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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. GB cod basic setup. Years 1978-2005 (27 years) Ages 1-25, 10+ Lengths 1-170 cm 3 market categories

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George bank cod l.jpg
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


Gb cod basic setup l.jpg
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)


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GB cod test cases

  • Fleet_dome

    • Moved ascending limb of selectivity curve left to allow for nearly full selectivity at peak of dome


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GB cod test cases

  • Survey_dome

    • Each survey mirrored for descending limb of selectivity curve at age 7



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AIM

Issues with low (or no) sampling in some years




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SCALE

Issues with very low sampling in some years



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VPA (SSB)

Poor performance for ages>6


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VPA (FAA)

Poor performance for ages>6






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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


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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)


Vpa pr l.jpg

Base

Fleet Dome

VPA PR

2002

2003

2004




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