Geostatistical modelling of the spatial life history of post-larval deepwater hake Merluccius paradoxus in the Benguela Current Large Marine Ecosystem

Abstract

Optimal and sustainable management of fish resources cannot be ensured without a thorough understanding of the migration patterns and population (demographic  stock) structure. Recent studies suggest that these aspects of the economically and ecologically important deepwater hake Merluccius paradoxus are not reflected  in the current assessment and management practices for the Benguela Current  Large Marine Ecosystem. In this study, we compiled data from multiple demersal  trawl surveys from the entire distribution area and applied state-ofthe-art  geostatistical population modelling (GeoPop) to estimate growth rate, mortality, and  spatial and temporal distribution patterns of M. paradoxus. The data and the model enabled us to follow temporal and spatial changes in the distribution and infer  movements from the recruitment/nursery areas, through the juvenile phase and the adults’ migration to the spawning areas outside/upstream of the nursery areas. The results indicated one primary recruitment/nursery area on the west coast of South Africa and a  secondary less-productive recruitment/nursery area on the south coast near Port Elizabeth. Juveniles initially migrated away from the main recruitment area, followed by natal homing by larger individuals. This pattern was highly  consistent through the time-series of the study. This perception of a, primarily,  panmictic population that performs transboundary migrations between Namibia and South Africa corresponds largely to the hypothesis and data plots given in recent  studies. We recommend that fisheries assessment, advice and management take into consideration these aspects of the distribution and population (stock) structure of M. paradoxus.

Keywords: demersal trawl survey, GeoPop model, mortality, Namibia, natal homing,  population structure, South Africa, Template Model Builder, transboundary migration