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

Abstract

This document presents a first attempt at a spatially structured model for the South African hake (the model equations are set out in Appendix 1). It is currently assumed that M. paradoxus and M. capensis both consist of a single stock across the South African west and south coasts (and possibly extending to Namibia). From catch-at-length information, it is however clear that the fish are not distributed evenly in terms of age/length in different areas. M. capensis is usually found in depths of less than 400 m, with the largest biomass in the 100-200 m depth range, while the depth distribution of M. paradoxus ranges mainly from 150 m to 500 m. There is also a tendency for hake to move offshore into deeper water as they grow older. Age information from the surveys furthermore suggests that young (up to age 3) M. capensis are primarily restricted to the west coast. At intermediate ages, a large proportion of these fish move to the south coast. However, for the oldest fish (ages 6+), there is some movement back to the west coast. Similarly for M. paradoxus, the smaller fish tend to be found more on the west coast.