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Modeling Natural Mortality in Stock Synthesis

Modeling Natural Mortality in Stock Synthesis. Modeling population processes 2009 IATTC workshop. M options in Stock Synthesis v3. Single value for all ages Broken stick (piecewise linear) where the number of breakpoints can be set

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Modeling Natural Mortality in Stock Synthesis

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  1. Modeling Natural Mortality in Stock Synthesis Modeling population processes2009 IATTC workshop

  2. M options in Stock Synthesis v3 • Single value for all ages • Broken stick (piecewise linear) where the number of breakpoints can be set • Scaled Lorenzen curve where the curve is scaled to an estimable value at a given age • Age-specific vector of user-specified fixed values

  3. Broken stick

  4. Broken stick Age zero Zero exponential offset

  5. More on Mortality • Value for males offset from females • Can be time-varying like other parameters • If broken stick is used (piecewise linear), values before and after range of breakpoints are constant at first/last value

  6. Mortality in seasonal models • Mortality is function of real age based on birth season, not calendar age • User-specified values have choice of same value for each season within year, or interpolated values for each season

  7. Lorenzen mortality • Mortality is a function of mean size at age • Parameter for M at user-specified reference age • Based on initial growth curve, so does not work well with time-varying growth Ref: Lorenzen, K. 1996. The relationship between body weight and natural mortality in juvenile and adult fish—a comparison of natural ecosystems and aquaculture. Journal of Fish Biology49, 627–647

  8. Lorenzen mortality (my guess) b=-0·288

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