Microsatellite DNA markers discriminate between two Octopus vulgaris (Cephalopoda : Octopoda) fisheries along the northwest African coast

Two main commercial Octopus vulgaris fisheries occur on the Northwest African coast and are managed along national boundaries between Western Sahara and Mauritania, with the division at 21degreesN. This study aims to determine, using microsatellite DNA loci, whether octopus in the two fisheries are genetically distinct and to try to locate the origin of the samples by comparison with samples collected by research cruises from known locations. A sample from each fishery, and three samples from known positions along the Saharan Bank (north, mid and south), were screened at three highly polymorphic loci. These loci revealed high levels of variability (mean H-e = 0.91), and an exact test for overall heterogeneity indicated highly significant structuring among the samples (P < 0.0005); overall F-ST was low but significant (F-ST = 0.0095 P = 0.005). Comparison of Mauritanian and Western Saharan fisheries demonstrated highly significant differentiation between areas (heterogeneity exact test P = 0.000), although neither sample clustered very closely with any of the research cruise samples. The large genetic distance between samples and possible Wahlund effects detected, suggest a high degree of genetic structuring along this coast; links between genetic differentiation and oceanographic features are discussed.