The role of diet in promoting health and preventing disease is difficult to elucidate due to its complex network of foods and nutrients. Besides total energy intake, dietary composition is probably the most important discriminator within and between populations. Dietary composition is reflected in dietary patterns, which have recently gained popularity. The present paper reviews the most commonly applied methods to identify dietary patterns, data-driven methods such as factor and cluster analysis, investigator-driven methods such as indices and score, and methods combining the two, namely reduced rank regression. We describe the techniques and their application, discuss strengths and limitations, and discuss the usefulness of dietary pattern analyses.

Data on the diet of species are important for understanding ecosystem dynamics and are fundamental for the implementation of recent approaches in stock assessment and consequently for the establishment of more ecological management measures. In mainland Portugal, as in most European countries, skates and rays represent an important proportion of commercial landings. The four main species landed are Raja clavata and Raja brachyura, followed by Leucoraja naevus and Raja montagui. This paper analyses their diets based on the examination of stomach contents. Food items were identified to the lowest identifiable taxon and were further assembled into major taxonomic groups designated as prey. Intra- and interspecific comparisons were made according to size and sex. All four species had generalized diets with differences in prey preference among them. Decapods and bony fish were the most frequent prey. Furthermore, an ontogenetic dietary shift was evident in all species at around 45−55 cm total length. Both intra- and interspecific differences observed seem to be related to size and morphological characteristics of the species, as well as type of dentition. These variations allow different species, as well as small and large specimens from the same species, to exploit a larger diversity of habitats.