Landscape Genetics Reveals Population Subdivision in Bering Sea and Aleutian Islands Pacific Cod

Landscape genetics of Pacific cod Gadus macrocephalus within the Bering Sea and Aleutian Islands (BSAI) management area of Alaska was examined in samples from nine spawning locations, including one temporal replicate sample, using 17 microsatellite DNA markers. This study examined fine-scale population structure of Pacific cod in the BSAI with the goal of identifying breaks in genetic continuity associated with physical barriers to migration and larval transport. Samples were taken from spawning fish collected from the western Aleutian Islands east to Unimak Pass and as far north as the Pribilof Islands. Overall, this work confirms previous studies, which found that genetic differentiation between samples is proportional to the distance between them, and also resolves population structure on a scale not previously possible. Results indicate that dispersal is not continuous at a fine scale and several distinct genetic groups were identified that correspond to differences in the physical environment of the BSAI. The data provide evidence for limited connectivity among spawning groups; in particular, there is evidence that a barrier exists between the Aleutian Islands and the eastern Bering Sea. In addition, analysis of molecular variance and Monmonier algorithm results suggest that, within the Bering Sea, the Unimak Pass and Pribilof Islands spawning groups may be distinct from each other, and the Wombling analysis indicates that samples west of Amchitka Pass in the western Aleutians may be distinct from those in the eastern Aleutians.