The use of stomach fullness and colour indices to assess Sardina pilchardus feeding

Abstract

Scales for stomach fullness and colour were developed and calibrated in order to provide an easy and reliable way to determine feeding intensity and food quality in sardines. The categories of the fullness scale reproduce the amount of food intake as indicated by the weight of the stomachs. The levels of the colour scale reflect the type of plankton eaten as shown by concentration of a-type phaeopigments and prey analysis of the stomach contents. Individuals of a wide length range were used in this study, leading us to suggest that these indices can be applied to the entire juvenile and adult sardine population. The use of the colour and fullness scales provides a rapid and efficient means of characterizing sardine feeding. Based on the colour and fullness categories of the stomachs the majority of stomachs were almost empty or at most half-full and the diet was composed of different proportions of phyto- and zooplankton items. As indicated by the prey analyses of the contents the most important constituent of the diet, in volume, were zooplankton prey.