Diet pattern of food intake in whiting (Merlangius merlangus) investigated from the weight of partly digested food particles in the stomach and laboratory determined particle decay functions

The daily periodicity of the food intake of North Sea whiting feeding on sandeels was investigated by means of analysing the weight of partly digested prey particles found in the stomachs. The digestion times corresponding to the weights of partly digested sandeels were estimated from the assumed weight at ingestion as derived from the length-weight relationship of the prey and a gastric evacuation model that was based on experimental data with whiting fed on sandeels. The results indicated a single feeding peak with a maximum feeding between 2200 and 2400 h and minimal food intake between 0800 and 1000 h. Additional simulation exercises were performed to investigate the precision of the back-calculation method. These simulations revealed that the scatter of individual weights around the mean weight at a given length is transformed into a corresponding scatter in the estimated times of food intake. The main conclusion from the analysis that whiting appear to feed during the night hours was found to be robust against changes of the actual parameters of the particle decay Function within the range of the most likely values. (C) 1997 International Council for the Exploration of the Sea.