Some Aspects of the Walleye Pollock (Theragra chalcogramma) Biology and Fishery Related to the Size and Age Structure in the Southwestern Chukchi Sea

The distribution of catches and the size/age structure of walleye pollock are considered on the basis of data obtained through surveys conducted by TINRO in the Russian waters of the Chukchi Sea in 2018-2020. The age estimation using otoliths revealed two modal age groups of walleye pollock present in catches: the first group was comprised of underyearlings and age-1 fish; the second group consisted of fish at ages of from 7 to 22 years, of which age-8-15 individuals made up 90%. Age-3-6 fish were almost absent from catches. This size/age structure suggests that the stock could be formed by fish that had migrated from the northern Bering Sea. As a comparison of the size/age characteristics of walleye pollock from these two areas has shown, the fish that arrive from the Bering Sea do not fully or partially migrate back, while the fish remaining in the Chukchi Sea that are exposed to harsher conditions begin to grow at a markedly lower rate. An analysis of the distribution of fast- and slow-growing individuals in the survey area of the Chukchi Sea has shown disjunction of their aggregations. Although the walleye pollock with the Bering Sea growth type were found quite widely, including in the offshore part of the study area, the distribution of resident walleye pollock indicated their preference for coastal waters. The walleye pollock fishery launched in the Chukchi Sea in 2021 has shown that aggregations are mainly confined to coastal waters in the southern part of the sea, which suggests that the fishery is based mainly on resident walleye pollock.

Automated summary

Based on surveys conducted in the Russian waters of the Chukchi Sea, this study examines the distribution and size/age structure of walleye pollock. The results show two main age groups in the catches, with younger and older individuals dominating the size/age structure. The study also reveals differences in growth rates between walleye pollock migrating from the Bering Sea and those remaining in the Chukchi Sea. The resident pollock show a preference for coastal waters.