Genetic markers reveal a gradient of hybridization between cape hakes (Merluccius capensis and Merluccius paradoxus) in their sympatric geographic distribution

• Cape hakes are essential African fishing resources.
• The two species Merluccius capensis and M. paradoxus hybridize.
• A North–South hybridization gradient is revealed by genetic markers.
• A hybrid zone was detected in Namibian waters.
• Special management of the Namibian populations is recommended.

The cape hakes Merluccius capensis and Merluccius paradoxus are important fishing resources for African countries such as Namibia and South Africa. In this study we have genetically analyzed adult samples from the overlapping distribution of these species. Eight microsatellite loci, the nuclear 5S rDNA locus and the Cytochrome Oxidase subunit I (COI) gene were employed as molecular markers. A North–South gradient of interspecific hybridization was found, with discordant mitochondrial and nuclear genotypes at the northernmost edge of M. paradoxus distribution. These results suggest intense introgression in North Benguela off the Namibian coast. Independent hake stock assessment is recommended in this region for sustainable management of this valuable resource.