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 fishery managers 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).

The West Bering Sea appears as area 1 in this map of Russian Far East fishing areas, and the Navarinsky population resides in its eastern half, east of longitudinal Meridian 174ºE. This population of pollock, the second largest in Russian waters, migrates from the East Bering Sea over to the west to feed (Federal Fisheries Agency 2020); (TINRO 2020). With reference to this map of Bering Sea fishing zones, this profile covers zone 398 (Federal Research Centre the Southern Scientific Centre of the Russian Academy of Sciences et al. 2018). A separate, smaller, west Bering population of pollock is found west of 174ºE in zone 399 – the fishery there has been closed to commercial fishing targeting pollock since 2016 (TINRO 2020).

Since 2016, separate TACs have been issued for zones 398 and 399. Zone 304 – Chukhotka – also has its own TAC, although stock assessments for Navarinsky pollock encompass fish residing in both zone 398 and zone 304. The population residing in zone 399 (west of 174ºE) receives separate attention in stock assessments.