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Workshop on Stock Assessment Methods 7-11 November 2005. IATTC, La Jolla, CA, USA

Workshop on Stock Assessment Methods 7-11 November 2005. IATTC, La Jolla, CA, USA. General Stock Assessment Models. A-SCALA (IATTC ) MULTIFAN-CL (SPC) Stock Synthesis II (NMFS) CASAL (NIWA). Questions. 1) How to model fishing mortality 2) How to model selectivity

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Workshop on Stock Assessment Methods 7-11 November 2005. IATTC, La Jolla, CA, USA

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  1. Workshop on Stock Assessment Methods7-11 November 2005.IATTC, La Jolla, CA, USA

  2. General Stock Assessment Models • A-SCALA (IATTC ) • MULTIFAN-CL (SPC) • Stock Synthesis II (NMFS) • CASAL (NIWA)

  3. Questions • 1) How to model fishing mortality • 2) How to model selectivity • 3) Do we need to integrate across random effects • 4) How to estimate uncertainty • 5) How to include environmental data • 6) How to perform forward projections • 7) What likelihood functions to use and how to weight data sets • 8) Spatial structure in the population dynamics

  4. Changes of IATTC assessments • Estimate sd for effort deviates/CPUE • Effective sample size for C@L or cvs • Treat catch as exact: Use popes approximation or solve catch equation • Selectivity using splines or functional form /time varying • Correct length selectivity • Growth model/time varying • Variable length bin size/compression of tails of LF bins • Non-spatial tag data • Aging error

  5. Move to other models • Spatial population dynamics • Spatial Tag data • Sex structure

  6. Changes to assessments • Estimate C@L cvs from bootstrapping data (add process error) • Optimal number of fisheries • Reduce size of length bins

  7. Research priorities • When do spatial structured models improve the assessment results? • What data is needed • How to include environmental data in the model, particularly when there is missing environmental data. • Structural relationships vs index fitting • How to estimate the sd of the effort deviates . • Comparison of random effects versus penalized likelihood • Is integration needed • Should the sd be estimated

  8. Research priorities • Comparison of methods that use known catch vs those that model catch uncertainty • Computational demands • Methods to model selectivity • Need to use model selection methods • Time varying • Investigation of LF samples by space time and vessels etc • Explore the interaction between flexibility in selectivity (time varying) and adjustments to likelihood variance and how this influences results. • How to calculate confidence distributions, how well they perform, and how they compare to Bayesian analysis.

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