Estimating the mean time between meals in the field from stomach content data and gastric evacuation functions of whiting (Merlangius merlangus L.) feeding on sandeel (Ammodytes marinus Raitt)

The evacuation of sandeels in whiting stomachs was investigated in double meal evacuation experiments. The experiments revealed accelerated evacuation of the first sandeel after the intake of a second sandeel when compared to the evacuation rate of a single sandeel in a stomach. The second sandeel was evacuated at a decreased rate such that the overall gastric evacuation rate was equal to the single meal situation again. The evacuatio functions derived from these experiments were applied to whiting stomachs from a small scale field, investigation, where whiting were found to feed exclusively on sandeel. From those whitings which contained two sandeels in their stomachs the mean time between the intake of the first and the second sandeel was estimated as 2 d. Since the majority of whiting in the field samples had less than two sandeels in their stomachs, a simulation model was, set up, which mimics on an individual base the food intake and gastric evacuation for the whole local whiting population. Parameter values, including the probability of prey encounter were varied to minimize the deviation between the observed and the simulated stomach content distribution. The best fit was obtained assuming a probability of prey encounter of 0.3/day and under these conditions the average time between successive meals for the whole local whiting populatio was 4 d. (C) 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.