Trophic ecology of Atlantic cod Gadus morhua on the northeast US continental shelf

Atlantic cod Gadus morhua is an extremely important fish in the northern hemisphere with respect to culture, economics, and ecology. However, the effects of over-fishing, environmental change, fish community dynamics and other factors that have altered the trophic ecology of cod are not well understood. We present an analysis of the trophic patterns of cod in the northeast US shelf ecosystem from a 25 yr time series of food habits data. Additionally, we compared the diet of this species with the spatio-temporal distribution of its prey species and evaluated prey preference over time. Atlantic cod exhibit an omnivorous diet; we assessed the temporal, spatial, and ontogenetic trends in this diet by examination of >15 000 stomachs. Ontogenetic shifts in diet were observed; early juveniles consumed more pelagic than benthic invertebrates, medium cod consumed benthic invertebrates and fish, and larger cod consumed larger amounts of fish. Cannibalism also increased with ontogeny. Diet shifted significantly over a period of 3 decades, concurrent with changes in forage species abundance and distribution. Most of the major prey species were eaten in periods when they had high spatio-temporal overlap with cod and were abundant, indicating opportunistic feeding by cod, Similar to many other ecosystems, cod prefer sand lance, Cancer spp. crabs and herring, regardless of the abundance or spatio-temporal overlap with these prey species, It is unclear whether the observed changes in the trophic dynamics of cod have broad implications for cod populations, yet the evidence does suggest that cod are not likely to influence the abundance and distribution of their prey populations in this ecosystem.