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Assessment Method For Alaska

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Assessment Method For Alaska


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Research Model


The Assessment Method for Alaska (AMAK) was developed in the NMFS Alaska Fisheries Science Center by Dr. James Ianelli using AD Model Builder. This is an age based estimation model that supports multiple fisheries and sparse data availability.


The AMAK model is an explicit age-structured model that uses a forward projection approach and maximum likelihood estimation to solve for model parameters. The operational population dynamics model is defined by the standard catch equation with various modifications such as those described by Fournier and Archibald (1982),  Hilborn and Walters (1992) and Schnute and Richards (1995).  


The model simultaneously fits parameters for up to seven components of a penalized likelihood function.  The likelihood function includes parameters for


  1. abundance indices

  2. selectivity

  3. recruitment regularity

  4. catch biomass

  5. proportion at age

  6. fishing mortality regularity

  7. prior distributions on natural mortality and survey catchability.   


Survey and fishery selectivity are modeled similarly using one of 4 alternative functional forms and a time-varying curvature penalty which allows the model parameters to change over time as well as age. Fishery age composition, modeled as a multinomial distribution, requires a measure of effective sample size for each year. The posterior distribution of the estimated parameters can be approximated using the Markov Chain Monte Carlo method.


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