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Brandon Owashi David Sampson

Characterizing Shape and Interannual Variability in Population Selectivity (Scaled F-at-age) for West Coast Groundfish. Brandon Owashi David Sampson. Importance. Simplify multiple fisheries to one fishery  large reduction in parameters

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Brandon Owashi David Sampson

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  1. Characterizing Shape and Interannual Variability in Population Selectivity (Scaled F-at-age) for West Coast Groundfish Brandon Owashi David Sampson

  2. Importance • Simplify multiple fisheries to one fishery  large reduction in parameters • Need mechanism that can produce the many shapes that the combination multiple fisheries can produce • Determine information needed to mimic the population fishery selection

  3. Population vs. Fishery (Contact) Selection Curves • Population curves vary from fishery curves and change on a year to year basis Gear 1 = 0.2 Gear 2 = 0.1

  4. Population vs. Fishery (Contact) Selection Curves • Population curves vary from fishery curves and change on a year to year basis Gear 1 = 0.2 Gear 2 = 0.15

  5. Stock Assessments Used • Most recent stock assessment available • Z-at-age  F-at-age  Max F-at-age  Selectivity Coefficients

  6. Logit Transformation • Logit = ln(p / (1 – p)) • 0 = (smallest non-zero sel coefficient) / 2 • 1 = - (logit of “0”)

  7. Smooth Spline • Cubic smoothing spline in R (smooth.spline) • Continuity at knots • Second derivative on either side of knot equal each other • Fit curve to logit selectivity data

  8. Knots • Fixed x values that the curve must go through • Find number of knots  best fit • Extract y component from knots • Calculate standard deviation for each y component of the knot over time

  9. Examples Blackgill Rockfish Cabezon - Oregon Pacific Whiting Greenspotted Rockfish - South

  10. Results – Curve Shape • Shape definitions from Sampson & Scott (2011) • Increasing • Asymptotic • Domed • Saddle

  11. Results – Curve Shape • Shape definitions from Sampson & Scott (2011) • Increasing • Asymptotic • Domed • Saddle

  12. Results – Curve Shape • Shape definitions from Sampson & Scott (2011) • Increasing • Asymptotic • Domed • Saddle

  13. Results – Curve Shape • Shape definitions from Sampson & Scott (2011) • Increasing • Asymptotic • Domed • Saddle

  14. Results – Curve Shape • Shape definitions from Sampson & Scott (2011) • Increasing • Asymptotic • Domed • Saddle

  15. Pacific Whiting

  16. Blackgill Rockfish

  17. Greenspotted Rockfish

  18. Greenspotted Rockfish

  19. Cabezon

  20. Results – Interannual Variability • Calculated the standard deviation at each knot (logit transformation) • Sampson & Scott (2011) • Highest variability found in either youngest or second youngest age class

  21. Pacific Whiting

  22. Blackgill Rockfish

  23. Greenspotted Rockfish

  24. Cabezon

  25. Conclusions • Must have very flexible mechanism for generating population selectivity curves • Double normal is not flexible enough • High variability occurs in different age ranges depending on species • High number of fisheries does not always result in high levels of variability

  26. Conclusions • Must have very flexible mechanism for generating selectivity curves • Double normal is not flexible enough • High variability occurs in different age ranges depending on species • High number of fleets does not always result in high levels of variability

  27. Conclusions • Must have very flexible mechanism for generating population selectivity curves • Double normal is not flexible enough • High variability occurs in different age classes depending on species • High number of fisheries does not always result in high levels of variability

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