Evidence of a genetic cline for Sardina pilchardus along the Northwest African coast

Abstract

In all, 700 Sardina pilchardus from 14 locations throughout the Atlantic and Mediterranean Moroccan coastlines were screened for eight enzymatic loci that show polymorphism. Analysis of allelic frequencies showed a genetic break in the area of the Bay of Agadir, segregating two groups of samples, confirmed by analysis of molecular variance; a first consisting of Sidi Ifni (29°12′N) and southern samples down to the southern limit of the species in Mauritania (19°03′N 16°28′W), and a second starting in the Bay of Agadir (30°48′N) and consisting of northern samples that appeared homogeneous with the Mediterranean samples. Specifically, a survey of the SOD* loci demonstrated a genetic cline in allelic frequencies along the coastline. Using a clinal variation model under a state of equilibrium, we estimate a dispersal rate of 189 ± 52 km per generation between Mauritania and Ras Kebdana. This major break towards the south of the Bay of Agadir offers a new perspective on the management of sardine, which ideally ought now to be managed as two stocks along the Moroccan coast. The break is most likely induced by hydrodynamic influences that virtually isolate southern from northern populations. © 2008 International Council for the Exploration of the Sea. Published by Oxford Journals. All rights reserved.