Atlantic cod (Gadus morhua) feeding over deep water in the high Arctic

The Atlantic cod (Gadus morhua) is a highly adaptive demersal, boreal species with a broad distribution on the continental shelves on both sides of the North Atlantic. However, whether the species also uses adjoining deeper water basins as feeding grounds or migration corridors remain unknown. In this study, we aimed to describe the vertical and horizontal distributions of Atlantic cod observed feeding over the northern Fram Strait, between Greenland and Svalbard, and relate this to the prey field and environmental conditions. During surveys in 2014 and 2015, we combined biological sampling of cod, caught in ten pelagic trawls, with environmental data and acoustic registrations. The findings reveal that cod leave the continental-shelf waters and migrate westwards into the deeper water (> 2800 m) of Fram Strait, as they feed on a mesopelagic layer of krill, amphipods, and small fishes. We suggest that leaving the shelf waters to feed over deeper water is a mechanism for the cod to avoid competition for food on their normal feeding grounds over the shelf, or it may demonstrate the phenomenon of a high-risk taker exceeding the limits of its natural demersal environment. The observed migration behavior may be widespread or else linked to ecological features involving physical factors or competition for food, possibly in combination with a large stock of cod. Thus, although the permanent distributions of Atlantic cod are constrained by depth, migration across deeper straits or basins must be considered.