Chapter 4 – Growth and Mortality in Settled Atlantic Cod in Relation to Diet—Evidence for a Recruitment Mechanism

A hypothesis suggesting that variability in recruitment of Atlantic cod (Gadus morhua) is caused by variable energy flow patterns in the community during the post-settlement 0-group phase was tested. Studies of diets, growth, and survival patterns in contrasting locations on the Norwegian Skagerrak coast show that for the 0 to 3 months after attaining a benthic mode of life, cod juveniles continue to depend on planktonic prey with high energy content. Early shifts to hyperbenthic prey such as fish and prawns result in poor condition and low survival. It is suggested that gradual eutrophication may induce abrupt shifts in the energy flow pattern in the plankton community that are propagated to higher trophic levels. This may explain repeated incidents of abrupt and persistent recruitment collapses in fishes along the Norwegian Skagerrak.