Comparative habitat associations in juvenile Pacific cod and other gadids using seines, baited cameras and laboratory techniques

Pacific cod are commercially and ecologically important in the North Pacific, currently ranking 2nd in tonnage and value landed in the Alaskan groundfish fishery. To date, few studies have focused on the habitat requirements of Pacific cod, and as a result, our understanding of their ecology has largely been borrowed from better-studied gadid species, especially Atlantic cod. In July-Aug 2006, we used field and laboratory techniques to explicitly examine habitat associations of Pacific cod and two co-occurring gadids, saffron cod (Eleginus gracilis) and walleye pollock (Theragra chalcogramma), in coastal areas around Kodiak Island, AK. Pacific cod were the most abundant gadid in seine collections, followed by saffron cod and walleye pollock respectively. Small Pacific cod (3.5-7.5 cm TL) were most highly associated with Laminaria and eelgrass beds but moved into open habitats at larger sizes i.e., > 8.0 cm TL. Baited cameras indicated that the majority of juvenile Pacific cod were nearshore in August (i.e., ≤ 4.5 m), but schools were also seen in deeper (6.0-13.5 m), unstructured habitats. In contrast, age-0 saffron cod were almost exclusively restricted to eelgrass beds (Zostera marina) (3.5-13.0 cm) as were later year-classes i.e., 18-50 cm. Pollock were highly variable in their distribution, and were almost absent from the nearshore in late August. In 2 m experimental aquaria, Pacific and saffron cod chose macrophyte habitats under increased predation risk but also associated with these habitats at larger scales (i.e., c. 10 m tank) in the absence of a predator. Our results indicate both distinct differences and parallels between Pacific and Atlantic cod that will guide future process-oriented habitat research in both species.