Biochemical genetic variation in the highly abundant squid species from the North Pacific Ocean was examined in relation to their intraspecific differentiation and population structure. A large amount of data collected over a period of approximately 15 yrs was analyzed using protein
electrophoresis as a basic research tool. In total, approximately 750 individuals of Ommastrephes bartramii (LeSueur, 1821), 300 individuals of Todarodes pacificus Steenstrup, 1880, and 5800 individuals of Berryteuthis magister (Berry, 1913) were covered by the approach.
A geographic pattern of population genetic variability was observed in O. bartramii, with major genetic differentiation attributable to inconsistency in allele frequency distribution and in levels of genetic variation between the squid from the western and eastern parts of the species
broad range in the North Pacific Ocean. In T. pacificus from the Japan Sea, significant intraspecific genetic differentiation was largely due to allele frequency variability between two groups of seasonal cohorts: autumn group, consisting of the autumn-spawning squid, and non-autumn
group, comprised of the winter-, spring- and summer-spawning squid. An apparent pattern of genetic differentiation was observed in B. magister, which could be related to intersubspecific differences between the squid from the Japan Sea, and northwest Pacific Ocean region, including
the Kuril and Commander islands, and Okhotsk and Bering seas. Much less pronounced though significant population genetic variability was revealed between conspecific aggregations of the squid within the northwest Pacific Ocean, where they differ from each other according to geographic proximity,
and the most clear differentiation appeared between the Okhotsk-Kuril and Bering groups of the squid.
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