Stock structure of Pacific cod (Gadus macrocephalus) around the Korean Peninsula: an otolith microchemical perspective

Sustainable management of fishery resources is predicated on a foundational understanding of the biogeography of fish stocks and the delineation of stocks into appropriate management units. Despite notable fluctuations in the catch of commercially valuable Pacific cod (Gadus macrocephalus) in South Korea, relatively little is known regarding the stock structure and migratory trends of this species in the region. Here, otolith microchemistry was used to evaluate the stock structure and ontogenetic migratory trends of Pacific cod from five spawning grounds around the Korean Peninsula. Statistically significant between-region discrimination was evident and resolved Pacific cod around the Korean Peninsula into two distinct stocks. Specimens were classified to region of capture using quadratic discriminant analysis of age-0 and capture elemental signatures with overall accuracies of 71.12 and 79.1% respectively, lending support to the notion that Pacific cod demonstrate natal philopatry. Analysis of the elemental signatures over the first 2 years of life exhibited clear trends indicative of shifts in habitat use, suggesting that trace elements function well as indicators of ontogenetic migration. Our work provides information that is complementary to other direct and indirect methods of monitoring migratory trends and delineating stocks, which are integral components of effective species and ecosystem management plans.

Automated summary

By using otolith microchemistry, this study investigated the stock structure and migratory trends of Pacific cod around the Korean Peninsula, identifying two distinct stocks and supporting natal philopatry in the species. Analysis of elemental signatures revealed clear ontogenetic migration trends in the first 2 years of life.