Genetic stock structure of the southern African hakes Merluccius capensis and M. paradoxus

Abstract

We estimated the genetic components of geographic variation among stocks of 2 syrnpatric southern African hakes, Merluccius capensis and M.paradoxus, using allozyme population markers detected by protein electrophoresis. In M. capensis 6 of 33 protein-coding loci were sufficiently polymorphic to test hypotheses of genetic stock structure. Significant but unexplained allele frequency lfferences were detected between sexes at 5 locations. Significant allele frequency differences between Namibian and South African samples were detected for Ck-A, indicating at least some genetic subdivision between these regional stocks. The absolute amount of differentiation, however, was small (average genetic distance only 0.0008). On average over loci, 98.3 O/O of the total gene diversity was contained within samples, 0.7 % was due to Mferences between sexes, 0.7 % to dfferences among locations within regions, and 0.3 % to ddferences between regions. In M. paradoxus significant allele frequency differences were detected for Mpi among the South African samples, but the amount of differentiation between samples was very small. There were no significant allele frequency differences between Namibian and South African samples. Most of the gene diversity (98.7 %) was contained on average within samples, 0.3 % was due to differences between sexes, 0.2 % to differences between locations within regions and 0.3 % to differences between regions. A review of morphological variation together with the genetic data presented here suggest that both species of hake are minimally subhvided into 2 regional stocks. The most conservative approach to the management of the regional stocks of hake is to manage the Narnibian and South African stocks independently of one another.