Population structure of Alaskan shortraker rockfish, Sebastes borealis, inferred from microsatellite variation

Alaskan shortraker rockfish population structure was analyzed by examining allelic variation at eight microsatellite loci. Samples were collected along the continental shelf and upper slope from the south end of Baranof Island to the western Aleutian Islands, and collections were pooled into eight geographically distinct groups. An exact test of homogeneity indicated population structure ( p < 0.0006) among groups. The proportion of the total variation that was attributable to divergence among populations (theta = 0.0014) was not statistically significant, and no evidence of a geographic cline of structure was detected. Finer scale analyses that compared adjacent collections indicated that the collection from the southern end of the range differed from all remaining collections at three loci. Structure related to geographic location was detected by partitioning the variation among populations. The size distributions of shortraker rockfish varied among collections from east to west. The size differences may reflect divergent oceanographic and biological factors acting on populations that have restricted migration and movement. Alternatively, if there is substantial movement accompanied by lengthy reverse migration to natal grounds, the size differences may be related to ages of cohorts that are differentially distributed along the Pacific Rim. Further biological information including size, age composition, and age of maturity data, as well as information on other life history characteristics will be required to explain shortraker rockfish population structure.