Food consumption and daily feeding periodicity: comparison between pelagic and demersal whiting in the North Sea

Pelagic North Sea whiting Merlagius merlangus fed at night, while demersal whiting fed by day. The estimated specific daily ration ranged from 4·38 to 7·84% in 1992 and from 3·99 to 10·31% in 1993 using the in situ rate of gastric evacuation. Using Andersen's evacuation model the specific daily ration ranged from 0·41 to 1·66% in 1992 and from 0·78 to 1·75% in 1993. The specific daily rations were significantly different where energy density of stomach content by length class of whiting was significantly different between the two layers and years. The fact that daily ration was related to prey composition and energy density of the prey and spatial distribution of the whiting, demonstrates the need for a sampling design that includes both pelagic and demersal layers when quantifying the food consumption of whiting.