – Data from 1982 RC – ASPM

  25. ADAPT-VPA comparisons VPA as Mayo and Col (2006) RC-VPA Alt-VPA, a=1 Alt-VPA, a=est ASPM – Data from 1982 RC – ASPM

  26. ADAPT-VPASelectivities RC-VPA

  27. ADAPT-VPASelectivities RC-VPA Alt-VPA, a=1

  28. ADAPT-VPASelectivities RC-VPA Alt-VPA, a=1 Alt-VPA, a=est

  29. ADAPT-VPASelectivities RC-VPA Alt-VPA, a=1 Alt-VPA, a=est ASPM – Data from 1982

  30. ADAPT-VPASelectivities RC-VPA Alt-VPA, a=1 Alt-VPA, a=est ASPM – Data from 1982 RC – ASPM

  31. ADAPT-VPA Results

  32. ADAPT-VPA Results

  33. ADAPT-VPA Results

  34. ConclusionsGeneral • Careful treatment of plus-group • Fully flexible Sa parametrization • Take care with use of Beverton-Holt S/R relationship

  35. ConclusionsGulf of Maine cod • close to and • 2003 difference as ADAPT-VPA imposed asymp. flat selectivity • Asymp. flat selectivity statistically inconsistent with data Independent evidence of mechanisms to give dome shape ? Robust to sensitivities • SCAA to be preferred Enables use of pre-1982 data Greater range of Bsp Better precision of estimates M-S Act focus on MSY

  36. Thank you for your attention

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