Spawning and nursery areas, longitudinal and cross-shelf migrations of the Merluccius capensis stock in the northern Benguela

We investigate the spatial distributions of juvenile and adult hake Merlucciuscapensis on the Namibian continental shelf using data from 25 biomass surveys (1990-2007) to identify (i) nursery/spawning areas, their spatial or temporal separation and change and (ii) length, depth and latitude preference patterns. The density of fish (number-of-fish per30-min-haul) was examined in relation to fish total length (TL) and latitude and TL and bottom depth. Nursery aggregations were most frequent in central (22-25 degrees S) and southern (26-29 degrees S) Namibia, increasing in density in the south since 2000. Hatch dates of 17cm fish were calculated from juvenile growth rates. Peaks occurred in winter and summer-autumn in the centre and slightly later in the south. Spawning areas appear to have shifted southward since the late 1970s, showing the plasticity of this stock as a response to fishing pressure and environmental variability and change. Merlucciuscapensis show a stable pattern of latitude preference over the 25 surveys examined. They first occur on the mid-shelf <9cm, generally moving to the inner-shelf at 9-15cm (<1yr old). They generally prefer the northern and mid-shelf area between 24 and 45cm (1.5-3.5yr old), probably for feeding and building resources for spawning purposes. They later move to the outer-shelf and return southward and to the mid-shelf region to spawn at 45cm TL (3.5years old), a contained stock unit in the northern Benguela. We propose a complete migration life history of M.capensis for the first time, showing their extensive longitudinal migrations, similar to Merluccius species elsewhere.