Two-area population models for Antarctic toothfish in the Amundsen Sea Region were developed further as current single area models did not fully explain the patterns in the observed data on tag recaptures and age composition. Although the hypothesised stock structure spans SSRUs 88.2C–H, these models were limited to data collected in SSRU 88.2H as there were few data available to inform estimation of biomass in SSRUs 88.2C–G. Additional data resulting from a two-year research plan implemented in 2014/15 are expected to better inform the assessment of the entire stock including SSRUs 88.2C–G in the future.
Results showed that a two-area model with sex- and age-specific migrations from SSRUs 88.2C-G to SSRU 88.2H and back provided the best fits to the age and tag data collected in SSRU 88.2H. Furthermore, a resident population in 88.2H was not required to explain the patterns observed in the data, nor was annually-varying or density-dependent migration. Finally, using subsets of the data, or excluding small tagged fish, did not improve the fits to the data.
We recommend this model be further developed once additional age and tag data have been collected in SSRUs 88.2C–H as part of the two-year research plan.