# Presentation: 680720

## 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
- 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)

## GB cod test cases

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

## GB cod test cases

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

## Georges Bank Cod

|  | BASE | Fleet Dome | Survey Dome | Fleet&Surv. Dome |
| --- | --- | --- | --- | --- |
| AIM | SSB: strong bias
F: -40% to+20% |  |  |  |
| ASPIC | One way trip problem |  |  |  |
| SCALE | SSB: 5-30% +
F: ~30% - |  |  |  |
| VPA | SSB: slightly +
F: slightly - |  |  |  |
| ASAP | SSB: slightly +
F: slightly - |  |  |  |

## AIM

- Issues with low (or _no_) sampling in some years

## Georges Bank Cod

|  | BASE | Fleet Dome | Survey Dome | Fleet&Surv. Dome |
| --- | --- | --- | --- | --- |
| AIM | SSB: strong bias
F: -40% to+20% | Division by zero problem |  |  |
| ASPIC | One way trip problem |  |  |  |
| SCALE | SSB: 5-30% +
F: ~30% - |  |  |  |
| VPA | SSB: slightly +
F: slightly - |  |  |  |
| ASAP | SSB: slightly +
F: slightly - |  |  |  |

## Georges Bank Cod

|  | BASE | Fleet Dome | Survey Dome | Fleet&Surv. Dome |
| --- | --- | --- | --- | --- |
| AIM | SSB: strong bias
F: -40% to+20% | Division by zero problem |  |  |
| ASPIC | One way trip problem |  |  |  |
| SCALE | SSB: 5-30% +
F: ~30% - | Low simulated length sampling obscured
the effect we were testing for |  |  |
| VPA | SSB: slightly +
F: slightly - |  |  |  |
| ASAP | SSB: slightly +
F: slightly - |  |  |  |

## SCALE

- Issues with very low sampling in some years

## Georges Bank Cod

|  | BASE | Fleet Dome | Survey Dome | Fleet&Surv. Dome |
| --- | --- | --- | --- | --- |
| AIM | SSB: strong bias
F: -40% to+20% | Division by zero problem |  |  |
| ASPIC | One way trip problem |  |  |  |
| SCALE | SSB: 5-30% +
F: ~30% - | Low simulated length sampling obscured
the effect we were testing for |  |  |
| VPA | SSB: slightly +
F: slightly - | slightly -
slightly + | Same as base (‘E.coast way’) | Same as “Fleet Dome” |
| ASAP | SSB: slightly +
F: slightly - |  |  |  |

## VPA (SSB)

- Poor performance for ages>6

## VPA (FAA)

- Poor performance for ages>6

## Georges Bank Cod

|  | BASE | Fleet Dome | Survey Dome | Fleet&Surv. Dome |
| --- | --- | --- | --- | --- |
| AIM | SSB: strong bias
F: -40% to+20% | Division by zero problem |  |  |
| ASPIC | One way trip problem |  |  |  |
| SCALE | SSB: 5-30% +
F: ~30% - | Low simulated length sampling obscured
the effect we were testing for |  |  |
| VPA | SSB: slightly +
F: slightly - | slightly -
slightly + | Same as base (‘E.coast way’) | Same as “Fleet Dome” |
| ASAP | SSB: slightly +
F: slightly - | slightly -
slightly - | Same as base (‘E.coast way’) | Same as “Fleet Dome” |

## ASAP

## VPA vs ASAP (NAA)

## VPA vs ASAP (NAA)

## 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

## 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

- Base

- Fleet Dome

- 2002

- 2003

- 2004

## VPA Fleet Dome Retro

## VPA q “East Coast Style”

- Survey Dome

- Base