The population structure of North Pacific pollock is complex and scientific understanding is evolving. In Russia, West Bering Sea Karaginsky, West Bering Sea Chukotsky, Sea of Okhotsk, and Sea of Japan pollock stocks are considered reproductively isolated from one another, albeit with some inter-migration between them, and are addressed separately from one another by the Russian authorities for purposes of stock assessment (Federal Fisheries Agency, Kamchatka Branch 2020); (Kotenev and Glubokov 2007). Russian authorities also recognize that there are fish that originate in the Japanese EEZ harvested in Russian waters (i.e., a separate Japanese Pacific stock) (Ovsyannikova 2012).

Within these groupings, the degree of differentiation among various populations is nuanced. Complications in elucidating pollock population structure include life histories that entail different habitats for spawning, overwintering, and feeding; larval drift from one region to another; and different population dynamics at low and high abundance (Kotenev and Glubokov 2007); (Grant et al. 2010).

With reference to this map of Far East fishing zones, this profile covers the portion of sub-area 1 that is west of longitudinal Meridian 174ºE (roughly half of the sub-area, the southwestern portion) and the adjacent sub-area 2, Karaginsk. The larger, separate, Navarinsk population of pollock is targeted by the fishery in the northeastern portion of sub-area 1--this population is likely subject to immigration of pollock from the East Bering Sea. This profile addresses the much smaller fishery in the Karaginsk sub-area and also incorporates the portion of sub-area 1 west of 174ºE, which has been closed to commercial fishing since 2016 (TINRO 2020).