Size distribution and genetic diversity of the offshore rockfish (Pontinus kuhlii) from three Atlantic archipelagos and seamounts

The offshore rockfish (Pontinus kuhlii) is a widespread demersal fish in the temperate eastern Atlantic. This species inhabits hard bottoms at depths between 100 and 600 m and it is an important resource for the Azorean commercial fishing fleet. During several research fishing surveys in the Azores, Madeira and Cape Verde archipelagos diverse biological data on this species were collected. The degree of geographical population differentiation across the three Atlantic archipelagos was examined using two mitochondrial markers, control region (CR) and cytochrome b (cyt b). A total of 44 specimens were sequenced for each marker revealing high haplotypic diversity (CR: Hd=0.9736; cyt b: Hd=0.8520) and low nucleotide diversity (CR: π=0.0171; cyt b: π=0.0059). The sample size from the different subareas was limited but sufficient to reveal that no genetic structure was evident (ΦST=−0.0465 to −0.0224), suggesting the existence of one panmictic population. Despite very different exploitation rates between archipelagos, the size structure of P. kuhlii was very similar and inter-annual variation was also low. Exploitation rates are probably too low to significantly affect the size structure, even in the Azores where the species is a secondary target of the commercial fishery. In the Azores region this species is more abundant on seamounts, however bigger fishes tend to occur on island slope than on seamounts.