A BAYESIAN-ESTIMATION AND DECISION-ANALYSIS FOR AN AGE-STRUCTURED MODEL USING BIOMASS SURVEY DATA

The use of Bayesian estimation and decision analysis is described and applied to estimate the probability distribution of virgin stock size, and expected consequences of future quotas for an age- and sex-struct ured model fit to biomass survey data. It is shown that Bayesian metho ds can be easily used with complex models when uncertainty in a single parameter is considered. An example from the fishery for hoki (Macrur onus novaezelandiae) in New Zealand is presented, in which the weight, vulnerability schedule, fecundity schedules, natural mortality rate a nd the sensitivity of recruitment to spawning stock are assumed known. Results with a uniform prior probability on stock size are compared w ith those where an informed prior probability distribution is availabl e. Three alternative harvest policies are compared and the expected va lues of several indicators of performance are computed for different q uotas. The problems in extending the model to calculate Bayesian poste rior distributions with multiple indicators of abundance, many more fr ee parameters, and a stochastic model are considered.