They feed on a wide variety of organisms on the bottom, but capelin seems to be the key with respect to their growth and spawning potential. It's so high in calories; it comes right in to the coast to spawn; it's so aggregated that it is easy for cod to catch. It is certainly one of the most important things for the northern cod in particular, especially to sustain a large population.
On September 21st, 2016. See this statement in context.