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Characterizing Shape and Interannual Variability in Population Selectivity for West Coast Groundfish

This study simplifies multiple fisheries into one, determining mechanisms for shaping population selectivity curves. It uses stock assessments, Logit transformation, and Smooth Spline for curve fitting. Examples include Blackgill Rockfish and Cabezon, showing different curve shapes and interannual variability. Conclusions highlight the need for flexibility in generating selectivity curves and the varying levels of variability based on species and fishery number.

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Characterizing Shape and Interannual Variability in Population Selectivity for West Coast Groundfish

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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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