The effect of meal size on gastric evacuation in whiting

Gastric evacuation experiments were performed on whiting Merlangius merlangus fed discrete meals of different sizes. Herring Clupea harengus, sandeel Ammodytes tobianus, common goby Pomatoschistus microps, and brown shrimp Crangon crangon were tested as prey. A simple power model to describe gastric evacuation was evaluated and compared with a power model expanded as a function of meal size. The model parameters were estimated by means of nonlinear least squares. When all meal sizes were included the estimates of the power (curvature) parameter in the expanded model were within the range 0.36-0.77 for the different prey. The power estimates in the simple model were generally close to 0.5. The exception was crustacean prey, which gave a higher value. In the simple model the power estimate represents a compromise between the curvatures of the curves fitted to the observations for each meal size and the relationship between meal size and overall evacuation rate. Compared with an expanded model a simple model with a power value of 0.5 gave a suitable description of the gastric evacuation of fish prey independent of meal size. The variation of data was proportional to meal size, and this could be taken into account in the estimation procedure by expressing stomach contents relative to meal size. (C) 1998 The Fisheries Society of the British Isles