Feeding ecology of larval and juvenile walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) in the Southeastern Bering Sea

Abstract

Poor recruitment success during warm years (e.g., 2001-2005) was hypothesized to lead to reduced gadid recruitment in the southeastern Bering Sea. These groundfishes are of particular importance, both commercially and ecologically in the southeastern Bering Sea. The spatial and temporal overlap of early life stages of walleye pollock and Pacific cod may explain their strongly correlated recruitment trends in the southeastern Bering Sea. The goal of this study was to compare feeding patterns of larval and juvenile walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) in the southeastern Bering Sea, and to assess the possibility of prey resource competition. Larvae and juveniles from both species collected between May and September 2008, an exceptionally cold year, were used to analyze stomach contents. Fish body size was most consistently related to diet composition within species, however, spatial and depth factors also had an influence. Feeding success and diet composition of these two gadid species were consistently different throughout the spring, summer, and especially fall seasons. Pacific cod larvae and juveniles consistently consumed larger prey items in every season and progressively fewer prey items, especially in the fall. This data suggests that competition for prey resources was unlikely during cold 2008.