Interannual changes in distribution of age-0 walleye pollock near the Pribilof Islands, Alaska, with reference to the prediction of pollock year-class strength

Walleye pollock (Theragra chalcogramma) is a key species and a major commercial fishery target in the eastern Bering Sea (EBS). Recruitment of juveniles to the adult stock is largely determined by first-year survival in favourable nursery areas, and the waters around the Pribilof Islands are an important nursery area. Based on a six-year acoustic survey programme (September 1994-1999) to investigate abundance and distribution variations of age-0 pollock, we developed a set of predictive indices relating the age-0 Pribilof population to the EBS pollock stock at recruitment (age-3). EBS year-class strength at recruitment correlates with age-0 density, the spatial relationship between juveniles and euphausiids, and the degree of centricity of the age-0 distributions around the Pribilof Islands, i.e. neither too far inshore nor offshore. Seabird numbers and density ratios of predatory groundfish also influenced age-0 pollock distribution, but did not provide consistent discrimination among year classes. We hypothesize that age-0 pollock must transition from a copepod diet to a euphausiid diet by September to maximize their survival potential and to estab ish a strong adult cohort.