Equations and values used to estimate changes in energy density (ED) during the feeding period (t) for predator species (pred.sp): NEA mackerel, herring and blue whiting.

For blue whiting, the energy content in liver (E.Lv) is added to the constant energy density of the fish muscles for gadoids (EDG.m.), assumed in previous studies. t: Day of Year; EDt,pred: Energy Density of fish (pred: predator species) at day t. E.Lv: Energy content in liver (based on observations for Pollock, in kJ); W.Lv: Weight of the liver (g); ED.Lv: Energy Density in liver (J g-1); Lind: liver index; W’t: total weight of fish (as a function of time t); DM.Lv: Proportion of dry material in liver; O.Lv: Proportion of oil in liver.