An initial attempt at a spatially structured stock assessment for the South African hake resource including explicit movement

The distribution area for the South African hake population is separated into nine regions to accommodate an initial attempt at a model of the dynamics which reflects explicit movement of the two species of hake both longshore and offshore. Commercial selectivities-at-length are modelled by logistic curves to reflect a gear only and no availability effect, but it proves necessary to allow for doming in the survey selectivities-at length. Although most abundance and size structure data are reasonably well fitted by the model, the model tends to overestimate the proportion of hake in the smallest and largest length groups for the surveys. Spawning biomass trends for M. paradoxus and M. capensis are broadly similar to those estimated by the current assessment approach which uses differing selectivity patterns by species and area as a surrogate for movement. Suggestions are made regarding issues for possible further investigation.