Size-Dependent Spatial Distribution of Hake (Merluccius capensis and Merluccius paradoxus) in Namibian Waters

Abstract

Data on hake (Merluccius capensis and Merluccius paradoxus) abundance along the Namibian coast showed both species to have strongly aggregated spatial distributions. In addition, average fish size increased with depth, suggesting that the formation of hake aggregation is based on size-dependent shoaling behaviour. Hake spacing was size dependent with areal fish density and biomass being scaled to the −5 and −2 power, respectively, of fish length. The equations describing the size dependence of the areal fish density were log density (fish∙m−2) = 5.06-4.91 log size (cm) for M. capensis and log density (fish∙m−2) = 5.28-4.74 log size (cm) for (M. paradoxus). The maximum areal densities, presumably corresponding to those within the shoals, exceeded those described by the equations above by 20- and 13-fold for M. capensis and M. paradoxus, respectively. The size dependence of hake spacing implies that fishing pressure targeting aggregates of small hake (i.e. shallow shoals) should have a disproportionate effect on fish mortality and recruitment compared with similar fishing pressure targeting aggregates of larger hake (i.e. deep shoals).