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George Bank Cod: Dome Assessment and Comparison with VPA and ASAP

This study assesses the ability of models to estimate correctly when doming occurs in George Bank Cod. It compares the performance of VPA and ASAP methods and analyzes the impact of dome effect on fleet and survey data. The study also addresses issues with low sampling and poor performance for older age groups.

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George Bank Cod: Dome Assessment and Comparison with VPA and ASAP

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  1. George Bank Cod • Base • Similar to GARM2005 assessment • Fleet_dome • Survey_dome • Survey_and_Fleet_dome • Purpose: test models ability to estimate correctly when doming occurs

  2. GB cod basic setup • Years 1978-2005 (27 years) • Ages 1-25, 10+ • Lengths 1-170 cm • 3 market categories • 3 surveys (CVs 20%, 30%, 25%) • CV on landings 5% • Growth stdevs 5.0 initial, 2.0 projection • Von B params 148.2, 0.1198, -0.6173 • 50% Mature ~42 cm • Selectivity flat-topped, 50% selected 64 cm • M = 0.2 • F high (0.5-2.4) then reduced in final years (0.48, 0.35)

  3. GB cod test cases • Fleet_dome • Moved ascending limb of selectivity curve left to allow for nearly full selectivity at peak of dome

  4. GB cod test cases • Survey_dome • Each survey mirrored for descending limb of selectivity curve at age 7

  5. Georges Bank Cod

  6. AIM Issues with low (or no) sampling in some years

  7. Georges Bank Cod

  8. Georges Bank Cod

  9. SCALE Issues with very low sampling in some years

  10. Georges Bank Cod

  11. VPA (SSB) Poor performance for ages>6

  12. VPA (FAA) Poor performance for ages>6

  13. Georges Bank Cod

  14. ASAP

  15. VPA vs ASAP (NAA)

  16. VPA vs ASAP (NAA)

  17. Precision (SSB and F) • AIM: ~ 0.1, did not vary by case • SCALE: 0.2-0.5 (increased with retros) • VPA*: 0.05-0.4 (poor ages>6), did not vary • ASAP: <0.05, did not vary *VPA CVs are for age-specific SSB, F

  18. GB Cod Conclusions • Simulation set-up precluded model comparisons for AIM, ASPIC, and SCALE • Between VPA and ASAP, bias was similar, but VPA estimates at age degraded faster than ASAP; ASAP more precise • Dome not an issue for survey because of age-specific indices (rather than age comp. for total N index) • Dome effect in fleet probably minimized because of large simulated F (fewer older fish, so misspecifying those selectivities added little bias)

  19. Base Fleet Dome VPA PR 2002 2003 2004

  20. VPA Fleet Dome Retro

  21. VPA q “East Coast Style” Base Survey Dome

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