Population genetics and phylogeography of the blue rockfish (Sebastes mystinus) from Washington to California

Blue rockfish (Sebastes mystinus) are a major component of nearshore ecology and fisheries on the west coast of the United States, but the extent of spatial structuring between localized populations is unknown. I sampled 245 blue rockfish at eight locations from Washington to California and sequenced a 498 base pair portion of the mitochondrial DNA control region to describe genetic diversity, population structure, and phylogeography. Haplotype diversity was high, but nucleotide diversity was low, indicating historically unstable population dynamics. Significantly high levels of population differentiation were detected among sample sites (maximum pairwise FST: full sequence = 0.25, reduced sequence = 0.74, P < 0.001), with a distinct break (ΦCT: full sequence = 0.12; reduced sequence = 0.36, P < 0.05) north and south of Cape Mendocino and no overall trend between geographic and genetic distances. Cape Mendocino may prove an important biogeographic barrier to other marine organisms, but it has not been extensively explored as such. The northern subpopulation derived from the southern subpopulation, but little contact has been made between the populations for potentially thousands of years. Therefore, repopulation of a depleted southern subpopulation is unlikely to come from the less-fished northern subpopulation.