Lack of geographic structure in mitochondrial DNA sequences of Bering Sea walleye pollock, Theragra chalcogramma.

: We compared 511 nucleotides of mitochondrial DNA from 162 walleye pollock from 32 locations in the Bering Sea, the Shelikof Strait, and the Gulf of Alaska to learn about population structuring in this economically important species. Specifically, we tested for evidence of genetic heterogeneity among three sequence data sets: a 76-bp spacer, the control region, and spacers and control regions combined among six geographic regions: southwest Bering Sea, northern Bering Sea, western Aleutians, eastern Aleutians, the Donut Hole, and the Gulf of Alaska. No significant genetic heterogeneity was detected among spacer sequences or control regions, or spacers and control regions combined among areas of the Bering Sea. Slight genetic heterogeneity was detected when a "Western Bering" sample (southwest Bering and northern Bering) and an "Eastern Bering" sample (western Aleutians and eastern Aleutians) were compared. Presence of an abundant and widespread haplotype suggests recent establishment of the walleye pollock population in the Bering Sea. However, the ratio of nucleotide transitions to transversions in these pollock is extremely low, suggesting that the population may be old. Presence of a widespread and abundant haplotype, together with numerous rare ones, suggests a high variance in reproductive success for relatively few females, which may be disproportionately contributing to the survival of individual haplotypes. Sequencing of control regions in pollock may be less informative than conventional analysis of restriction fragment length polymorphisms or RFLP analysis of amplified variable sites.