Incipient genetic isolation of a temperate migratory coastal sciaenid fish (Argyrosomus inodorus) within the Benguela Cold Current system

The Benguela Current is considered to be a major biogeographic barrier for tropical and warm-temperate marine fish, but there is limited knowledge regarding its influence on population sub-structuring of in more cold-tolerant species. Employing genetic variation within the mitochondrial DNA Control Region and six cross-specific nuclear microsatellite markers, a preliminary study was conducted to investigate population sub-structuring in Argyrosomus inodorus, a highly exploited, cold-temperate migratory species, across the Benguela Current region. Results revealed evidence of incipient genetic differentiation (mtDNA phi(ST) = 0.092; nuclear F-ST = 0.036 and D-ST = 0.104, P < 0.05) between the two sampling sites, suggesting the presence of two regional populations. Estimates of contemporary migration rates between populations were low, and similar in range to those reported in tagging surveys. Although preliminary, these results suggest that the oceanographic features of the Benguela Current may have influenced the evolutionary history of A. inodorus, and that the species is likely to be composed of two populations in the Benguela region. As the species is considered overexploited both in Namibia and South Africa, information on the distribution, population dynamics and long-term dispersal patterns across the Benguela Current region would support a comprehensive evaluation of genetic structure, which should be incorporated into fishery management arrangements.