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Assessing Age-Length Uncertainty in White Hake: Model Testing and Age Error Considerations

This study investigates the effects of uncertainty in age-length keys on modeling White Hake populations. Using data from 1989 to 2001, we analyze 12 years of age (1-30 years) and length (1-200 cm) data from three surveys. We explore different models including VPA and ASAP, assessing their robustness against age data biases and errors. Findings show that models not reliant on precise age data (AIM, SCALE) remained robust despite aging error, while ASAP provided lower bias magnitudes. The implications for management of White Hake stocks are significant.

timothy-davidson
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Assessing Age-Length Uncertainty in White Hake: Model Testing and Age Error Considerations

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  1. White Hake • Base • Similar to 2002 VPA results • FractionSamples • Introduces uncertainty in age-length key • AgeError • Ageing imprecise • FractionandAgeError • Purpose: test models under high ageing uncertainty and bias

  2. White hake basic setup • Years 1989-2001 (12 years) • Ages 1-30, 9+ • Lengths 1-200 cm • 2 market categories • 3 surveys • (CVs vary by age, 20%-50%) • CV on landings 5% • Growth stdevs 5.0 initial, 1.0 projection • Von B params 189, 0.081, 0.062 • 50% Mature ~35 cm • Selectivity flat-topped, 50% selected 39 cm • M = 0.2 • F high all years (0.5-2.1)

  3. White hake test cases • Fractionsamples • 40% of lengths used to create ALK • AgeError • Adds uncertainty but not much bias

  4. White Hake

  5. White Hake

  6. AIM

  7. White Hake

  8. SCALE

  9. White Hake

  10. VPA (SSB)

  11. VPA (FAA)

  12. White Hake

  13. ASAP

  14. VPA vs ASAP NAA

  15. VPA vs ASAP NAA

  16. Precision (SSB and F) • AIM: ~ 0.1-0.2, did not vary by case • SCALE: ~0.1, did not vary by case • VPA*: <0.2 (poor ages>7) • ASAP: ~0.05, did not vary *VPA CVs are for age-specific SSB, F

  17. White Hake Conclusions • Models that do not fit age data (AIM, SCALE) were robust to aging errors (assuming correct von B for SCALE) • Bias pattern similar for VPA and ASAP, but magnitude was far less for ASAP

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