Causes of Variation in Abundance, Growth, and Mortality in 0-Group Gadoids After Settlement and a Hypothesis Underlying Recruitment Variability in Atlantic Cod

A time series of annual beach seine surveys run since 1919 on the Norwegian Skagerrak coast revealed repeated incidents of abrupt and persistent recruitment collapses in young-of-the-year gadoids in relation to increasing nutrient loads. To explore potential underlying causes of the recruitment patterns, a three-year study of processes associated with settlement and the postsettlement period in gadoids was conducted. With Atlantic cod (Gadus morhua) as a model species, the following hypothesis underlying the recruitment collapses is proposed: The survival of 0-group cod is limited by food availability after settlement (3–5 months old), and recruitment variability results from differences in food supply due to inter-annual variability in the energy flow pattern at low trophic levels of the pelagic food web. By postulating that food availability shows high inter-annual variation and that gradually increasing nutrient loads results in abrupt and persistent food deprivation of the 0-group gadoids, this hypothesis potentially explains both natural recruitment variability and eutrophication-induced recruitment collapses of cod and the other gadoids.