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AIGKC Model. North Pacific Fishery Management Council Crab Modeling W orkshop Report. Highlights. Progress on development, but not acceptable for management advice. Model code & data was provided for independent review by CPT members (this work continues).
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AIGKC Model North Pacific Fishery Management Council Crab Modeling Workshop Report.
Highlights • Progress on development, but not acceptable for management advice. • Model code & data was provided for independent review by CPT members (this work continues). • Population dynamics for new/old shell, extreme sensitivity to molting probability parameter(s). • Time series data split pre and post 2004 (rationalization). • Molting probability based prior distribution (derived from tagging study), these data should be included in the model. • Retained and discarded CPUE data are not independent. • CPUE standardization using GLMs is high priority and will be reviewed May 2012.
Summary of Model Workshop Discussions • Discussions focused primarily on the input data into the model. • Tagging data • Length composition data • CPUE data • Model runs were requested to examine sensitivities and to better understand structural assumptions.
Tagging data • Tagging studies conducted in the eastern area. • growth information imputed for both areas • data used to estimate exploitation rates of LMB in the eastern area. • Quality of data is questionable with 5-8% recovery rates. • Workshop agreed that tagging data should not be used as priors for exploited legal male biomass due to lack of information on reporting rates and other tagging related uncertainties.
Length Composition data • Length composition data may be over-weighted. • Suggestion to use multinomial rather than robust-normal likelihood. • Need better diagnostic tools to characterize if these data are being over or under fitted. • Fit to dockside length comps and use the model to differentiate between discards and landings (consistent with Tanner crab model).
CPUE data • Discard and retained CPUE are not independent observations (made by observers, and divided by the same effort units). • Dockside CPUE is not used, and may be preferable (after standardization). • More details on raw CPUE data (samples sizes, number of vessels, etc.) are necessary.
Model runs • Model Runs examined influence of the Retained and Discarded CPUE and the use of Dockside CPUE. • General results: • Trends were similar using dockside CPUE and down weighting discard CPUE. • Results were counter intuitive, but considered preliminary due to lack of time during the workshop.
Recommendations for AIGKC model • Near term (prior to May 2012): • Length data compilations: • Observer vs dockside (as in the case of Tanner crab) • Examine issues that dockside might be difficult to associate to area. • Comparative analysis of dockside and observer length frequencies (is there + covariance in legal males?). • CPUE standardizations • Develop method for including tagging data to jointly estimate growth.
Recommendations for AIGKC model • Long Term: • Improve documentation of data compilation. • Include rationales for selection of weighting components used in the likelihoods. • Use SAFE report guidelines • Modeling: • Adopt a more generalized framework to avoid area specific code and compile-dependent changes to explore alternative hypotheses. • Standardized output diagnostics (e.g. SDNRs MADs). • R-Scripts for producing standardized outputs. • Examine alternative likelihoods for length composition data. • Two-area model with shared parameters.
